Process for high yield fabrication of MEMS devices

DETAILED DESCRIPTION The present invention provides a MEMS fabrication process that minimizes the thickness of the silicon device layers and the required etch times, provides exceptionally precise layer to layer alignment of the device components, does not require a wet etch to release the moveable device structure, employs a supporting substrate having no device features on one side, and utilizes low-temperature metal-metal bonding which is also less sensitive to environmental particulates than high temperature silicon-silicon oxide bonding.
The process of the present invention can be used to fabricate a wide variety of MEMS devices, including sensors, but is particularly useful for fabrication of active MEMS devices (for example, electrical switches, variable capacitors and inductors, high frequency resonators, and mircromirrors for optical scanning and switching), which are often difficult to fabricate with high yield using prior art processes.
Active MEMS devices typically use an electrostatic comb actuator but the process of the present invention could also be used to fabricate devices employing other types of actuators.
The basic steps of a preferred embodiment of the process of the present invention for fabrication of an active MEMS device are as follows.
Alignment marks are etched into the surface of the first silicon device layer on a first silicon-on-insulator (SOI) wafer, which comprises a first etch stop layer (e.
g.
, silicon oxide) sandwiched between the first silicon device layer and a supporting substrate (e.
g.
, silicon).
An etch resistant layer (e.
g.
, silicon oxide) is applied to the first silicon device layer and is patterned and etched to expose silicon in predetermined contact and bond pad areas, which are selectively metallized by deposition of a metal layer (e.
g.
, Cr/Au) and liftoff of the remaining photoresist and extraneous metal.
The etch resistant layer is then patterned again and etched (preferably by dry oxide plasma etching) and the underlying silicon is etched (preferably by deep silicon plasma etching) to form the stationary actuator structure, which is protected from subsequent etching by the remaining etch resistant layer