Growth, patterning and microelectronic applications of epitaxial cobaltdisilicide

We report on the epitaxial growth of CoSi₂ on silicon using ion beam synthesis and molecular beam allotaxy. The latter process uses molecular beam epitaxy to grow a silicide precipitate distribution embedded in single crystalline silicon and thermal annealing to form the epitaxial layer. Both, ion beam synthesis and molecular beam allotaxy, are capable to grow epitaxial buried and surface CoSi₂ layers on Si(100) and Si(111) of high quality. We show that nanometer patterning becomes possible by local oxidation of thin (20 nm) epitaxial CoSi₂ surface layers. We use a patterned nitride as a diffusion barrier for the oxidant. The oxidized regions separate from the protected areas during oxidation. Very narrow gaps as small as 50 nm can be obtained between the silicide layers by rapid thermal oxidation. The generated gaps (lines) in the silicide layer follow in a self-adjusted manner the contours of the oxidation mask. A Monte Carlo code was developed to simulate the patterning process. We found that the stress at the edge of the oxidation mask modifies the diffusion processes during the oxidation, such that a separation of the layers occurs. The separation is highly uniform. As an application of epitaxial buried layers we present an ultrafast MSM (metal-semiconductor-metal) photodetector. The device was manufactured on an epitaxial CoSi₂ ground plane on silicon. The single crystalline silicon on top of the silicide acts as the photosensitive layer. The MSM photodiodes show a photo response as short as 3.5 ps FWHM on Si(111) and 6.7 ps (FWHM) on Si(100), respectively.