Interface Characterization and Analysis of 4H-SiC Direct Bonding Structure Based on Plasma Processing

Abstract

A plasma-assisted direct bonding method for 4H-SiC is put forward to prepare all-SiC vacuum-sealed cavity in this paper. This method takes three significant steps of bonding surface treatment, hydrophilic pre-bonding and hot pressing bonding. The SiC bonded sample with a cylindrical sealing cavity structure was prepared under a pressure of 2 MPa for a period of 1 h at 1000 °C using the direct bonding method. The bonded sample’s airtightness is approximately 0.1 × 10−9 pa·m3 s−1, and the bonding strength reaches 24.9 MPa, meeting the requirements of most pressure sensors. The cavity structure of the bonded sample is unbroken and the bonding interface is smooth without stress concentration under a scanning electron microscope (SEM). Transmission electron microscope (TEM) observation results reveal that bonding interface is amorphous with a thickness of less than 1 nm. The bonding interface is mainly composed of carbon and silicon which is analyzed through energy dispersive X-ray (EDX). It is speculated that the transition layer of ultrathin amorphous SiC is formed during bonding process. Finally, the SiC bonding mechanism is discussed in detail based on the experimental results. All-SiC bonding structures with a vacuum-sealed cavity can be applied to fabricate mechanical quantity sensors for use in severe environment.