Study On CMP Technology Of Single Crystal MgO Substrates For High Temperature Superconductors

Single crystal MgO has such performances as good chemical stability, heat-conduction and insulation under the high temperature, very low dielectric constant and dissipation in high frequency. It is a kind of important substrate for high temperature superconductor (HTS) thin film. The substrate surface quality, such as surface roughness, micro-structure directly influences the quality of HTS thin film grown on it. So, it is an important problem how to get MgO substrate with high surface quality. Because single crystal MgO is a kind of typical hard and brittle material and has some special physical and chemical properties, there are some disadvantages in mechanical polishing of single crystal MgO substrates, such as low material removal rate (MRR), poor surface quality and high percent of fragment waste. Moreover, to the author's best knowledge, systematic study on ultra-precision polishing of MgO substrates has not been reported. In this thesis, the chemical mechanical polishing (CMP) technology of MgO substrate is studied in order to efficiently obtain the ultra smooth and free damage surface of MgO substrates by use of the chemical and mechanical interaction.A series of CMP experimental studies on the influences of the main factors (polishing pad, polishing slurry, polishing load, table rotational speed) on the surface quality of substrate are carried out. According to the physical and chemical properties of single crystal MgO, the applied polishing slurry for MgO is developed. The main characteristic parameters of different kind of polishing pad are measured and appraised. The effects of the different polishing pads are compared and analyzed through CMP experiments under the same process parameters, and then a kind of polishing pad for single crystal MgO substrates is chosen. Finally, the suitable CMP parameters for single crystal MgO are obtained by using the orthogonal experiment method. It is proved that the surface roughness of MgO substrate can reach Ra 0.4nm and the MRR of MgO substrate is improved. Furthermore, aiming at the difficulty to control the flatness of single crystal MgO substrate, especially to thinner substrate, the influences of CMP parameters on the flatness of MgO substrate is investigated.