An improved TMAH Si-etching solution without attacking exposed aluminum

In this paper, an improved Tetramethyl Ammonium Hydroxide (TMAH) etching method is reported. The process features higher silicon etching rate and results in smooth silicon surface and at the same time, no significant aluminum etching is observed. We believe that after TMAH etching the aluminum surface is protected by the coating of by-products, which prevents etching of the underlying aluminum films by the TMAH solution. The etchant used in the study consists of 5 wt.% TMAH solution, 1.4 wt.% (or above) dissolved silicon, and 0.4-0.7 wt.% (NH ₄)₂S₂O₈ oxidant additive. Silicon etching rate of 0.9-1.0 μm/min and zero aluminum etching rate is be achieved using the process. Moreover the silicon surface remains smooth after etching. The etching process demonstration in this work is readily applicable to MEMS device fabrication such as polysilicon like sacrificial layer removal after metallization is completed