Optimization of Temporary Wafer Bonding Materials and Processes for 3D IC Integration

Abstract

A 3D stacked IC technology has promoted technological developments to satisfy the great demand for high-end applications such as flexible ICs, system-in-packaging (SiP), high-integration microelectronics, and power application. Temporary wafer bonding has become a critical element in device processing over the past decades. The release layer and adhesive materials used for bonding a device wafer onto a carrier wafer play a key role in the manufacture of ultrathin devices and high-performance packages.We optimize the process integration and manufacturing aspects of the release layer in a temporary wafer bonding process, which is used for three-dimensional integrated circuits (3D IC) package. We provide optical performance data on the materials and attempt to establish a standard route for temporary wafer bonding in order to cost-effective and increase the reliability and yield of integration schemes. This manuscript covers three parts: focused ion beam (FIB) observation the morphology of the release layer, temporary bonding of a device wafer onto a carrier wafer, and de-bonding of the wafer from the carrier. The purpose of release layer observation is to identify its thickness and monitor the morphology of the release layer. Temporary bonding can attach the device wafer onto the carrier wafer prior to the back-grinding for preventing thinned device wafer chipping or cracking. The wafer bonding defect and thickness variation are discussed. It is noticed that the critical step in temporary bonding is plasma active process for forming a release layer. Hence, three types of plasma active release layers are assessed to bond a device wafer onto a silicon wafer. Plasma active time starts from 360 seconds reduced to 120 seconds and 100 seconds, the corrugated release layer becomes much flatter. Three bonded stacks are debonded by SUSS DB12T de-bonder to qualify the performance of the temporary bonding process. Bonded stack with maximum plasma active time is failed for de-bonding, less of them are succeeded in wafer separating process.