Study On Ducile Lapping Of Crystal Sapphire Wafer

Single crystal sapphire is an important substrate material in the field of photo electronic device manufacturing. With the continuous improvement of optoelectronic devices product, the sapphire crystal substrate is demanded extreme lower surface roughness, but it is brittle material and hard to process for ultra-precision machining. The lapping is a necessary and important process before sapphire polishing, at present, there are few paper dealing with ultra-precision grinding technology of sapphire substrate. So this paper did related research on sapphire ductile lapping. The main work and research results are as follows:In order to minimize the impact of machinery vibration on machining processing, natural frequency of chassis in Nano-max machines was identified, natural frequencies of spindle and workbench was also identified through LMS modal test software, and signals was analyzed based on wavelet. Best speed was determined as 10rpm for sapphire abrasive charging.Charging technology was adopted to make diamond stand on the lapping plate. Keyence device was applied to characterize surface after charging to make sure that charging technology is successful. Followed by single sapphire lapping experiment to further verify the charging process, surface was characterized by SEM and white light interferometer(Veeco) later. Charging technology could really achieve ductile lapping. Surface with Ra10nm and Rt100nm was obtained after lapping, this could fully meet the requirements of the following polishing. obtain the best load of 21KPa in ductile lapping was obtained. Lapping process of single crystal sapphire were investigated in relation to crystallographic orientation, the influence of the crystal anisotropy under different lapping liquid concentration, loading forces on materials removal rate and roughness in sapphire lapping was discussed. Experimental results showed that surface roughness was depend on the fracture toughness, surface orientation with higher fracture toughness such as C-plane would get better roughness during lapping, and surface orientation with lower fracture toughness and elastic modulus such as R-plane would get worse material removal rate during lapping.Curves hardness vs depth was got by Nano-indentation technique. Conclusion was obtained as following: When depth of cut was less than 200nm, R and C surface had the same depth of damaged layer about 100nm, when depth of cut was larger than 200nm, depth of C surface damage layer was about 200 ~ 300nm ,and R surface had the damage layer of depth about 100nm.With TEM characterization of sapphire from the atomic level, conclusions was got as following: surface organizations had changed after lapping, with the depth increasing, sapphire had better crystal organization, the surface damage distributed uneven after lapping . Basal plane slip occurred during the sapphire lapping, depth of R plane damage layer was about 3 ~ 4μm, C plane damage depth was about 2 ~ 3μm, compared with the C plane, damage layer in R plane was more uniform.