The Deformation of Polycrystalline-Silicon Deposited on Oxide-Covered Single Crystal Silicon Substrates

The cause of the bowing of wafers with thick polycrystalline-silicon layers deposited by the hydrogen reduction of trichlorosilane has been studied. High temperature dilatometer measurements show that the expansion coefficient of the polycrystalline-silicon layer in the temperature range 100 degrees-900 degrees C is 2.3-4.2 x 10(-6)degrees C(-1), and that the polycrystalline-silicon layers contract perpendicularly to the direction of growth at temperatures higher than about 1000 degrees C The experimental data indicate that the bowing of wafers is caused by the intrinsic tensile stress generated by the contraction of the polycrystalline-silicon layer buried behind the advancing surface of the growing layer, and not by the the thermal stress generated by the difference in the thermal expansion coefficients between the grown layer and the substrate. This contraction of the polycrystalline layer may be induced by a mechanism similar to sintering.