SIMPLE - A TECHNIQUE OF SILICON MICROMACHINING USING PLASMA-ETCHING

Micromachining of bulk silicon with directional plasma etching can ach ieve both small lateral dimensions and large structural layer thicknes s. In this paper, a novel bulk-micromachining technique called SIMPLE (silicon micromachining by plasma etching) is described. An n(+) burie d layer is formed on the substrate before the growth of a lightly n-do ped epitaxial layer. A Cl-2/BCl3 plasma etches the epitaxial layer ani sotropically but lateral etching occurs when the n(+) buried layer is exposed to the plasma. Thus the silicon beam with vertical sidewalls c an be patterned and released from the substrate in a single plasma etc h due to the lateral etching of the n(+) layer. The lateral etching of the n(+) buried layer is dependent on the doping concentration, with a threshold of approximately 8 X 10(19) cm(-3). The lateral etch rate reduces when the spacing between the beams is less than 3 mu m and wit h increasing etch time. Arsenic is found to be the most suitable dopan t for the n(+) buried layer. The plasma-etching process is optimized u sing an orthogonal design and the optimized process yields a lateral e tch rate of the heavily n-doped buried layer of 2000 Angstrom A min(-1 ), while keeping the etching of the lightly doped silicon anisotropic and uniform. The technique features simplicity and the ability for cir cuit-compatible on-chip microstructure fabrication.