Optimization of an isotropic etching process on silicon wafers

Etching process involves various chemical reactions and reflects significantly on silicon wafer quality. Etching parameters are evaluated in order to optimize the isotropic etching process. For optimization purpose, Design of Experiment (DOE) with full factorial design is employed. Etching factors namely the bubbling flow rate, wafer rotation, and etchant temperature are randomised with additional three centre points to observe any curvature. The responses studied are etching removal, total thickness variation (TTV) and wafer brightness. It is found that etchant temperature gives major impact on all three responses stated above. The etchant temperature is the main effect factor and significantly affects TTV. Additionally, the etchant temperature and bubbling flow rate provide interaction effects on both the etching removal and wafer brightness. A higher bubbling flow rate is required to ensure etching removal and brightness within specification. Besides studying these three responses, the wafer surface after etching is additionally analysed using ADE Infotool software which captures the etched profile and its thickness. The ADE result indicates that a higher temperature contributes to a more concave shape of etched wafer, thus resulting in higher TTV and sending the wafers out of specification. Finally, the optimum condition is tested on a final run. The removal uniformity is observed in removal distribution graphs. The etching performance is enhanced with the optimized value of bubbling flow rate, etchant temperature and wafer rotation to achieve the best removal distribution.