The Use of Metallographic and SEM Analysis for Characterization of Sidewall Surfaces in MEMS Devices with DRIE Processing

Abstract

The use of Bosch process Deep Reactive Ion Etch (DRIE) processing for manufacturing MEMS and MOEMS devices requiring high aspect ratio (depth/width) trenches has become commonplace. However, process conditions (etch rate, process parameters etc.) have a significant effect on the surface quality of the trench sidewalls. For many device types [1] (grates, waveguides) surface condition of the sidewall can have a large impact on the functionality of the device and therefore must be controlled to achieve performance requirements. Optical microscopy techniques are not capable of the depth of focus and resolution necessary to adequately control processing within deep trenches where surface roughness of < 10nm may be required. Scanning Electron Microscopy (SEM) is capable of this resolution, but even SEM is incapable of determining surface roughness within the deep trenches. Metallographic techniques, mounting and polishing a sample to reveal a section view through the trench, along with SEM, to image and measure the surface roughness is a requirement. An experiment was designed, using etch parameters to vary the DRIE recipe, and then cross sectioning and SEM imaging of the devices were performed. The purpose of the experiment was to quantify the effect of the DRIE recipe on the sidewall surface roughness within the trench, and to demonstrate the use of metallographic techniques with SEM to accomplish this goal.