A process of deep reactive-ion etching (DRIE) using a fluorine-based gas mixture enhanced by induction-coupled plasma (ICP) has been demonstrated to be effective in forming high-aspect-ratio three-dimensional patterns in fused silica. The patterns are defined in part by an etch mask in the form of a thick, highquality aluminum film. The process was developed to satisfy a need to fabricate high-aspect-ratio fused-silica resonators for vibratory microgyroscopes, and could be used to satisfy similar requirements for fabricating other fused-silica components.
The development of the process involved manipulation of some process parameters, including the selection of gases, the mixture ratios of the gases, the process pressure, and power of the radio-frequency signal used to excite the ICP. It was found that polymeric materials that contained silicon and/or fluorine were formed on the side walls during etching and were subsequently etched away, resulting in anisotropic etching. It was also found that helium added to gas mixtures contributes to cooling of substrates and thereby helps in forming vertical side-wall patterns.
One version of the process was found to effect etching of vertical side walls in 100-μm-deep fused silica at a rate of about 0.4 μm/min. Some of the parameters of this version of the process were the following:
- ICP power 1.2 kW;
- Reactive-ion etching power 0.5 kW;
- Process pressure 6 mtorr (≈0.8 Pa);
- Gas mixture of 1 part C4F8 to 1.6 parts of H2; and
- Thickness of aluminum mask 5 μm.
The rate of etching of the fused silica was found to be about 5 times the rate of etching of the aluminum.
This work was done by Karl Yee, Kirill Shcheglov, Jian Li, and Daniel Choi of Caltech for NASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-43837, volume and number of this NASA Tech Briefs issue, and the page number.