I believe that Analog Devices has a Patent on that process, you may want to
contact Analog micromachine division

Rick

Rick Morrison
Sr. Semiconductor Engineer
Radant Mems Inc.
255 Hudson Road
Stow Ma, 01775
Tel- 978-562-3866
Cell 508-801-4796
AMS Phone: 508-770-3521
EMAIL  rmorrison@radanttechnologies.com