A New Breed of High Volume Wafer Processing Equipment - In Situ Aligned Wafer Bonding Systems for 3D Integration

Although wafer bonding techniques have been used for decades in various areas of microelectronics research and manufacturing, mainly the requirements of high volume MEMS (Micro Electro Mechanical Systems) packaging have triggered commercial equipment vendors to concentrate on the development of such wafer bonding systems. These early commercial drivers of wafer bonding technology primarily required well controlled environmental conditions during the bond cycle such as low pressure / vacuum or inert gases to be encapsulated in between die on the wafers. Post bond alignment has always been a secondary criterion with typical requirements in the 5um to 25um+ range.

With the advent of 3D Integration concepts and strategies on a wafer level as a potential enabler for the continuation of Moore's law, the aligned wafer bonding requirements have shifted significantly. The primary focus has become post-bond alignment accuracy over large area wafers (200 and 300mm). Requirements have increased by approximately an order of magnitude into the range of 0.5um-2.5um. Post-bond alignment precision across the wafer represents the gating element defining size and density of layer-to-layer interconnections. Control of environmental conditions during the bond cycle however is now secondary and only needs to meet the requirements of the actual physical or chemical bond mechanism utilized.

The following paper provides a brief summary of wafer to wafer alignment approaches as used today and describes the revolutionary concept of in-situ aligned wafer bonding. The paper further discusses the main contributors to post-bond misalignment and how in-situ alignment prior to bonding addresses these issues. Lastly the paper provides a comprehensive overview of a new generation of "In-Situ Aligned Wafer Bonding Equipment".