| AVS 54th International Symposium | |
| MEMS and NEMS | Monday Sessions |
| Session MN-MoA |
| Session: | Materials Processing, Characterization and Fab Aspects |
| Presenter: | J.-F. Veyan, Rutgers, The State University of New Jersey |
| Authors: | J.-F. Veyan, Rutgers, The State University of New Jersey Y.J. Chabal, Rutgers, The State University of New Jersey M.Y. Yan, Qualcomm E. Gusev, Qualcomm A.L. Londergan, Qualcomm |
| Correspondent: | Click to Email |
XeF2 is used for etching a number of materials during MEMS fabrication, such as silicon,1 and metals. Its strong reactivity with silicon and metals leads to rather violent reactions that make it difficult to characterize with typical surface science techniques under typical manufacturing conditions (XeF2 pressure in a few Torr range). The fundamental reactions involved under these conditions are therefore harder to understand than typical elementary surface reactions in ultra-high vacuum conditions. It is therefore important to investigate etching mechanisms under such conditions. This work focuses on the characterization of gas phase, surface species, and substrate surfaces during XeF2 etching using in-situ infrared absorption spectroscopy (IRAS) for both silicon and silicon oxide surfaces under typical etching conditions. To that end, a compact reactor has been constructed out of non-reactive materials (e.g. stainless steel, aluminum, Teflon and Kalrez o-rings), with the capability to perform IR spectroscopy. Despite these precautions, IRAS is critical to detect the presence and role of fluorinated contaminants (from reaction with molecules adsorbed on the walls) and the presence of products.2 Thus, while XeF2 induces a strongly exothermal reaction with Si, producing large amounts of SiF4 gas (with a characteristic IR signature), and the incorporation of SiF, SiF2 and SiF3 in the subsurface region (~30Å deep) as previously observed in UHV studies, the presence of H2O and HF gas, and CFx and othe r adsorbed impurities can also be observed, pointing to side reactions on the walls despite thorough baking. XeF2 etching of SiO2 is much weaker and thereby harder to study. IRAS studies confirm that amorphous SiO2 is etched at the rate of ~2-3Å/cycle at room temperature, where a cycle consists of 2Torr in 427cm3 (i.e. ~ 3.1019 XeF2 molecules). Although SiF4 gas is also detected, it is not possible to exclude the potential etching of Si due to scratches. In contrast, no measurable SiF4 gas is observed when crystal quartz is placed in contact with XeF2, indicating that quartz does not etch. Preliminary data indicate that SiO2 etching is highly dependent on the substrate temperature. Based on IRAS data, this talk will discuss various etching mechanisms and optimization of etching conditions for both Si and SiO2.
1 Harold.F Winter and I.C. Plumb J. Vac. Sci. Tech. B 9(1) 197 (1990)
2 J. I. Steinfeld, Chem. Rev., 89, 1291, (1989)