JPH0539504A - Mold for hot pressing - Google Patents

Abstract

PURPOSE:To provide a mold for hot pressing preventing contamination by thermal diffusion at the time of hot-pressing high purity metal or ceramic powder and enabling the production of a high purity dense sintered body. CONSTITUTION:This mold for hot pressing is a cylindrical one forming the furnace core part of a device for hot-pressing metal powder, etc. The outer cylinder 1 of the mold is made of a carbon bonded carbon fiber composite material contg. <=900ppm impurities including <=25ppm Na, <=25ppm K, <=80ppm Fe, <=90ppm Al, <=15ppm Ni, <=10ppm Cr and <=30ppm V except C as an essential component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot pressing mold used for sintering metal powder and ceramic powder.

[0002]

2. Description of the Related Art In order to obtain a sintered body such as a metal powder or a ceramic powder, the following method has been conventionally used. That is, first, an outer cylinder made of a carbon-bonded carbon fiber composite material (C / C composite material) is prepared, and an inner cylinder to be provided on the inner surface thereof is made of a heat resistant material such as graphite. Then, the outer cylinder and the inner cylinder are set in an appropriate induction furnace while having a predetermined fitting relationship, and a required hot pressing mold is obtained. Then, by loading a powdered substance to be sintered or a preformed substance to be sintered onto this hot press mold, and press-sintering under various conditions such as a predetermined temperature, time and pressure. Allowed to obtain the desired sintered body. However, according to this conventional method, a harmful element from the outer cylinder of the mold made of the C / C composite material infiltrates into the sintered body by thermal diffusion in the above-mentioned pressure sintering process, and the sintered body concerned. Under the present circumstances, it is not possible to obtain a satisfactory sintered product by remarkably deteriorating the various properties of the above, or by causing a decrease in its purity.

[0003]

The object of the present invention is to clarify the cause of adverse effects on the sintering of such metal powder or ceramic powder, and to provide a hot pressing mold capable of producing a dense and high-purity sintered body. To provide.

[0004]

[Means for Solving the Problems] Examples of the sintered metal produced by hot pressing include simple metals such as tungsten, molybdenum, titanium, rhenium, hafnium, chromium, and cobalt, and metal compounds such as silicides of the above metals. Can be mentioned. One of the specific uses of high-purity substances among these simple metals and metal silicides is
It is to be used as a wiring material for LSI as a sputtering target material. By the way, since there is such an application, with respect to the metal simple substance or the metal silicide, which should be of high purity, the following various impurity content rates in the hot pressing mold are set to be equal to or less than a predetermined value. Is needed. That is, an alkali metal which is ionized in a semiconductor element and easily moves in the gate insulating film to deteriorate the MOS interface characteristics; iron, aluminum, chromium, nickel, etc. which cause interface states or junction leakage It is necessary to set the content of impurities such as various metals; and vanadium that acts as a reducing agent to a predetermined value or less.

On the other hand, ceramic sintered materials produced by hot pressing that require high purity include ceramic target materials used for sputtering as well as metals. Such a ceramic target material is used as a thermal head, a transparent conductive film, a protective film, etc., and is also advantageous for rust prevention of various metals, surface strengthening, solar heat collectors, window frame materials for amorphous solar cells, etc. Is what is used. By the way, in order to exert the function of the thin film here, the material needs to maintain a certain degree of purity. Then, for this purpose, it was found that each impurity contained in the hot pressing mold has a specific critical impurity content rate.

Therefore, in order to obtain a dense and high-purity sintered product, the ultrafine powder raw material must be hot-pressed without adding a sintering aid which is harmful to the final product. At the same time, a sintering process must be performed so that thermal diffusion of impurities from the hot pressing mold does not occur.

Therefore, what has been taken in accordance with the present invention is that the content of impurities in the C / C composite material, which is the base material of the hot pressing mold, is 900 ppm or less, and that the heat diffusion from the hot pressing mold is specified. To reduce harmful elements to a certain level or less.

As one of the specific examples of the present invention, as a result of investigation and research on the cause of junction leakage of semiconductor electrodes, the following was found in the case of a sputtering target material manufactured by the hot pressing method. That is, the iron content of the C / C composite material, which is the outer cylinder of the mold, is 80 ppm or less; the aluminum content is 90 ppm or less; the nickel content is 1
When the content of chromium was 5 ppm or less; the content of chromium was 10 ppm or less; and the content of vanadium was 30 ppm or less, it was found that the trouble did not occur. At the same time, research and study were also conducted on the influence of alkali metals that cause deterioration of the interface characteristics of the MOS. As a result, the sodium content of the C / C composite material, which is the outer cylinder, was 25 ppm or less. It was also found that no problem occurs when the potassium content is 25 ppm or less.

However, when the total content of impurities contained in the C / C composite material, which is the outer cylinder of the mold used for hot pressing, exceeds 900 ppm, gasification of the impurities causes the formation of the above-mentioned specific impurities. Even if the content is below a certain amount, its diffusion rate increases,
As a result, it causes trouble. Therefore, the total content of the impurities should be 900 ppm or less.

Further, regarding the ceramic target material such as the thermal head, the transparent conductive film and the protective film, the C / C which is the outer cylinder of the hot pressing mold used in the production thereof is also used.
In the composite material, the iron content is 80 ppm or less; the aluminum content is 90 ppm or less; the nickel content is 15 ppm or less; the chromium content is 10 ppm or less; the vanadium content is 30 ppm or less; and the total impurity content. When the amount was 900 ppm or less; it was confirmed that the trouble of contamination by impurities was drastically reduced.

The shape of the hot pressing mold according to the present invention may be a cylindrical shape, a rectangular tube shape, or a free-form shape having various curved shapes, depending on the shape of the sintered body to be finally obtained. Applicable.

The C / C composite material used in the present invention is manufactured by the following typical method. That is, first
A cylindrical structure is assembled using carbon fibers starting from synthetic polymer materials such as polyacrylonitrile, rayon, and phenol resin, or carbon fibers starting from petroleum pitch, coal pitch, or the like. Next, after impregnating such a structure with a carbonizing resin such as a phenol resin or a furan resin or pitches and curing the structure, 700 ° C
By firing and carbonizing at the above heating temperature, a C / C composite material as a final product can be obtained. In order to obtain a more dense and high-strength C / C composite material, it is appropriate to repeat the above-mentioned resin impregnation-curing-carbonization process a required number of times.

As another method for obtaining such a C / C composite material, instead of the method of resin impregnation as described above, pyrolytic carbon is uniformly deposited in the carbon fiber structure by a CVD process. There is also a way to do it.

[0014]

According to the present invention, the content of each of iron, aluminum, nickel, chromium and vanadium contained in the C / C composite material, which is the outer cylinder of the hot pressing mold, is set to a certain value or less. Contamination during sintering of an electrode sputtering target for a semiconductor is prevented. Then, this suppresses the generation of the interface state of the thin film based on the obtained sputtering target, and as a result, acts to eliminate the cause of junction leak and the like. Similarly, by setting the content of the alkali metal contained in the C / C composite material, which is the outer cylinder of the hot pressing mold, to a certain value or less, the MOS interface characteristics of the thin film based on the obtained sputtering target. It acts to prevent deterioration of the. It is considered that the ceramic target material has the same action.

Further, according to the present invention, the total amount of impurities of the C / C composite material, which is the outer cylinder of the hot pressing mold, is set to a certain value or less, so that the elements gasified from the hot pressing mold are changed. Based effects can be minimized.

[0016]

EXAMPLES Next, examples of the present invention will be described. Figure 1
It is a schematic sectional drawing of the hot press apparatus in which the mold for hot pressing which concerns on this invention is used. In FIG. 1, reference numeral 1 denotes a hot press mold outer cylinder made of a C / C composite material,
Reference numeral 2 denotes an inner cylinder of a hot pressing mold, which are fitted to each other. Reference numeral 3 denotes a heat insulating material having an appropriate material and shape, which is configured to surround the hot press mold outer cylinder 1 and the hot press mold inner cylinder 2. Reference numeral 4 denotes a required substance to be sintered, which is loaded in the hot press mold inner cylinder 2. One set of punch 5, push rod 6 and press base 7 is provided above and below the hot press mold inner cylinder 2 in which the substance to be sintered 4 is charged. The pressure required for 4 is applied. Further, an induction heating coil 8 is provided on the outer periphery of the heat insulating material 3, and the material to be sintered 4 is
Used for heating. For comparison with the case of the embodiment of the present invention, the case not according to the embodiment of the present invention is given as a comparative example.

[Example 1]: The following results were obtained when the ash content analysis by the emission spectroscopy was performed on the C / C composite material which was heated in a chlorine gas atmosphere and deashed. That is, the total content of impurities is 50 ppm; the content of iron is 3.1 ppm; the content of aluminum is 4.1 pp.
m; nickel content is 2.5 ppm; chromium content is 1.1 ppm; vanadium content is 0.9 ppm;
The sodium content was 1.0 ppm; and the potassium content was 0.7 ppm.

Using such a C / C composite material as an outer cylinder of a mold and an inner cylinder made of a high-purity graphite material, a hot press mold having an outer diameter of Φ350 mm × an inner diameter of Φ200 × height of 200 mm was prepared. .. Then, the following molybdenum silicide (MoSi
2) 14.0 kg of powder was charged. That is, the content of iron, aluminum, nickel, chromium, vanadium, sodium, and potassium as metal impurities is 0.03 ppm or less, and molybdenum silicide (MoSi) is used.
2) 14.0 kg of powder was charged. Put this in a hot press furnace and 300 kg / cm2 under argon gas atmosphere.
The temperature was maintained at 1320 ° C. for 2 hours while pressurizing. After that, the target disc was obtained as a final product by cooling at an appropriate pace. A part of the target disk thus obtained was taken out as a sample piece, and the content of impurities was measured for this.The content of iron, aluminum, nickel, chromium, vanadium, sodium, and potassium was
All were 0.03 ppm or less.

Example 2 The required ash content of the C / C composite material, which had been subjected to a predetermined thermal deashing treatment in a vacuum heating furnace, was analyzed and the results are as follows. That is, the total content of impurities is 470 ppm; the content of iron as individual impurities is 50.5 ppm; the content of aluminum is 61.2 pp
m; chromium content is 2.7 ppm; nickel content is 8.1 ppm; vanadium content is 3.8 ppm;
The sodium content was 10.0 ppm; and the potassium content was 4.5 ppm. C / C like this
Using a hot pressing mold having a composite material as an outer cylinder, the content of iron, nickel, chromium, vanadium, sodium and potassium as metal impurities was 0.07 ppm or less, as in the case of Example 1 above. 6.5 kg of silicon carbide (SiC) powder was charged into the hot pressing mold. Put this in a hot press furnace,
The temperature was maintained at 2000 ° C. for 1 hour while pressurizing to 350 Kg / cm 2 under an argon gas atmosphere. After that, the target disc was obtained as a final product by cooling at an appropriate pace. A part of the target disk thus obtained was taken out as a sample piece, and the content of impurities was measured for it. Iron, nickel, chromium, vanadium, sodium,
And the content of potassium is 0.09ppm
It was below.

[Comparative Example 1]: Total impurity content is 960 p
pm; content of iron as individual impurities is 93.3 pp
m; aluminum content 95.2 ppm; nickel content 2.5 ppm; chromium content 8.8 pp
m; vanadium content 17.1 ppm; sodium content 41.0 ppm; and potassium content 10.9 ppm C / C composite material as an outer cylinder,
Outer diameter Φ350mm × inner diameter Φ200mm × height 200mm
A hot pressing mold was prepared. Following this, iron, aluminum, nickel, chromium as metal impurities,
Molybdenum silicide (MoSi) with vanadium, sodium and potassium contents of 0.03 ppm or less
2) Add powder to this hot press mold at 14.0K
Charged only g. Then, hot pressing was performed under the same conditions as in Example 1 described above to produce a target disk as a final product. The results of measuring the impurity content of the sample piece taken out from the target disk thus produced were as follows. That is,
Content of iron as individual impurities is 9.0 ppm; content of aluminum is 4.4 ppm; content of nickel is 2.2 ppm; content of chromium is 3.0 ppm; content of vanadium is 1.9 ppm; sodium Content is 7.0 ppm; and potassium content is 1.1 pp
It was m.

[Comparative Example 2]: Using the same hot pressing mold as in Comparative Example 1 described above, iron, aluminum, nickel, chromium, vanadium as metal impurities,
The content of both potassium and potassium is 0.07
6.5 kg of silicon carbide (SiC) powder below ppm was charged. On the other hand, hot pressing was performed under the same conditions as in Example 2 to produce a target disk as a final product. Then, with respect to the sample piece taken out from the target disk thus obtained, the measurement result of the predetermined impurity content was as follows. That is, the content of iron as an individual impurity is 7.9.
ppm; aluminum content is 4.0 ppm; nickel content is 2.1 ppm; chromium content is 3.2 p
pm; vanadium content was 2.5 ppm; sodium content was 8.0 ppm; and potassium content was 2.1 ppm.

[0022]

As described above, by hot-pressing high-purity metal powder or ceramic powder using the hot-pressing mold of the present invention, contamination due to thermal diffusion is prevented, and high-purity and homogeneous sintering is performed. The body can be manufactured with good yield. In particular, the use of the hot pressing mold according to the present invention makes it possible to remove the influence of contamination by a certain specific impurity when producing a sputtering target material made of metal or ceramics, and various electric It is extremely useful for obtaining thin films having excellent physical properties and electronic properties.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a hot press machine in which a hot press mold according to the present invention is used.

[Explanation of symbols]

1 --- C / C composite material hot press mold outer cylinder, 2 --- hot press mold inner cylinder, 3 --- heat insulating material, 4 --- sintered substance, 5--punch, 6 --- pushing rod, 7 --- Stamp, 8 --- Induction heating coil.

Claims (1)

[Claims] 1. A cylindrical hot pressing mold that constitutes a furnace core of a device for hot pressing metal powder or ceramic powder, wherein the outer cylinder of the mold is made of carbon-bonded carbon fiber composite material. The total content of impurities other than carbon as the main component of the carbon-bonded carbon fiber composite material is 900 p
pm or less; sodium content in the above impurities is 25 ppm or less; potassium content is 25 ppm or less;
Iron content is 80 ppm or less; Aluminum content is 90 ppm or less; Nickel content is 15 ppm or less;
Content of chromium is 10 ppm or less; Content of vanadium is 30 ppm or less;