UCLA

This study investigates the mechanisms of helium implantation induced blistering andexfoliation in lithium niobate (LiNbO3). Wafers of LiNbO3 were implanted to a dose of 2.3×1016 He+ /cm2 and an accelerating voltage of 250 keV. The wafer was cooled such that it remained at room temperature during the implantation to limit helium diffusion or bubble growth due to the heating caused by the ion implantation process. The implant profile and exfoliation behavior of the samples for various annealing recipes were investigated using high resolution X-Ray diffraction (HRXRD), optical microscopy and contact profilometry. It was found that a low temperature “defect nucleation” anneal at 120 ˚C followed by a high temperature “bubble growth” anneal at 200 ˚C caused millimeter-scale large-area exfoliation of thin-film lithium niobate with a thickness of 800 nm, which is the projected range of the helium ion implantation done at 250 keV. In comparison, a single anneal at 200 ˚C caused µm-scale small-area exfoliation also referred to as blistering [1]. Large-area exfoliation is preferred over blistering, as it facilitates the next processing step of chemical mechanical polishing (CMP). Also, the long low temperature annealing improves the interfacial bond strength of the bonded wafers in the “Smart Cut” technique.