Isotropic etching of silicon using xenon difluoride is an ideal solution for releasing MEMS devices. XeF2 shows nearly infinite selectivity to silicon over almost all standard semiconductor materials including photoresist, silicon dioxide, silicon nitride and aluminum. Being a vapor phase etchant, XeF2 avoids many of the problems typically associated with wet or plasma etch processes. For more information see our summary on the unique advantages of xenon difluoride etching.
Please see below for some application examples:
Al Cantilevers released using XeF2
Image courtesy of Prof. Chad O'Neal
Louisiana Technical University
Silicon Micro-Mirror released using XeF2 to overcome selectivity problems with long etches. The silicon device was protected using a thin oxide layer during release.
Image courtesy of Analog Devices
T.J. Brosnihan, et al., "Optical iMEMS - A Fabrication Process for MEMS Optical Switches with Integrated On-Chip Electronics," Transducers '03
Pixels released using XeF2
Image courtesy of Qualcomm
Used XeF2 to release mixed material resonators including ZnO, Al and SiO2
Image courtesy of Dr. Don L. DeVoe, University of Maryland
Dr. Don L Devoe, "Piezoelectric Thin Film Micromechanical Beam Resonators," Sensors and Actuators A88 (2001)
As part of a sensor structure, covered trenches were created by removing sacrificial polysilicon with XeF2.
Image courtesy of Dr. Oliver Brand, Georgia Tech
Polymer protecting sidewall in Bosch process used as mask for isotropic etch with xenon difluoride
Image courtesy of Carnegie Mellon University MEMs Laboratory
D. Gaugel, K. Gabriel, "CMOS-Compatible Micro-Fluidic Chip Cooling Using Buried Channel Fabrication," Proceedings of IMECE '02, New Orleans, 2002
- 25 nm to 100 nm in diameter
- Up to 5 um long
A combination of wet-etching and isotropic XeF2 etching is used to create equally undercut circular silica disks on a silicon support pillar.
Image courtesy of the Department of Applied Physics, California Institute of Technology
Material stress used to achieve desired shape after release using XeF2.
Image courtesy of Dr. Cindy Harnett, University of Louisville
E Moiseeva, Y M Senousy, S McNamara and C K Harnett, "Single-mask Microfabrication of Three-dimensional Objects from Strained Bimorphs," Journal of Micromechanics and Microengineering, Volume 17, Number 9, August, 2007
Silicon Carbide array with 5 um openings released using XeF2
Image courtesy of Prof. Roger Howe, Stanford University
J. Provine, P. B. Catrysse, C. Roper, R. Maboudian. S. Fan, and R. T. Howe, “Phonon polaritron reflectance spectra in a silicon carbide membrane hole array,” Annual Meeting of the IEEE Laser and Electro-Optics Society, Lake Buena Vista, Florida, October 21-25, 2007
Polysilicon 2 removed without damaging dielectric layer underneath.
Mirror array exposed by backside etch using XeF2 after bump bonding and package insertion.
Image courtesy of Daniel Lopez, Argonne National Labs
Nagesh Basavanhally, et al., "High-Density Solder Bump Interconnect for MEMS Hybrid Integration," IEEE Transactions on Advanced Packaging, Volume 30, Number 4, November 2007
Photograph of cantilever RF switch released using XeF2
Image courtesy of IBM