Application Note: Silicon Etching Process Using Laser Milling Techniques

Prepared by Yu Zhou, PhD Candidate, under the supervision of Prof. Cyrus Shafai, both from University of Manitoba; in co-operation with James Dietrich from CMC Microsystems.

This application note proposes a silicon etching process based on a laser milling technique as an alternative to the reactive ion etching (RIE) process that is commonly use to etch and release silicon structures. The RIE process is highly responsive to the surface topography of the etched structure, has a finite selectivity towards material and has a highly recipe-dependent anisotropic rate, and requires a mask to be functional. These drawbacks limit its implementation in some applications, such as micromachining. The laser milling process, as a purely physical process, provides high selectivity, a maximum of 90 % anisotropy, easy accessibility, and does not require a mask. With some tuning of the laser system, a minimum line width of 18 µm and 20 µm in the x-axis and y-axis respectively can be achieved. The process described here produced a reliable etching of 15 µm thick silicon. With this process, an etching of a MEMS structure with complex surface topography can be achieved.