JP2024047597A - Semiconductor Device - Google Patents

Abstract

To provide a voltage dividing circuit capable of suppressing current consumption and increasing voltage dividing accuracy.SOLUTION: A voltage dividing circuit 100 includes a plurality of resistance elements 111 to 113, 131, 141, 151 to 159 that divide an input voltage, and a plurality of switching elements 121 to 124, 161 to 169 that are connected to a plurality of resistance elements 111 to 113, 131, 151 to 159, and adjust the divided voltages of the plurality of resistance elements 111 to 113, 131, 141, 151 to 159 by selectively turning on. At least one of the plurality of switching elements 121 to 124 and 161 to 169 is a thin film transistor using an oxide semiconductor film 161b.SELECTED DRAWING: Figure 2

Description

The present invention relates to a semiconductor device.

For example, secondary batteries used in portable devices deteriorate when overcharged or overdischarged, so a semiconductor device that monitors the battery voltage and protects the battery is often connected between the positive and negative terminals. Such semiconductor devices are required to have a detection accuracy of about 10 mV or less, and there are cases where the variation in voltage detection between individual devices cannot be ignored.

One technique for detecting a predetermined voltage involves dividing a reference voltage or a voltage to be measured using a voltage divider circuit and comparing the divided voltages. Various voltage divider circuits have been proposed to improve the detection accuracy.
As an example, a voltage divider circuit has been proposed in which a voltage divider circuit is formed by combining multiple resistive elements and multiple switching elements, and the voltage divider resistance value is trimmed by setting the on/off states of the multiple switching elements, thereby improving the accuracy of voltage detection (see Patent Document 1).

Japanese Patent Application Laid-Open No. 05-110370

One aspect of the present invention aims to provide a semiconductor device having a voltage divider circuit that can reduce current consumption and improve voltage division accuracy.

The voltage divider circuit in one embodiment of the present invention comprises:
A plurality of resistor elements for dividing an input voltage;
a plurality of switching elements connected to at least any of the plurality of resistive elements and selectively turned on to adjust a voltage divided by the plurality of resistive elements;
Equipped with
At least one of the plurality of switching elements is a thin film transistor using an oxide semiconductor film.

According to one aspect of the present invention, an object is to provide a semiconductor device having a voltage divider circuit that can suppress current consumption and improve voltage division accuracy.

FIG. 1 is a circuit diagram showing a voltage divider circuit included in a semiconductor device according to this embodiment. FIG. 2 is a schematic cross-sectional view showing the voltage divider circuit shown in FIG. FIG. 3A is an explanatory diagram showing a method of manufacturing the voltage divider circuit shown in FIG. FIG. 3B is an explanatory diagram showing a method of manufacturing the voltage divider circuit shown in FIG. FIG. 3C is an explanatory diagram showing a method of manufacturing the voltage divider circuit shown in FIG. FIG. 4 is a circuit diagram showing an example of a reference voltage generating circuit connected to the voltage dividing circuit shown in FIG.

The semiconductor device according to one embodiment of the present invention is based on the finding that in a voltage divider circuit such as that described in Patent Document 1, if the switching element is a MOS (Metal-Oxide-Semiconductor) transistor, an error occurs in the divided voltage, which is the output, due to leakage current.
Specifically, in a voltage divider circuit that can trim the voltage divider resistance value by combining multiple resistance elements and multiple MOS transistors, the leakage current flowing through the parasitic diodes of the source and drain flows through the resistance elements, causing a voltage drop and resulting in an error in the divided voltage. Also, if the number of minute steps by the resistance elements is increased in order to improve the accuracy of the divided voltage, the number of switching elements also increases proportionally, increasing the error due to the leakage current, which hinders the improvement of the accuracy of the divided voltage, especially at high temperatures where the leakage current becomes large.

Therefore, in one embodiment of the present invention, a thin film transistor using an oxide semiconductor film is used as the switching element instead of a MOS transistor. A thin film transistor using an oxide semiconductor film can reduce leakage current to 1/1000th of that of a MOS transistor, so current consumption can be suppressed and the accuracy of voltage division can be improved. In particular, the accuracy of the divided voltage can be sufficiently improved even at high temperatures, and the error in the reference voltage can be reduced to improve the accuracy of voltage detection.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
In the drawings, the same components are denoted by the same reference numerals, and duplicate explanations may be omitted.
In addition, the X-axis, Y-axis, and Z-axis shown in the drawings are mutually orthogonal. The X-axis direction may be referred to as the "width direction", the Y-axis direction as the "depth direction", and the Z-axis direction as the "height direction" or "thickness direction". The surface of each film on the +Z direction side may be referred to as the "front surface" or "upper surface", and the surface on the -Z direction side as the "rear surface" or "lower surface".
Furthermore, the drawings are schematic, and the ratios of width, depth, and thickness are not as shown. The number, position, shape, structure, size, etc. of a plurality of films or layers, or a semiconductor element obtained by structurally combining them, are not limited to the embodiments shown below, and may be any number, position, shape, structure, size, etc. that is preferable for implementing the present invention.

FIG. 1 is a circuit diagram showing a voltage divider circuit included in a semiconductor device according to this embodiment.
As shown in FIG. 1, a semiconductor device 10 includes a circuit that divides a reference voltage output from a reference voltage generating circuit VR by a voltage dividing circuit 100 and outputs the divided voltage.
The voltage divider circuit 100 includes a first resistor section 100A, a second resistor section 100B, a third resistor section 100C, and a fourth resistor section 100D. The first resistor section 100A, the second resistor section 100B, and the third resistor section 100C are connected in series. The fourth resistor section 100D is connected in parallel to the third resistor section 100C.

The first resistor section 100A includes resistor elements 111 to 113 connected in series, and thin film transistors 121 to 124 serving as switching elements connected to the respective nodes of the resistor elements 111 to 113. The first resistor section 100A performs coarse adjustment of the divided voltage by selectively turning on the thin film transistors 121 to 124.
Specifically, in this embodiment, a case is considered in which the resistance values of the resistor elements 111 to 113 connected in series are 8RΩ, 4RΩ, and 2RΩ (R is an arbitrary resistance value), respectively. In this case, the combined resistance value of the first resistor unit 100A can be varied in the range of 0Ω to 14RΩ by selectively turning on the four thin film transistors 121 to 124. For example, the combined resistance value of the first resistor unit 100A is 14RΩ when only the thin film transistor 121 is turned on, 6RΩ when only the thin film transistor 122 is turned on, 2RΩ when only the thin film transistor 123 is turned on, and 0Ω when only the thin film transistor 124 is turned on.

In this embodiment, the second resistor section 100B and the third resistor section 100C are resistor elements 131 and 141, each having a resistance value of RΩ.

The fourth resistor section 100D comprises resistor elements 151-159 connected in series, and thin film transistors 161-169 as switching elements connected to the nodes of the resistor elements 151-159. This fourth resistor section 100D divides the potential difference in the fourth resistor section 100D into small steps using the nine resistor elements 151-159 with a resistance value lower than RΩ, and by selectively turning on the nine thin film transistors 161-169, finely adjusts the divided voltage and outputs it from the OUT terminal.

The trimming method using this voltage divider circuit 100 is performed by selectively turning on thin-film transistors 121-124 and 161-169, which serve as switching elements, to gradually change the series resistance value of the voltage divider circuit 100.

Next, the structure of the voltage divider circuit 100 will be described.
Fig. 2 is a schematic cross-sectional view of the voltage divider circuit shown in Fig. 1. Fig. 2 mainly shows the structures of a resistor element 151 and a thin film transistor 161 as an example.
Other resistor elements and other thin film transistors are similar to these, and therefore will not be described.

As shown in FIG. 2, the resistor elements 151 are each formed of a polysilicon film on the surface of an element isolation insulating layer 12 provided on a semiconductor substrate 11, and both ends are low-resistance sections into which ions are highly doped.

The interlayer insulating film 13 is formed over the entire upper surfaces of the semiconductor substrate 11 and the element isolation insulating layer 12 so as to cover the upper surface and side surfaces of the resistor element 151. The upper surface of the interlayer insulating film 13 is flattened.
Further, contact holes are opened in the interlayer insulating film 13 to form a plurality of plugs P1 so as to be electrically connected to the resistance elements 151, respectively.

The metal wiring 180 is made of an aluminum alloy and is formed on the upper surface of the interlayer insulating film 13. This metal wiring 180 is electrically connected to the resistive element 151 via a plug P1 that penetrates the interlayer insulating film 13.

The interlayer insulating film 14 is formed over the entire upper surface of the interlayer insulating film 13 so as to cover the upper and side surfaces of the multiple metal wirings 180. This interlayer insulating film 14 is planarized by etch-back or CMP (Chemical Mechanical Polishing).

The thin film transistor 161 is formed on the upper surface of the interlayer insulating film 14, and is located above the resistance element 151. This thin film transistor 161 is a thin film transistor using an oxide semiconductor film 161b, and has a bottom gate structure including an etching stopper film 161c.
The thin film transistor 161 using the oxide semiconductor film 161b can be manufactured at a low heat treatment temperature of about 300° C., which reduces the influence of the heat treatment on various circuits including the metal wiring 180 made of an aluminum alloy (melting point: about 660° C.) present in the lower layer. This allows the thin film transistor 161 to be formed so as to overlap the resistance element 151 via the interlayer insulating film 14, thereby reducing the chip area.

The gate electrode 161a is formed on the upper surface of the interlayer insulating film 14, and is covered with an insulating film 15 formed on the entire upper surface of the interlayer insulating film 14. This insulating film 15 functions as a gate insulating film for the thin film transistor 161.
Furthermore, in order to enable electrical connection to predetermined metal wiring 180, contact holes are opened in the interlayer insulating film 14 and the insulating film 15, and a plurality of plugs P2 are formed.

The oxide semiconductor film 161b is formed to cover the gate electrode 161a with the insulating film 15 interposed therebetween.
The oxide semiconductor may be appropriately selected as long as it is unlikely to affect various circuits, including the metal wiring 180 present thereunder, during heat treatment during manufacture. Among such oxide semiconductors, In-Gz-Zn-O (IGZO) is preferable because it can increase the current ratio between when the thin film transistor 161 is on and when it is off, and can increase the on current and decrease the off current.

The etching stopper film 161c is a silicon oxide film and is formed on the highest surface of the oxide semiconductor film 161b. This etching stopper film 161c functions as a stopper when the molybdenum deposited on it is separated by etching to form the drain electrode 161d and the source electrode 161e.

The drain electrode 161d is formed so as to be electrically connected to one end of the resistor element 151 via multiple plugs P1, P2 and metal wiring 180.

The passivation film 16 is formed to cover the entire area.

Next, the manufacturing method of the semiconductor device 10 in this embodiment will be described with reference to Figures 3A to 3C.

First, in the so-called substrate process (FEOL: Front End Of The Line), as shown in FIG. 3A, a shallow trench isolation (STI) is formed on the surface of a semiconductor substrate 11 by photolithography, and an element isolation insulating layer 12 is formed on the upper surface of the semiconductor substrate 11. A polysilicon layer is formed on the upper surface of this element isolation insulating layer 12 by photolithography and dry etching, and ions are implanted into this polysilicon layer to a concentration that realizes a predetermined resistance value, forming a resistor element 151.

Next, in the so-called wiring process (BEOL: Back End Of The Line), as shown in FIG. 3B, an interlayer insulating film 13 is formed over the entire upper surface and planarized by CMP. Contact holes are opened on the planarized upper surface of the interlayer insulating film 13 by photolithography and dry etching, and tungsten is embedded using titanium as a base to form multiple plugs P1. On the upper surface of these multiple plugs P1, multiple metal wirings 180 are formed of aluminum alloy by photolithography and dry etching, so that they can be electrically connected to the resistance elements 151 via the multiple plugs P1. After forming the metal wirings 180, an interlayer insulating film 14 is formed over the entire surface of the semiconductor substrate 11 and planarized by CMP.

Next, as shown in FIG. 3C, molybdenum is deposited over the entire top surface of the planarized interlayer insulating film 14 by sputtering, then a pattern is formed by photolithography, and the gate electrode 161a is formed by dry etching. A silicon oxide film is deposited over the entire top surface of the interlayer insulating film 14 on which the gate electrode 161a has been formed by plasma CVD, forming the insulating film 15.

Next, In-Gz-Zn-O is deposited as oxide semiconductor film 161b on part of the upper surface of insulating film 15 by sputtering, and then a silicon oxide film is deposited on the upper surface by plasma CVD. The deposited silicon oxide film is patterned into a predetermined shape, and the In-Gz-Zn-O is etched using the silicon oxide film of that shape as a mask. The silicon oxide film is then further patterned to form etching stopper film 161c, and RTA (Rapid Thermal Anneal) is then performed at 290°C.

Next, contact holes are opened in the interlayer insulating film 14 and the insulating film 15 to form a plurality of plugs P2 so as to be electrically connected to the predetermined metal wiring 180. Molybdenum is then deposited by sputtering, and the drain electrode 161d and the source electrode 161e are formed by patterning, followed by RTA at 270°C.

Thus, the thin-film transistor 161 formed on the planarized upper surface of the interlayer insulating film 14 can be formed at a low temperature of about 300°C, so that the laminate including the metal wiring 180 formed of an aluminum alloy with a melting point of about 660°C is less susceptible to heat effects.

FIG. 4 is a circuit diagram showing an example of a reference voltage generating circuit connected to the voltage dividing circuit shown in FIG.
4, the reference voltage generating circuit VR is a bandgap reference circuit, and includes an operational amplifier circuit A1, NPN bipolar transistors Q1 and Q2, and resistor elements R1 to R3.

In the reference voltage generating circuit VR, a resistor element R3 and an NPN bipolar transistor Q1 are connected in series between the output terminal of the operational amplifier circuit A1 and the ground potential. Furthermore, in the reference voltage generating circuit VR, a resistor element R2, a resistor element R1 and an NPN bipolar transistor Q2 are connected in series between the output terminal of the operational amplifier circuit A1 and the ground potential. The collectors and bases of the NPN bipolar transistors Q1 and Q2 are electrically connected to each other and diode-connected. In the operational amplifier circuit A1, the non-inverting input terminal is connected to the node between the resistor element R3 and the NPN bipolar transistor Q1, and the inverting input terminal is connected to the node between the resistor element R1 and the resistor element R2.
By connecting in this manner, the reference voltage generating circuit VR outputs the output of the operational amplifier circuit A1, which is fed back using the resistor elements R1 to R3, as the reference voltage VREF.

As described above, the voltage divider circuit according to one embodiment of the present invention includes a plurality of resistive elements that divide an input voltage, and a plurality of switching elements that are connected to at least one of the resistive elements and selectively turned on to adjust a voltage divided by the resistive elements, and at least one of the switching elements is a thin film transistor using an oxide semiconductor film.
As a result, the voltage divider circuit according to one embodiment of the present invention can reduce leakage current to 1/1000 of that of a MOS transistor, thereby making it possible to suppress current consumption and improve voltage division accuracy.

In the semiconductor device of the above embodiment, all of the MOS transistors are replaced with thin-film transistors using oxide semiconductor films, but at least one of them may be replaced, or only the switching elements in the fourth resistor section, which is the larger in number, may be replaced.

In addition, the semiconductor device of the above embodiment has been described as having a function of dividing the reference voltage output from the reference voltage generating circuit using a voltage divider circuit and outputting the divided voltage, but the present invention is not limited to this and can be appropriately selected as long as the function uses a voltage divider circuit.

Furthermore, in the above embodiment, the reference voltage circuit is described as a bandgap reference circuit, but it is not limited to this, and may be an ED type using enhancement and depletion type MOS transistors, a bandgap type using the bandgap of a semiconductor, etc.

REFERENCE SIGNS LIST 10 semiconductor device 11 semiconductor substrate 12 element isolation insulating layer 13, 14 interlayer insulating film 100 voltage divider circuit 100A first resistance portion 100B second resistance portion 100C third resistance portion 100D fourth resistance portion 111 to 113, 131, 141, 151 to 159 resistance elements 121 to 124, 161 to 169 thin film transistors (switching elements)
180 Metal wiring VR Reference voltage generation circuit

Claims (7)

A plurality of resistor elements for dividing an input voltage;
a plurality of switching elements connected to at least any of the plurality of resistive elements and selectively turned on to adjust a voltage divided by the plurality of resistive elements;
Equipped with
At least one of the plurality of switching elements is a thin film transistor using an oxide semiconductor film. the plurality of resistive elements are incorporated into a first resistive section, a second resistive section, a third resistive section and a fourth resistive section;
the first resistor unit, the second resistor unit, and the third resistor unit are connected in series to divide the input voltage;
2. The voltage divider circuit according to claim 1, wherein the fourth resistance section is connected in parallel to the second resistance section, and the plurality of built-in resistance elements are connected in series. The voltage divider circuit according to claim 2, in which the fourth resistor section has a plurality of switching elements connected to each node of the plurality of resistor elements connected in series, and outputs a divided voltage by selectively turning on the plurality of switching elements. the voltage divider circuit further includes metal wiring electrically connecting the plurality of resistance elements and the plurality of switching elements;
the resistor element is formed on an element isolation insulating layer provided on a semiconductor substrate,
the metal wiring is formed on an interlayer insulating layer provided on an upper surface of the element isolation insulating layer;
2. The voltage divider circuit according to claim 1, wherein the thin film transistor is formed in a layer above the metal wiring. The voltage divider circuit according to claim 4, wherein the thin-film transistor is formed at a position where it at least partially overlaps with the resistive element in a plan view. The voltage divider circuit according to claim 5, wherein the length of the wiring connecting the resistive element and the thin-film transistor is 5 μm or less. 7. A semiconductor device comprising the voltage divider circuit according to claim 1.

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