Effect of ultrathin palladium layer in achieving a low temperature and pressure wafer level aluminum to aluminum bonding

Abstract

Metal-Metal diffusion bonding was reassuring for micro electro mechanical system (MEMS) packaging and three dimensional (3D) integration. Despite copper and gold, aluminum (Al) is also proficient for wafer-level bonding due to its CMOS compatibility. As of now, a successful bonding reported with a temperature requirement is >300 °C, due to chemically unwavering surface oxide on the aluminum surface. In this work, a facile method of successful Al–Al bonding at a low temperature and pressure by passivating Al surface with another ultrathin noble metal has been reported. Here, a systematic study for selecting a required optimum ultrathin passivation layer thickness in making the surface to be free from surface oxide formation is provided. Also, looking over in an enhancement of surface morphology and microstructure by varying the thickness of an ultrathin passivation layer. Added to this, after obtaining the required oxide-free surface, we conducted wafer-level thermo-compression bonding for optimizing low temperature (∼250 °C) and pressure (∼3 MPa) by inspecting interface quality and reliability studies. We put forward that the proposed bonding technique is promising to use at the wafer-level, to integrate high-performance chip stack interconnects and facile packaging methods for micro-electro-mechanical systems.