Hydrophilic thermocompression bonding of single-crystalline 3C-SiC thin film on sapphire substrate

Microelectronic devices for harsh environment applications require new wafer bonding methods that can overcome the large thermal mismatch between functional layer and supporting substrate during bonding process. This paper presents a bonding strategy that leverages the thermocompression bond formation between a wide band gap semiconductor (i.e., silicon carbide (SiC)) and a robust substrate (i.e., sapphire) for the first time for harsh environment applications. The wafer bonding process was executed through chemical bonding, facilitated with the hydrophilic surfaces on both silicon carbide and sapphire surfaces. The enhanced hydrophilicity was obtained by plasma treatment, resulting in the formation of hydroxyl groups (-OH) on the bonding surfaces. The bonding was done immediately after oxygen plasma activation steps to avoid any loss of the generated -OH groups. To further assist bonding through the hydrophilic surfaces, the bonding temperature of 250 °C and pressing force of 10 kN were applied on a 20 mm x 20 mm bonding sample for 30 minutes to form strong chemical bonds (Si-C-O-Al). The bonding results of this study revealed a bonding strength of 0.6 MPa at the SiC/sapphire interface. This strength is attributed to the presence of an ∼25 nm amorphous transition layer formed at the interface between sapphire and SiC. Furthermore, high-resolution STEM results showed that both surfaces were atomically bonded through the transition layer with enriched carbon element. Our thermocompression bonding technique enables the formation of single-crystalline SiC thin-film on Sapphire (SiCOS) heterostructures, which offers great potentials for power electronics and MEMS devices in harsh environment applications. • Developed a novel thermocompression bonding method for SiC thin film on sapphire for harsh environment applications. • Achieved heterostructure bonding success via plasma-activated hydrophilic and thermocompression bonding methods. • Demonstrated SiC/sapphire bonding with ∼25 nm amorphous layer, enabling potential use in power electronics and MEMS.