JPH042540B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a high-melting point metal silicide target, and particularly to a high-density and high-density target used for forming thin films such as electrodes and wiring materials of semiconductor devices. This invention relates to a method for manufacturing high-quality high-melting-point metal silicide targets with high productivity.
The high-melting point metal includes Mo, W, Ti, Nb, Ta, etc., and Mo and W are particularly representative examples here. This target is especially suitable for VLSI/MOS
It is useful for manufacturing gate electrodes and drain electrodes of devices.

Background of the Invention Electrodes or wiring of semiconductor devices, especially MOS/
Polysilicon has traditionally been used as the gate electrode and drain electrode of LSI, but
As devices become more highly integrated, signal propagation delays due to the resistance of polysilicon gate electrodes and drain electrodes become a problem. On the other hand, in order to facilitate the formation of MOS elements by the self-alignment method, it is desired to use materials with high melting points for the gate electrode and the drain electrode. Under these circumstances, research is progressing on high-melting point metal gate electrodes and drain electrodes, which have lower resistivity than polysilicon, while research on high-melting point metal silicide electrodes, which prioritize compatibility with silicon gate processes, is actively progressing. . Promising examples of such refractory metal silicides are molybdenum silicide (MoSix) and tungsten silicide (WSix).

Sputtering methods and electron beam evaporation methods are effective methods for forming refractory metal silicide thin films for electrodes or wiring of semiconductor devices. The sputtering method is a method in which a target plate is bombarded with argon ions to release metal, and the released metal is deposited on a substrate facing the target plate. The electron beam evaporation method is a method in which an ingot evaporation source is melted by an electron beam and vapor deposition is performed. In any case, the purity and other properties of the produced film depend on the purity, composition, sputtering characteristics, etc. of the target plate or evaporation source.

Hereinafter, in this specification, "target" means
This term includes all refractory metal silicide articles shaped into plates or other forms as sputtering sources or vapor deposition sources.

Prior art and its problems JP-A-60-66425 discloses a method for producing a molybdenum silicide target, particularly using molybdenum as a high melting point metal. Here, we start with a process of mixing specially prepared high-purity molybdenum powder and commercially available high-purity silicon powder, and then (1) pressure molding (cold isostatic processing method) and (2)
Produce a sintered body through the process of sintering, followed by (3)
A MoSix ingot is produced by an electron beam melting process, and (4) the ingot is given a desired shape by a plastic working process (hot extrusion method or vacuum forging method), and finally, cutting, surface finishing, etc. The target is manufactured through finishing processing.

The target produced by the above method has extremely high purity, with trace amounts of alkali metal elements and radioactive elements harmful to semiconductor devices being reduced, and is useful for producing gate electrodes and the like.
However, there are the following problems regarding the process: (a) As the process goes through the four steps of cold isobaric processing, sintering, electron beam melting, and plastic working as described above, there are many steps and Each process itself requires effort, time, and expensive equipment, making it unsuitable for industrial scale production.

(b) There is a lot of volatilization loss of silicon during electron beam melting, which makes it difficult to adjust x of MoSix.

On the other hand, apart from the above method, there is a method of manufacturing by a sintering method that does not involve a melting process, but conventionally, high melting point metal silicide targets manufactured by the sintering method have a density ratio of about 80 to 90%. Due to the low air gap,
Due to the presence of 10 to 20%, heat conduction is not uniform within the target during sputtering, resulting in a serious drawback that the target cracks. Cracking of the target has the problem of deteriorating the sputtering properties of the target and preventing the formation of a good quality thin film.

Summary of the Invention In view of these problems, the present inventors first achieved a density of 97% or more from synthesized high-melting point metal silicide powder by uniaxial compression molding under conditions of high temperature, high vacuum, and high press pressure. proposed a method for producing a high melting point metal silicide target as a sintered product (Japanese Patent Application No. 1986-210086). This method is
This method completely abandons the four processes of cold isopressure pressing, sintering, electron beam melting, and plastic processing, and manufactures high-density sintered product targets using only the uniaxial compression molding process. It was revolutionary in that it simultaneously achieved two difficult-to-achieve goals: simplification and improvement of the target density ratio.

After that, as a result of continued trials, although the process was greatly simplified, the process time was long.
The drawback of not being able to increase productivity to the desired level has become newly recognized. In the above proposed method, the upper limit of the heating temperature during uniaxial compression molding was set at 1300°C. This is because the melting point of Si is 1410°C, so using a high temperature exceeding 1300°C may cause partial melting of the material and was considered dangerous.

However, the inventor of the present invention dared to try machining in a high temperature range exceeding this upper limit setting of 1300℃, and found that if the temperature exceeds 1300℃ and reaches 1380℃,
It was confirmed that the work could be carried out without the risk of part of the material melting. Surprisingly, it was also found that in this high temperature range of over 1300°C, the molding time to obtain the desired density was significantly shorter than expected. For example, it would take 3 hours at 1300°C, but at 1320°C, which is just 20°C higher, the time is reduced to 0.5 hours. This shortening effect was completely unexpected. Furthermore, the higher the temperature, the greater the deoxidizing effect, and there is the advantage that a low-oxygen product can be obtained. The demand for low-oxygen products has been increasing recently, and from this point of view, molding at high temperatures above 1300°C is effective. Through this high-temperature pressing, we succeeded in achieving an ultra-high density of 99.9%.

Under these considerations, the present invention provides high melting point metal silicide powder at high temperatures of over 1300°C up to 1380°C, high vacuum of 10 ^-5 to ^{10 -6} mbar and 250 to 250 mbar.
It has a density ratio of over 97% and is characterized by being uniaxially compression molded under high press pressure conditions of 600Kg/ ^cm2 .
A method for manufacturing a target made of high melting point metal silicide, which is a sintered product, is provided. High melting point metal silicide powder is produced by mixing high melting point metal powder and silicon powder in a predetermined ratio, synthesizing the silicide under high temperature vacuum, crushing and classifying the synthetic silicide, adding silicon powder to the synthetic silicide powder, and wet-mixing. It can be obtained by washing and drying under vacuum.

DETAILED DESCRIPTION OF THE INVENTION First, an example of synthesis of high melting point metal silicide powder will be described. As high melting point metal powder represented by tungsten and molybdenum and silicon powder raw materials, those with low radioactive element and low alkali metal content are used. Such raw silicon powder having a purity of 9N or higher is easily commercially available. Recently, the alkali metal content of raw material high melting point metal powder has also increased.
Technology has been established to prepare highly purified products of 5N or higher with a radioactive element content of 1000 ppb or less and a radioactive element content of 100 ppb or less. This method involves dissolving conventionally commercially available high melting point metals or their compounds to produce an aqueous solution, purifying the aqueous solution, crystallizing high melting point metal crystals, and solid-liquid separation, washing and drying of the crystals. After that, high-purity high-melting point metal powder is prepared by heating and reducing the powder. Further, by subjecting these powders to purification treatment such as redissolution, even higher purity can be obtained.

These raw material powders are mixed using a V-type mixer etc. under a predetermined ratio corresponding to WSix, MoSix, etc.
For example, thermal synthesis is performed in a vacuum resistance furnace. 10 ^-3
Synthesis is carried out under the conditions of ~10 ^-5 mbar x 1050~1250°C for a sufficient time according to the following formula: W (Mo) + xSi → WSix (MoSix) Thus, carmela-like silicide (WSix,
MoSix) is synthesized.

The synthetic silicide is pulverized using a vibrating mill or other pulverizer, and classified into 35 to 45 mesh particles to obtain synthetic silicide powder.

Here, compensation silicon is added corresponding to the volatilization loss of silicon throughout the process. Preferably, the compensating silicon is also of the same size as the synthetic silicide powder. The synthetic silicide powder and the additional silicon powder are thoroughly mixed by wet mixing using, for example, a V-type mixer. after that,
After sufficient washing and vacuum drying, a high melting point metal silicide powder suitable for use in the subsequent uniaxial compression molding process can be obtained.

Uniaxial compression molding is performed at a pressure of 15 ^-5 to 10 ^-6 mbar, preferably 10 ^-6 to 5 to achieve a density ratio of 97% or more.
×10 ^-6 mbar high vacuum atmosphere, high temperature above 1300°C and up to 1380°C, preferably 1310~
High temperature of 1380℃ and 250-600Kg/ ^cm2 , preferably
It is carried out using a hot press capable of applying a high pressing pressure of 350 to 500 kg/cm ² .

If the temperature exceeds 1,380°C, there is a risk that part of the material will melt because the melting point of silicon is 1,410°C. Previously, partial melting of this material was 1300
This was thought to be the upper limit of 1,380 degrees Celsius, but even considering temperature variations depending on location, accuracy of temperature measurement, and other factors, it can be carried out without any worries up to 1380 degrees Celsius.
In particular, it was found that when the temperature exceeds 1300°C, the hot press properties are significantly improved, and a density of 97% or more can be obtained in a short time, which led to the present invention.

High-melting point metal silicide powder is placed in a mold and the temperature begins to rise. Once the target temperature is reached, which is between 1300°C and 1380°C, maintain that temperature level and start applying a predetermined constant high press pressure. . The molding material is
As press pressure is applied, the thickness of the material is gradually reduced, but after a certain point the material thickness reaches a certain level and is no longer reduced. After fully confirming this saturated state of thickness reduction, high temperature pressurization is stopped. Generally, high temperature pressurization is completed within one hour. 30 above 1320℃
Within minutes.

After that, the target is completed by removing burrs, etc., and if necessary, performing finishing processes such as surface finishing.

The target obtained is 80-90% of that of conventional sintered products.
It has a high density ratio of 97% to 99.9% compared to the % density ratio, and the purity is extremely high with radioactive element content of 10ppb or less, oxygen content of 300ppm or less, and alkali and other metal content of 10ppm or less. High purity can be achieved.

One of the characteristics of this target is its low oxygen content of 50 to 150 ppm. The low oxygen content is
This is because the deoxidation reaction of Si+O→SiO(g)↑ progresses even more easily in the high-temperature pressurizing process.

High vacuum, high temperature and high press pressure work together97
It is a surprising fact that we were able to achieve a density ratio of more than 20%. High vacuum and high temperature also enhance the impurity removal effect. Since the electron beam melting required in the prior art is not performed, the amount of silicon volatilization loss is small, and the composition can be adjusted accordingly.

Effect of the invention 1: By improving the target density ratio, the strength of the target increases, cracks, chips, etc. do not occur, and the target life becomes longer. Also, encapsulated gaseous impurities are reduced. Furthermore, it is possible to realize an even higher density ratio than in the prior application.

2. High purity targets with particularly low oxygen content can be produced.

3. Productivity is truly improved by simplifying processes and shortening process time.

4 Target composition can be obtained more easily than before.

Example 1 8.2 kg of W with purity of 5N and 2.6 kg of silicon powder with purity of 5N
Kg was mixed in a V-type mixer, and W silicide was synthesized in a vacuum resistance furnace at 1300°C x 10 ^-4 mbar. The synthesized carmela-like silicide was pulverized using a vibration mill and then classified into 42 mesh under. In addition to this, Si powder of 42 mesh under
Add 0.8Kg and mix the powder with a V-type mixer into a mold with dimensions of 187mmφ x 150mm, and make a 10 ^-5 m
Hot pressing was carried out for 0.5 hour under the conditions of bar×1320°C×350Kg/cm ² . The obtained target density ratio is
It was 97%. A density ratio of 97% was achieved in a short period of 30 minutes. Also, the oxygen content of the target is
It was 100ppm.

Example 2 15.2 kg of W powder with a purity of 5N and 4.8 kg of Si powder with a purity of 5N were mixed in a V-type mixer and heated in a vacuum resistance furnace.
W silicide was synthesized under the conditions of 1300°C x 10 ^-4 mbar. The synthesized carmela-like silicide was pulverized using a vibration mill and then classified into 42 mesh under. Similarly to this, 42 mesh under Si powder 1.4
Kg was added and the powder was mixed using a V-type mixer.
Place in a mold with dimensions of 254 mmφ x 150 mm and heat to 10 ^-5 mbar x
Hot pressing was carried out for 0.5 hour under the conditions of 1380°C x 520Kg/cm ² . The density ratio of the target obtained was 99.9%
It was hot. It is truly surprising that a density ratio of 99.9% was obtained in 30 minutes. Furthermore, the oxygen content of the target was 50 ppm.

Example 3 12.4 kg of Mo powder with a purity of 5N and 7.4 kg of Si powder with a purity of 5N were
Mixed in a mold mixer and heated in a vacuum resistance furnace at 1200
Mo silicide was synthesized under the conditions of ℃×10 ^-4 mbar. The synthesized carmela-like silicide was pulverized using a vibration mill and then classified into 42 mesh under.
Take 4 kg out of this, add 0.1 kg of Si powder of 42 mesh under, put the mixed powder in a V-type mixer into a mold with dimensions of 187 mmφ x 150 mm, and heat it to 10 ^-5 mbar x 1380℃ x 350 kg/ Hot pressed for 0.5 hour under cm ² condition. The density ratio of the target obtained was still as high as 99.9%.
Furthermore, the oxygen content of the target was 50 ppm.

Claims (1)

[Claims] 1. High melting point metal silicide powder is subjected to high temperature of over 1300°C to 1380°C, high vacuum of 10 ^-5 to 10 ^-6 mbar, and high press pressure of 250 to 600 Kg/cm ² A method for producing a target made of high melting point metal silicide, which is a sintered product and has a density ratio of 97% or more, which is characterized by uniaxial compression molding under the same conditions. 2. The method according to claim 1, wherein the high melting point metal is molybdenum or tungsten. 3 High melting point metal silicide powder is produced by mixing high melting point metal powder and silicon powder at a predetermined ratio, synthesizing silicide under high temperature vacuum, and pulverizing the synthesized silicide.
The method according to claim 1, which is obtained by classifying and mixing synthetic silicide powder with silicon powder.