JP5367660B2 - Oxide sintered body and oxide semiconductor thin film - Google Patents

Description

  The present invention relates to an oxide sintered body and an oxide semiconductor thin film that are useful for manufacturing a thin film transistor in a display device.

  An oxide semiconductor is used as an active layer of a thin film transistor in a display device such as a liquid crystal display device, a plasma display device, and an organic EL display device, as well as an electrode of a solar cell or a touch panel. Conventionally, a transparent In—Ga—Zn—O-based (hereinafter referred to as “IGZO-based”) is known as an oxide semiconductor (see Non-Patent Document 1), and tin ( There is also a report on a system to which Sn) is added (see Patent Documents 1 and 2). However, gallium (Ga), which is an essential component of these systems, is a rare element and has a large limitation in terms of industrial use because of its high price.

  As a transparent oxide semiconductor not using Ga, an In—Zn—O system (see Patent Document 3), an In—Zn—Sn—O system (see Patent Document 4), and a Zn—Sn—O system (Patent Document 5). Report).

JP 2008-280216 A JP 2010-118407 A JP 2007-142195 A Japanese Patent Application Laid-Open No. 2008-243928 JP 2007-142196 A

Nature 432, p488-492, October 2004

  The oxide semiconductors described in Patent Documents 3 to 5 do not use Ga, which is an essential component of the IGZO system, and are advantageous in terms of manufacturing cost. The problem is still inferior. In addition, zinc (Zn), which is another essential constituent element of the IGZO system, is an element that easily volatilizes, and the density of the sintered body decreases due to volatilization during the production of the sintered body, and the target composition due to volatilization during sputter deposition This is an impediment to the stability of the film, such as deviation of the film and changes in resistivity of the film over time.

  Therefore, the present invention is a rare resource, expensive gallium (Ga), and oxide sinter for producing an oxide semiconductor film that does not contain zinc (Zn), which easily volatilizes and has a problem in film stability. The challenge is to provide a body. Another object of the present invention is to provide an oxide semiconductor thin film having the same composition as the oxide sintered body.

  As a result of diligent investigations to solve the above problems, the present inventor has used oxide-stable magnesium (Mg) as an alternative to zinc (Zn), which is volatile, and is a rare and expensive element of gallium (Ga). Alternatively, aluminum (Al) and iron (Fe), which are the same trivalent metal elements as gallium, and tin (Sn) and titanium (Ti), which are the tetravalent metal elements, are used. It has been found that an oxide sintered body and an oxide semiconductor thin film for producing an oxide semiconductor film that do not contain gallium (Ga) and zinc (Zn) can be obtained by adjusting the manufacturing conditions of the aggregate and the film. .

The present invention completed on the basis of the above knowledge, in one aspect, indium (In), magnesium (Mg), and metal element X (where X is one or more selected from Al, Fe, Sn, Ti) Element) and oxygen (O), and the atomic ratio of indium (In), magnesium (Mg), and metal element X is 0.2 ≦ [In] / [In + Mg + X] ≦ 0. 8,0.1 ≦ [Mg] / [in + Mg + X] ≦ 0.5, and, 0.1 ≦ [X] / meets [in + Mg + X] ≦ 0.5, the oxide sintered relative density of 98% or more It is a ligation.

  In yet another embodiment, the oxide sintered body according to the present invention has a bulk resistance of 3 mΩ or less.

In another aspect of the present invention, indium (In), magnesium (Mg), a metal element X (where X represents one or more elements selected from Al, Fe, Sn, Ti), The atomic ratio of indium (In), magnesium (Mg), and metal element X is 0.2 ≦ [In] / [In + Mg + X] ≦ 0.8, 0.1 ≦ [Mg]. /[In+Mg+X]≦0.5, 0.1 ≦ [X] / [In + Mg + X] ≦ 0.5 , and an oxide semiconductor thin film having a carrier concentration of 10 ¹⁶ to 10 ¹⁸ cm ⁻³ .

  In another embodiment, the oxide semiconductor thin film according to the present invention is amorphous.

In still another embodiment, the oxide semiconductor thin film according to the present invention has a mobility of 1 cm ² / Vs or more.

  In yet another aspect, the present invention is a thin film transistor including the oxide semiconductor thin film as an active layer.

  In still another aspect, the present invention provides an active matrix drive display panel including the thin film transistor.

  According to the present invention, oxide sinter for manufacturing an oxide semiconductor film that does not contain rare gallium (Ga) and zinc (Zn) that is easily evaporated and has a problem in film stability. The body can be provided. Moreover, according to this invention, the oxide semiconductor thin film which has the same composition as the said oxide sinter can be provided.

(Composition of oxide sinter)
The oxide sintered body according to the present invention includes indium (In), magnesium (Mg), and a metal element X (where X represents one or more elements selected from Al, Fe, Sn, and Ti). And oxygen (O) as a constituent element. However, elements that are inevitably included in the purification process of raw materials that are usually available, and impurity elements that are inevitably mixed in the oxide sintered body manufacturing process, are inevitably contained at a concentration, for example, each element. What contains about 10 ppm is included in the sintered compact which concerns on this invention.

  The ratio [In] / [In + Mg + X] of the number of atoms of indium to the total number of atoms of indium, magnesium and metal element X is 0.2 to 0.8. If [In] / [In + Mg + X] is less than 0.2, the relative density at the time of target production becomes small, the bulk resistance becomes high, and abnormal discharge at the time of sputtering tends to occur. If [In] / [In + Mg + X] exceeds 0.8, the carrier concentration of the film obtained by sputtering the target of the composition becomes too high, and the on / off ratio of the channel layer of the transistor becomes small. [In] / [In + Mg + X] is more preferably in the range of 0.25 to 0.6, and still more preferably in the range of 0.3 to 0.5. Here, [In] represents the number of atoms of indium, [Mg] represents the number of atoms of magnesium, and [X] represents the number of atoms of the metal element X.

  The ratio [Mg] / ([In] + [Mg] + [X]) of the number of magnesium atoms to the total number of atoms of indium, magnesium and metal element X is 0.1 to 0.5. When [Mg] / ([In] + [Mg] + [X]) is less than 0.1, the carrier concentration of the film becomes too high, and abnormal discharge during sputtering is likely to occur. When [Mg] / ([In] + [Mg] + [X]) exceeds 0.5, the relative density at the time of target fabrication becomes small. [Mg] / ([In] + [Mg] + [X]) is more preferably in the range of 0.15 to 0.4, and still more preferably in the range of 0.2 to 0.35.

  The ratio [X] / ([In] + [Mg] + [X]) of the total number of atoms of the metal element X to the total number of atoms of indium, magnesium and the metal element X is 0.1 to 0.5. When [X] / ([In] + [Mg] + [X]) is less than 0.1, the carrier concentration of the film obtained by sputtering the target having the composition becomes too high, and the channel of the transistor As a layer, the on / off ratio becomes small. Conversely, if [X] / ([In] + [Mg] + [X]) exceeds 0.5, the relative density during target fabrication decreases, the bulk resistance increases, and abnormal discharge during sputtering occurs. Is likely to occur. [X] / ([In] + [Mg] + [X]) is more preferably in the range of 0.15 to 0.4, and still more preferably in the range of 0.2 to 0.35.

(Relative density of sintered oxide)
The relative density of the oxide sintered body has a correlation with the generation of joules on the surface during sputtering. When the oxide sintered body has a low density, when the oxide sintered body is processed into a target and formed into a sputter film, a projection that is a lower oxide of indium on the surface in accordance with the progress of the sputter film formation. A high resistance portion called a nodule is generated, and tends to be the starting point of abnormal discharge during subsequent sputtering. In the present invention, the relative density of the oxide sintered body can be set to 98% or more by optimizing the appropriate range of the composition and the manufacturing conditions. If this density is high, there is almost no adverse effect due to nodules during sputtering. Absent. The relative density is preferably 99% or more, more preferably 99.5% or more.
The relative density of the oxide sintered body is obtained by dividing the density calculated from the weight and outer dimensions after processing the oxide sintered body into a predetermined shape by the theoretical density of the oxide sintered body. Can be sought.

(Bulk resistance of sintered oxide)
The bulk resistance of the oxide sintered body has a correlation with the ease of occurrence of abnormal discharge during sputtering, and when the bulk resistance is high, abnormal discharge is likely to occur during sputtering. In the present invention, the bulk resistance can be reduced to 3 mΩcm or less by optimizing the appropriate range of composition and manufacturing conditions. With such a low bulk resistance, there is almost no adverse effect on the occurrence of abnormal discharge during sputtering. The bulk resistance is preferably 2.7 mΩcm or less, more preferably 2.5 mΩcm or less.
Bulk resistance can be measured using a resistivity meter by the four-probe method.

(Method for manufacturing oxide sintered body)
The oxide sintered body having various compositions according to the present invention includes, for example, the mixing ratio of raw material powders such as indium oxide and magnesium oxide as raw materials, the particle size of the raw material powder, the pulverization time, the sintering temperature, and the sintering. It can be obtained by adjusting conditions such as time and kind of sintering atmosphere gas.

  The raw material powder preferably has an average particle size of 1 to 2 μm. When the average particle diameter exceeds 2 μm, the density of the sintered body is difficult to improve. Therefore, wet pulverization or the like is performed as the raw material powder alone or as a mixed powder, and the average particle diameter is preferably reduced to about 1 μm. For the purpose of improving the sinterability before wet mixing and pulverization, it is also effective to perform calcination. On the other hand, raw materials having a size of less than 1 μm are difficult to obtain, and if it is too small, aggregation between particles tends to occur and it becomes difficult to handle. Here, the average particle diameter of the raw material powder indicates a value measured by a laser diffraction measurement method. It is preferable to mold the pulverized raw material mixed powder after granulating it with a spray dryer or the like to improve fluidity and moldability. For molding, a method such as normal pressure molding or cold isostatic pressing can be employed.

  Thereafter, the molded product is sintered to obtain a sintered body. Sintering is preferably performed at 1400 to 1600 ° C. for 2 to 20 hours. Thereby, a relative density can be 98% or more. If the sintering temperature is less than 1400 ° C., the density is difficult to improve. If the sintering temperature exceeds 1600 ° C., the composition of the sintered body changes due to volatilization of constituent elements, or the density decreases due to void generation due to volatilization. It may cause. Air can be used as the atmosphere gas during sintering, and a high-density sintered body can be obtained due to the effect of suppressing volatilization from the sintered body. However, depending on the composition of the sintered body, a sufficiently high density sintered body can be obtained even if the atmospheric gas is oxygen.

(Sputter deposition)
The oxide sintered body obtained as described above can be used as a sputtering target by performing processing such as grinding and polishing, and by using this film, the same composition as that of the target can be obtained. It is possible to form an oxide film having At the time of processing, it is desirable that the surface roughness (Ra) be 5 μm or less by grinding the surface by a method such as surface grinding. By reducing the surface roughness, the starting point of nodule generation that causes abnormal discharge can be reduced.

  The sputtering target is affixed to a backing plate made of copper or the like, placed in a sputtering apparatus, and sputtered under appropriate conditions such as an appropriate degree of vacuum, atmospheric gas, and sputtering power, so that the film has almost the same composition as the target. Can be obtained.

In the case of sputtering, it is desirable that the degree of vacuum reached in the chamber before film formation is 2 × 10 ⁻⁴ Pa or less. If the pressure is too high, the mobility of the obtained film may decrease due to the influence of impurities in the residual atmospheric gas.

  As the sputtering gas, a mixed gas of argon and oxygen can be used. As a method for adjusting the oxygen concentration in the mixed gas, for example, a gas cylinder with 100% argon and a gas cylinder with 2% oxygen in argon are used, and the supply flow rate from each gas cylinder to the chamber is appropriately set by mass flow. Can be done. Here, the oxygen concentration in the mixed gas means oxygen partial pressure / (oxygen partial pressure + argon partial pressure), and is equal to the oxygen flow rate divided by the sum of oxygen and argon flow rates. The oxygen concentration may be appropriately changed according to the desired carrier concentration, but can typically be 1 to 3%, more typically 1 to 2%.

  The total pressure of the sputtering gas is about 0.3 to 0.8 Pa. If the total pressure is lower than this, the plasma discharge is difficult to stand up, and even if it stands, the plasma becomes unstable. On the other hand, if the total pressure is higher than this, the film formation rate becomes slow, which causes inconveniences such as adversely affecting productivity.

The sputtering power is about 200 to 1200 W when the target size is 6 inches. If the sputtering power is too low, the film forming speed is low and the productivity is poor. Conversely, if the sputtering power is too high, problems such as cracking of the target occur. 200 to 1200 W is 1.1 W / cm ^{2 to} 6.6 W / cm ² in terms of sputtering power density, and is desirably 3.2 to 4.5 W / cm ² . Here, the sputtering power density is a value obtained by dividing the sputtering power by the area of the sputtering target, and even with the same sputtering power, the power actually received by the sputtering target varies depending on the sputtering target size, and the film formation speed differs. It is an index for uniformly expressing the power applied to the sputtering target.

  As a method for obtaining a film from an oxide sintered body, a vacuum deposition method, an ion plating method, a PLD (pulse laser deposition) method, or the like can be used. This is a DC magnetron sputtering method that satisfies requirements such as film formation and discharge stability.

  There is no need to heat the substrate during sputter deposition. This is because a relatively high mobility can be obtained without heating the substrate, and it is not necessary to spend time and energy for raising the temperature. When sputter deposition is performed without heating the substrate, the resulting film becomes amorphous. However, since the same effect as annealing after film formation at room temperature can be expected by heating the substrate, the film may be formed by heating the substrate.

(Carrier concentration of oxide film)
The carrier concentration of the oxide film correlates with various characteristics of the transistor when the film is used for the channel layer of the transistor. If the carrier concentration is too high, a minute leakage current is generated even when the transistor is turned off, and the on / off ratio is lowered. On the other hand, if the carrier concentration is too low, the current flowing through the transistor becomes small. In the present invention, the carrier concentration of the oxide film can be set to 10 ¹⁶ to 10 ¹⁸ cm ⁻³ depending on an appropriate range of the composition and the like, and a transistor with favorable characteristics can be manufactured within this range.

(Mobility of oxide film)
The mobility is one of the most important characteristics of the transistor, and the oxide semiconductor has a mobility of 1 cm ² / Vs or more which is the mobility of amorphous silicon which is a competitive material used as a channel layer of the transistor. Is desirable. Basically, the higher the mobility, the better. The oxide film according to the present invention can have a mobility of 1 cm ² / Vs or more, preferably a mobility of 3 cm ² / Vs or more, more preferably 5 cm ² depending on an appropriate range of the composition. It can have a mobility of / Vs or higher. Thereby, it becomes a characteristic superior to amorphous silicon, and industrial applicability is further increased.

  The oxide semiconductor thin film according to the present invention can be used, for example, as an active layer of a thin film transistor. In addition, the thin film transistor obtained by using the above manufacturing method can be used as an active element and used for an active matrix drive display panel.

  Examples of the present invention will be described below together with comparative examples, but these examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention. Accordingly, the present invention encompasses all aspects or modifications other than the examples within the scope of the technical idea of the present invention.

In the following Examples and Comparative Examples, the physical properties of the sintered bodies and films were measured by the following methods.
(A) Composition of sintered body and film It was determined by an ICP (high frequency inductively coupled plasma) analysis method using a model SPS3000 manufactured by SII Nanotechnology.
(A) Relative density of sintered body The relative density was determined from the measurement results of weight and outer dimensions and the theoretical density from the constituent elements.
(C) Bulk resistance of sintered body The bulk resistance was determined by a four-point probe method (JIS K7194) using a model Σ-5 + apparatus manufactured by NPS.
(D) Film thickness It was determined using a step meter (Veeco, Model Dektak8 STYLUS PROFILER).
(E) Carrier concentration and mobility of film The formed glass substrate was cut into about 10 mm square, indium electrodes were attached to the four corners, and the measurement was carried out by setting in a Hall measuring device (manufactured by Toyo Technica, Model Reset 8200).
(F) Crystal or amorphous structure of film Crystallinity was determined using a RINT-1100 X-ray diffractometer manufactured by Rigaku Corporation. By this X-ray diffraction, a significant peak above the background level was not recognized, and it was judged to be amorphous.
(G) Average particle diameter of powder The average particle diameter of the powder was measured by SALD-3100 manufactured by Shimadzu Corporation.

<Example 1>
Indium oxide powder (average particle size: 1.0 μm), magnesium oxide powder (average particle size: 1.0 μm), and aluminum oxide powder (average particle size: 1.0 μm) are mixed with an atomic ratio of metal elements (In: Mg: Sn). ) Was 0.4: 0.3: 0.3, and wet mixed and pulverized. The average particle size of the mixed powder after pulverization was 0.8 μm. This mixed powder was granulated with a spray dryer, filled in a mold, press-molded, and sintered in an air atmosphere at a high temperature of 1450 ° C. for 10 hours. The obtained sintered body was processed into a disk shape having a diameter of 6 inches and a thickness of 6 mm to obtain a sputtering target. With respect to the target, the relative density was calculated from the measurement results of the weight and the external dimensions and the theoretical density, and found to be 99.8%. Moreover, the bulk resistance of the sintered compact measured by the four probe method was 2.1 mΩcm.

The sputtering target produced above was affixed to a copper backing plate using indium as a brazing material, and installed in a DC magnetron sputtering apparatus (AELVA SPL-500 sputtering apparatus). The glass substrate uses Corning 1737, and the sputtering conditions are as follows: substrate temperature: 25 ° C., ultimate pressure: 1.2 × 10 ⁻⁴ Pa, atmospheric gas: Ar 99%, oxygen 1%, sputtering pressure (total pressure): 0. A thin film having a thickness of about 100 nm was prepared at 5 Pa and input power of 500 W. No abnormal discharge was observed during the formation of the oxide semiconductor thin film.

  The hole of the obtained film was measured to determine the carrier concentration and mobility. As a result of measurement by X-ray diffraction, the film was amorphous.

<Example 2 to Example 15>
An oxide sintered body and an oxide semiconductor thin film were obtained in the same manner as in Example 1 except that the composition ratio of the raw material powder was set to the respective values shown in Table 1. The relative density, bulk resistance, carrier concentration, and mobility of each were as shown in Table 1. The composition of the sintered body and the film was the same as the composition ratio of the raw material powder. No abnormal discharge was observed during the formation of the oxide semiconductor thin film.

<Comparative Examples 1 to 12>
An oxide sintered body and an oxide semiconductor thin film were obtained in the same manner as in Example 1 except that the composition ratio of the raw material powder was set to the respective values shown in Table 1. The relative density, bulk resistance, carrier concentration, and mobility of each were as shown in Table 1. The composition of the sintered body and the film was the same as the composition ratio of the raw material powder.

In Examples 1 to 15, the carrier concentration was in the range of 10 ¹⁶ to 10 ¹⁸ cm ⁻³ , and the mobility was 1 cm ² / Vs or higher.
On the other hand, in Comparative Examples 1, 4, 6, 8, 10, and 12, the carrier concentration was less than 10 ¹⁶ cm ⁻³ and the mobility was less than 1 cm ² / Vs.
In Comparative Examples 2, 3, 5, 7, 9, and 11, the carrier concentration was more than 10 ¹⁸ cm ⁻³ .

Claims (7)

Indium (In), magnesium (Mg), metal element X (where X represents one or more elements selected from Al, Fe, Sn, Ti) and oxygen (O),
The atomic ratios of indium (In), magnesium (Mg), and metal element X are 0.2 ≦ [In] / [In + Mg + X] ≦ 0.8 and 0.1 ≦ [Mg] / [In + Mg + X] ≦, respectively. 0.5, and, 0.1 ≦ [X] / [ in + Mg + X] ≦ 0.5 meets, oxide sintered body relative density of 98% or more. The oxide sintered body according to claim 1 , wherein the bulk resistance is 3 mΩ or less. Indium (In), magnesium (Mg), metal element X (where X represents one or more elements selected from Al, Fe, Sn, Ti) and oxygen (O),
The atomic ratio of indium (In), magnesium (Mg), and metal element X is 0.2 ≦ [In] / [In + Mg + X] ≦ 0.8, 0.1 ≦ [Mg] / [In + Mg + X] ≦ 0.5 , 0.1 ≦ [X] / [ in + Mg + X] ≦ 0.5 meets, oxide semiconductor thin film carrier concentration is 10 ¹⁶ ~10 ¹⁸ cm ^-3. The oxide semiconductor thin film according to claim 3 which is amorphous. The oxide semiconductor thin film according to claim 3 or 4 , wherein the mobility is 1 cm ² / Vs or more. A thin film transistor comprising the oxide semiconductor thin film according to claim 3 as an active layer. An active matrix drive display panel comprising the thin film transistor according to claim 6 .