Chemical mechanical planarization (CMP) is an enabling technology in the fabrication of advanced semiconductor devices. The surface topography of the starting bare silicon substrate before CMP can have a significant impact on the results of the CMP process, specifically on the uniformity of the oxide film final thickness. The quantitative studies of this phenomenon an just beginning. In this article, a laser based optical scanning measurement was used to determine the front surface topography of the bare silicon substrates prior to thermal oxide growth. Fast two-dimensional mapping of the surface height variation is obtained with very high spatial and height resolution. The one-dimensional cross-section profile extracted from the measurement is demonstrated to have good correlation with the stylus based profiler measurement. A thermal oxide layer was grown and then polished in a high efficiency planarization process on a group of substrates, which had difficult levels of surface topography variations on the starting surface. A signature match between the oxide thickness variation and the silicon substrate front surface topography was identified. The resultant correlation reveals the potential impact on CMP process window from the starting material due to the degradation of within-die and die-to-die uniformity. Consequently, the product yield could be threatened. The optical topographical measurement using this laser scanning measurement is demonstrated here to be capable of providing fast, vital and unique information critical to achieving satisfactory results in the oxide CMP process.