Film thickness effects in the CoSi{sub 1{minus}x}Ge{sub x} solid phase reaction
- Department of Physics and Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)
The thickness dependence of the reaction of cobalt with epitaxial silicon{endash}germanium alloys (Si{sub 1{minus}x}Ge{sub x}) has been studied. The reaction products of Co with (100)-oriented Si{sub 0.79}Ge{sub 0.21} after annealing at 800thinsp{degree}C depended on the thickness of the Co film. Complete conversion to CoSi{sub 2} occurred only when the thickness of the Co layer exceeded 350 {Angstrom}. Interface reactions with Co layers thinner than 50 {Angstrom} resulted in CoSi formation, while a mixture of CoSi and CoSi{sub 2} was formed at intermediate thicknesses. X-ray diffraction and extended x-ray absorption fine structure measurements indicated no measurable incorporation of Ge had occurred in either the CoSi or CoSi{sub 2}. The threshold thickness for nucleation of CoSi{sub 2} on (100)-oriented Si{sub 1{minus}x}Ge{sub x} was determined in the range 0{le}x{le}0.25. The threshold thickness increased superlinearly with the Ge concentration {ital x}, and did not depend on the doping of the Si(100) substrate or the strain state of the Si{sub 1{minus}x}Ge{sub x} film. The observed thickness effect was attributed to preferential Co{endash}Si bonding in the reaction zone and the energy cost of Ge segregation, which accompanies the formation of CoSi and CoSi{sub 2} during the reaction of Co with Si{sub 1{minus}x}Ge{sub x}. {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 659298
- Journal Information:
- Journal of Applied Physics, Vol. 84, Issue 8; Other Information: PBD: Oct 1998
- Country of Publication:
- United States
- Language:
- English
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