TWI542714B - An oxide sintered body, and a sputtering target made of the oxide sintered body - Google Patents

Description

Oxide sintered body and sputtering target composed of the oxide sintered body

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

Conventionally, in FPD (Planar Display), the TFT (thin film transistor) of the bottom plate has been using α-Si (amorphous germanium). However, α-Si cannot obtain sufficient electron mobility, and research and development of TFTs using In-Ga-Zn-O-based oxides (IGZO) having higher electron mobility than α-Si have been under development in recent years. Moreover, the next generation high-performance flat panel display using IGZO-TFT has been partially put into practical use.

The IGZO film is mainly formed by sputtering a target made of an IGZO sintered body. As an IGZO sputtering target, for example, Patent Document 1 discloses that a structure containing In, Ga, and Zn and having a higher content of In than that of the surrounding can be produced, and the specific resistance can be made even without performing a reduction treatment at a high temperature. The target. Further, in Patent Document 2, it is disclosed that by containing a specific ratio of In, Ga, and Zn, two or more kinds of homogeneous crystals are coexisted, and sputtering can be stabilized, and generation of particles can be reduced.

Therefore, when such an IGZO film is used as an active layer of a TFT film, the amount of oxygen deficiency in the film is one of the factors that affect the electrical characteristics of the film. In order to control the amount of oxygen deficiency, oxygen is generally introduced in addition to an inert gas such as argon at the time of sputtering film formation. Oxygen The sputtering efficiency is lower than that of argon. When oxygen is introduced during sputtering, the amount of atoms that are sputtered is reduced, and the film formation rate is lowered. In the sputtering film formation of the IGZO film, in order to control the carrier concentration of the film to a desired value, a large amount of oxygen must be introduced, so that there is a problem that the film formation rate is lowered and the productivity is lowered.

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2011-105995

[Patent Document 2] Japanese Patent No. 5288141

An object of the present invention is to provide an IGZO oxide sintered body which can reduce the oxygen concentration at the time of sputtering necessary for obtaining a film having a desired carrier concentration. The sputtering target composed of the sintered body can increase the sputtering rate and can significantly improve productivity.

In order to solve the problem, the inventors of the present invention have made an effort to reduce the carrier concentration of the film by increasing the content of Zn (zinc) in the IGZO sintered body, and as a result, the oxygen concentration at the time of sputtering can be reduced. The present inventors have provided the following invention based on the above findings.

1) An oxide sintered body comprising indium (In), gallium (Ga), zinc (Zn), oxygen (O), and unavoidable impurities, characterized by having an atom of In, Ga, and Zn The IGZO (111) phase composed of In:Ga:Zn is 1:1:1 and the IGZO phase containing more Zn than the IGZO (111) phase, wherein the IGZO phase containing more Zn than the IGZO (111) phase In the area ratio, the atomic ratio of In, Ga, and Zn is composed of In:Ga:Zn=1:1:(1.02 to 1.10).

2) The oxide sintered body according to the above 1), which has an average particle diameter of 20 μm or less.

(3) The oxide sintered body according to any one of the above 1) or 2), which has a bulk resistance of 30 m?cm or less.

The oxide sintered body according to any one of the above 1) to 3, wherein the sintered body has a sintered body density of 6.3 g/cm ³ or more.

5) A sputtering target produced by the oxide sintered body according to any one of the above 1) to 4).

In the IGZO-based oxidized sintered body composed of (In), gallium (Ga), zinc (Zn), oxygen (O), and unavoidable impurities, the IGZO phase containing a large amount of Zn is provided to reduce the formation of IGZO phase. The oxygen concentration at the time of sputtering necessary for the film having the desired carrier concentration has an excellent effect of increasing the sputtering rate.

Fig. 1 is a view showing a tissue image obtained by EPMA of the oxide sintered body of Example 1.

Fig. 2 is a view showing a tissue image obtained by EPMA of the oxide sintered body of Example 2.

Fig. 3 is a view showing a tissue image obtained by EPMA of the oxide sintered body of Example 3.

Fig. 4 is a view showing a tissue image obtained by EPMA of an oxide sintered body of a comparative example.

Fig. 5 is a graph showing the relationship between the oxygen concentration in the film formation environment and the film formation rate.

Fig. 6 is a graph showing the relationship between the oxygen concentration in the film formation environment and the carrier concentration of the film.

The oxidized sintered body of the present invention is characterized in that it is composed of indium (In), gallium (Ga), zinc (Zn), oxygen (O), and unavoidable impurities, and has an atomic ratio of In, Ga, and Zn. :Ga:Zn is an IGZO (111) phase composed of 1:1:1 and an IGZO phase containing more Zn than the IGZO (111) phase, and an IGZO phase containing more Zn than the IGZO (111) phase is measured by area ratio. It is 1~10%. By having an IGZO phase (an Zn-rich IGZO phase) containing more Zn than the IGZO (111) phase, the oxygen concentration at the time of sputtering necessary for obtaining a film having a desired carrier concentration can be reduced, thereby enhancing the sputtering. Plating rate (film formation rate).

If IGZO sintered body containing ZnZO phase containing a large amount of Zn is used for sputtering Film formation, although the mechanism is not clear, but the carrier concentration of the membrane will decrease. By using such a target, the concentration of oxygen introduced to obtain a desired carrier concentration can be lowered lower than in the related art, so that the decrease in the sputtering rate due to the oxygen concentration can be suppressed. Further, the oxide sintered body of the present invention has an effect of lowering the concentration of the carrier when the oxygen concentration is set to be the same as in the related art, and it is needless to say that the reduction in the sputtering rate does not become a requirement of the present invention.

The IGZO phase (IGZ phase rich in Zn) containing more Zn than the IGZO (111) phase is preferably 1 to 10% in area ratio in the sintered body. If the area ratio of the Zn-rich IGZO phase is less than 1%, the effect of lowering the carrier concentration of the film is insufficient. On the other hand, if the area ratio of the Zn-rich IGZO phase exceeds 10%, the film is deposited by sputtering. The carrier concentration of the membrane is increased.

Further, 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 to 1.10). Thereby, the Zn-rich phase can be efficiently produced, and the carrier concentration of the film can be lowered. If the atomic ratio of Zn is less than 1.02, the effect of lowering the carrier concentration of the film becomes small. On the other hand, when the atomic ratio of Zn exceeds 1.10, the carrier concentration of the film tends to increase as compared with the case where the oxide sintered body is a single phase of the IGZO (111) phase. Therefore, the atomic ratio of In, Ga, and Zn of the IGZO sintered body is preferably in the above numerical range.

The oxide sintered body of the present invention preferably has an average particle diameter of 20 μm or less. The mechanical strength can be improved by reducing the average particle diameter. When the average particle diameter exceeds 20 μm, the mechanical strength is lowered, and when excessive electric power is applied during sputtering, there is a possibility that a stress generated by a difference in thermal expansion between the sputtering target and the backing plate to which the target is bonded may cause the sintered body to occur. rupture.

Moreover, the bulk resistance of the oxide sintered body of the present invention is preferably 30 mΩcm or less. When the bulk resistance is low, the possibility of occurrence of abnormal discharge during sputtering becomes low, and generation of particles which adversely affect the film in the film formation can be suppressed. On the other hand, if the bulk resistance exceeds 30mΩcm, then Even in the case of DC sputtering, abnormal discharge may occur during long-time sputtering. Depending on the situation, there may be no discharge in DC, and RF sputtering with high device cost and reduced film formation rate must be used. plating.

Moreover, the sintered body density of the oxide sintered body of the present invention is preferably 6.2 g/cm ³ or more. When the oxide sintered body of the present invention is used as a sputtering target, the high density of the sintered body has an effect of improving the uniformity of the sputtering film and significantly reducing the generation of particles during sputtering.

A representative example of the production steps 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) were prepared as raw materials. In order to prevent impurities from adversely affecting electrical characteristics, it is preferred to use a raw material having a purity of 4N or more. Each raw material is weighed to a specific composition ratio. Furthermore, these raw materials contain unavoidable impurities.

Next, each raw material is added and mixed so that the oxide sintered body becomes a specific composition ratio. When the mixing is insufficient at this time, segregation occurs in each component in the target, which causes abnormal discharge such as arc during sputtering, or causes particles to be generated. Therefore, it is preferable to sufficiently mix. Further, by finely pulverizing and granulating the mixed powder, the formability and the sinterability of the mixed powder are improved, and a sintered body having a high density can be obtained. As means for mixing and pulverizing, for example, a commercially available mixer, a ball mill, a bead mill or the like can be used, and as a means for granulation, for example, a commercially available spray dryer can be used.

Then, the mixed powder was filled in a metal mold, and uniaxially pressurized under the conditions of a surface pressure of 400 to 1000 kgf/cm ² for 1 to 3 minutes to obtain a molded body. If the surface pressure is not 400 kgf/cm ² , a molded body having a sufficient density cannot be obtained. Further, even if an excessive surface pressure is applied, it is difficult to increase the density of the molded body to a certain value or more, and the uniaxial pressing principle is likely to cause a density distribution in the molded body, which causes deformation or cracking during sintering. Therefore, the surface pressure of 1000 kgf/cm ² or more is not considered to be particularly required in production.

Next, the molded body was double vacuum-packed with a plastic, and CIP (cold pressure equalization method) was carried out under the conditions of a pressure of 1500 to 4000 kgf/cm ² and maintaining 1 to 3 minutes. If the pressure is not 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 hard to increase to a certain value or more, so 4000 kgf/cm ² The above surface pressure is not considered to be particularly necessary in production.

Then, the formed body is sintered at a temperature of 1300 to 1500 ° C for a period of 5 to 24 hours, in an atmosphere or an oxygen atmosphere, to obtain a sintered body. When the sintering temperature is lower than 1300 ° C, a sintered body having a sufficient density cannot be obtained. When the sintering temperature is 1500 ° C or higher, the size of the crystal grains in the sintered body becomes excessively large, and the mechanical strength of the sintered body is lowered. Further, if the maintenance time is less than 5 hours, a sintered body having a sufficient density cannot be obtained, and if the maintenance time exceeds 24 hours, it is not preferable from the viewpoint of production cost.

Further, in the molding and sintering process, in addition to the above methods, HP (hot pressing method) or HIP (heat equalizing method) may be used. The sintered body obtained by the above method can be formed into a target shape by mechanical processing such as grinding or polishing to thereby form a sputtering target.

When the oxide sintered body of the present invention is produced, the sputtering target obtained in the above manner is sputter-deposited under specific conditions, and the film is annealed at a specific temperature as necessary, whereby an oxide semiconductor film can be obtained. Further, when the thin film transistor of the present invention is produced, the above oxide semiconductor film is used as a gate electrode as shown in Fig. 1, whereby a thin film transistor can be obtained.

[Examples]

Hereinafter, description will be made based on examples and comparative examples. Furthermore, this embodiment is only an example, and the present invention is not limited by this example. That is, the present invention is limited only by the scope of the patent application, and includes various modifications other than the embodiments included in the invention.

(Example 1)

In the case where the composition ratio of the sintered body is 1.00:1.00:1.02 in terms of the atomic ratio of In, Ga, and Zn, the In ₂ O ₃ powder, the Ga ₂ O ₃ powder, and the ZnO powder are weighed, and the powder is wet-processed. After mixing and finely pulverizing, it was dried and granulated by a spray dryer to obtain a mixed powder. Next, the mixed powder was uniaxially pressed at a surface pressure of 400 to 1000 kgf/cm ² to obtain a molded body. Then, the obtained molded body was double vacuum-packed with plastic, CIP molding was performed at 1500 to 4000 kgf/cm ^{2 , and} then sintered at a temperature of 1430 ° C for 20 hours in an oxygen atmosphere.

A photograph of the structure of the IGZO sintered body obtained in this manner from EPMA is shown in Fig. 1 (in the figure, the white portion corresponds to the Zn-rich IGZO phase). It was confirmed from the tissue photograph of EPMA that the sintering system 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 photomicrograph, and the area ratio of the Zn-rich IGZO phase was calculated from the ratio of the area of the IGZO phase. As a result, the area ratio of the Zn-rich IGZO phase was 1.7%.

Further, the sintered body had an average particle diameter of 19.7 μm and a sintered body density of 6.3 g/cm ³ . Further, the volume resistance is as low as 30.0 m Ω cm. The above results are shown in Table 1. Further, the average particle diameter was calculated by a chord method, the sintered body density was determined by the Archimedes method, and the bulk resistance was calculated by a four-probe method.

Then, the sintered body was machined and finished into a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions are as follows: 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 , oxygen at the time of film formation The concentration was changed to 2 vol%, 6 vol%, and 10 vol% to form a film having a thickness of about 4000 Å.

The film formation rate of each oxygen concentration was calculated from the film thickness measurement value and the film formation time obtained by the surface topographer. The results are shown in Table 1 and Figure 4. As shown in Table 1, it was confirmed that the film formation rate was slightly improved as compared with the comparative example described below.

Further, for each film, annealing was performed at 400 ° C for 1 hour in the atmosphere, and the Hall effect was measured, thereby measuring the carrier concentration and the Hall mobility. The results are shown in Table 1 and Figure 6. As shown in Table 1, it was confirmed that the carrier concentration of each oxygen concentration was lowered as compared with the comparative example described below. Furthermore, the ResiTest 8400 manufactured by Dongyang Teknika Co., Ltd. was used for the measurement of the Hall effect.

(Example 2)

The In ₂ O ₃ powder, the Ga ₂ O ₃ powder, and the ZnO powder are weighed so that the composition ratio of the sintered body is 1.00:1.00:1.05 in terms of the atomic ratio of In, Ga, and Zn, and the powders are mixed in a wet manner. After the fine pulverization, drying and granulation were carried out in a spray dryer to obtain a mixed powder. Next, the mixed powder was uniaxially pressed at a surface pressure of 400 to 1000 kgf/cm ² to obtain a molded body. Then, the obtained molded body was double vacuum-packed with plastic, CIP molding was performed at 1500 to 4000 kgf/cm ^{2 , and} then sintered at a temperature of 1430 ° C for 20 hours in an oxygen atmosphere.

The IGZO sintered body obtained in this manner was obtained from EPMA, and the photograph of the structure is shown in Fig. 2 (in the figure, the white portion corresponds to the Zn-rich IGZO phase). It was confirmed from the tissue photograph of EPMA that the sintering system of Example 2 was composed of an IGZO (111) phase and a Zn-rich IGZO phase. Further, as a result of calculating the area of the Zn-rich IGZO phase in the same manner as in Example 1, the area ratio of the Zn-rich IGZO phase was 5.2%.

Further, the sintered body had an average particle diameter of 14.9 μm and a sintered body density of 6.3 g/cm ³ . Further, the volume resistance was as low as 23.0 m Ω cm. The above results are shown in Table 1. Further, in the measurement of the average particle diameter, the sintered body density, and the bulk resistance, the same method as in Example 1 was used.

Then, the sintered body was machined and finished into a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions were set to be the same as in the first embodiment. Then, the film formation rate of each oxygen concentration was calculated from the film thickness measurement value obtained by the surface topographer and the film formation time. The results are shown in Table 1 and Figure 5. As shown in Table 1, it was confirmed that the film formation rate was improved as compared with the comparative example described below.

Next, the respective films were annealed at 400 ° C for 1 hour in the atmosphere, and the Hall effect was measured, thereby measuring the carrier concentration and the Hall mobility. The results are shown in Table 1 and Figure 6. As shown in Table 1, it was confirmed that the carrier concentration of each oxygen concentration was lowered as compared with the comparative example described below.

(Example 3)

The In ₂ O ₃ powder, the Ga ₂ O ₃ powder, and the ZnO powder are weighed so that the composition ratio of the sintered body is 1.00:1.00:1.10 in terms of the atomic ratio of In, Ga, and Zn, and the powders are mixed in a wet manner. After the fine pulverization, drying and granulation were carried out in a spray dryer to obtain a mixed powder. Next, this mixed powder at a surface pressure of 400 ~ 1000kgf / cm ² to uniaxial pressing to obtain a molded body. Then, the obtained molded body was double vacuum-packed with plastic, CIP molding was performed at 1500 to 4000 kgf/cm ^{2 , and} then sintered at a temperature of 1430 ° C for 20 hours in an oxygen atmosphere.

The photograph of the structure obtained by EPMA obtained from the IGZO sintered body obtained in this manner is shown in Fig. 3 (in the figure, the white portion corresponds to the Zn-rich IGZO phase). From the tissue photograph of EPMA, it was confirmed that the sintering system of Example 3 consisted of an IGZO (111) phase and a Zn-rich IGZO phase. Further, as a result of calculating the area of the Zn-rich IGZO phase in the same manner as in Example 1, the area ratio of the Zn-rich IGZO phase was 9.8%.

Further, the sintered body had an average particle diameter of 8.9 μm and a sintered body density of 6.3 g/cm ³ . Further, the volume resistance was as low as 21.0 m Ω cm. The above results are shown in Table 1. Further, in the measurement of the average particle diameter, the sintered body density, and the bulk resistance, the same method as in Example 1 was used.

Then, the sintered body was machined and finished into a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions were set to be the same as in the first embodiment. Then, the film formation rate of each oxygen concentration was calculated from the film thickness measurement value obtained by the surface topographer and the film formation time. The results are shown in Table 1 and Figure 5. As shown in Table 1, it was confirmed that the film formation rate was improved as compared with the comparative example described below.

Next, the respective films were annealed at 400 ° C for 1 hour in the atmosphere, and the Hall effect was measured, thereby measuring the carrier concentration and the Hall mobility. The results are shown in Table 1 and Figure 6. As shown in Table 1, it was confirmed that the carrier concentration of each oxygen concentration was lowered as compared with the comparative example described below.

(Comparative example)

The In ₂ O ₃ powder, the Ga ₂ O ₃ powder, and the ZnO powder are weighed so that the composition ratio of the sintered body is 1.00:1.00:1.00 in terms of an atomic ratio of In, Ga, and Zn, and the powders are mixed in a wet manner. After the fine pulverization, drying and granulation were carried out in 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. Then, the obtained molded body was vacuum-packed into a plastic bag to a weight of ^2, and CIP was formed at 1500 to 4000 kgf/cm ^{2 , and} then sintered at a temperature of 1430 ° C for 20 hours in an oxygen atmosphere.

The photograph of the structure 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 was confirmed from the tissue photograph of EPMA that the sintered body of the comparative example was composed only of the IGZO (111) phase.

Further, a high-density material having an average particle diameter of the sintered body of 24.6 μm and a sintered body density of 6.3 g/cm ³ was obtained. Further, a low resistance of 37.3 mΩcm was obtained. The above results are shown in Table 1. Further, in the measurement of the average particle diameter, the sintered body density, and the bulk resistance, the same method as in Example 1 was used.

Then, the sintered body was machined and finished into a 6-inch sputtering target, and sputtering was performed using this target. The sputtering conditions were set to be the same as in the first embodiment. Then, the film formation rate of each oxygen concentration was calculated from the film thickness measurement value and the film formation time obtained from the surface topographer. The results are shown in Table 1 and Figure 5. As shown in Table 1, as a result, the film formation rate became lower as compared with the examples. Next, the respective films were annealed at 400 ° C for 1 hour in the atmosphere, and the Hall effect was measured, thereby measuring the carrier concentration and the Hall mobility. The results are shown in Table 1 and Figure 6. As shown in Table 1, it was confirmed that the carrier concentration result was higher as compared with the examples.

From the above results, it was confirmed that the carrier concentration of any of the Zn compositions of the examples of 1.02, 1.05, and 1.10 was lower than that of the Zn composition of the comparative example. It is found that in the comparative example, it is necessary to set the oxygen concentration to 10% or more and to reduce the carrier concentration to a certain level or less (for example, 1e ^{+ 15} cm ^-3 or less), but in Examples 1 to 3, 2% is sufficient. Further, even in the case of film formation at the same oxygen concentration, the film formation rate of the examples is slightly higher than that of the comparative example, so it is not necessary to obtain the desired carrier concentration (the carrier concentration of the conventional TFT film is from 1e ^{+ 15} cm). ^-3 or less) while increasing oxygen, a high film formation rate can be maintained.

[Industrial Availability]

The oxide sintered body of the present invention can be used as a sputtering target, and when the sputtering target is used for sputtering, the oxygen concentration in the sputtering environment can be reduced, so that the sputtering rate (film formation rate) can be improved. Therefore, by using a sputtering target as described above, it is excellent in that the oxide semiconductor film and the thin film transistor can be stably mass-produced. The oxide semiconductor film of the present invention can function particularly as an active layer of a TFT of a substrate such as a flat panel display or a flexible panel display.

Claims (6)

An oxide sintered body comprising indium (In), gallium (Ga), zinc (Zn), oxygen (O), and unavoidable impurities, characterized by having an atomic ratio of In, Ga, and Zn In:Ga:Zn is an IGZO (111) phase composed of 1:1:1 and an IGZO phase containing more Zn than the IGZO (111) phase, wherein the IGZO phase containing more Zn than the IGZO (111) phase is in an area The ratio is 1 to 10%, and the atomic ratio of In, Ga, and Zn of the oxide sintered body is composed of In:Ga:Zn = 1:1: (1.02 to 1.10). The oxide sintered body of the first aspect of the patent application has an average particle diameter of 20 μm or less. The oxide sintered body of the first aspect of the patent application has a bulk resistance of 30 mΩcm or less. The oxide sintered body of the second aspect of the patent application has a bulk resistance of 30 mΩcm or less. The oxide sintered body according to any one of claims 1 to 4, which has a sintered body density of 6.3 g/cm ³ or more. A sputtering target comprising the oxide sintered body according to any one of claims 1 to 5.