Study On Chemical Mechanical Polishing Of Tantalum Lithium Crystal Wafer

Tantalum lithium (LiTaO3), a novel single crystal material, developed and industrialized with the development of communication and information industries recently, owns the excellent performances such as high Mechanical-electrical coupling coefficient, lower wear-resistance, excellent high-temperature stability, excellent high-frequency capability, etc. However, researches on tantalum lithium single crystal wafer around world are still lacking. LiTaO3 wafers are machined ususlly by chemical mechnical polishing in industry. Based on the investigation of the mechanical property of tantalum lithium crystal wafer and theory analysis of polishing movement tracks, this thesis discusses its mechanism of CMP, presents its polishing characteristics and analyzes the effects of polishing condition parameters upon CMP.To find out the effective slurry with suitable type of oxidizer and concentration, chemical etching experiment was applied to the LiTaO3 wafer.the chemical etching effects were analysed by measuring etching rate and X-ray spectrum. The experimental results indicate that for LiTaO3 the oxidizers are NaClO and H2O2, the stabilizator is KOH and the most suitable pH value is 10.The scratching test was carried out with a single diamond tool to study the removal mechanism of LiTaO3 wafer by load. The AE signals were measured, and the scratched surfaces of LiTaO3 wafers in different conditions were observed by metallography microscope. The results show that the scratched surfaces change from elastic deformation area, plastic deformation area and fracture area with squama and crack. For removing material of LiTaO3 wafer by plastic deformation mode, the polishing pressure should be low than 7.25kPa.For selecting suitable CMP conditions, the movement of polishing was modelling and simulating. The analysed results show that the reasonable rotating speed np and distance e between workpiece plate center and polishing plate center are 60rpm and 100mm on Ultra-precision surface polishing machine with correction rings,respectively.The CMP experiment was carried out systematically on LiTaO3 wafer. The polished surface foughness and material removal rate in different polishing conditions were measured and the effects of polishing pad material and its condition, pressure, rotating speed of the polishing plate, the type and size of abrasive, and the properties of the polishing slurry on the surface routhness and material removal rate were analysed in details.