MEMS Retroreflector Fabrication and Packaging
Integration of 3-D devices, IC or MEMS, often requires a handle wafer which is removed before final packaging of the devices. This process usually uses lapping, chemical etch or high temperature heating to de-bond the handle wafer. A new technique to release a Pyrex handle wafer using laser ablation is presented. Pulsed energy, from a 248nm excimer laser is delivered transparently through the Pyrex handle wafer. This causes delamination of the bonded silicon structures from the handle wafer. This technique offers fast throughput at chip and wafer levels and protects the fragile and delicate active devices from harsh physical, chemicals and potential thermal stresses. We present a method wherein the handle wafer used in 3-D assembly of a MEMS device was released using laser micromachining. A Pyrex handle wafer rigidly supports anisotropically etched, through-silicon wafer, vertical mirrors during thermo-compression bonding to active MEMS parts. After this first thermo-compression bond, the Pyrex handle wafer was lifted off using laser ablation, leaving clearance for additional bond steps, which includes additional components and a package frame. Multiple Au-Au thermo-compression bonds of vertical surfaces onto a single MEMS chip were performed, to assemble and package 3-D MEMS devices.
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