Dual-doped TMAH silicon etchant for microelectromechanical structures and systems applications

Tetra-methyl ammonium-hydroxide (TMAH), is an anisotropic silicon etchant t hat is gaining considerable use in silicon micromachining due to its excell ent silicon etch rate. etch selectivity to masking layers, degree of anisot ropy, and relatively low toxicity. However, a shortcoming of TMAH is that i t aggressively etches exposed aluminum layers. A dual-doped low concentrati on TMAH solution is presented, which incorporates a silicate additive for a luminum passivation and an oxidizer additive for improving etch rate and su rface quality. Using etch and under-etch experiments, the dual-doped 5 wt% TMAH solution is shown to have characteristics comparable to those of high concentration TMAH solutions with the added benefit of improved etch rate, smoother etched surfaces, and selectivity to silicon over aluminum. Such an etchant can find effective use in batch fabrication and integration of mic roelectromechanical systems within the framework of standard foundry proces ses. (C) 2000 American Vacuum Society. [S0734-2101(00)06302-8].