Successful direct wafer bonding between InP and silicon-on-insulator (SOI) wafers has been demonstrated by adopting a 20-nm-thick Al2O3 as the intermediate layer. A detailed investigation on the property of the bonding interface is carried out. Water contact angle test reveals an improved hydrophilicity for both the InP and the Al2O3/SOI wafers after oxygen plasma surface activation. X-ray photoelectron spectroscopy is employed to characterize the bonding interface before and after the wafer bonding process. It is found that oxides are formed on the bonding interface during bonding, which helps ensure high quality hydrophilic bonding.
The effect of NH 4 OH treatment on InP/Al 2 O 3 /SOI direct wafer bonding is investigated. The atomic force microscope (AFM) and water contact angle (CA) results reveal a decrease in root-mean-square (RMS) surface roughness and CA of the NH 4 OH-treated InP wafer. X-ray photoelectron spectroscopy (XPS) analysis is carried out to ascertain the chemical composition of the bonding surfaces. It is found that NH 4 OH treatment followed by plasma activation increases the content of oxides on the surface of InP wafer. Based on these results, it is concluded that NH 4 OH treatment helps increase hydrophilicity and contact area of the bonding surface, thus contributing to the success of plasma-assisted InP/Al 2 O 3 /SOI wafer bonding.
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