Surface Metrology of Silicon Wafers using a Femtosecond Pulse Laser

摘要

We investigated the technical possibility of exploiting a femtosecond pulse laser as the light source of low-coherenceinterferometry for topographical inspection of silicon wafers. The intention was to measure both the front- and rear-surface profiles of a silicon wafer simultaneously by illuminating from one side of the wafer only. To the end, thespectrum of the femtosecond laser was widened using a photonic crystal fiber to yield wavelengths over the particularrange of 1000 to 1200 nm, which is not only transmittable through silicon but also detectable by an ordinary CCDphotodetector array. This tomographic scheme enables complete measurement of thickness profile and also detection ofinternal voids such as cracks residing inside the wafer with high lateral and depth resolutions, which could be useful fornondestructive testing of multi-layered packages of silicon wafers.