Warp of Czochralski Wafer with Back-Surface Polycrystalline Silicon Film

Warp of Czochralski (CZ) Si wafers with back-surface polycrystalline silicon (BPS) film was measured with elevation of ambient temperature to 620-680°C, using a film internal stress meter (ULVAC Corporation FIS-1000). For the first time, to the aurthors' knowledge, it was clarified that the wafers were warped because of film-induced stress occurring at the film deposition temperature. Film-induced stress is divided into temperature-dependent stress (thermal stress) and residual stress at room temperature. Thermal stress is quantified under the assumption that warp depends on the apparent linear thermal expansion coefficients of the BPS film. Residual stress was measured by means of the X-ray diffraction method.