JPH03150356A - Tungsten or molybdenum target and production thereof - Google Patents

Abstract

PURPOSE:To obtain a W or Mo target having a fine structure and very high density and not causing cracking at the time of sputtering by presintering powder of W or Mo as a high m.p. metal and carrying out hot plastic working under specified conditions when a W or Mo target for forming a W or Mo film by sputtering is produced. CONSTITUTION:When a target for forming a film of W or Mo as a high m.p. metal by sputtering is produced, W or Mo powder having >99.999% purity and <=5mum average Fischer particle size is presintered by the conventional sintering method, hot isostatic pressing, hot pressing or other method and the density of the presintered body is increased by hot plastic working at 1,100-1,500 deg.C and >=60% working rate to produce a high quality W or Mo target having a fine structure of <10mum average particle size and >=99% relative density and not causing cracking at the time of sputtering.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a high-purity tungsten or molybdenum target used for forming electrodes and wiring materials used in semiconductor tapeis. [Prior art] With the recent increase in the integration of VLSIs, the wiring width has decreased and the wiring length has increased, resulting in signal delays due to the resistance of wiring materials, and materials with lower resistance values are required. . High melting point metals such as tungsten and molybdenum, which have low resistance values, are promising as gate electrode materials. Methods for forming tungsten and molybdenum films include sputtering and CVD, but sputtering is advantageous in terms of productivity and stability of film formation. The method for manufacturing tungsten and molybdenum sputtering targets used in the sputtering method is a melting method using electron beam melting (Japanese Patent Laid-Open No. 60-6642).
5, JP-A No. 61-107728) and a powder-sintering method using a hot press or the like.

[Problem to be solved by the invention]

However, the ingot produced by the melting method has a high melting point of tungsten and molybdenum, W: 3422°C, Mo
: 2623°C) and high purity, the crystal grains become coarse. If the crystal grains become coarse, they will easily break during subsequent machining, and if sputtering is performed using a target with coarse grains, a uniform film will not be formed due to the anisotropy of the crystal grains. A method has been proposed (see Japanese Patent Laid-Open No. 116835/1983) to prevent this crystal grain coarsening using additives, but the additives may deteriorate the film properties. On the other hand, targets produced by the powder-sintering method have fine crystal grains, but it is extremely difficult to obtain high density because tungsten and molybdenum are high melting point materials. For example, Japanese Patent Publication No. Sho 60-58289 discloses a method for increasing the density of a high Cr alloy material having a relatively high melting point (1905° C.). According to Special Publication No. 60-58289,
It is said that a sintered body with almost true density is obtained by removing gas and moisture adsorbed on the raw material powder and then pressurizing it under specific conditions, but W and Mo have higher melting points than Or. Therefore, it is difficult to increase the density under the conditions such as the sintering temperature disclosed in Japanese Patent Publication No. 60-58289, and according to the study of the present inventor, hot pressing or HIP (hot isostatic pressing) treatment The relative density is about 85%. Severe processing conditions (e.g. holding temperature 1500℃ or higher for 200℃)
Although it is possible to obtain a high density if the pressure is set to 00at (high pressure of the intestine), it is unrealistic considering the equipment. When sputtering is performed using a target with a low density, there is a high possibility of cracking during sputtering, and the number of particles (foreign objects) in the generated film increases significantly, causing a decrease in wafer yield. In view of the above circumstances, an object of the present invention is to provide a tungsten or molybdenum target having a small mass and high density, and a method for manufacturing the same. [Means for Solving the Problems J] As a result of various studies to achieve the above object, the inventor has found that
After obtaining a preliminary sintered body made of W or Mo, it is possible to obtain a high-density sintered target having a fine structure and a relative density of just above 99% by performing hot plastic working. We have discovered that this can be done, and have completed the present invention. The present invention will be explained in detail below. In the present invention, raw material powders of W and Mo are first prepared. Since this raw material powder is required to have high purity as a target, it is desirable that the raw material powder has high purity, especially 99.999999999.
It is desirable that the purity is 1 or more. The particle size of the powder is preferably 5 microns or less in terms of FSSS (Fisher particle size). Next, a preliminary sintered body is manufactured using the above powder. Here, as the sintering method, in addition to normal sintering, known sintering means such as HIP and hot pressing can be employed. In order to simplify the subsequent hot plastic working process, it is desirable that the pre-sintered body has a high density, and in this case,
HIP or hot pressing is preferred as the sintering method. When applying HIP, it is required to fill the powder into a pressure-tight enclosure can (hereinafter referred to as HIP can) and heat it to 200°C or higher under a vacuum of 10 torr or higher to remove gas and moisture adsorbed to the powder. be done. This is because the presence of gas and moisture leads to a decrease in sinterability. After completing this operation, HI
The P can is vacuum degassed, sealed, and subjected to HIP. HIP conditions include HIP temperature 1150-1350℃
, HIP pressure of 1000 atm or more is desirable. The reason why the HIP temperature is set to 1150°C or higher is that the density cannot be sufficiently increased below this temperature, and the reason why the HIP temperature is set to 1350°C or lower is that if it exceeds 1350°C, the structure becomes coarse. In addition, setting the HIP pressure to 1000at- or more requires 1
This is because if it is less than 000at■, it is difficult to achieve a sufficient density improvement. According to the above conditions, a pre-sintered body consolidated to a relative density of about 85% can be obtained. The obtained pre-sintered body is subjected to hot plastic working to increase its density. For example, if the density of the preliminary sintered body is about 85%, by applying a processing rate of about 60%,
% or more can be obtained. The processing temperature is preferably in the range of 1200 to 200°C. This is because if the temperature is less than 1200°C, sufficient density improvement will not be achieved, and if it exceeds 1500°C, the structure will become coarse. In addition, it is necessary to avoid contamination during hot processing as much as possible, and HI
When using P, the sintered body is completely enclosed in the HIP can, so there is no contamination, but when using other means, the preliminary sintered body must be enclosed in the can in the same way as HIP. desired. According to the above method, a high-density tungsten or molybdenum target having a fine structure with an average grain size of 10 mm or less and a relative density of 99% or more can be obtained. [Example] High purity tungsten powder (W≧99.999% [Radioactive element content 3ppb or less, alkali metal content 100p
Pb or less], particle size FSSS (Fisher particle size) is 5
Fill a pressure-tight enclosure can (HIP can) with an internal volume of 400 x 300 x 30 (■) (5 x 11)" T
Heat at 400°C for 5 hours while evacuating to orr.
Surface adsorbed gas and moisture were released. After heating and degassing, seal and HIP at 1250°C x 2 hours at 1000 atm.
Processed. The density of the sintered body obtained at this time is 80-85% in terms of relative density. Thereafter, the sintered body together with the HIP can was hot-rolled several times at a temperature of 1300° C. at a processing rate of 10 to 30% each time until the cross section became 1100×330 mm and the thickness 10 mm. After rolling, processing strain was removed by strain relief annealing at 1200°C. After removing the HIP can, the obtained rolled material was machined into a predetermined shape to obtain a target with a diameter of 300 mm. The average particle size of the obtained target was 7 μl. Moreover, the relative density was 99.9% or more, which is almost the same value as the theoretical density. In terms of purity, there is no contamination during the manufacturing process, and W≧
99.999% [Radioactive element content was 3 ppb or less, alkali metal content was 100 ppb or less. ], the oxygen content was as low as 230 ppm. The sputtered film formed using this target was uniform and contained 50 particles on a 6-inch wafer. (Comparative example) High purity tungsten powder (W≧99.999% (radioactive element content 3ppb or less, alkali metal content 100p)
I) B or less], particle size FSSS (Fisher particle size), 5 μl or less) was filled into a die with an inner diameter of φ400■, and
Hot pressing was carried out under the conditions of 00°C x 300kg/ad x 0.5 hours. The obtained hot pressed body is cut,
Obtained the target of φ300 Kaku. The relative density of the target was 831. The number of particles in the sputtered film formed using this target was significantly greater than 200 particles on 76-inch wafers, which caused a decrease in wafer yield. [Effects of the Invention] As described above, according to the present invention, a tungsten or molybdenum target with a fine structure and a high density of 99% or more in relative density can be obtained. therefore,
Since cracks do not occur when machining the target and there is no anisotropy of crystal grains during sputtering, a uniform film can be formed. Procedural amendment (voluntary) 1999 1999 Patent application No. 286699 2 Name of the invention Tungsten or molybdenum target and its manufacturing method 3 Relationship to the person making the amendment Patent application Address 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Name (508) Hitachi Metals Co., Ltd. 4
Target of amendment Contents of amendment 10 The column of detailed explanation of the invention in the specification is amended as follows. (1) “Relative density is 99%” on page 4, line 17 of the specification.
Correct ``Netherworld'' to ``Relative density is 99% or more J.'' (2) "Process simplification J" on page 5, line 12 of the circular is corrected to "process simplification." (3) The rHIP cans in lines 1 and 2 of page 6 of the circular are vacuum degassed, sealed, and subjected to HIP. ” [HIP The can is sealed and subjected to HIP. Correct to J. (4) Circular, page 6, lines 19-20, ``The processing temperature is preferably in the range of 1200-1500℃.
[The processing temperature is preferably in the range of 1100-1500°C. If the temperature is less than 1100°C, hot workability is poor.'' (5) In the same book, page 9, lines 17 to 18, "A uniform film can be formed" was changed to "A uniform film can be formed and the number of particles in the film can be significantly reduced. The wafer yield is improved. Corrected to 6J.

Claims (1)

[Scope of Claims] 1. A tungsten or molybdenum target characterized by having a fine structure with an average grain size of 10 μm or less and a relative density of 99% or more. 2. A method for producing a tungsten or molybdenum target, which comprises producing a pre-sintered body using a high-purity tungsten or molybdenum powder raw material and then subjecting it to hot plastic working.