KR102237339B1 - Sputtering target and method for producing same - Google Patents

Abstract

The sputtering target of the present invention has a composition of the formula: Zn _x Sn _y O _z (however, x + y = 2, further z = x + 2y-α (x + 2y)), and the defect coefficient α = 0.002 to 0.03 And a sintered body made of ZnSn oxide that satisfies the condition of the oxygen component ratio z=2.1 to 3.8, wherein the sintered body has a variation of the average specific resistance in the thickness direction of 50% or less.

Description

Sputtering target and its manufacturing method TECHNICAL FIELD

The present invention relates to a sputtering target capable of stably forming a uniform semiconductor film of ZnSn oxide, a protective film for metal thin films, and the like by direct current (DC) sputtering, and a method of manufacturing the same.

This application claims priority based on Japanese Patent Application No. 2013-163051 filed in Japan on August 6, 2013, and Japanese Patent Application No. 2014-157914 filed in Japan on August 1, 2014, I use the content here.

It is proposed to use a mixture of _{zinc oxide (ZnO) or tin oxide (SnO 2} ) (ZnSn oxide: ZTO) as a material for an electrode that is conductive and transparent to light in a liquid crystal display or a solar cell. In addition, _{since both ZnO and SnO 2} are semiconductors, ZTO can be used not only as a transparent electrode but also as an oxide semiconductor (for example, refer to Patent Document 1). _{In particular, a Zn 2} SnO ₄ thin film, which is a semiconductor having practical mobility, can be formed at room temperature using a ZTO sputtering target. This can be formed, for example, on an organic film and used as a material for a thin film transistor (TFT). In this case, unlike the case of the transparent electrode, since the conductivity of the sputtering target does not increase, film formation is often performed by a high-frequency (RF) sputtering method rather than a direct current (DC) sputtering method.

In addition, since the Zn ₂ SnO ₄ thin film is transparent and has high refractive index characteristics, it is also used as a protective film for a transparent far-infrared reflective film made of a metal film such as an Au thin film, an Ag thin film, and a Cu thin film. In order to obtain good far-infrared reflection performance while securing high transmittance, for example, a Zn ₂ SnO ₄ thin film is formed as a transparent high refractive index film on an Ag thin film. The sputtering method is also adopted for this lamination formation.

As described above, since Zn ₂ SnO ₄ itself has high resistance, a _{sputtering target made of Zn 2} SnO ₄ does not have a conductivity such that DC sputtering becomes possible. In order to form a Zn ₂ SnO ₄ thin film using this sputtering target, an RF sputtering method must be employed, and the film forming speed is also low. Therefore, in order to lower the resistance in the sputtering target for forming a _{Zn 2} SnO _{4 thin film, ZnSnO 3} is used as the main phase or a dopant is added to lower the resistance of the sputtering target, and DC sputtering is possible. It is proposed to do this (see, for example, Patent Documents 2 to 4).

Japanese Patent Laid-Open Publication No. 2010-037161 Japanese Unexamined Patent Publication No. 2007-277075 Japanese Unexamined Patent Publication No. 2007-314364 Japanese Unexamined Patent Publication No. 2012-121791

_{As described above, in the ZTO sputtering target having ZnSnO 3} as the main phase proposed in Patent Documents 2 and 3, even if the specific resistance of the target was able to be lowered, the film sputtered by using this ZTO sputtering target has a carrier concentration. It has high and low resistance, so it is not suitable as a semiconductor film.

On the other hand, _{it is proposed to realize a low resistance by treating a sputtering target containing Zn 2} SnO ₄ in a reducing atmosphere to promote an increase in oxygen vacancies in the ZnSn oxide. However, in the case of this method, since the treatment process increases, productivity is poor. Furthermore, even if the high-density sputtering target is subjected to reduction treatment, an increase in oxygen vacancies is promoted in the surface portion of the target, but the reduction does not proceed toward the inside of the target, and the reduction state changes in the target thickness direction. An increase in oxygen vacancies in the target center cannot be expected.

For example, in the case of attempting to manufacture a ZTO sputtering target exceeding a size of 100 mm in diameter and 10 mm in thickness, the surface portion of the target is sufficiently reduced, but as it advances inside the target, an image in which the effect of reduction is insufficient remains. Therefore, variation in specific resistance occurs over the thickness direction of this sputtering target. When sputtering is performed with this sputtering target, the specific resistance is low in the surface portion, and DC sputtering is possible. However, with the progress of sputtering, when the target is dug up to the inside, since the portion with high specific resistance is exposed on the surface, abnormal discharges occur frequently, sputtering cannot be stably performed, and the film formation rate is also changed. Discard it. In this way, not only it becomes impossible to stably perform DC sputtering, there is also a problem that a uniform film cannot be formed.

Moreover, although the ZTO sputtering target disclosed in the said patent document 3 has ZnSnO ₃ as a main phase, it contains _{SnO 2 phase.} When this SnO ₂ phase is present in the sputtering target, there is a problem that abnormal discharge and generation of particles are caused in the sputtering film formation using DC sputtering, and the target itself is easily cracked.

Therefore, the present invention promotes the increase of oxygen vacancies uniformly and sufficiently over the thickness direction (depth direction before transfer) of the ZnSn oxide (ZTO) sputtering target, and promotes the reduction reaction during sintering, and the thickness direction A sputtering target made of ZnSn oxide, suitable for forming a semiconductor film or a protective film for metal thin films, and the It is an object of the present invention to provide a manufacturing method.

In the above-described ZnSn oxide (ZTO) sputtering target, paying attention to the fact that the specific resistance of the target is low at the target surface portion and increases as it goes inside the target. As a method of making the change of a certain amount constant, dry a mixture of a predetermined amount of zinc oxide (ZnO) powder and tin oxide (SnO ₂ ) powder, granulate it, heat treatment in a reducing atmosphere, and then in a non-oxidizing atmosphere. The knowledge that pressure sintering is sufficient was obtained. In the heat treatment, reduction is promoted to the inside of the mixture, reduction proceeds throughout the mixture, and an oxygen-deficient state is generated. Thereby, the target specific resistance is lowered throughout the entire target thickness direction, and as a result of promoting the movement of oxygen atoms during sintering, the density of the sintered body is improved. As a result, it was found that a ZTO sputtering target capable of always stable DC sputtering was obtained.

So, commercially available zinc oxide powder (ZnO powder) and tin oxide powder (SnO ₂ powder) were mixed with a wet ball mill or bead mill in a ratio of 1: 1 in the atomic ratio of Zn and Sn, and then dried and granulated. Thereafter, it was put into a carbon crucible, and heat treatment was performed in a vacuum at 800° C. for 3 hours. Then, the obtained powder was pulverized, and pressure sintered at 900°C for 3 hours and under the conditions of 29.4 MPa (300 kgf/cm 2) to obtain a ZnSn oxide (ZTO) sintered body. As a result of manufacturing a ZTO sputtering target by machining this ZTO sintered compact into a predetermined shape, it was confirmed that the target specific resistance could be further lowered over the entire thickness direction of the target. In film formation of a ZTO film using this ZTO sputtering target, it was confirmed that stable DC sputtering was always possible.

Since this was heat-treated in a reducing atmosphere at the stage of the mixture before pressure sintering was performed, sufficient reduction was performed throughout the mixture, and oxygen deficiency was achieved throughout the thickness direction to the inside of the pressure sintered ZTO sintered body. It has been found that this contributes to a further lowering of the target specific resistance.

Accordingly, the present invention is obtained from the above findings, and adopts the following configuration in order to solve the above problems.

(1) The sputtering target of the present invention has a composition of the formula: Zn _x Sn _y O _z (however, x + y = 2, and also z = x + 2y-α (x + 2y)), and the defect coefficient α = A sintered body made of ZnSn oxide that satisfies the conditions of 0.002 to 0.03 and the oxygen component ratio z = 2.1 to 3.8, and the variation of the average specific resistance in the thickness direction of the sintered body is 50% or less.

(2) In the sputtering target of the above (1), the density ratio is 90% or more.

(3) In the sputtering target of the above (1) and (2), the breaking strength is 100 N/mm 2 or more.

(4) In the sputtering targets of the above (1) to (3), the specific resistance is 1 Ω·cm or less.

(5) The present invention is a method of manufacturing the sputtering targets of the above (1) to (4). In the manufacturing method, a mixture of a predetermined amount of zinc oxide powder and tin oxide powder is dried, granulated, and then in a reducing atmosphere. A heat treatment step of performing heating and a sintering step of obtaining a sintered body by pressing the heat-treated mixture in a non-oxidizing atmosphere, and an oxygen deficiency state in the heat treatment step is increased.

(6) In the manufacturing method of the above (5), the heat treatment step and the sintering step are continuously performed in a heating furnace.

As described above, in the sintered body of the ZnSn oxide (ZTO) sputtering target of the present invention, the oxygen vacancy state remains, and the oxygen vacancy state is increasing throughout the interior of the sintered body. For this reason, the specific resistance is lowered to the extent that DC sputtering is possible in the entire target thickness direction (depth direction before transfer), and the variation in the specific resistance in the target thickness direction is small. As a result, DC sputtering can be stably performed up to the target life, and cracking of the target at the time of sputtering can be suppressed, and further, uniform film formation can be realized.

In addition, the manufacturing method of the present invention includes a heat treatment step in which a predetermined amount of a mixture of zinc oxide powder and tin oxide powder is dried and granulated, and then heated in a reducing atmosphere, and the heat-treated mixture is pressurized and sintered in a non-oxidizing atmosphere. Since a sintering step for obtaining a sintered body is provided, an increase in oxygen vacancies is promoted in the heat treatment step, and in the sintering step, sintering is performed while remaining oxygen vacancies. Therefore, it becomes the same state as the reduction proceeded to the inside of the sintered body, and the state of oxygen vacancies uniformly increases throughout the inside of the sintered body. According to the manufacturing method of the present invention, it is possible to manufacture a ZTO sputtering target having a low specific resistance across the entire target thickness direction and a small variation in specific resistance.

Therefore, according to the sputtering target of the present invention, since the target specific resistance is low in the entire thickness direction and is constant within the target surface, stable DC sputtering is always possible, which contributes to productivity improvement.

1: is a figure explaining the measurement of the specific resistance of a sputtering target in the direction inside a sputtering surface.

Next, an oxide sputtering target according to an embodiment of the present invention and an embodiment of a manufacturing method thereof will be described.

The sputtering target of this embodiment is constituted by a sintered body made of ZnSn oxide having a composition of the _{formula: Zn x} Sn _y O _z. The components of zinc (Zn) and tin (Sn) are set so that the component ratio of Zn and Sn is in the range of the target ZnSn oxide film on the condition that x+y=2 is satisfied. Further, since Zn ₂ SnO ₄ itself has a high specific resistance, the target specific resistance is lowered by making the _{ZnSn oxide (Zn 2} SnO _{4) into an oxygen-deficient state.} It is preferable to set z=2.1 to 3.8 with respect to the component ratio z of oxygen (O) in this oxygen-deficient ZnSn oxide.

Here, if a defect factor indicates that the increase of the oxygen deficiency state stimulated by α, the formula of ZnSn oxide of the oxygen deficiency state increase: composition ratio z of oxygen in the Zn _x Sn _y O _z is, z = x + 2y It can be represented by -α(x+2y). By blending the ZnO powder and the SnO ₂ powder so as to satisfy the condition of x + y = 2 and heat-treating the mixture, the defect coefficient α in the mixture is adjusted and the oxygen component ratio is changed. By hot pressing the mixture in which the defect coefficient α is adjusted in a non-oxidizing atmosphere, a sintered body made of ZnSn oxide having an increased oxygen defect state can be obtained. Moreover, by setting it as the range of the defect coefficient α=0.002 to 0.03, the oxygen component ratio z=2.1 to 3.8 was achieved.

In the sputtering target of the present embodiment, the defect coefficient α is in the range of 0.002 to 0.03. When the defect coefficient α exceeds 0.03, _{a part of tin oxide (SnO 2} ) in the structure may be reduced, and metallic tin (Sn) may be eluted. If this Sn is eluted, Sn adheres to the furnace during manufacture, causing damage to the furnace, and lowering productivity due to cleaning in the furnace. It is a problem that the composition deviates. On the other hand, if the defect coefficient α is less than 0.002, since the target specific resistance does not decrease, it becomes difficult to perform DC sputtering. Therefore, in the present embodiment, the defect coefficient α is in the range of 0.002 or more and 0.03 or less. In addition, although it is more preferable to set the defect coefficient α to be 0.008 or more and 0.02 or less, it is not limited thereto.

In addition, when the oxygen component ratio z is less than 2.1, the ratio of the ZnO powder becomes too high, and there is a fear that the film formation rate decreases. On the other hand, when the oxygen component ratio z exceeds 3.8, _{the proportion of SnO 2} powder becomes too high, and there is a concern that the specific resistance increases, abnormal discharge increases, cracks during sputtering, and the like are liable to occur. Therefore, in the present embodiment, the oxygen component ratio z is in the range of 2.1 or more and 3.8 or less. Moreover, although it is more preferable to make the component ratio z of oxygen into 2.7 or more and 3.6 or less, it is not limited to this.

In addition, in the sputtering target of this embodiment, the variation with respect to the average of the specific resistance in the thickness direction of the said sintered body was made into 50% or less. The reason for this limitation is that when this variation exceeds 50%, stable DC sputtering cannot be performed, and uniform film formation cannot be obtained. By reducing the variation of the specific resistance in the target thickness direction, DC sputtering can be stabilized until the target lifespan, and uniform film formation can be achieved. Moreover, target cracking at the time of sputtering can be suppressed. Further, it is more preferable that the variation of the specific resistance in the thickness direction of the sintered body with respect to the average is 30% or less.

Here, in the sputtering target of the present embodiment, when the density ratio is set to 90% or more, cracks are less likely to occur during sputtering, and the film formation speed can be improved. In addition, in order to reliably succeed in this effect, the density ratio is preferably set to 95% or more.

In addition, in the sputtering target of the present embodiment, when the transverse strength is 100 N/mm 2 or more, cracks do not easily occur during sputtering, and the film formation speed can be improved. In addition, in order to reliably succeed in this action and effect, it is preferable to set the cross section strength to 130 N/mm 2 or more.

In addition, in the sputtering target of the present embodiment, when the specific resistance is set to 1 Ω·cm or less, DC sputtering can be stably performed and the film forming speed can be improved. In addition, in order to reliably succeed in this effect, the specific resistance is preferably 0.1 Ω·cm or less.

In addition, in the manufacturing method of the present embodiment, DC sputtering is possible, a target specific resistance suitable for film formation such as a semiconductor film or a protective film for a metal thin film is obtained, and ZTO sputtering in which the variation in specific resistance related to the target thickness direction is reduced. It aims to get a target. In addition, the manufacturing method of this embodiment includes a heat treatment step of drying and granulating a mixture of a predetermined amount of zinc oxide (ZnO) powder and tin oxide (SnO ₂ ) powder, followed by heating in a reducing atmosphere, and the heat-treated mixture. It has a sintering step in which a sintered body is obtained by pressure sintering in a non-oxidizing atmosphere, and in the heat treatment step, the oxygen vacancies of ZnO are increased. In addition, the defect coefficient α indicating the oxygen vacancies varies depending on the temperature and treatment time of the reduction treatment in the heat treatment step, and increases as the temperature increases and the time increases.

In the heat treatment step, _{the mixture obtained by mixing ZnO powder and SnO 2} powder so as to satisfy the condition of x + y = 2 in the composition of the _{formula: Zn x} Sn _y O _z , and mixing with a wet ball mill or bead mill After drying and granulating, it is put into a carbon crucible and heat treatment is performed in a vacuum. Oxygen vacancies are promoted by this heat treatment, and the range of the oxygen (O) deficit coefficient α = 0.002 to 0.03 can be realized. In the following sintering process, the obtained mixture was subjected to conditions of 800 to 980°C, 2 to 9 hours, and 9.8 to 49 MPa (100 to 500 kgf/cm 2 ), specifically, for example, 900°C, 3 hours, 29.4 Pressurization sintering is performed under the conditions of MPa (300 kgf/cm 2) to obtain a ZnSn oxide (ZTO) sintered body. In the sintered compact obtained in this sintering step, even after sintering, the oxygen vacancies remain in the entire thickness direction. Then, the sintered body is naturally cooled, taken out from the furnace, the sintered body is machined, and a backing plate is bonded to produce a ZTO sputtering target. As a result, it is possible to reduce the variation of the specific resistance in the target thickness direction, and DC sputtering can be stably performed until the target life.

In addition, in the above description, a case in which the heat treatment process and the sintering process are manufactured using separate heating furnaces has been described, but the heat treatment process and the sintering process may be successively performed using the same heating furnace. For example, a carbon mold may be filled with powder after granulation, heated to 900°C in a vacuum, and then subjected to sintering by hot pressing by directly applying a press pressure of 29.4 MPa (300 kgf/cm 2) for 3 hours. do. Here, the increase of the oxygen deficiency state is promoted by heating in the previous step of applying the press pressure, and as a result of this increase in the oxygen deficiency state, sintering proceeds, so that the oxygen deficiency state remains in the entire thickness direction even after sintering. As a result, the same sintered body as in the case of using a separate heating furnace is obtained.

Next, a sputtering target according to an embodiment of the present invention and a method for producing the same will be specifically described below by way of examples.

[Example]

First, a zinc oxide (ZnO) powder having a purity of 4N and an average particle diameter: D ₅₀ = 1.0 µm, and a tin oxide (SnO ₂ ) powder having a purity of 4N and an average particle diameter: D ₅₀ = 15 µm were prepared. Each of these powders was weighed so as to obtain the composition shown in Table 1. Each of the weighed raw material powders and zirconia balls (diameter 5 mm and 10 mm in the same weight) of three times (weight ratio) were placed in a poly container, and wet-mixed with a ball mill device for 24 hours to obtain a mixed powder. In addition, alcohol is used as a solvent at this time, for example. Further, instead of the above-described zirconia balls, zirconia beads (diameter 0.5 mm) may be used and mixed with a bead mill device to obtain a mixed powder.

After drying the slurry obtained by this ball mill mixing (or bead mill mixing), it was granulated and charged into a heating furnace. Here, heating was started and the process shifted to the heat treatment process. In this heat treatment step, the temperature is raised to 800° C. in a vacuum, and an increase in oxygen vacancies is promoted. Subsequently, the temperature of the heating furnace was further increased to shift to the sintering process. In Examples 1-7, a press pressure of 29.4 MPa (300 kgf/cm 2) was applied at a temperature of 900°C for 3 hours, and sintering was performed by hot pressing. In Example 8, a press pressure of 34.3 MPa (350 kgf/cm 2) was applied at a temperature of 930°C for 3 hours to perform sintering by hot pressing. In Example 9, a press pressure of 34.3 MPa (350 kgf/cm 2) was applied at 900°C for 3 hours, and sintering was performed by hot pressing. In Example 10, a press pressure of 29.4 MPa (300 kgf/cm 2) was applied at a temperature of 850°C for 3 hours to perform sintering by hot pressing. In addition, the sintering process was performed in a vacuum.

After the sintering process was completed, the obtained sintered body was taken out from the heating furnace, and the sintered body was machined to prepare ZTO sputtering targets of Examples 1 to 10 having a diameter of 125 mm.

[Comparative Example]

In order to compare with the ZTO sputtering target of the above example, the ZTO sputtering targets of Comparative Examples 1 to 4 shown in Table 1 were prepared. The hot press conditions were the same as in Example 1. In all of Comparative Examples 1 to 4, as in the case of each example, a _{mixed powder was obtained by mixing ZnO powder and SnO 2} powder, but in Comparative Example 1, a large number of SnO ₂ powders were blended, and the oxygen component ratio z was 3.8. Exceeded. In Comparative Example 2, many ZnO powders were blended, and the oxygen component ratio z was less than 2.1. Further, in Comparative Examples 3 and 4, _{the blending of ZnO powder and SnO 2} powder was the same as in Examples 3 and 6 to 10, but in Comparative Examples 3 and 4, the defect coefficient α indicating the oxygen deficiency state was within the range of this embodiment. Was deviating.

<Defect coefficient α>

Here, the defect coefficient α of the ZnSn oxide constituting the ZTO sputtering targets of the obtained Examples and Comparative Examples was calculated in the following procedure.

(Procedure 1) The ZnSn oxide powder obtained by pulverizing the target was heated at 100°C for 1 hour and dried.

(Step 2) 1 g of the dried ZnSn oxide powder was weighed, heat-treated beforehand, and placed in a constant weight crucible. Here, the weight of the dried ZnSn oxide powder is a and the weight of the crucible is b.

(Procedure 3) After heating at 800°C for 2 hours in an electric furnace, and standing to cool in a desiccator for 30 to 60 minutes, it was precisely weighed. This was repeated until a constant weight was reached. The weight of the ZnSn oxide powder and the crucible after heat treatment is taken as c.

(Step 4) The oxygen deficiency coefficient α was calculated according to the following calculation formula. In addition, the atomic weight of oxygen is [O], the atomic weight of Zn is [Zn], and the atomic weight of Sn is [Sn].

Steps 1 to 4 were repeated 3 times, and the average value of the obtained defect coefficient α is shown in Table 1.

<Measurement of specific resistance>

About the obtained ZTO sputtering targets of Examples and Comparative Examples, specific resistance was measured with a resistance measuring device.

Here, a ZTO sputtering target having a diameter of 125 mm x 10 mm in thickness was prepared by the above-described manufacturing method, and cut from the surface (0 mm) to 2 mm and 5 mm in the depth direction (thickness direction of the target) before the erosion, and therein The specific resistance was measured. In addition, the variation in the specific resistance in the thickness direction was expressed as a percentage of the coefficient of variation. In addition, the coefficient of variation was obtained by dividing the standard deviation of the specific resistance in the target thickness direction by the average value of the specific resistance in the target thickness direction.

In addition, at the surface (0 mm) of the ZTO sputtering target of Examples and Comparative Examples, and at positions 2 mm and 5 mm from the surface (0 mm), five points in the target sputtering surface shown in Fig. 1 (A to E) The specific resistance was measured for the measurement point of. Table 2 shows the average value of the measured specific resistance in the plane. In addition, the measurement points A to E are A (X = 0 mm, Y = 55 mm), B (X = -55 mm, Y = 0 mm), C on the XY coordinate with the center of the sputtering surface as the origin. (X = 0 mm, Y = 0 mm), D (X = 55 mm, Y = 0 mm), E (X = 0 mm, Y = -55 mm).

In this measurement, a low resistivity meter (Loresta-GP) manufactured by Mitsubishi Chemical Co., Ltd. was used as a resistance measuring device, and specific resistance (Ω·cm) was measured by a four-probe method. The temperature at the time of measurement was 23±5°C, and the humidity was 50±20%.

<Density ratio>

The density ratio was calculated|required for the ZTO sputtering target of the obtained Example and the comparative example.

After the sintered body was machined to a predetermined size, the weight was measured to obtain the bulk density, and then the density ratio was calculated by dividing by the _{theoretical density ρ fn.} In addition, the theoretical density ρ _fn was calculated by the following formula based on the weight of a raw material. Further, the density of _{SnO 2 is ρ 1} , the mass% of _{SnO 2 is C 1} , the density of ZnO is ρ ₂ , and the mass% of ZnO is C ₂ .

<Sectional strength>

By the same method as the ZTO sputtering targets of the Examples and Comparative Examples shown in Table 1, test pieces (3 mm × 4 mm × 35 mm) corresponding to each composition were prepared, and using an autograph AG-X manufactured by Shimadzu Corporation. , The stress curve was measured at an indentation speed of 0.5 mm/min, and the maximum point stress in the elastic region was determined, and this was taken as the modulus strength.

Next, with respect to the obtained ZTO sputtering targets of Examples and Comparative Examples, the number of occurrences of abnormal discharge at the time of sputtering, the film formation rate, and the presence or absence of target cracks at the time of sputtering were measured.

<Number of abnormal discharges>

With respect to the obtained ZTO sputtering targets of Examples and Comparative Examples, the number of occurrences of abnormal discharge during sputtering was measured in the following procedure.

Using the ZTO sputtering targets of Examples and Comparative Examples, a film formation test was performed under the following film formation conditions.

Power: DC 800 W/DC 1200 W 2 conditions

Voltage: 0.4 Pa

Sputtering gas: Ar = 28.5 sccm, O ₂ = 1.5 sccm

·Target-substrate (TS) distance: 70 ㎜

In the above film forming conditions, sputtering was performed for 1 hour, and the number of occurrences of micro-arc abnormal discharge was automatically measured with an arcing counter attached to the sputtering power supply device. Table 3 shows the measurement results.

<Measurement of film formation speed>

In the measurement of the film formation rate, sputtering was performed for 100 seconds under the film formation conditions described above, a target material was deposited on a masked glass substrate, and the height of the step generated after removing the masking was measured using a step gauge, and film formation. The speed was calculated. Table 3 shows the measurement results.

<Observation of target crack>

After measuring the number of occurrences of the above-described abnormal discharge, the target surface was visually observed, and the presence or absence of cracks was confirmed. Table 3 shows the observation results. In Table 3, the case where the target crack was confirmed was indicated as "Yes", and the case where the target crack was not confirmed was indicated as "None", respectively.

According to the results shown in each of the above tables, in any of the ZTO sputtering targets of the examples, the defect coefficient α is in the range of 0.002 to 0.03, and the resistance can be reduced over the entire target thickness direction, and the target thickness It was found that there was little deviation in direction. In addition, even in sputtering using the ZTO sputtering target of such an example, the occurrence of abnormal discharge can be significantly reduced, and no target crack was observed under the conditions of DC 800 W. Therefore, since the target specific resistance could be lowered all over the target thickness direction, stable DC sputtering was always possible, the film formation speed was improved, and a uniform film could be formed.

Further, in Example 10 in which the density ratio was 87% and the breaking strength was 89 N/mm 2, no target crack was observed under the conditions of DC 800 W, but the target crack was recognized under the conditions of DC 1200 W. Moreover, the number of abnormal discharges is slightly increased.

In contrast, in Example 8 in which the density ratio was 97% and the breaking strength was 141 N/mm2, and Example 9 in which the density ratio was 95% and the breaking strength was 130 N/mm2, even under the conditions of DC 1200 W. It was confirmed that no target crack was observed, and the number of occurrences of abnormal discharge was also suppressed.

On the other hand, in both the ZTO sputtering targets of the comparative examples, as in the examples, mixed powders were obtained by mixing _{ZnO powder and SnO 2 powder.} In Comparative Example 1, a _{large amount of SnO 2} powder was blended, and since the oxygen component ratio z exceeded 3.8, the specific resistance was high, the number of abnormal discharges was also large, and cracks were confirmed during sputtering, so that the film formation was performed. Couldn't. In Comparative Example 2, a large amount of ZnO powder was blended, and since the oxygen component ratio z was less than 2.1, the film formation rate was not improved. In Comparative Examples 3 and 4, the defect coefficient α representing the oxygen defect state deviated from the range of 0.002 to 0.03, and in Comparative Example 3, since the defect coefficient α was too small, the conductivity was small, and the specific resistance in the target thickness direction was within the measurement range. It was too high to the outside, and DC sputtering could not be performed, and in Comparative Example 4, since the defect coefficient α was too high, there was elution of the metal (Sn) in the sputtering target, and sputtering could not be performed.

As described above, according to the present invention, the specific resistance is lowered throughout the thickness direction of the ZTO sputtering target, and variations in specific resistance can also be reduced. Such an effect is the same even if the target shape is flat (flat plate shape) or cylinder. In addition, in the heat treatment step of the present invention, a reducing atmosphere is obtained by carrying out in a vacuum using a carbon crucible, but a reducing gas such as _{CO, SO 2} or H _{2 may be used.} Moreover, although the sintering process in Examples and Comparative Examples is performed in a vacuum, the same effect is obtained if it is a non-oxidizing atmosphere.

Industrial applicability

According to the sputtering target of the present invention, it is possible to stably form a semiconductor film, a protective film for a metal thin film, or the like by direct current (DC) sputtering until the life of the target. Further, according to the method for producing a sputtering target of the present invention, a sputtering target capable of stably forming a semiconductor film, a protective film for a metal thin film, or the like through direct current (DC) sputtering for the life of the target can be produced.

Claims (6)

Chemical formula: Zn _x Sn _y O _z (however, x + y = 2, and z = x + 2y-α (x + 2y)) has a composition, a defect coefficient α = 0.002 to 0.03, and a component ratio of oxygen z = 2.1 A sintered body made of ZnSn oxide satisfying the conditions of -3.8,
The deviation from the average of the specific resistance in the thickness direction of the sintered body is 50% or less,
The sintered body is a sputtering target in an oxygen-deficient state in the entire thickness direction to the inside. The method of claim 1,
A sputtering target having a density ratio of 90% or more. The method of claim 1,
A sputtering target having a breaking strength of 100 N/mm2 or more. The method of claim 1,
A sputtering target with a specific resistance of 1 Ω·cm or less. As a method for producing the sputtering target according to any one of claims 1 to 4,
A heat treatment step of drying and granulating a mixture of a predetermined amount of zinc oxide powder and tin oxide powder, followed by heating in a reducing atmosphere; and
It has a sintering step of obtaining a sintered body by pressing the heat-treated mixture for 2 to 9 hours in a non-oxidizing atmosphere,
In the heat treatment process, oxygen vacancies are increased,
The method of manufacturing a sputtering target in which the sintered body is in an oxygen-deficient state in the entire thickness direction to the inside. The method of claim 5,
The heat treatment step and the sintering step are performed continuously in a heating furnace.

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