UV surface exposure for low temperature hydrophilic silicon direct bonding

The ultraviolet (UV) surface exposure is applied in hydrophilic silicon direct bonding as an additional treatment following the traditional wet chemical activation processes. Infrared inspection and tensile strength test are then performed. It is found that improvement in bond-rate, interface uniformity as well as high tensile strength is obtained. The mechanism of UV exposure including surface cleaning and surface modification is discussed in detail. Mixed spectrum emitted from the UV source comprising 254 and 185 nm wavelength efficiently removes the resided organic contaminations on silicon surface by photosensitization and oxidation effects. Besides, considerable hydroxyl incorporations are generated by UV reacting with surface water molecular and silicon dioxide. Thus, appropriate UV exposure will render the silicon surface more hydrophilic and improve bondability. It is concluded that as an additional cleaning and modification treatment, UV exposure is effective and promising to enhanced bond quality in low temperature hydrophilic silicon direct bonding.