Multilayer Surface Inspection Using Gated Wavefront Sensing

The importance of quality control in semiconductor manufacturing process is to prevent surface roughness, since the behavior of the material is determined by its surfaces. Recently, multilayer surface profiling and inspection has been considered an emerging topic that can be used to solve various manufacturing inspection problems to prevent surface roughness. This thesis develops and investigates the effectiveness of a multilayer surface inspection system using gated wavefront sensing approach. The system setup consists of pulse laser, collimator, beam splitter, well-defined focusing lens, testing specimen, and gated wavefront sensing assembly (e.g., lenslet and gated camera). By synchronizing the laser pulses to the camera gate time, discriminating a multilayer wavefront from its neighboring discrete layer reflections is possible. The wavefront from different surfaces can be distinguished based on the range estimation. However, the wavefront can be distorted by the prior surfaces (reflected wavefront) or post surfaces (transmitted wavefront). As such a correction method is applied to correct distortion for multilayer surface reconstruction. The results show that the error is reduced after the correction technique is applied.