TW201525169A - Sputtering target and method of manufacturing the same - Google Patents

Abstract

A sputtering target of the present invention is a sintered compact consisting of ZnSn oxide which has a composition expressed by the chemical formula: ZnxSnyOz (x+y=2 and z=x+2y-[alpha](x+2y)), and which has a deficiency coefficient [alpha] of 0.002 to 0.03 and fraction of oxygen z of 2.1 to 3.8. The variation of the specific resistance with respect to the average thereof in the thickness direction of the sintered compact is equal to or less than 50%.

Description

Sputtering target and manufacturing method thereof

The present invention relates to a sputtering target which can be stably formed by a ZnSn oxide by a direct current (DC) sputtering, or a sputtering target such as a protective film for a metal thin film, and a method for producing the same.

The present application claims priority based on Japanese Patent Application No. 2013-163051, filed on Jan. 6, 2013, in Japan, and Japanese Patent Application No. 2014-157914, filed on Jan. In this article.

As a material for an electrode which is electrically conductive and transparent to light in a liquid crystal display or a solar cell, a mixture of zinc oxide (ZnO) or tin oxide (SnO ₂ ) (ZnSn oxide: ZTO) has been proposed. 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 (see, for example, Patent Document 1). In particular, a ZTO sputtering target can be used to form a film of a Zn ₂ SnO ₄ film having a practically mobile semiconductor at room temperature. This can be used as a material of, for example, a thin film transistor (TFT) formed on an organic film. In this case, unlike the case of the transparent electrode, in order not to increase the conductivity of the sputtering target, film formation is often performed by a higher frequency (RF) sputtering method than direct current (DC) sputtering.

Further, since the Zn ₂ SnO ₄ thin film is transparent and has a high refractive index, it is also used as a protective film of 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. In order to ensure high transmittance on the one hand and good far-infrared reflection performance on the one hand, for example, a Zn ₂ SnO ₄ film is formed on the Ag film as a transparent high refractive index film. This laminate is also formed by sputtering.

As described above, since Zn ₂ SnO ₄ itself has high resistance, the sputtering target made of Zn ₂ SnO ₄ hardly has conductivity which can be DC-sputtered. When the Zn ₂ SnO ₄ thin film is formed by using the sputtering target, the RF sputtering method cannot be used, and the film formation speed is also slow. Therefore, in order to reduce the electric resistance in the sputtering target for forming a Zn ₂ SnO ₄ film, it is proposed to use ZnSnO ₃ as a main phase or to add a dopant to reduce the resistance of the sputtering target, thereby causing DC sputtering. This is possible (see, for example, Patent Documents 2 to 4).

[Previous Technical Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-037161

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2007-277075

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2007-314364

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2012-121791

As described above, in the above-described Patent Documents 2 and ₃ , the ZTO sputtering target having ZnSnO ₃ as a main phase can reduce the specific resistance of the target, but the carrier concentration of the film formed by sputtering using the ZTO sputtering target is as described above. High, low resistance, still not suitable as a semiconductor film.

On the other hand, it has been proposed to treat a sputtering target containing Zn ₂ SnO ₄ in a reducing environment, and to promote an increase in oxygen defects in the ZnSn oxide, thereby achieving low resistance. However, due to the use of this method, the number of processing steps is increased, so productivity is poor. Further, when the high-density sputtering target is reduced and treated, the oxygen deficiency of the target surface portion is promoted, but the reduction is not performed inside the target, and the reduction state in the target thickness direction is changed, so that the target center portion cannot be predicted. Oxygen deficiency increases.

For example, when a ZTO sputtering target having a diameter of more than 100 mm and a thickness of 10 mm is produced, the surface portion of the target is sufficiently reduced, but as the inside of the target is entered, the phase having insufficient reduction effect remains. Therefore, the specific resistance in the thickness direction of the sputtering target varies. When sputtering is performed by the sputtering target, the specific resistance of the surface portion is low, and DC sputtering can be performed. However, as the sputtering progresses, when the target is recessed inside, a portion having a higher specific resistance is exposed on the surface, so that abnormal discharge occurs frequently, sputtering cannot be stably performed, and the film formation speed also changes. Thus, there is a problem that not only the DC sputtering cannot be stably performed, but also the film cannot be uniformly formed.

Further, the ZTO sputtering target disclosed in Patent Document 3 contains ZnSnO ₃ as a main phase, but contains a SnO ₂ phase. When the SnO ₂ phase is present in the sputtering target, the sputtering is performed by DC sputtering, which causes abnormal discharge or particle generation, and further, the target itself is liable to be broken.

Accordingly, it is an object of the present invention to provide a uniform and sufficient increase in oxygen deficiency in the thickness direction (corrosion depth direction) of a ZnSn oxide (ZTO) sputtering target, while promoting a reduction reaction during sintering, further reducing the thickness The target specific resistance in the direction of the target, and the DC sputtering can be stably performed until the target lifetime, and it is not easily broken during sputtering, and is formed of a ZnSn oxide which is suitable for film formation of a protective film for a semiconductor film or a metal thin film. Sputter target and its manufacturing method.

In the above-mentioned ZnSn oxide (ZTO) sputtering target, attention is paid to the fact that the specific resistance of the target is lower at the surface of the target and becomes higher as it enters the inside of the target, and the following observation is obtained: if the specific resistance can be made inside the target At the same time, as a method of changing the specific resistance, a specific amount of a mixture of zinc oxide (ZnO) powder and tin oxide (SnO ₂ ) powder is dried, and after granulation, a reducing environment is used. After the heat treatment, pressure sintering may be performed in a non-oxidizing atmosphere. In this heat treatment, reduction is promoted to the inside of the mixture, and reduction is performed throughout the entire mixture to form an oxygen-deficient state. Thereby, the target specific resistance is lowered in the entire thickness direction of the target, and the result of promoting the movement of oxygen atoms during sintering increases the density of the sintered body. As a result, it was found that a ZTO sputtering target which can stably perform DC sputtering can be obtained.

Therefore, a commercially available zinc oxide powder (ZnO powder) and a tin oxide powder (SnO ₂ powder) are blended at an atomic ratio of Zn and Sn of 1:1, and a mixture obtained by mixing with a wet ball mill or a bead mill is used. After drying, granulation, the mixture was poured into carbon crucible, and heat treatment was performed at 800 ° C for 3 hours in a vacuum. Subsequently, the obtained powder was pulverized and pressure-sintered at 900 ° C and 29.4 MPa (300 kgf / cm ² ) for 3 hours to obtain a sintered body of ZnSn oxide (ZTO). After the ZTO sintered body was machined into a shape and a ZTO sputtering target was produced, it was confirmed that the target specific resistance in the entire thickness direction of the target can be further reduced. When ZTO film formation using this ZTO sputtering target was confirmed, it was confirmed that DC sputtering was always performed stably.

This can be seen as follows: at the stage of the mixture before the pressure sintering, since the heat treatment is performed in a reducing environment, the entire body of the mixture is sufficiently reduced to allow the thickness of the ZTO sintered body to be pressure-sintered. When the direction until the entire interior becomes an oxygen defect state, it contributes to further decrease in the target specific resistance.

Therefore, the present invention has been made in view of the above findings, and the following configuration is adopted to solve the above problems.

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

(2) The sputtering target according to (1) above, wherein the density ratio is 90% or more.

(3) The sputtering target according to (1) or (2) above, wherein the bending strength is 100 N/mm ² or more.

(4) The sputtering target of (1) to (3) above, wherein the specific resistance is 1 Ω. Below cm.

(5) The present invention is a method for producing the sputtering target of the above (1) to (4), which has the following steps: after drying and granulating a mixture of a specific amount of zinc oxide powder and tin oxide powder, The heat treatment step of heating in a reducing environment is performed by press-sintering the heat-treated mixture in a non-oxidizing atmosphere to obtain a sintered body, and in the heat treatment step, the oxygen deficiency state is increased.

(6) The production method according to (5) above, wherein the heat treatment step and the sintering step are continuously performed in a heating furnace.

As described above, the sintered body of the ZnSn oxide (ZTO) sputtering target of the present invention has an oxygen deficient state remaining, and the oxygen deficiency state increases in the entire interior of the sintered body. Therefore, in the entire thickness direction of the target (the direction of the etching depth), the specific resistance is lowered to the extent that DC sputtering can be performed, and the deviation of the specific resistance in the thickness direction of the target becomes small. As a result, DC sputtering can be stably performed until the life of the target, and further, cracking of the target at the time of sputtering can be suppressed, and uniform film formation can be achieved.

Further, the production method of the present invention includes a heat treatment step of heating a mixture of a specific amount of a mixture of zinc oxide powder and tin oxide powder in a reducing environment, and a heat treatment of the mixture described above. Sintering step of obtaining a sintered body by pressure sintering in an oxidizing atmosphere Therefore, in the aforementioned heat treatment step, an increase in the oxygen deficiency state is promoted, and in the aforementioned sintering step, sintering is performed in a state in which an oxygen deficiency remains. Therefore, up to the inside of the sintered body, the reduction progresses to the same state, and the oxygen defect state uniformly increases in the entire 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 and a small specific resistance deviation in the entire thickness direction of the target.

According to the sputtering target of the present invention, since the specific resistance of the target in the entire thickness direction is low and the same in the target surface, DC sputtering can be stably performed, which contributes to improvement in productivity.

Fig. 1 is a view showing the specific resistance measurement of the direction of the sputtering surface of the sputtering target.

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

The sputtering target of the present embodiment is composed of a sintered body of a ZnSn oxide having a chemical formula of Zn _x Sn _y O _z . The components of zinc (Zn) and tin (Sn) are set to satisfy the condition of x + y = 2, and the ratio of the composition of Zn to Sn is a target ZnSn oxide film. 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. The composition ratio z of oxygen (O) in the ZnSn oxide in the oxygen-deficient state is preferably z = 2.1 to 3.8.

Here, when the defect coefficient indicating that the increase in the oxygen deficiency state is promoted is α, the chemical formula of the ZnSn oxide in which the oxygen deficiency state is increased: the oxygen component ratio z in Zn _x Sn _y O _z is expressed as z=x+2y- 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 can be adjusted, and the oxygen composition ratio can be changed. When the adjusted mixture of the defect coefficient α is thermally pressurized in a non-oxidizing atmosphere, a sintered body composed of a ZnSn oxide having an increased oxygen deficiency state can be obtained. Further, as the range of the defect coefficient α=0.002 to 0.03, the oxygen component ratio z=2.1 to 3.8 is achieved.

The sputtering target system of the present embodiment has a range of the defect coefficient α=0.002 to 0.03. When the defect coefficient α exceeds 0.03, part of the tin oxide (SnO ₂ ) in the structure is reduced, and there is a possibility that metal tin (Sn) is eluted. When the Sn is eluted, Sn adheres to the furnace during the production, which not only causes damage to the furnace, but also causes a decrease in productivity due to cleaning in the furnace, and the composition of the sputtering target is generated by the amount of Sn dissolved. The problem of deviation. On the other hand, when the defect coefficient α is less than 0.002, since the target specific resistance does not decrease, it is difficult to perform DC sputtering. Therefore, in the present embodiment, the defect coefficient α is set to be within a range of 0.002 or more and 0.03 or less. Moreover, it is more preferable to set the defect coefficient α to 0.008 or more and 0.02 or less, but it is not limited thereto.

Further, when the oxygen component ratio z is less than 2.1, the ratio of the ZnO powder becomes too high and the film formation rate is lowered. On the other hand, when the oxygen component ratio z exceeds 3.8, the ratio of the SnO ₂ powder becomes too high, and the specific resistance rises, the abnormal discharge increases, and cracking occurs during sputtering. Therefore, in the present embodiment, the oxygen component ratio z is in the range of 2.1 or more and 3.8 or less. Further, the oxygen component ratio z is preferably 2.7 or more and 3.6 or less, but is not limited thereto.

In addition, in the sputtering target of the present embodiment, the specific resistance of the sintered body in the thickness direction is set to 50% or less. The reason for this limitation is that when the deviation exceeds 50%, DC sputtering cannot be stably performed, and film formation cannot be performed uniformly. By reducing the deviation of the specific resistance in the direction of the target thickness, DC sputtering can be stabilized and a uniform film formation can be achieved until the lifetime of the target. Furthermore, the cracking of the target at the time of sputtering can be suppressed. Further, it is more preferable that the specific resistance of the sintered body in the thickness direction is 30% or less with respect to the average deviation.

Here, in the sputtering target of the present embodiment, when the density ratio is 90% or more, cracking is less likely to occur during sputtering, and the film formation speed can be increased. Further, in order to surely exhibit the effect, the density is preferably 95% or more.

Further, in the sputtering target of the present embodiment, when the bending strength is 100 N/mm ² or more, cracking is less likely to occur during sputtering, and the film formation speed can be increased. Further, in order to surely exhibit the effect, the bending strength is preferably 130 N/mm ² or more.

Further, in the sputtering target of the present embodiment, the specific resistance is set to 1 Ω. When it is less than cm, DC sputtering can be performed stably, and the film formation speed can be improved. Moreover, in order to surely exert this effect, the specific resistance is preferably 0.1 Ω. Below cm.

Further, the object of the production method of the present embodiment is to obtain a sputtering specific resistance which can be formed by a DC sputtering, a film suitable for a semiconductor film or a protective film for a metal thin film, and a specific resistance in the thickness direction of the target. Less ZTO sputtering targets. Further, the manufacturing method of the present embodiment has the following steps: a heat treatment step of heating a mixture of a specific amount of a mixture of zinc oxide (ZnO) powder and tin oxide (SnO ₂ ) powder in a reducing environment, and The heat-treated mixture is pressure-sintered in a non-oxidizing atmosphere to obtain a sintering step of the sintered body, and in the heat treatment step, the oxygen-deficient state of ZnO is increased. Further, the defect coefficient α indicating the oxygen deficiency state varies depending on the temperature of the reduction treatment in the heat treatment step and the treatment time, and the higher the temperature and the longer the time.

In the foregoing heat treatment step, the ZnO powder and the SnO ₂ powder are formulated in such a manner as to satisfy the condition of x + y = 2 in the composition of the chemical formula: Zn _x Sn _y O _z , and are mixed by a wet ball mill or a bead mill. The mixture was dried, granulated, poured into carbon crucible, and heat-treated in a vacuum. By this heat treatment, oxygen defects are promoted, and the range of the oxygen (O) defect coefficient α = 0.002 to 0.03 can be achieved. The subsequent sintering step is such that the resulting mixture is subjected to conditions of 800 to 980 ° C, 2 to 9 hours, 9.8 to 49 MPa (100 to 500 kgf / cm ² ), specifically, for example, at 900 ° C, 3 hours, and 29.4 MPa (300 kgf). The condition of /cm ² ) was pressure-sintered to obtain a sintered body of ZnSn oxide (ZTO). The sintered body obtained by this sintering step remains in a residual oxygen-deficient state in the entire thickness direction after sintering. Next, the sintered body was naturally cooled, taken out from the furnace, the sintered body was machined, and a backing plate was adhered to prepare a ZTO sputtering target. As a result, the specific resistance deviation in the direction of the thickness of the target can be reduced, and DC sputtering can be stably performed until the target life.

Further, the above description has been described with respect to the case where the heat treatment step and the sintering step are carried out using different heating furnaces, but the heat treatment step and the sintering step may be continuously performed using the same heating furnace. For example, the granulated powder may be filled in a carbon mold, heated to 900 ° C in a vacuum, and then directly pressed at 29.4 MPa (300 kgf / cm ² ) for 3 hours, and sintered by a hot plate. Here, by the heating in the stage before the application of the pressurization, the increase in the oxygen deficiency state is promoted, and the sintering is performed after the oxygen deficiency state is increased, so that the entire thickness direction remains the residual oxygen defect state after the sintering, and is obtained and used. A sintered body of the same condition as in different heating furnaces.

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

[Examples]

First, a zinc oxide (ZnO) powder having a purity of 4 N and an average particle diameter of D ₅₀ = 1.0 μm, a tin oxide (SnO ₂ ) powder having a purity of 4 N and an average particle diameter of D ₅₀ = 15 μm was prepared. Each of these powders was weighed to have the composition shown in Table 1. Each of the weighed raw material powders was fed into a plastic container with 3 times (by weight) of zirconia balls (the same weight of 5 mm and 10 mm in diameter), and wet-mixed for 24 hours in a ball mill apparatus to obtain a mixed powder. Further, in this case, for example, an alcohol is used as the solvent. Further, zirconia beads (0.5 mm in diameter) were used instead of the above zirconia balls, and they were mixed by a bead mill apparatus to obtain a mixed powder.

The slurry obtained by mixing in the ball mill (or mixed by a bead mill) is dried, granulated, and placed in a heating furnace. Heating is started here and proceeds to the heat treatment step. This heat treatment step is carried out by heating to 800 ° C in a vacuum to promote an increase in the oxygen deficiency state. Next, the temperature of the heating furnace is further increased to proceed to the sintering step. Examples 1 to 7 were subjected to a pressurization of 29.4 MPa (300 kgf/cm ² ) for 3 hours at a temperature of 900 ° C, and were sintered by hot pressurization. In Example 8, a press of 34.3 MPa (350 kgf/cm ² ) was applied at a temperature of 930 ° C for 3 hours, and sintering was performed by hot pressurization. In Example 9, a pressurization of 34.3 MPa (350 kgf/cm ² ) was applied at a temperature of 900 ° C for 3 hours, and sintering was performed by hot pressurization. In Example 10, a pressurization of 29.4 MPa (300 kgf/cm ² ) was applied at a temperature of 850 ° C for 3 hours, and sintering was performed by hot pressurization. Further, the sintering step is carried out in a vacuum.

After the sintering step 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]

The ZTO sputtering targets of Comparative Examples 1 to 4 shown in Table 1 were prepared for comparison with the ZTO sputtering targets of the above examples. The hot pressurization conditions were the same as in Example 1. Comparative Examples 1 to 4 were the same as in the respective examples, and a mixed powder was obtained by mixing ZnO powder and SnO ₂ powder, but in Comparative Example 1, a large amount of SnO ₂ powder was blended, and the oxygen component ratio z exceeded 3.8. In Comparative Example 2, a large amount of ZnO powder was blended, and the oxygen component ratio z was less than 2.1. Further, the ZnO powder and the SnO ₂ powder prepared in Comparative Examples 3 and 4 were the same as those in Examples 3 and 6 to 10. However, the defect coefficients α of the oxygen-defective state in Comparative Examples 3 and 4 were all outside the range of the present embodiment.

<Defect coefficient α>

Here, the defect coefficient α of the ZnSn oxide constituting the ZTO sputtering target of the obtained examples and the comparative examples was calculated in the following order.

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

(Sequence 2) 1 g of the dried ZnSn oxide powder was weighed and fed into a crucible which was preheated to constant weight. Here, the weight of the dried ZnSn oxide powder is a, and the weight of ruthenium is b.

(Sequence 3) The electric scale was heated at 800 ° C for 2 hours, and after being allowed to cool in the dryer for 30 to 60 minutes, the fine scale was performed. Repeat this step until you reach constant weight. The weight of the heat-treated ZnSn oxide powder and niobium was set to c.

(Sequence 4) The oxygen defect coefficient α is calculated according to the following calculation formula. Further, the amount of oxygen atoms is set to [O], the amount of Zn atoms is set to [Zn], and the atomic weight of Sn is set to [Sn].

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

<Measurement of specific resistance>

With respect to the ZTO sputtering targets of the obtained examples and comparative examples, the specific resistance was measured by a resistance measuring device.

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

Further, for the ZTO sputtering target surface (0 mm) of the examples and the comparative examples, and at a position of 2 mm and 5 mm from the surface (0 mm), the five portions in the sputtering target surface shown in Fig. 1 (A~E) The measurement point is determined by the specific resistance. The average value of the in-plane specific resistance measured is shown in Table 2. Further, in the measurement points A to E, the center of the sputtering surface is set as the XY coordinate of the origin, and is set to A (X = 0 mm, Y = 55 mm), B (X = -55 mm, Y = 0 mm), C ( 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 Corporation was used as a resistance measuring device, and a 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 determined for the ZTO sputtering targets of the obtained examples and comparative examples.

After the sintered body was machined to a specific size, the weight was measured, the bulk density was determined, and the density ratio was calculated by dividing the theoretical density ρ _fn . Further, the theoretical density ρ _fn is calculated based on the weight of the raw material by the following formula. Further, the SnO ₂ density is ρ ₁ , the SnO ₂ mass% is C ₁ , the ZnO density is ρ ₂ , and the ZnO mass % is C ₂ .

<Flexural strength>

A test piece (3 mm × 4 mm × 35 mm) corresponding to each composition was produced in the same manner as the ZTO sputtering target of the examples and the comparative examples shown in Table 1, and Autograph AG-X manufactured by Shimadzu Corporation was used at a press-in speed. The stress curve was measured at 0.5 mm/min, and the maximum point stress of the elastic region was determined, and this was used as the bending strength.

Next, with respect to the ZTO sputtering targets of the obtained 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 cracking of the target during sputtering were measured.

<Abnormal discharge times>

With respect to the ZTO sputtering targets of the obtained examples and comparative examples, the number of occurrences of abnormal discharge at the time of sputtering was measured in the following order.

Using the ZTO sputtering target of the examples and the comparative examples, a film formation test was carried out under the following film formation conditions.

. Power supply: DC800W/DC1200W 2 conditions

. Total pressure: 0.4Pa

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

. Target substrate - (TS) distance: 70mm

The sputtering was performed for 1 hour under the film formation conditions described above, and the number of occurrences of the micro-arc abnormal discharge was automatically measured by an arc counter attached to the sputtering power supply device. The results of the measurement are shown in Table 3.

<Measurement of film formation speed>

The film formation rate was measured by sputtering for 100 seconds under the film formation conditions described above, and the target was deposited on the glass substrate to be shielded, and the step height after removal of the mask was measured using a step gauge to calculate the film formation speed. The measurement results are shown in Table 3.

<Observation of target rupture>

After the number of occurrences of the abnormal discharge described above was measured, the surface of the target was visually observed to confirm the presence or absence of cracking. The observation results are shown in Table 3. In Table 3, it is confirmed that "target" is indicated when the target is broken, and "not" is indicated when the target is not broken.

According to the results shown in the above tables, it is understood that the defect coefficient α of the ZTO sputtering target of the example is in the range of 0.002 to 0.03, and the entire resistance in the thickness direction of the target can be reduced, and the variation in the thickness direction of the target is small. Further, in the sputtering using the ZTO sputtering target of the examples, the occurrence of abnormal discharge was greatly reduced, and the target crack was not confirmed under the condition of DC800W. Accordingly, since the entire thickness direction of the target can reduce the specific resistance of the target, DC sputtering can be stably performed, and the film formation speed can be improved, and a uniform film can be formed.

Further, in Example 10 in which the density ratio was 87% and the flexural strength was 89 N/mm ² , the target crack was not confirmed under the condition of DC 800 W, but the target crack was confirmed under the condition of DC 1200 W. Moreover, the number of abnormal discharges is slightly larger.

On the other hand, Example 8 having a density ratio of 97%, a flexural strength of 141 N/mm ² , and a density ratio of 95% and a flexural strength of 130 N/mm ² were not confirmed under the condition of DC1200W. When the target is broken, it is confirmed that the number of occurrences of abnormal discharge can also be suppressed.

On the other hand, in the ZTO sputtering target of the comparative example, a mixed powder was obtained by mixing ZnO powder and SnO ₂ powder as in the examples. In Comparative Example 1, a large amount of SnO ₂ powder was prepared, and the oxygen component ratio z was more than 3.8. Therefore, the specific resistance was high, and the number of abnormal discharges was also large. Further, it was confirmed that the film was broken at the time of sputtering, and film formation was impossible. In Comparative Example 2, a large amount of ZnO powder was blended, and the oxygen component ratio z was less than 2.1, so that the film formation rate was not increased. In Comparative Examples 3 and 4, the defect coefficient α of the oxygen deficiency state was outside the range of 0.002 to 0.03, and in Comparative Example 3, the defect coefficient α was too small, so that the conductivity was small, and the specific resistance in the target thickness direction was too high. Outside the range, DC sputtering could not be performed. In Comparative Example 4, since the defect coefficient α was too high, metal (Sn) was melted in the sputtering target, and sputtering could not be performed.

As described above, according to the present invention, the specific resistance of the entire thickness direction of the ZTO sputtering target is low, and the specific resistance deviation can also be reduced. These effects are the same even if the shape of the target is flat (flat) or the cylinder. Further, the heat treatment step of the present invention is carried out in a vacuum using carbon crucible, but a reducing gas such as CO, SO ₂ or H ₂ may be used. Further, the sintering steps in the examples and the comparative examples were carried out in a vacuum, but the same effect was obtained in the case of a non-oxidizing atmosphere.

[Industrial Applicability]

According to the sputtering target of the present invention, the semiconductor film or the metal thin film can be stably formed into a film by a protective film by direct current (DC) sputtering until the target lifetime. Further, according to the method for producing a sputtering target of the present invention, it is possible to manufacture a sputtering target which can stably form a semiconductor film or a metal thin film with a protective film by direct current (DC) sputtering until the target life.

Claims (6)

A sputtering target is a sintered body made of ZnSn oxide having a chemical formula: Zn _x Sn _y O _z (only, x + y = 2, and z = x + 2y - α (x + 2y) The composition of the)) satisfies the condition that the defect coefficient α=0.002 to 0.03 and the oxygen component ratio z=2.1 to 3.8, and the average deviation of the specific resistance in the thickness direction of the sintered body is 50% or less. For example, in the sputtering target of claim 1, the density ratio is 90% or more. A sputtering target according to claim 1 or 2, wherein the bending strength is 100 N/mm ² or more. A sputtering target according to any one of claims 1 to 3, wherein the specific resistance is 1 Ω. Below cm. A method for producing a sputtering target, which is a method for producing a sputtering target according to any one of claims 1 to 4, which has the following steps: a mixture of a specific amount of zinc oxide powder and tin oxide powder is passed through After drying and granulating, a heat treatment step of heating in a reducing environment, and a sintering step of subjecting the heat-treated mixture to pressure sintering in a non-oxidizing environment to obtain a sintered body, and in the aforementioned heat treatment step, oxygen deficiency The status is increased. The method for producing a sputtering target according to claim 5, wherein the heat treatment step and the sintering step are continuously performed in a heating furnace.