| AVS 55th International Symposium & Exhibition | |
| MEMS and NEMS | Monday Sessions |
| Session MN+NC-MoA |
| Session: | Fabrication at the Micro- and Nano- Scales for MEMS/NEMS |
| Presenter: | J.-F. Veyan, University of Texas at Dallas |
| Authors: | J.-F. Veyan, University of Texas at Dallas Y.J. Chabal, University of Texas at Dallas X.-M. Yan, Qualcomm A. Londergan, Qualcomm E. Gousev, Qualcomm |
| Correspondent: | Click to Email |
XeF2 is a widely used isotropic etchant in MEMS and NEMS fabrication because it selectively removes a large variety of pure compounds (e.g. Si, Ge, Mo, W) but not their stoichoimetric oxides. Understanding the etching mechanisms is crucial to achieve highly selective etching. We have studied and compared the XeF2 etching of Silicon oxide-Silicon and Molybdenum Oxide -Molybdenum systems, under typical pressure conditions used in industry (~ few Torr). Using in-situ Infrared Absorption Spectroscopy (IRAS) we have investigated the reaction kinetics and characterized the gas phase, surface and subsurface species after and during the etching process. To reduce side effects due to reaction with the reactor walls and sample holders, an all aluminum chamber has been designed, with Teflon gasket and Kalrez O-ring for sealing. The length of stainless steel tubing for gas transport has also been reduced. To minimize reactions with contaminants such as water and hydrocarbon, the reactor is pumped to 10-5 Torr prior any XeF2 introduction. The sample temperature prior and during XeF2 exposure is controlled by heaters made with Ta filaments inserted in a ceramic frame imbedded inside the sample holders. A chromel-alumel thermocouple is placed directly in contact with the sample surface. With the sample out of the IR beam path the reaction products are monitored during and after etching process. Transmission is used to probe SiO2/Si, and grazing angle reflection to probe MoO3/Mo, and surface and subsurface species are detected/identified during and after etch reactions. XeF2 induces a strongly exothermal reaction with both Si and Mo, producing gaseous SiF4 (1030 cm-1)and MoF6 (741 cm-1), and incorporating Fluorine species into the subsurface region. No reactions have been observed with stoichiometric Silicon Oxide and Molybdenum Oxide, but both oxides are completely removed when overlaying the pure material. The removal of the oxide overlayers is believed to be due to fluorine migration through the oxide and reaction with the elemental Si or Mo at the oxide-element interfaces.