JPS63179027A - Smelting method - Google Patents

Abstract

PURPOSE:To stably smelt an alloy which involves an exothermic reaction at the time of synthesis at a high yield while suppressing splashing by forming a component element which is a part of alloy constituting component elements as a molten bath and adding the other component element in the form of specific diameter particles into the molten bath. CONSTITUTION:Silicon having high purity (about >=9N) is melted in a vacuum or under the reduced pressure of argon in a crucible in the case of smelting the alloy or intermetallic compd. which involves the exothermic reaction at the time of alloying or synthesizing; for example, in the case of smelting titanium silicide. Titanium of particles or pellets having 1-5mm diameter is added to the bath thereof and is gradually melted. The additives are classified, and the additives of smaller sizes are added little by little at first, and additives of larger sizes are added thereto in the later period so as to decrease the reaction amount in an initial period when the exothermic reaction is vigorous and to increase the reaction amount with gradual settling down of the reaction. The splashing is thereby suppressed and the titanium silicide is synthesized at a high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing alloys or intermetallic compounds that involve an exothermic reaction, and particularly relates to a method for producing alloys or intermetallic compounds that generate a large amount of heat during alloying or synthesis. This invention relates to a method for melting while avoiding splashes and other problems caused by heat generation. According to the present invention, alloys or intermetallic compounds that achieve the target can be stably produced in high yield, and furthermore, by carrying out an appropriate exothermic reaction, the effect of purifying harmful elements can also be achieved. . The present invention is directed to the melting of high-melting point metal silicides such as titanium silicide, molybdenum silicide, and tungsten silicide, and at least Fe-Co-heavy rare earth elements (Tb, Gd, sD7, etc.), which are known as target materials for photothermal magnetic elements. 1) Effectively applied to fields such as alloy melting.

In particular, the high melting point metal silicide (Tiltx1Mo81+cSwst process) produced according to the present invention can be used for electrodes or wiring of semiconductor devices, especially gate electrodes, source electrodes, and drains of MOS-LSI devices. Useful for target production purposes for pole formation.

BACKGROUND OF THE INVENTION In producing alloys or all inter-114 compounds (t-a), the melting process of adding additive elements that remain in the melt of the component elements constituting the system is widely practiced. In the case of an exothermic reaction system that generates a large amount of heat, it is difficult to implement. This is basically because splashes occur due to exothermic reactions, resulting in deterioration of yield, fluctuations in composition and temperature, etc. However, on the other hand, if such inconveniences can be avoided, the sintering method is Unlike the condensation method, etc.), large, high-density products can be manufactured easily and in large quantities, and it is expected to have a purification effect by removing volatile impurities under vacuum or inert gas reduced pressure (by exothermic reaction). This is a very advantageous method. Typical examples of such exothermic reactions that generate a large amount of heat are high-melting point metal silicides, particularly titanium silicide, molybdenum silicide, and tungsten silicide. The above-mentioned situation will now be explained in detail using titanium silicide as an example.

Polysilicon has traditionally been used for electrodes or wiring in semiconductor devices, especially as gate electrodes in MOS-LSIs, but as MO$-LSIs become more highly integrated, signal recording delays due to the resistance of polysilicon gate electrodes have become a problem. ing. On the other hand, in order to facilitate the formation of MO5 elements using the self-line method, it is possible to make MO5 elements easier to form. It is desirable to use materials with high melting points for the poles, source electrodes, and drain electrodes. Under these circumstances, research is progressing on high-melting point metal gate electrodes, source electrodes, and drain electrodes that have lower resistivity than polysilicon, while research on high-melting point metal silicide electrodes, which prioritize compatibility with silicon gate processes, is also active. It's progressing. Promising practical examples of warped refractory metal silicides are titanium silicide, as well as molybdenum silicide and tungsten silicide.

Sputtering and electron beam evaporation are effective methods for forming titanium silicide thin films for electrodes or wiring in semiconductor devices. The sputtering method is a method in which a target plate is bombarded with argon ions to release metal, and all of the released metal is deposited on a substrate facing the target plate. In the electron beam evaporation method, a di-ingot evaporation source t-
This method involves melting and vapor deposition. In any case, the purity and other properties of the generated layer depend on the purity, composition, sputtering characteristics, etc. of the target plate or evaporation source (hereinafter collectively referred to as target).

In the case of a titanium silicide target, high-purity titanium powder and silicon powder are mixed in a predetermined ratio, molded, vacuum sintered, and then processed into the desired target shape using a sintering method and a predetermined method using Rutsuho. A melting method is known in which a blend of silicon and titanium is melted, but the sintering method does not produce a high-density product and causes problems such as target hiding and contamination due to a large amount of voids. Therefore, attention has been focused on the production of titanium silicide by the melting method.The traditional method of producing titanium silicide by the melting method was as follows: in a high frequency induction furnace or resistance heating furnace in a vacuum or argon reduced pressure atmosphere. The silicone is then dissolved in a regular aluminum tube. Contains a predetermined amount of titanium pieces or powder (8 d)
The container is placed in a furnace, and titanium pieces or powder are poured into the silicon from above the molten silicon bath to dissolve the titanium in the silicon and produce titanium silicide.

This method has the following problems: t When titanium pieces are introduced into molten silicon, a rapid exothermic reaction between titanium and silicon occurs, resulting in tin lash from the bath surface. Yields are poor because such splashes are dissipated outside the crucible and around the edges. Bath temperature control is difficult.

2. It is difficult to obtain titanium silicide having the target composition due to the occurrence of the above-mentioned splash and volatilization loss due to the rapid increase in bath temperature.

& By dropping water from above the small titanium tube bath, the water surface shakes violently and splashes are more likely to occur.

In the case of adding soft powder, there is loss due to powder scattering during addition or entrainment during vacuum evacuation, and it also floats after addition and does not dissolve well.

The above specifically mentioned titanium silicide, but
It is clear that a similar situation occurs in the melting of tungsten silicide and molybdenum silicide by adding tungsten or molybdenum to molten silicon. Furthermore, the first mentioned Fe-Co-heavy rare earth element system is replaced by Fe-C.

A similar situation occurs when melting is performed by adding heavy rare earths to the melt. Purpose of the Invention In view of the above situation, the present invention aims to produce alloys and intermetallic compounds involved in exothermic reactions in a high yield and in a stable manner. The fundamental cause of the above-mentioned problems in the prior art is a complete lack of consideration to the size of additives. Due to what happened. As a result of repeated tests on the possibility of establishing a dimensional form that does not cause tin lash or scattering, the present inventors added additives to the melt in the form of particles or pellets with a diameter of 1 to 5 strokes. We have come to confirm that these problems can be resolved by doing so.

This is a significant finding that can be called a kind of blind spot in a situation where conventionally no consideration has been given to the size of additives.

Thus, the present invention provides an alloy or intermetallic compound system that involves an exothermic reaction during alloying or synthesis by adding component elements that remain in the melt bath of at least one of the component elements constituting the group system. In the melting method, the additive element is gradually melted by adding it to the melt in the form of particles or pellets with a diameter of 1 to 5 mm. Provided is a method for producing an intermediate compound system.

First, an example of melting titanium silicide will be explained.

In this case, titanium grains or pellets are added and melted into a silicon melt bath in a melting furnace. As a melting furnace,
A crucible with a heater for storing the silicon melt at the bottom, a means for adding titanium grains or pellets at the top, and capable of melting under vacuum or reduced pressure of argon (inert gas) may be used. For example, a high frequency induction furnace, a resistance heating furnace, etc. can be used. The furnace is equipped with an exhaust port and an observation port. Generally, the vacuum is at a level of 10-4 to 10-5 Torr and the argon reduced pressure is at a level of 100 to 500 Torr.

In a melting furnace, silicon is first melted in a melting furnace using a heater. As a silicon raw material, 9 N (99
, 9999999%) or higher and low in content of radioactive elements or alkali metals that are harmful to sputtering sources, and are easily commercially available, such high-purity materials are used. It is preferable to use a material with as high a density as possible to avoid the problem of holes being formed due to damage to the material due to heat generation. In addition, it is preferable to use a highly purified product in order to avoid contamination of the product due to impurities leached from the rutsuho. A high-purity aluminum crucible, a high-purity silica crucible, a high-purity calcined crucible, etc. can be used. For example, high-purity (95!95%) aluminum crucibles with a density ratio of 100% are produced by compressing high-purity alumina to the theoretical density.・It is commercially available as a crucible.

After dissolving the silicon, titanium grains or pellets are added to the silicon bath. The diameter of the titanium grains or pellets is controlled to be 1-5tIs. diameter is 1
(2) If it is too small, scattering may occur during addition or loss may occur due to vacuum evacuation. On the other hand, if it exceeds 5 s+ai, the drop impact becomes large and large fluctuations or splashes of the molten metal surface are likely to occur during addition.

Basically, titanium grains or pellets are added by dropping them into the crucible from a container holding them, but it is also useful to use the following measures to minimize tin lash tubes. Yes: t In order to reduce the initial reaction amount when the exothermic reaction is intense, and then increase the reaction amount as the reaction heat gradually subsides, (a) classify the additives and add them little by little starting from the smallest.
Add something big in the second half.

(b) Taper the bottom of the addition container into a funnel shape and add small amounts at a time.

(c) Attach a stirring valve to the bottom of the addition container to appropriately control the flow rate.

2. Adjust the additives to the optimum size that does not cause the above problems, and add them at an appropriate rate.

It goes without saying that the titanium grains or pellets added in this way should also be of high purity.

If the temperature of the silicon bath becomes higher than necessary, volatilization loss increases, so it is desirable to maintain the temperature slightly higher than the liquidus line shown in the phase diagram. The Ti-8I system has a eutectic liquid phase MA that descends on both sides of the T18h compound (melting point 1540°C).
It is convenient to set the liquid phase a temperature a little higher than that corresponding to the target composition of about T15h.

The target composition of Ti81X is generally selected from the range of 15≦X≦27.

Adjustment of the bath temperature during melting is based on the heat of reaction between silicon and titanium (
(i.e., by adjusting the titanium size, shape and fall rate) and the input power of the furnace heater.

In the present invention, since there is no sudden generation of reaction heat, the bath temperature can be controlled very easily.

In this way, titanium is gradually dissolved into the silicon bath, producing titanium silicide.

In the case of melting molybdenum silicide or tungsten silicide, it can be carried out in the same manner as described above. Either molybdenum or tungsten grains or powder pellets thereof can be used. At present, techniques for producing high-purity molybdenum or tungsten have been established. When high-purity molybdenum or tungsten is added to a high-purity silicon melt, exothermic reactions occur even more significantly, but even in such cases, the exothermic reactions can be sufficiently controlled by using the present invention.

Further, it becomes possible to easily melt even high melting point metals such as molybdenum and tungsten.

In the case of melting an F@-Co-heavy rare earth element (at least one kind such as Tb5Gd%Dy) alloy, grains or pellets of the heavy rare earth element are added to the Fs-Co melt.

The present invention is not limited to these specific examples, but is equally applicable to situations where it is desired to control the initial explosive reaction progress during the melting of alloys and metal compounds that are involved in exothermic reactions.

Effects of the Invention t As a result of being able to perform alloying or synthesis under a very stable exothermic reaction, volatile impurity elements such as alkali metals such as Na 1 are reduced. Since the presence of alkali metals in gate, source, and drain electrodes impairs operational reliability, high quality electrodes can be produced by manufacturing targets for forming such electrodes under the present invention.

2 In case of silicide synthesis, 81+O→810(g)↑
Oxygen can be reduced by this reaction. The presence of oxygen is harmful during sputtering or evaporation.

& Splash can be suppressed, improving yield.

The soft melting operation is easy to manage and damage to the melting tube is avoided, improving safety and economic efficiency.

& Since there is no loss due to volatilization or splash, products with the target composition can be produced.

4. By casting, it is possible to manufacture large-sized products of any desired shape with a density ratio of nearly 100%.

l It is possible to alloy or synthesize high-purity metals.

a. It is possible to manufacture high melting point alloys.

2 No scattering occurs when adding powder.

1α It is easy to control the bath temperature.

Example: 5 x 10-' Torr in a high-frequency induction furnace
Titanium silicide was melted under a vacuum atmosphere. As the glue, ultra-high purity aluminum slip cast with a density ratio of 100% manufactured by Tateho Chemical Co., Ltd. was used. The size of the crucible was 101 mm inner diameter x 201 mm deep. First of all,
A 9N silicon lump was melted in a rutsuho for 2,000 hours.

After that, 170 pieces of high-purity titanium grains (2 to 4 pieces in size)
5p was added little by little and dissolved. The temperature of the silicon bath was initially set at 1.450°C and was maintained within ±100°C by adjusting the input power. The temperature could be easily adjusted and stable melting operations could be performed. After melting, the entire edge of the crucible was visually inspected, but almost no deposits were observed. The composition of the produced titanium silicide is determined by TI according to the analysis results. Well, we passed the target value. Furthermore, titanium grains are 5
00 ppm O oxygen, but the product 9
The oxygen content had decreased to 1100 pp.

Claims (1)

[Scope of Claims] 1) An alloy or intermetallic compound system that undergoes an exothermic reaction during alloying or synthesis by adding at least one component element that remains in the melt bath of the component elements constituting the system. An alloy or metal that participates in an exothermic reaction characterized by gradually melting the additive element in the melting method by adding the additive element in the form of particles or pellets with a diameter of 1 to 5 mm to the melt. Intermediate compound melting method. 2) Add titanium grains or pellets to the silicon bath,
2. The melting method according to claim 1, wherein titanium silicide is synthesized by gradually dissolving titanium in silicon. 3) Molybdenum silicide or tungsten silicide is synthesized by adding particles or pellets of molybdenum or tungsten to a silicon bath and gradually dissolving the molybdenum or tungsten in the silicon.
Melting method described in section. 4) Add grains or pellets of at least one heavy rare earth element such as Tb, Gd, Dy, etc. to the Fe-Co melt bath, and
Fe-Co is produced by gradually dissolving heavy rare earth elements in e-Co.
- A melting method according to claim 1 for preparing a heavy rare earth element alloy.