JP2012119672A - Semiconductor device, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable semiconductor device by a method of forming an oxygen-excess oxide semiconductor with good reproducibility, and a device configuration where hydrogen or water is not mixed in the oxide semiconductor device from the outside as much as possible.SOLUTION: In the method of manufacturing a transistor including an oxide semiconductor, the percentage of oxygen flow rate to the total flow rate of sputtering gas is set to 90%-100%, an oxide semiconductor layer is formed in oxygen-excess state by sputtering a metal oxide, and the oxide semiconductor layer is sealed in a dense metal oxide thus obtaining a device configuration where impurities such as hydrogen or water is not mixed as much as possible.

Description

One embodiment of the present invention relates to a semiconductor device including a transistor or a circuit including the transistor. For example, the present invention relates to a transistor in which a channel formation region is formed using an oxide semiconductor or a semiconductor device including a circuit including the transistor.

A technique in which a transistor or the like is manufactured using an oxide semiconductor film in a channel formation region and applied to a display device has attracted attention. For example, a transistor using zinc oxide (ZnO) or a transistor using InGaO ₃ (ZnO) _m can be given as the oxide semiconductor film. Patent Documents 1 and 2 disclose a technique in which a transistor including these oxide semiconductor films is formed over a light-transmitting substrate and used as a switching element of an image display device.

JP 2007-123861 A JP 2007-96055 A

In the device manufacturing process, when oxygen vacancies are generated in an oxide semiconductor, the electrical conductivity thereof may be changed. The same applies to the case where hydrogen or water forming an electron donor is mixed in the oxide semiconductor. Such a phenomenon becomes a variation factor of electrical characteristics for a transistor including an oxide semiconductor.

Therefore, it is preferable that the oxide semiconductor be formed in an oxygen-excess state and have a device configuration in which hydrogen and water are not mixed from the outside as much as possible.

Therefore, an object of one embodiment of the present invention is to provide a method for forming an oxygen-excess oxide semiconductor with high reproducibility. Another object is to provide a device structure in which hydrogen and water are not mixed into an oxide semiconductor from the outside as much as possible.

One embodiment of the present invention disclosed in this specification is a method for forming an oxide semiconductor layer in an oxygen-excess state in a method for manufacturing a transistor including an oxide semiconductor. The present invention relates to a device configuration in which impurities such as water are not mixed as much as possible.

In one embodiment of the present invention disclosed in this specification, a base film is formed over an insulating surface, an oxide semiconductor layer is formed over the base film, and a source electrode layer and a drain electrode which are in contact with part of the oxide semiconductor layer Forming a layer, forming a gate insulating layer over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer, and forming the gate electrode layer over the gate insulating layer so as to overlap with the oxide semiconductor layer. The oxide semiconductor layer is formed by sputtering a metal oxide containing indium, gallium, and zinc at a ratio of the oxygen flow rate to the total flow rate of the sputtering gas of 90% to 100%. It is a manufacturing method of an apparatus.

In another embodiment of the present invention disclosed in this specification, a base film is formed over an insulating surface, a gate electrode layer is formed over the base film, a gate insulating layer is formed over the gate electrode layer, and gate insulating An oxide semiconductor layer is formed over the layer, a source electrode layer and a drain electrode layer in contact with part of the oxide semiconductor layer are formed, and a protective film is formed over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer In the process, the oxide semiconductor layer is formed by sputtering a metal oxide containing indium, gallium, and zinc with a ratio of an oxygen flow rate to a total flow rate of a sputtering gas of 90% to 100%. This is a method for manufacturing a semiconductor device.

As the base film, the gate insulating layer, and the protective film, a Ga—Zn—O film formed by sputtering a metal oxide containing gallium and zinc is preferably used. The metal oxide is very dense and has a high barrier property. Therefore, by sandwiching the oxide semiconductor layer with the metal oxide, entry of impurities such as hydrogen and water into the oxide semiconductor layer can be suppressed.

The gate electrode layer is a stacked layer, and at least a layer in contact with the gate insulating layer is formed by sputtering a metal oxide containing indium, gallium, and zinc using a sputtering gas containing nitrogen. It is preferable to use an In—Ga—Zn—O film containing. By using an In—Ga—Zn—O film containing nitrogen for the gate electrode layer, the threshold voltage of the electrical characteristics of the transistor can be positive, and a so-called normally-off switching element can be realized.

Another embodiment of the present invention disclosed in this specification includes an oxide semiconductor layer containing indium, gallium, and zinc, and a gate in contact with one surface of the oxide semiconductor layer, containing gallium and zinc. An insulating layer; and a gate electrode layer that includes indium, gallium, zinc, and nitrogen and overlaps with the oxide semiconductor layer with the gate insulating layer interposed therebetween, and the other surface of the oxide semiconductor layer includes gallium, and A semiconductor device is in contact with a metal oxide containing zinc.

A highly reliable semiconductor device can be formed by providing a method for forming an oxygen-excess oxide semiconductor with high reproducibility and a device configuration in which hydrogen and water are not mixed into the oxide semiconductor from the outside as much as possible.

6A and 6B are cross-sectional views illustrating a transistor of one embodiment of the present invention. 4A to 4D are cross-sectional views illustrating a transistor of one embodiment of the present invention and a manufacturing method thereof. 4A to 4D are cross-sectional views illustrating a transistor of one embodiment of the present invention and a manufacturing method thereof. 4A to 4D are cross-sectional views illustrating a transistor of one embodiment of the present invention and a manufacturing method thereof. 4A to 4D are cross-sectional views illustrating a transistor of one embodiment of the present invention and a manufacturing method thereof. 8A and 8B illustrate a semiconductor device of one embodiment of the present invention and an equivalent circuit diagram of a pixel portion. FIG. 14 illustrates one embodiment of an electronic device. The graph which shows an ESR analysis result. The figure which shows the model of atomic arrangement | positioning. The graph which shows the carrier concentration calculated | required by Hall measurement. The graph which shows a XRD measurement result. 6A and 6B are cross-sectional views illustrating a transistor of one embodiment of the present invention. 3A and 3B illustrate a crystal structure of an oxide material. 3A and 3B illustrate a crystal structure of an oxide material. 3A and 3B illustrate a crystal structure of an oxide material.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed. In addition, the present invention is not construed as being limited to the description of the embodiments below.

(Embodiment 1)
In this embodiment, a structure and a manufacturing method of a semiconductor device according to one embodiment of the present invention will be described.

FIG. 1 is a cross-sectional view of a top-gate transistor. The transistor 120 includes a base film 101, an oxide semiconductor layer 108a, a source electrode layer 104a, a drain electrode layer 104b, and a gate insulator over a substrate 100 having an insulating surface. The structure includes the layer 102, the gate electrode layer 112, the protective film 110a, and the protective film 110b.

A material used for the oxide semiconductor layer 108a preferably contains at least indium (In) or zinc (Zn). In particular, In and Zn are preferably included. In addition, it is preferable that gallium (Ga) be included in addition to the stabilizer for reducing variation in electrical characteristics of the transistor including the oxide semiconductor. Moreover, it is preferable to have tin (Sn) as a stabilizer. Moreover, it is preferable to have hafnium (Hf) as a stabilizer. Moreover, it is preferable to have aluminum (Al) as a stabilizer.

As other stabilizers, lanthanoids such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb) , Dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), or lutetium (Lu).

For example, as an oxide semiconductor, indium oxide, tin oxide, zinc oxide, binary metal oxides such as In—Zn oxide, Sn—Zn oxide, Al—Zn oxide, Zn—Mg oxide Oxides, Sn—Mg oxides, In—Mg oxides, In—Ga oxides, In—Ga—Zn oxides (also referred to as IGZO) which are oxides of ternary metals, In— Al-Zn oxide, In-Sn-Zn oxide, Sn-Ga-Zn oxide, Al-Ga-Zn oxide, Sn-Al-Zn oxide, In-Hf-Zn oxide In-La-Zn-based oxide, In-Ce-Zn-based oxide, In-Pr-Zn-based oxide, In-Nd-Zn-based oxide, In-Sm-Zn-based oxide, In-Eu -Zn oxide, In-Gd-Zn oxide, In-Tb-Zn oxide, n-Dy-Zn-based oxide, In-Ho-Zn-based oxide, In-Er-Zn-based oxide, In-Tm-Zn-based oxide, In-Yb-Zn-based oxide, In-Lu-Zn -Based oxides, In-Sn-Ga-Zn-based oxides that are oxides of quaternary metals, In-Hf-Ga-Zn-based oxides, In-Al-Ga-Zn-based oxides, In-Sn- An Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or an In—Hf—Al—Zn-based oxide can be used.

An In—Ga—Zn-based oxide semiconductor material has characteristics in which resistance in a no electric field is sufficiently high, off-state current can be sufficiently reduced, and field-effect mobility is high. In addition, a transistor including an In—Sn—Zn-based oxide semiconductor material can have field effect mobility three times higher than that of a transistor including an In—Ga—Zn-based oxide semiconductor material; The threshold voltage is easy to make positive. These semiconductor materials are one of suitable materials that can be used for the transistor included in the semiconductor device of one embodiment of the present invention.

Note that here, for example, an In—Ga—Zn-based oxide means an oxide containing In, Ga, and Zn as its main components, and there is no limitation on the ratio of In, Ga, and Zn. Moreover, metal elements other than In, Ga, and Zn may be contained.

Alternatively, a material represented by InMO ₃ (ZnO) _m (m> 0 is satisfied, and m is not an integer) may be used as the oxide semiconductor. Note that M represents one metal element or a plurality of metal elements selected from Ga, Fe, Mn, and Co. Alternatively, a material represented by In ₃ SnO ₅ (ZnO) _n (n> 0 is satisfied, and n is an integer) may be used as the oxide semiconductor. For example, In: Ga: Zn = 1: 1: 1 (= 1/3: 1/3: 1/3) or In: Ga: Zn = 2: 2: 1 (= 2/5: 2/5: 1). / 5) atomic ratio In—Ga—Zn-based oxides and oxides in the vicinity of the composition can be used. Alternatively, In: Sn: Zn = 1: 1: 1 (= 1/3: 1/3: 1/3), In: Sn: Zn = 2: 1: 3 (= 1/3: 1/6: 1) / 2) or In: Sn: Zn = 2: 1: 5 (= 1/4: 1/8: 5/8) atomic ratio In—Sn—Zn-based oxide or oxide in the vicinity of the composition Should be used.

However, the composition is not limited thereto, and a material having an appropriate composition may be used depending on required semiconductor characteristics (mobility, threshold value, variation, etc.). In order to obtain the required semiconductor characteristics, it is preferable that the carrier density, impurity concentration, defect density, atomic ratio of metal element to oxygen, interatomic bond distance, density, and the like be appropriate.

For example, high mobility can be obtained relatively easily with an In—Sn—Zn-based oxide. However, mobility can be increased by reducing the defect density in the bulk also in the case of using an In—Ga—Zn-based oxide.

Note that for example, the composition of an oxide in which the atomic ratio of In, Ga, and Zn is In: Ga: Zn = a: b: c (a + b + c = 1) has an atomic ratio of In: Ga: Zn = A: B: being in the vicinity of the oxide composition of C (A + B + C = 1), a, b and c are (a−A) ² + (b−B) ² + (c−C) ² ≦ r ² R may be 0.05, for example. The same applies to other oxides.

The oxide semiconductor may be single crystal or non-single crystal. In the latter case, it may be amorphous or polycrystalline. Moreover, the structure which contains the part which has crystallinity in an amorphous may be sufficient, and a non-amorphous may be sufficient.

Since an oxide semiconductor in an amorphous state can obtain a flat surface relatively easily, interface scattering when a transistor is manufactured using the oxide semiconductor can be reduced, and relatively high mobility can be obtained relatively easily. be able to.

In addition, in an oxide semiconductor having crystallinity, defects in a bulk can be further reduced, and mobility higher than that of an oxide semiconductor in an amorphous state can be obtained by increasing surface flatness. In order to improve the flatness of the surface, it is preferable to form an oxide semiconductor on the flat surface. Specifically, the average surface roughness (Ra) is 1 nm or less, preferably 0.3 nm or less, more preferably Is preferably formed on a surface of 0.1 nm or less.

In this embodiment, an In—Ga—Zn—O film which is a metal oxide film containing indium (In), gallium (Ga), and zinc (Zn) is used. In the In—Ga—Zn—O film, when oxygen which is a constituent element is deficient, a defect level is formed, and thus electric conductivity may change. Since the change in electrical conductivity greatly affects not only the initial characteristics of the transistor but also long-term reliability, the In—Ga—Zn—O film is preferably formed in an oxygen-excess state.

Note that an oxygen-excess In—Ga—Zn—O film refers to an In—Ga—Zn—O film having excess oxygen which does not have a bond to a metal element of In, Ga, or Zn in the film. Say. The presence or absence of excess oxygen can be confirmed by performing ESR (electron spin resonance) analysis.

In the ESR analysis, a parameter called g value is obtained from the value (H ₀ ) of the magnetic field where microwave absorption occurs using the formula g = hv / βH ₀ . Here, h is a Planck constant, β is a Bohr magneton, and both are constants.

FIG. 8 shows an ESR signal obtained by analyzing the In—Ga—Zn—O film at room temperature (300 K) with microwaves having a frequency of 9.5 GHz. Sample A has a sputtering gas flow rate of argon: oxygen = 30 sccm: 15 sccm. A film formed at room temperature, sample B is a film formed at 200 ° C. under the same sputtering gas conditions as sample A, and sample C is 200 ° C. at a sputtering gas flow rate of argon: oxygen = 0 sccm: 40 sccm (oxygen 100%). It is the formed film.

Other film formation conditions are common, and a metal oxide (made by Mitsui Metals) with In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1 [molar ratio] is used as a film formation target. A film having a thickness of 100 nm is formed on a quartz glass having a thickness of 0.5 mm with a pressure of 0.4 Pa and a DC power of 0.5 kW (cathode size: 12 inches φ).

In sample A, a signal of g = 2.008 due to an oxygen dangling bond is observed, and the spin density is 3.8 × 10 ¹⁸ spins / cm ³ . In sample B, a signal of g = 2.008 is hardly observed, and the spin density is less than 1.0 × 10 ¹⁶ spins / cm ³ below the measurement lower limit.

From this result, the sample A formed at room temperature has a metastable structure in which a large amount of dangling bonds of oxygen exists, as in the atomic arrangement model shown in FIG. It can be said that this is a stable structure with a small number of oxygen dangling bonds. That is, the atomic arrangement is stabilized by heating during film formation. Note that it is known that heating the sample A also reduces the spin density as in the sample B and stabilizes the atomic arrangement.

On the other hand, sample C has a film formation by heating, but a signal of g = 2.008 is observed, the spin density is 2.0 × 10 ¹⁸ spins / cm ³ , and the analysis is similar to sample A and the ESR signal. The result is obtained. The result that a signal of g = 2.008 is observed from the sample C, which should have a stable structure by heating film formation, is that there is surplus oxygen in the film as shown in FIG. 9B. This suggests that oxygen has lone electrons. That is, an oxygen-excess In—Ga—Zn—O film can be formed by increasing the ratio of the oxygen flow rate to the total flow rate of the sputtering gas.

The source electrode layer 104a and the drain electrode layer 104b can be formed using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing any of these materials as its main component. Note that in FIG. 1, the source electrode layer 104 a and the drain electrode layer 104 b are illustrated as a single layer, but a stack of the above materials may be used. For example, a stack of aluminum whose side is in contact with the oxide semiconductor layer 108a and titanium is used.

For the gate insulating layer 102, an insulating film such as silicon oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, gallium oxide, gallium zinc oxide, aluminum oxynitride, aluminum nitride oxide, or hafnium oxide can be used. In particular, gallium zinc oxide (Ga—Zn—O) can form a very dense film and thus has an excellent effect of suppressing entry of impurities such as hydrogen and water into the oxide semiconductor layer 108a. In the case where an In—Ga—Zn—O film is used for the oxide semiconductor layer 108a, the interface characteristics are improved, and the electrical characteristics of the transistor can be improved.

Note that the above insulating film can also be used for the base film 101, and when gallium zinc oxide is used for the gate insulating layer 102 and the base film 101, the effect of suppressing entry of impurities into the oxide semiconductor layer 108 a can be obtained. It can be further increased.

For the gate electrode layer 112, a stack of a conductive film and an In—Ga—Zn—O film containing nitrogen is preferably used. The work function of the In—Ga—Zn—O film containing nitrogen is 5 eV or more, and the threshold voltage of a transistor using the In—Ga—Zn—O film as a semiconductor layer can be increased by using the work function in contact with the gate insulating film. It can be a positive value. Note that an In—Sn—O film containing nitrogen, an In—Ga—O film containing nitrogen, an In—Zn—O film containing nitrogen, an Sn—O film containing nitrogen, and an In—O film containing nitrogen are used. A film or a metal nitride film (InN, SnN, etc.) can also be used.

In a transistor using a silicon semiconductor, an impurity element whose conductivity type can be changed is mainly added to the silicon semiconductor layer in the channel formation region in a small amount to adjust the work function difference between the gate electrode and the semiconductor layer in the channel formation region. By controlling the threshold voltage, the threshold voltage is controlled. On the other hand, in a transistor including an oxide semiconductor (in this case, an In—Ga—Zn—O film) in this embodiment, a channel formation region is formed using an In—Ga—Zn—O film containing nitrogen as a gate electrode. The threshold voltage is controlled by adjusting the work function difference. Specifically, a so-called normally-off type switching element can be realized by setting the threshold voltage to a positive value.

Note that an In—Ga—Zn—O film intentionally containing nitrogen and an In—Ga—Zn—O film not intentionally containing nitrogen have greatly different film qualities. One embodiment of the present invention utilizes the characteristics of an In—Ga—Zn—O film intentionally containing nitrogen.

FIG. 10 shows a sample with a thickness of 300 nm obtained by forming an In—Ga—Zn—O film containing nitrogen over a quartz substrate at substrate temperatures of 200 ° C. and 400 ° C., and the sample at 450 ° C. in a nitrogen atmosphere. It is the result of having performed the Hall effect measurement (Hall effect measuring device: ResiTest8300 series, Toyo Technica Co., Ltd. use) of the sample which performed the heat processing for time. The vertical axis of the graph shown in FIG. 10 indicates the carrier concentration, and the horizontal axis indicates the ratio of nitrogen gas to the entire deposition gas. As the ratio of nitrogen gas to the entire deposition gas increases, the carrier concentration increases, and it can be seen from FIG. 10 that the carrier concentration tends to increase also by heat treatment. This result indicates that the carrier in the In—Ga—Zn—O film containing nitrogen is an electron, and the carrier type of the In—Ga—Zn—O film containing nitrogen can be determined to be n-type.

In this manner, by intentionally including nitrogen in the In—Ga—Zn—O film, the carrier concentration can be increased and the In—Ga—Zn—O film can be used as a conductive layer. In addition, as described above, the work function can be set to 5 eV or more by intentionally including nitrogen in the In—Ga—Zn—O film, and the threshold voltage can be controlled by using the In—Ga—Zn—O film as a gate electrode. You can also

In addition, a sample was formed on a quartz substrate at a substrate temperature of 400 ° C. and a nitrogen gas flow rate of 40 sccm, and a film was formed on a quartz substrate at a substrate temperature of 400 ° C. and an oxygen gas flow rate of 40 sccm. FIGS. 11A and 1B show the results of XRD measurement performed on each of the samples on which the film was formed by OUT OF PLANE. The In—Ga—Zn—O film containing nitrogen has high crystallinity immediately after deposition, and a sharp peak can be confirmed as shown in FIG. In addition, it can be seen that an In—Ga—Zn—O film formed only with oxygen gas has lower crystallinity than an In—Ga—Zn—O film containing nitrogen. As described above, the In—Ga—Zn—O film and the In—Ga—Zn—O film containing nitrogen are greatly different in film quality immediately after film formation.

In FIG. 1, the gate electrode layer 112 is illustrated such that the end surfaces of the stacked conductive layers continuously form slopes, but as shown in FIG. 12, the stacked conductive layers are illustrated. The end face of the layer may not be continuous, and a step may be formed. In this case, the width of the conductive layer on the side in contact with the gate insulating layer is wide, and the width of the conductive layer on the side not in contact with the gate insulating layer is narrow. The shape of this gate electrode layer can also be applied to a transistor having a structure different from that in FIGS.

The protective film 110a and the protective film 110b are formed using silicon oxide, silicon nitride, gallium oxide, gallium zinc oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, aluminum nitride, aluminum oxynitride, aluminum nitride oxide, hafnium oxide, or these A single layer or stacked layers can be formed using a mixed material. Note that although an example in which the protective film 110a and the protective film 110b have a two-layer structure is described in this embodiment, a single-layer structure may be used.

2A to 2E, a process for manufacturing a transistor which is one embodiment of the present invention over a substrate will be described below.

First, the base film 101 is formed over the substrate 100 (see FIG. 2A).

For the substrate 100, a glass material such as aluminosilicate glass, aluminoborosilicate glass, or barium borosilicate glass is used. For mass production, it is preferable to use a mother glass of the eighth generation (2160 mm × 2460 mm), the ninth generation (2400 mm × 2800 mm, or 2450 mm × 3050 mm), the tenth generation (2950 mm × 3400 mm), or the like. Since the mother glass has a high processing temperature and contracts significantly when the processing time is long, when mass production is performed using the mother glass, the heat treatment in the manufacturing process is 600 ° C. or lower, preferably 450 ° C. or lower. It is desirable.

As the base film 101, a gallium zinc oxide (Ga—Zn—O) film with a thickness of 50 nm to 600 nm is formed by a sputtering method. For example, a metal oxide containing gallium and zinc, typically gallium zinc oxide (Ga ₂ O ₃ : ZnO = 1: 1 or 5: 1 [molar ratio]) is used as a deposition target, and argon is used. A gallium zinc oxide film can be formed by sputtering the target with a rare gas such as a rare gas, a rare gas and oxygen, or oxygen.

The base film 101 preferably includes oxygen in the film (in the bulk) at least in an amount exceeding the stoichiometric ratio. By increasing the thickness of the base film 101, the amount of oxygen released from the base film 101 in heat treatment performed later can be increased, and the increase in the thickness of the base film 101 and the oxide semiconductor film formed later can be increased. Defects at the interface can be reduced.

Note that the base film 101 can be formed using an insulating film such as silicon oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, gallium oxide, aluminum oxynitride, aluminum nitride oxide, or hafnium oxide.

In the case of using a glass substrate containing an impurity such as an alkali metal, a nitride insulating layer may be provided between the base film 101 and the substrate 100 in order to prevent alkali metal from entering the semiconductor layer and the gate insulating layer. . Examples of the nitride insulating layer include a silicon nitride film and an aluminum nitride film, which can be formed by PCVD or sputtering. Since alkali metals such as lithium (Li) and sodium (Na) cause deterioration in transistor characteristics, it is preferable not to enter from the substrate 100.

Next, the oxide semiconductor film 108 is formed over the base film 101 by a sputtering method (see FIG. 2B). The oxide semiconductor film 108 is formed using an In—Ga—Zn—O-based metal oxide (In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1 or 1: 1: 2 [mol number] as a deposition target. Ratio]), the distance between the substrate and the target is 170 mm, the substrate temperature is 200 ° C. or more and 450 ° C. or less, the pressure is 0.4 Pa, the direct current (DC) power is 0.5 kW (cathode size 12 inches φ), and sputtering is performed. The gas can be formed using only oxygen or a rare gas and oxygen. As the rare gas, argon is typically used, but neon, krypton, or xenon may be used.

In the case where an In—Zn—O-based material is used as the oxide semiconductor, the composition ratio of the target to be used is an atomic ratio, and In: Zn = 50: 1 to 1: 2 (when converted to a molar ratio, In ₂ O ₃ : ZnO = 25: 1 to 1: 4), preferably In: Zn = 20: 1 to 1: 1 (In ₂ O ₃ : ZnO = 10: 1 to 1: 2 in terms of mol number ratio), More preferably, In: Zn = 15: 1 to 1.5: 1 (in ₂ O ₃ : ZnO = 15: 2 to 3: 4 in terms of mol number ratio). For example, a target used for forming an In—Zn-based oxide semiconductor satisfies Z> 1.5X + Y when the atomic ratio is In: Zn: O = X: Y: Z.

In addition, for the formation of an In—Sn—Zn-based oxide, In: Sn: Zn is an atomic ratio of 1: 2: 2, 2: 1: 3, 1: 1: 1, or 20:45:35. An oxide target is used.

Here, the ratio of the oxygen flow rate to the total flow rate of the sputtering gas is 90% to 100%, preferably 95% to 100%, and more preferably 100%. By increasing the ratio of the oxygen flow rate to the total flow rate of the sputtering gas, an oxygen-excess In—Ga—Zn—O film can be formed, and a film in which oxygen vacancies are unlikely to occur can be obtained.

Further, it is preferable to use a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or a hydride are removed as the sputtering gas. Note that when the pressure in the treatment chamber in which the oxide semiconductor film 108 is formed is 0.4 Pa or less, contamination of impurities such as alkali metal and hydrogen into the surface of the oxide semiconductor film 108 and the film is reduced. be able to. In addition, by setting the leak rate of the treatment chamber in which the oxide semiconductor film 108 is formed to 1 × 10 ⁻¹⁰ Pa · m ³ / second or less, alkali metal, hydrogen, Incorporation of impurities such as water, hydroxyl group or hydride can be reduced. Further, by using an adsorption-type vacuum pump as an exhaust system, backflow of impurities such as alkali metal, hydrogen, water, hydroxyl group, or hydride from the exhaust system can be reduced.

In addition, by setting the purity of the target for forming the oxide semiconductor film 108 to 99.99% or more, alkali metal, hydrogen, water, a hydroxyl group, hydride, or the like mixed in the oxide semiconductor film 108 is reduced. can do. Further, by using the target, the oxide semiconductor film 108 has a lithium concentration of 5 × 10 ¹⁵ / cm ³ or less, preferably 1 × 10 ¹⁵ / cm ³ or less, and a sodium concentration of 5 × 10 ¹⁶ / cm ³ or less. ³ or less, preferably 1 × 10 ¹⁶ / cm ³ or less, more preferably 1 × 10 ¹⁵ / cm ³ or less, and the concentration of potassium is 5 × 10 ¹⁵ / cm ³ or less, preferably 1 × 10 ¹⁵ / cm ³ or less. can do.

Alkali metal and alkaline earth metal are malignant impurities for the crystalline oxide semiconductor film, and it is better that they are less. In particular, among alkali metals, sodium diffuses into the oxide insulating layer in contact with the oxide semiconductor and becomes Na ⁺ . Further, in the oxide semiconductor, the bond between the metal and oxygen is broken or interrupted. As a result, the transistor characteristics are deteriorated, for example, normally-on (shift of the threshold voltage to negative), the mobility is lowered, and the like. In addition, it causes variation in characteristics. Such a problem becomes prominent particularly when the concentration of hydrogen in the oxide semiconductor film is sufficiently low. Therefore, when the concentration of hydrogen in the crystalline oxide semiconductor film is 5 × 10 ¹⁹ / cm ³ or less, particularly 5 × 10 ¹⁸ / cm ³ or less, the alkali metal concentration can be set to the above value. It is strongly demanded.

By forming an oxide semiconductor film under the above conditions, the concentration of alkali metal is 5 × 10 ¹⁶ atoms / cm ³ or less and the concentration of hydrogen is 1 × 10 ¹⁹ atoms / cm ³ or less. Thus, the oxygen-excess oxide semiconductor film 108 can be formed.

Note that the oxide semiconductor film 108 thus obtained is in a single crystal state, a polycrystalline (also referred to as polycrystal) state, an amorphous state, or the like.

Preferably, the oxide semiconductor film is a CAAC-OS (C Axis Crystallized Oxide Semiconductor) film.

The CAAC-OS film is not completely single crystal nor completely amorphous. The CAAC-OS film is an oxide semiconductor film with a crystal-amorphous mixed phase structure where crystal parts are included in an amorphous phase. Note that the crystal part is often large enough to fit in a cube whose one side is less than 100 nm. Further, in the observation image obtained by a transmission electron microscope (TEM), the boundary between the amorphous part and the crystal part included in the CAAC-OS film is not clear. Further, a grain boundary (also referred to as a grain boundary) cannot be confirmed in the CAAC-OS film by TEM. Therefore, in the CAAC-OS film, reduction in electron mobility due to grain boundaries is suppressed.

In the crystal part included in the CAAC-OS film, the c-axis is aligned in a direction parallel to the normal vector of the formation surface of the CAAC-OS film or the normal vector of the surface, and triangular when viewed from the direction perpendicular to the ab plane. It has a shape or hexagonal atomic arrangement, and metal atoms are arranged in layers or metal atoms and oxygen atoms are arranged in layers as viewed from the direction perpendicular to the c-axis. Note that the directions of the a-axis and the b-axis may be different between different crystal parts. In this specification, a simple term “perpendicular” includes a range from 85 ° to 95 °. In addition, a simple term “parallel” includes a range from −5 ° to 5 °.

Note that the distribution of crystal parts in the CAAC-OS film is not necessarily uniform. For example, in the formation process of the CAAC-OS film, when crystal growth is performed from the surface side of the oxide semiconductor film, the ratio of crystal parts in the vicinity of the surface of the oxide semiconductor film is higher in the vicinity of the surface. In addition, when an impurity is added to the CAAC-OS film, the crystal part in a region to which the impurity is added becomes amorphous in some cases.

Since the c-axis of the crystal part included in the CAAC-OS film is aligned in a direction parallel to the normal vector of the formation surface of the CAAC-OS film or the normal vector of the surface, the shape of the CAAC-OS film (formation surface) Depending on the cross-sectional shape of the surface or the cross-sectional shape of the surface). Note that the c-axis direction of the crystal part is parallel to the normal vector of the surface where the CAAC-OS film is formed or the normal vector of the surface. The crystal part is formed by film formation or by performing crystallization treatment such as heat treatment after film formation.

A transistor including a CAAC-OS film can reduce variation in electrical characteristics due to irradiation with visible light or ultraviolet light. Therefore, the transistor has high reliability.

Note that part of oxygen included in the oxide semiconductor film may be replaced with nitrogen.

The CAAC-OS film is a conductor, a semiconductor, or an insulator depending on its composition or the like. Further, it is transparent or opaque to visible light depending on its composition.

As an example of such a CAAC-OS film, a triangular or hexagonal atomic arrangement is observed when observed from a direction perpendicular to the film surface or the supporting substrate surface, and a metal cross section when the film cross section is observed. Mention may also be made of crystals in which a layered arrangement of atoms or metal atoms and oxygen atoms (or nitrogen atoms) is observed.

An example of a crystal structure included in the CAAC-OS film will be described in detail with reference to FIGS. Unless otherwise specified, in FIGS. 13 to 15, the upward direction is the c-axis direction, and the plane orthogonal to the c-axis direction is the ab plane. Note that the upper half and the lower half simply refer to the upper half and the lower half when the ab surface is used as a boundary. In FIG. 13, O surrounded by a circle represents tetracoordinate O and O surrounded by a double circle represents tricoordinate O.

FIG. 13A illustrates a structure including one hexacoordinate In and six tetracoordinate oxygen atoms adjacent to In (hereinafter, tetracoordinate O). Here, a structure in which only one oxygen atom is adjacent to one metal atom is referred to as a small group. The structure in FIG. 13A has an octahedral structure, but is illustrated as a planar structure for simplicity. Note that three tetracoordinate O atoms exist in each of an upper half and a lower half in FIG. In the small group illustrated in FIG. 13A, electric charge is 0.

FIG. 13B illustrates one pentacoordinate Ga, three tricoordinate oxygen atoms adjacent to Ga (hereinafter, tricoordinate O), and two tetracoordinates close to Ga. And a structure having O. All tricoordinate O atoms are present on the ab plane. One tetracoordinate O atom exists in each of an upper half and a lower half in FIG. In addition, since In also has five coordination, the structure illustrated in FIG. 13B can be employed. In the small group illustrated in FIG. 13B, electric charge is 0.

FIG. 13C illustrates a structure including one tetracoordinate Zn and four tetracoordinate O adjacent to Zn. In FIG. 13C, there is one tetracoordinate O in the upper half and three tetracoordinate O in the lower half. Alternatively, three tetracoordinate O atoms may exist in the upper half of FIG. 13C and one tetracoordinate O atom may exist in the lower half. In the small group illustrated in FIG. 13C, electric charge is 0.

FIG. 13D illustrates a structure including one hexacoordinate Sn and six tetracoordinate O adjacent to Sn. In FIG. 13D, there are three tetracoordinate O atoms in the upper half and three tetracoordinate O atoms in the lower half. In the small group illustrated in FIG. 13D, electric charge is +1.

FIG. 13E illustrates a small group including two Zn atoms. In FIG. 13E, one tetracoordinate O atom exists in the upper half and one tetracoordinate O atom exists in the lower half. In the small group illustrated in FIG. 13E, electric charge is -1.

Here, an aggregate of a plurality of small groups is referred to as a medium group, and an aggregate of a plurality of medium groups is referred to as a large group (also referred to as a unit cell).

Here, a rule for combining these small groups will be described. The three Os in the upper half of 6-coordinate In shown in FIG. 13A each have three adjacent Ins in the lower direction, and the three Os in the lower half each have three in the upper direction. Of adjacent In. One O in the upper half of the five-coordinate Ga shown in FIG. 13B has one adjacent Ga in the lower direction, and one O in the lower half has one adjacent in the upper direction. Ga is included. One O in the upper half of the tetracoordinate Zn shown in FIG. 13C has one adjacent Zn in the lower direction, and the three Os in the lower half each have three in the upper direction. It has neighboring Zn. Thus, the number of tetracoordinate O atoms close to the upper direction of the metal atom is equal to the number of adjacent metal atoms in the lower direction of the O, and the number of tetracoordinate atoms adjacent to the lower direction of the metal atom is the same. The number of O is equal to the number of adjacent metal atoms above the O. Since O which contributes to the bond between the small groups is tetracoordinate, the sum of the number of adjacent metal atoms below O and the number of adjacent metal atoms above O is 4. Therefore, when the sum of the number of tetracoordinate O atoms in the upward direction of a metal atom and the number of tetracoordinate O atoms in the downward direction of another metal atom is four, Groups can be joined together. For example, in the case where a hexacoordinate metal atom (In or Sn) is bonded via tetracoordinate O in the lower half, since there are three tetracoordinate O atoms, a pentacoordinate metal atom (Ga or In) or a tetracoordinate metal atom (Zn).

The metal atoms having these coordination numbers are bonded via tetracoordinate O in the c-axis direction. In addition, a plurality of small groups are combined to form a middle group so that the total charge of the layer structure becomes zero.

FIG. 14A illustrates a model diagram of a middle group included in an In—Sn—Zn—O-based layer structure. FIG. 14B illustrates a large group including three medium groups. Note that FIG. 14C illustrates an atomic arrangement in the case where the layered structure in FIG. 14B is observed from the c-axis direction.

In FIG. 14A, for simplicity, tricoordinate O is omitted, and tetracoordinate O is only the number. For example, three tetracoordinates are provided in each of the upper half and the lower half of Sn. The presence of O is shown as 3 in a round frame. Similarly, in FIG. 14A, one tetracoordinate O atom exists in each of the upper half and the lower half of In, which is shown as 1 in a round frame. Similarly, in FIG. 14A, the lower half includes one tetracoordinate O, the upper half includes three tetracoordinate O, and the upper half includes one. In the lower half, Zn having three tetracoordinate O atoms is shown.

In FIG. 14A, the middle group forming the In—Sn—Zn—O-based layer structure includes three tetracoordinate O atoms in the upper half and the lower half in order from the top. Are bonded to In in the upper and lower halves one by one, and the In is bonded to Zn having three tetracoordinate O atoms in the upper half. A small group consisting of two Zn atoms with four tetracoordinate O atoms in the upper half and the lower half through Coordinate O, and the In is composed of two Zn atoms with one tetracoordinate O atom in the upper half. In this configuration, three tetracoordinate O atoms are bonded to Sn in the upper and lower halves through one tetracoordinate O atom in the lower half of the small group. A plurality of medium groups are combined to form a large group.

Here, in the case of tricoordinate O and tetracoordinate O, the charges per bond can be considered to be −0.667 and −0.5, respectively. For example, the charges of In (6-coordinate or 5-coordinate), Zn (4-coordinate), and Sn (5-coordinate or 6-coordinate) are +3, +2, and +4, respectively. Therefore, the small group including Sn has a charge of +1. Therefore, in order to form a layer structure including Sn, a charge −1 that cancels the charge +1 is required. As a structure that takes charge −1, as illustrated in FIG. 13E, a small group including two Zn atoms can be given. For example, if there is one small group containing Sn and one small group containing 2 Zn, the charge is canceled out, so the total charge of the layer structure can be zero.

Specifically, when the large group illustrated in FIG. 14B is repeated, an In—Sn—Zn—O-based crystal (In ₂ SnZn ₃ O ₈ ) can be obtained. Note that an In—Sn—Zn—O-based layer structure obtained can be represented by a composition formula, In ₂ SnZn ₂ O ₇ (ZnO) _m (m is 0 or a natural number).

In addition, an In—Sn—Ga—Zn-based oxide, which is an oxide of a quaternary metal, and an In—Ga—Zn-based oxide, which is an oxide of a ternary metal (also referred to as IGZO). In-Al-Zn-based oxide, Sn-Ga-Zn-based oxide, Al-Ga-Zn-based oxide, Sn-Al-Zn-based oxide, In-Hf-Zn-based oxide, In -La-Zn oxide, In-Ce-Zn oxide, In-Pr-Zn oxide, In-Nd-Zn oxide, In-Sm-Zn oxide, In-Eu-Zn oxide Oxide, In-Gd-Zn-based oxide, In-Tb-Zn-based oxide, In-Dy-Zn-based oxide, In-Ho-Zn-based oxide, In-Er-Zn-based oxide, In- Tm-Zn-based oxides, In-Yb-Zn-based oxides, In-Lu-Zn-based oxides, and binary metal acids In-Zn oxides, Sn-Zn oxides, Al-Zn oxides, Zn-Mg oxides, Sn-Mg oxides, In-Mg oxides, In-Ga oxides The same applies when an oxide or the like is used.

For example, FIG. 15A illustrates a model diagram of a middle group included in an In—Ga—Zn—O-based layer structure.

In FIG. 15A, the middle group that forms the In—Ga—Zn—O-based layer structure has four tetracoordinate O atoms in the upper half and the lower half in order from the top. Is bonded to Zn in the upper half, and through four tetracoordinate O atoms in the lower half of the Zn, Ga in which one tetracoordinate O atom is present in the upper half and the lower half one by one In this structure, three tetracoordinate O atoms are bonded to In in the upper half and the lower half through one tetracoordinate O atom in the lower half of the Ga. A plurality of medium groups are combined to form a large group.

FIG. 15B illustrates a large group including three medium groups. Note that FIG. 15C illustrates an atomic arrangement in the case where the layered structure in FIG. 15B is observed from the c-axis direction.

Here, charges of In (6-coordinate or 5-coordinate), Zn (4-coordinate), and Ga (5-coordinate) are +3, +2, and +3, respectively. The small group including the charge is 0. Therefore, in the case of a combination of these small groups, the total charge of the medium group is always zero.

In addition, the middle group included in the In—Ga—Zn—O-based layer structure is not limited to the middle group illustrated in FIG. 15A and is a combination of middle groups having different arrangements of In, Ga, and Zn. Groups can also be taken.

Next, after the oxide semiconductor film 108 is formed, in an atmosphere containing almost no hydrogen and moisture (for example, a nitrogen atmosphere, an oxygen atmosphere, or a dry air atmosphere (for example, a dew point of −40 ° C. or less, preferably a dew point of −60 ° C. or less) The first heat treatment (temperature range of 200 ° C. to 450 ° C.) may be performed. This first heat treatment can also be referred to as dehydration or dehydrogenation in which H, OH, and the like are desorbed from the oxide semiconductor film, and the temperature is raised in an inert atmosphere, and the atmosphere is changed to an atmosphere containing oxygen. When performing the heat treatment to be switched or when performing the heat treatment in an oxygen atmosphere, it can also be referred to as an oxidization treatment.

Next, the oxide semiconductor film 108 is processed to form an island-shaped oxide semiconductor layer 108a. The oxide semiconductor film 108 can be processed by forming a mask having a desired shape over the oxide semiconductor film 108 and then etching the oxide semiconductor film 108. The above-described mask can be formed using a method such as photolithography. Alternatively, the mask may be formed using a method such as an inkjet method.

Note that the etching of the oxide semiconductor film 108 may be dry etching or wet etching. Of course, these may be used in combination.

Next, a conductive film for forming a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over the oxide semiconductor layer 108a, the conductive film is processed, and the source The electrode layer 104a and the drain electrode layer 104b are formed (see FIG. 2C). The source electrode layer 104a and the drain electrode layer 104b are formed by a sputtering method or the like using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing these as a main component. It can be formed in layers or stacked.

Next, the gate insulating layer 102 is formed so as to be in contact with part of the oxide semiconductor layer 108a and cover the source electrode layer 104a and the drain electrode layer 104b (see FIG. 2D). A material similar to that of the base film 101 can be used for the gate insulating layer 102. In this embodiment, gallium zinc oxide which is the same as the base film 101 is used as the gate insulating layer 102, and the thickness thereof is 10 nm to 200 nm.

Here, second heat treatment may be performed after the gate insulating layer 102 is formed. The conditions for the second heat treatment are 200 ° C. to 400 ° C. in an inert atmosphere, an oxygen atmosphere, or a mixed atmosphere of oxygen and nitrogen. The heating time for the second heat treatment is 1 minute to 24 hours. By the second heat treatment, oxygen is supplied from the gate insulating layer 102 to the oxide semiconductor layer 108a, so that oxygen vacancies are filled. As a result, the change with time of the threshold voltage of the transistor can be reduced.

Next, a conductive film to be a gate electrode layer is formed over the gate insulating layer 102. In this embodiment, an In—Ga—Zn—O film containing nitrogen is used for one of the stacks of the conductive films. As the film formation conditions, an oxide target (made by Mitsui Metals) with In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 2: 2: 1 [molar ratio] was used, and the distance between the substrate and the target (TS) 40 mm to 300 mm, pressure 0.4 Pa to 0.6 Pa, argon gas flow rate 0 sccm to 175 sccm, nitrogen gas flow rate 25 sccm to 200 sccm, DC power 1 kW to 5 kW (cathode size 12 inches φ), The substrate temperature is 80 ° C. or higher and lower than 450 ° C.

The In—Ga—Zn—O film containing nitrogen formed under the above conditions is polycrystalline with c-axis alignment and has high crystallinity. Note that in the case where the sputtering gas is formed only with nitrogen gas (flow rate: 40 sccm), an In—Ga—Zn—O film containing nitrogen having a work function of 5.6 eV as a single film can be obtained. By using such an In—Ga—Zn—O film containing nitrogen for the gate electrode layer, the threshold voltage of the transistor can be a positive value.

Further, the heat treatment may be performed on the In—Ga—Zn—O film containing nitrogen because heat resistance is reduced. However, in the case where the gate electrode layer is formed by stacking with another metal material or the like, heat treatment is performed at a temperature at which the metal material does not change. For example, heat treatment is preferably performed at 380 ° C. or lower when aluminum is used as a material to be laminated, and 450 ° C. or lower when copper is used.

Note that another conductive film included in the stacked gate electrode layer includes a low-resistance conductive film, specifically, an aluminum film or a copper film, or titanium (Ti), tantalum (Ta), or tungsten (including these films). It is preferable to use an alloy film in which one or more elements selected from W), molybdenum (Mo), chromium (Cr), neodymium (Nd), and scandium (Sc) are combined. Note that the In—Ga—Zn—O film containing nitrogen is formed on the side in contact with the gate insulating layer.

Further, a metal nitride film functioning as a barrier layer, for example, titanium nitride, tantalum nitride, tungsten nitride, molybdenum nitride, chromium nitride, or the like is provided between the low-resistance conductive layer and the In—Ga—Zn—O film containing nitrogen. It may be provided.

Next, the gate electrode layer 112 is formed by a photolithography process and an etching process. The gate electrode layer 112 is formed so as to overlap with part of the oxide semiconductor layer 108a with the gate insulating layer 102 interposed therebetween.

Next, a protective film 110a and a protective film 110b are formed to cover the gate electrode layer 112 and the gate insulating layer 102 (see FIG. 2E).

The protective film 110a and the protective film 110b are formed using silicon oxide, silicon nitride, gallium oxide, gallium zinc oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, aluminum nitride, aluminum oxynitride, aluminum nitride oxide, hafnium oxide, or these A single layer or stacked layers can be formed using a mixed material.

In this embodiment, a 300 nm silicon oxide film obtained by a sputtering method is used as the protective film 110a, and heat treatment is performed at 250 ° C. for one hour in a nitrogen atmosphere. Thereafter, a silicon nitride film obtained by a sputtering method is formed as the protective film 110b in order to prevent moisture from entering and alkali metal from entering. Since alkali metals such as lithium (Li) and sodium (Na) are impurities, the content is preferably reduced. The oxide semiconductor layer 108a has a content of 2 × 10 ¹⁶ / cm ³ or less, preferably 1 × 10. The concentration is ¹⁵ / cm ³ or less.

Through the above process, the top-gate transistor 120 is formed. The transistor has an oxide semiconductor layer in which oxygen is excessive, and has a structure in which the oxide film semiconductor layer is sealed with a dense gallium zinc oxide capable of suppressing intrusion of impurities, and has high reliability. Has stable electrical characteristics.

Note that this embodiment can be freely combined with any of the other embodiments.

(Embodiment 2)
In this embodiment, an example of a process that is partly different from that in Embodiment 1 is described with reference to FIGS. 3, the same reference numerals are used for the same portions as in FIG. 2, and detailed description of the same reference numerals is omitted here. In addition, each component of the transistor in this embodiment is formed using the same material as each component of the transistor described in Embodiment 1.

FIG. 3D is a cross-sectional view of a top-gate transistor. The transistor 130 includes a base film 101, a source electrode layer 104a, a drain electrode layer 104b, and an oxide semiconductor layer 108a over a substrate 100 having an insulating surface. The gate insulating layer 102, the gate electrode layer 112, the protective film 110a, and the protective film 110b are included.

Hereinafter, a process for manufacturing the transistor 130 over the substrate will be described with reference to FIGS.

First, the base film 101 is formed on the substrate 100.

Next, a conductive film for forming a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over the base film 101, the conductive film is processed, and the source electrode layer 104a Then, the drain electrode layer 104b is formed (see FIG. 3A).

Next, the oxide semiconductor film 108 is formed over the source electrode layer 104a and the drain electrode layer 104b (see FIG. 3B).

Next, heat treatment is performed as necessary. The heat treatment is performed at a temperature of 200 ° C. or higher and 450 ° C. or lower in an atmosphere (a nitrogen atmosphere, an oxygen atmosphere, or a dry air atmosphere) that hardly contains hydrogen and moisture.

Next, the oxide semiconductor film 108 is processed to form an island-shaped oxide semiconductor layer 108a. Note that the oxide semiconductor film 108 may not be processed into an island shape.

Next, the gate insulating layer 102 is formed over the oxide semiconductor layer 108a (see FIG. 3C).

Next, after a conductive film is formed over the gate insulating layer 102, the gate electrode layer 112 is formed by a photolithography process and an etching process. The gate electrode layer 112 is formed so as to overlap with part of the oxide semiconductor layer 108a with the gate insulating layer 102 interposed therebetween.

Next, a protective film 110a and a protective film 110b are formed to cover the gate electrode layer 112 and the gate insulating layer 102 (see FIG. 3D).

Through the above process, the top-gate transistor 130 is formed. The transistor has an oxide semiconductor layer in which oxygen is excessive, and has a structure in which the oxide film semiconductor layer is sealed with a dense gallium zinc oxide capable of suppressing intrusion of impurities, and has high reliability. Has stable electrical characteristics.

Note that this embodiment can be freely combined with any of the other embodiments.
(Embodiment 3)
In this embodiment, an example of a process that is partly different from that in Embodiment 1 is described with reference to FIGS. 4, the same reference numerals are used for the same portions as in FIG. 1, and detailed description of the same reference numerals is omitted here. In addition, each component of the transistor in this embodiment is formed using the same material as each component of the transistor described in Embodiment 1 unless otherwise described.

FIG. 4F is a cross-sectional view of the bottom-gate transistor 140. The transistor 140 includes a base film 101, a gate electrode layer 112, a gate insulating layer 102, and a source electrode layer 104a over a substrate 100 having an insulating surface. The drain electrode layer 104b, the oxide semiconductor layer 108a, the protective film 110a, and the protective film 110b are included.

Hereinafter, a process for manufacturing the transistor 140 over a substrate will be described with reference to FIGS.

First, the base film 101 is formed on the substrate 100.

Next, after a conductive film is formed over the base film 101, the gate electrode layer 112 is formed by a photolithography process and an etching process (see FIG. 4A).

Next, the gate insulating layer 102 is formed over the gate electrode layer 112 (see FIG. 4B).

Next, a conductive film for forming a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over the gate insulating layer 102, the conductive film is processed, and the source electrode layer 104a and a drain electrode layer 104b are formed (see FIG. 4C).

Next, the oxide semiconductor film 108 is formed over the source electrode layer 104a and the drain electrode layer 104b (see FIG. 4D).

Next, heat treatment is performed as necessary. The heat treatment is performed at a temperature of 200 ° C. or higher and 450 ° C. or lower in an atmosphere (a nitrogen atmosphere, an oxygen atmosphere, or a dry air atmosphere) that hardly contains hydrogen and moisture.

Next, the oxide semiconductor film 108 is processed to form an island-shaped oxide semiconductor layer 108a (see FIG. 4E).

The oxide semiconductor film 108 can be processed by forming a mask having a desired shape over the oxide semiconductor film 108 and then etching the oxide semiconductor film 108. The above-described mask can be formed using a method such as photolithography. Alternatively, the mask may be formed using a method such as an inkjet method.

Note that the etching of the oxide semiconductor film 108 may be dry etching or wet etching. Of course, these may be used in combination.

Next, a protective film 110a and a protective film 110b are formed to cover the oxide semiconductor layer 108a, the source electrode layer 104a, and the drain electrode layer 104b (see FIG. 4F). Note that in this embodiment, gallium zinc oxide is used for the protective film 110a.

In addition, heat treatment is preferably performed after the protective film 110a is formed or after the protective film 110b is formed. By the heat treatment, oxygen is supplied from the protective film 110a to the oxide semiconductor layer 108a. The conditions for the heat treatment are 200 ° C. to 400 ° C. in an inert atmosphere, an oxygen atmosphere, and a mixed atmosphere of oxygen and nitrogen. The heating time for this heat treatment is 1 minute to 24 hours.

Through the above process, the bottom-gate transistor 140 is formed. The transistor has an oxide semiconductor layer in which oxygen is excessive, and has a structure in which the oxide film semiconductor layer is sealed with a dense gallium zinc oxide capable of suppressing intrusion of impurities, and has high reliability. Has stable electrical characteristics.

Note that this embodiment can be freely combined with any of the other embodiments.

(Embodiment 4)
In this embodiment, an example of a process that is partly different from that in Embodiment 3 will be described with reference to FIGS. 5, the same reference numerals are used for the same portions as those in FIG. 3, and detailed description of the same reference numerals is omitted here. In addition, each component of the transistor in this embodiment is formed using the same material as each component of the transistor described in Embodiment 1 unless otherwise described.

FIG. 5E is a cross-sectional view of a bottom-gate transistor 150. The transistor 150 includes a base film 101, a gate electrode layer 112, a gate insulating layer 102, and an oxide semiconductor layer over a substrate 100 having an insulating surface. 108a, the source electrode layer 104a, the drain electrode layer 104b, the protective film 110a, and the protective film 110b.

Hereinafter, a process for manufacturing the transistor 150 over a substrate will be described with reference to FIGS.

First, the base film 101 is formed on the substrate 100.

Next, after a conductive film is formed over the base film 101, the gate electrode layer 112 is formed by a photolithography process and an etching process (see FIG. 5A).

Next, the gate insulating layer 102 is formed over the gate electrode layer 112 (see FIG. 5B).

Next, the oxide semiconductor film 108 is formed over the gate insulating layer 102 (see FIG. 5C).

Next, heat treatment is performed as necessary. The heat treatment is performed at a temperature of 200 ° C. or higher and 450 ° C. or lower in an atmosphere (a nitrogen atmosphere, an oxygen atmosphere, or a dry air atmosphere) that hardly contains hydrogen and moisture.

Next, the oxide semiconductor film 108 is processed to form an island-shaped oxide semiconductor layer 108a (see FIG. 5D).

The oxide semiconductor film 108 can be processed by forming a mask having a desired shape over the oxide semiconductor film 108 and then etching the oxide semiconductor film 108. The above-described mask can be formed using a method such as photolithography. Alternatively, the mask may be formed using a method such as an inkjet method.

Note that the etching of the oxide semiconductor film 108 may be dry etching or wet etching. Of course, these may be used in combination.

Next, a conductive film for forming a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over the oxide semiconductor layer 108a, the conductive film is processed, and the source electrode A layer 104a and a drain electrode layer 104b are formed.

Note that a protective film having an insulating property may be provided over the oxide semiconductor layer 108a so as to overlap with the gate electrode layer 112 before the conductive film is formed. By providing the protective film, the oxide semiconductor layer 108a can be protected from damage during processing of the conductive film. Note that a channel etch type in which the protective film is not provided and a structure in which the protective film is provided are also referred to as a channel protective type.

Next, a protective film 110a and a protective film 110b are formed to cover the oxide semiconductor layer 108a, the source electrode layer 104a, and the drain electrode layer 104b (see FIG. 5E). Note that in this embodiment, gallium zinc oxide is used for the protective film 110a.

In addition, heat treatment is preferably performed after the protective film 110a is formed or after the protective film 110b is formed. By the heat treatment, oxygen is supplied from the protective film 110a to the oxide semiconductor layer 108a. The conditions for the heat treatment are 200 ° C. to 400 ° C. in an inert atmosphere, an oxygen atmosphere, and a mixed atmosphere of oxygen and nitrogen. The heating time for this heat treatment is 1 minute to 24 hours.

Through the above process, the bottom-gate transistor 150 is formed. The transistor has an oxide semiconductor layer in which oxygen is excessive, and has a structure in which the oxide film semiconductor layer is sealed with a dense gallium zinc oxide capable of suppressing intrusion of impurities, and has high reliability. Has stable electrical characteristics.

Note that this embodiment can be freely combined with any of the other embodiments.

(Embodiment 5)
In this embodiment, an example in which at least part of a driver circuit and a transistor placed in a pixel portion are formed over the same substrate will be described below.

The transistor provided in the pixel portion is formed according to any one of Embodiments 1 to 4. In addition, since the transistor described in any of Embodiments 1 to 4 is an n-channel transistor, part of the driver circuit that can be formed using an n-channel transistor is formed over the same substrate as the transistor in the pixel portion. To do.

An example of an active matrix display device is shown in FIG. A pixel portion 5301, a first scan line driver circuit 5302, a second scan line driver circuit 5303, and a signal line driver circuit 5304 are provided over the substrate 5300 of the display device. In the pixel portion 5301, a plurality of signal lines are extended from the signal line driver circuit 5304, and a plurality of scan lines are extended from the first scan line driver circuit 5302 and the scan line driver circuit 5303. Yes. Note that pixels each having a display element are provided in a matrix in the intersection region between the scan line and the signal line. Further, the substrate 5300 of the display device is connected to a timing control circuit (also referred to as a controller or a control IC) through a connection unit such as an FPC (Flexible Printed Circuit).

In FIG. 6A, the first scan line driver circuit 5302, the second scan line driver circuit 5303, and the signal line driver circuit 5304 are formed over the same substrate 5300 as the pixel portion 5301. For this reason, the number of components such as a drive circuit provided outside is reduced, so that cost can be reduced. Further, in the case where a drive circuit is provided outside the substrate 5300, it is necessary to extend the wiring, and the number of connections between the wirings increases. In the case where a driver circuit is provided over the same substrate 5300, the number of connections between the wirings can be reduced, so that reliability or yield can be improved.

An example of a circuit configuration of the pixel portion is shown in FIG. Here, a pixel structure of a VA liquid crystal display panel is shown.

In this pixel structure, one pixel has a plurality of pixel electrode layers, and a transistor is connected to each pixel electrode layer. Each transistor is configured to be driven with a different gate signal. In other words, a multi-domain designed pixel has a configuration in which a signal applied to each pixel electrode layer is controlled independently.

The gate wiring 602 of the transistor 628 and the gate wiring 603 of the transistor 629 are separated so that different gate signals can be given. On the other hand, the source or drain electrode layer 616 functioning as a data line is used in common for the transistor 628 and the transistor 629. As the transistor 628 and the transistor 629, any one of the transistors in Embodiments 1 to 5 can be used as appropriate.

The first pixel electrode layer and the second pixel electrode layer which are electrically connected to the transistor 628 or the transistor 629 have different shapes and are separated by a slit. A second pixel electrode layer is formed so as to surround the outside of the first pixel electrode layer extending in a V shape. The timing of the voltage applied to the first pixel electrode layer and the second pixel electrode layer is made different between the transistor 628 and the transistor 629, whereby the alignment of the liquid crystal is controlled. The transistor 628 is connected to the gate wiring 602, and the transistor 629 is connected to the gate wiring 603. By supplying different gate signals to the gate wiring 602 and the gate wiring 603, the operation timings of the transistor 628 and the transistor 629 can be different.

In addition, a storage capacitor is formed by the capacitor wiring 690, the gate insulating layer functioning as a dielectric, and the capacitor electrode electrically connected to the first pixel electrode layer or the second pixel electrode layer.

A first liquid crystal element 651 is formed by overlapping the first pixel electrode layer, the liquid crystal layer, and the counter electrode layer. In addition, the second pixel electrode layer, the liquid crystal layer, and the counter electrode layer overlap with each other, so that a second liquid crystal element 652 is formed. In addition, the multi-domain structure in which the first liquid crystal element 651 and the second liquid crystal element 652 are provided in one pixel.

Note that the pixel structure illustrated in FIG. 6B is not limited thereto. For example, a switch, a resistor, a capacitor, a transistor, a sensor, a logic circuit, or the like may be newly added to the pixel illustrated in FIG.

Another example of the circuit configuration of the pixel portion is shown in FIG. Here, a pixel structure of a display panel using an organic EL element is shown.

In the organic EL element, by applying a voltage to the light emitting element, electrons and holes are respectively injected from the pair of electrodes into the layer containing the light emitting organic compound, and a current flows. Then, these carriers (electrons and holes) recombine, whereby the light-emitting organic compound forms an excited state, and emits light when the excited state returns to the ground state. Due to such a mechanism, such a light-emitting element is referred to as a current-excitation light-emitting element.

FIG. 6C illustrates an example of a pixel structure to which digital time grayscale driving can be applied as an example of a semiconductor device.

A structure and operation of a pixel to which digital time gray scale driving can be applied will be described. Here, an example is shown in which two n-channel transistors each using an oxide semiconductor layer for a channel formation region are used for one pixel.

The pixel 6400 includes a switching transistor 6401, a driving transistor 6402, a light-emitting element 6404, and a capacitor 6403. The switching transistor 6401 has a gate electrode layer connected to the scan line 6406, a first electrode (one of the source electrode layer and the drain electrode layer) connected to the signal line 6405, and a second electrode (the source electrode layer and the drain electrode layer). Is connected to the gate electrode layer of the driving transistor 6402. In the driving transistor 6402, the gate electrode layer is connected to the power supply line 6407 through the capacitor 6403, the first electrode is connected to the power supply line 6407, and the second electrode is connected to the first electrode (pixel electrode) of the light emitting element 6404. It is connected. The second electrode of the light emitting element 6404 corresponds to the common electrode 6408. The common electrode 6408 is electrically connected to a common potential line formed over the same substrate.

Note that a low power supply potential is set for the second electrode (the common electrode 6408) of the light-emitting element 6404. Note that the low power supply potential is a potential that satisfies the low power supply potential <the high power supply potential with reference to the high power supply potential set in the power supply line 6407. For example, GND, 0V, or the like is set as the low power supply potential. Also good. The potential difference between the high power supply potential and the low power supply potential is applied to the light emitting element 6404 and a current is caused to flow through the light emitting element 6404 so that the light emitting element 6404 emits light. Each potential is set to be equal to or higher than the forward threshold voltage.

Note that the capacitor 6403 can be omitted by using the gate capacitance of the driving transistor 6402 instead. As for the gate capacitance of the driving transistor 6402, a capacitance may be formed between the channel formation region and the gate electrode layer.

Here, in the case of the voltage input voltage driving method, a video signal is input to the gate electrode layer of the driving transistor 6402 so that the driving transistor 6402 is sufficiently turned on or off. To do. That is, the driving transistor 6402 is operated in a linear region. In order to operate the driving transistor 6402 in a linear region, a voltage higher than the voltage of the power supply line 6407 is applied to the gate electrode layer of the driving transistor 6402. Note that a voltage equal to or higher than (power supply line voltage + threshold voltage of the driving transistor 6402) is applied to the signal line 6405.

Further, in the case of performing analog grayscale driving instead of digital time grayscale driving, the same pixel structure as that in FIG. 6C can be used by changing signal input.

When analog gradation driving is performed, a voltage equal to or higher than the forward voltage of the light-emitting element 6404 + the threshold voltage of the driving transistor 6402 is applied to the gate electrode layer of the driving transistor 6402. The forward voltage of the light-emitting element 6404 refers to a voltage for obtaining desired luminance, and includes at least a forward threshold voltage. Note that when a video signal that causes the driving transistor 6402 to operate in a saturation region is input, a current can flow through the light-emitting element 6404. In order to operate the driving transistor 6402 in the saturation region, the potential of the power supply line 6407 is set higher than the gate potential of the driving transistor 6402. By making the video signal analog, current corresponding to the video signal can be supplied to the light-emitting element 6404 to perform analog gradation driving.

Note that the pixel structure illustrated in FIG. 6C is not limited thereto. For example, a switch, a resistor, a capacitor, a sensor, a transistor, a logic circuit, or the like may be newly added to the pixel illustrated in FIG.

Note that this embodiment can be freely combined with any of the other embodiments.

(Embodiment 6)
The semiconductor device disclosed in this specification can be applied to a variety of electronic devices (including game machines). Examples of the electronic device include a television device (also referred to as a television or a television receiver), a monitor for a computer, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone (a mobile phone or a mobile phone). Large-sized game machines such as portable game machines, portable information terminals, sound reproduction apparatuses, and pachinko machines. Examples of electronic devices each including the display device described in the above embodiment will be described.

FIG. 7A illustrates a portable information terminal including a main body 3001, a housing 3002, display portions 3003a and 3003b, and the like. The display portion 3003b is a touch panel, and screen operation and character input can be performed by touching a keyboard button 3004 displayed on the display portion 3003b. Needless to say, the display portion 3003a may be configured as a touch panel. By manufacturing a liquid crystal panel or an organic light-emitting panel using the transistor described in Embodiment 1 as a switching element and applying it to the display portions 3003a and 3003b, a highly reliable portable information terminal can be provided.

FIG. 10A illustrates a function for displaying various information (still images, moving images, text images, etc.), a function for displaying a calendar, date, time, or the like on the display unit, and operating or editing information displayed on the display unit A function, a function of controlling processing by various software (programs), and the like can be provided. In addition, an external connection terminal (such as an earphone terminal or a USB terminal), a recording medium insertion portion, or the like may be provided on the rear surface or side surface of the housing.

The portable information terminal illustrated in FIG. 7A may be configured to transmit and receive information wirelessly. It is also possible to adopt a configuration in which desired book data or the like is purchased and downloaded from an electronic book server wirelessly.

FIG. 7B illustrates a portable music player. A main body 3021 is provided with a display portion 3023, a fixing portion 3022 to be attached to the ear, a speaker, operation buttons 3024, an external memory slot 3025, and the like. By manufacturing a liquid crystal panel or an organic light-emitting panel using the transistor described in any of Embodiments 1 to 4 as a switching element and applying it to the display portion 3023, a highly reliable portable music player can be provided.

Furthermore, if the portable music player shown in FIG. 7B is provided with an antenna, a microphone function, and a wireless function and is linked to a mobile phone, a wireless hands-free conversation is possible while driving a passenger car or the like.

FIG. 7C illustrates a mobile phone, which includes two housings, a housing 2800 and a housing 2801. A housing 2801 is provided with a display panel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, a camera 2807, an external connection terminal 2808, and the like. The housing 2800 is provided with a solar battery 2810 for charging the mobile phone, an external memory slot 2811, and the like. An antenna is incorporated in the housing 2801. By applying the transistor described in any of Embodiments 1 to 4 to the display panel 2802, a highly reliable mobile phone can be obtained.

Further, the display panel 2802 is provided with a touch panel. A plurality of operation keys 2805 which are displayed as images is illustrated by dashed lines in FIG. Note that a booster circuit for boosting the voltage output from the solar battery 2810 to a voltage necessary for each circuit is also mounted.

For example, a power transistor used for a power supply circuit such as a booster circuit can be formed by setting the thickness of the oxide semiconductor layer 108a of the transistor described in any of Embodiments 1 to 4 to 2 μm to 50 μm.

In the display panel 2802, the display direction can be appropriately changed depending on a usage pattern. In addition, since the camera 2807 is provided on the same surface as the display panel 2802, a videophone can be used. The speaker 2803 and the microphone 2804 can be used for videophone calls, recording and playing sound, and the like as well as voice calls. Further, the housing 2800 and the housing 2801 can be slid to be in an overlapped state from the developed state as illustrated in FIG. 7C, so that the size of the mobile phone can be reduced.

The external connection terminal 2808 can be connected to various types of cables such as a charging cable or a USB cable, and charging and data communication with a personal computer or the like are possible. Further, a recording medium can be inserted into the external memory slot 2811 so that a larger amount of data can be stored and moved.

In addition to the above functions, an infrared communication function, a television reception function, or the like may be provided.

FIG. 7D illustrates an example of a television set. In the television device 9600, a display portion 9603 is incorporated in a housing 9601. Images can be displayed on the display portion 9603. Here, a structure in which the housing 9601 is supported by a stand 9605 with a built-in CPU is shown. By applying the transistor described in any of Embodiments 1 to 4 to the display portion 9603, the television set 9600 can have high reliability.

The television device 9600 can be operated with an operation switch provided in the housing 9601 or a separate remote controller. Further, the remote controller may be provided with a display unit that displays information output from the remote controller.

Note that the television set 9600 is provided with a receiver, a modem, and the like. General TV broadcasts can be received by a receiver, and connected to a wired or wireless communication network via a modem, so that it can be unidirectional (sender to receiver) or bidirectional (sender and receiver). It is also possible to perform information communication between each other or between recipients).

In addition, the television device 9600 includes an external connection terminal 9604, a storage medium playback / recording unit 9602, and an external memory slot. The external connection terminal 9604 can be connected to various types of cables such as a USB cable, and data communication with a personal computer or the like is possible. The storage medium playback / recording unit 9602 can insert a disk-shaped recording medium, read data stored in the recording medium, and write data to the recording medium. In addition, an image, a video, or the like stored in the external memory 9606 inserted into the external memory slot can be displayed on the display portion 9603.

Note that this embodiment can be freely combined with any of the other embodiments.

100 Substrate 101 Base film 102 Gate insulating layer 104a Source electrode layer 104b Drain electrode layer 108 Oxide semiconductor film 108a Oxide semiconductor layer 110a Protective film 110b Protective film 112 Gate electrode layer 120 Transistor 130 Transistor 140 Transistor 150 Transistor 602 Gate wiring 603 Gate Wiring 616 Drain electrode layer 628 Transistor 629 Transistor 651 Liquid crystal element 652 Liquid crystal element 690 Capacitance wiring 2800 Case 2801 Case 2802 Display panel 2803 Speaker 2804 Microphone 2805 Operation key 2806 Pointing device 2807 Camera 2808 External connection terminal 2810 Solar cell 2811 External memory slot 3001 Main body 3002 Housing 3003a Display unit 3003b Display unit 3004 -Board button 3021 Main body 3022 Fixed portion 3023 Display portion 3024 Operation button 3025 External memory slot 5300 Substrate 5301 Pixel portion 5302 Scan line driver circuit 5303 Scan line driver circuit 5304 Signal line driver circuit 6400 Pixel 6401 Switching transistor 6402 Driver transistor 6403 Capacitor element 6404 Light emitting element 6405 Signal line 6406 Scanning line 6407 Power supply line 6408 Common electrode 9600 Television apparatus 9601 Housing 9602 Storage medium reproduction recording unit 9603 Display unit 9604 External connection terminal 9605 Stand 9606 External memory

Claims (7)

Form a base film on the insulating surface,
Forming an oxide semiconductor layer on the base film;
Forming a source electrode layer and a drain electrode layer in contact with part of the oxide semiconductor layer;
Forming a gate insulating layer over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer;
In the step of forming a gate electrode layer overlying a part of the oxide semiconductor layer on the gate insulating layer,
The oxide semiconductor layer is formed by sputtering a metal oxide containing indium, gallium, and zinc with a ratio of an oxygen flow rate to a total flow rate of a sputtering gas of 90% to 100%. Device fabrication method. Form a base film on the insulating surface,
Forming a gate electrode layer on the base film;
Forming a gate insulating layer on the gate electrode layer;
Forming an oxide semiconductor layer on the gate insulating layer;
Forming a source electrode layer and a drain electrode layer in contact with part of the oxide semiconductor layer;
In the step of forming a protective film on the oxide semiconductor layer, the source electrode layer, and the drain electrode layer,
The oxide semiconductor layer is formed by sputtering a metal oxide containing indium, gallium, and zinc with a ratio of an oxygen flow rate to a total flow rate of a sputtering gas of 90% to 100%. Device fabrication method. 3. The method for manufacturing a semiconductor device according to claim 2, wherein the protective film is formed by sputtering of a metal oxide containing gallium and zinc. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the base film and the gate insulating film are formed by sputtering a metal oxide containing gallium and zinc. 5. The metal oxide layer according to claim 1, wherein the gate electrode layer is a stacked layer, and at least a layer in contact with the gate insulating layer is oxidized with a sputtering gas containing nitrogen using indium, gallium, and zinc. A method for manufacturing a semiconductor device, comprising forming an object by sputtering. 6. The method for manufacturing a semiconductor device according to claim 1, wherein the oxide semiconductor layer is formed at a substrate temperature of 200 ° C. to 450 ° C. 6. An oxide semiconductor layer containing indium, gallium, and zinc;
A gate insulating layer containing gallium and zinc and in contact with one surface of the oxide semiconductor layer;
A gate electrode layer containing indium, gallium, zinc, and nitrogen and overlapping the oxide semiconductor layer with the gate insulating layer interposed therebetween;
Have
The semiconductor device is characterized in that the other surface of the oxide semiconductor layer is in contact with a metal oxide containing gallium and zinc.