JPH10183341A - Tungsten or molybdenum target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tungsten or molybdenum target having the fine structure of a specified value or below in average grain size and moreover having the relative density of a specified value or above by applying hot plastic working after obtaining a preliminarily sintered body consisting of W or Mo. SOLUTION: The target, having the fine structure of 10μm or below in average grain size and having the relative density of 99% or above, is obtained. Since high purity is required for the target in material powder of W or Mo, the purity of 99% or above is especially preferable. Also, the grain size of powder is preferably 10μm or below in Fisher grain size. A preliminarily sintered body is manufactured using above powder. HIP or hot press is preferable as the sintering method. In the case of applying HIP, powder is charged into an enclosing can for compacting and heated under vacuum, and a gas and water adsorbed to powder are removed. After finishing this operation, the HIP can is vacuum deaerated and sealed and used in HIP, and the preliminarily sintered body is obtained. Hot plastic working is applied to the body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode used in a semiconductor device and a high-purity tungsten or molybdenum target used for forming a wiring material.

[0002]

2. Description of the Related Art With the recent increase in integration of VLSIs, a reduction in wiring width and an increase in wiring length have caused a problem of signal delay due to resistance of wiring material, and a material having a lower resistance value has been required. As a gate electrode material, a high melting point metal such as tungsten or molybdenum having a low resistance value is promising. As a method for forming a tungsten or molybdenum film, there are a sputtering method and a CVD method, and the sputtering method is advantageous in terms of productivity and stability of film formation. As a method of manufacturing a tungsten and molybdenum sputtering target used in the sputtering method, a melting method using an electron beam melting (JP-A-60-66425, JP-A-61-107728) and a hot press are used. There is a powder-sintering method.

[0003]

However, in the ingot produced by the melting method, since tungsten and molybdenum have a high melting point (W: 3422 ° C., Mo: 2623 ° C.) and a high purity, crystal grains are coarsened. . When the crystal grains become coarse, they are easily broken during subsequent machining. Further, when sputtering is performed using a target for coarsening crystal grains, a uniform film cannot be formed due to anisotropy of crystal grains. A method to prevent this coarsening of grains with additives is proposed.
(See Japanese Patent Application Laid-Open No. 61-116835), however, additives may deteriorate the film properties in some cases. On the other hand, although the target manufactured by the powder-sintering method has fine crystal grains, it is extremely difficult to obtain a high density because tungsten and molybdenum are high melting point materials.

For example, Japanese Patent Publication No. Sho 60-58289 discloses a technique for increasing the density of a high Cr alloy material having a relatively high melting point (1905 ° C.). According to Japanese Examined Patent Publication No. 60-58289, a sintered compact of almost true density is obtained by removing the gas and water adsorbed on the raw material powder and then sintering under pressure under specific conditions. , W and Mo have a higher melting point than Cr, and it is difficult to achieve a high density under the conditions such as the sintering temperature disclosed in Japanese Patent Publication No. 60-58289. (Hot isostatic pressing) treatment is limited to a relative density of about 85%.

If the processing conditions are severe (for example, a holding temperature of 1500 ° C. or higher and a high pressure of 2000 atm), a high density can be obtained, but this is not easy in view of equipment. When sputtering is performed using a low-density target, the possibility of cracking during sputtering is high. In addition, the number of particles (foreign matter) in the generated film is remarkably increased, which causes a decrease in the yield of the wafer. The present invention
In view of the above circumstances, an object is to provide a tungsten or molybdenum target having a fine structure and high density.

[0006]

As a result of various studies to achieve the above object, the present inventor obtained a pre-sintered body made of W or Mo, and then subjected to hot plastic working to obtain a fine sintered body. Having a structure, and found that a relative density of 99% or more can obtain a high-density sintered body target,
The present invention has been completed. That is, the present invention is a tungsten or molybdenum target having a fine structure with an average particle size of 10 μm or less and a relative density of 99% or more.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, first, raw material powders of W and Mo are prepared. Since the raw material powder is required to have high purity as a target, it is desirable that the raw material powder has high purity, particularly 99.999%
It is desirable that the purity be as above. The particle size of the powder is desirably 5 μm or less in FSSS (Fisher particle size). Next, a preliminary sintered body is manufactured using the above powder. Here, as the sintering method, well-known sintering means such as HIP and hot pressing can be employed in addition to normal sintering. In order to simplify the subsequent hot plastic working process, it is desirable that the density of the pre-sintered body be high. In this case, HIP or hot pressing is desirable as the sintering method.

[0008] When HIP is applied, the powder is filled into a sealing can (hereinafter referred to as HIP can), and 10 minus 5
It is required to heat the powder to 200 ° C. or more under a vacuum more than the power of torr to remove gas and moisture adsorbed on the powder. This is because the presence of gas and moisture may cause a decrease in sinterability. After this operation, the HIP can is degassed in vacuum, sealed, and subjected to HIP. The HIP conditions include a HIP temperature of 1150 to 135
0 ° C, HIP pressure 1000atm or more is desirable. The reason why the HIP temperature is set to 1150 ° C. or higher is that if the temperature is lower than this temperature, the density cannot be sufficiently improved.
This is because, if it exceeds, the organization becomes coarse. Also, HIP
The reason why the pressure is set to 1000 atm or more is that if the pressure is less than 1000 atm, it is difficult to achieve sufficient density improvement. According to the above conditions, a pre-sintered body having a relative density of about 85% can be obtained.

The obtained pre-sintered body is subjected to hot plastic working to increase the density. For example, when the density of the pre-sintered body is about 85%, a substantially true density sintered body of 99.9% or more can be obtained by giving a processing rate of about 60%. The processing temperature is desirably in the range of 1200 to 1500 ° C. If the temperature is lower than 1200 ° C., the density cannot be sufficiently improved, and if it exceeds 1500 ° C., the structure becomes coarse. It is necessary to avoid contamination during hot working as much as possible. In the case of HIP, there is no contamination since the sintered body is completely enclosed in the HIP can. It is desired to encapsulate the sintered body in a can in the same manner as HIP. According to the above method, having a microstructure of 10μm or less average particle size,
In addition, a tungsten or molybdenum target with a relative density of 99% or more can be obtained.

[0010]

[Example] High-purity tungsten powder (W ≧ 99.999% [radioactive element content 3 ppb or less, alkali metal content 100 ppb or less], particle size FSSS (Fisher particle size) 5 μm or less)
Of 400 x 300 x 30 (mm) in a sealed can for consolidation (HIP can)
While evacuating to 5 × 10 minus 5 Torr,
It was heated at 400 ° C for 5 hours to release the surface adsorbed gas and moisture. After degassing by heating, sealing was performed, and HIP treatment was performed under the conditions of 1250 ° C. × 2 hours and 1000 atm. The density of the sintered body obtained at this time is 80 to 85% in relative density. Thereafter, the sintered body together with the HIP can was processed at a temperature of 1300 ° C. and a processing rate of 10 to 30% at one time, and the cross section was 110
Hot rolling was repeated several times until it reached a size of 0 × 330 mm and a thickness of 10 mm. After rolling, working strain was removed at 1200 ° C. by strain relief annealing. After removing the obtained rolled material from the HIP can, it was machined into a predetermined shape to obtain a target having a diameter of 300 mm.

The average particle size of the obtained target was 7 μm. The relative density was 99.9% or more, almost the same value as the theoretical density. In terms of purity, there is no contamination during the manufacturing process.
≧ 99.999% [The radioactive element content was 3 ppb or less, and the alkali metal content was 100 ppb or less. ] And oxygen was as low as 230 ppm. The sputtering film formed by this target was uniform, and the number of particles was 50/6 inch wafer.

Comparative Example High-purity tungsten powder (W ≧ 99.
999% [radio element content 3 ppb or less, alkali metal content 100 ppb or less], particle size FSSS (Fisher particle size)
5 μm or less) in a die with an inner diameter of 400 mm,
Hot pressing was performed under the condition of 300 kg / cm ² × 0.5 hour. The obtained hot pressed body was cut to obtain a target of φ300 mm. The relative density of the target was 83%. The number of particles in the sputtering film formed by this target was remarkably large for 200 or more / 6-inch wafers, which caused a decrease in wafer yield.

[0013]

As described above, according to the present invention, a tungsten or molybdenum target having a fine structure and a relative density of 99% or more can be obtained.
Therefore, when the target is machined, no crack is generated, and since there is no anisotropy of crystal grains even in sputtering, a uniform film can be formed.

Claims (1)

[Claims] (1) a fine structure having an average particle size of 10 μm or less;
A tungsten or molybdenum target having a relative density of 99% or more.