AVS 46th International Symposium
    Electronic Materials and Processing Division Tuesday Sessions
       Session EM-TuM

Paper EM-TuM10
STM Studies of the Site-specific Reactivity of Isopropanol in Aqueous Silicon Etching: Controlling Morphology with Surface Chemistry

Tuesday, October 26, 1999, 11:20 am, Room 608

Session: Si Surface Chemistry and Etching, Passivation, and Oxidation
Presenter: M.A. Hines, Cornell University
Authors: M.A. Hines, Cornell University
T.A. Newton, Cornell University
Y.-C. Huang, Cornell University
L.A. Lepak, Cornell University
Correspondent: Click to Email
Aqueous silicon etchants play an important role in the fabrication of microelectromechanical systems (MEMS). To improve performance, a reputedly inactive chemical agent -- isopropanol [(CH@sub 3@)@sub 2@CHOH] -- is often added to the etchant. Not only does this simple additive reduce undercutting by up to 75%, it also produces much smoother etched surfaces, in part by suppressing the formation of pyramidal etch hillocks. Using a combination of STM measurements and kinetic Monte Carlo simulations, we will show that these morphological changes have a simple, chemical origin. The site-specific rates of isopropanol reaction on vicinal Si(111) surfaces were studied by kinetic competition with an etchant of known anisotropy and quantified using concentration-dependent changes in the etched surface morphology. The unique properties of isopropanol-enhanced etchants are explained by the relatively high reactivity of the isopropoxide ion. Once formed, the silicon isopropoxy species transiently suppresses etching at specific surface sites and modifies the anisotropy of the etchant.