Thick SiO2 and B2O3-P2O5-SiO2 cladding materials for waveguide are fabricated on single crystal silicon substrate by flame hydrolysis deposition and high-temperature consolidation. The micro-morphologies and phase structures of the samples are observed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The main research focuses on the cracking and crystallizing of the thick silica film deposited on silicon substrate. It can be seen from the SEM photo that the silica particles are porous and like a honeycomb. These particles have very high ratio surface area, which make it consolidated to form glass easily. The XRD spectrum indicates that these particles are completely non-crystal. But after consolidation, it can be seen obviously from the SEM photo that cracks appears on the silica film on the silicon substrate. And the XRD result shows a little of silica crystallized. However, the above-mentioned cracks and crystallization disappeared thoroughly by doping with small amount of B2O3 and P2O5 into SiO2. The silica waveguide cladding material fabricated by this procedure has a thickness above 20 micrometers. It has smooth and crack free surface and non-crystal phase structure. This B2O3-P2O5-SiO2 cladding material is very fit for fabricating all kinds of silica-on-silicon waveguide devices.