SiO(2) Particulates Dispersed in CVD Reactor

The number of size variations with time of vitreous silicate particulates in a CVD reactor for SiO(2) film deposition are measured by observation of Mie scattering of a He-Ne laser light on the submicron particles (0.1-0.5 mu m diam). The predominant particles are found to be 0.2-0.3 mu m in diameter. The size distribution varies with time during the reaction period. Particulates greater than 0.3 mu m diam decrease in number with time, whereas the number of smaller particles gradually increases or does not change except at reaction initiation. The size distributions are affected by substrate temperature and reactant and dopant concentrations. Generally, these parameters influence the number of large particles more than smaller particulates. Large particles greater than 0.3 mu m diam decrease in number with O(2) flow rate at O(2)/SiH(4) ratios greater than 100 and also with the PH(3) flow rate. However, the number of small particles does not vary radically with these gas flow rates. Lowering the substrate temperature results in a reduction in the large particle number. This large particle phenomenon is primarily caused by small particle coagulation. Furthermore, the small particles (0.1-0.2 mu m diam) before coagulation reflect the particle nucleus number.