SCREAM I: A single mask, single-crystal silicon, reactive ion etching process for microelectromechanical structures

A single-crystal silicon, high aspect ratio, low-temperature process sequence for the fabrication of suspended microelectromechanical structures (MEMS) using a single lithography step and reactive ion etching (RIE) is presented. The process is called SCREAM I (single-crystal reactive etching and metallization). SCREAM I is a bulk micromachining process that uses RIE of a silicon substrate to fabricate suspended movable single-crystal silicon (SCS) beam structures. Beam elements with aspect ratios of 10 to 1 and widths ranging from 0.5 to 4.0 μm have been fabricated. All process steps are low temperature (<300 °C), and only conventional silicon fabrication tools are used: photolithography, RIE, MIE, plasma-enhanced chemical-vapor deposition (PECVD) and sputter deposition. SCREAM I is a self-aligned process and uses a single lithography step to define beams and structures simultaneously as well as all necessary contact pads, electrical interconnects and lateral capacitors. SCREAM I has been specifically designed for integration with standard integrated circuit (IC) processes, so MEM devices can be fabricated adjacent to prefabricated analog and digital circuitry. In this paper we present process parameters for the fabrication of discrete SCREAM I devices. We also discuss mask design rules and show micrographs of fabricated devices.