Ultra thin silicon films directly bonded onto silicon wafers

Ultra thin film of silicon bonded on 4 in. (001) silicon wafers have been obtained by combining a direct hydrophobic silicon bonded technique with a layer transfer. The twist angle between the ultra thin Si film and the Si substrate was varied from 0 to 15°. X-ray reflectivity measured the thickness and the roughness of the ultra thin films. Complementary results concerning the interface structure were obtained with high resolution transmission electronic microscopy. It is shown that an ultra thin film (a few nm) can be reproductively prepared upon the full 4 in. wafers. Moreover, this process gives very small thickness fluctuations and a small surface roughness. The bonding interface has a low concentration of oxide precipitates and presents two arrays dislocations respectively, due to the twist (screw dislocations) and a residual tilt angle (mixed dislocations) of the crystals. Dissociation of the screw dislocations is also observed on the lowest twist angle sample.