JP2003055758A - Tungsten sintered compact target for sputtering, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a tungsten sputtering target having high density and fine crystal structure so far impossible to attain by the conventional pressure sintering method alone and also having greatly improved transverse rupture strength by the improvement of the sintering characteristics and manufacturing conditions of tungsten powder to be used, hereby suppressing the occurrence of particle defect on a sputter-deposited film, and stably manufacturing the tungsten target at a low cost. SOLUTION: The tungsten target of sintered compact for sputtering has >=99% relative density, <=100 μm average particle size, <=20 ppm oxygen content and >=500 MPa transverse rupture strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tungsten target used for forming gate electrodes or wiring materials of ICs, LSIs, etc. by a sputtering method and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the high integration of VLSI, studies have been made on the use of materials having lower electric resistance values as electrode materials and wiring materials. High-purity tungsten, which is thermally and chemically stable, is regarded as a promising material for electrodes and wiring. The electrode material and wiring material for the VLSI are generally manufactured by a sputtering method or a CVD method. The sputtering method has a relatively simple structure and operation of the apparatus, can easily form a film, and is low in cost. Therefore, it is more widely used than the CVD method. However, when forming a film of an electrode material or wiring material for a VLSI by a sputtering method, if defects called particles are present on the film formation surface, failures such as wiring defects occur and the yield decreases. In order to reduce the generation of particles on the film formation surface, a tungsten target with high density and fine crystal grains is required.

Conventionally, as a method of manufacturing a tungsten target, an ingot is manufactured by using an electron beam melting method and hot-rolled (see Japanese Patent Laid-Open No. 61-10772).
8), a method in which tungsten powder is pressure-sintered and then rolled (hot rolled) (JP-A-3-150356, JP-A-6-220625) and a tungsten layer is laminated on one surface of a tungsten bottom plate by a CVD method. A so-called CVD-W method (Japanese Patent Laid-Open No. 6-158300) is known. However, the tungsten target produced by the electron beam melting method or the method of rolling the tungsten powder under pressure after sintering is mechanically fragile because the crystal grains are easily coarsened, and particle defects occur on the sputtered film. There is a problem that it is easy. For example, the transverse rupture strength of the target obtained by hot-rolling the tungsten powder after sintering is 400 MPa or less, which is considered to be due to the embrittlement peculiar to the rolling structure of the tungsten sintered material. Furthermore, a particular problem with rolled tungsten products is that starting from a block-shaped sintered material and subjecting this to a strong rolling process, a thick target or a target with a large target is only that. Requires large sintered materials. This is because such a large-sized sintered body is virtually unmanufacturable due to variations in composition segregation and composition. Recently, there has been a demand for a target having a thickness of more than 10 mm or a large target having a target size of 400φ or more, but there is a problem that a rolled product cannot meet these requirements. On the other hand, CVD
The -W method shows good sputtering characteristics, but it takes a lot of time and cost to manufacture a target, and there is a problem in that it is inferior in economic efficiency.

[0004]

DISCLOSURE OF THE INVENTION The present inventors focused their attention on a powder sintering method whose manufacturing process is relatively simple, and improved the sintering characteristics and manufacturing conditions of the tungsten powder to be used to improve the conventional method. We have created a tungsten target for sputtering that has a high density and fine crystal structure that could not be achieved only by the pressure sintering method, and dramatically increased the transverse rupture strength. It is intended to obtain a method of suppressing the cost and stably manufacturing the tungsten target at low cost.

[0005]

The present invention includes: 1. A tungsten sintered compact target for sputtering, which has a relative density of 99% or more, an average particle diameter of 100 μm or less, an oxygen content of 20 ppm or less, and a transverse rupture strength of 500 MPa or more. The total amount of alkali metals such as Na and K is 1 ppm or less,
The above 1 characterized in that the total amount of radioactive elements such as U and Th is 10 ppb or less, the carbon content is 10 ppm or less, and the total amount of transition metals or heavy metals such as Fe, Ni, Cr and Mo is 10 ppm or less. 2. Tungsten sintered compact target for sputtering The tungsten sintered compact target for sputtering according to the above 1 or 2, characterized in that the density is 99.5% or more, the average grain size is 80 μm or less, and the crystal grain size is isotropic and randomly oriented. 4. Powder specific surface area of 0.4 m ² / g (BET method) or more,
4. A method for producing a tungsten sintered compact target for sputtering, which comprises sintering using a tungsten powder having an oxygen content of 1000 ppm or less. Powder specific surface area of 0.6m ² /g~0.8m ² / g
5. The method for producing a tungsten sintered compact target for sputtering according to the above 4, which is (BET method) and has an oxygen content of 800 ppm or less. Using tungsten powder having a powder specific surface area of 0.4 m ² / g (BET method) or more, in a vacuum or a reducing atmosphere,
6. A method for producing a tungsten sintered compact target for sputtering, which comprises performing hot press sintering at a pressurization start temperature of 1200 ° C. or lower, and then hot isostatic pressing (HIP). Powder specific surface area of 0.6m ² /g~0.8m ² / g
(BET method) The method for manufacturing a tungsten sintered compact target for sputtering according to the above 6, which is the above. 8. 8. The method for producing a tungsten sintered compact target for sputtering according to the above 4 to 7, wherein the relative density is 93% or more by hot press sintering. Temperature 1600 ° C or higher, applied pressure 150 kg / cm ²
10. The method for producing a tungsten sintered compact target for sputtering according to each of 4 to 8 above, which is characterized by hot pressing. Hot isostatic pressing without capsulation (HI
11. P) The manufacturing method of the tungsten sintered compact target for sputtering as described in each of 4 to 9 above. Temperature 1700 ° C or higher, pressure 1000kg / c
12. The method for producing a tungsten sintered compact target for sputtering according to each of 4 to 10 above, wherein hot isostatic pressing is performed at m ² or more. Temperature over 1850 ° C, pressure 1800kg / c
A method for producing a tungsten sintered compact target for sputtering according to each of the above 4 to 10, wherein hot isostatic pressing is performed at m ² or more.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Generally, commercially available high-purity tungsten powder having a purity of 5N or more has a powder specific surface area of 0.3.
It is of m 2 ^{/ g} or less, an attempt to produce a tungsten target relative density of 99% or more by pressure sintering using tungsten powder is required firing temperatures above 2000 ° C. However, at a firing temperature of 2000 ° C. or higher, the crystal grains become larger than 100 μm and become coarse. Further, such pressure sintering at high temperature becomes an important problem such as a reaction between a die and tungsten in a hot pressing method or a reaction with an encapsulant in HIP, which increases the manufacturing cost.

It is generally known in powder metallurgy that the finer the particle size of the powder used, that is, the larger the specific surface area, the better the sinterability. However, as described above, the commercially available high-purity tungsten powder has a specific surface area of about 0.2 m ² / g even if it is fine. Therefore, the inventors of the present invention used ammonium metatungstate as a starting material, and carried out purification purification to obtain a purity of 5%.
By accelerating the removal rate of the hydrogen gas supply amount of the reaction product gas at the time of hydrogen reduction to N or more tungstate crystals having a specific surface area of 0.4m ² /g~0.8m ² / g, particle size 0.4 ~ 0.8μm, and oxygen content is 1000pp
A tungsten powder of m or less, preferably 800 ppm or less was prepared and used. Oxygen content is 1000p
If it exceeds pm, the sinterability will decrease, so it is desirable that the oxygen content of the tungsten powder used is low. Furthermore, as the material of the tungsten target of the present invention, the total amount of alkali metals such as Na and K that affect the semiconductor characteristics is 1 ppm or less, and the total amount of radioactive elements such as U and Th is 1 ppm.
0 ppb or less, carbon content of 10 ppm or less, Fe,
The sum of transition metals such as Ni, Cr and Mo or heavy metals is 1
Tungsten powder of 0 ppm or less is used.

Tungsten powder having such a large specific surface area is 1600 ° C. or higher, preferably 1800 ° C.
By hot pressing at a temperature of C or higher, a pressing force of 150 kg / cm ² or higher, and a pressure starting temperature of 1200 ° C. or lower,
Since the relative density was 93% or more and the pore morphology became closed pores, it became possible to perform HIP treatment without encapsulation. If the pressurization start temperature exceeds 1200 ° C, the growth of crystal grains will occur and the sinterability will decrease, and the density of closed pores (93% or more) that enables HIP without capsules.
Therefore, the hot pressing temperature of 2000 ° C. or higher is required, and there are problems as described later. Therefore, it is desirable to set the pressurization start temperature to 1200 ° C. or lower. As described above, if the hot pressing temperature is 2000 ° C or higher, it is effective for densification, but problems such as coarsening of crystal grains and reaction with a die occur. Therefore, hot pressing at 1900 ° C or lower is preferable. It is desirable to do. Further, when hot pressing is performed, by using carbon sheets on the upper surface and the lower surface, it is possible to promote the dissociation of oxygen from the material.

Then, the HIP process is further performed at a temperature of 1700.
° C or higher, preferably 1850 ° C or higher, pressure 1000 kg / cm ² or higher, preferably 1800 kg
/ Cm ² or more, a relative density of 99% or more,
Average crystal grain size of 100 μm or less, and further average crystal grain size of 8
A tungsten target of 0 μm or less can be obtained. In this case, the crystal grain shape is an isotropic shape and has a random orientation, unlike the rolled product, which does not have irregular shaped grains. Further, the HIP processing in this case can be performed without capsules. The larger the specific surface area of the tungsten powder, the higher the density of the tungsten sintered body after hot pressing and the finer crystal structure, so that the density increase by the HIP treatment becomes easier and the density after the HIP treatment also becomes higher.
Generation of particle defects was significantly reduced on the film produced using the tungsten target obtained by this.

[0010]

[Examples and Comparative Examples] Hereinafter, examples and comparative examples will be described. The present embodiment is merely an example, and the present invention is not limited to this example. That is,
It is intended to cover other aspects or variations included in the invention.

(Example 1, Example 2, Example 3) Powder specific surface areas 0.42 m ^{2 /} g, 0.62 m ^{2 /} g, 0.7
8m ² / g oxygen content 360ppm, 54 respectively
Pressurized with 800 ppm and a pressure of 300 kg / cm ² using 0 ppm and 840 ppm of tungsten powder,
Hot press firing was performed at 00 ° C and 1800 ° C for 2 hours (Example 1, Example 2, and Example 3 respectively). Table 1 shows the relative density of the obtained tungsten sintered body. This tungsten sintered body is further processed at 1800 ° C, 1
Relative density, average particle size, oxygen content, three-point bending transverse strength of a sintered body obtained by HIP treatment under the conditions of 500 kg / cm ² and 2 hr, and when sputtering was performed using this tungsten sintered body. Table 2 shows the number of particles on the film formation. As shown in Table 1, the relative density of the sintered body after hot pressing was 93.7% to 98.2%. Moreover, as shown in Table 2, the relative density of the tungsten sintered body after the HIP treatment was 99% to 99.8%. The average crystal grain size of the sintered body obtained as described above is 55 μm to 88 μm,
All were 100 μm or less. Further, the oxygen content is 20 ppm or less, and the transverse rupture strength is 520 MPa.
It was ~ 630 MPa and was 500 MPa or more. The number of particles on the film sputtered using this tungsten sintered body was 0.03 to 0.07 particles / cm ² , and all were 0.1 particles / cm ² or less, and a very good film was obtained.

[0012]

[Table 1]

[0013]

[Table 2]

(Examples 4 and 5) Tungsten oxide powders obtained by hydrogen reduction were preserved without exposing the tungsten powders to the atmosphere, and the specific surface areas of the powders were 1.1 m ² / g and 1.4 m ² / g. , And oxygen content is 790pp each
m and 890 ppm of tungsten powder were used (Examples 4 and 5 respectively), and various characteristics of the hot-press sintered body and the sintered body after HIP treatment which were produced under the same conditions as in Example 1 were the same. It shows in Table 1 and Table 2. From these results, all the sintered bodies had a relative density of 99.5% or more, an oxygen content of 20 ppm or less, an average crystal grain size of 60 μm or less, and a transverse rupture strength of 600 MPa or more. The number of particles on the film formed using this tungsten sintered body was 0.01 particles / cm ^{2 to} 0.05 particles / cm ² , and a good film was obtained.

(Examples 6, 7 and 8) Tungsten powder having a specific surface area of 0.78 m ² / g and an oxygen content of 840 ppm was used, and the pressing force by hot pressing was 150,
Various characteristics of the hot-press sintered body and the sintered body after HIP treatment, which were produced under the same conditions as in Example 3, except that they were set to ²⁰⁰ and 300 kg / cm ² (Example 6, Example 7 and Example 8 respectively). It shows in Table 3. The relative density of the obtained sintered body is 9
9.7% to 99.8%, average particle size is 67 μm to 72 μm
Thus, a sintered body having a relative density of 99% or more and an average particle size of 100 μm or less could be obtained.

[0016]

[Table 3]

(Examples 9 and 10) Specific surface area 0.7
Using tungsten powder of 8 m ² / g and oxygen content of 840 ppm, a pressure of 300 kg / cm ² was applied from 1000 ° C. and 1200 ° C. (Example 9 and Example 10 respectively), and hot pressing was performed at 1800 ° C. for 2 hours. Table 3 shows the relative density and average crystal grain size of the tungsten sintered body produced under the same conditions as in Example 3 except that firing was performed. Both are H
The relative density after IP treatment was 99% or more, and the average crystal grain size was 100 μm or less.

(Comparative Example 1, Comparative Example 2, Comparative Example 3) Using tungsten powder having a specific surface area of 0.23 m ² / g and an oxygen content of 210 ppm, a pressing force of 300 kg / cm ² and a temperature of 16 were used.
HIP treatment was performed on the sintered bodies that were respectively hot-press fired at 00 ° C., 1800 ° C., and 2200 ° C. under the same conditions as in Example 1 (Comparative Example 1, Comparative Example 2, and Comparative Example 3). Various properties of the obtained sintered body are also shown in Table 1.
Comparative Example 1 temperature 1600 ° C and Comparative Example 2 1800 °
The relative density of the sintered body hot-pressed with C was 99% or less after the HIP treatment, and the number of particles on the film formed by sputtering was 0.6 / cm ² and 1.7 / cm ^2, which were large. It was not suitable for practical use. In addition, 2200 of Comparative Example 3
Although the relative density after HIP treatment reached 99%, the average grain size was 17
The particle size was as large as 7 μm, and the number of particles on the film formed by sputtering was large at 0.3 particle / cm ² .

(Comparative Example 4) A tungsten powder having a specific surface area of 1.1 m ² / g and an oxygen content of 1310 ppm was used.
Hot press firing was performed at 800 ° C. and 300 kg / cm ² . Then, HIP treatment was performed under the same conditions as in Example 1. Various properties of the obtained sintered body are also shown in Table 1. H
The relative density of the sintered body after IP treatment was 97.5%, which was 9
It was 9% or less.

(Comparative Example 5) The hot press pressure was 120 k.
A tungsten sintered body was produced under the same conditions as in Example 3 except that g / cm ² was used. The relative density and average particle size of the obtained sintered body are similarly shown in Table 2. Average crystal grain size is 55 μm
However, the relative density was as low as 94.7%.

(Comparative Example 6) Table 2 shows the relative density and average crystal grain size of a tungsten sintered body produced under the same conditions as in Example 4, except that the pressure starting temperature during hot pressing was 1400 ° C. Show. The average crystal grain size is 98μm and 100μ
Although it was less than m, it was larger than the average crystal grain size obtained in other examples, and the relative density was 99% or less, which is unsuitable as a target for high quality film formation. It was

[0022]

The sputtering tungsten target produced by the method of the present invention is characterized in that it has a higher density and a smaller crystal grain size than the tungsten target obtained by the conventional pressure sintering method. Folding power can be dramatically increased, and conventional CVD-W
It has an effect that the manufacturing cost can be remarkably reduced as compared with the method. Further, by sputtering using this tungsten target, particle defects on the film are remarkably reduced and the product yield is greatly improved.

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[Procedure amendment]

[Submission date] September 21, 2001 (2001.9.2)
1)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 5

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

Conventionally, as a method of manufacturing a tungsten target, an ingot is manufactured by using an electron beam melting method and hot-rolled (see Japanese Patent Laid-Open No. 61-10772).
8), a method in which tungsten powder is pressure-sintered and then rolled (hot rolled) (JP-A-3-150356, JP-A-6-220625) and a tungsten layer is laminated on one surface of a tungsten bottom plate by a CVD method. A so-called CVD-W method (Japanese Patent Laid-Open No. 6-158300) is known. However, the tungsten target produced by the electron beam melting method or the method of rolling the tungsten powder under pressure after sintering is mechanically fragile because the crystal grains are easily coarsened, and particle defects occur on the sputtered film. There is a problem that it is easy. For example, the transverse rupture strength of the target obtained by hot-rolling the tungsten powder after sintering is 400 MPa or less, which is considered to be due to the embrittlement peculiar to the rolling structure of the tungsten sintered material. Furthermore, a particular problem with rolled tungsten products is that starting from a block-shaped sintered material and subjecting this to a strong rolling process, a thick target or a target with a large target is only that. Requires large sintered materials. Such a large sintered body has a different structure and density.
Non-uniformity is likely to occur . Recently, the target thickness is 1
More than 0 mm or target size is 400φ
The above-mentioned large targets are required, but there is a problem that rolled products cannot meet these requirements. On the other hand, CVD-W method shows good sputtering characteristics, it takes much time and cost for production of the target, if there is a problem of poor economy at the same time, columnar structure
Therefore, there is also a problem that the mechanical strength is low .

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

[0005]

The present invention includes: 1. A tungsten sintered compact target for sputtering, which has a relative density of 99% or more, an average particle diameter of 100 μm or less, an oxygen content of 20 ppm or less, and a transverse rupture strength of 500 MPa or more. The total amount of alkali metals such as Na and K is 1 ppm or less,
The above 1 characterized in that the total amount of radioactive elements such as U and Th is 10 ppb or less, the carbon content is 10 ppm or less, and the total amount of transition metals or heavy metals such as Fe, Ni, Cr and Mo is 10 ppm or less. 2. Tungsten sintered compact target for sputtering The tungsten sintered compact target for sputtering according to the above 1 or 2, characterized in that the density is 99.5% or more, the average grain size is 80 μm or less, and the crystal grain size is isotropic and randomly oriented. 4. Powder specific surface area of 0.4 m ² / g (BET method) or more,
4. A method for producing a tungsten sintered compact target for sputtering, which comprises sintering using a tungsten powder having an oxygen content of 1000 ppm or less. Powder specific surface area of 0.6m ² /g~0.8m ² / g
A (BET method), the following data oxygen content 800ppm
5. A method for producing a tungsten sintered compact target for sputtering according to the above item 4, characterized in that it is sintered by using a tungsten powder . Using tungsten powder having a powder specific surface area of 0.4 m ² / g (BET method) or more, in a vacuum or a reducing atmosphere,
6. A method for producing a tungsten sintered compact target for sputtering, which comprises performing hot press sintering at a pressure starting temperature of 1200 ° C. or lower, and then hot isostatic pressing (HIP). Powder specific surface area of 0.6m ² /g~0.8m ² / g
(BET method) The method for manufacturing a tungsten sintered compact target for sputtering according to the above 6, which is the above. 8. 8. The method for producing a tungsten sintered compact target for sputtering according to the above 4 to 7, wherein the relative density is 93% or more by hot press sintering. Temperature 1600 ° C or higher, applied pressure 150 kg / cm ²
10. The method for producing a tungsten sintered compact target for sputtering according to each of 4 to 8 above, which is characterized by hot pressing. Hot isostatic pressing without capsulation (HI
11. P) The manufacturing method of the tungsten sintered compact target for sputtering as described in each of 4 to 9 above. Temperature 1700 ° C or higher, pressure 1000kg / c
12. The method for producing a tungsten sintered compact target for sputtering according to each of 4 to 10 above, wherein hot isostatic pressing is performed at m ² or more. Temperature over 1850 ° C, pressure 1800kg / c
A method for producing a tungsten sintered compact target for sputtering according to each of the above 4 to 10, wherein hot isostatic pressing is performed at m ² or more.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) // B22F 1/00 B22F 1/00 PF term (reference) 4K018 AA20 BA09 BB04 BB10 EA02 EA12 EA13 EA19 KA29 4K029 BA02 BD02 DC03 DC09 4M104 BB18 DD40 HH20

Claims (12)

[Claims] 1. A relative density of 99% or more and an average particle size of 100 μm.
m or less, oxygen content 20ppm or less, bending strength of 500M
A tungsten sintered compact target for sputtering, characterized in that it is at least Pa. 2. The total amount of alkali metals such as Na and K is 1 p.
pm or less, total amount of radioactive elements such as U and Th is 10 ppb
Hereinafter, the carbon content is 10 ppm or less, Fe, Ni, C
The total amount of transition metals such as r and Mo or heavy metals is 10 ppm
The tungsten sintered compact target for sputtering according to claim 1, wherein: 3. The density is 99.5% or more, and the average particle size is 80 μm.
The tungsten sintered compact target for sputtering according to claim 1 or 2, wherein the sputtering target is for m or less, the crystal grain shape is isotropic, and randomly oriented. 4. A powder specific surface area of 0.4 m ² / g (BET
Method), and sintering using a tungsten powder having an oxygen content of 1000 ppm or less. 5. The powder has a specific surface area of 0.6 m ^{2 /} g to 0.8.
m ² / g (BET method), oxygen content 800 ppm
The method for manufacturing a tungsten sintered compact target for sputtering according to claim 4, wherein: 6. The powder has a specific surface area of 0.4 m ² / g (BET
Method), using the above-mentioned tungsten powder, performing hot press sintering at a pressure starting temperature of 1200 ° C or lower in a vacuum or a reducing atmosphere, and then hot isostatic pressing (HIP)
A method of manufacturing a tungsten sintered compact target for sputtering, comprising: 7. The powder has a specific surface area of 0.6 m ^{2 /} g to 0.8.
The method for producing a tungsten sintered compact target for sputtering according to claim 6, characterized in that it is at least m ² / g (BET method). 8. The relative density is 93 by hot press sintering.
% Or more, and the method for manufacturing a tungsten sintered compact target for sputtering according to claim 4 or 7. 9. A temperature of 1600 ° C. or higher and a pressing force of 150 k
The method for producing a tungsten sintered compact target for sputtering according to each of claims 4 to 8, wherein hot pressing is performed at g / cm ² or more. 10. The method for producing a tungsten sintered compact target for sputtering according to claim 4, wherein hot isostatic pressing (HIP) is performed without capsulation. 11. A temperature of 1700 ° C. or higher and a pressing force of 100.
The method for producing a tungsten sintered compact target for sputtering according to each of claims 4 to 10, wherein hot isostatic pressing is performed at 0 kg / cm ² or more. 12. A temperature of 1850 ° C. or higher and a pressing force of 180.
The method for producing a tungsten sintered compact target for sputtering according to each of claims 4 to 10, wherein hot isostatic pressing is performed at 0 kg / cm ² or more.