JPH0413292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for synthesizing molybdenum silicide or tungsten silicide with a low oxygen content, and in particular to a method for synthesizing molybdenum silicide or tungsten silicide with a low oxygen content, and in particular to a method for synthesizing molybdenum silicide or tungsten silicide with a low oxygen content. The present invention relates to a method for easily synthesizing molybdenum silicide or tungsten silicide containing oxygen. Molybdenum silicide or tungsten silicide targets are useful for forming thin films in electronic industry applications, such as gate electrodes, source electrodes, and drain electrodes of MOS/LSI devices. Background of the Invention Electrodes or wiring of semiconductor devices, especially MOS/
Polysilicon has traditionally been used as gate electrodes in LSIs, but as MOS/LSIs become more highly integrated, signal propagation delays due to the resistance of polysilicon gate electrodes have 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, source electrode, and drain electrode. Under these circumstances, research is progressing on high-melting-point metal gate electrodes, source 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. It is being done. Promising practical examples of such refractory metal silicides are molybdenum silicide (MOSi _x ) and tungsten silicide (WSi _x ).
It is. 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. These targets use synthesized molybdenum silicide or tungsten silicide powder as a starting material, and then undergo molding and vacuum sintering or pressure sintering processes to produce a silicide sintered body, which is then machined into the target. It will be finished. During sputtering and vapor deposition of such a target, if oxygen is contained in the target, the characteristics of the thin film formed, such as an electrode, will be deteriorated. In order to reduce the oxygen content in the target, it is important to reduce the oxygen content of the silicide powder to be synthesized. Although it is possible to remove oxygen during the sintering process mentioned above after synthesis, this is somewhat difficult, especially with pressure sintering, and the basic oxygen content during synthesis is the final oxygen content in the target. Determine the quantity. Prior art and its problems The conventional method for synthesizing molybdenum silicide or tungsten silicide is to mix high-purity molybdenum powder or tungsten powder and high-purity silicon powder at a predetermined molar ratio, and then to mix the mixture in hydrogen or vacuum. It consisted of reaction synthesis of both by heating to a temperature of 800 to 1400°C, usually 800 to 1300°C. Silicon tetrachloride may be used as a catalyst during the reaction. The synthesis reaction is an exothermic reaction according to Mo(W)+xSi→MoSi _x (WSi _x ) (x=2 to 3.5). Silicide targets have only recently been studied, and it can be said that little attention has been paid to the harmful effects of trace amounts of oxygen in the targets. Therefore, at present, almost no attempts have been made to reduce the oxygen content of synthetic silicide powder. In the above synthesis process, the method of using silicon tetrachloride as a catalyst in hydrogen makes it possible to produce silicide powder with a relatively low oxygen content, but the oxygen content level is still not sufficient and the equipment is complicated. , running costs for catalysts, etc. are required, and the work is troublesome. OBJECTS OF THE INVENTION The object of the present invention is to establish a method for easily producing molybdenum silicide or tungsten silicide powder with low oxygen content at low cost. Summary of the Invention The present inventors have repeatedly studied measures for reducing oxygen content toward the above objective. Although the Mo, W, and Si powders used as raw materials are of high purity, the Mo and W powders contain 1000 to 1500 ppm of oxygen, and the Si powder contains 1500 to 2000 ppm of oxygen. Such oxygen is the source of the oxygen content in the synthetic silicide powder. The present inventors have found that deoxidation proceeds very effectively and efficiently by subsequently holding the synthesized silicide at a high temperature in vacuum. It has been found that oxygen can be effectively removed as SiO(g) by placing synthetic silicide under vacuum at a sufficiently high temperature. Moreover, this method can be carried out using the same equipment following the synthesis process, so it is advantageous in terms of workability and simplicity. Thus, the present invention proposes a two-step method for the purpose of deoxidizing, and uses molybdenum silicide or tungsten silicide (MoSi _x or WSi _x ≦X≦3.5) In a method for producing powder, (1) Mo powder or W powder and Si powder are blended in excess of Si from a predetermined molar ratio to produce a mixed powder; (2) the mixing Synthesize molybdenum silicide powder or tungsten silicide powder by heating the powder in a vacuum at a temperature of 800 to less than 1300°C, and (3) synthesize the synthesized molybdenum silicide powder or tungsten silicide powder to a temperature of 1300 to less than 1300°C in a vacuum.
The excess Si is removed by holding at a temperature of 1500°C.
Provided is a method for producing molybdenum silicide powder or tungsten silicide powder with a low oxygen content, which is characterized in that oxygen is removed by converting oxygen into SiO. Adding synthesized silicide powder to the mixed powder prevents deterioration of the crushability of the product. DETAILED DESCRIPTION OF THE INVENTION High purity raw material silicon powder and raw material molybdenum or tungsten powder are used. In particular, for the preparation of targets used in the electronic industry, it is desirable to have a low content of radioactive elements, alkali metals and transition metals. High purity silicon powder is easily commercially available. Regarding molybdenum and tungsten, technology has been established to prepare high-purity products with few impurities, and furthermore,
Several methods have been proposed for this improvement. These raw material molybdenum or tungsten powder and silicon powder are thoroughly mixed at a molar ratio of 1:2 to 3.5. Mixing is performed using, for example, a V-type mixer. It is necessary to set the amount of silicon to be blended slightly in excess of the target molar ratio in consideration of silicon volatilization loss in the synthesis process and deoxidation process. The excess amount can be established empirically, taking into account the temperature and time of subsequent steps. Synthesis is carried out in hydrogen or vacuum atmosphere at 800~
It is carried out by heating the mixed powder to below 1300°C. However, for the purposes of the present invention it is preferred to perform the synthesis in vacuum. This is because deoxidation can be promoted during the synthesis stage, and the process can proceed directly to the next deoxidation stage, making the work simpler. The vacuum atmosphere is preferably 10 ⁻⁴ torr or less. Some deoxidation can also be achieved in this synthesis step. However, the low temperature does not result in sufficient deoxidation, and therefore, according to the present invention, a deoxidation treatment is employed in which the synthetic silicide powder is held in a high-temperature vacuum. Deoxidation treatment is performed at 1300-1500°C. The holding time is preferably 1 hr or more in order to recover from the increase in vacuum pressure caused by the gas generated during the reaction, but is not particularly limited. As the holding temperature increases, the oxygen content of the silicide powder decreases. From this point of view, higher temperatures are preferable, but if the temperature exceeds 1500°C, evaporation of Si becomes significant and it becomes difficult to control the molar ratio, so there is no upper limit. The temperature was 1500℃. The effect is 1300
It becomes noticeable when the temperature exceeds 1330°C, especially above 1330°C. It is even more effective when the temperature is 1400℃ or higher. As the holding temperature increases, the degree of sintering progresses,
However, in order to avoid this, in the synthesis process, the already synthesized and pulverized synthetic silicide powder, more preferably the low oxygen content silicide powder produced according to the present invention, is used separately or It is advisable to repeatedly add an appropriate amount, for example 2 to 40% by weight. The larger the amount added, the more pulverizable silicide can be synthesized. By adding 2%, pulverization becomes possible easily, and the effect of the addition is observed. By adding 15% or more, a silicide that is particularly easily powdered can be obtained. However, if the amount of repeated addition is too large, the synthesis reaction will be hindered, the pulverization effect will be saturated, and the manufacturing cost will increase.
It is necessary to keep it within %. The synthetic silicide thus obtained basically has good pulverizability, so even if it is subsequently held at a high temperature for the purpose of deoxidizing, the pulverization property does not deteriorate to the extent shown above. The grindability of silicide products is a very important issue. If pulverization is difficult, it will take a long time to pulverize, and the pulverization cost will be very high, which will be a burden on the target cost. Grinding is generally carried out using a ball mill, but long-term grinding increases the chance of contamination from balls, containers, etc., and there is a risk that the amount of target impurities will increase accordingly. Targets for electronic industry applications, especially those related to semiconductor devices, are extremely averse to iron and other impurities, and the raw materials used are molybdenum, tungsten, and silicon that are of high purity and are low in such impurities. Contamination can undermine those efforts. The synthetic silicide thus deoxidized is pulverized by a ball mill or other pulverizer, and classified into 35 to 45 mesh particles to obtain synthetic silicide powder. In order to prevent the amount of O ₂ from increasing during ball mill grinding, consideration must be given to carrying out the grinding in an Ar-substituted atmosphere. Furthermore, it is preferable to use molybdenum lining balls, molybdenum balls, etc. for the purpose of preventing contamination with Fe and the like. After this, the powder is sent to a target forming process. This is done in accordance with conventional methods by forming and vacuum sintering or by pressure sintering to produce a silicide sintered body, which is then machined into the final target form. Since the target forming process is not directly related to the present invention, its explanation will be omitted. just,
In connection with the present invention, the same deoxidation reaction proceeds during high-temperature treatment, making it possible to remove a small amount of oxygen. However, the amount of deoxidation is small, and it is necessary to perform sufficient deoxidation during synthesis. The more sufficient deoxidation is performed during synthesis, the lower the oxygen content will be in the final target. Effects of the Invention According to the present invention, molybdenum silicide or tungsten silicide having a lower oxygen content equivalent to or higher than that obtained by a catalyst method can be obtained without using a catalyst. This will make a major contribution to the production of silicide targets for semiconductor devices, which are increasingly demanding higher quality. Examples and Comparative Examples High-purity molybdenum powder and high-purity silicon powder were blended at a molar ratio of 1:2.3, mixed in a V-type mixer,
The synthesis was carried out at approximately 1250°C in a vacuum atmosphere of 10 ^-5 Torr. Thereafter, the temperature was raised to the temperature shown in Table 1 in the same vacuum atmosphere and maintained for 2 hours. The oxygen content of the obtained silicide powder is shown in Table 1. 【table】

Claims (1)

[Claims] 1 Molybdenum silicide or tungsten silicide (MoSi _x or WSi _x X: Mo or W
represents the molar ratio of X and Si, and is 2≦X≦3.5. )
In a method for producing powder, (1) a mixed powder is produced by blending Mo powder or W powder and Si powder in excess of Si than a predetermined molar ratio, and (2) the mixed powder is heated in a vacuum at 800 to 1300°C. (3) synthesize the synthesized molybdenum silicide powder or tungsten silicide powder by heat treatment at a temperature of less than 1300℃ in vacuum;
The excess Si is removed by holding at a temperature of 1500°C.
A method for producing molybdenum silicide powder or tungsten silicide powder with a low oxygen content, characterized by deoxidizing oxygen by converting it into SiO. 2. The method according to claim 1, wherein a synthesized silicide powder is added to the mixed powder.