INFLUENCE OF GAS-PHASE CHEMISTRY ON THE PROPERTIES OF HYDROGENATED AMORPHOUS-SILICON AND SILICON-CARBON ALLOYS GROWN BY HACVD

We report on the properties of a-/mu c-Si:H and a-SiC:H grown by hydro gen assisted chemical vapour deposition (HACVD) of different gas mixtu res depending on various deposition parameters. Silicon films were gro wn by using gas mixtures of H-2/SiH4 and H-2/Si2H6, whereas silicon-ca rbon films were deposited using H-2/CH4/SiH4, H-2/C2H4/SiH4, H-2/C2H4/ Si2H6 and H-2/SiH3CH3. The composition and bulk properties of the depo sited films are investigated by FT-LR and Raman, XPS, RES, SEM, conduc tivity measurements and UV/VIS. As proved by Raman and conductivity me asurements, mu c-Si:H films are obtained using total pressures P-tot s maller than 5.5 Torr. Above a certain total pressure P-tot (6.5 Torr) a-Si:H films are obtained. As shown by SEM, the amorphous films exhibi t a rather smooth surface morphology, whereas the ye films show a grai n structure. In the pressure range from 5.5 to 6.5 Torr, a phase trans ition occurs. Carbon-rich a-SiC:H-films (up to X-c = 0.7) are obtained using C2H4 as carbon source, whereas the use of CH, leads to films wi th minor amounts of carbon. Films based on CH3SiH3 exhibit a nearly st oichiometric composition and a high degree of chemical order. The comp osition is influenced by several gas phase parameters, e.g., total pre ssure P-tot, substrate temperature T-s and the mole fraction of the re action gases. A gas phase kinetic simulation has been carried out and the validation of the model is tested by comparison with experimental results of silicon film deposition. As a result, the pressure P-calc, at which the concentration of disilene is a hundred fold higher than t hat of atomic hydrogen, and the characteristic pressure P of the mu c -/a-Si:H phase transition plotted as a function of Phi(SiH4)/Phi(tot) behave very similar. These results were used to extend the model to th e deposition of silicon-carbon films in order to correlate and to disc uss the material properties of the silicon-carbon system. (C) 1998 Pub lished by Elsevier Science S.A. All rights reserved.