Silicon wafer-to-wafer bonding at T<200 °C with polymethylmethacrylate

A versatile method for low temperature (T<200 °C) bonding of silicon and oxidized silicon wafers is reported using spun cast films of polymethylmethacrylate (PMMA) as the bonding material. The PMMA films are thermoplastic, transparent, dielectric, planarizing, and photopatternable. Bonding was achieved with both unpatterned and patterned, 1-μm-thick films. Tensile bond strengths of 3.12 MPa were typical (although the strongest bond had a strength of 5.85 MPa) and thin film stresses of 10 MPa (tensile) were measured. Photopatterned PMMA films exhibited approximately 14% lateral pattern smear after bonding.