Feb 5, 2018

Temperature-dependent interface characteristic of silicon wafer bonding based on an amorphous germanium layer deposited by DC-magnetron sputtering


We propose a new method for low-temperature near-bubble-free Si wafer-bonding.
The magnetron-sputtered a-Ge is verified to be extremely hydrophilic for bonding.
The crystallization of a-Ge starts from the bubble center and sprawls to the edge.
The crystallization of a-Ge at bubble position results in the absence of bubbles.
The H2 by-product is verified to be absorbed by the intermediate Ge during annealing.


We report a near-bubble-free low-temperature silicon (Si) wafer bonding with a thin amorphous Ge (a-Ge) intermediate layer. The DC-magnetron-sputtered a-Ge film on Si is demonstrated to be extremely flat (RMS = 0.28 nm) and hydrophilic (contact angle = 3°). The effect of the post-annealing temperature on the surface morphology and crystallinity of a-Ge film at the bonded interface is systematically identified. The relationship among the bubble density, annealing temperature, and crystallinity of a-Ge film is also clearly clarified. The crystallization of a-Ge film firstly appears at the bubble region. More interesting feature is that the crystallization starts from the center of the bubbles and sprawls to the bubble edge gradually. The H2 by-product is finally absorbed by intermediate Ge layer with crystalline phase after post annealing. Moreover, the whole a-Ge film out of the bubble totally crystallizes when the annealing time increases. This Ge integration at the bubble region leads to the decrease of the bubble density, which in turn increases the bonding strength.
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