Low temperature hybrid bonding using self-alignment

An efficient C2C/C2W oxide bonding technique using self-alignment effect of a pair of hydrophilic chip surfaces, which are activated by atmospheric plasma, is applied to 3D stacking of multichip package in this work. Self-alignment and pre-bonding technique can provide high-speed bonding process and high-precision chip alignment accuracy simultaneously without high-precision chip manipulator. Conventional Cu to Cu bonding requires high bonding temperature above 400 °C to get high bonding interface energy and form perfect bonding interface. In order to reduce bonding temperature, plasma activated oxide bonding and metal bonding simultaneously is applied, which is called as low temperature hybrid bonding. In addition, atmospheric N₂ plasma is used to form hydrophilic surface and reduce bonding temperature because atmospheric N₂ plasma shortens bonding process time compared to vacuum plasma. Contact angle variation is investigated according to gas concentration, voltage and time. Bonding interface energy is measured using 4 point bending method with respect to bonding temperature experimentally. Through experiments, we could acquire high bonding interface energy of 10.69J/m² at 200°C.