Low Cost Technologies for Manufacturing of Thin Film Lithium Niobate

Since thin-film lithium niobate (TFLN) wafers became commercially available, they have quicklyemerged as one of the most promising platforms for photonic integrated circuits (PICs) due to theirbroadband transparency, large Pockel's coefficient, and significantly improved integration compared tobulk LN technology. Despite rapid technical advancements worldwide, there is only one Asian waferprovider for high quality TFLN wafers, who has perfected the crystal ion slicing process for TFLN wafermanufacturing. This is partly due to the lack of a dedicated, cost-effective ion implantation serviceprovider in the U.S. that can generate the high-dose defect layers required for crystal ion slicing. Toaddress this limitation, we propose two alternative TFLN manufacturing approaches that do not rely onion implantation. We will collaborate with Penn State University to develop a low-cost TFLN wafermanufacturing process based on mechanical thinning and polishing, where uniform polishing is ensuredby introducing metal polishing stops through a highly selective etching process and a lift-off metaldeposition process. Additionally, we will work with SRI International to develop a controlled spallingprocess that allows for the controlled cracking of a thin LN film along a crystal facet parallel to the wafersurface, with film thickness determined by a metal stress layer applied to the top surface. In Phase I, wewill focus on developing a defect-free wafer bonding process with engineered stress levels to meetsubsequent processing requirements. Two CMP processes will be developed: the first to thin an LN waferto less than 5µm with nonuniformity below 1µm, and the second to polish the LN film down to 600nmwhile reducing nonuniformity to less than 30nm. The high-selectivity wet LN etch process will be refinedto maximize selectivity between the LN and SiO2 stop layer. Parallelly, we will optimize the controlledspalling process to enhance film uniformity and size. Proof-of-concept experiments will be conducted tovalidate the manufacturability and scalability of the spalling process. Finally, we will evaluate bothapproaches based on their benefits, risks, and costs, which will guide our Phase II work plan. With ourextensive experience in TFLN PIC development and manufacturing, and the introduction of these newcost-effective manufacturing approaches, PSI is well-positioned to establish a fully integrated U.S.-basedTFLN PIC foundry capable of producing a diverse range of TFLN PIC products using in-house TFLNwafers.