Veronica Burrows

Release etch modeling analysis and the use of laser scanning microscopy for etch time prediction of micromachined structures

An alternative non-destructive analysis method using laser scanning microscopy (LSM) was used to study etch release distances in MEMS pressure sensor. The LSM method eliminates samples preparation and is easy to implement in a MEMS manufacturing environment. In this study, various diaphragm structures were etched using a highly concentrated HF based solution. Experimental etch data were obtained for both SiO2 and PSG films under these various structures. Both the height and the width of the sacrificial layer port/channel had a significant effect on etch rate for both films. As expected, a non-linear etch rate was obtained for both SiO2 and PSG films. Since the HF concentration changes over time in a manufacturing bath process, careful selection of processing time is required in order to fully release MEMS structures. Future theoretical modeling with the assistance of experimental data obtained in this study is being pursued to strengthen past work done by Eaton et al, Monk et al, and Liu et al.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Surface Chemistry of GaAs(100) after Treatment with Aqueous H 3 PO 4 Solution

The interaction of semiconductor surfaces with aqueous acid solutions is important in chemical cleaning and etching. Wet chemical treatments are advantageous because they cause little damage to the surface and do not usually require high temperatures. The surface chemistry of GaAs after treatment with phosphoric acid was studied using multiple internal reflection infrared spectroscopy. The treatment left behind a thin film containing several types of P x O y bonds. The chemical nature of the film was observed to change with time as new species would form on the surface.

Electrochemical Sulfur Treatments of GaAs Using Na 2 S and (NH 4 ) 2 S Solutions: A Surface Chemical Study

Chemical sulfur treatments of GaAs have been shown to improve the GaAs surface electronic properties. These treatments result in lower surface state density, lower surface recombination velocity, and shifting or unpinning of the Fermi level, in addition to improvement in the performance of devices. However, there is still considerable controversy regarding the chemical nature of the surface film which results from this chemical sulfidation. It has been shown that this film is not stable chemically and electronically. The improved surface electronic properties decay with time and are sensitive to the chemical environment of the material. In this study, using surface infrared reflection spectroscopy (SIRS) and x-ray photoelectron spectroscopy (XPS), we have investigated the electrochemical sulfidation of GaAs as a possible new method to produce a GaAs surface that is stable chemically and electronically. We have found that anodic treatments with Na 2 S and (NH 4 S solutions result in the removal of the pre-existing oxide of GaAs and the formation of films comprising sulfur, sodium carbonate, ammonium thiosulfate, and sulfide and sulfur-oxygen compounds of arsenic. Rinsing the GaAs with water removes the bulk of the film, leaving behind a surface on which only arsenic sulfide was detected.