Characterization of Semi-Insulating Polycrystalline Silicon Prepared by Low Pressure Chemical Vapor Deposition

We employed the multiple angle incident ellipsometer to study the growth mechanism and optical properties of semi-insulating polycrystalline silicon (SIPOS) films deposited by the low-pressure chemical vapor deposition (LPCVD) technique. A significant difference of the imaginary part of the refractive index between film at the edge and those in the central region of the wafer was observed. Our analyses showed that it was consistent with the N20 depletion model. This N20 depletion phenomenon was confirmed by Auger analysis. Moreover, we found that spatial N20 depletion at the edge of the wafer was greatly influenced by the flow rate of Sill4 to N20 gases. Excessively high N20 flow rate suppressed the silicon microcrystal formation, resulting in a thinner SIPOS film.