Optimal process design for on-chip micro-lenses with quality engineering

It is necessary for a lens fabrication technique to realize a precise optimal shape in order to effectively converge incident light rays even in the influence of noises. In this work, novel optimization procedures were utilized to estimate process parameters to fabricate spherical on-chip micro-lenses on the surface of CMOS image sensor using computer simulation (TCAD) technique and the quality engineering methods. The optimization of categorical factors were examined by DOE and analyzed by the T method. The optimization of numerical factors was also investigated taking into account of noise effects by adopting a L18×L8 experimental design. Standardized SN ratios were applied to evaluate sphericity of the lenses.