Characterization of the silicon on insulator film in bonded wafers by high resolution x-ray diffraction

High resolution x-ray diffraction (HRXRD) is proposed as a nondestructive tool for the characterization of the silicon on insulator (SOI) film in bonded wafers. Although the bonded stack may consist of many amorphous layers, the measured diffraction spectra only show the crystalline SOI layer, thus providing a direct measurement of the film. We have demonstrated that HRXRD is capable of accurately measuring the film thickness, the tilt of the film planes with respect to the substrate planes, and the rotation misalignment of the bonded film with respect to the carrier substrate. SOI films with thicknesses down to 30 nm were readily measured with accuracy better than 1%. It is shown that an angular separation between the layer and the substrate diffraction peaks is maintained due to an unintentional miscut which usually exists in the starting wafers used for bonding. This angular separation is unique to bonded wafers as opposed to separation by implanted oxygen (SIMOX) wafers where the layer and substrate peaks are nonseparable. Calculated diffraction spectra based on the kinematic approach showed excellent agreement with the measured diffraction.