SIMPLE — A technique of silicon micromachining using plasma etching

Abstract

Micromachinign of bulk silicon with directional plasma etching can achieve both small lateral dimensions and large structural layer thickness. In this paper, a novel bulk-micromachining technique called SIMPLE ( silicon micromaching by plasma etching) is described An n + buried layer is formed on the substrate before the growth of a lightly n-doped epitaxial layer. A Cl 2/BCl 3 plasma etches the epitaxial layer anisotropically but lateral etching occurs when the n + buried layer is exposed to the plasma. Thus the silicon beam with vertical sidewalls can be patterned and released from the substrate in a single plasma etch 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 × 10 19cm −3. The lateral etch rate reduces when the spacing between the beams is less than 3 μm and with increasing etch time. Arsenic is found to be the most suitable dopant for the n + buried layer. The plasma-etching process is optimized using an orthogonal design and the optimized process yields a lateral etch rate of the heavily n-doped buried layer of 2000 Å min −1, while keeping the etching of the lightly doped silicon anisotropic and uniform. The technique features simplicity and the ability for circuit-compatible on-chip microstructure fabrication.