The role of hydrogen in silicon wafer bonding: an infrared study

In this work, we utilize infrared absorption spectroscopy (IRAS) to probe the chemical purity of both wafer surfaces immediately prior to bonding and the wafer interface right after joining. The IRAS technique can give partial chemical information, particularly for hydrogen and can also indicate the nature of the interactions (van der Waals, H-bonding, chemical bonds). Experimentally, we probe the surfaces of Si wafers in two ways: either with multiple internal reflections (MIR) using the wafer itself to trap the IR radiation, or with MIR using a germanium plate to trap the IR radiation. The first approach is a convenient way to probe all vibrations above 1500 cm/sup -1/. The second is a sensitive way to access lower frequency vibrations (>700 cm/sup -1/), but is insensitive to the components parallel to the interface. To probe the interface of joined wafers, we use the technique of multiple internal transmission (MIT), using the joined Si wafers themselves to trap the IR radiation. This configuration is again limited to frequencies above 1500 cm/sup -1/, but its sensitivity to vibrations perpendicular to the interface is 20 times that of MIR.