Polymolding: Two Wafer Polysilicon Micromolding of Closed-Flow Passages for Microneedles and Microfluidic Devices

Abstract

A two wafer polysilicon micromolding process we call Poly molding has been developed that permits the fabrication of hollow tubes and other structures useful for fluidic systems and relatively large mechanical structures. A related process known as HexSil, developed by Chris Keller at UC Berkeley, involves the deposition of an oxide release layer and polysilicon on a single mold wafer from which polysilicon structures are subsequently released (1). In contrast, this new process uses two mold wafers that are tempo rarily bonded together after the deposition of the oxide release layer. The two wafers form a complete mold with internal cham bers. Then amorphous polysilicon is vapor deposited and coats the internal chambers of the mold via access holes in the top mold wafer. After some further processing, the wafers are separated and the structures are released. This process is particularly useful for fluidic applications because complex closed flow passages, such as microfilters, interconnected chambers, fluid manifolds etc. can be easily be created. Polysilicon microneedles from 100 to 200 microns in diameter and 1 mm to 7 mm in length and sub-micron tip radii have been fabricated using this process. These micronee dles are valuable for small volume drug injection where minimal tissue damage and/or minimal pain are desired. In addition, the Polymolding process does not damage the mold wafers, so they can be reused many times at a huge cost savings.