New fluid filter structure in silicon fabricated using a self-aligning technique

Abstract

A new fluid filter structure in silicon has been designed and fabricated. The structure consists of two hole membranes of silicon displaced laterally relative to each other. The size of the largest particles which can pass through the structure is determined by the thickness of the silicon dioxide spacers separating the two hole membranes. One single-hole pattern is used in combination with a special two-step self-aligning technique involving heavy boron diffusion, anisotropic silicon etching, and silicon dioxide undercut etching. Structures with membrane separation distances of 50 and 200 nm have been made. Since the structure electrically is a capacitor, other applications are possible.