Surface activated bonding for new flip chip and bumpless interconnect systems

As microelectronic integration trends move toward ultrafine density flip chips and bumpless interconnect systems, it is necessary to develop a low cost, ultra-high density, low-damage and low-temperature interconnect technology. To satisfy this requirement, a new bonding method, the surface activated bonding (SAB), was introduced. In this process, the bonding pads on chips and bumps on substrates are first cleaned by Ar plasma or atom beam irradiation, precisely aligned with an accuracy of less than ±0.5 μm. Then they are bonded directly to each other only by contact at room temperature or low temperature in a newly developed flip chip bonder. This procedure, which enables the bonding in an inert ambient atmosphere of N_2, under atmospheric pressure, cuts down the bonding condition requirements and decreased the process cost. Some preliminary experiments have led to Au-Au and Au-Cu direct bonding, demonstrating the performance of the new bonding system.