A Microlens Reactive Ion Etching Process Study on CMOS Image Sensor - Wen-Hao Lo

Microlens arrays have extensively application on image sensors for focusing incident light appropriately into photo sensing region. As a result, the quantum efficiency of photodiode array can be enhanced, and the optical crosstalk can also be suppressed. There are several microlens formation methods, including thermal reflow of photoresist, microlens transferring with reactive ion etch (RIE) and their combination. The combination of thermal reflow of photoresist and RIE can achieve zero gap microlenses, i.e. 100% fi ll factor [6]. With minimized surface scattering effects, a smooth microlens is needed. The process condition of RIE is the key for microlens profile. Both etching bias power and etchant chemistry are very sensitive about modifying surface roughness and etching selectivity as well as shape of microlens. In this study, we focus on microlens profile and surface roughness which are affected by RIE tool type and etchant chemistry. Etching process induced microlens defects is also discussed.