Metal Vapour Vacuum Arc Ion Source to Synthesize Refractory Metal Silicides
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various metal-silicide phases to grow. When the imp ytation was condi ted~at 40 kV, the Nb ion current density was up to 76 pA/cm at a dose of 4x10 /cm , anA the Ta, W and Mo ion current densities were up to 65 ILA/cm at a dose of 5x10" ions/cm2, hexagonal NbSi, TaSi, MoSi1 and WSi2 were formed. Post annealing transformed the WSi 2 an' MoSi phases from hexagonal to tetragonal structure, featuring lower resistance than that of the as-implanted ones. LINTRODUCTION In recent years, the silicides of refractory metals have found growing application in the microelectronics technology because of their low electrical resistance, high chemical resistivity and thermal stability. However, direct thermal diffusion to form silicides from refractory metal films deposited on Si is seldom used in device fabrication because of the difficulties in obtaining reproducible results [1]. As a result of these limitations, the use of energetic beams to react metal and silicon was investigated, including laser and electron beam [2-4] reaction, and ion beam mixing [5]. Since early 1980s, a numbler of reports on the production of silicide layers of refractory metals using ion beam mixing or implantation through metal (ITM) silicidation technique have been published [6-101. Recently, an alternative technique to synthesize metal silicides was initiated by the authors' group, ie. to form metal silicides by high current metal ion implantation using Metal Vapour Vacuum Arc (MEVVA) ion source. MEVVA ion source, a new ion source invented in the mid of 80s by Brown et.al [11], was capable of providing high current ions of almost all the metal ion species, e.g. a MEVVA ion source implantor made in Beijing, Chia, can provide most of the metal ions with an ion current density to 150 PA/cm in an implanted area of 10 cm diameter at an extracted voltage of 50 kV [12]. By employing thiB ion souzce, direct implantation of various metal ions with high dose exceeding 10 ions/cm becomes readily. Furthermore, it can be considered that the high current density can provide a simultaneous thermal annealing which might satisfy the requirement for the formation of metal silicides. In other words, synthesizing metal silicides by MEVVA source is a promising means for the device application. Actually, the successful formation of C54-TiSi 2 on Si [131 by MEVVA source, for the first time, have suggested that this technique is of great potential in synthesizing the refractory metal silicides. The present work is dedicated to the formation of NbSit, TaSi2 , WSi and MoSk on single crystalline Si by MEVVA ion source implantation. This study is supported by the National Natural Science Foundation of China. 191 Mat. Res. Soc. Symp. Proc. Vol. 320. ©1994 Materials Research Society
II. EXPERIMENTAL PROCEDURE The silicon wafers used in this study were p-type Si(111) with a resistance of 8-13 Qcm. The wafers were cut into lx1 cm" samples, cleaned by a standard chemical procedure and then loaded onto a steel-made sample holder in the target chamber of the MEVVA implantor at a vacuu
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