JP2015052165A - Sputtering target and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering target including ZnSn oxide, which allows depositing a protection film for a semiconductor film or a metal film using DC sputtering until an end of a target life, and a manufacturing method of the target.SOLUTION: A sputtering target according to the invention includes a sintered body consisting of ZnSn oxide which has a composition of a chemical formula:ZnSnO(where x+y=2 and z=x+2y-α(x+2y)) and satisfies conditions of a defect coefficient α=0.002 - 0.03 and oxygen component ratio z=2.1 - 3.8. Variation in specific resistance to a specific resistance average in a thickness direction of the sintered body is 50% or less.

Description

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

It has been proposed to use a mixture of zinc oxide (ZnO) and tin oxide (SnO ₂ ) (ZnSn oxide: ZTO) as a material for conductive and transparent electrodes in liquid crystal displays and solar cells. ing. Furthermore, since both ZnO and SnO ₂ are semiconductors, ZTO can be used not only as a transparent electrode but also as an oxide semiconductor (see, for example, 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, which is formed on an organic film, for example, for a thin film transistor (TFT). It can be used as a material. In this case, unlike the transparent electrode described above, the conductivity of the sputtering target does not increase. Therefore, film formation is often performed by radio frequency (RF) sputtering rather than direct current (DC) sputtering.

Further, the Zn ₂ SnO ₄ thin film is transparent and has a high refractive index characteristic. Therefore, the Zn ₂ SnO ₄ thin film 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, or a Cu thin film. Yes. In order to obtain good far-infrared reflection performance while ensuring high transmittance, for example, a Zn ₂ SnO ₄ thin film is laminated as a transparent high refractive index film on an Ag thin film. A sputtering method is also employed for this lamination formation.

As described above, since Zn ₂ SnO ₄ itself has a high resistance, the sputtering target made of Zn ₂ SnO ₄ does not have a conductivity enough to enable DC sputtering. In order to form a Zn ₂ SnO ₄ thin film using this sputtering target, the RF sputtering method must be employed, and the deposition rate is also slow. Therefore, in order to reduce the resistance in the sputtering target for forming the Zn ₂ SnO ₄ thin film, the resistance of the sputtering target is lowered by using ZnSnO ₃ as a main phase or adding a dopant, It has been proposed to enable DC sputtering (see, for example, Patent Documents 2 to 4).

JP 2010-037161 A JP 2007-277075 A JP 2007-314364 A JP 2012-121791 A

As described above, in the ZTO sputtering target mainly composed of ZnSnO ₃ proposed in Patent Documents 2 and 3, even if the target specific resistance can be lowered, the film formed by sputtering using this ZTO sputtering target. Has a high carrier concentration and low resistance, and is not suitable as a semiconductor film.

On the other hand, it has been proposed to realize a low resistance by treating a sputtering target containing Zn ₂ SnO ₄ under a reducing atmosphere to promote an increase in oxygen vacancies in the ZnSn oxide. However, according to this method, the number of processing steps increases, so that productivity is poor. Furthermore, even if a high-density sputtering target is reduced, an increase in oxygen vacancies is promoted at the target surface portion, but the reduction does not proceed toward the inside of the target, and the reduction state is achieved in the target thickness direction. Because of the change, an increase in oxygen vacancies at the center of the target cannot be expected.

  For example, when an attempt is made to produce a ZTO sputtering target that exceeds the size of 100 mm in diameter and 10 mm in thickness, the target surface portion is sufficiently reduced, but as the process proceeds into the target, a phase with an insufficient reduction effect remains. Resulting in. Therefore, the specific resistance varies in the thickness direction of the sputtering target. When sputtering is performed with this sputtering target, the surface portion has a low specific resistance, and DC sputtering is possible. However, as sputtering progresses, the part with high specific resistance is exposed on the surface as the inside of the target is dug, so abnormal discharge occurs frequently, and sputtering cannot be performed stably, and the film formation rate also changes. As a result, DC sputtering cannot be performed stably, and a uniform film cannot be formed.

Further, ZTO sputtering target disclosed in Patent Document 3, but in which the ZnSnO ₃ as a main phase, which contain SnO ₂ phase. When this SnO ₂ phase is present in the sputtering target, there is a problem that in sputtering film formation using DC sputtering, abnormal discharge and particles are generated, and the target itself is easily broken.

  Therefore, the present invention promotes an increase in oxygen vacancies uniformly and sufficiently over the thickness direction (erosion depth direction) of the ZnSn oxide (ZTO) sputtering target and reduces the reduction reaction during sintering. The target specific resistance is further reduced throughout the thickness direction, stable DC sputtering is always possible up to the target life, and it is difficult to break even during sputtering, and film formation of semiconductor films, protective films for metal thin films, etc. It is an object of the present invention to provide a sputtering target composed of a ZnSn oxide and a method for producing the same.

In the above-described ZnSn oxide (ZTO) sputtering target, the target specific resistance is low at the target surface, and increases as it goes into the target. As a method for making the change uniform, a mixture of a predetermined amount of zinc oxide (ZnO) powder and tin oxide (SnO ₂ ) powder is dried, granulated, and heat-treated in a reducing atmosphere. The knowledge that pressure sintering should be performed in a non-oxidizing atmosphere 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, so that the target specific resistance is reduced in the entire region in the target thickness direction, and As a result of accelerating the movement of oxygen atoms during sintering, it was found that the density of the sintered body was improved, and a ZTO sputtering target capable of always performing stable DC sputtering was obtained.

Therefore, a mixture obtained by mixing a commercially available zinc oxide powder (ZnO powder) and tin oxide powder (SnO ₂ powder) in a wet ball mill or bead mill with a 1: 1 atomic ratio of Zn and Sn. After being dried and granulated, it was put into a carbon crucible and subjected to heat treatment at 800 ° C. for 3 hours in a vacuum. Thereafter, the obtained powder was pulverized and subjected to pressure sintering under conditions of 29.4 MPa (300 kgf / cm ² ) at 900 ° C. for 3 hours to obtain a ZnSn oxide (ZTO) sintered body. When this ZTO sintered body was machined into a predetermined shape to produce a ZTO sputtering target, it was confirmed that the target specific resistance could be further reduced over the entire region in the thickness direction of the target. It was confirmed that stable DC sputtering was always possible in forming a ZTO film using this ZTO sputtering target.

  This is because the heat treatment is performed in a reducing atmosphere at the stage of the mixture before pressure sintering, so that the ZTO sintered body is subjected to pressure reduction and subjected to sufficient reduction throughout the mixture. As a result, it was found that the oxygen deficient state was able to contribute to the further reduction of the target specific resistance throughout the entire thickness direction.

Therefore, the present invention has been obtained from the above findings, and the following configuration has been adopted in order to solve the above problems.
(1) The sputtering target of the present invention has a composition of the chemical formula: Zn _x Sn _y O _z (where x + y = 2 and z = x + 2y−α (x + 2y)), and a defect coefficient α = 0.002. 0.03 and a sintered body made of a ZnSn oxide satisfying the condition of oxygen component ratio z = 2.1 to 3.8, the variation of the specific resistance in the thickness direction of the sintered body being 50 % Or less.
(2) The sputtering target of (1) is characterized in that the density ratio is 90% or more.
(3) The sputtering target according to (1) or (2) is characterized in that the bending strength is 100 N / mm ² or more.
(4) The sputtering target according to (1) to (3) is characterized in that the specific resistance is 1 Ω · cm or less.
(5) The present invention is a method for producing the sputtering target according to (1) to (4) above, in which a mixture of a predetermined amount of zinc oxide powder and tin oxide powder is dried to produce. A heat treatment step of heating in a reducing atmosphere after graining, and a sintering step of obtaining a sintered body by pressure-sintering the heat-treated mixture in a non-oxidizing atmosphere, the heat treatment In the process, the oxygen deficiency state is increased.
(6) The manufacturing method of (5) is characterized in that the heat treatment step and the sintering step are continuously performed in a heating furnace.

The sputtering target of the present invention is composed of a sintered body made of a ZnSn oxide having a composition of the chemical formula: Zn _x Sn _y O _z , and the components of zinc (Zn) and tin (Sn) are x + y = 2. On the condition of satisfying, the component ratio of Zn and Sn is set to be within the target ZnSn oxide film range. Furthermore, since Zn ₂ SnO ₄ itself has a high specific resistance, ZnSn oxide (Zn ₂ SnO ₄ ) is brought into an oxygen deficient state to reduce the target specific resistance. The component ratio z of oxygen (O) in this oxygen-deficient ZnSn oxide is preferably set to z = 2.1 to 3.8.

Here, if a defect factor indicating that an increase in oxygen deficiency state is promoted and alpha, the chemical formula of ZnSn oxide oxygen defect condition has increased: Zn _x Sn _y O _z component ratio z of oxygen in the, z = x + 2y−α (x + 2y). This is because ZnO powder and SnO ₂ powder are blended so that the condition of x + y = 2 is satisfied, and the mixture is heat treated to adjust the deficiency coefficient α in the mixture, and the component ratio of oxygen Changes. If the mixture in which the deficiency coefficient α is adjusted is hot-pressed in a non-oxidizing atmosphere, a sintered body made of ZnSn oxide having an increased oxygen deficiency state can be obtained. Note that the oxygen component ratio z = 2.1 to 3.8 was achieved in the range of the defect coefficient α = 0.002 to 0.03.

In the sputtering target of the present invention, the defect coefficient α is in the range of 0.002 to 0.03. However, when the defect coefficient α exceeds 0.03, a part of tin oxide (SnO ₂ ) in the structure is reduced. This is because metal tin (Sn) may be eluted. If this Sn is eluted, Sn will adhere to the furnace during production, causing damage to the furnace, leading to a decrease in productivity due to cleaning in the furnace, and sputtering due to the eluted Sn. The compositional variation of the target becomes a problem. On the other hand, if the deficiency coefficient α is less than 0.002, the target specific resistance does not decrease, so that it is difficult to perform DC sputtering. Therefore, in the present invention, the defect coefficient α is set in the range of 0.002 to 0.03.
On the other hand, if the oxygen component ratio z is less than 2.1, the ratio of ZnO powder becomes too high, and the film formation rate may decrease. On the other hand, if the oxygen component ratio z exceeds 3.8, the ratio of the SnO ₂ powder becomes too high, and there is a risk that the specific resistance increases, abnormal discharge increases, cracks during sputtering, and the like are likely to occur. Therefore, in the present invention, the oxygen component ratio z is set in the range of 2.1 to 3.8.

  Furthermore, in the sputtering target of the present invention, the variation with respect to the average specific resistance in the thickness direction of the sintered body was set to 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 in specific resistance in the target thickness direction, DC sputtering can be stabilized and uniform film formation can be achieved until the target lifetime. Furthermore, target cracking during sputtering can be suppressed.

  Here, in the sputtering target of the present invention, when the density ratio is 90% or more, cracking hardly occurs during sputtering, and the film formation rate can be improved. In order to ensure that this effect is achieved, the density ratio is preferably 95% or more.

Further, in the sputtering target of the present invention, when the bending strength is 100 N / mm ² or more, cracks are hardly generated at the time of sputtering, and the film formation rate can be improved. In addition, in order to ensure that this effect is achieved, the bending strength is preferably 130 N / mm ² or more.

  Furthermore, in the sputtering target of the present invention, when the specific resistance is 1 Ω · cm or less, DC sputtering can be performed stably, and the film formation rate can be improved. In order to ensure the effect of this action, the specific resistance is preferably 0.1 Ω · cm or less.

In addition, the manufacturing method of the present invention can perform DC sputtering, and can obtain a target specific resistance suitable for forming a semiconductor film, a protective film for a metal thin film, and the like, and also has a specific resistance in the target thickness direction. For the purpose of obtaining a ZTO sputtering target with less variation in size, a mixture of a predetermined amount of zinc oxide (ZnO) powder and tin oxide (SnO ₂ ) powder is dried, granulated, and heated in a reducing atmosphere And a sintering step of obtaining a sintered body by pressure-sintering the heat-treated mixture in a non-oxidizing atmosphere, and in the heat treatment step, an oxygen deficiency of ZnO The state is increased. Note that the deficiency coefficient α representing the oxygen deficient state varies depending on the temperature and 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, ZnO powder and SnO ₂ powder are blended so as to satisfy the condition of x + y = 2 in the composition of the chemical formula: Zn _x Sn _y O _z and mixed by a wet ball mill or bead mill. After drying and granulating the body, it is put into a carbon crucible and subjected to heat treatment in a vacuum. Oxygen deficiency is promoted by this heat treatment, and a range of oxygen (O) deficiency coefficient α = 0.002 to 0.03 can be realized. In the next sintering step, the obtained mixture is subjected to 800 to 980 ° C., 2 to 9 hours, 9.8 to 49 MPa (100 to 500 kgf / cm ² ), for example, 900 ° C., 3 hours, 29.4 MPa ( A ZnSn oxide (ZTO) sintered body is obtained by pressure sintering under conditions of 300 kgf / cm ² . In the sintered body obtained in this sintering step, an oxygen deficient state remains throughout the entire thickness direction even after sintering. And it cools naturally, it takes out from a furnace, the sintered compact is machined, a backing plate is adhere | attached, and a ZTO sputtering target is produced. Therefore, variation in specific resistance in the target thickness direction can be reduced, and DC sputtering can be stably performed until the target lifetime.

In the above, the case where the heat treatment step and the sintering step are manufactured using separate heating furnaces has been described. However, the heat treatment step and the sintering step are continuously performed using the same heating furnace. You can also. For example, a carbon mold is filled with the granulated powder, heated to 900 ° C. in a vacuum, and then subjected to a hot press at a press pressure of 29.4 MPa (300 kgf / cm ² ) for 3 hours. You may make it perform sintering by. Here, the increase in the oxygen deficient state is promoted by the heating before the press pressure is applied, and the sintering proceeds when the oxygen deficient state is increased. The oxygen deficient state remains in the entire region, and a sintered body similar to that obtained when using a separate heating furnace is obtained.

  As described above, according to the present invention, the sintered body of the ZnSn oxide (ZTO) sputtering target remains in the oxygen deficient state, and the oxygen deficient state increases in the entire area inside the sintered body. Therefore, the specific resistance is low enough to enable DC sputtering in the entire target thickness direction (erosion depth direction), and the specific resistance variation in the target thickness direction is small. Further, DC sputtering can be stably performed until the target lifetime, and further, target cracking during sputtering can be suppressed, and uniform film formation can be realized.

  Further, according to the production method of the present invention, a predetermined amount of a mixture of zinc oxide powder and tin oxide powder is dried, granulated, and then heated in a reducing atmosphere, and the heat-treated mixture And a sintering step of obtaining a sintered body by pressure-sintering the body in a non-oxidizing atmosphere, and in the heat treatment step, an increase in an oxygen deficient state is promoted, and the sintering In the process, sintering is performed with the oxygen deficient state remaining. For this reason, the state is the same as when the reduction has proceeded to the inside of the sintered body, and the oxygen deficient state is uniformly increased throughout the interior 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 and a small variation in specific resistance over the entire region in the target thickness direction.

  Therefore, according to the sputtering target of the present invention, the target specific resistance is low throughout the thickness direction and is uniform in the target surface, so that stable DC sputtering is always possible, which improves productivity. Contribute.

It is a figure explaining the specific resistance measurement of the sputtering surface direction of a sputtering target.

  Next, the sputtering target and the manufacturing method thereof according to the present invention will be specifically described below with reference to 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 have the composition shown in Table 1. Each of the weighed raw material powders and three times the weight (weight ratio) of zirconia balls (diameters 5 mm and 10 mm are the same weight) are placed in a plastic container and wet-mixed for 24 hours in a ball mill device to obtain a mixed powder . In addition, alcohol is used for the solvent in this case, for example. In addition, instead of the above-mentioned zirconia balls, zirconia beads (diameter 0.5 mm) may be used and mixed by a bead mill apparatus to obtain a mixed powder.

The slurry obtained by this ball mill mixing (or bead mill mixing) was dried, granulated, and charged into a heating furnace. Here, heating was started and the heat treatment process was started. In this heat treatment step, the temperature is raised to 800 ° C. in a vacuum, and the increase in the oxygen deficiency state is promoted. Next, the temperature of the heating furnace was further increased, and the process shifted to the sintering step. In Examples 1 to 7, sintering was performed by hot pressing at a temperature of 900 ° C. and a press pressure of 29.4 MPa (300 kgf / cm ² ) over 3 hours. In Example 8, sintering was performed by hot pressing at a temperature of 930 ° C. and a pressing pressure of 34.3 MPa (350 kgf / cm ² ) over 3 hours. In Example 9, sintering was performed by hot pressing at a temperature of 900 ° C. and a press pressure of 34.3 MPa (350 kgf / cm ² ) for 3 hours. In Example 10, sintering was performed by hot pressing at a temperature of 850 ° C. and a press pressure of 29.4 MPa (300 kgf / cm ² ) for 3 hours. The sintering process was performed in a vacuum.
After finishing the sintering process, the sintered body was taken out from the heating furnace, and the sintered body was machined to produce 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 said Example, the ZTO sputtering target of Comparative Examples 1-4 shown by Table 1 was prepared. The conditions for hot pressing are the same as in Example 1. Each of Comparative Examples 1 to 4 is a case of mixing ZnO powder and SnO ₂ powder as in the case of each Example, but in Comparative Example 1, a large amount of SnO ₂ powder is blended, and the component ratio of oxygen z is over 3.8. In Comparative Example 2, a large amount of ZnO powder is blended, and the oxygen component ratio z is less than 2.1. In Comparative Examples 3 and 4, the composition of the ZnO powder and SnO ₂ powder is the same as in Examples 3 and 6 to 10, but both Comparative Examples 3 and 4 are deficient in an oxygen deficient state. This is a case where the coefficient α deviates from the scope of the present invention.

手順１〜手順４を３回繰り返して行い、得られた欠損係数αの平均値を表１に示す。 <Defect coefficient α>
Here, the defect coefficient α of the ZnSn oxide composing the obtained ZTO sputtering target of Examples and Comparative Examples was calculated by the following procedure.
(Procedure 1) ZnSn oxide powder obtained by pulverizing the target is heated at 100 ° C. for 1 hour and dried.
(Procedure 2) 1 g of dried ZnSn oxide powder is weighed and placed in a crucible that has been heat-treated in advance and constant in weight. Here, the weight of the ZnSn oxide powder after drying is a, and the weight of the crucible is b.
(Procedure 3) Heat at 800 ° C. for 2 hours in an electric furnace, cool in a desiccator for 30 to 60 minutes, and accurately weigh. This is repeated until a constant weight is reached. Let c be the weight of the ZnSn oxide powder crucible after the heat treatment.
(Procedure 4) The oxygen deficiency coefficient α is calculated according to the following calculation formula. The atomic weight of oxygen is [O], the atomic weight of Zn is [Zn], and the atomic weight of Sn is [Sn].

The procedure 1 to the procedure 4 are repeated three times, and the average value of the obtained defect coefficient α is shown in Table 1.

<Measurement of specific resistance>
About the ZTO sputtering target of the obtained Example and the comparative example, specific resistance was measured with the resistance measuring apparatus.
Here, a ZTO sputtering target having a diameter of 125 mm and a thickness of 10 mm was produced by the above-described manufacturing method, and the surface (0 mm) was shaved from 2 mm to 5 mm in the erosion depth direction, and the specific resistance was measured there. In addition, the variation in specific resistance in the thickness direction was expressed as a percentage of the coefficient of variation. The coefficient of variation was obtained by dividing the standard deviation of the target thickness direction specific resistance by the average value of the target thickness direction specific resistance.

In addition, in the position of 2 mm and 5 mm from the surface (0 mm) of the ZTO sputtering target of an Example and a comparative example, and the surface (0 mm), five places (AE) in the target sputtering surface shown in FIG. The specific resistance was measured for the points. Table 2 shows the average value of the measured in-plane specific resistance. The measurement points A to E are A (X = 0 mm, Y = 55 mm), B (X = −55 mm, Y = 0 mm), C (X = 0 mm) on the XY coordinates with the center of the sputtering surface as the origin. , Y = 0 mm), D (X = 55 mm, Y = 0 mm), and E (X = 0 mm, Y = −55 mm).
In this measurement, a specific resistance (Ω · cm) was measured by a four-probe method using a low resistivity meter (Loresta-GP) manufactured by Mitsubishi Chemical Corporation as a resistance measuring device. The measurement temperature was 23 ± 5 ° C. and the humidity was 50 ± 20%.

<Density ratio>
The density ratio was calculated | required about the obtained ZTO sputtering target of the Example and the comparative example.
After the sintered body was machined to a predetermined size, the weight density was measured to determine the bulk density, and then calculated by dividing by the theoretical density ρ _fn . The theoretical density ρ _fn was calculated by the following formula based on the weight of the raw material. Note that 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 .

<Folding strength>
Test pieces (3 mm × 4 mm × 35 mm) corresponding to the respective compositions were prepared by the same method as the ZTO sputtering targets of the examples and comparative examples shown in Table 1, and Autograph AG-X manufactured by Shimadzu Corporation was used. The stress curve was measured at an indentation speed of 0.5 mm / min to determine the maximum point stress in the elastic region.

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

<Number of abnormal discharge>
About the obtained ZTO sputtering target of an Example and a comparative example, the frequency | count of abnormal discharge generation | occurrence | production at the time of sputtering was measured in the following procedures.
Using the ZTO sputtering targets of Examples and Comparative Examples, film formation tests were performed under the following film formation conditions.
・ Power supply: 2 conditions of DC800W / DC1200W ・ Total pressure: 0.4Pa
Sputtering gas: Ar = 28.5 sccm, O ₂ = 1.5 sccm
-Target-substrate (TS) distance: 70 mm
Sputtering was performed for 1 hour under the above film forming conditions, and the number of occurrences of micro-arc abnormal discharge was automatically measured with an arcing counter attached to the sputtering power supply. The measurement results are shown in Table 3.

<Measurement of deposition rate>
The film formation speed is measured by sputtering for 100 seconds under the above film formation conditions, depositing the target material on the masked glass substrate, and removing the mask using the step meter. Measurements were made and the film formation rate was calculated. The measurement results are shown in Table 3.

<Observation of target cracks>
After measuring the number of occurrences of the abnormal discharge described above, the target surface was visually observed to check for cracks. The observation results are shown in Table 3. In Table 3, “Yes” is displayed when the target crack is confirmed, and “No” is displayed when the target crack is not confirmed.

  According to the results shown in 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 covers the entire target thickness direction. It has been found that the resistance can be reduced and there is little variation in the target thickness direction. Furthermore, even in the sputtering using the ZTO sputtering target of such an example, the occurrence of abnormal discharge can be greatly reduced, and no target crack was confirmed under the condition of DC800W. Therefore, since the target specific resistance can be lowered in the entire area in the target thickness direction, stable DC sputtering can always be performed, and uniform film formation can be obtained while improving the film formation speed.

In Example 10 in which the density ratio was 87% and the bending strength was 89 N / mm ² , target cracking was not confirmed under the condition of DC 800 W, but target cracking was observed under the condition of DC 1200 W. In addition, the number of abnormal discharges is slightly increased.
In contrast, the density ratio of 97%, bending strength carried was set to 141N / mm ² Example 8 and the density ratio of 95%, in Example 9, the transverse rupture strength is a 130N / mm ² is The target crack was not confirmed even under the condition of DC 1200 W, and it was confirmed that the number of occurrences of abnormal discharge was suppressed.

On the other hand, all of the ZTO sputtering targets of the comparative examples are cases of mixing ZnO powder and SnO ₂ powder, as in the case of the examples, but in Comparative Example 1, a lot of SnO ₂ powder is blended, Since the oxygen component ratio z exceeded 3.8, the specific resistance was high, the number of abnormal discharges was large, and cracks were confirmed during sputtering, so that film formation could not be performed. In Comparative Example 2, since a large amount of ZnO powder was blended and the oxygen component ratio z was less than 2.1, the film formation rate was not improved. In Comparative Examples 3 and 4, the deficiency coefficient α indicating the oxygen deficient state deviates from the range of 0.002 to 0.03. In Comparative Example 3, since the deficiency coefficient α is too small, the conductivity is small, and the target thickness The specific resistance in the vertical direction is too high outside the measurement range, so that DC sputtering cannot be performed. In Comparative Example 4, since the defect coefficient α is too high, elution of metal (Sn) occurs in the sputtering target, and sputtering is performed. Could not be implemented.

As described above, according to the present invention, the specific resistance is reduced in the entire area in the thickness direction of the ZTO sputtering target, and variations in the specific resistance can be reduced. Therefore, even if the target shape is flat, The same applies to a cylinder. The heat treatment step of the present invention is performed in a vacuum using a carbon crucible to form a reducing atmosphere, but a reducing gas such as CO, SO ₂ or H ₂ may be used. Moreover, although the sintering process in an Example and a comparative example is performed in the vacuum, the same effect will be acquired if it is a non-oxidizing atmosphere.

Claims (6)

Chemical formula: Zn _x Sn _y O _z (where x + y = 2 and z = x + 2y−α (x + 2y)), deficiency coefficient α = 0.002 to 0.03 and oxygen component ratio z = A sintered body made of ZnSn oxide satisfying the conditions of 2.1 to 3.8,
The sputtering target characterized in that the variation with respect to the average specific resistance in the thickness direction of the sintered body is 50% or less.   The sputtering target according to claim 1, wherein a density ratio is 90% or more. The sputtering target according to claim 1 or ^{2, wherein the} bending strength is 100 N / mm ² or more.   The specific resistance is set to 1 Ω · cm or less, and the sputtering target according to any one of claims 1 to 3. A method for producing a sputtering target according to any one of claims 1 to 4,
A heat treatment step in which a mixture of a predetermined amount of zinc oxide powder and tin oxide powder is dried and granulated, and then heated in a reducing atmosphere; and
A sintering step of obtaining a sintered body by pressure-sintering the heat-treated mixture in a non-oxidizing atmosphere, and
A method for manufacturing a sputtering target, wherein the oxygen deficiency state is increased in the heat treatment step.   The said heat treatment process and the said sintering process are performed continuously in a heating furnace, The manufacturing method of the sputtering target of Claim 5 characterized by the above-mentioned.

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