Transmission Laser Welding Via Two-Photon Absorption

Micro-electromechanical systems (MEMS) are widely employed instead of conventionally machined devices due to high performance in an extremely small size, weight, and power package. MEMS manufacturing often requires bonding of silicon wafers. Direct molecular bonding consists of appropriately preparing and placing two wafers in intimate contact at high temperatures so that intermolecular bonds develop across the wafer. This process requires numerous and tedious steps in a clean room environment and processes like thermal annealing or plasma activation of the surface to achieve modest bond strength. The direct bonding of etched silicon surfaces is still practically precluded due to surface roughness. To overcome this, thin interfacial layers, such as eutectic metals, are added to the material; however, the mismatch in thermal expansion between these materials may impact performance (long-term creep) or even catastrophic failure (delamination). Development of a simple and reliable direct wafer bonding process that avoids these steps and is applicable to etched surfaces will benefit MEMS manufacturing for multiple military and commercial applications. In this context, transmission laser micro-welding is a highly desirable approach for the fabrication of complex-architecture semiconductor systems inaccessible by current methods. Cornerstone Research Group (CRG) Inc. will partner with Photon Automation Inc. to develop a manufacturing process to laser weld etched silicon. Using two-photon absorption via a 2090 nm wavelength holmium YAG laser, CRG will work to solve the longstanding problem of semiconductor welding. Compared to current wafer bonding methods, the developed laser bonding method represents a cost-effective and flexible solution as it will allow similar and dissimilar material assembly and will not require clean room environment.