Papers by Author: Xiao Yan Liu

Abstract: Chemical mechanical planarization (CMP) of copper interconnection in hydrogen peroxide (H2O2) as oxidizer based alkaline slurry was investigated. The new model is put forward, which is based on the characteristic of H2O2, chemical kinetics and mechanical removal. This properties of H2O2 can be effectively compensated the defect of surface topology during the process of polishing. Researcher previous study has shown that the surface is largely copper metal with Cu2O at low H2O2 concentrations and largely CuO at high H2O2 concentrations. Cu2O is more easily removed by both chemical and mechanical processes than CuO. During the CMP process, as the oxidizer concentration increases, the removal rate goes up initially followed by a gradual decay. This characteristic of oxidizer is used to achieve copper surface global planarity. The surface planarity was achieved by removing high area on the surface more quickly relative to the low area, because the concentration of Cu2O in the low area as the passivation film is more than the high area. Meanwhile the passivation film of the low area is thicker than the high area. In order to achieve polishing process optimization, the influence of pH adjustment and pressure, are also taken into consideration. Combining both RR and PE, the optimal H2O2 concentration and pressures are in range 1.0 ~1.5 vol% and 0.04 ~0.07 mpa, respectively. The roughness of surface which is measured by AFM is 0.49 after CMP.

Abstract: The stability of μc-Si:H materials for solar cells was well researched. The light induced degradation of intrinsic μc-Si:H single layer material with different crystal volume fraction deposited were studied. The dependence of light-sensitivity as well as sub gap absorption on light soaking time was monitored. The results clearly showed that the magnitude of relative light induced degradation is closely related to material structure. Amorphous fraction is the key determining factor to light induced degradation. The results showed clearly that the magnitude of relative efficiency degradation is increase with amorphous fraction. The more amorphous fraction located in material, the more degradation was been found. With better structure and optical properties, microcrystalline silicon with transition region is more suitable for the manufacturing of stable Microcrystalline silicon solar cells due to the structure and optical properties.

Abstract: Sapphire (α-Al2O3) single crystal, as an important photoconducting device substrate material, stringent surface quality requirements, i.e. surface finish and flatness, are required. The use of chemical mechanical polishing (CMP) technique can produce high quality surface finishes at low cost and with fast material removal rates. The polishing mechanism was studied in this paper, and it was pointed that there were chemical and mechanical kinetics process respectively. The chosen polishing temperature was 40 oC. SiO2 sol was chosen as abrasive and the particle size is 40nm. The pH value was determined at 11.5~12. During CMP process C6382I-W/YJ single side polisher and SUBA 600 pad were used. After polishing and cleaning of sapphire surface, the measured removal rate was above 183.3nm /min and the surface roughness by using AFM was lower than Ra 0.3 nm. From the results, it was found that using such method, the optimal sapphire surface can be gotten, which is advantaged for epitaxial growth and device making-up.