NITROGENATION OF SILICON-CARBIDE LAYERS DEPOSITED ON SILICON SINGLE-CRYSTAL WAFERS VIA PYROLYSIS OF POLY(METHYLSILANE)

Poly(methylsilane) (PMS), produced by the (eta(5)-C5H5)(2)Zr(CH3)(2)-c atalyzed dehydrocoupling of CH3SiHCl2, can be pyrolyzed into silicon c arbide (SiC) and deposited as thin films on silicon single-crystal waf ers to form SiC/Si heterojunctions. Two procedures have been developed for in situ doping the SiC layers in such heterojunctions with nitrog en. In the first, the Si-C bonds in a PMS sample containing 0.25 wt % of the organozirconium catalyst are partially converted into Si-N bond s by performing the pyrolysis in the presence of gaseous ammonia. The extent of nitrogenation of the polymer can be controlled by varying th e NH3 partial pressure, and products with a wide range of resistivitie s are obtained. The second nitrogenation method involves ammination of the residual Si-Cl bonds in a Wurtz-coupled prepolymer, prior to pyro lysis. Both nitrogen-doping methods afford thin layers of n-type mater ials. Films ranging in thickness from 100 nm to 2.5 mu m and resistivi ties ranging from 30 m Omega cm to 10 Omega cm have been obtained. FT- IR spectroscopy, SEM, and EDX, together with ellipsometry, have been u sed to monitor the progress of the pyrolyses and to characterize the n ew materials produced. Additional information on the composition of th e new materials has been obtained from Si-29 MAS-NMR spectroscopy and AFM measurements.