JP2017110291A - Sputtering target material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering target material capable of suppressing generation of a crack in handling during a machine work of the sputtering target material, or during an inversion work in a bonding process or the like.SOLUTION: There is provided a sputtering target having a vacancy having an equivalent circle diameter exceeding 2.0 μm, as many as less than one per 1,050 μm, in which a mean value of a relative density is preferably 98.5% or more and dispersion from the mean value is more preferably 0.3% or less, which is an oxide sintered body containing Sn as much as 20 atom% to 50 atom% and Zn as much as 50 atom% to 80 atom% to the whole metal component.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sputtering target material comprising an oxide sintered body used for forming an oxide semiconductor layer of a thin film transistor for driving, for example, a large liquid crystal display or an organic EL display.

  Conventionally, in a display device such as a liquid crystal display or an organic EL display driven by a thin film transistor (hereinafter referred to as “TFT”), an amorphous silicon film or a crystalline silicon film is mainly used as a TFT channel layer. It is. With the demand for higher definition of displays, oxide semiconductors have attracted attention as materials used for TFT channel layers. For example, an oxide semiconductor film containing In (indium), Ga (gallium), Zn (zinc), and O (oxygen) (hereinafter referred to as “IGZO thin film”) has excellent TFT characteristics. Practical use has been started. In and Ga contained in the I-G-Z-O thin film are rare and expensive metals designated as rare metal stockpiling target steel types in Japan.

  Therefore, a Zn—Sn—O-based oxide semiconductor film (hereinafter referred to as “ZTO thin film”) is attracting attention as an oxide semiconductor film containing no In or Ga contained in the IGZO thin film. is there. And this ZTO thin film is formed into a film by the sputtering method using a sputtering target. In this sputtering method, ions, atoms, or clusters collide with the surface of the sputtering target, and the surface of the material is scraped (or skipped) to deposit components constituting the material on the surface of a substrate or the like. It is a method to form a film.

Here, since the ZTO thin film is a thin film containing oxygen, a so-called reactive sputtering method in which the film is formed in an atmosphere containing oxygen is used in the sputtering method. This reactive sputtering method is a method of sputtering in a mixed gas atmosphere composed of argon gas and oxygen gas. Sputtering while reacting ions, atoms or clusters with oxygen forms an oxide thin film. It is a technique to do.
And the sputtering target used for this reactive sputtering method was formed by bonding a sputtering target material made of a ZTO-based oxide sintered body having a component composition approximate to the component composition of the ZTO thin film onto a backing plate with a brazing material. Used in state.
For example, in Patent Document 1, as a sputtering target material made of a ZTO-based oxide sintered body, a predetermined amount of ZnO powder and SnO ₂ powder are mixed, mixed by a ball mill, granulated, and calcined powder that has been calcined. There has been proposed a method of manufacturing a body, granulating and molding the calcined powder again to produce a molded body, and performing the main firing.

JP 2010-37161 A

  According to the study of the present inventor, the sputtering target material made of the ZTO-based oxide sintered body produced by the method disclosed in Patent Document 1 described above generates cracks during machining or inversion work in the bonding process. It was confirmed that cracking may occur during handling.

  An object of the present invention is to solve the above-mentioned problems and to provide a sputtering target material that is unlikely to crack during handling such as reversing work during machining or a bonding process.

  As a result of studying the above-mentioned problems, the present inventor has found that the cracks generated in the ZTO-based oxide sintered sputtering target are caused by vacancies existing in the sputtering target material. And it discovered that the problem of the crack of a sputtering target material could be solved by making this void | hole below a predetermined size per unit area, and making the number below a predetermined value, and reached | attained this invention.

That is, the sputtering target material of the present invention is an oxide sintered body containing 20 atomic% to 50 atomic% of Sn and 50 atomic% to 80 atomic% of Zn with respect to the entire metal component, and per 1050 μm ² . The number of holes having an equivalent circle diameter exceeding 2.0 μm is less than one.
In addition, the sputtering target material of the present invention preferably has 5 or less holes having an equivalent circle diameter of 0.1 to 2.0 μm per 1050 μm ² .

  The sputtering target material of the present invention preferably has an average value of relative density of 98.5% or more. And the variation from the average value of the relative density is more preferably 0.3% or less.

  The sputtering target material of this invention can suppress the crack which generate | occur | produces at the time of handling, such as a reversing operation | work at the time of machining or a bonding process. Thus, the present invention is a useful technique for forming a TFT channel layer in a manufacturing process of a large liquid crystal display or an organic EL display.

The electron micrograph of the sputtering target material of the example 1 of this invention. The electron micrograph of the sputtering target material of the example 2 of this invention. The electron micrograph of the sputtering target material of the example 3 of this invention. The electron micrograph of the sputtering target material of the example 4 of this invention. The electron micrograph of the sputtering target material of the example 5 of this invention. The electron micrograph of the sputtering target material of a comparative example. The figure which shows an example of the measurement site | part of the density of a sputtering target material.

The sputtering target material of the present invention has less than one hole having a circle-equivalent diameter exceeding 2.0 μm per unit area of 1050 μm ² . As described above, the sputtering target material is usually used after being processed into a predetermined shape by machining. Here, the machining is performed with a diamond grindstone. At this time, the sputtering target material receives a high load such as compression or shear due to grinding.
Further, even during handling such as carrying work and reversing work in the bonding process, only a part of the sputtering target material is supported, and the rest of the work is carried out without support, so that it receives a high load such as bending.

The sputtering target material of the present invention is less than one hole having an equivalent circle diameter exceeding 2.0 μm per 1050 μm ² , so that the sputtering target can be subjected to a high load such as compression, shear, bending, etc. Propagation of cracks between pores present in the material is suppressed, and cracking of the sputtering target material itself can be prevented.
In the sputtering target material of the present invention, in order to improve crack resistance, it is preferable that the number of holes having a circle-equivalent diameter of 0.1 μm or more and 2.0 μm or less per 1050 μm ² is 5 or less.
Here, the equivalent circle diameter of the vacancies referred to in the present invention is obtained by photographing the vacancies shown in black in the reflected electron image with a scanning electron microscope in any three fields of view of the sputtering surface of the sputtering target material. Measurement can be performed using image analysis software (for example, “Scandium” manufactured by OLYMPUS SOFT IMAGES SOLUTIONS GMBH).

The sputtering target material of the present invention is an oxide sintered body containing 20 atomic% to 50 atomic% of Sn and 50 atomic% to 80 atomic% of Zn with respect to the entire metal component. And in this invention, by making Sn amount into 20 atomic% or more, the ratio of Zn amount, ie, ZnO, is reduced, the void | hole produced | generated when ZnO evaporates is suppressed, and the density of a sputtering target material is improved. Can do. On the other hand, by setting the Sn amount to 50 atomic% or less, it is possible to suppress an excess of SnO ₂ , improve the sinterability, and improve the density of the sputtering target material. The Sn content is preferably 20 atomic% to 40 atomic%, more preferably 25 atomic% to 35 atomic%.
Further, in the present invention, by setting the Zn amount to 50 atomic% or more, the Sn ratio, that is, SnO ₂ is reduced, the SnO ₂ is prevented from becoming excessive, the sinterability is improved, and the density of the sputtering target material Can be improved. On the other hand, by setting the amount of Zn to 80 atomic% or less, it is possible to suppress vacancies generated by evaporation of ZnO having a high vapor pressure and improve the density of the sputtering target material. The Zn content is preferably 60 atom% to 80 atom%, and more preferably 65 atom% to 75 atom%.
In the sputtering target material of the present invention, when the entire metal component is 100 atomic%, a part of Zn is one or more of Al, Si, Ga, Mo, and W in total 0.005 atomic%. Substitution can be made in the range of ˜4.00 atomic%. Among these elements, Al, Ga, Mo, and W are useful elements for controlling carrier mobility and preventing photodegradation. Si is an element useful for improving sinterability.
In the sputtering target material of the present invention, the remainder other than the metal component is composed of oxygen and inevitable impurities. The content of inevitable impurities in the sputtering target material of the present invention is preferably small, and may contain inevitable impurities such as nitrogen and carbon as long as the effects of the present invention are not impaired.

The sputtering target material of the present invention preferably has an average value of relative density of 98.5% or more. Thereby, generation | occurrence | production of a nodule can also be suppressed in addition to the quality improvement of the ZTO thin film formed by suppressing generation | occurrence | production of the abnormal discharge at the time of sputtering, and obtaining stable discharge. In the present invention, the relative density is more preferably more than 99.0% from the viewpoint of improving the cracking resistance of the sputtering target material.
Further, the sputtering target material of the present invention preferably has a variation from the average value of the relative density of 0.3% or less, thereby suppressing the occurrence of cracks and chips during machining of the sputtering target material. be able to.

The relative density of the sputtering target material in the present invention refers to a value obtained by dividing the bulk density of the sputtering target material measured by the Archimedes method by its theoretical density in percentage. Here, the theoretical density uses a value obtained as a weighted average calculated by a mass ratio obtained from a composition ratio.
In addition, if the measurement position of relative density is a disk-shaped sputtering target material as shown in FIG. 7, for example, in the center part, the site | part i-the site | part iv equivalent to the outer peripheral part of the obtained sputtering target material, The total number of corresponding parts v is five. Further, in the case of a rectangular sputtering target material such as a rectangle, there are a total of five sites including four portions corresponding to the corner portions of the obtained sputtering target material and portions corresponding to the central portion. In the present invention, an average value of these five relative density values is employed.

Below, the example of the manufacturing method of the sputtering target material of this invention is demonstrated.
In the sputtering target material of the present invention, for example, ZnO powder and SnO ₂ powder are mixed with pure water and a dispersant to form a slurry. After the slurry is dried, a granulated powder is produced. Baking to prepare a calcined powder (Zn ₂ SnO ₄ ). The calcined powder can be obtained by pulverizing the calcined powder by wet crushing, producing a molded body by casting, and baking it in a normal atmospheric atmosphere through degreasing.
The calcining temperature of the granulated powder for producing the calcined powder is preferably set to 1000 to 1200 ° C. By setting the calcining temperature to 1000 ° C. or higher, the reaction between the ZnO powder and the SnO ₂ powder can sufficiently proceed. On the other hand, by setting the calcining temperature to 1200 ° C. or lower, an appropriate powder particle size can be maintained, and a dense sputtering target material can be obtained.
The firing temperature in the air atmosphere is preferably set to 1300 to 1500 ° C. By setting the firing temperature to 1300 ° C. or higher, sintering can be promoted and a dense sputtering target material can be obtained. By using a dense sputtering target material, cracking can be suppressed even in a state where a high load is applied. Further, as this dense sputtering target material, a sputtering target material having less than one hole having an equivalent circle diameter exceeding 2.0 μm per 1050 μm ² can be obtained. On the other hand, by setting the firing temperature to 1500 ° C. or lower, the ZnO powder can be prevented from evaporating, and a dense sputtering target material can be obtained.

Moreover, the sputtering target material of this invention can also be obtained by press-sintering the granulated powder produced by crushing, granulating, and degreasing the calcined powder obtained by the same method as the above. As a means for pressure sintering, methods such as hot pressing, discharge plasma sintering, hot isostatic pressing can be applied. Among these, hot press and spark plasma sintering are preferable because the residual stress of the sintered body can be reduced and cracking of the sputtering target material can be prevented.
The sintering temperature in the pressure sintering is preferably set to 900 to 1100 ° C. Sintering can be promoted by setting the sintering temperature to 900 ° C. or higher, and a dense sputtering target material can be obtained. By using a dense sputtering target material, cracking can be suppressed even in a state where a high load is applied. Further, as this dense sputtering target material, a dense sputtering target material having less than one hole having an equivalent circle diameter exceeding 2.0 μm per 1050 μm ² can be obtained. On the other hand, by setting the sintering temperature to 1100 ° C. or lower, in addition to suppressing evaporation of the ZnO powder, it is possible to suppress a reduction reaction in which the SnO ₂ powder reacts with the pressure sintering member.
The pressure for pressure sintering is preferably set to 20 to 40 MPa. By setting the applied pressure to 20 MPa or more, a dense sputtering target material having less than one hole having an equivalent circle diameter exceeding 2.0 μm per 1050 μm ² can be obtained. On the other hand, by setting the applied pressure to 40 MPa or less, it is possible to suppress cracking of the pressure sintering member and cracking of the obtained sputtering target material.
The sintering time for pressure sintering is preferably set to 3 to 15 hours. By setting the sintering time to 3 hours or more, the sintering can be sufficiently advanced, and a dense sputtering target having less than one hole having an equivalent circle diameter exceeding 2.0 μm per 1050 μm ^2. A material can be obtained. On the other hand, the fall of manufacturing efficiency can be suppressed by making sintering time into 15 hours or less.

First, ZnO powder having an average particle size (D50 of cumulative particle size distribution) of 0.70 μm and an average particle size (cumulative particle size) so as to contain 30 atomic percent of Sn and 70 atomic percent of Zn with respect to the entire metal component. A SnO ₂ powder having a distribution D50) of 1.85 μm was weighed, put into a stirring vessel containing a predetermined amount of pure water and a dispersant, and mixed to obtain a slurry. After this slurry was dried, pulverization, granulation, and degreasing were performed to obtain a granulated powder having an average particle size (D50 of cumulative particle size distribution) of 45 μm.
Next, the granulated powder obtained above was calcined at 1090 ° C. to obtain a calcined powder. The calcined powder was wet crushed, and the resulting slurry was cast and molded to produce three molded bodies.
Next, one of the obtained compacts was fired at 1400 ° C. for 10 hours under atmospheric conditions at atmospheric pressure, and further heat treated under nitrogen reducing atmosphere at 1400 ° C. for 10 hours to obtain a sintered body. .
The obtained sintered body was subjected to plate thickness processing by surface grinding using a diamond grindstone, and then using a water jet cutting machine, a sputtering target material of the present invention example 1 having a thickness of 10 mm and an outer diameter of 100 mm was formed. Produced.

Also, one of the molded bodies obtained above was fired at 1400 ° C. for 5 hours under atmospheric pressure at atmospheric pressure, and further heat treated under nitrogen reducing atmosphere at 1400 ° C. for 12 hours to obtain a sintered body. .
The obtained sintered body was subjected to plate thickness processing by surface grinding using a diamond grindstone, and then a sputtering target material serving as Example 2 of the present invention having a thickness of 10 mm and an outer diameter of 100 mm was used using a water jet cutting machine. Produced.

  One of the molded bodies obtained above was fired at 1400 ° C. for 5 hours under atmospheric pressure to obtain a sintered body. The sintered body was subjected to plate thickness processing by surface grinding using a diamond grindstone, and then a sputtering target material serving as Invention Example 3 having a thickness of 10 mm and an outer diameter of 100 mm was produced using a water jet cutting machine. .

In addition, the calcined powder obtained above is filled in a carbon pressure vessel, placed inside the furnace body of a discharge plasma sintering apparatus, and subjected to pressure sintering under conditions of 950 ° C., 40 MPa, 12 hours. After carrying out pressure sintering, it was taken out from the carbon pressure vessel to obtain a sintered body.
The obtained sintered body was subjected to plate thickness processing by surface grinding using a diamond grindstone, and then a sputtering target material serving as Invention Example 4 having a thickness of 10 mm and an outer diameter of 100 mm was formed using a water jet cutting machine. Produced.

Further, the calcined powder obtained above was filled into a carbon pressure vessel, placed inside a furnace body of a hot press apparatus, and subjected to pressure sintering under conditions of 970 ° C., 20 MPa, 12 hours. .
The obtained sintered body was subjected to plate thickness processing by surface grinding using a diamond grindstone, and then a sputtering target material serving as Invention Example 5 having a thickness of 10 mm and an outer diameter of 100 mm was formed using a water jet cutting machine. Produced.

As a comparative example, a sputtering target material was manufactured as follows. First, ZnO powder having an average particle size (D50 of cumulative particle size distribution) of 0.70 μm and an average particle size (cumulative particle size) so as to contain 30 atomic percent of Sn and 70 atomic percent of Zn with respect to the entire metal component. A SnO ₂ powder having a distribution D50) of 1.85 μm was weighed, put into a stirring vessel containing a predetermined amount of pure water and a dispersant, and mixed to obtain a slurry. After this slurry was dried, pulverization, granulation, and degreasing were performed to obtain a granulated powder having an average particle size (D50 of cumulative particle size distribution) of 45 μm. This granulated powder was wet pulverized, and the resulting slurry was cast to form a molded body.
Next, the obtained molded body was fired at 1550 ° C. under normal pressure for 4 hours.
The obtained sintered body was subjected to plate thickness processing by surface grinding using a diamond grindstone, and then a sputtering target material serving as a comparative example having a thickness of 10 mm and an outer diameter of 100 mm was produced using a water jet cutting machine. .

A 10 mm × 10 mm × 10 mm sample for electron microscope observation was cut out from each sintered body obtained above, and the sample surface was mirror-polished and observed. Then, the surface of each sintered body is reflected electron images of a scanning electron microscope, and among the arbitrary fields of view, three fields of 1050 μm ² are observed. The equivalent circle diameter of the holes was measured, and the number of holes exceeding 2.0 μm and the number of holes of 0.1 μm to 2.0 μm was measured.

From the results of Table 1 and FIGS. 1 to 5, when the sputtering target material of the present invention observes an arbitrary unit area of 1050 μm ² , there is no hole whose equivalent circle diameter exceeds 2.0 μm in any field of view. Was confirmed. Further, even in the field of view having the largest number of holes having an equivalent circle diameter of 0.1 μm or more and 2.0 μm or less, it was confirmed that the number was 5 or less.
Next, a sputtering test was performed using the ZTO sputtering target material of the present invention example. Sputtering was performed under the conditions of an Ar atmosphere, a pressure of 0.5 Pa, and a DC power of 300 W for an integrated time of 4 hours. In addition, this time, in order to evaluate the sputtering target itself, the sputtering test was performed in an Ar atmosphere instead of reactive sputtering.
When the sputtering target material used as the example of the present invention after the sputter test was visually confirmed, the occurrence of cracks was not confirmed in any sputtering target material.

On the other hand, as shown in FIG. 6, the sputtering target material of the comparative example had three vacancies having an equivalent circle diameter exceeding 2.0 μm when an arbitrary unit area of 1050 μm ² was observed in one field of view.
Next, a sputtering test was performed under the same conditions as described above using the sputtering target material of the comparative example. When a sputtering target material serving as a comparative example after the sputtering test was visually confirmed, it was confirmed that four cracks were generated in a radial pattern from the approximate center of the surface of the sputtering target material.

  Further, from each of the sintered bodies obtained above, each 10 mm × 20 mm × 20 mm sample for analysis was cut out from each measurement site shown in FIG. 7, the true density of each site was measured, and the relative density was measured by the method described above. Was calculated. The results are shown in Tables 2 and 3.

  From the results of Tables 2 and 3, the sputtering target material of the present invention was subjected to density measurement at five locations, i.e., the site i to the site iv corresponding to the outer peripheral portion and the site v corresponding to the central portion. The relative density in the region was 98.5% or more. Moreover, it has confirmed that the dispersion | variation from the average value of a relative density was 0.3% or less. And in this invention example 1 and this invention example 4, the average value of relative density exceeded 99.0%, and it was able to be set as the sputtering target material which has a high relative density.

  On the other hand, the density of the sputtering target material of the comparative example was measured at five locations, ie, the region i to the region iv corresponding to the outer peripheral portion and the region v corresponding to the central portion. Was less than. Moreover, the variation from the average value of the relative density was 0.7% at the maximum, which was larger than the variation of the sputtering target material of the present invention.

1 Zn ₂ SnO ₄ phase 2 ZnO phase 3 Vacancy

Claims (4)

It is an oxide sintered body containing 20 atomic% to 50 atomic% of Sn and 50 atomic% to 80 atomic% of Zn with respect to the entire metal component, and has an equivalent circle diameter exceeding 2.0 μm per 1050 μm ^2. The sputtering target material characterized by having less than one hole. ^2. The sputtering target material according to claim 1, wherein the number of holes having an equivalent circle diameter of 0.1 μm or more and 2.0 μm or less per 1050 μm ² is 5 or less.   The average value of relative density is 98.5% or more, The sputtering target material of Claim 1 or Claim 2 characterized by the above-mentioned. 4. The sputtering target material according to claim 3, wherein the variation [(maximum value−minimum value) / average value × 100 (%)] of the relative density from the average value is 0.3% or less.