Bonding characteristics of 3C-SiC wafers with hydrofluoric acid for high-temperature MEMS applications

T his paper describes the bonding characteristics of 3C-SiC wafers using plasma enhanced chemical vapor deposition (PECVD) oxide and hydrofluoric acid (HF) treatment for SiC-on-insulator (SiCOI) structures and high-temperature microelectromechanical system (MEMS) applications. In this work, insulator layers were formed on a heteroepitaxial 3C-SiC film grown on a Si (0 0 1) wafer by thermal wet oxidation and a PECVD process, successively. The pre-bonding of two polished PECVD oxide layers was made under definite pressure after the treatment of hydrophilic surface activation in HE The bonding processes were carried out under various HF concentration and external applied pressure. The bonding characteristics were evaluated by the effects of HF concentration used in the surface treatment on the roughness of the oxide and the pre-bonding strength, respectively. Hydrophilic character of the oxidized 3C-SiC film surface was investigated by attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR). The root-mean-square (RMS) surface roughness of the oxidized 3C-SiC layers was measured by atomic force microscope (AFM). The strength of the bonded wafer was measured by tensile strength meter (TSM). The bonded interface was also analyzed by scanning electron microscope (SEM). The values of the bonding strength ranged from 0.52 to 1.52 MPa according to HF concentrations without the external applied load during pre-bonding process. The bonding strength initially increases with increasing HF concentration and reaches the maximum at 2.0% of HF concentration and then decreases. Consequently, low temperature 3C-SiC wafer direct bonding technique using a PECVD oxide layer and HF could be applied as a fabrication process of high quality substrates for high performance electronic devices and harsh environment MEMS applications. (c) 2004 Elsevier B.V. All rights reserved.