WLTS

The wafer is contacted with liquid HF in an electrolytic cell, which removes the oxide and passivates the surface. The HF also provides an electrical contact on front and back side of the wafer. A laser generates minority carriers below the surface causing diffusion and recombination of carriers depending on the electrical field applied across the wafer. The residual carriers collected at the back side, called back side photo current (BPC), are proportional to the concentration of recombination centers like Fe impurities. Scanning with a focused laser beam allows mapping of bulk impurities.

• Wafer manufacturing
• Gettering
  
• Incoming wafer inspection
• Monitoring of front end production tools (wet clean, furnace epitaxy, dry processing)
• Tracing of contamination sources (chucks, vacuum tips, handling)
• Injection level spectroscopy for identifying elements

• Fast imaging
• High resolution
• Unsurpassed sensitivity
• Distinction of bulk and surface defects
• Identification of defect types
• ASTM standard method
• No sample preparation