JP6267297B1 - Sintered body, sputtering target and manufacturing method thereof - Google Patents

Abstract

Disclosed are a sintered body, a sputtering target, and a method for manufacturing the same, which can effectively suppress variations in bulk resistance between the surface and the inside of the sintered body. The sintered body of the present invention is an oxide sintered body made of In, Zn, and O, and has a bulk resistivity Rs at a depth of 1 mm from the surface of the sintered body in the thickness direction. And the ratio of the bulk resistivity Rd at the depth position of 4 mm in the thickness direction from the surface of the sintered body divided by the bulk resistivity Rd at the depth position of 4 mm (Rs−Rd) / The absolute value of Rd is 20% or less expressed as a percentage. [Selection figure] None

Description

  The present invention relates to a sintered body made of In, Zn, O, a sputtering target for forming a transparent conductive film, which is made of the sintered body, and is sometimes referred to as a so-called IZO target, and a method for manufacturing the same. In particular, the present invention proposes a technique that can contribute to stable IZO film formation during sputtering.

  Sputtering targets are used, for example, for manufacturing liquid crystal displays (LCD), electroluminescence (EL) and other various display device electrodes mounted on personal computers, word processors, etc., electrodes for films such as touch panels and electronic paper, etc. In addition, it may be used in a sputtering method for forming a transparent conductive film made of a metal composite oxide on a film-forming substrate such as glass or plastic.

  As this type of transparent conductive film, ITO (Indium Tin Oxide) film, which is excellent in light transmissivity and conductivity, is currently the mainstream, and since this ITO film made of In, Sn, and O is produced, ITO targets are widely used. It is used.

  However, since the ITO film has a relatively low moisture resistance and has a disadvantage that the electrical resistance value increases due to moisture, the transparent conductive film is replaced with the ITO film, but IZO (InZO, Zn, O) is used. (Indium Zinc Oxide) film, and using an IZO target to produce this IZO film is under study.

By the way, in order to perform stable film formation, the sputtering target is required to have a high density and a low resistance, and it is also important that the density and resistance are uniform over the entire target.
Especially for resistance, if the variation in bulk resistivity in the thickness direction of the target is large, the film properties change during sputtering, and the sputtering target that combines multiple pieces tends to cause variation in bulk resistivity between pieces. Thus, the quality stability of the entire target is impaired. Therefore, in the sputtering target, it is necessary to ensure the uniformity of the bulk resistivity in the thickness direction. The conventional IZO target has a problem that a stable IZO film cannot be formed because the bulk resistivity variation in the thickness direction is large.

  In addition, the bulk resistivity generally tends to be higher on the surface of the sintered body than the inside of the sintered body constituting the sputtering target, and the bulk resistivity of the sintered body becomes uneven in the thickness direction. However, it is considered that the uniformity of the bulk resistivity can be secured to some extent by increasing the amount of grinding on the surface of the sintered body to produce a sputtering target. Since it is necessary to manufacture by setting the thickness of the body to be thick, there is a concern about a decrease in density at the center position in the thickness direction and a decrease in product yield due to an increase in the amount of grinding.

Regarding such a bulk resistance, Patent Document 1 discloses that after manufacturing a sputtering target containing at least indium oxide and zinc oxide, the bulk resistance of the obtained sintered body is uniform as a whole. However, it is preferable to perform a reduction treatment in the reduction step, although it is an optional step.
In Patent Document 2, it is preferable that the bulk resistivity of the high-density, low-resistance In—Sn—Zn—Al-based sputtering target is 10 mΩcm or less, and that after sintering when manufacturing such a target. In order to prevent the occurrence of cracks during cooling and to obtain a predetermined crystal form, it is described that the cooling rate is 10 ° C./min or less, further 5 ° C./min or less.

  Patent Document 3 relates to an ITO target, not an IZO target, and discloses a sputtering target in which the difference in bulk resistivity in the thickness direction of the target is 20% or less. In Patent Document 3, in order to reduce the difference in bulk resistivity in the thickness direction of the target, the atmosphere at the time of cooling is mainly an air atmosphere, and the average cooling rate is 0.1 to 3.0 ° C./min. It is described to do. Furthermore, it is shown that the difference in bulk resistivity in the sintered body is highly correlated with the difference in resistance of the thin film formed on the target.

JP 2011-68993 A JP 2014-218706 A International Publication No. 2014/156234

In Patent Document 1 described above, there is no description about reducing the variation in bulk resistivity in the thickness direction. Further, by performing reduction treatment as a separate process after sintering, the bulk resistivity is uniform. Even if the process can be realized, the introduction of such a separate process causes an increase in cost and an increase in man-hours, which is undesirable from the viewpoint of production.
Patent Document 2 mentions that it is preferable that the bulk resistivity is low, but does not discuss any variation in the bulk resistivity in the thickness direction. It is not intended to stabilize the system.

  Since Patent Document 3 relates to an ITO target, not an IZO target, the proposed technique cannot be applied to the IZO target as it is. In particular, unlike the ITO target, the IZO target has a surface-modified layer on the surface of the sintered body, and the bulk resistivity near the surface-modified layer is further increased. However, depending on the proposed technology for the temperature lowering process, the variation in the bulk resistivity could not be reduced sufficiently.

  An object of the present invention is to solve such problems of the prior art, and the purpose thereof is an IZO target, which effectively suppresses variations in bulk resistivity between the surface of the sintered body and the inside thereof. An object of the present invention is to provide a sintered body, a sputtering target, and a manufacturing method thereof.

In manufacturing an IZO target, oxygen is introduced during heating to increase the density of the sintered body and realize excellent film characteristics when the molded body formed into a predetermined shape is heated and sintered. Oxygen sintering or atmospheric sintering is preferred, but the inventors have intensively studied. As a result, oxygen deficiency in the vicinity of the surface of the sintered body decreases as a result of reducing the oxygen deficiency near the surface of the sintered body. The knowledge that the difference of the bulk resistivity in the thickness direction of the target is greatly different was obtained.
Therefore, the atmosphere at the time of temperature reduction after heating and sintering of the molded body is different from that at the time of temperature rising, and by reducing the oxygen deficiency near the surface of the sintered body by using a nitrogen atmosphere or an argon atmosphere, the thickness direction It has been found that a sputtering target having more uniform bulk characteristics can be manufactured while suppressing variation in bulk resistivity.

Based on such knowledge, the sintered body of the present invention is an oxide sintered body composed of In, Zn, and O, and contains Zn / (In + Zn) at 7 at% to 20 at%. The difference between the bulk resistivity Rs at a depth position of 1 mm in the thickness direction from the surface of the body and the bulk resistivity Rd at a depth position of 4 mm in the thickness direction from the surface of the sintered body is expressed as the depth of 4 mm. The absolute value of the ratio (Rs−Rd) / Rd divided by the bulk resistivity Rd at the position is 20% or less expressed as a percentage.

Here, the absolute value of the ratio (Rs−Rd) / Rd is preferably 15% or less, more preferably 10% or less, expressed as a percentage.
The sintered body may contain Zn / (In + Zn) , preferably at 10 at% to 17 at%.

The sputtering target of the present invention is an oxide sputtering target composed of In, Zn, and O , contains Zn / (In + Zn) at 7 at% to 20 at%, and is 0 mm in the thickness direction from the surface of the sputtering target. The difference between the bulk resistivity Rf at the depth position and the bulk resistivity Ra at the depth position of 3 mm in the thickness direction from the surface of the sputtering target is expressed as the bulk resistivity Ra at the depth position of 3 mm. The absolute value of the ratio (Rf−Ra) / Ra divided is 20% or less expressed as a percentage.

Here, the absolute value of the ratio (Rf−Ra) / Ra is preferably 15% or less, more preferably 10% or less, expressed as a percentage.
The sputtering target may contain Zn / (In + Zn) , preferably at 10 at% to 17 at%.

The method for producing a sputtering target according to the present invention includes mixing and forming a powder raw material containing indium oxide powder and zinc oxide powder, and heating and sintering the resulting molded body, and then heating and sintering the molded body. the cooling after, are performed by the under nitrogen or argon atmosphere, is to produce a sputtering target containing Zn / a (in + Zn) in 7 atomic% to 20 at%.

In this manufacturing method, the rate of temperature reduction at the time of temperature reduction is preferably a rate exceeding 1 ° C./min, more preferably a rate exceeding 3 ° C./min.
Moreover, in this manufacturing method, it is preferable to heat-sinter a molded object in air | atmosphere or oxygen atmosphere.

  According to the present invention, the difference in bulk resistivity between the surface and the inside of the sputtering target can be reduced, so that the change in film characteristics during sputtering is reduced, and stable thin film formation can be realized. Moreover, since the amount of grinding of the surface of a termination | terminus body required for manufacture of the sputtering target of the stable quality becomes small, a material yield can be improved.

Hereinafter, embodiments of the present invention will be described in detail.
A sintered body according to an embodiment of the present invention is a sintered body made of indium, zinc, and oxygen, and has a bulk resistivity Rs at a depth position of 1 mm in the thickness direction from the surface of the sintered body, Ratio (Rs−Rd) / Rd obtained by dividing the difference from the bulk resistivity Rd at a depth position of 4 mm in the thickness direction from the surface of the sintered body by the bulk resistivity Rd at the depth position of 4 mm. The absolute value is 20% or less expressed as a percentage.
A sputtering target according to an embodiment of the present invention is a sputtering target made of a sintered body made of indium, zinc, and oxygen, and has a depth position of 0 mm in the thickness direction from the surface of the sputtering target (that is, sputtering). The difference between the bulk resistivity Rf at the target surface position) and the bulk resistivity Ra at the depth position of 3 mm from the surface of the sputtering target in the thickness direction is the bulk resistivity at the depth position of 3 mm. The absolute value of the ratio (Rf-Ra) / Ra divided by Ra is 20% or less expressed as a percentage.

(composition)
The sintered body constituting the sputtering target is made of In, Zn, and O, and includes, for example, an amorphous oxide represented by the general formula In ₂ O ₃ (ZnO) _m . Here, m in the general formula is an integer, and this m value can take a value in the range of 3-20.

Zinc may be contained in an atomic ratio of Zn / (In + Zn) of 7 at% to 20 at%, typically 10 at% to 17 at%. The amount of zinc can be appropriately changed according to the conductivity of the target film.
The content of line segments such as In and Zn can be measured by fluorescent X-ray analysis (XRF).

  In addition to In and Zn, the sintered body may further contain other elements as long as the characteristics of the present invention are not impaired. For example, when including at least one element of Fe, Al, Si, Cu and Pb, the content of each element can be 100 wtppm or less, and at least one of Sn and Zr When elements are included, the content of each element can be 1000 wtppm or less.

(Bulk resistivity)
In the embodiment of the sintered body, the bulk on the surface (1 mm depth position) exposed by grinding 1 mm in the thickness direction from the surface of the sintered body obtained after heating and sintering and lowering the temperature as described later. The difference between the resistivity Rs and the bulk resistivity Rd at the surface (4 mm depth position) exposed by grinding 4 mm in the thickness direction from the surface of the sintered body is the target surface at the 4 mm depth position. The absolute value of the ratio (Rs−Rd) / Rd divided by the bulk resistivity Rd at 20% or less is expressed as a percentage.

If this ratio (Rs−Rd) / Rd exceeds 20%, stable film formation cannot be performed due to a change in film characteristics during sputtering when the sintered body is used as a sputtering target. Requires a large amount of grinding of the sintered body surface. As a result, in order to produce a sputtering target having a predetermined thickness, a thick sintered body must be prepared in advance in consideration of the grinding amount. In this case, the density at the center position in the thickness direction must be There is a concern about the decrease, and the material yield is decreased due to the increase in the grinding amount.
Therefore, from this viewpoint, the ratio (Rs−Rd) / Rd is more preferably 15% or less, and particularly preferably 10% or less.

  In the embodiment of the sputtering target, the bulk resistivity Rf on the surface (0 mm depth position) of the sputtering target obtained by polishing the sintered body and 3 mm grinding in the thickness direction from the surface of the sputtering target. The absolute value of the ratio (Rf−Ra) / Ra obtained by dividing the difference from the bulk resistivity Ra at the surface (3 mm depth position) by the bulk resistivity Ra at the 3 mm depth position is The percentage is preferably 20% or less.

Thereby, stable film formation can be realized at the time of sputtering. In other words, if this ratio exceeds 20%, the film characteristics change as the thickness decreases during sputtering, so that the film formation is not stable.
The ratio (Rf-Ra) / Ra is preferably 15% or less, more preferably 10% or less.

  The above-described bulk resistivity measurement in a sintered body or a sputtering target was performed on a surface finished with a grinding thickness of 0.2 mm by using a fine abrasive powder of # 400 as defined in JIS R6001 (1998). Can be done.

  The above-described bulk resistivity can be measured based on the four-probe method described in JIS R1637. More specifically, the measurement surface of the sintered body or the sputtering target is measured at a total of five locations, a four-corner area and a central area, which are divided into 9 × 3 × 3 in the vertical and horizontal directions. The average value of the measured values at can be used as the bulk resistivity in the present invention. The measurement point can be the center of each area, for example.

(Crystal grain size)
By setting the resistance difference in the thickness direction as described above, the crystal grain size Ds in the structure of the surface ground by 1 mm from the surface and the crystal grains in the surface ground by 4 mm from the surface (for example, the surface at the central position in the thickness direction) The difference in size Dd can be 20% or less. As for the size of the crystal grains, arbitrary four points are selected and observed from the 5 mm square of the center of the target surface. Then, the size of the crystal grain is obtained as an average value from a photograph of 300 times the SEM image by a code method. The difference between the crystal grains is a comparison between a surface ground by 1 mm from the surface and a surface ground by 4 mm from the surface (for example, a surface at the thickness center position), and the relative difference in size (Ds−Dd) / Let the absolute value of Dd be the difference in crystal grain size.
Moreover, the average crystal grain size of the sintered compact constituting the sputtering target can be set to, for example, 1.0 μm to 5.0 μm, preferably 2.0 μm to 3.0 μm. The crystal grain size can be measured by observing an SEM image after cutting a part of the obtained sintered body and mirror-polishing the cut surface.

(density)
The relative density of the sintered body and the sputtering target can be 95% or more, preferably 98% or more.
In particular, in this invention, since the variation in bulk resistivity in the thickness direction is reduced, the amount of polishing when producing a sputtering target from the sintered body can be reduced, so the density at the center position in the thickness direction is also reduced. It can be increased. In other words, if the variation in bulk resistivity in the thickness direction is large, it is necessary to manufacture a thick sintered body in advance in anticipation of an increased amount of polishing of the sintered body during the sputtering target preparation. When the thickness is large, heat is hardly transmitted to the vicinity of the center in the thickness direction at the time of heating and sintering, and the density at the center position in the thickness direction of the obtained sintered body or sputtering target is reduced.

The relative density is calculated from the theoretical density calculated from the density of the raw material powder and the density of the sintered body measured by Archimedes method. Relative density = (Density measured by Archimedes method) ÷ (Theoretical density) x 100 (%) Can be calculated. The theoretical density of IZO 10.7% is 7.00 g / cm ³ .

(Production method)
The sintered body and the sputtering target as described above can be manufactured by the following method, for example.
First, for example, a powder raw material containing at least indium oxide powder and zinc oxide powder is mixed with a molding binder as necessary.

Next, the mixed powder raw material is filled into a mold and pressure-molded to produce a molded body having a predetermined shape. Here, for example, a pressure of 400 to 1000 kgf / cm ² can be applied for 1 minute to 3 minutes.
And this molded object is heated and sintered to the temperature of 1350 degreeC-1500 degreeC within a sintering furnace, for example. The holding time of the heating temperature can be 1 hour to 100 hours, preferably 5 hours to 30 hours. This heat sintering is preferably performed in an oxidizing atmosphere such as air or an oxygen atmosphere because a sputtering target having high density and excellent film characteristics can be obtained.

  It is important for the temperature drop after the above-mentioned heat sintering to cool in a nitrogen atmosphere or an argon atmosphere instead of the air or oxygen atmosphere. By setting it as nitrogen atmosphere, the reduction | decrease of the oxygen deficiency in the surface vicinity of a sintered compact is suppressed, and it becomes possible to suppress the dispersion | variation in the bulk resistance in the thickness direction of a sintered compact to the extent mentioned above. In other words, when this temperature decrease is performed in an air atmosphere or an oxygen atmosphere, oxygen vacancies near the surface are reduced, and as a result, the bulk resistance in the thickness direction varies greatly and becomes non-uniform.

Furthermore, in order to obtain the effect of suppressing the reduction of oxygen deficiency, the temperature lowering rate after the heating and sintering is preferably a rate exceeding 1 ° C./min, more preferably a rate exceeding 3 ° C./min, In particular, a speed exceeding 5 ° C./min is even more preferable. Thereby, since the dispersion | variation in the bulk resistivity in the thickness direction of a sintered compact is suppressed further, the sintered compact which has a more uniform bulk resistivity can be manufactured.
The temperature can be lowered, for example, by introducing cold air with adjusted temperature, preferably nitrogen / argon, into the sintering furnace.
The above-mentioned atmosphere / temperature decreasing rate is preferably within a range of at least 1400 ° C. to 1000 ° C. at the time of temperature decrease, and a temperature lower than 1000 ° C. may be a natural temperature decrease. This is because, in the IZO target, the temperature-decreasing speed and temperature-decreasing atmosphere particularly in a high-temperature region greatly affect the bulk characteristics.

The surface of one side of the sintered body obtained after the temperature drop is known in the thickness direction of the sintered body, for example, 1% to 20%, preferably 1% to 10%, such as mechanical grinding or chemical grinding. The sputtering target can be manufactured by grinding by a method. Specifically, the amount of grinding can be set to, for example, 0.1 mm to 2.0 mm, preferably 0.1 mm to 1.0 mm, in the thickness direction of the sintered body. However, the amount of grinding at the time of manufacturing a sputtering target is not limited to such a range, and can be an arbitrary amount. This grinding can be performed using a fine abrasive powder for polishing having a particle size of # 80 defined in JIS R6001 (1998).
In this embodiment, since the variation in the bulk resistivity in the thickness direction is small as described above, the required amount of grinding is reduced. Thereby, the material yield can be improved.

  Next, a sputtering target according to the present invention was prototyped and its performance was confirmed, which will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

Indium oxide powder and zinc oxide powder are mixed and pulverized so as to have each composition shown in Table 1, and this is put into a mold, and a pressure of 800 kgf / cm ² is applied for 1 minute to obtain a molded body. Obtained. The molded body was heated to 1400 ° C. in an electric furnace, and held for 10 hours to sinter and then cooled.
Here, the temperature drop after the heating and sintering was performed in a nitrogen atmosphere in Examples 1 to 7, while it was performed in an air atmosphere in Comparative Examples 1 to 5. Moreover, in Examples 1-7 and Comparative Examples 1-5, as shown in Table 1, the temperature rising and holding atmosphere at the time of heat sintering and the temperature decreasing rate were changed. The rate of temperature decrease shown in Table 1 is a rate when the temperature is between 1400 ° C. and 1000 ° C. After the temperature is decreased to less than 1000 ° C., the temperature is decreased naturally.

The sintered body thus obtained was manually cut using a sandpaper of fine powder # 80 for polishing to produce a sputtering target by scraping 1 mm from the surface of the sintered body in the thickness direction. Further, the surface of the sintered body is finally ground to about 5 mm by the same polishing method, and a resistivity measuring device (model number: Σ-5 +) manufactured by NPS Co., Ltd. is used at each halfway position. The bulk resistivity was measured, the bulk resistivity Rs at a depth of 1 mm from the surface of the sintered body, the bulk resistivity Rd at a depth of 4 mm from the surface of the sintered body, and the surface of the sintered body The bulk resistivity Rb was measured. Prior to measuring each bulk resistivity, the surface to be measured was finished by manually grinding a thickness of 0.2 mm with sandpaper of # 400 fine powder for polishing. Also, using them, the ratio of the difference between Rs and Rd (Rs−Rd) / Rd × 100 and the ratio of the difference between Rb and Rd (Rb−Rd) / Rd × 100 were calculated, respectively. The results are shown in Table 1.
In this example, the bulk resistivity Rs at a depth of 1 mm from the surface of the sintered body is equal to the bulk resistivity Rf at a depth of 0 mm from the surface of the sputtering target. The bulk resistivity Rd at a depth of 4 mm from the surface is equal to the bulk resistivity Ra at a depth of 3 mm from the surface of the sputtering target.

  In Table 1, “maximum difference ratio (%)” is the ratio between the maximum and minimum differences in bulk resistance measured at each depth position up to a depth position of about 5 mm. The “grinding amount (mm) when 20% can be confirmed” is 20% as the bulk resistance ratio based on the bulk resistivity at the depth position where the grinding amount is 4 mm becomes deeper from the surface. It means the grinding amount when it becomes.

  In addition, when the crystal grain in Example 1 was measured, it was 2.45 μm on the 1 mm ground surface and 2.59 μm on the 4 mm ground surface from the sintered body surface, and the absolute value of the relative difference (Ds−Dd) / Dd was 5 4%.

As shown in Table 1, in each of Examples 1 to 7 in which the temperature-decreasing atmosphere is nitrogen, whether the temperature-raising / holding atmosphere is oxygen or air, regardless of the composition, 1 mm of the sintered body is used. The ratio of the difference between the bulk resistivity Rs at the depth position and the bulk resistivity Rd at the 4 mm depth position of the sintered body was 20% or less, and it was possible to reduce the bulk resistivity and suppress the variation.
In particular, in Examples 3 and 6 where the temperature was lowered at a high speed exceeding 5 ° C./min, it was possible to further reduce the bulk resistivity and suppress the variation.

  On the other hand, in Comparative Examples 1-5, the sintered compact was heated and sintered, and then the temperature was lowered in the air atmosphere, so that the bulk resistivity Rs at the 1 mm depth position and the sintered body were sintered. The ratio of the difference in bulk resistivity Rd at a depth of 4 mm in the body exceeded 20% and became considerably large, resulting in large variations in bulk resistivity.

  As described above, according to the present invention, it has been found that the variation in bulk resistivity between the sintered body surface and inside can be effectively suppressed.

Claims (12)

A sintered body of an oxide composed of In, Zn, and O , containing Zn / (In + Zn) at 7 at% to 20 at% , and bulk at a depth position of 1 mm from the surface of the sintered body in the thickness direction. A ratio (Rs−) obtained by dividing the difference between the resistivity Rs and the bulk resistivity Rd at a depth position of 4 mm from the surface of the sintered body by the bulk resistivity Rd at the depth position of 4 mm. A sintered body having an absolute value of Rd) / Rd expressed as a percentage of 20% or less.   2. The sintered body according to claim 1, wherein the absolute value of the ratio (Rs−Rd) / Rd is 15% or less in terms of percentage.   2. The sintered body according to claim 1, wherein the absolute value of the ratio (Rs−Rd) / Rd is 10% or less in terms of percentage.   The sintered compact according to any one of claims 1 to 3, wherein Zn / (In + Zn) is contained at 10 at% to 17 at%. A sputtering target of an oxide composed of In, Zn, and O , containing Zn / (In + Zn) at 7 at% to 20 at% , and bulk resistivity at a depth position of 0 mm in the thickness direction from the surface of the sputtering target. The ratio of Rf and the bulk resistivity Ra at the depth position of 3 mm from the surface of the sputtering target in the thickness direction divided by the bulk resistivity Ra at the depth position of 3 mm (Rf−Ra) / A sputtering target in which the absolute value of Ra is 20% or less as a percentage. The sputtering target according to claim 5 , wherein the absolute value of the ratio (Rf−Ra) / Ra is 15% or less expressed as a percentage. The sputtering target according to claim 5 , wherein the absolute value of the ratio (Rf−Ra) / Ra is 10% or less as a percentage. The sputtering target according to any one of claims 5 to 7 , wherein the sputtering target contains Zn / (In + Zn) at 10 at% to 17 at%. The method includes mixing and molding powder raw materials containing indium oxide powder and zinc oxide powder, and heating and sintering the resulting molded body. The temperature drop after heating and sintering the molded body can be performed in a nitrogen atmosphere or an argon atmosphere. It is performed by the under, to produce a sputtering target containing Zn / a (in + Zn) in 7 atomic% to 20 at%, the manufacturing method of the sputtering target. The manufacturing method of the sputtering target of Claim 9 which makes the temperature-fall rate in the case of the said temperature fall the speed | rate exceeding 1 degree-C / min. The manufacturing method of the sputtering target of Claim 9 which makes the temperature-fall rate in the case of the said temperature fall the speed | rate exceeding 3 degree-C / min. The heat sintering of the molded body, carried out under air or oxygen atmosphere, the production method of a sputtering target according to any one of claims 9-11.