X-ray reflectivity of ultrathin twist-bonded silicon wafers

Ultrathin Si (001) layers (< 15 nm) are hydrophobic bonded to a full 4 in. Si (001) wafer. The interface quality and surface roughness, checked by specular x-ray reflectivity, are very good. This technique, well suited to measure the homogeneity thickness, shows that the samples have very small thickness fluctuations, and no extended defects. Quantitative analysis proves that the interfacial layer resulting from the bonding is very thin (about 8 Angstrom). Its atomic density is significantly different from bulk Si only for large bonding twist angles (> 5 degrees). (C) 1999 American Institute of Physics. [S0003-6951(99)01448-5].