EXPERIMENTAL INVESTIGATION OF HIGH SI AL SELECTIVITY DURING ANISOTROPIC ETCHING IN TETRA-METHYL AMMONIUM HYDROXIDE/

This work contributes to the understanding of anisotropic etching of s ilicon, for microsystems technology, by studying Si/Al selectivity dur ing anisotropic etching of silicon in tetra-methyl ammonium hydroxide (TMAH). By under-etch experiments using a wagon-wheel mask pattern, Si /Al selectivity is studied in relation to trends in etch anisotropy, e tched surface morphology, and variations of under-etch behavior with m ask-edge angle, TMAH at 5 wt % is used. with or without the additives: dissolved silicon and ammonium persulfate, High Si/Al selectivity is accompanied by obvious changes in the roughness, flatness, and etch ra te of the {100} cavity bottoms, by large changes in anisotropy as seen in under-etch rate curves, by lower ratio of {100} to {100} etch rate s, and by more regular [101]-oriented steps on non-{111} cavity sidewa lls. The conditions are consistent with a low rate of attack of [101]- directed periodic bond chains in the Si lattice, (C) 1998 American Vac uum Society. [S0734-2101(98)04702-2].