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Effect of ion-beam mixing temperature on cobalt silicide formation

: Kasko, I.; Dehm, C.; Frey, L.; Ryssel, H.


Nuclear instruments and methods in physics research, Section A. Accelerators, spectrometers, detectors and associated equipment 80/81 (1993), pp.786-789
ISSN: 0167-5087
ISSN: 0168-9002
Journal Article
Fraunhofer IIS B ( IISB) ()
cobalt; ion beam mixing; Monte Carlo methods; rapid thermal annealing; Rutherford backscattering; sheet resistance; silicide; silicide formation; silicon; transmission electromicroscopy

In this work, the influence of ion-beam mixing at enhanced substrate temperatures on CoSi2 formation was investigated. For this purpose, 19nm Co layers were mixed using 1 x 10 high15 cm high-2, 60 keV Ge ions at temperatures ranging from 25 to 500 degree Celsius. By RBS and TEM analysis, it could be shown that silicidation resulting in a mixture of Co2Si, CoSi and CoSi2 occurs during mixing in case of mixing temperatures at or above 400 degree Celsius whereas a native oxide layer between the Co and the Si substrate is still present in case of lower mixing temperatures. A two-step annealing process at 700 degree Celsius for 10 s was necessary to achieve CoSi2 formation for all other implanted samples. By RBS and TEM investigations, it could be revealed, however, that for samples mixed below 400 degree Celsius, large, separate CoSi2 grains embedded in the silicon were formed whereas smooth, low resistivity CoSi2 layers were achieved for mixing at or above 400 degree Celsius. From these i nvestigations, it can be concluded that during implantation at higher temperatures at or above 400 degree Celsius, radiation enhanced diffusion occurs leading to an improved effectivity of mixing. This effect enables homogeneous nucleation and partial silicidation during mixing as well as formation of smooth CoSi2 layers with abrupt CoSi2-Si interfaces by subsequent annealing. The Ge dose of 1 x 10 high15 cm high-2 which was used for mixing should amorphize the substrate only for implantation temperatures at or below 200 degree Celsius so that amorphization can be excluded for samples mixed at higher temperatures. Therefore, it can be assumed that the responsible effect for homogeneous silicidation by ion-beam mixing is primarily due to an increased metal concentration at the silicon surface but not due to substrate amorphization like it was proposed by Okabayashi (2). It can be concluded that smooth silicidation by ion-beam mixing at room temperature and subsequent annealing is only a chieved if a critical metal amount has been mixed into the silicon surface. An alternative to room temperature implantation is, however, to perform mixing at or above a critical substrate temperature which enables an improved effectivity of mixing by radiation enhanced diffusion.