Evolution of Co/Ge Films on Si(100) and Ge(100) Substrates
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INTRODUCTION The formation of cobalt silicides by MBE techniques (Co deposition on Si followed by annealing) and ion beam synthesis (mesotaxy [1]) has attracted a great deal of interest due to their potential applications in the microelectronics industry. Another system of great practical interest is Sil.Gex, for its use in, e.g. Si/Ge superlattices and SiGe transistor bases. Devices in the future may require combinations of both cobalt silicides and Si/Ge alloys so a complete study
of semiconducting materials involving Co/Ge/Si structures is required. The formation of CoSi 2 layers in SiGe structures using ion beam synthesis techniques have recently been studied [2,3]. Co implantation in SiGe alloys [2] produces Ge segregation away from the silicide forming region during post-implant annealing while Co implantation into SiGe/Si heterostructures [3], produces Co diffusion into the Si layers and there forms a silicide. In both cases, the final buried silicide contains very little Ge. The evolution and quality of the buried silicide [4] obtained by Co implantation into SiGe alloys was also examined evidencing that the different lattice constant of the SiGe alloys (as compared to pure Si) changes the strain, and thus the evolution and quality of the final buried silicide layer. For MBE grown cobalt silicides, the reaction between the deposited Co and Si substrate, which forms CoSi 2, occurs in the temperature range of about 500 C [5] while MBE grown cobalt germanides (CoGe,.) form at around 400 C [6]. Thus it is possible to form germanides on Si substrates with minimal CoSi 2 formation. However, the influence of the Si substrate on cobalt germanide is not known. In addition, of potential interest is the formation of CoSi2 layers when intermediate Ge or SiGe alloy layers are present. In this paper, we present preliminary results of the effect of a Ge layer on the solid phase reaction of CoSi2 at 700 C - a typical annealing temperature for the formation of CoSi2 without a Ge layer. For comparison, we also examine the influence of the Si(100) substrate on the film morphology by doing experiments on Ge(100) substrates under the same conditions as the Si substrates. 419 Mat. Res. Soc. Symp. Proc. Vol. 382 0 1995 Materials Research Society
EXPERIMENTAL DETAILS The growth experiments were carried out in a ultra-high vacuum MBE deposition system. The growth chamber consists of three electron beam evaporation sources charged with Si, Co and Ge. Each source is accompanied by a quartz crystal oscillator to monitor the growth rate during deposition. The sample manipulation stage is equipped with electron beam heating and is capable of reaching 1100 C. The chamber is surrounded with a water-cooling shroud and the base pressure is less than 2 x 10`0 Torr. The Si(100) substrate preparation was as follows: 2 inch Si(100) wafers were cut into approximately 1 cm 2 pieces. After a thorough degreasing in organic solvents, the Si was put in a bath of H20/NH4OH/H 20 2 (4: 1:1 ratio) at 80 C for 5 minutes. Following this was an HF dip an
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