JP5884001B1 - Oxide sintered body and sputtering target comprising the oxide sintered body - Google Patents

Abstract

An oxide sintered body composed of indium (In), gallium (Ga), zinc (Zn), oxygen (O), and inevitable impurities, wherein In: Ga: Zn = 1 at an atomic ratio of In, Ga, and Zn IGZO (111) phase composed of 1: 1, and an IGZO phase containing more Zn than the IGZO (111) phase, and the IGZO phase containing more Zn than the IGZO (111) phase has an area ratio of 1 to 10 The oxide is characterized in that the atomic ratio of In, Ga, and Zn in the oxide sintered body is In: Ga: Zn = 1: 1: (1.02-1.10). Sintered body. It is an object of the present invention to provide an IGZO oxide sintered body capable of reducing the oxygen concentration during sputtering necessary for obtaining a film having a desired carrier concentration. [Selection] Figure 1

Description

  The present invention is generally referred to as oxide ("IGZO") consisting of indium (In), gallium (Ga), zinc (Zn), oxygen (O), and inevitable impurities. In particular, the present invention relates to an IGZO sintered body and a sputtering target made of the oxide sintered body.

  Conventionally, in an FPD (flat panel display), α-Si (amorphous silicon) has been used for a TFT (thin film transistor) of the backplane. However, sufficient electron mobility cannot be obtained with α-Si, and in recent years, research and development of TFTs using In—Ga—Zn—O-based oxides (IGZO), which have higher electron mobility than α-Si, have been conducted. Has been done. A part of next-generation high-functional flat panel displays using IGZO-TFTs has been put into practical use and attracting attention.

  The IGZO film is mainly formed by sputtering a target made from an IGZO sintered body. As an IGZO sputtering target, for example, Patent Document 1 includes In, Ga, and Zn, and by generating a structure having a higher In content than the surroundings, a specific resistance can be obtained without performing a reduction treatment at a high temperature. It is disclosed that a low target can be produced. Patent Document 2 discloses that when two or more kinds of homologous crystals coexist in a predetermined ratio of In, Ga, and Zn, sputtering is stabilized and generation of particles can be reduced. .

  Incidentally, when such an IGZO film is used as an active layer of a TFT, one of the factors affecting the electrical characteristics of the film is the amount of oxygen defects in the film. In order to control the amount of oxygen defects, oxygen gas is generally introduced in addition to an inert gas such as argon during sputtering film formation. The sputtering efficiency of oxygen is lower than that of argon. When oxygen gas is introduced at the time of sputtering, the amount of sputtered atoms is reduced and the film formation rate is lowered. In sputter deposition of an IGZO film, it is necessary to introduce a large amount of oxygen in order to control the carrier concentration of the film to a desired value, which causes a problem that the deposition rate is lowered and productivity is lowered. It was.

JP 2011-105995 A Patent No. 5288141

  An object of the present invention is to provide an IGZO oxide sintered body capable of reducing the oxygen concentration during sputtering necessary for obtaining a film having a desired carrier concentration. The sputtering target made of the sintered body can increase the sputtering rate and can significantly improve the productivity.

In order to solve the above-mentioned problems, the present inventors have conducted intensive research, and as a result, by increasing the content of Zn (zinc) in the IGZO sintered body, the carrier concentration of the film can be lowered, As a result, it was found that the oxygen concentration during sputtering can be reduced. Based on the above findings, the present inventors provide the following invention.
1) An oxide sintered body composed of indium (In), gallium (Ga), zinc (Zn), oxygen (O), and inevitable impurities, and the atomic ratio of In, Ga, and Zn is In: Ga: Zn. = 1: 1: 1 IGZO (111) phase and an IGZO phase containing more Zn than the IGZO (111) phase, and the area ratio of the IGZO phase containing more Zn than the IGZO (111) phase is 1 The atomic ratio of In, Ga, and Zn of the oxide sintered body is In: Ga: Zn = 1: 1: (1.02-1.10). Oxide sintered body.
2) The oxide sintered body according to 1) above, wherein the average particle size is 20 μm or less.
3) The oxide sintered body according to any one of 1) and 2) above, wherein the bulk resistance is 30 mΩcm or less.
4) The oxide sintered body according to any one of 1) to 3) above, wherein the sintered body density is 6.3 g / cm ³ or more.
5) A sputtering target produced from the oxide sintered body according to any one of 1) to 4) above.

 The present invention provides an IGZO-based oxide sintered body composed of indium (In), gallium (Ga), zinc (Zn), oxygen (O), and unavoidable impurities, by including an IGZO phase containing a large amount of Zn. Since the oxygen concentration during sputtering necessary for forming a thin film having a desired carrier concentration can be reduced, the sputter rate can be improved.

It is a figure which shows the structure | tissue image by EPMA of the oxide sintered compact of Example 1. FIG. It is a figure which shows the structure | tissue image by EPMA of the oxide sintered compact of Example 2. FIG. It is a figure which shows the structure | tissue image by EPMA of the oxide sintered compact of Example 3. It is a figure which shows the structure | tissue image by EPMA of the oxide sintered compact of a comparative example. It is a figure which shows the relationship between the oxygen concentration in film-forming atmosphere, and the film-forming rate. It is a figure which shows the relationship between the oxygen concentration in film-forming atmosphere, and the carrier concentration of a thin film.

 The oxide sintered body of the present invention comprises indium (In), gallium (Ga), zinc (Zn), oxygen (O), and unavoidable impurities, and has an In: Ga: Zn atomic ratio of In, Ga, and Zn. = 1: 1: 1 IGZO (111) phase and an IGZO phase containing more Zn than the IGZO (111) phase, and the area ratio of the IGZO phase containing more Zn than the IGZO (111) phase is 1 -10%. By providing an IGZO phase (Zn-rich IGZO phase) containing more Zn than the IGZO (111) phase, the oxygen concentration during sputtering necessary for obtaining a film having a desired carrier concentration can be reduced. The rate (deposition rate) can be improved.

 When a sputter film is formed using an IGZO sintered body containing a large amount of Zn and containing an IGZO phase, the mechanism is not clear, but the carrier concentration of the film decreases. By using such a target, the concentration of oxygen gas introduced to obtain a desired carrier concentration can be reduced as compared with the conventional case, so that a reduction in sputtering rate due to the oxygen concentration can be suppressed. . The oxide sintered body of the present invention has an effect that the carrier concentration can be lowered when the oxygen gas concentration is made equal to the conventional one, and the reduction of the sputtering rate is a requirement of the present invention. Needless to say, it doesn't happen.

 The IGZO phase (Zn-rich IGZO phase) containing more Zn than the IGZO (111) phase is preferably 1 to 10% in terms of area ratio in the sintered body. When the area ratio of the Zn-rich IGZO phase is less than 1%, the effect of reducing the carrier concentration of the film is not sufficient, while when the area ratio of the Zn-rich IGZO phase is more than 10%, sputtering is performed to form a film. The carrier concentration of the film may increase.

 In the present invention, the atomic ratio of In, Ga, and Zn in the oxide sintered body is preferably In: Ga: Zn = 1: 1: (1.02-1.10). Thereby, a Zn-rich phase can be generated efficiently, and the carrier concentration of the film can be reduced. When the atomic ratio of Zn is less than 1.02, the effect of lowering the carrier concentration of the film is reduced. On the other hand, when the atomic ratio of Zn exceeds 1.10, the carrier concentration of the film starts to increase although the carrier concentration of the film is lower than that in the case where the oxide sintered body is a single phase of IGZO (111) phase. Therefore, the atomic ratio of In, Ga, Zn in the IGZO sintered body is preferably in the above numerical range.

 The oxide sintered body of the present invention preferably has an average particle size of 20 μm or less. The mechanical strength can be increased by reducing the average particle size. If the average particle size exceeds 20 μm, the mechanical strength decreases, and if excessive power is applied during sputtering, the thermal expansion difference between the sputtering target (sintered body) and the backing plate bonding the target There is a possibility that cracks may occur in the sintered body due to the stress generated by.

 The oxide sintered body of the present invention preferably has a bulk resistance of 30 mΩcm or less. If the bulk resistance is low, the possibility of abnormal discharge during sputtering is reduced, and generation of particles that adversely affect the film being formed can be suppressed. On the other hand, if the bulk resistance is more than 30 mΩcm, even if DC sputtering is possible, abnormal discharge may occur during long-time sputtering, and in some cases, no discharge occurs in DC, which is In addition, there is a case where it is necessary to use RF sputtering which is high in cost and reduces the film formation rate.

The oxide sintered body of the present invention preferably has a sintered body density of 6.3 g / cm ³ or more. When the oxide sintered body of the present invention is used as a sputtering target, densification of the sintered body can increase the uniformity of the sputtered film and can significantly reduce the generation of particles during sputtering. Has an excellent effect.

A typical example of the manufacturing process of the oxide sintered body of the present invention is as follows.
Indium oxide (In ₂ O ₃ ), gallium oxide (Ga ₂ O ₃ ), and zinc oxide (ZnO) are prepared as raw materials. In order to avoid an adverse effect on electrical characteristics due to impurities, it is desirable to use a raw material having a purity of 4N or higher. Each raw material is weighed so as to have a predetermined composition ratio. These raw materials contain impurities inevitably contained.

 Next, each raw material is added and mixed so that the oxide sintered body has a predetermined composition ratio. If mixing is inadequate at this time, each component in the target will segregate, causing abnormal discharge such as arcing during sputtering or particle generation. Is preferred. Furthermore, by finely pulverizing and granulating the mixed powder, the moldability and sinterability of the mixed powder can be improved, and a high-density sintered body can be obtained. As a means for mixing and grinding, for example, a commercially available mixer, a ball mill, a bead mill or the like can be used, and as a means for granulating, for example, a commercially available spray dryer can be used.

Next, the mixed powder is filled in a mold and uniaxially pressed under conditions of a surface pressure of 400 to 1000 kgf / cm ² and a hold of 1 to 3 minutes to obtain a molded body. If the surface pressure is less than 400 kgf / cm ² , a molded body having a sufficient density cannot be obtained. In addition, it is difficult to improve the density of the molded body beyond a certain value even if excessive surface pressure is applied. In principle, density distribution tends to occur in the molded body with uniaxial pressing, and deformation and cracking during sintering Therefore, a surface pressure of 1000 kgf / cm ² or more is not particularly required for production.

Next, this molded body is double-vacuum packed with vinyl and subjected to CIP (cold isostatic pressing) under the conditions of pressure 1500 to 4000 kgf / cm ² and holding for 1 to 3 minutes. If the pressure is less than 1500 kgf / cm ² , sufficient CIP effect cannot be obtained. On the other hand, even if a pressure of 4000 kgf / cm ² or more is applied, the density of the molded body is hardly improved beyond a certain value. Therefore, a surface pressure of 4000 kgf / cm ² or more is not particularly required for production.

 Next, the compact is sintered in an air atmosphere or an oxygen atmosphere at a temperature of 1300 to 1500 ° C. and a holding time of 5 to 24 hours to obtain a sintered body. When the sintering temperature is lower than 1300 ° C., a sintered body having a sufficient density cannot be obtained, and when the sintering temperature is 1500 ° C. or higher, the size of the crystal grains in the sintered body becomes too large and the sintered body is sintered. There is a risk of reducing the mechanical strength of the body. Further, if the holding time is less than 5 hours, a sintered body having a sufficient density cannot be obtained, and if the holding time is longer than 24 hours, it is not preferable from the viewpoint of production cost.

 In the molding / sintering step, HP (hot press) and HIP (hot isostatic pressing) can be used in addition to the above-described method. The sintered body obtained as described above can be formed into a target shape by machining such as grinding and polishing, whereby a sputtering target can be prepared.

 In producing the oxide semiconductor film of the present invention, the sputtering target obtained as described above is formed by sputtering under predetermined conditions, and if necessary, this film is annealed at a predetermined temperature. Thus, an oxide semiconductor film can be obtained. In manufacturing the thin film transistor of the present invention, the thin film transistor can be obtained by using the oxide semiconductor film as a gate electrode as shown in FIG.

  Hereinafter, description will be made based on Examples and Comparative Examples. In addition, a present Example is an example to the last, and is not restrict | limited at all by this example. In other words, the present invention is limited only by the scope of the claims, and includes various modifications other than the examples included in the present invention.

Example 1
After weighing In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder so that the composition ratio of the sintered body is 1.00: 1.00: 1.02 in terms of atomic ratio of In, Ga, and Zn These powders were mixed and finely pulverized by a wet process, and then dried and granulated with a spray dryer to obtain a mixed powder. Next, this mixed powder was uniaxially pressed at a surface pressure of 400 to 1000 kgf / cm ² to obtain a molded body. Next, the obtained molded body was double vacuum packed with vinyl, CIP molded at 1500 to 4000 kgf / cm ² , and then sintered in an oxygen atmosphere at a temperature of 1430 ° C. for 20 hours.

The structure photograph by EPMA of the IGZO sintered body thus obtained is shown in FIG. 1 (in the figure, the white portion corresponds to the Zn-rich IGZO phase). It was confirmed from the structure photograph of EPMA that the sintered body of Example 1 was composed of an IGZO (111) phase and a Zn-rich IGZO phase. Further, the area of the Zn-rich IGZO phase was determined from the structure photograph, and the area ratio of the Zn-rich IGZO phase was calculated from the ratio to the area of the entire structure photograph. As a result, the area ratio of the Zn-rich IGZO phase was 1.7%.
Moreover, the average particle diameter of the sintered body was 19.7 μm, and the sintered body density was as high as 6.3 g / cm ³ . Furthermore, the bulk resistance was as low as 30.0 mΩcm. The results are shown in Table 1. The average particle size was calculated by the code method, the sintered body density was determined by the Archimedes method, and the bulk resistance was determined by the four-probe method.

Next, the sintered body was machined to finish a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions were film formation method: DC magnetron sputtering, film formation temperature: room temperature, film formation pressure: 0.5 Pa (O ₂ + Ar), input power: 2.74 W / cm ^2, and oxygen concentration during film formation was ² vol. %, 6 vol%, and 10 vol%, respectively, and a film having a thickness of about 4000 mm was formed.

The film formation rate at each oxygen concentration was calculated from the film thickness measured by the step gauge and the film formation time. The results are shown in Table 1 and FIG. As shown in Table 1, it was confirmed that the film formation rate was slightly improved as compared with Comparative Examples described later.
Each film was annealed in the atmosphere at 400 ° C. for 1 hour, and the carrier concentration and Hall mobility were measured by Hall effect measurement. The results are shown in Table 1 and FIG. As shown in Table 1, it was confirmed that the carrier concentration was lowered at any oxygen concentration as compared with the comparative example described later. For measurement of the Hall effect, ResiTest 8400 manufactured by Toyo Corporation was used.

(Example 2)
After weighing In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder so that the composition ratio of the sintered body is 1.00: 1.00: 1.05 in terms of atomic ratio of In, Ga, and Zn These powders were mixed and finely pulverized by a wet process, and then dried and granulated with a spray dryer to obtain a mixed powder. Next, this mixed powder was uniaxially pressed at a surface pressure of 400 to 1000 kgf / cm ² to obtain a molded body. Next, the obtained molded body was double vacuum packed with vinyl, CIP molded at 1500 to 4000 kgf / cm ² , and then sintered in an oxygen atmosphere at a temperature of 1430 ° C. for 20 hours.

The structure photograph by EPMA of the IGZO sintered body thus obtained is shown in FIG. 2 (in the figure, the white portion corresponds to the Zn-rich IGZO phase). It was confirmed from the structure photograph of EPMA that the sintered body of Example 2 was composed of an IGZO (111) phase and a Zn-rich IGZO phase. Moreover, as a result of calculating the area ratio of the Zn-rich IGZO phase by the same method as in Example 1, the area ratio of the Zn-rich IGZO phase was 5.2%.
Moreover, the average particle diameter of the sintered body was 14.9 μm, and the sintered body had a high density of 6.3 g / cm ³ . Furthermore, the bulk resistance was as low as 23.0 mΩcm. The results are shown in Table 1. In addition, the method similar to Example 1 was used for the measurement of an average particle diameter, a sintered compact density, and bulk resistance.

Next, the sintered body was machined to finish a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions were the same as in Example 1. And the film-forming rate in each oxygen concentration was computed from the film-thickness measurement value by a level difference meter, and film-forming time. The results are shown in Table 1 and FIG. As shown in Table 1, it was confirmed that the film formation rate was improved as compared with Comparative Examples described later.
Next, each film was annealed in the atmosphere at 400 ° C. for 1 hour, and the carrier concentration and Hall mobility were measured by Hall effect measurement. The results are shown in Table 1 and FIG. As shown in Table 1, it was confirmed that the carrier concentration was lowered at any oxygen concentration as compared with the comparative example described later.

(Example 3)
After weighing In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder so that the composition ratio of the sintered body is 1.00: 1.00: 1.10 in terms of atomic ratio of In, Ga, and Zn These powders were mixed and finely pulverized by a wet process, and then dried and granulated with a spray dryer to obtain a mixed powder. Next, this mixed powder was uniaxially pressed at a surface pressure of 400 to 1000 kgf / cm ² to obtain a molded body. Next, the obtained molded body was double vacuum packed with vinyl, CIP molded at 1500 to 4000 kgf / cm ² , and then sintered in an oxygen atmosphere at a temperature of 1430 ° C. for 20 hours.

The structure photograph by EPMA of the IGZO sintered body thus obtained is shown in FIG. 3 (in the figure, the white portion corresponds to the Zn-rich IGZO phase). From the structure photograph of EPMA, it was confirmed that the sintered body of Example 3 was composed of an IGZO (111) phase and a Zn-rich IGZO phase. Moreover, as a result of calculating the area ratio of the Zn-rich IGZO phase by the same method as in Example 1, the area ratio of the Zn-rich IGZO phase was 9.8%.
Moreover, the average particle diameter of the sintered body was 8.9 μm, and the sintered body density was as high as 6.3 g / cm ³ . Furthermore, the bulk resistance was as low as 21.0 mΩcm. The results are shown in Table 1. In addition, the method similar to Example 1 was used for the measurement of an average particle diameter, a sintered compact density, and bulk resistance.

Next, the sintered body was machined to finish a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions were the same as in Example 1. And the film-forming rate in each oxygen concentration was computed from the film-thickness measurement value by a level difference meter, and film-forming time. The results are shown in Table 1 and FIG. As shown in Table 1, it was confirmed that the film formation rate was improved as compared with Comparative Examples described later.
Next, each film was annealed in the atmosphere at 400 ° C. for 1 hour, and the carrier concentration and Hall mobility were measured by Hall effect measurement. The results are shown in Table 1 and FIG. As shown in Table 1, it was confirmed that the carrier concentration was lowered at any oxygen concentration as compared with the comparative example described later.

(Comparative example)
After weighing In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder so that the composition ratio of the sintered body is 1.00: 1.00: 1.00 as the atomic ratio of In, Ga, and Zn These powders were mixed and finely pulverized by a wet process, and then dried and granulated with a spray dryer to obtain a mixed powder. Next, this mixed powder was uniaxially pressed at a surface pressure of 400 to 1000 kgf / cm ² to obtain a molded body. Next, the obtained molded body was double vacuum packed with vinyl, CIP molded at 1500 to 4000 kgf / cm ² , and then sintered in an oxygen atmosphere at a temperature of 1430 ° C. for 20 hours.

The structure photograph by EPMA of the IGZO sintered body thus obtained is shown in FIG. 4 (in the figure, the white portion corresponds to the Zn-rich IGZO phase). It confirmed that the sintered compact of the comparative example was comprised only from the IGZO (111) phase from the structure | tissue photograph of EPMA.
The average particle size of the sintered body was 24.6 μm, and the sintered body density was 6.3 g / cm ³ . Furthermore, the bulk resistance was 37.3 mΩcm. The results are shown in Table 1. In addition, the method similar to Example 1 was used for the measurement of an average particle diameter, a sintered compact density, and bulk resistance.

 Next, the sintered body was machined to finish a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions were the same as in Example 1. And the film-forming rate in each oxygen concentration was computed from the film-thickness measurement value by a level difference meter, and the film-forming time. The results are shown in Table 1 and FIG. As shown in Table 1, the film formation rate was lower than that of the example. Next, each film was annealed in the atmosphere at 400 ° C. for 1 hour, and the carrier concentration and Hall mobility were measured by Hall effect measurement. The results are shown in Table 1 and FIG. As shown in Table 1, the carrier concentration was higher than that of the example.

From the above results, in any of the Zn compositions 1.02, 1.05, and 1.10 of the examples, a decrease in carrier concentration was confirmed as compared with the Zn composition 1.00 of the comparative example. In the comparative example, the oxygen concentration needs to be 10% or more to lower the carrier concentration below a certain level (for example, 1e ⁺¹⁵ cm ⁻³ or less), but in Examples 1 to 3, 2% is sufficient. I understand. Further, even when the film is formed at the same oxygen concentration, the film formation rate in the example is slightly higher than that in the comparative example, so that the desired carrier concentration (in a general TFT, the carrier concentration of the film is 1e ⁺¹⁵ It is not necessary to increase oxygen in order to obtain a film of about ³ cm ^-3 or less, and a high film formation rate can be maintained.

The oxide sintered body of the present invention can be used as a sputtering target. When sputtering film formation is performed using this sputtering target, the oxygen concentration in the sputtering atmosphere can be reduced. Rate) can be improved. Therefore, the use of such a sputtering target has an excellent effect that the oxide semiconductor film and the thin film transistor can be stably mass-produced. The oxide semiconductor film of the present invention is particularly useful as an active layer of a TFT in a backplane such as a flat panel display or a flexible panel display.

Claims (5)

 An oxide sintered body composed of indium (In), gallium (Ga), zinc (Zn), oxygen (O), and inevitable impurities, wherein In: Ga: Zn = 1 at an atomic ratio of In, Ga, and Zn IGZO (111) phase composed of 1: 1, and an IGZO phase containing more Zn than the IGZO (111) phase, and the IGZO phase containing more Zn than the IGZO (111) phase has an area ratio of 1 to 10 The oxide is characterized in that the atomic ratio of In, Ga, and Zn in the oxide sintered body is In: Ga: Zn = 1: 1: (1.02-1.10). Sintered body.  2. The oxide sintered body according to claim 1, wherein the average particle diameter is 20 μm or less.  The oxide sintered body according to claim 1 or 2, wherein the bulk resistance is 30 mΩcm or less. 4. The oxide sintered body according to claim 1, wherein the sintered body density is 6.3 g / cm ³ or more. The sputtering target which consists of oxide sinter as described in any one of Claims 1-4.