Plasma-activated bonding

The decrease of temperature is based on the increase of bonding strength using plasma activation on clean wafer surfaces.

[2] Based on ambient pressure, two main surface activation fields using plasma treatment are established for wafer preprocessing to lower the temperatures during annealing.

[3] To establish maximum surface energy at low temperatures (< 100 °C) numerous parameters for plasma activation and annealing need to be optimized according to the bond material.

[1] Atmospheric Pressure-Plasma Activated Bonding enables the possibility to ignite plasma at specific local areas or the whole surface of the substrate.

[3] The wafer pairs pass the following process flow: The optimal gas mixture for the plasma treatment is depending on the annealing temperature.

[5] If using glass, based on the high surface roughness, a chemical-mechanical planarization (CMP) step after rinsing is necessary to improve the bonding quality.

[1] The activation equipment consists of the grounded chuck acting as wafer carrier and an indium tin oxide (ITO) coated glass electrode.

[6] Due to its positive orientation the massive ions, that are not able to follow the HF field, move to the negatively charged electrode, where the wafer is placed.

The maximal bond strength is achieved with nitrogen and oxygen as process gases and is sufficiently high with a homogeneous dispersion over the wafers after annealing at 250 °C.