AVS 47th International Symposium
    Semiconductors Wednesday Sessions
       Session SC+EL+SS-WeM

Paper SC+EL+SS-WeM3
Using Micromachined Test Patterns to Study Surface Chemistry: An Investigation of Etchant Anisotrophy

Wednesday, October 4, 2000, 9:00 am, Room 306

Session: Passivation and Etching of Semiconductors
Presenter: M.A. Hines, Cornell University
Authors: M.A. Hines, Cornell University
R.A. Wind, Cornell University
Correspondent: Click to Email
We have developed a new technique for the rapid quantification of etchant anisotropy (i.e. orientation-dependent etch rates), which uses micromachined test patterns. Although macroscopic anisotropy cannot be inverted to provide detailed atomic mechanisms, macroscopic anisotropies do provide important clues to the underlying chemical reactions. For example, an etchant that produces atomically flat silicon surfaces -- a "perfect" etchant -- must selectively etch all defect sites, while leaving the flat surface virtually untouched. Macroscopically, this implies that a perfect etchant must attack vicinal surfaces much more rapidly than flat surfaces. Our standard test pattern consists of 180 1°-wide wedges arranged in an evenly spaced, circular array. Each wedge is bounded by a different set of vertical planes, so the sides of each wedge etch with a characteristic, face-dependent rate. Anisotropic etching leads to the development of a "flower pattern," which can be analyzed to yield absolute, face-spec ific etch rates of 180 surfaces simultaneously. Etch rates measured with this technique are in good agreement with those previously reported in the literature. This technique opens to door to a pseudo-combinatorial approach to etchant development. For qu a ntitative interpretation of these data, we constructed a simple model of orientation-dependent etching that is based on step-flow etching. We tested this model on a number of different anisotropic etchants, and the model performed surprisingly well. Interestingly, there was no evidence of direct step-step interactions or step coalescence on vicinal Si(111) surfaces during etching (within approx. 20° of the close-packed plane).