JP7327927B2 - semiconductor equipment - Google Patents

Description

One aspect of the present invention relates to an article, method, or manufacturing method. Alternatively, the invention relates to a process, machine, manufacture, or composition of matter. One embodiment of the present invention relates to a method for manufacturing a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device. In particular, the present invention relates to a semiconductor device using an oxide semiconductor and a manufacturing method thereof.

In this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic devices are all semiconductor devices.

Another embodiment of the present invention relates to a charging control system and a charging control method using a semiconductor device, and an electronic device including a secondary battery.

Note that in this specification, a power storage device generally refers to elements and devices having a power storage function. For example, storage batteries such as lithium ion secondary batteries (also referred to as secondary batteries), lithium ion capacitors, all-solid-state batteries, electric double layer capacitors, and the like are included.

In recent years, various power storage devices such as lithium-ion secondary batteries, nickel-hydrogen secondary batteries, lithium-ion capacitors, and air batteries have been actively developed. In particular, lithium-ion secondary batteries, which have high output and high energy density, are used in mobile devices such as mobile phones, smart phones, tablets, personal digital assistants such as notebook computers, portable music players, and digital cameras. In addition, lithium ion secondary batteries are also used in medical equipment, next-generation clean energy vehicles such as hybrid vehicles (HEV), electric vehicles (EV), or plug-in hybrid vehicles (PHEV), electric motorcycles, It is also used in electric vehicles such as electrically assisted bicycles. As described above, the demand for lithium-ion secondary batteries has rapidly expanded in line with the development of the semiconductor industry, and they have become indispensable in the modern information society as a source of rechargeable energy.

The secondary battery is repeatedly used by the user and recharged when the remaining amount of the battery decreases. Repetitive charging causes the secondary battery to deteriorate, and efforts have been made to extend the life of the secondary battery by changing charging conditions according to the degree of deterioration of the secondary battery. Secondary batteries have individual differences even immediately after manufacture, deteriorate with the number of cycles, and are further affected by various parameters such as battery voltage, charge/discharge current, temperature, and internal resistance.

In addition, secondary batteries using lithium ions are known to experience thermal runaway due to internal short circuits, overcharging, and the like due to deterioration. It is desired to detect abnormalities that are signs of thermal runaway and take safety measures.

In personal digital assistants, electric vehicles, and the like, a plurality of secondary batteries are connected in series or in parallel to provide a protection circuit, and used as a battery pack (also called assembled battery). A battery pack refers to a battery module consisting of a plurality of secondary batteries housed inside a container (metal can, film outer packaging) together with a predetermined circuit in order to facilitate the handling of secondary batteries. .

Also, if all the secondary batteries that make up the assembled battery function normally, there is no problem, but if even one malfunctions, the other secondary batteries will be adversely affected. The battery will stop working.

In addition, in mobile information terminals, the housing is becoming smaller and thinner, and it is desired that the housing of the mobile information terminal is small and the capacity of the secondary battery is large. is limited.

Conventionally, a protection circuit for preventing overcharge and overdischarge is mounted on a rigid substrate (printed wiring board) as an IC chip in order to ensure safety from abnormalities in secondary batteries. Also, a switching circuit for conducting and interrupting the discharge current is formed by an IC chip, and a plurality of these IC chips are combined and mounted on a rigid substrate.

Patent Literature 1 discloses a battery state detection device that detects a micro short circuit in a secondary battery and a battery pack containing the same.

In addition, as for oxide semiconductors (also referred to as oxide semiconductors), not only monocomponent metal oxides such as indium oxide and zinc oxide, but also multicomponent metal oxides are known. In--Ga--Zn oxides (also referred to as IGZO) have been extensively studied among multicomponent metal oxides.

Research on IGZO has found a CAAC (c-axis aligned crystalline) structure and an nc (nanocrystalline) structure, which are neither single crystal nor amorphous, in oxide semiconductors (Non-Patent Documents 1 to 3). 3, see).

Non-Patent Document 1 and Non-Patent Document 2 disclose a technique for manufacturing a transistor using an oxide semiconductor having a CAAC structure. Furthermore, Non-Patent Document 4 and Non-Patent Document 5 show that even an oxide semiconductor having a crystallinity lower than that of the CAAC structure and the nc structure has minute crystals.

Non-Patent Document 6 reports that a transistor using an oxide semiconductor has a very small off-state current, and Non-Patent Documents 7 and 8 report an LSI ( Large Scale Integration) and displays have been reported.

JP 2010-66161

S. Yamazaki et al. , "SID Symposium Digest of Technical Papers", 2012, volume 43, issue 1, p. 183-186 S. Yamazaki et al. , "Japanese Journal of Applied Physics", 2014, volume 53, Number 4S, p. 04ED18-1-04ED18-10 S. Ito et al. , "The Proceedings of AM-FPD'13 Digest of Technical Papers", 2013, p. 151-154 S. Yamazaki et al. , "ECS Journal of Solid State Science and Technology", 2014, volume 3, issue 9, p. Q3012-Q3022 S. Yamazaki, "ECS Transactions", 2014, volume 64, issue 10, p. 155-164 K. Kato et al. , "Japanese Journal of Applied Physics", 2012, volume 51, p. 021201-1-021201-7 S. Matsuda et al. , "2015 Symposium on VLSI Technology Digest of Technical Papers", 2015, p. T216-T217 S. Amano et al. , "SID Symposium Digest of Technical Papers", 2010, volume 41, issue 1, p. 626-629

To ensure safety by detecting abnormalities in secondary batteries, for example, early detection of phenomena that reduce the safety of secondary batteries, warning the user, or stopping the use of secondary batteries. This is one of the issues.

Another issue is to realize a configuration that can cope with space saving due to the miniaturization of the housing while mounting a circuit that safely controls the drive of the secondary battery.

In order to solve the above problems, a charge control circuit is provided on a flexible substrate and attached to the outer surface of the secondary battery. At least one of the two terminals of the secondary battery is electrically connected to the charge control circuit to control charging.

One of the structures of the invention disclosed in this specification is a semiconductor device having a secondary battery having a top surface, a bottom surface, and side surfaces, and a charge control circuit is provided on the side surface of the secondary battery via a flexible substrate. the charge control circuit includes a transistor including an oxide semiconductor, the charge control circuit is electrically connected to a first terminal on the top surface of the secondary battery, and the second terminal on the bottom surface of the secondary battery and a charge control circuit are electrically connected to each other.

A transistor including an oxide semiconductor is preferably used for the charge control circuit because power consumption can be reduced. A transistor including an oxide semiconductor for a semiconductor layer has very low leakage current in an off state. In a transistor using an oxide semiconductor, the off-state current normalized by the channel width can be reduced to approximately several yA (yoctoampere)/μm or more and several zA (zeptoampere)/μm or less.

Further, since the charge control circuit can be used in a high-temperature environment, it is preferable to use a transistor using an oxide semiconductor. To simplify the process, the charging control circuit may be formed using unipolar transistors. A transistor using an oxide semiconductor for a semiconductor layer has a wider operating ambient temperature of −40° C. or more and 150° C. or less than single crystal Si, and changes in characteristics are smaller than those of single crystal even when the secondary battery is heated. The off-state current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of the temperature even at 150° C. However, the off-state current characteristics of a single crystal Si transistor are highly dependent on temperature. For example, at 150° C., a single crystal Si transistor has an increased off current and does not have a sufficiently large current on/off ratio.

A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor is sometimes referred to as a BTOS (battery operating system or battery oxide semiconductor).

In the case of a cylindrical secondary battery, the flexible substrate can be bent and installed so as to be wound around the curved side surface of the secondary battery.

In addition, by providing the protection circuit, the cutoff switch, and the charge control circuit on the same flexible substrate, a configuration that can cope with the space saving associated with the miniaturization of the housing is realized.

An organic resin film or a metal film can be used for the flexible substrate. Examples of materials for the organic resin film include polyester resins such as PET and PEN, polyacrylonitrile resins, acrylic resins, polyimide resins, polymethyl methacrylate resins, PC resins, PES resins, polyamide resins (nylon, aramid, etc.), and polysiloxanes. resins, cycloolefin resins, polystyrene resins, polyamideimide resins, polyurethane resins, polyvinyl chloride resins, polyvinylidene chloride resins, polypropylene resins, PTFE resins, ABS resins, and the like.

Note that stainless steel, aluminum, or the like can be used as the metal film.

As a manufacturing method for forming the charge control circuit over the flexible substrate, a method of forming the charge control circuit over the semiconductor substrate and then fixing it onto the flexible substrate after peeling using a peeling method is used. A known technique can be used for the peeling method. Moreover, after forming on a semiconductor substrate, after polishing a back surface, the method of fixing on a flexible substrate may be used. Alternatively, a method of partially cutting using a laser beam, that is, so-called laser cutting, and then fixing onto a flexible substrate may be used. Alternatively, a method of directly forming a charge control circuit on a flexible substrate may be used. In addition, a method is used in which the charge control circuit formed over the glass substrate is fixed on the flexible substrate after peeling using a peeling method.

In this specification, the charging control circuit refers to a circuit that executes any one or all of control of charging voltage and amount of charging current, control of amount of charging current according to the degree of deterioration, and detection of micro-shorts.

A micro-short refers to a minute short circuit inside a secondary battery, and it does not mean that the positive electrode and negative electrode of the secondary battery are short-circuited and cannot be charged or discharged. It refers to a phenomenon in which a slight short-circuit current flows. Since a large voltage change occurs in a relatively short time and even at a small location, the abnormal voltage value may affect subsequent estimation.

One of the causes of micro-shorts is that the non-uniform distribution of the positive electrode active material caused by repeated charging and discharging causes localized concentration of current in a portion of the positive electrode and a portion of the negative electrode, resulting in a separator failure. It is said that a micro short-circuit occurs due to the generation of a portion where a part fails or the generation of a side reaction product due to a side reaction.

Further, it can be said that the charge control circuit detects not only the micro-short circuit but also the terminal voltage of the secondary battery and manages the charging/discharging state of the secondary battery.

One of the configurations of the other invention disclosed in this specification includes a secondary battery, and a first transmission line connected to a first terminal of the secondary battery and transmitting power output from the secondary battery. , a charging control circuit connected to the first transmission path and provided on the flexible substrate in contact with the side surface of the secondary battery; and a second terminal connecting the charging control circuit and the second terminal of the secondary battery. and a switch that cuts off the second transmission line, the switch cuts off the second transmission line when the secondary battery is overcharged or overdischarged, and cuts off the second transmission line during charging of the secondary battery This charging control system cuts off a second transmission line to stop charging when the charging control circuit determines that there is an abnormality.

The switch that cuts off the second transmission line is a switch for controlling conduction and cutoff operations, and can also be called a protection circuit. Also, this switch may be combined with a diode to form a protection circuit. It can be said that such a protection circuit and the above-described charging control circuit provide double protection, so that the charging control system can be said to be highly safe.

In this specification, a protection circuit refers to a circuit that implements any one or all of overcharge prevention, overcurrent prevention, and overdischarge prevention. In some cases, the protection circuit includes a cutoff switch for cutting off charging.

The flexible substrate provided with the charging control circuit described above can be incorporated not only in batteries but also in card-type electronic money, RFID tags, and the like.

By providing the protection circuit, charging control circuit, and abnormality detection circuit on a single flexible sheet provided on the side of the secondary battery, the printed circuit board that mounted multiple of these as IC chips becomes unnecessary, and the function is improved. A miniaturized device can be realized without reducing the

1 is a conceptual diagram showing one embodiment of the present invention; FIG. 1 is an example of a block diagram illustrating one aspect of the present invention; FIG. 1A and 1B are a perspective view and a conceptual diagram illustrating one embodiment of the present invention; FIG. 1 is an example of a flowchart illustrating an aspect of the present invention; 1 is a conceptual diagram showing one embodiment of the present invention; FIG. It is a perspective view showing one mode of the present invention. FIG. 2 is a cross-sectional view showing a configuration example of a semiconductor device; (A, B, C) Cross-sectional views showing structural examples of transistors. 1A is a top view showing a structure example of a transistor, and 1B and 1C are cross-sectional views showing a structure example of a transistor; 1A is a top view showing a structure example of a transistor, and 1B and 1C are cross-sectional views showing a structure example of a transistor; 1A is a top view showing a structure example of a transistor, and 1B and 1C are cross-sectional views showing a structure example of a transistor; 1A is a top view showing a structure example of a transistor, and 1B and 1C are cross-sectional views showing a structure example of a transistor; 1A is a top view showing a structure example of a transistor, and 1B and 1C are cross-sectional views showing a structure example of a transistor; 1A is a top view showing a structure example of a transistor, and 1B and 1C are cross-sectional views showing a structure example of a transistor; 1A is a top view illustrating a structural example of a transistor, and FIG. 1B is a perspective view illustrating a structural example of a transistor; 4A and 4B are cross-sectional views showing structural examples of transistors; 1A and 1B are diagrams each illustrating an example of an electronic device;

Embodiments of the present invention will be described in detail below with reference to the drawings. However, those skilled in the art will easily understand that the present invention is not limited to the following description, and that the forms and details thereof can be variously changed. Moreover, the present invention should not be construed as being limited to the description of the embodiments shown below.

(Embodiment 1)
FIG. 1A is a conceptual diagram of a charge control system in which a charge control circuit 10 formed on a flexible substrate 11, which is a flexible film, is mounted on a cylindrical secondary battery 15. FIG. The charge control system has at least a cylindrical secondary battery 15, a charge control circuit 10, and a switch.

Cylindrical secondary battery 15 has first terminal 12 on the top surface and second terminal 13 on the bottom surface. A first transmission path, which is connected to the first terminal 12 of the cylindrical secondary battery and transmits power output from the cylindrical secondary battery 15, is electrically connected to the terminal of the charging control circuit via the electrode 18. Connected. Also, the second transmission line connected to the second terminal 13 of the cylindrical secondary battery is connected via the electrode 19 to a switch that cuts off the second transmission line.

In FIG. 1A, two switches (also called cutoff switches) are provided to cut off the second transmission line, and diodes are also connected to prevent overdischarge, overcharge, or overcurrent. It functions as a protection circuit for The switch controls conduction and interruption operations, and can also be called switching means for switching between supply and interruption. A third terminal 14 , which is the other terminal of the second transmission line formed on the flexible substrate 11 , is connected to a charger 16 and a mobile device 17 .

A manufacturing method for forming the charge control circuit 10 on the flexible substrate 11 uses a method of forming it on a semiconductor substrate and then fixing it onto the flexible substrate 11 after peeling using a peeling method. A known technique can be used for the peeling method. Moreover, after forming on a semiconductor substrate, the back surface may be polished and then fixed on the flexible substrate 11 . Alternatively, a method of partially cutting using a laser beam, that is, fixing onto the flexible substrate 11 after so-called laser cutting may be used. Alternatively, a method of forming the charging control circuit 10 directly on the flexible substrate 11 may be used. Also, a method is used in which the charge control circuit 10 formed on the glass substrate is fixed on the flexible substrate 11 after being peeled off using a peeling method.

This embodiment shows an example in which these diodes and switches are also formed or mounted on the flexible substrate 11, but the configuration is not particularly limited to this.

When the charging control circuit 10 detects an abnormality such as a micro-short, the second transmission line can be cut off by inputting a signal to the gate of the switch that cuts off the second transmission line. By interrupting the second transmission line, the current supply from the charger 16 or the current supply to the mobile device 17 can be stopped. Further, by holding the signal voltage applied to the gate of the switch that cuts off the second transmission line in the memory circuit (including a transistor including an oxide semiconductor), cutoff can be maintained for a long time. Therefore, a highly safe charging control system can be provided.

FIG. 1B is a process diagram showing a state immediately before bonding the cylindrical secondary battery 15 and the flexible substrate 11 together, and shows the contact surface side of the flexible substrate 11 . As shown in FIG. 1(B), the body of the cylindrical secondary battery 15 is applied to the contact surface of the flexible substrate 11 and rolled, and the flexible substrate 11 is wrapped around the body in the circumferential direction and adhered. do. Moreover, although the electrodes 18 and 19 are arranged in the Y direction on the flexible substrate 11, the arrangement is not particularly limited, and one of the electrodes may be shifted in the X direction. FIG. 1(C) is a diagram after the upheaval.

An exterior film is attached so as to cover the outer peripheral surface of the body of the cylindrical secondary battery 15 . This exterior film is used to protect the metal can for sealing the internal structure of the secondary battery and to provide insulation from the metal can.

If the outer surface of the cylindrical secondary battery 15 (excluding the terminal portion) is a metal surface without using an outer film, insert an insulating sheet between the electrode 18 and the electrode 19. is preferred. The electrodes 18 and 19 are conductive metal foils, conductive tapes made of conductive materials, and lead wires. Connect by method. Electrode 18 or electrode 19 is connected to a terminal of the charge control circuit by soldering or wire bonding.

An example of a block diagram of a specific circuit of the charging control circuit 10 is shown in FIG.

As shown in FIG. 2A, the charge control circuit 10 for the secondary battery 101 includes at least a comparison circuit 102, a first memory 103, a second memory 104, and a control circuit .

Although the secondary battery 15 and the cutoff switch 105 are shown separately from the charge control circuit 10 in FIG. 1A, the cutoff switch 105 and the charge control circuit 10 can be formed over the same substrate.

The comparison circuit 102 compares the magnitude relationship between the two input voltages and outputs the result. The comparison circuit 102 can also be a unipolar circuit using a transistor including an oxide semiconductor in a channel formation region.

The first memory 103 is an analog memory and stores the offset analog potential of the secondary battery. Data of the offset voltage value of the secondary battery can be created by applying a write signal to the gate of the transistor of the first memory 103 and using the parasitic capacitance between the gate electrode and the drain electrode. The first memory 103 includes one transistor having an oxide semiconductor in a channel formation region and a capacitor. The first memory 103 can also be called a highly accurate charging voltage monitor circuit. In addition, the first memory 103 can take advantage of low leakage current of a transistor including an oxide semiconductor in a channel formation region.

The second memory 104 has the same element structure as the first memory 103 and includes one transistor having an oxide semiconductor in a channel formation region and a capacitor. The second memory 104 holds the data of the cutoff switch 105 .

The cutoff switch 105 is a switch for cutting off power supply to the power supply of the secondary battery in which an abnormality has occurred. The cut-off switch 105 has the circuit configuration shown in FIG. 2A, so that the secondary battery 15 in which an abnormality occurs can be prevented from being continuously charged and ignited due to overcharging.

FIG. 2A shows an example of stopping power supply to the secondary battery after an abnormality is detected using the cutoff switch 105. Charging conditions are changed or charging is temporarily stopped according to the number of times an abnormality is detected. or warning display.

FIG. 2B shows memory cells that can be used for the first memory 103 and the second memory 104 shown in FIG. 2A. FIG. 2B is a circuit configuration example of the memory cell 100 in which a transistor has a back gate.

The memory cell 100 has a transistor M1 and a capacitor CA. Note that the transistor M1 has a front gate (also simply referred to as a "gate") and a back gate. The back gate is arranged so as to sandwich the channel forming region of the semiconductor layer between the gate and the back gate. Note that the terms gate and backgate are used for convenience, and when one is referred to as a "gate", the other is referred to as a "backgate". Therefore, the terms gate and backgate can be used interchangeably. One of the gate and the back gate may be called "first gate" and the other may be called "second gate".

one of the source and the drain of the transistor M1 is electrically connected to one electrode of the capacitor CA, the other of the source and the drain of the transistor M1 is electrically connected to one of the bit line BL and the bit line BLB; A gate of the transistor M1 is electrically connected to one of the word line WLa or the word line WLb, and a back gate of the transistor M1 is electrically connected to the wiring BGL. The other electrode of the capacitor CA is connected to the wiring CAL.

The wiring CAL functions as a wiring for applying a predetermined potential to the other electrode of the capacitor CA. A fixed potential such as VSS is preferably supplied to the wiring CAL when data is written and read.

The wiring BGL functions as a wiring for applying a potential to the back gate of the transistor M1.

FIG. 2C shows an example of Id-Vg characteristics, which are electrical characteristics of a transistor. The Id-Vg characteristic indicates changes in drain current (Id) with respect to changes in gate voltage (Vg). The horizontal axis of FIG. 2C indicates Vg on a linear scale. Also, the vertical axis of FIG. 2(C) indicates Id on a log scale. As shown in FIG. 2C, when a positive bias voltage +Vbg is supplied to the wiring BGL as the back gate voltage (Vbg), the Id-Vg characteristic shifts in the negative direction of Vg. When a negative bias voltage -Vbg is supplied to the wiring BGL, the Id-Vg characteristic shifts in the positive direction of Vg. The shift amount of the Id-Vg characteristic is determined by the magnitude of the voltage supplied to the wiring BGL. By applying an arbitrary voltage to the wiring BGL, the threshold voltage of the transistor M1 can be increased or decreased.

In writing and reading data, a potential for turning on the transistor M1 is supplied to the word line WL, the transistor M1 is turned on, and the bit line BL or the bit line BLB and one electrode of the capacitor CA are connected. by electrically connecting the

By using an OS transistor as the transistor M1, leakage current of the transistor M1 can be significantly reduced. In other words, since written data can be held for a long time by the transistor M1, the frequency of refreshing the memory cell can be reduced. Also, the refresh operation of the memory cells can be made unnecessary. Also, since the leakage current is very low, analog data can be retained for the memory cell.

As shown in FIG. 1A, when power is supplied from the cylindrical secondary battery 15 to the mobile device 17, the cylindrical secondary battery 15 is in a discharged state, and the first terminal 12 and the second terminal 13 The charging control circuit 10 monitors the behavior of voltage, current, and the like, and when an abnormality is detected, the second transmission path is cut off to stop discharging.

The mobile device 17 indicates a configuration other than a secondary battery, and the power source for the mobile device 17 is the cylindrical secondary battery 15 . Note that the mobile device 17 is an electronic device that can be carried around in a form.

When the cylindrical secondary battery 15 is charged by being supplied with electric power from the charger 16, the cylindrical secondary battery 15 is in a charged state, and the voltage and current at the first terminal 12 and the second terminal 13 are changed. The behavior is monitored by the charge control circuit 10, and when an abnormality is detected, the second transmission path is cut off to stop charging.

The charger 16 refers to a device that has an adapter that connects to an external power source, or a device that transmits power using a wireless signal. Note that the charger 16 may be built in the mobile device 17 in some cases.

As in the past, when using a protection circuit in which an IC chip is mounted on a circular rigid substrate that overlaps the bottom surface of a cylindrical secondary battery, physical pressure is applied to the socket and the spring contacts the socket, causing failure. There is fear. Compared with the conventional art, in the present invention, physical pressure is not applied because it is provided on the side surface of the cylindrical secondary battery. In addition, in the conventional case, when a circular rigid substrate is placed on the bottom, the size of the battery must be reduced to match the space, resulting in a small capacity. In the present invention, as compared with the prior art, since it is provided on the side surface of the cylindrical secondary battery, it is possible to save space without reducing the capacity.

Thus, it is useful to provide the charge control circuit 10 and the protection circuit on the curved side surface area of the cylindrical secondary battery. For example, an 18650 battery has a diameter of 18 mm and a length of 65 mm. , the length in the Y direction is 65 mm) or less. In the case of a 26650 battery, since it has a diameter of 26 mm and a length of 65 mm, the area of the flexible substrate 11 is 3.14×26 mm in the X direction and 65 mm in the Y direction.

Further, when the cylindrical secondary battery 15 is a 18650 battery, when the flexible substrate 11 is attached, the curved surface area of the flexible substrate 11 has a radius of curvature of about 9 mm. Because the radius of curvature may not be uniformly about 9 mm due to the influence of the circuits and wiring provided on the flexible substrate 11, the smallest radius of curvature is defined as the radius of curvature of the surface in this specification and the like. When the curved surface has a shape with multiple centers of curvature, the term refers to the radius of curvature of the curved surface with the smallest radius of curvature among the radii of curvature at each of the multiple centers of curvature. Depending on the size of the cylindrical secondary battery 15 used, the flexible substrate 11 can be bent within a radius of curvature of 30 mm or more, preferably 9 mm or more.

Here, a cylindrical secondary battery will be described with reference to FIGS. 3(A) and 3(B). As shown in FIG. 3B, the cylindrical secondary battery 15 has a positive electrode cap (battery cover) 201 on its top surface and battery cans (armor cans) 202 on its side and bottom surfaces. The positive electrode cap and the battery can (outer can) 202 are insulated by a gasket (insulating packing) 210 .

FIG. 3B is a diagram schematically showing a cross section of a cylindrical secondary battery. A battery element in which a strip-shaped positive electrode 204 and a strip-shaped negative electrode 206 are wound with a separator 205 interposed therebetween is provided inside a hollow cylindrical battery can 202 . Although not shown, the battery element is wound around a center pin. The battery can 202 is closed at one end and open at the other end. The battery can 202 can be made of a metal such as nickel, aluminum, or titanium that is resistant to corrosion by the electrolyte, or an alloy thereof or an alloy of these metals with another metal (for example, stainless steel). . Also, in order to prevent corrosion due to the electrolyte, it is preferable to coat with nickel, aluminum, or the like. Inside the battery can 202, the battery element in which the positive electrode, the negative electrode and the separator are wound is sandwiched between a pair of insulating plates 208 and 209 facing each other. A non-aqueous electrolyte (not shown) is filled inside the battery can 202 in which the battery element is provided. A secondary battery includes a positive electrode containing an active material such as lithium cobalt oxide (LiCoO ₂ ) or lithium iron phosphate (LiFePO ₄ ), a negative electrode containing a carbon material such as graphite capable of intercalating and deintercalating lithium ions, and an ethylene It is composed of a non-aqueous electrolytic solution or the like in which an electrolyte made of a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an organic solvent such as carbonate or diethyl carbonate.

Since the positive electrode and the negative electrode used in the cylindrical secondary battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive collector lead) 203 is connected to the positive electrode 204 , and a negative electrode terminal (negative collector lead) 207 is connected to the negative electrode 206 . A metal material such as aluminum can be used for both the positive terminal 203 and the negative terminal 207 . The positive terminal 203 and the negative terminal 207 are resistance welded to the safety valve mechanism 212 and the bottom of the battery can 202, respectively. The safety valve mechanism 212 is electrically connected to the positive electrode cap 201 via a PTC element (Positive Temperature Coefficient) 211 . The safety valve mechanism 212 disconnects the electrical connection between the positive electrode cap 201 and the positive electrode 204 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 211 is a thermal resistance element whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO ₃ ) semiconductor ceramics or the like can be used for the PTC element.

A lithium ion secondary battery using an electrolytic solution has a positive electrode, a negative electrode, a separator, an electrolytic solution, and an outer casing. In a lithium ion secondary battery, the anode (anode) and the cathode (cathode) are switched between charging and discharging, and the oxidation reaction and the reduction reaction are switched. is called the negative electrode. Therefore, in this specification, the positive electrode is the “positive electrode” or “positive electrode” or “positive electrode” during charging, discharging, reverse pulse current, or charging current. A negative electrode is called a “negative electrode” or a “negative electrode”. The use of the terms anode and cathode in relation to oxidation and reduction reactions can be confusing as they are reversed during charging and discharging. Accordingly, the terms anode and cathode are not used herein. If the terms anode or cathode are to be used, specify whether it is charging or discharging, and indicate whether it corresponds to the positive electrode (positive electrode) or the negative electrode (negative electrode). do.

A charger is connected to two terminals illustrated in FIG. 3C, and the storage battery 1400 is charged. As the charging of the storage battery 1400 progresses, the potential difference between the electrodes increases. In FIG. 3C, from the terminal outside the storage battery 1400, it flows toward the positive electrode 1402, flows from the positive electrode 1402 toward the negative electrode 1404 in the storage battery 1400, and flows from the negative electrode toward the external terminal of the storage battery 1400. The direction of current is assumed to be the positive direction. That is, the direction in which the charging current flows is the direction of the current.

In this embodiment, an example of a lithium ion secondary battery is shown, but the invention is not limited to the lithium ion secondary battery. For example, a material containing element A, element X, and oxygen can be used as the positive electrode material of the secondary battery. can be done. Element A is preferably one or more selected from Group 1 elements and Group 2 elements. Alkali metals such as lithium, sodium, and potassium can be used as the Group 1 elements. Also, for example, calcium, beryllium, magnesium, or the like can be used as the Group 2 element. As the element X, for example, one or more selected from metal elements, silicon and phosphorus can be used. Also, the element X is preferably one or more selected from cobalt, nickel, manganese, iron, and vanadium. Typical examples include lithium cobalt composite oxide (LiCoO ₂ ) and lithium iron phosphate (LiFePO ₄ ).

The negative electrode has a negative electrode active material layer and a negative electrode current collector. Moreover, the negative electrode active material layer may have a conductive aid and a binder.

As the negative electrode active material, an element capable of performing charge-discharge reaction by alloying/dealloying reaction with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such an element has a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh/g.

Also, the secondary battery preferably has a separator. Examples of separators include fibers containing cellulose such as paper, non-woven fabrics, glass fibers, ceramics, synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, and polyurethane. can be used.

FIG. 4 shows an example of the flow of a charge control system in the case where the mobile device 17 in which the charge control circuit 10 is installed in the secondary battery 15 is detected multiple times during one charge.

First, voltage value data of the secondary battery 15 is acquired by voltage value acquisition means such as a voltage monitor. (S1) Next, the offset voltage data of the secondary battery is written in the first memory 103 for each sampling period Δt. (S2)

Next, the comparison circuit 102 compares voltage values measured at the current time and at different times. (Comparison step: S3) As a result of the comparison, if the difference between the two input voltages is small, the acquisition and comparison of the data described above are repeated. If the charging continues without detection of an abnormality and reaches full charge (S7), the charging is stopped (S8).

In the comparison step S3, if the difference between the two input voltages is large, it is judged to be abnormal and the charging of the secondary battery is stopped (S8). When charging is to be stopped, the cut-off switch 105 is turned off. The second memory 104 holds the data of the cutoff switch 105 .

In addition, although the configuration for detecting an abnormality such as a micro-short has been mainly described here, there is no particular limitation, and over-discharging prevention, over-charging prevention, cell balance in the assembled battery, temperature, and degree of deterioration. Control of the amount of charging current, etc., may also be performed during the same charging.

In the charging control system described above, the timing of comparison may be performed every period Δt, and is not particularly limited as long as it is within the period that the first memory 103 can hold. Since the first memory 103 includes a transistor including an oxide semiconductor, the period Δt, which is a retention period, can be longer than that of a memory including silicon. The period Δt can also be shortened, enabling real-time detection of micro-shorts.

(Embodiment 2)
In this embodiment, another structural example of the cylindrical secondary battery of Embodiment 1 will be described with reference to FIGS. 5 and 6. FIG.

FIG. 5A is an external view of a battery pack including a flat secondary battery 913, a charge control circuit 914, and a connection terminal 911. FIG.

A charging control circuit 914 is formed or fixed on the flexible substrate 910 . A charge control circuit 914 detects an abnormality such as a micro-short. Furthermore, it may have a function as a protection circuit that protects the secondary battery 913 from overcharge, overdischarge, and overcurrent.

The charge control circuit 10 described in Embodiment 1 can be used as the charge control circuit 914 . Since the same circuit configuration can be used, detailed description is omitted here.

An antenna and a receiving circuit may be provided in addition to the charging control circuit 914 . The secondary battery 913 can also be charged without contact using an antenna. The antenna is not limited to a coil shape, and may be linear or plate-shaped, for example. Further, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. The antenna has a function of performing data communication with an external device, for example. As a communication method between the battery pack and the other device via the antenna, a response method such as NFC that can be used between the battery pack and the other device can be applied.

As shown in FIG. 5B, the connection terminal 911 is electrically connected to terminals 951 and 952 of the secondary battery 913 through the charge control circuit 914 . Note that a plurality of connection terminals 911 may be provided, and each of the plurality of connection terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

The battery pack has an insulating sheet layer 916 between the charging control circuit 914 and the secondary battery 913 . The insulating sheet layer 916 has a function of preventing a short circuit caused by the secondary battery 913, for example. As the insulating sheet layer 916, for example, an organic resin film or an adhesive sheet can be used.

Further, an internal structure example of the secondary battery 913 is described with reference to FIG.

The structure of a wound body 950 provided inside the secondary battery 913 is shown in FIG. A wound body 950 has a negative electrode 931 , a positive electrode 932 , and a separator 933 . The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked more than once.

The negative electrode 931 is connected to the connection terminal 911 shown in FIG. 5 via one of the terminals 951 and 952 . The positive electrode 932 is connected to the connection terminal 911 shown in FIG. 5 through the other of the terminals 951 and 952 .

A wound body 950 shown in FIG. 6A is impregnated with an electrolytic solution inside the exterior body. A housing made of metal is used as the exterior body. A film may be used as the exterior body, and in that case, the film may be provided with a charging control circuit formed on a flexible substrate.

A secondary battery 913 illustrated in FIG. 6B includes a wound body 950 provided with a terminal 951 and a terminal 952 inside a housing 930 . The wound body 950 is impregnated with the electrolytic solution inside the housing 930 . The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 6B , the housing 930 is shown separately for the sake of convenience. extending outside. As the housing 930, a metal material (such as aluminum) or a resin material can be used.

As the housing 930, an insulating material such as a metal material or an organic resin can be used.

FIG. 5A shows an example in which an insulating sheet layer 916 is provided on the surface of the housing and the flexible substrate is fixed with the surface on which the charging control circuit is provided facing inward; Instead, the terminal 951 and the terminal 952 may be connected with the surface on which the charge control circuit is formed facing outward. However, in that case, the connection part will be exposed, and there is a risk of electrostatic breakdown or short circuit, so careful assembly is required.

Since the charge control circuit 914 electrically connected to the connection terminal 911 is the charge control circuit 10 described in Embodiment 1, the secondary battery 913 can be highly safe.

This embodiment mode can be freely combined with the first embodiment mode.

(Embodiment 3)
In this embodiment, a structural example of an OS transistor that can be used in the charge control circuit 10 described in the above embodiment will be described. Note that the OS transistor is a thin film transistor and can be formed over a separation layer provided over a glass substrate or stacked over a single crystal silicon substrate.

Embodiment 1 is an example in which a flexible substrate provided with a charge control circuit is attached to the curved surface of a secondary battery. It is fixed to the flexible substrate by the peeling method. In addition, since Embodiment 1 is an example in which the secondary battery is attached to the plane of the secondary battery, after the OS transistor is formed over the single crystal silicon substrate, for example, the back surface of the single crystal silicon substrate is polished to be thinned. An object is fixed to a flexible substrate. Alternatively, the OS transistor may be separated from the single crystal silicon substrate by a hydrogen ion implantation separation method and fixed to the flexible substrate.

In this embodiment, a structure example of a semiconductor device in which an OS transistor is provided above a Si transistor formed over a single crystal silicon substrate will be described below.

<Structure example of semiconductor device>
A semiconductor device illustrated in FIG. 7 includes a transistor 300 , a transistor 500 , and a capacitor 600 . 8A is a cross-sectional view of the transistor 500 in the channel length direction, FIG. 8B is a cross-sectional view of the transistor 500 in the channel width direction, and FIG. 8C is a cross-sectional view of the transistor 300 in the channel width direction. It is a diagram.

The transistor 500 is a transistor (OS transistor) including a metal oxide in a channel formation region. The transistor 500 has the characteristics that a high voltage can be applied between the source and the drain, the off-state current does not easily increase even in a high-temperature environment, and the ratio of the on-state current to the off-state current is large even in a high-temperature environment. In terms of form, by using this in the charging control circuit 10, the mobile device can be a highly safe semiconductor device.

The semiconductor device described in this embodiment includes a transistor 300, a transistor 500, and a capacitor 600 as illustrated in FIG. The transistor 500 is provided above the transistor 300 , and the capacitor 600 is provided above the transistors 300 and 500 .

The transistor 300 is provided over a substrate 311 and includes a conductor 316, an insulator 315, a semiconductor region 313 formed of part of the substrate 311, and low-resistance regions 314a and 314b functioning as source and drain regions. have.

In the transistor 300, as shown in FIG. 8C, a top surface and side surfaces in the channel width direction of a semiconductor region 313 are covered with a conductor 316 with an insulator 315 interposed therebetween. By making the transistor 300 Fin-type in this manner, the effective channel width is increased, so that the on-characteristics of the transistor 300 can be improved. In addition, since the contribution of the electric field of the gate electrode can be increased, the off characteristics of the transistor 300 can be improved.

Note that the transistor 300 may be of either p-channel type or n-channel type.

A region in which a channel of the semiconductor region 313 is formed, a region in the vicinity thereof, low-resistance regions 314a and 314b serving as a source region or a drain region, and the like preferably contain a semiconductor such as a silicon-based semiconductor. It preferably contains crystalline silicon. Alternatively, a material including Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), or the like may be used. A structure using silicon in which the effective mass is controlled by applying stress to the crystal lattice and changing the lattice spacing may be used. Alternatively, the transistor 300 may be a HEMT (High Electron Mobility Transistor) by using GaAs, GaAlAs, or the like.

The low-resistance region 314a and the low-resistance region 314b are made of an element imparting n-type conductivity such as arsenic or phosphorus, or an element imparting p-type conductivity such as boron, in addition to the semiconductor material applied to the semiconductor region 313. contains elements that

The conductor 316 functioning as a gate electrode is a semiconductor material such as silicon containing an element imparting n-type conductivity such as arsenic or phosphorus or an element imparting p-type conductivity such as boron, a metal material, or an alloy. material, or a conductive material such as a metal oxide material can be used.

Note that since the work function is determined by the material of the conductor, Vth of the transistor can be adjusted by changing the material of the conductor. Specifically, it is preferable to use a material such as titanium nitride or tantalum nitride for the conductor. Furthermore, in order to achieve both conductivity and embeddability, it is preferable to use a metal material such as tungsten or aluminum as a laminate for the conductor, and it is particularly preferable to use tungsten from the viewpoint of heat resistance.

Note that the transistor 300 illustrated in FIG. 7 is an example, and the structure thereof is not limited, and an appropriate transistor may be used depending on the circuit configuration and the driving method.

An insulator 320 , an insulator 322 , an insulator 324 , and an insulator 326 are stacked in this order to cover the transistor 300 .

As the insulator 320, the insulator 322, the insulator 324, and the insulator 326, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like is used. Just do it.

The insulator 322 may function as a planarization film that planarizes a step caused by the transistor 300 or the like provided therebelow. For example, the top surface of the insulator 322 may be planarized by a chemical mechanical polishing (CMP) method or the like to improve planarity.

For the insulator 324, it is preferable to use a film having a barrier property such that hydrogen or impurities do not diffuse from the substrate 311, the transistor 300, or the like to the region where the transistor 500 is provided.

As an example of a film having a barrier property against hydrogen, silicon nitride formed by a CVD method can be used. Here, diffusion of hydrogen into a semiconductor element including an oxide semiconductor, such as the transistor 500, might degrade the characteristics of the semiconductor element. Therefore, it is preferable to use a film that suppresses diffusion of hydrogen between the transistor 500 and the transistor 300 . Specifically, the film that suppresses diffusion of hydrogen is a film from which the amount of desorption of hydrogen is small.

The desorption amount of hydrogen can be analyzed using, for example, a temperature-programmed desorption spectroscopy (TDS analysis) method. For example, the amount of hydrogen released from the insulator 324 is the amount of hydrogen atoms released per area of the insulator 324 when the surface temperature of the film is in the range of 50° C. to 500° C. in TDS analysis. , 10×10 ¹⁵ atoms/cm ² or less, preferably 5×10 ¹⁵ atoms/cm ² or less.

Note that the insulator 326 preferably has a lower dielectric constant than the insulator 324 . For example, the dielectric constant of insulator 326 is preferably less than 4, more preferably less than 3. Also, for example, the dielectric constant of the insulator 326 is preferably 0.7 times or less, more preferably 0.6 times or less, that of the insulator 324 . By using a material with a low dielectric constant as the interlayer film, the parasitic capacitance generated between wirings can be reduced.

In addition, the insulator 320 , the insulator 322 , the insulator 324 , and the insulator 326 are embedded with a conductor 328 and a conductor 330 that are connected to the capacitor 600 or the transistor 500 . Note that the conductors 328 and 330 function as plugs or wirings. In addition, conductors that function as plugs or wiring may have a plurality of structures collectively given the same reference numerals. Further, in this specification and the like, the wiring and the plug connected to the wiring may be integrated. That is, there are cases where a part of the conductor functions as a wiring and a part of the conductor functions as a plug.

As a material of each plug and wiring (the conductor 328, the conductor 330, etc.), a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material is used as a single layer or a laminated layer. can be used. It is preferable to use a high-melting-point material such as tungsten or molybdenum that has both heat resistance and conductivity, and it is preferable to use tungsten. Alternatively, it is preferably made of a low-resistance conductive material such as aluminum or copper. Wiring resistance can be reduced by using a low-resistance conductive material.

A wiring layer may be provided over the insulator 326 and the conductor 330 . For example, in FIG. 7, an insulator 350, an insulator 352, and an insulator 354 are stacked in order. A conductor 356 is formed over the insulators 350 , 352 , and 354 . The conductor 356 functions as a plug or wiring connected to the transistor 300 . Note that the conductor 356 can be provided using a material similar to that of the conductors 328 and 330 .

Note that for the insulator 350 , for example, an insulator having a barrier property against hydrogen is preferably used, like the insulator 324 . Further, the conductor 356 preferably contains a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in the opening of the insulator 350 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

Note that tantalum nitride or the like may be used as the conductor having a barrier property against hydrogen, for example. Further, by stacking tantalum nitride and tungsten having high conductivity, diffusion of hydrogen from the transistor 300 can be suppressed while the conductivity of the wiring is maintained. In this case, it is preferable that the tantalum nitride layer having a barrier property against hydrogen be in contact with the insulator 350 having a barrier property against hydrogen.

A wiring layer may be provided over the insulator 354 and the conductor 356 . For example, in FIG. 7, an insulator 360, an insulator 362, and an insulator 364 are stacked in order. A conductor 366 is formed over the insulators 360 , 362 , and 364 . Conductor 366 functions as a plug or wiring. Note that the conductor 366 can be provided using a material similar to that of the conductors 328 and 330 .

Note that for the insulator 360, for example, an insulator having a barrier property against hydrogen is preferably used, like the insulator 324. Further, the conductor 366 preferably contains a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in the opening of the insulator 360 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

A wiring layer may be provided over the insulator 364 and the conductor 366 . For example, in FIG. 7, an insulator 370, an insulator 372, and an insulator 374 are stacked in order. A conductor 376 is formed over the insulators 370 , 372 , and 374 . Conductor 376 functions as a plug or wiring. Note that the conductor 376 can be provided using a material similar to that of the conductors 328 and 330 .

Note that for the insulator 370, for example, an insulator having a barrier property against hydrogen is preferably used like the insulator 324. Further, the conductor 376 preferably contains a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in the opening of the insulator 370 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

A wiring layer may be provided over the insulator 374 and the conductor 376 . For example, in FIG. 7, an insulator 380, an insulator 382, and an insulator 384 are stacked in order. A conductor 386 is formed over the insulators 380 , 382 , and 384 . Conductor 386 functions as a plug or wiring. Note that the conductor 386 can be provided using a material similar to that of the conductors 328 and 330 .

Note that for the insulator 380, for example, an insulator having a barrier property against hydrogen is preferably used like the insulator 324. Further, the conductor 386 preferably contains a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in the opening of the insulator 380 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

The wiring layer including the conductor 356, the wiring layer including the conductor 366, the wiring layer including the conductor 376, and the wiring layer including the conductor 386 are described above. It is not limited to this. The number of wiring layers similar to the wiring layer including the conductor 356 may be three or less, or the number of wiring layers similar to the wiring layer including the conductor 356 may be five or more.

An insulator 510 , an insulator 512 , an insulator 514 , and an insulator 516 are stacked in this order over the insulator 384 . Any of the insulator 510, the insulator 512, the insulator 514, and the insulator 516 is preferably a substance having barrier properties against oxygen and hydrogen.

For the insulators 510 and 514, for example, a film having a barrier property that prevents hydrogen or impurities from diffusing from the substrate 311, a region where the transistor 300 is provided, or the like to a region where the transistor 500 is provided is used. is preferred. Therefore, a material similar to that of the insulator 324 can be used.

As an example of a film having a barrier property against hydrogen, silicon nitride formed by a CVD method can be used. Here, diffusion of hydrogen into a semiconductor element including an oxide semiconductor, such as the transistor 500, might degrade the characteristics of the semiconductor element. Therefore, it is preferable to use a film that suppresses diffusion of hydrogen between the transistor 500 and the transistor 300 . Specifically, the film that suppresses diffusion of hydrogen is a film from which the amount of desorption of hydrogen is small.

It is preferable to use a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide for the insulators 510 and 514, which are films having a barrier property against hydrogen.

In particular, aluminum oxide has a high shielding effect of preventing the penetration of both oxygen and impurities such as hydrogen and moisture, which cause variations in the electrical characteristics of the transistor. Therefore, aluminum oxide can prevent impurities such as hydrogen and moisture from entering the transistor 500 during and after the manufacturing process of the transistor. In addition, release of oxygen from the oxide forming the transistor 500 can be suppressed. Therefore, it is suitable for use as a protective film for the transistor 500 .

Further, for example, the insulator 512 and the insulator 516 can be formed using a material similar to that of the insulator 320 . Also, by using a material having a relatively low dielectric constant as the interlayer film, the parasitic capacitance generated between wirings can be reduced. For example, the insulators 512 and 516 can be formed using a silicon oxide film, a silicon oxynitride film, or the like.

In addition, the insulator 510 , the insulator 512 , the insulator 514 , and the insulator 516 are embedded with a conductor 518 , a conductor forming the transistor 500 (the conductor 503 ), and the like. Note that the conductor 518 functions as a plug or wiring that is connected to the capacitor 600 or the transistor 300 . The conductor 518 can be provided using a material similar to that of the conductors 328 and 330 .

In particular, a conductor 518 in a region in contact with the insulator 510 and the insulator 514 is preferably a conductor having barrier properties against oxygen, hydrogen, and water. With this structure, the transistor 300 and the transistor 500 can be separated by a layer having barrier properties against oxygen, hydrogen, and water, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

A transistor 500 is provided above the insulator 516 .

As shown in FIGS. 8A and 8B, the transistor 500 is provided with a conductor 503 embedded in insulators 512 and 516 and over the insulators 516 and 503 . an insulator 520 placed over the insulator 520, an insulator 522 placed over the insulator 520, an insulator 524 placed over the insulator 522, an oxide 530a placed over the insulator 524, and an oxide Oxide 530b over 530a, conductors 542a and 542b spaced apart over oxide 530b, and conductors 542a and 542b over and over conductors 542a and 542b. An insulator 580 with an opening overlapping between conductors 542b, a conductor 560 arranged in the opening, an oxide 530b, a conductor 542a, a conductor 542b, an insulator 580, and a conductor. an insulator 550 interposed between a body 560, an oxide 530b, a conductor 542a, a conductor 542b, an insulator 580, and an oxide 530c interposed between the insulator 550; have.

8A and 8B, an insulator 544 is preferably provided between the oxides 530a, 530b, the conductors 542a and 542b, and the insulator 580. . 8A and 8B, the conductor 560 includes a conductor 560a provided inside the insulator 550 and a conductor 560a embedded inside the conductor 560a. 560b and . Further, an insulator 574 is preferably provided over the insulator 580, the conductor 560, and the insulator 550 as shown in FIGS.

Note that the oxide 530a, the oxide 530b, and the oxide 530c may be collectively referred to as the oxide 530 below. Further, the conductor 542a and the conductor 542b may be collectively referred to as a conductor 542 in some cases.

Note that although the transistor 500 has a structure in which three layers of the oxide 530a, the oxide 530b, and the oxide 530c are stacked in a region where a channel is formed and in the vicinity thereof, the present invention is limited to this. not a thing For example, a single layer of the oxide 530b, a two-layer structure of the oxides 530b and 530a, a two-layer structure of the oxides 530b and 530c, or a stacked structure of four or more layers may be employed. Although the conductor 560 has a two-layer structure in the transistor 500, the present invention is not limited to this. For example, the conductor 560 may have a single-layer structure or a laminated structure of three or more layers. Further, the transistor 500 illustrated in FIGS. 7, 8A, and 8B is an example, and the structure is not limited thereto, and an appropriate transistor may be used depending on the circuit structure and driving method.

Here, the conductor 560 functions as a gate electrode of the transistor, and the conductors 542a and 542b function as source and drain electrodes, respectively. As described above, the conductor 560 is formed to be embedded in the opening of the insulator 580 and the region sandwiched between the conductors 542a and 542b. The placement of conductor 560 , conductor 542 a and conductor 542 b is selected in a self-aligned manner with respect to openings in insulator 580 . That is, in the transistor 500, the gate electrode can be arranged between the source electrode and the drain electrode in a self-aligned manner. Therefore, the conductor 560 can be formed without providing an alignment margin, so that the area occupied by the transistor 500 can be reduced. As a result, miniaturization and high integration of the semiconductor device can be achieved.

Furthermore, since conductor 560 is formed in a region between conductors 542a and 542b in a self-aligned manner, conductor 560 does not have a region that overlaps conductors 542a or 542b. Accordingly, parasitic capacitance formed between the conductor 560 and the conductors 542a and 542b can be reduced. Therefore, the switching speed of the transistor 500 can be improved and high frequency characteristics can be obtained.

Conductor 560 may function as a first gate (also called top gate) electrode. In some cases, the conductor 503 functions as a second gate (also referred to as a bottom gate) electrode. In that case, Vth of the transistor 500 can be controlled by changing the potential applied to the conductor 503 independently of the potential applied to the conductor 560 . In particular, by applying a negative potential to the conductor 503, Vth of the transistor 500 can be made higher than 0 V, and off current can be reduced. Therefore, when a negative potential is applied to the conductor 503, the drain current when the potential applied to the conductor 560 is 0 V can be made smaller than when no potential is applied.

The conductor 503 is arranged so as to overlap with the oxide 530 and the conductor 560 . Accordingly, when a potential is applied to the conductor 560 and the conductor 503, an electric field generated from the conductor 560 is connected to an electric field generated from the conductor 503, so that a channel formation region formed in the oxide 530 is covered. can be done. In this specification and the like, a transistor structure in which a channel formation region is electrically surrounded by electric fields of a first gate electrode and a second gate electrode is referred to as a surrounded channel (S-channel) structure.

In this specification and the like, in the S-channel structure, the side surfaces and the periphery of the oxide 530 in contact with the conductors 542a and 542b functioning as source and drain electrodes are said to be i-type like the channel formation region. It has characteristics. In addition, since the side surface and the periphery of the oxide 530 that are in contact with the conductors 542a and 542b are in contact with the insulator 544, they can be i-type like the channel formation region. In this specification and the like, type I can be treated in the same way as high-purity intrinsic, which will be described later. Also, the S-channel structure disclosed in this specification and the like is different from the Fin type structure and the planar type structure. By adopting the S-channel structure, it is possible to increase resistance to the short channel effect, in other words, to make the transistor less susceptible to the short channel effect.

The conductor 503 has a structure similar to that of the conductor 518. A conductor 503a is formed in contact with the inner walls of the openings of the insulators 514 and 516, and a conductor 503b is further formed inside.

The insulator 520, the insulator 522, the insulator 524, and the insulator 550 function as gate insulating films.

Here, the insulator 524 in contact with the oxide 530 preferably contains more oxygen than the stoichiometric composition. In other words, the insulator 524 preferably has an excess oxygen region. By providing such an insulator containing excess oxygen in contact with the oxide 530, oxygen vacancies in the oxide 530 can be reduced and the reliability of the transistor 500 can be improved.

Specifically, an oxide material from which part of oxygen is released by heating is preferably used as the insulator having the excess oxygen region. The oxide that desorbs oxygen by heating means that the desorption amount of oxygen in terms of oxygen atoms is 1.0×10 ¹⁸ atoms/cm ³ or more, preferably 1, in TDS (Thermal Desorption Spectroscopy) analysis. 0×10 ¹⁹ atoms/cm ³ or more, more preferably 2.0×10 ¹⁹ atoms/cm ³ or more, or 3.0×10 ²⁰ atoms/cm ³ or more. The surface temperature of the film during the TDS analysis is preferably in the range of 100° C. or higher and 700° C. or lower, or 100° C. or higher and 400° C. or lower.

In addition, when the insulator 524 has an excess oxygen region, the insulator 522 preferably has a function of suppressing diffusion of oxygen (eg, oxygen atoms, oxygen molecules, etc.) (the above oxygen is difficult to permeate).

Since the insulator 522 has a function of suppressing diffusion of oxygen and impurities, oxygen contained in the oxide 530 does not diffuse to the insulator 520 side, which is preferable. In addition, the conductor 503 can be prevented from reacting with oxygen contained in the insulator 524 and the oxide 530 .

Insulator 522 is, for example, a so-called high oxide such as aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO ₃ ) or (Ba,Sr)TiO ₃ (BST). It is preferable to use insulators containing -k materials in a single layer or a stack. As transistors are miniaturized and highly integrated, thinning of the gate insulating film may cause problems such as leakage current. By using a high-k material for the insulator functioning as the gate insulating film, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

In particular, an insulator containing an oxide of one or both of aluminum and hafnium, which is an insulating material having a function of suppressing diffusion of impurities and oxygen (through which oxygen hardly penetrates), is preferably used. As the insulator containing oxide of one or both of aluminum and hafnium, aluminum oxide, hafnium oxide, oxide containing aluminum and hafnium (hafnium aluminate), or the like is preferably used. When the insulator 522 is formed using such a material, the insulator 522 suppresses release of oxygen from the oxide 530 and entry of impurities such as hydrogen from the periphery of the transistor 500 into the oxide 530. act as a layer.

Alternatively, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide may be added to these insulators. Alternatively, these insulators may be nitrided. Silicon oxide, silicon oxynitride, or silicon nitride may be stacked over the above insulator.

Insulator 520 is also preferably thermally stable. For example, silicon oxide and silicon oxynitride are preferred because they are thermally stable. In addition, by combining an insulator made of a high-k material with silicon oxide or silicon oxynitride, the insulator 520 with a stacked structure that is thermally stable and has a high relative dielectric constant can be obtained.

Note that the insulator 520, the insulator 522, and the insulator 524 may have a stacked structure of two or more layers. In that case, it is not limited to a laminated structure made of the same material, and a laminated structure made of different materials may be used.

In the transistor 500, a metal oxide functioning as an oxide semiconductor is preferably used for the oxide 530 including a channel formation region. For example, as the oxide 530, In-M-Zn oxide (element M is aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium , hafnium, tantalum, tungsten, magnesium, or the like) may be used. Alternatively, as the oxide 530, an In--Ga oxide or an In--Zn oxide may be used.

A metal oxide with low carrier density is preferably used for the transistor 500 . In the case of lowering the carrier density of the metal oxide, the impurity concentration in the metal oxide should be lowered to lower the defect level density. In this specification and the like, a low impurity concentration and a low defect level density are referred to as high-purity intrinsic or substantially high-purity intrinsic. Impurities in metal oxides include, for example, hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, and silicon.

In particular, hydrogen contained in the metal oxide reacts with oxygen bound to the metal atom to form water, which may cause oxygen vacancies in the metal oxide. If the channel formation region in the metal oxide contains oxygen vacancies, the transistor may have normally-on characteristics. Furthermore, a defect in which hydrogen is added to an oxygen vacancy functions as a donor, and an electron, which is a carrier, may be generated. In addition, part of hydrogen may bond with oxygen that bonds with a metal atom to generate an electron that is a carrier. Therefore, a transistor using a metal oxide containing a large amount of hydrogen tends to have normally-on characteristics.

Defects with hydrogen in oxygen vacancies can function as donors for metal oxides. However, it is difficult to quantitatively evaluate the defects. Therefore, metal oxides are sometimes evaluated by carrier density instead of donor concentration. Therefore, in this specification and the like, instead of the donor concentration, the carrier density assuming a state in which no electric field is applied may be used as a parameter of the metal oxide. In other words, the “carrier density” described in this specification and the like may be rephrased as “donor concentration”.

Therefore, when a metal oxide is used for the oxide 530, hydrogen in the metal oxide is preferably reduced as much as possible. Specifically, in the metal oxide, the hydrogen concentration obtained by secondary ion mass spectrometry (SIMS) is less than 1×10 ²⁰ atoms/cm ³ , preferably 1×10 ¹⁹ atoms/cm It is less than ³ , more preferably less than 5×10 ¹⁸ atoms/cm ³ , still more preferably less than 1×10 ¹⁸ atoms/cm ³ . By using a metal oxide in which impurities such as hydrogen are sufficiently reduced for a channel formation region of a transistor, stable electrical characteristics can be imparted.

Further, when a metal oxide is used for the oxide 530, the carrier density of the metal oxide in the channel formation region is preferably 1×10 ¹⁸ cm ⁻³ or less and less than 1×10 ¹⁷ cm ⁻³ . is more preferably less than 1×10 ¹⁶ cm ⁻³ , still more preferably less than 1×10 ¹³ cm ⁻³ , even more preferably less than 1×10 ¹² cm ⁻³ . Although there is no particular limitation on the lower limit of the carrier density of the metal oxide in the channel forming region, it can be, for example, 1×10 ⁻⁹ cm ⁻³ .

In the case where a metal oxide is used for the oxide 530, the conductors 542 (the conductors 542a and 542b) are in contact with the oxide 530, whereby oxygen in the oxide 530 diffuses into the conductor 542. Conductor 542 may oxidize. Oxidation of the conductor 542 is highly likely to reduce the conductivity of the conductor 542 . Note that diffusion of oxygen in the oxide 530 to the conductor 542 can be rephrased as that the conductor 542 absorbs oxygen in the oxide 530 .

Further, oxygen in the oxide 530 diffuses into the conductor 542 (the conductor 542a and the conductor 542b), so that the conductor 542a and the oxide 530b and the conductor 542b and the oxide 530b are diffused. Different layers may form between them. Since the different layer contains more oxygen than the conductor 542, the different layer is presumed to have insulating properties. At this time, the three-layer structure of the conductor 542, the different layer, and the oxide 530b can be regarded as a three-layer structure composed of metal-insulator-semiconductor, and is called a metal-insulator-semiconductor (MIS) structure. Alternatively, it may be called a diode junction structure mainly composed of the MIS structure.

Note that the different layer is not limited to being formed between the conductor 542 and the oxide 530b. It may form between body 542 and oxide 530b and between conductor 542 and oxide 530c.

A metal oxide which functions as a channel formation region in the oxide 530 preferably has a bandgap of 2 eV or more, preferably 2.5 eV or more. By using a metal oxide with a large bandgap in this manner, off-state current of a transistor can be reduced.

Since the oxide 530 includes the oxide 530a under the oxide 530b, diffusion of impurities from a structure formed below the oxide 530a to the oxide 530b can be suppressed. In addition, by providing the oxide 530c over the oxide 530b, diffusion of impurities from a structure formed above the oxide 530c to the oxide 530b can be suppressed.

Note that the oxide 530 preferably has a layered structure with oxides having different atomic ratios of metal atoms. Specifically, in the metal oxide used for the oxide 530a, the atomic number ratio of the element M among the constituent elements is greater than the atomic number ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. is preferred. Further, in the metal oxide used for the oxide 530a, the atomic ratio of the element M to In is preferably higher than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. In addition, the atomic ratio of In to the element M in the metal oxide used for the oxide 530b is preferably higher than the atomic ratio of In to the element M in the metal oxide used for the oxide 530a. In addition, the oxide 530c can be a metal oxide that can be used for the oxide 530a or the oxide 530b.

In addition, it is preferable that the energies of the conduction band bottoms of the oxides 530a and 530c be higher than the energies of the conduction band bottoms of the oxide 530b. In other words, the electron affinities of the oxides 530a and 530c are preferably smaller than the electron affinities of the oxide 530b.

Here, the energy level at the bottom of the conduction band changes smoothly at the junction of the oxide 530a, the oxide 530b, and the oxide 530c. In other words, it can be said that the energy level of the bottom of the conduction band at the junction of the oxide 530a, the oxide 530b, and the oxide 530c continuously changes or continuously joins. In order to achieve this, the defect level density of the mixed layers formed at the interface between the oxides 530a and 530b and the interface between the oxides 530b and 530c should be lowered.

Specifically, the oxide 530a and the oxide 530b, and the oxide 530b and the oxide 530c have a common element (main component) other than oxygen, thereby forming a mixed layer with a low defect level density. be able to. For example, when the oxide 530b is an In--Ga--Zn oxide, the oxides 530a and 530c may be In--Ga--Zn oxide, Ga--Zn oxide, gallium oxide, or the like.

At this time, the main path of carriers is the oxide 530b. When the oxides 530a and 530c have the above structures, defect level densities at the interfaces between the oxides 530a and 530b and between the oxides 530b and 530c can be reduced. Therefore, the influence of interface scattering on carrier conduction is reduced, and the transistor 500 can obtain a high on-state current.

A conductor 542 (a conductor 542a and a conductor 542b) functioning as a source electrode and a drain electrode is provided over the oxide 530b. Conductors 542 include aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, It is preferable to use a metal element selected from lanthanum, an alloy containing the metal elements described above, or an alloy combining the metal elements described above. For example, tantalum nitride, titanium nitride, tungsten, nitride containing titanium and aluminum, nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxide containing strontium and ruthenium, oxide containing lanthanum and nickel, and the like are used. is preferred. Also, tantalum nitride, titanium nitride, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, and oxides containing lanthanum and nickel are difficult to oxidize. It is preferable because it is a conductive material or a material that maintains conductivity even after absorbing oxygen.

Further, as shown in FIG. 8A, regions 543 (regions 543a and 543b) are formed as low-resistance regions at the interface between the oxide 530 and the conductor 542 and in the vicinity thereof in some cases. be. At this time, the region 543a functions as one of the source region and the drain region, and the region 543b functions as the other of the source region and the drain region. A channel formation region is formed in a region sandwiched between the regions 543a and 543b.

By providing the conductor 542 so as to be in contact with the oxide 530, the oxygen concentration in the region 543 may be reduced. In some cases, a metal compound layer containing the metal contained in the conductor 542 and the component of the oxide 530 is formed in the region 543 . In such a case, the carrier density in region 543 increases and region 543 becomes a low resistance region.

An insulator 544 is provided to cover the conductor 542 and suppress oxidation of the conductor 542 . At this time, the insulator 544 may be provided so as to cover the side surface of the oxide 530 and be in contact with the insulator 524 .

As the insulator 544, a metal oxide containing one or more selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, or the like can be used. can.

In particular, as the insulator 544, an insulator containing one or both oxides of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate), is preferably used. In particular, hafnium aluminate has higher heat resistance than hafnium oxide film. Therefore, it is preferable because it is less likely to be crystallized in heat treatment in a later step. Note that the insulator 544 is not essential if the conductor 542 is made of a material having oxidation resistance or if the conductivity does not significantly decrease even if oxygen is absorbed. It may be appropriately designed depending on the required transistor characteristics.

The insulator 550 functions as a gate insulating film. Insulator 550 is preferably placed in contact with the inside (top and sides) of oxide 530c. The insulator 550 is preferably formed using an insulator from which oxygen is released by heating. For example, in TDS analysis, the desorption amount of oxygen in terms of oxygen atoms is 1.0×10 ¹⁸ atoms/cm ³ or more, preferably 1.0×10 ¹⁹ atoms/cm ³ or more, more preferably 2. It is an oxide film having a density of 0×10 ¹⁹ atoms/cm ³ or more, or 3.0×10 ²⁰ atoms/cm ³ or more. The surface temperature of the film during the TDS analysis is preferably in the range of 100° C. or higher and 700° C. or lower.

Specifically, silicon oxide having excess oxygen, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, and vacancies Silicon oxide can be used. In particular, silicon oxide and silicon oxynitride are preferable because they are stable against heat.

By providing an insulator from which oxygen is released by heating as the insulator 550 in contact with the top surface of the oxide 530c, oxygen is effectively introduced from the insulator 550 to the channel formation region of the oxide 530b through the oxide 530c. can be supplied. Further, similarly to the insulator 524, the concentration of impurities such as water or hydrogen in the insulator 550 is preferably reduced. The thickness of the insulator 550 is preferably 1 nm or more and 20 nm or less.

Further, a metal oxide may be provided between the insulator 550 and the conductor 560 in order to efficiently supply excess oxygen contained in the insulator 550 to the oxide 530 . The metal oxide preferably suppresses diffusion of oxygen from the insulator 550 to the conductor 560 . By providing the metal oxide that suppresses diffusion of oxygen, diffusion of excess oxygen from the insulator 550 to the conductor 560 is suppressed. That is, reduction in the amount of excess oxygen supplied to the oxide 530 can be suppressed. In addition, oxidation of the conductor 560 due to excess oxygen can be suppressed. As the metal oxide, a material that can be used for the insulator 544 may be used.

Although the conductor 560 functioning as the first gate electrode has a two-layer structure in FIGS. 8A and 8B, it may have a single-layer structure or a stacked structure of three or more layers. .

The conductor 560a has a function of suppressing diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (such as N ₂ O, NO, NO ₂ ), and copper atoms. Materials are preferably used. Alternatively, it is preferable to use a conductive material having a function of suppressing diffusion of oxygen (eg, at least one of oxygen atoms and oxygen molecules). Since the conductor 560a has a function of suppressing diffusion of oxygen, oxygen contained in the insulator 550 can suppress oxidation of the conductor 560b and a decrease in conductivity. As the conductive material having a function of suppressing diffusion of oxygen, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like is preferably used, for example.

A conductive material containing tungsten, copper, or aluminum as its main component is preferably used for the conductor 560b. In addition, since the conductor 560b also functions as a wiring, a conductor with high conductivity is preferably used. For example, a conductive material whose main component is tungsten, copper, or aluminum can be used. Further, the conductor 560b may have a layered structure, for example, a layered structure of titanium, titanium nitride, and the above conductive materials.

The insulator 580 is provided over the conductor 542 with the insulator 544 interposed therebetween. Insulator 580 preferably has excess oxygen regions. For example, the insulator 580 may be silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, or silicon oxide having vacancies. , or resin. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. In particular, silicon oxide and silicon oxide having vacancies are preferable because an excess oxygen region can be easily formed in a later step.

Insulator 580 preferably has excess oxygen regions. By providing the insulator 580 from which oxygen is released by heating in contact with the oxide 530c, oxygen in the insulator 580 can be efficiently supplied to the oxide 530 through the oxide 530c. Note that the concentration of impurities such as water or hydrogen in the insulator 580 is preferably low.

The opening of the insulator 580 is formed so as to overlap a region between the conductors 542a and 542b. Thus, the conductor 560 is formed so as to be embedded in the opening of the insulator 580 and the region sandwiched between the conductors 542a and 542b.

When miniaturizing a semiconductor device, it is required to shorten the gate length, but it is necessary to prevent the conductivity of the conductor 560 from being lowered. Therefore, when the thickness of the conductor 560 is increased, the conductor 560 can have a shape with a high aspect ratio. In this embodiment mode, since the conductor 560 is embedded in the opening of the insulator 580, the conductor 560 can be formed without collapsing during the process even if the conductor 560 has a high aspect ratio. can be done.

The insulator 574 is preferably provided in contact with the top surface of the insulator 580 , the top surface of the conductor 560 , and the top surface of the insulator 550 . By forming the insulator 574 by a sputtering method, excess oxygen regions can be provided in the insulators 550 and 580 . Thereby, oxygen can be supplied into the oxide 530 from the excess oxygen region.

For example, the insulator 574 can be a metal oxide containing one or more selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, or the like. can be done.

In particular, aluminum oxide has a high barrier property and can suppress the diffusion of hydrogen and nitrogen even in a thin film having a thickness of 0.5 nm or more and 3.0 nm or less. Therefore, the aluminum oxide film formed by the sputtering method can function not only as an oxygen supply source but also as a barrier film against impurities such as hydrogen.

An insulator 581 functioning as an interlayer film is preferably provided over the insulator 574 . Like the insulator 524 and the like, the insulator 581 preferably has a reduced concentration of impurities such as water or hydrogen in the film.

In addition, the conductors 540 a and 540 b are arranged in openings formed in the insulators 581 , 574 , 580 , and 544 . The conductor 540a and the conductor 540b are provided to face each other with the conductor 560 interposed therebetween. The conductors 540a and 540b have the same structure as the conductors 546 and 548, which will be described later.

An insulator 582 is provided over the insulator 581 . It is preferable that the insulator 582 use a substance that has a barrier property against oxygen and hydrogen. Therefore, a material similar to that of the insulator 514 can be used for the insulator 582 . For example, the insulator 582 is preferably formed using a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide.

In particular, aluminum oxide has a high shielding effect of preventing the penetration of both oxygen and impurities such as hydrogen and moisture, which cause variations in the electrical characteristics of the transistor. Therefore, aluminum oxide can prevent impurities such as hydrogen and moisture from entering the transistor 500 during and after the manufacturing process of the transistor. In addition, release of oxygen from the oxide forming the transistor 500 can be suppressed. Therefore, it is suitable for use as a protective film for the transistor 500 .

An insulator 586 is provided over the insulator 582 . A material similar to that of the insulator 320 can be used for the insulator 586 . Also, by using a material having a relatively low dielectric constant as the interlayer film, the parasitic capacitance generated between wirings can be reduced. For example, a silicon oxide film, a silicon oxynitride film, or the like can be used as the insulator 586 .

In addition, the insulator 520, the insulator 522, the insulator 524, the insulator 544, the insulator 580, the insulator 574, the insulator 581, the insulator 582, and the insulator 586 include the conductor 546, the conductor 548, and the like. is embedded.

The conductors 546 and 548 function as plugs or wirings that connect to the capacitor 600 , the transistor 500 , or the transistor 300 . The conductors 546 and 548 can be formed using a material similar to that of the conductors 328 and 330 .

Next, a capacitor 600 is provided above the transistor 500 . A capacitor 600 includes a conductor 610 , a conductor 620 , and an insulator 630 .

A conductor 612 may be provided over the conductor 546 and the conductor 548 . The conductor 612 functions as a plug or wiring connected to the transistor 500 . The conductor 610 functions as an electrode of the capacitor 600 . Note that the conductor 612 and the conductor 610 can be formed at the same time.

The conductors 612 and 610 are metal films containing an element selected from molybdenum, titanium, tantalum, tungsten, aluminum, copper, chromium, neodymium, and scandium, or metal nitride films containing any of the above elements as components. (tantalum nitride film, titanium nitride film, molybdenum nitride film, tungsten nitride film) or the like can be used. Alternatively, indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, and silicon oxide are added. Conductive materials such as indium tin oxide can also be applied.

Although the conductors 612 and 610 each have a single-layer structure in FIGS. 7A and 7B, they are not limited to this structure and may have a stacked structure of two or more layers. For example, between a conductor with a barrier property and a conductor with high conductivity, a conductor with a barrier property and a conductor with high adhesion to the conductor with high conductivity may be formed.

A conductor 620 is provided so as to overlap with the conductor 610 with an insulator 630 interposed therebetween. Note that the conductor 620 can be made of a conductive material such as a metal material, an alloy material, or a metal oxide material. It is preferable to use a high-melting-point material such as tungsten or molybdenum that has both heat resistance and conductivity, and it is particularly preferable to use tungsten. In addition, when forming simultaneously with another structure such as a conductor, a low-resistance metal material such as Cu (copper) or Al (aluminum) may be used.

An insulator 650 is provided over the conductor 620 and the insulator 630 . The insulator 650 can be provided using a material similar to that of the insulator 320 . In addition, the insulator 650 may function as a planarizing film that covers the uneven shape thereunder.

With the use of this structure, variation in electrical characteristics can be suppressed and reliability can be improved in a semiconductor device including a transistor including an oxide semiconductor. Alternatively, a transistor including an oxide semiconductor with high on-state current can be provided. Alternatively, a transistor including an oxide semiconductor with low off-state current can be provided. Alternatively, a semiconductor device with reduced power consumption can be provided. Alternatively, a semiconductor device including a transistor including an oxide semiconductor can be miniaturized or highly integrated.

<Example of transistor structure>
Note that the transistor 500 of the semiconductor device described in this embodiment is not limited to the above structure. Structural examples that can be used for the transistor 500 are described below.

<Transistor Structure Example 1>
A structural example of the transistor 510A is described with reference to FIGS. FIG. 9A is a top view of the transistor 510A. FIG. 9(B) is a cross-sectional view of the portion indicated by the dashed line L1-L2 in FIG. 9(A). FIG. 9(C) is a cross-sectional view of the portion indicated by the one-dot chain line W1-W2 in FIG. 9(A). Note that in the top view of FIG. 9A, some elements are omitted for clarity of illustration.

9A, 9B, and 9C, the transistor 510A and the insulators 511, 512, 514, 516, 580, 582, and 582 functioning as interlayer films. A body 584 is shown. Also shown are conductors 546 (a conductor 546a and a conductor 546b) that are electrically connected to the transistor 510A and function as contact plugs, and a conductor 503 that functions as a wiring.

The transistor 510A includes a conductor 560 (a conductor 560a and a conductor 560b) functioning as a first gate electrode, a conductor 505 (a conductor 505a and a conductor 505b) functioning as a second gate electrode, An insulator 550 functioning as a first gate insulating film; insulators 521, 522, and 524 functioning as a second gate insulating film; oxide 530a, oxide 530b, and oxide 530c);

Further, in the transistor 510A illustrated in FIG. 9, the oxide 530c, the insulator 550, and the conductor 560 are placed in an opening provided in the insulator 580 with the insulator 574 interposed therebetween. In addition, oxide 530c, insulator 550, and conductor 560 are placed between conductors 542a and 542b.

The insulators 511 and 512 function as interlayer films.

The interlayer film may be silicon oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO ₃ ) or (Ba, Sr). Insulators such as TiO ₃ (BST) can be used in single layers or stacks. Alternatively, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide may be added to these insulators. Alternatively, these insulators may be nitrided. Silicon oxide, silicon oxynitride, or silicon nitride may be stacked over the above insulator.

For example, the insulator 511 preferably functions as a barrier film that prevents impurities such as water or hydrogen from entering the transistor 510A from the substrate side. Therefore, for the insulator 511, it is preferable to use an insulating material that has a function of suppressing diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (through which the above impurities hardly penetrate). Alternatively, it is preferable to use an insulating material that has a function of suppressing diffusion of oxygen (eg, at least one of oxygen atoms, oxygen molecules, and the like) (the oxygen hardly permeates). Alternatively, for example, aluminum oxide, silicon nitride, or the like may be used as the insulator 511 . With this structure, impurities such as hydrogen and water can be prevented from diffusing from the substrate side of the insulator 511 toward the transistor 510A side.

For example, insulator 512 preferably has a lower dielectric constant than insulator 511 . By using a material with a low dielectric constant as the interlayer film, the parasitic capacitance generated between wirings can be reduced.

The conductor 503 is formed to be embedded in the insulator 512 . Here, the height of the top surface of the conductor 503 and the height of the top surface of the insulator 512 can be made approximately the same. Note that although the conductor 503 has a single-layer structure, the present invention is not limited to this. For example, the conductor 503 may have a multilayer structure of two or more layers. Note that the conductor 503 is preferably made of a highly conductive material containing tungsten, copper, or aluminum as its main component.

In transistor 510A, conductor 560 may function as a first gate (also called top gate) electrode. In some cases, the conductor 505 functions as a second gate (also referred to as a bottom gate) electrode. In that case, the potential applied to the conductor 505 is changed independently of the potential applied to the conductor 560, so that the threshold voltage of the transistor 510A can be controlled. In particular, by applying a negative potential to the conductor 505, the threshold voltage of the transistor 510A can be made higher than 0 V and the off current can be reduced. Therefore, when a negative potential is applied to the conductor 505, the drain current when the potential applied to the conductor 560 is 0 V can be made smaller than when no potential is applied.

Further, for example, when the conductor 505 and the conductor 560 are provided so as to overlap each other, when a potential is applied to the conductor 560 and the conductor 505, an electric field generated from the conductor 560 and an electric field generated from the conductor 505 , and can cover the channel formation region formed in the oxide 530 .

That is, the electric field of the conductor 560 functioning as the first gate electrode and the electric field of the conductor 505 functioning as the second gate electrode can electrically surround the channel formation region. That is, it has a surrounded channel (S-channel) structure like the transistor 500 described above.

The insulator 514 and the insulator 516 function as interlayer films similarly to the insulator 511 or the insulator 512 . For example, the insulator 514 preferably functions as a barrier film that prevents impurities such as water or hydrogen from entering the transistor 510A from the substrate side. With this structure, impurities such as hydrogen and water can be prevented from diffusing from the substrate side of the insulator 514 toward the transistor 510A side. Also, for example, the insulator 516 preferably has a lower dielectric constant than the insulator 514 . By using a material with a low dielectric constant as the interlayer film, the parasitic capacitance generated between wirings can be reduced.

A conductor 505 functioning as a second gate has a conductor 505a formed in contact with the inner walls of the openings of the insulators 514 and 516, and a conductor 505b formed inside. Here, the height of the top surfaces of the conductors 505a and 505b and the height of the top surface of the insulator 516 can be made approximately the same. Note that although the structure in which the conductors 505a and 505b are stacked is shown in the transistor 510A, the present invention is not limited to this. For example, the conductor 505 may be provided as a single layer or a laminated structure of three or more layers.

Here, for the conductor 505a, it is preferable to use a conductive material that has a function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (through which the above impurities hardly penetrate). Alternatively, it is preferable to use a conductive material that has a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms and oxygen molecules) (the above-mentioned oxygen hardly permeates). In this specification, the function of suppressing the diffusion of impurities or oxygen means the function of suppressing the diffusion of one or all of the impurities or oxygen.

For example, since the conductor 505a has a function of suppressing diffusion of oxygen, it is possible to suppress a decrease in conductivity due to oxidation of the conductor 505b.

In the case where the conductor 505 also functions as a wiring, the conductor 505b is preferably made of a highly conductive material containing tungsten, copper, or aluminum as its main component. In that case, the conductor 503 is not necessarily provided. Note that although the conductor 505b is shown as a single layer, it may have a layered structure, for example, a layered structure of titanium, titanium nitride, and any of the above conductive materials.

The insulators 521, 522, and 524 function as second gate insulating films.

Further, the insulator 522 preferably has a barrier property. Since the insulator 522 has a barrier property, it functions as a layer that prevents impurities such as hydrogen from entering the transistor 510A from the periphery of the transistor 510A.

The insulator 522 is made of, for example, aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO ₃ ) or ( It is preferable to use an insulator containing a so-called high-k material such as Ba,Sr)TiO ₃ (BST) in a single layer or a laminated layer. As transistors are miniaturized and highly integrated, thinning of the gate insulating film may cause problems such as leakage current. By using a high-k material for the insulator functioning as the gate insulating film, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

Also, the insulator 521 is preferably thermally stable. For example, silicon oxide and silicon oxynitride are preferred because they are thermally stable. In addition, by combining an insulator made of a high-k material with silicon oxide or silicon oxynitride, the insulator 521 with a stacked structure that is thermally stable and has a high relative dielectric constant can be obtained.

Note that FIG. 9 shows a stacked structure of three layers as the second gate insulating film, but a single layer or a stacked structure of two or more layers may be used. In that case, it is not limited to a laminated structure made of the same material, and a laminated structure made of different materials may be used.

Oxide 530 having a region functioning as a channel formation region includes oxide 530a, oxide 530b over oxide 530a, and oxide 530c over oxide 530b. By providing the oxide 530a under the oxide 530b, diffusion of impurities from a structure formed below the oxide 530a to the oxide 530b can be suppressed. In addition, by providing the oxide 530c over the oxide 530b, diffusion of impurities from a structure formed above the oxide 530c to the oxide 530b can be suppressed. As the oxide 530, an oxide semiconductor which is one of the metal oxides described above can be used.

Note that the oxide 530c is preferably provided in the opening provided in the insulator 580 with the insulator 574 interposed therebetween. When the insulator 574 has a barrier property, diffusion of impurities from the insulator 580 into the oxide 530 can be suppressed.

One of the conductors 542 functions as a source electrode and the other functions as a drain electrode.

The conductors 542a and 542b can be formed using a metal such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, or tungsten, or an alloy containing any of these as its main component. . In particular, a metal nitride film such as tantalum nitride is preferable because it has a barrier property against hydrogen or oxygen and has high oxidation resistance.

In addition, although a single layer structure is shown in FIG. 9, a laminated structure of two or more layers may be used. For example, a tantalum nitride film and a tungsten film are preferably stacked. Alternatively, a titanium film and an aluminum film may be stacked. A two-layer structure in which an aluminum film is stacked over a tungsten film, a two-layer structure in which a copper film is stacked over a copper-magnesium-aluminum alloy film, a two-layer structure in which a copper film is stacked over a titanium film, a two-layer structure in which a copper film is stacked over a titanium film, A two-layer structure in which copper films are stacked may be used.

In addition, a three-layer structure in which a titanium film or a titanium nitride film is laminated, an aluminum film or a copper film is laminated on the titanium film or the titanium nitride film, and a titanium film or a titanium nitride film is formed thereon, a molybdenum film or a There is a three-layer structure including a molybdenum nitride film, an aluminum film or a copper film laminated on the molybdenum film or the molybdenum nitride film, and a molybdenum film or a molybdenum nitride film formed thereon. Note that a transparent conductive material containing indium oxide, tin oxide, or zinc oxide may be used.

A barrier layer may be provided over the conductor 542 . The barrier layer preferably uses a substance having barrier properties against oxygen or hydrogen. With this structure, oxidation of the conductor 542 can be suppressed when the insulator 574 is formed.

A metal oxide, for example, can be used for the barrier layer. In particular, it is preferable to use an insulating film having a barrier property against oxygen and hydrogen, such as aluminum oxide, hafnium oxide, or gallium oxide. Alternatively, silicon nitride formed by a CVD method may be used.

By including the barrier layer, the selection of materials for the conductor 542 can be widened. For example, the conductor 542 can be made of a material having low oxidation resistance but high conductivity, such as tungsten or aluminum. Alternatively, for example, a conductor that can be easily formed into a film or processed can be used.

The insulator 550 functions as a first gate insulating film. The insulator 550 is preferably provided in the opening provided in the insulator 580 with the oxide 530c and the insulator 574 interposed therebetween.

As transistors are miniaturized and highly integrated, thinning of the gate insulating film may cause problems such as leakage current. In that case, the insulator 550 may have a stacked structure similarly to the second gate insulating film. By making the insulator that functions as the gate insulating film a laminated structure of a high-k material and a thermally stable material, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness. becomes. Moreover, it is possible to obtain a laminated structure that is thermally stable and has a high dielectric constant.

A conductor 560 functioning as a first gate electrode has a conductor 560a and a conductor 560b over the conductor 560a. For the conductor 560a, similarly to the conductor 505a, it is preferable to use a conductive material that has a function of suppressing diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms. Alternatively, it is preferable to use a conductive material having a function of suppressing diffusion of oxygen (eg, at least one of oxygen atoms and oxygen molecules).

Since the conductor 560a has a function of suppressing the diffusion of oxygen, the material selectivity of the conductor 560b can be improved. In other words, with the presence of the conductor 560a, oxidation of the conductor 560b is suppressed, and a decrease in conductivity can be prevented.

As the conductive material having a function of suppressing diffusion of oxygen, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like is preferably used, for example. Further, an oxide semiconductor that can be used as the oxide 530 can be used as the conductor 560a. In that case, by forming the conductor 560b by a sputtering method, the electric resistance value of the conductor 560a can be lowered and the conductor 560a can be a conductor. This can be called an OC (Oxide Conductor) electrode.

A conductive material containing tungsten, copper, or aluminum as its main component is preferably used for the conductor 560b. Further, since the conductor 560 functions as a wiring, a conductor with high conductivity is preferably used. For example, a conductive material whose main component is tungsten, copper, or aluminum can be used. Further, the conductor 560b may have a layered structure, for example, a layered structure of titanium or titanium nitride and the above conductive material.

An insulator 574 is placed between insulator 580 and transistor 510A. For the insulator 574, an insulating material having a function of suppressing diffusion of impurities such as water or hydrogen and oxygen is preferably used. For example, it is preferable to use aluminum oxide or hafnium oxide. In addition, metal oxides such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, or tantalum oxide, silicon nitride oxide, or silicon nitride can also be used.

With the insulator 574, impurities such as water and hydrogen contained in the insulator 580 can be prevented from diffusing into the oxide 530b through the oxide 530c and the insulator 550. FIG. In addition, oxidation of the conductor 560 due to excess oxygen in the insulator 580 can be suppressed.

The insulator 580, the insulator 582, and the insulator 584 function as interlayer films.

Like the insulator 514, the insulator 582 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen from entering the transistor 510A from the outside.

Insulators 580 and 584 preferably have lower dielectric constants than insulator 582, like insulator 516. By using a material with a low dielectric constant as the interlayer film, the parasitic capacitance generated between wirings can be reduced.

Transistor 510A may also be electrically connected to other structures through plugs or wires, such as conductor 546 embedded in insulator 580, insulator 582, and insulator 584. FIG.

As a material of the conductor 546, similarly to the conductor 505, a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material can be used as a single layer or a stacked layer. . For example, it is preferable to use a high-melting-point material such as tungsten or molybdenum that has both heat resistance and conductivity. Alternatively, it is preferably made of a low-resistance conductive material such as aluminum or copper. Wiring resistance can be reduced by using a low-resistance conductive material.

For example, the conductor 546 has a layered structure of tantalum nitride or the like, which is a conductor having a barrier property against hydrogen and oxygen, and tungsten, which has high conductivity, so that the conductivity of the wiring is maintained. , the diffusion of impurities from the outside can be suppressed.

With the above structure, a semiconductor device including a transistor including an oxide semiconductor with high on-state current can be provided. Alternatively, a semiconductor device including a transistor including an oxide semiconductor with low off-state current can be provided. Alternatively, it is possible to provide a semiconductor device in which variation in electrical characteristics is suppressed, stable electrical characteristics are obtained, and reliability is improved.

<Transistor structure example 2>
A structural example of the transistor 510B is described with reference to FIGS. FIG. 10A is a top view of the transistor 510B. FIG. 10(B) is a cross-sectional view of the portion indicated by the dashed line L1-L2 in FIG. 10(A). FIG. 10(C) is a cross-sectional view of the portion indicated by the one-dot chain line W1-W2 in FIG. 10(A). Note that in the top view of FIG. 10A, some elements are omitted for clarity of illustration.

Transistor 510B is a variation of transistor 510A. Therefore, in order to avoid repetition of description, differences from the transistor 510A are mainly described.

The transistor 510B has a region where the conductor 542 (the conductor 542a and the conductor 542b) overlaps with the oxide 530c, the insulator 550, and the conductor 560. FIG. With such a structure, a transistor with high on-state current can be provided. Further, a transistor with high controllability can be provided.

A conductor 560 functioning as a first gate electrode has a conductor 560a and a conductor 560b over the conductor 560a. For the conductor 560a, similarly to the conductor 505a, it is preferable to use a conductive material that has a function of suppressing diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms. Alternatively, it is preferable to use a conductive material having a function of suppressing diffusion of oxygen (eg, at least one of oxygen atoms and oxygen molecules).

Since the conductor 560a has a function of suppressing the diffusion of oxygen, the material selectivity of the conductor 560b can be improved. In other words, with the presence of the conductor 560a, oxidation of the conductor 560b is suppressed, and a decrease in conductivity can be prevented.

Further, an insulator 574 is preferably provided so as to cover the top surface and side surfaces of the conductor 560, the side surfaces of the insulator 550, and the side surfaces of the oxide 530c. Note that an insulating material having a function of suppressing diffusion of impurities such as water or hydrogen and oxygen is preferably used for the insulator 574 . For example, it is preferable to use aluminum oxide or hafnium oxide. In addition, metal oxides such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, or tantalum oxide, silicon nitride oxide, or silicon nitride can also be used.

By providing the insulator 574, oxidation of the conductor 560 can be suppressed. In addition, with the insulator 574, water and impurities such as hydrogen contained in the insulator 580 can be prevented from diffusing into the transistor 510B.

An insulator 576 (an insulator 576 a and an insulator 576 b ) having a barrier property may be placed between the conductor 546 and the insulator 580 . By providing the insulator 576, oxygen in the insulator 580 can be prevented from reacting with the conductor 546 and oxidation of the conductor 546 can be suppressed.

In addition, by providing the insulator 576 having a barrier property, the selection range of conductor materials used for plugs and wirings can be widened. For example, a semiconductor device with low power consumption can be provided by using a metal material having a property of absorbing oxygen and having high conductivity for the conductor 546 . Specifically, a material such as tungsten or aluminum that has low oxidation resistance but high conductivity can be used. Alternatively, for example, a conductor that can be easily formed into a film or processed can be used.

<Transistor structure example 3>
A structural example of the transistor 510C is described with reference to FIGS. FIG. 11A is a top view of the transistor 510C. FIG. 11(B) is a cross-sectional view of the portion indicated by the dashed line L1-L2 in FIG. 11(A). FIG. 11(C) is a cross-sectional view of the portion indicated by the one-dot chain line W1-W2 in FIG. 11(A). Note that in the top view of FIG. 11A, some elements are omitted for clarity.

Transistor 510C is a variation of transistor 510A. Therefore, in order to avoid repetition of description, differences from the transistor 510A are mainly described.

A transistor 510C illustrated in FIG. 11 has a conductor 547a between a conductor 542a and an oxide 530b, and a conductor 547b between a conductor 542b and an oxide 530b. Here, the conductor 542a (conductor 542b) has a region extending over the top surface of the conductor 547a (conductor 547b) and the side surface on the conductor 560 side and in contact with the top surface of the oxide 530b. Here, a conductor that can be used for the conductor 542 may be used as the conductor 547 . Furthermore, the film thickness of the conductor 547 is preferably at least thicker than that of the conductor 542 .

With the above structure, the transistor 510C illustrated in FIG. 11 can bring the conductor 542 closer to the conductor 560 than the transistor 510A. Alternatively, the conductor 560 can overlap the end of the conductor 542a and the end of the conductor 542b. Thereby, the substantial channel length of the transistor 510C can be shortened, and the on-current and frequency characteristics can be improved.

The conductor 547a (the conductor 547b) preferably overlaps with the conductor 542a (the conductor 542b). With such a structure, the conductor 547a (conductor 547b) functions as a stopper in etching for forming an opening for embedding the conductor 546a (conductor 546b), and overetching of the oxide 530b is prevented. can be prevented.

In addition, the transistor 510C illustrated in FIG. 11 may have a structure in which the insulator 545 is arranged over and in contact with the insulator 544 . The insulator 544 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen and excess oxygen from entering the transistor 510C from the insulator 580 side. As the insulator 545, the insulator that can be used for the insulator 544 can be used. Alternatively, the insulator 544 may be a nitride insulator such as aluminum nitride, aluminum titanium nitride, titanium nitride, silicon nitride, or silicon nitride oxide.

Further, unlike the transistor 510A shown in FIG. 9, the transistor 510C shown in FIG. 11 may have the conductor 505 with a single-layer structure. In this case, an insulating film to be the insulator 516 is formed on the pattern-formed conductor 505, and the upper portion of the insulating film is removed by CMP or the like until the upper surface of the conductor 505 is exposed. good. Here, it is preferable to improve the flatness of the upper surface of the conductor 505 . For example, the average surface roughness (Ra) of the upper surface of the conductor 505 may be 1 nm or less, preferably 0.5 nm or less, more preferably 0.3 nm or less. Accordingly, planarity of the insulating layer formed over the conductor 505 can be improved, and crystallinity of the oxides 530b and 530c can be improved.

<Transistor structure example 4>
A structural example of the transistor 510D is described with reference to FIGS. FIG. 12A is a top view of the transistor 510D. FIG. 12(B) is a cross-sectional view of the portion indicated by the dashed line L1-L2 in FIG. 12(A). FIG. 12(C) is a cross-sectional view of the portion indicated by the dashed line W1-W2 in FIG. 12(A). Note that in the top view of FIG. 12A, some elements are omitted for clarity of illustration.

Transistor 510D is a variation of the above transistor. Therefore, in order to avoid repetition of description, differences from the above transistor will be mainly described.

In FIGS. 12A to 12C, the conductor 503 is not provided, and the conductor 505 functioning as the second gate also functions as a wiring. Further, an insulator 550 is provided over the oxide 530 c and a metal oxide 552 is provided over the insulator 550 . A conductor 560 is provided over the metal oxide 552 and an insulator 570 is provided over the conductor 560 . An insulator 571 is provided over the insulator 570 .

The metal oxide 552 preferably has a function of suppressing oxygen diffusion. By providing the metal oxide 552 that suppresses diffusion of oxygen between the insulator 550 and the conductor 560, diffusion of oxygen to the conductor 560 is suppressed. That is, reduction in the amount of oxygen supplied to the oxide 530 can be suppressed. In addition, oxidation of the conductor 560 by oxygen can be suppressed.

Note that the metal oxide 552 may function as part of the first gate. For example, an oxide semiconductor that can be used as the oxide 530 can be used as the metal oxide 552 . In that case, by forming the conductor 560 by a sputtering method, the electrical resistance of the metal oxide 552 can be lowered to form a conductive layer. This can be called an OC (Oxide Conductor) electrode.

In some cases, the metal oxide 552 functions as part of the gate insulating film. Therefore, when silicon oxide, silicon oxynitride, or the like is used for the insulator 550, the metal oxide 552 is preferably a high-k material with a high dielectric constant. By using the laminated structure, a laminated structure that is stable against heat and has a high relative dielectric constant can be obtained. Therefore, it is possible to reduce the gate potential applied during transistor operation while maintaining the physical film thickness. Also, the equivalent oxide thickness (EOT) of the insulating layer functioning as the gate insulating film can be reduced.

Although the metal oxide 552 is shown as a single layer in the transistor 510D, it may have a stacked structure of two or more layers. For example, a metal oxide functioning as part of the gate electrode and a metal oxide functioning as part of the gate insulating film may be stacked.

When the metal oxide 552 functions as a gate electrode, the on-state current of the transistor 510D can be improved without weakening the influence of the electric field from the conductor 560. FIG. Alternatively, in the case of functioning as a gate insulating film, the distance between the conductor 560 and the oxide 530 is maintained by the physical thicknesses of the insulator 550 and the metal oxide 552, thereby Leakage current with the oxide 530 can be suppressed. Therefore, by providing the stacked structure of the insulator 550 and the metal oxide 552, the physical distance between the conductor 560 and the oxide 530 and the electric field intensity applied from the conductor 560 to the oxide 530 can be reduced to It can be easily adjusted accordingly.

Specifically, the metal oxide 552 can be used as the metal oxide 552 by reducing the resistance of an oxide semiconductor that can be used for the oxide 530 . Alternatively, a metal oxide containing one or more selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, or the like can be used.

In particular, it is preferable to use an insulating layer containing one or both oxides of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate). In particular, hafnium aluminate has higher heat resistance than hafnium oxide film. Therefore, it is preferable because it is less likely to be crystallized in heat treatment in a later step. Note that the metal oxide 552 is not an essential component. It may be appropriately designed depending on the required transistor characteristics.

For the insulator 570, an insulating material having a function of suppressing permeation of impurities such as water or hydrogen and oxygen is preferably used. For example, it is preferable to use aluminum oxide or hafnium oxide. Accordingly, oxidation of the conductor 560 by oxygen from above the insulator 570 can be suppressed. In addition, impurities such as water or hydrogen from above the insulator 570 can be prevented from entering the oxide 530 through the conductor 560 and the insulator 550 .

Insulator 571 functions as a hard mask. By providing the insulator 571, when the conductor 560 is processed, the side surface of the conductor 560 is substantially vertical. Preferably, it can be 80 degrees or more and 95 degrees or less.

Note that the insulator 571 may also function as a barrier layer by using an insulating material which has a function of suppressing permeation of impurities such as water or hydrogen and oxygen. In that case, the insulator 570 may not be provided.

Using the insulator 571 as a hard mask, the insulator 570, the conductor 560, the metal oxide 552, the insulator 550, and part of the oxide 530c are selectively removed so that their sides are substantially flush. and a portion of the oxide 530b surface can be exposed.

Transistor 510D also has regions 531a and 531b on a portion of the exposed oxide 530b surface. One of region 531a or region 531b functions as a source region and the other functions as a drain region.

The regions 531a and 531b are formed by, for example, introducing an impurity element such as phosphorus or boron into the exposed surface of the oxide 530b using ion implantation, ion doping, plasma immersion ion implantation, plasma treatment, or the like. It can be realized by Note that in this embodiment and the like, the term “impurity element” refers to an element other than the main component element.

In addition, after exposing part of the surface of the oxide 530b, a metal film is formed and heat treatment is performed to diffuse an element contained in the metal film into the oxide 530b to form the regions 531a and 531b. You can also

A region of the oxide 530b into which the impurity element is introduced has a lower electrical resistivity. Therefore, the regions 531a and 531b are sometimes referred to as "impurity regions" or "low resistance regions".

By using the insulator 571 and/or the conductor 560 as a mask, the regions 531a and 531b can be formed in a self-aligned manner. Therefore, the region 531a and/or the region 531b does not overlap with the conductor 560, and parasitic capacitance can be reduced. Also, no offset region is formed between the channel forming region and the source/drain region (region 531a or region 531b). By forming the regions 531a and 531b in a self-aligned manner, it is possible to increase the ON current, reduce the threshold voltage, and improve the operating frequency.

Note that an offset region may be provided between the channel formation region and the source/drain region in order to further reduce the off current. The offset region is a region having a high electric resistivity, and is a region where the above-described impurity element is not introduced. The formation of the offset region can be achieved by introducing the impurity element described above after the insulator 575 is formed. In this case, the insulator 575 also functions as a mask like the insulator 571 and the like. Therefore, the impurity element is not introduced into the region of the oxide 530b overlapping with the insulator 575, and the electrical resistivity of the region can be kept high.

In addition, the transistor 510D has an insulator 575 on the sides of the insulator 570, the conductor 560, the metal oxide 552, the insulator 550, and the oxide 530c. The insulator 575 is preferably an insulator with a low dielectric constant. For example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, silicon oxide having vacancies, resin, or the like. Preferably. In particular, it is preferable to use silicon oxide, silicon oxynitride, silicon nitride oxide, or silicon oxide having vacancies for the insulator 575 because an excess oxygen region can be easily formed in the insulator 575 in a later step. In addition, silicon oxide and silicon oxynitride are preferable because they are thermally stable. Further, the insulator 575 preferably has a function of diffusing oxygen.

In addition, the transistor 510D has an insulator 575 and an insulator 574 over the oxide 530 . The insulator 574 is preferably deposited using a sputtering method. By using a sputtering method, an insulator containing few impurities such as water or hydrogen can be formed. For example, aluminum oxide may be used as the insulator 574 .

Note that an oxide film formed by sputtering may extract hydrogen from a structure to be formed. Therefore, the insulator 574 absorbs hydrogen and water from the oxide 530 and the insulator 575, whereby the hydrogen concentrations in the oxide 530 and the insulator 575 can be reduced.

<Transistor structure example 5>
A structural example of the transistor 510E is described with reference to FIGS. FIG. 13A is a top view of the transistor 510E. FIG. 13(B) is a cross-sectional view of the portion indicated by the dashed line L1-L2 in FIG. 13(A). FIG. 13(C) is a cross-sectional view of the portion indicated by the dashed-dotted line W1-W2 in FIG. 13(A). Note that in the top view of FIG. 13A, some elements are omitted for clarity.

Transistor 510E is a variation of the above transistor. Therefore, in order to avoid repetition of description, differences from the above transistor will be mainly described.

In FIGS. 13A-13C, the conductor 542 is not provided, and a portion of the exposed oxide 530b surface has regions 531a and 531b. One of region 531a or region 531b functions as a source region and the other functions as a drain region. An insulator 573 is provided between the oxide 530 b and the insulator 574 .

Regions 531 (regions 531a and 531b) shown in FIG. 13 are regions in which the following element is added to the oxide 530b. Region 531 can be formed by using a dummy gate, for example.

Specifically, it is preferable to provide a dummy gate over the oxide 530b and use the dummy gate as a mask to add an element that reduces the resistance of the oxide 530b. That is, the element is added to a region where the oxide 530 does not overlap with the dummy gate, so that a region 531 is formed. Examples of the method for adding the element include an ion implantation method in which an ionized source gas is added after mass separation, an ion doping method in which an ionized source gas is added without mass separation, a plasma immersion ion implantation method, and the like. can be used.

As an element for reducing the resistance of the oxide 530, typically, boron or phosphorus can be mentioned. Alternatively, hydrogen, carbon, nitrogen, fluorine, sulfur, chlorine, titanium, rare gas, or the like may be used. Representative examples of noble gases include helium, neon, argon, krypton, and xenon. The concentration of the element may be measured using secondary ion mass spectrometry (SIMS) or the like.

Boron and phosphorus are particularly preferred because they allow the use of equipment in amorphous silicon or low temperature polysilicon production lines. Existing equipment can be diverted, and equipment investment can be suppressed.

Subsequently, an insulating film to be the insulator 573 and an insulating film to be the insulator 574 may be formed over the oxide 530b and the dummy gate. By stacking the insulating film to be the insulator 573 and the insulating film to be the insulator 574, a region where the region 531 overlaps with the oxide 530c and the insulator 550 can be provided.

Specifically, after an insulating film to be the insulator 580 is provided over the insulating film to be the insulator 574, the insulating film to be the insulator 580 is subjected to CMP (Chemical Mechanical Polishing) treatment, whereby the insulator 580 and the insulator 580 are separated from each other. A part of the insulating film is removed to expose the dummy gate. Subsequently, when removing the dummy gate, part of the insulator 573 in contact with the dummy gate is preferably removed. Therefore, the insulator 574 and the insulator 573 are exposed on the side surfaces of the opening provided in the insulator 580, and part of the region 531 provided in the oxide 530b is exposed on the bottom surface of the opening. do. Next, after an oxide film to be the oxide 530c, an insulating film to be the insulator 550, and a conductive film to be the conductor 560 are sequentially formed in the opening, CMP treatment or the like is performed until the insulator 580 is exposed. By removing part of the oxide film to be the oxide 530c, the insulating film to be the insulator 550, and part of the conductive film to be the conductor 560, the transistor illustrated in FIG. 13 can be formed.

Note that the insulators 573 and 574 are not essential components. It may be appropriately designed depending on the required transistor characteristics.

An existing device can be used for the transistor shown in FIG. 13, and cost can be reduced because the conductor 542 is not provided.

<Structure Example 6 of Transistor>
A structural example of the transistor 510F is described with reference to FIGS. FIG. 14A is a top view of the transistor 510F. FIG. 14(B) is a cross-sectional view of the portion indicated by the dashed line L1-L2 in FIG. 14(A). FIG. 14(C) is a cross-sectional view of the portion indicated by the one-dot chain line W1-W2 in FIG. 14(A). Note that in the top view of FIG. 14A, some elements are omitted for clarity.

Transistor 510F is a variation of transistor 510A. Therefore, in order to avoid repetition of description, differences from the above transistor will be mainly described.

In the transistor 510A, part of the insulator 574 is provided in an opening provided in the insulator 580 so as to cover the side surface of the conductor 560 . On the other hand, in the transistor 510F, the insulator 580 and the insulator 574 are partly removed to form an opening.

An insulator 576 (an insulator 576 a and an insulator 576 b ) having a barrier property may be placed between the conductor 546 and the insulator 580 . By providing the insulator 576, oxygen in the insulator 580 can be prevented from reacting with the conductor 546 and oxidation of the conductor 546 can be suppressed.

Note that in the case where an oxide semiconductor is used as the oxide 530, it is preferable that oxides having different atomic ratios of metal atoms have a stacked structure. Specifically, in the metal oxide used for the oxide 530a, the atomic ratio of the element M among the constituent elements is greater than the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. is preferred. Further, in the metal oxide used for the oxide 530a, the atomic ratio of the element M to In is preferably higher than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. In addition, the atomic ratio of In to the element M in the metal oxide used for the oxide 530b is preferably higher than the atomic ratio of In to the element M in the metal oxide used for the oxide 530a. In addition, the oxide 530c can be a metal oxide that can be used for the oxide 530a or the oxide 530b.

The oxides 530a, 530b, and 530c preferably have crystallinity, and in particular, CAAC-OS is preferably used. A crystalline oxide such as CAAC-OS has few impurities and defects (such as oxygen vacancies) and has a dense structure with high crystallinity. Therefore, extraction of oxygen from the oxide 530b by the source electrode or the drain electrode can be suppressed. Accordingly, extraction of oxygen from the oxide 530b can be reduced even if heat treatment is performed, so that the transistor 510F is stable against high temperatures (so-called thermal budget) in the manufacturing process.

Note that one or both of the oxide 530a and the oxide 530c may be omitted. Oxide 530 may be a single layer of oxide 530b. When the oxide 530 is a stack of oxides 530a, 530b, and 530c, the energies of the conduction band bottoms of the oxides 530a and 530c are higher than the energies of the conduction band bottoms of the oxide 530b. It is preferable to be In other words, the electron affinities of the oxides 530a and 530c are preferably smaller than the electron affinities of the oxide 530b. In this case, the oxide 530c is preferably a metal oxide that can be used for the oxide 530a. Specifically, in the metal oxide used for the oxide 530c, the atomic ratio of the element M among the constituent elements is greater than the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. is preferred. Moreover, in the metal oxide used for the oxide 530c, the atomic ratio of the element M to In is preferably higher than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. In addition, the atomic ratio of In to the element M in the metal oxide used for the oxide 530b is preferably higher than the atomic ratio of In to the element M in the metal oxide used for the oxide 530c.

Here, the energy level at the bottom of the conduction band changes smoothly at the junction of the oxide 530a, the oxide 530b, and the oxide 530c. In other words, it can be said that the energy level of the bottom of the conduction band at the junction of the oxide 530a, the oxide 530b, and the oxide 530c continuously changes or continuously joins. In order to achieve this, the defect level density of the mixed layers formed at the interface between the oxides 530a and 530b and the interface between the oxides 530b and 530c should be lowered.

Specifically, the oxide 530a and the oxide 530b, and the oxide 530b and the oxide 530c have a common element (main component) other than oxygen, thereby forming a mixed layer with a low defect level density. be able to. For example, when the oxide 530b is an In--Ga--Zn oxide, the oxides 530a and 530c may be In--Ga--Zn oxide, Ga--Zn oxide, gallium oxide, or the like. Alternatively, the oxide 530c may have a stacked structure. For example, a stacked structure of In--Ga--Zn oxide and Ga--Zn oxide on the In--Ga--Zn oxide, or In--Ga--Zn oxide and on the In--Ga--Zn oxide can be used. In other words, a stacked structure of an In--Ga--Zn oxide and an oxide that does not contain In may be used as the oxide 530c.

Specifically, a metal oxide of In:Ga:Zn=1:3:4 [atomic ratio] or 1:1:0.5 [atomic ratio] may be used as the oxide 530a. As the oxide 530b, a metal oxide of In:Ga:Zn=4:2:3 [atomic ratio] or 3:1:2 [atomic ratio] may be used. Further, as the oxide 530c, In:Ga:Zn=1:3:4 [atomic ratio], In:Ga:Zn=4:2:3 [atomic ratio], Ga:Zn=2:1 [atomic number ratio] or Ga:Zn=2:5 [atomic number ratio]. Further, as a specific example of the case where the oxide 530c has a stacked structure, In:Ga:Zn=4:2:3 [atomic ratio] and Ga:Zn=2:1 [atomic ratio] are stacked. Structure, layered structure of In: Ga: Zn = 4:2:3 [atomic ratio] and Ga: Zn = 2:5 [atomic ratio], In: Ga: Zn = 4:2:3 [atomic number ratio] and a laminated structure with gallium oxide.

At this time, the main path of carriers is the oxide 530b. When the oxides 530a and 530c have the above structures, defect level densities at the interfaces between the oxides 530a and 530b and between the oxides 530b and 530c can be reduced. Therefore, the influence of interface scattering on carrier conduction is reduced, and the transistor 510F can obtain high on-current and high frequency characteristics. Note that when the oxide 530c has a stacked structure, in addition to the effect of reducing the defect level density at the interface between the oxide 530b and the oxide 530c, constituent elements of the oxide 530c are on the insulator 550 side. It is expected to suppress the diffusion of More specifically, the oxide 530c has a stacked structure, and the oxide that does not contain In is positioned above the stacked structure, so that In that can diffuse toward the insulator 550 can be suppressed. Since the insulator 550 functions as a gate insulator, the characteristics of the transistor are deteriorated when In is diffused. Therefore, by forming the oxide 530c into a stacked structure, a highly reliable display device can be provided.

A metal oxide that functions as an oxide semiconductor is preferably used as the oxide 530 . For example, it is preferable to use a metal oxide having a bandgap of 2 eV or more, preferably 2.5 eV or more, as the metal oxide that serves as the channel formation region of the oxide 530 . By using a metal oxide with a large bandgap in this manner, off-state current of a transistor can be reduced. By using such a transistor, a semiconductor device with low power consumption can be provided.

<Structure Example 7 of Transistor>
7 and 8, the structural example in which the conductor 560 functioning as a gate is formed inside the opening of the insulator 580 is described. A structure provided with a body can also be used. Structural examples of such a transistor are shown in FIGS. 15 and 16. FIG.

FIG. 15A is a top view of a transistor, and FIG. 15B is a perspective view of the transistor. FIG. 16A shows a cross-sectional view along X1-X2 in FIG. 15A, and FIG. 16B shows a cross-sectional view along Y1-Y2.

The transistors illustrated in FIGS. 15 and 16 include a conductor BGE functioning as a back gate, an insulator BGI functioning as a gate insulating film, an oxide semiconductor S, and an insulator functioning as a gate insulating film. It has a body TGI, a conductor TGE functioning as a front gate, and a conductor WE functioning as a wiring. Also, the conductor PE functions as a plug for connecting the conductor WE with the oxide S, the conductor BGE, or the conductor TGE. Note that here, an example in which the oxide semiconductor S is composed of three layers of oxides S1, S2, and S3 is shown.

(Embodiment 4)
In this embodiment, a structure of a metal oxide that can be used for the OS transistor described in the above embodiment will be described.

<Structure of Metal Oxide>
In this specification and the like, it may be referred to as CAAC (c-axis aligned crystal) and CAC (cloud-aligned composite). Note that CAAC represents an example of a crystal structure, and CAC represents an example of a function or material configuration.

CAC-OS or CAC-metal oxide has a conductive function in a part of the material, an insulating function in a part of the material, and a semiconductor function in the whole material. Note that when CAC-OS or CAC-metal oxide is used for a channel formation region of a transistor, the function of conductivity is to flow electrons (or holes) that serve as carriers, and the function of insulation is to serve as carriers. It is a function that does not flow electrons. A switching function (on/off function) can be imparted to the CAC-OS or CAC-metal oxide by causing the conductive function and the insulating function to act complementarily. By separating each function in CAC-OS or CAC-metal oxide, both functions can be maximized.

Also, CAC-OS or CAC-metal oxide has a conductive region and an insulating region. The conductive regions have the above-described conductive function, and the insulating regions have the above-described insulating function. In some materials, the conductive region and the insulating region are separated at the nanoparticle level. Also, the conductive region and the insulating region may be unevenly distributed in the material. In addition, the conductive region may be observed to be connected like a cloud with its periphery blurred.

In CAC-OS or CAC-metal oxide, the conductive region and the insulating region are each dispersed in the material with a size of 0.5 nm or more and 10 nm or less, preferably 0.5 nm or more and 3 nm or less. There is

Also, CAC-OS or CAC-metal oxide is composed of components having different bandgaps. For example, CAC-OS or CAC-metal oxide is composed of a component having a wide gap resulting from an insulating region and a component having a narrow gap resulting from a conductive region. In the case of this configuration, when the carriers flow, the carriers mainly flow in the component having the narrow gap. In addition, the component having a narrow gap acts complementarily on the component having a wide gap, and carriers also flow into the component having a wide gap in conjunction with the component having a narrow gap. Therefore, when the above CAC-OS or CAC-metal oxide is used for a channel formation region of a transistor, high current drivability, that is, large on-current and high field-effect mobility can be obtained in the on-state of the transistor.

That is, CAC-OS or CAC-metal oxide can also be called a matrix composite or a metal matrix composite.

<Structure of Metal Oxide>
Oxide semiconductors are classified into single-crystal oxide semiconductors and non-single-crystal oxide semiconductors. Non-single-crystal oxide semiconductors include, for example, CAAC-OS (c-axis aligned crystalline oxide semiconductor), polycrystalline oxide semiconductors, nc-OS (nanocrystalline oxide semiconductors), pseudo-amorphous oxide semiconductors (a-like OS: amorphous-like oxide semiconductor), amorphous oxide semiconductor, and the like.

A thin film with high crystallinity is preferably used as an oxide semiconductor used for a semiconductor of a transistor. By using the thin film, the stability or reliability of the transistor can be improved. Examples of the thin film include a thin film of a single crystal oxide semiconductor and a thin film of a polycrystalline oxide semiconductor. However, in order to form a thin film of a single crystal oxide semiconductor or a thin film of a polycrystalline oxide semiconductor over a substrate, a high temperature or laser heating step is required. Therefore, the cost of the manufacturing process increases, and the throughput also decreases.

Non-Patent Document 1 and Non-Patent Document 2 report that an In--Ga--Zn oxide having a CAAC structure (referred to as CAAC-IGZO) was discovered in 2009. Here, it is reported that CAAC-IGZO has c-axis orientation, does not clearly identify grain boundaries, and can be formed on a substrate at low temperatures. Furthermore, it has been reported that transistors using CAAC-IGZO have excellent electrical characteristics and reliability.

In 2013, an In--Ga--Zn oxide having an nc structure (referred to as nc-IGZO) was discovered (see Non-Patent Document 3). Here, it is reported that nc-IGZO has periodicity in atomic arrangement in a minute region (for example, a region of 1 nm or more and 3 nm or less), and no regularity in crystal orientation is observed between different regions. there is

Non-Patent Document 4 and Non-Patent Document 5 show changes in the average crystal size due to electron beam irradiation of each of the thin films of CAAC-IGZO, nc-IGZO, and IGZO with low crystallinity. In thin films of IGZO with low crystallinity, crystalline IGZO of about 1 nm has been observed even before electron beam irradiation. Therefore, it is reported here that the presence of a completely amorphous structure could not be confirmed in IGZO. Furthermore, it has been shown that CAAC-IGZO thin films and nc-IGZO thin films have higher stability against electron beam irradiation than IGZO thin films with low crystallinity. Therefore, a thin film of CAAC-IGZO or a thin film of nc-IGZO is preferably used as a semiconductor of a transistor.

CAAC-OS has a c-axis orientation and a distorted crystal structure in which a plurality of nanocrystals are connected in the ab plane direction. The strain refers to a portion where the orientation of the lattice arrangement changes between a region with a uniform lattice arrangement and another region with a uniform lattice arrangement in a region where a plurality of nanocrystals are connected.

Although nanocrystals are basically hexagonal, they are not limited to regular hexagons and may have non-regular hexagons. Also, the distortion may have a lattice arrangement of pentagons, heptagons, and the like. In CAAC-OS, a clear crystal grain boundary (also called a grain boundary) cannot be confirmed even in the vicinity of strain. That is, it can be seen that the distortion of the lattice arrangement suppresses the formation of grain boundaries. This is because the CAAC-OS can tolerate strain due to the fact that the arrangement of oxygen atoms is not dense in the ab plane direction and the bond distance between atoms changes due to the substitution of metal elements. It is considered to be for

CAAC-OS is a layered crystal in which a layer containing indium and oxygen (hereinafter referred to as an In layer) and a layer containing the element M, zinc, and oxygen (hereinafter referred to as a (M, Zn) layer) are stacked. It tends to have a structure (also called layered structure). Note that indium and the element M can be substituted with each other, and when the element M in the (M, Zn) layer is substituted with indium, the layer can also be expressed as an (In, M, Zn) layer. In addition, when indium in the In layer is replaced with the element M, it can also be expressed as an (In, M) layer.

CAAC-OS is an oxide semiconductor with high crystallinity. On the other hand, since a clear grain boundary cannot be confirmed in CAAC-OS, it can be said that the decrease in electron mobility caused by the grain boundary is unlikely to occur. In addition, since the crystallinity of an oxide semiconductor may be deteriorated by contamination with impurities, generation of defects, or the like, a CAAC-OS can be said to be an oxide semiconductor with few impurities and defects (such as oxygen vacancies). Therefore, an oxide semiconductor including CAAC-OS has stable physical properties. Therefore, an oxide semiconductor including CAAC-OS is resistant to heat and has high reliability. CAAC-OS is also stable against high temperatures (so-called thermal budget) in the manufacturing process. Therefore, the use of CAAC-OS for the OS transistor makes it possible to expand the degree of freedom in the manufacturing process.

The nc-OS has periodic atomic arrangement in a minute region (eg, a region of 1 nm to 10 nm, particularly a region of 1 nm to 3 nm). Also, nc-OS shows no regularity in crystal orientation between different nanocrystals. Therefore, no orientation is observed in the entire film. Therefore, an nc-OS may be indistinguishable from an a-like OS or an amorphous oxide semiconductor depending on the analysis method.

An a-like OS is an oxide semiconductor having a structure between an nc-OS and an amorphous oxide semiconductor. An a-like OS has void or low density regions. That is, a-like OS has lower crystallinity than nc-OS and CAAC-OS.

Oxide semiconductors have various structures and each has different characteristics. An oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, an nc-OS, and a CAAC-OS.

<Transistor including oxide semiconductor>
Next, the case where the above oxide semiconductor is used for a transistor is described.

Note that by using the above oxide semiconductor for a transistor, a transistor with high field-effect mobility can be achieved. Further, a highly reliable transistor can be realized.

Further, a transistor including the above oxide semiconductor has an extremely small leakage current in a non-conducting state, specifically, an off current per 1 μm of channel width of the transistor is on the order of yA/μm (10 ⁻²⁴ A/μm). Non-Patent Document 6 shows that there is. For example, a low-power-consumption CPU and the like that utilize a characteristic of a transistor including an oxide semiconductor, such as low leakage current, have been disclosed (see Non-Patent Document 7).

In addition, application of a transistor including an oxide semiconductor to a display device has been reported, which utilizes a characteristic of a transistor including a low leakage current (see Non-Patent Document 8). In a display device, displayed images are switched several tens of times per second. The number of image switching times per second is called a refresh rate. Also, the refresh rate is sometimes called a driving frequency. Such high-speed screen switching, which is difficult for the human eye to perceive, is considered to be the cause of eye fatigue. Therefore, it has been proposed to reduce the number of times the image is rewritten by lowering the refresh rate of the display device. In addition, power consumption of the display device can be reduced by driving at a reduced refresh rate. Such a driving method is called idling stop (IDS) driving.

An oxide semiconductor with low carrier density is preferably used for a transistor. In the case of lowering the carrier density of the oxide semiconductor film, the concentration of impurities in the oxide semiconductor film may be lowered to lower the defect level density. In this specification and the like, a low impurity concentration and a low defect level density are referred to as high-purity intrinsic or substantially high-purity intrinsic.

Further, since a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low defect level density, the trap level density may also be low. Note that the carrier density of the oxide semiconductor that can be used in one embodiment of the present invention may be in the range described in Embodiment 2.

In addition, the charge trapped in the trap level of the oxide semiconductor takes a long time to disappear and may behave like a fixed charge. Therefore, a transistor whose channel formation region is formed in an oxide semiconductor with a high trap level density might have unstable electrical characteristics.

Therefore, it is effective to reduce the impurity concentration in the oxide semiconductor in order to stabilize the electrical characteristics of the transistor. In order to reduce the impurity concentration in the oxide semiconductor, it is preferable to also reduce the impurity concentration in adjacent films. Impurities include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, silicon, and the like.

<Impurities>
Here, the influence of each impurity in the oxide semiconductor is described.

When an oxide semiconductor contains silicon or carbon which is one of Group 14 elements, a defect level is formed in the oxide semiconductor. Therefore, the concentration of silicon and carbon in the oxide semiconductor and the concentration of silicon and carbon in the vicinity of the interface with the oxide semiconductor (concentration obtained by secondary ion mass spectrometry (SIMS)) are 2. ×10 ¹⁸ atoms/cm ³ or less, preferably 2 × 10 ¹⁷ atoms/cm ³ or less.

Further, when an oxide semiconductor contains an alkali metal or an alkaline earth metal, a defect level may be formed to generate carriers. Therefore, a transistor using an oxide semiconductor containing an alkali metal or an alkaline earth metal tends to have normally-on characteristics. Therefore, it is preferable to reduce the concentration of the alkali metal or alkaline earth metal in the oxide semiconductor. Specifically, the concentration of alkali metal or alkaline earth metal in the oxide semiconductor obtained by SIMS is set to 1×10 ¹⁸ atoms/cm ³ or less, preferably 2×10 ¹⁶ atoms/cm ³ or less.

In addition, when an oxide semiconductor contains nitrogen, electrons as carriers are generated, the carrier density increases, and the oxide semiconductor tends to be n-type. As a result, a transistor including an oxide semiconductor containing nitrogen as a semiconductor tends to have normally-on characteristics. Therefore, nitrogen content in the oxide semiconductor is preferably reduced as much as possible. For example, the concentration of nitrogen in the oxide semiconductor is less than 5×10 ¹⁹ atoms/cm ³ , preferably 5×10 ¹⁸ atoms/cm ³ or less, more preferably 1×10 ¹⁸ atoms/cm 3 or less, and further preferably 1×10 18 atoms/cm ³ or less according to SIMS. It is preferably 5×10 ¹⁷ atoms/cm ³ or less.

Further, hydrogen contained in the oxide semiconductor reacts with oxygen that bonds to a metal atom to form water, which may cause oxygen vacancies. When hydrogen enters the oxygen vacancies, electrons, which are carriers, may be generated. In addition, part of hydrogen may bond with oxygen that bonds with a metal atom to generate an electron, which is a carrier. Therefore, a transistor including an oxide semiconductor containing hydrogen is likely to have normally-on characteristics. Therefore, hydrogen in the oxide semiconductor is preferably reduced as much as possible. Specifically, in the oxide semiconductor, the hydrogen concentration obtained by SIMS is less than 1×10 ²⁰ atoms/cm ³ , preferably less than 1×10 ¹⁹ atoms/cm ³ , more preferably less than 5×10 ¹⁸ atoms/cm Less than ³ , more preferably less than 1×10 ¹⁸ atoms/cm ³ .

By using an oxide semiconductor in which impurities are sufficiently reduced for a channel formation region of a transistor, stable electrical characteristics can be imparted.

The discovery of the CAAC structure and the nc structure has contributed to improvements in electrical characteristics and reliability of transistors using an oxide semiconductor having the CAAC structure or the nc structure, as well as cost reduction and throughput improvement in the manufacturing process. In addition, application research of the transistor to display devices and LSIs is underway, taking advantage of the characteristic of the transistor having a low leakage current.

Note that this embodiment can be implemented in appropriate combination with any of the other embodiments described in this specification.

(Embodiment 5)
In the above embodiments, an example in which the charge control circuit is provided over the flexible substrate is shown; however, there is no particular limitation, and a protection circuit, a cutoff switch, an antenna, a sensor, and the like may be provided over the same substrate. The charging control circuit is formed on a flexible substrate, which is bendable and capable of detecting an abnormality such as a micro-short in the secondary battery. In addition, the charging control circuit of one embodiment of the present invention can be provided on the side surface of the secondary battery, which can save space and reduce the number of components used.

In this embodiment, an example of an electronic device including a charge control circuit will be described with reference to FIGS.

The robot 7100 includes a secondary battery, an illumination sensor, a microphone, a camera, a speaker, a display, various sensors (infrared sensor, ultrasonic sensor, acceleration sensor, piezo sensor, optical sensor, gyro sensor, etc.), a moving mechanism, and the like. By applying the charge control circuit of one embodiment of the present invention to the secondary battery of the robot 7100, an abnormality such as a micro-short in the secondary battery can be detected.

A microphone has a function of detecting acoustic signals such as a user's voice and environmental sounds. The speaker also has the function of emitting audio signals such as voice and warning sounds. The robot 7100 can analyze an audio signal input via a microphone and emit a necessary audio signal from a speaker. Robot 7100 can communicate with the user using a microphone and speaker.

The camera has a function of capturing images around the robot 7100 . Robot 7100 also has a function of moving using a moving mechanism. The robot 7100 can capture an image of its surroundings using a camera, analyze the image, and sense the presence or absence of an obstacle when moving.

The flying object 7120 has a propeller, a camera, a secondary battery, and the like, and has a function of autonomous flight.

Further, by applying the charge control circuit of one embodiment of the present invention to the secondary battery of the flying object 7120, in addition to weight reduction, an abnormality such as a micro-short in the secondary battery can be detected.

The cleaning robot 7140 has a secondary battery, a display arranged on the top surface, a plurality of cameras arranged on the side surface, a brush, operation buttons, various sensors, and the like. Although not shown, the cleaning robot 7300 is provided with tires, a suction port, and the like. The cleaning robot 7300 can run by itself, detect dust, and suck the dust from a suction port provided on the bottom surface. By applying the charging control circuit of one embodiment of the present invention, which is electrically connected to the secondary battery of the cleaning robot 7140, the number of parts used can be reduced and an abnormality such as a micro-short in the secondary battery can be detected. can.

An electric vehicle 7160 is shown as an example of a mobile object. An electric vehicle 7160 has a secondary battery, tires, brakes, a steering device, a camera, and the like. By applying the charging control circuit of one embodiment of the present invention connected to the secondary battery of the electric vehicle 7160, the number of components used can be reduced and an abnormality such as a micro-short in the secondary battery can be detected.

In addition, although an electric vehicle is described above as an example of a mobile object, the mobile object is not limited to an electric vehicle. For example, moving objects include trains, monorails, ships, flying objects (helicopters, unmanned aerial vehicles (drone), airplanes, rockets), etc. By applying the charging control circuit of one embodiment of the invention, the number of parts used can be reduced and an abnormality such as a micro-short in a secondary battery can be detected.

A cylindrical secondary battery including the charge control circuit 700 and/or a battery pack including the charge control circuit 730 can be incorporated in the smartphone 7210, the PC 7220 (personal computer), the game machine 7240, or the like. A cylindrical secondary battery including charge control circuit 700 corresponds to charge control circuit 10 described in the first embodiment. A battery pack including charge control circuit 730 corresponds to charge control circuit 914 described in the second embodiment.

A smartphone 7210 is an example of a mobile information terminal. A smartphone 7210 has a microphone, a camera, a speaker, various sensors, and a display portion. These peripheral devices are controlled by the charging control circuit 730 . By applying the charging control circuit of one embodiment of the present invention, which is electrically connected to the secondary battery of the smartphone 7210, the number of components used can be reduced and an abnormality such as a micro-short in the secondary battery can be detected. , can increase safety.

Each PC7220 is an example of a notebook PC. By applying the charging control circuit of one embodiment of the present invention, which is electrically connected to the secondary battery of the notebook PC, the number of parts used can be reduced and an abnormality such as a micro-short in the secondary battery can be detected. can improve safety.

Game machine 7240 is an example of a handheld game machine. The game machine 7260 is an example of a home-use stationary game machine. A controller 7262 is wirelessly or wiredly connected to the game machine 7260 . By incorporating a battery pack with a charge control circuit 730 and/or a cylindrical secondary battery with a charge control circuit into the controller 7262, the number of parts used can be reduced and abnormalities such as micro-shorts of the secondary battery can be prevented. can be detected.

This embodiment can be implemented in appropriate combination with the structures described in other embodiments and the like.

10 charging control circuit 11 flexible substrate 12 first terminal 13 second terminal 14 third terminal 15 cylindrical secondary battery 16 charger 17 mobile device 18 electrode 19 electrode 100 memory cell 101 secondary battery 102 comparison circuit 103 Memory 104 Memory 105 Cutoff switch 106 Control circuit 201 Positive electrode cap 202 Battery can 203 Positive electrode terminal 204 Positive electrode 205 Separator 206 Negative electrode 207 Negative electrode terminal 208 Insulating plate 209 Insulating plate 211 PTC element 212 Safety valve mechanism 300 Transistor 311 Substrate 313 Semiconductor region 314a Low resistance region 314b low resistance region 315 insulator 316 conductor 320 insulator 322 insulator 324 insulator 326 insulator 328 conductor 330 conductor 350 insulator 352 insulator 354 insulator 356 conductor 360 insulator 362 insulator 364 insulation Body 366 Conductor 370 Insulator 372 Insulator 374 Insulator 376 Conductor 380 Insulator 382 Insulator 384 Insulator 386 Conductor 500 Transistor 503 Conductor 503a Conductor 503b Conductor 505 Conductor 505a Conductor 505b Conductor 510 Insulation body 510A transistor 510B transistor 510C transistor 510D transistor 510E transistor 510F transistor 511 insulator 512 insulator 514 insulator 516 insulator 518 conductor 520 insulator 521 insulator 522 insulator 524 insulator 530 oxide 530a oxide 530b oxide 530c Oxide 531 Region 531a Region 531b Region 540a Conductor 540b Conductor 542 Conductor 542a Conductor 542b Conductor 543 Region 543a Region 543b Region 544 Insulator 545 Insulator 546 Conductor 546a Conductor 546b Conductor 547 Conductor 547a Conductor 547b conductor 548 conductor 550 insulator 552 metal oxide 560 conductor 560a conductor 560b conductor 570 insulator 571 insulator 573 insulator 574 insulator 575 insulator 576 insulator 576a insulator 576b insulator 580 insulator 581 Insulator 582 Insulator 584 Insulator 586 Insulator 600 Capacitive element 610 Conductor 612 Conductor 620 Conductor 630 Insulator 650 Insulator 700 Charging control circuit 730 Charging control circuit 910 Flexible substrate 911 Connection terminal 913 Secondary battery 914 Charging control circuit 916 Insulating sheet layer 930 Case 931 Negative electrode 932 Positive electrode 933 Separator 950 Winding body 951 Terminal 952 Terminal 1400 Storage battery 1402 Positive electrode 1404 Negative electrode 7100 Robot 7120 Airplane 7140 Cleaning robot 7160 Electric vehicle 7210 Smartphone 7220 PC
7240 game machine 7260 game machine 7262 controller 7300 cleaning robot

Claims (4)

a secondary battery;
a first transmission line connected to a first terminal of the secondary battery and transmitting power output from the secondary battery;
a charging control circuit connected to the first transmission line and provided on a flexible substrate in contact with the side surface of the secondary battery;
a second transmission line connecting the charging control circuit and a second terminal of the secondary battery;
a switch that cuts off the second transmission line,
The switch has a function of interrupting the second transmission line when the secondary battery is overcharged or overdischarged, and when the charging control circuit determines that an abnormality occurs during charging of the secondary battery. has a function of interrupting the second transmission line to stop charging,
The charge control circuit includes a transistor having an oxide semiconductor,
A semiconductor device, in which a top surface and side surfaces of the oxide semiconductor are covered with a conductor via an insulator, as viewed in a cross section in the channel width direction of the transistor. In claim 1,
A semiconductor device in which side surfaces of the secondary battery and the flexible substrate have curved surfaces. In claim 1 or claim 2,
A semiconductor device comprising the charging control circuit, the protection circuit, and the switch on the flexible substrate. In any one of claims 1 to 3,
The semiconductor device, wherein the secondary battery has a cylindrical shape.

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