After oxide hard mask etching and strip/clean, the silicon wafer surface retains adsorbed moisture, chemical residues, and potentially volatile organics P2. The Vacuum Bake step operates immediately prior to Rapid Thermal Processing (RTP) and Aluminum Oxide (AlO) high-k dielectric deposition P3. In a nanoscale Backside Illuminated (BSI) CMOS Image Sensor, the backside silicon surface must achieve extremely low surface recombination velocities to minimize dark current and white pixel defects P1.