Liftoff of single crystal diamond by epitaxial lateral overgrowth using SiO2 masks

Abstract

We describe a method that allows an easy separation of a single crystal diamond layer grown by homoepitaxy in a chemical vapour deposition (CVD) process from the growth substrate. In a first step a thin SiO2 layer is deposited on top of the seed crystal. This layer is patterned by photolithography and reactive ion etching (RIE) to obtain a mask with open windows and covered areas. In an epitaxial lateral overgrowth (ELO) process diamond is grown homoepitaxially through the free window areas and laterally across the covered areas until the mask is completely covered by diamond. During cool down from deposition temperature tensile stress σzz perpendicular to the growth surface is formed in the diamond bridges grown in the window areas. The absolute value of the stress depends on growth temperature, difference in coefficients of thermal expansion (CTE) between diamond and the specific mask material and finally on the fill factor (FF). The stress amplitude can reach more than +2 GPa and stress intensity factors in the range of typical fracture toughness values reported for single crystal diamond. Our experiments demonstrate that an immediate crack formation can be achieved which facilitates an easy separation between the CVD grown diamond layer and the seed crystal. The described concept develops its highest potential with increasing lateral dimensions of the seed wafers.