Research On Mechanism And Process Of Polishing Germanium Thin Wafer With Ice Fixed Abrasives

Germanium is the most important semiconductor except silicon. In addition to the semiconductor industry, the germanium in the field of high-frequency, infrared, aerospace, solar cells, chemical catalysts, biomedical field and others have a wide range of applications. Industrially, the requirements of single crystal germanium wafer are nanoscale surface accuracy and surface roughness, as a base material, it was also proposed with no damage surface or sub-surface with thin thickness. Therefore, germanium is brittle materials, to obtain high quality surface of single crystal germanium thin wafer faced difficulty. In this paper, against difficulties in ultra-precision machining of single-crystal germanium thin wafer, an innovation process of ice fixed abrasive polishing(IFAP) single-crystal germanium thin wafer is proposed based on subzero plastic removal. The brittle-ductile transition mechanism of single crystal germanium thin wafer has been studied. Ice fixed abrasive polishing disc has been prepared. Mechanism of IFAP is in-depth study. The research carried out actively exploring for practical use of IFAP process.The main work in this paper is as follows:1. Brittle-ductile transition mechanism of single-crystal germanium wafer in subzero.Hardness and crack length of single-crystal germanium wafer were studied by using Vickers hardness tester at-10 and 25℃ ℃. The effect of temperature on brittle ductile transition mechanism of single-crystal germanium thin wafer was analyzed. Under the same load, the temperature decreases, the crack length can be shortened.2. Critical cutting depth of single crystal germanium wafer in plastic processing.Indentations and scratches were performed with Single crystal germanium wafer by using scratch tester at 25 ℃. The dynamic brittle-ductile transition process of single crystal germanium wafer is analyzed. The corresponding critical scratch depth is 302.4 nm. The critical cutting depth model of dynamic brittle-ductile transition of crystal was analyzed. Parameter modification of model was based on characteristics of single crystal germanium wafer. Correction model is consistent with experimental data. According to correction model, the critical depth of cut under-10 ℃is slightly deeper than the depth at 25 ℃, which means that the critical cutting depth of single crystal germanium wafer at room temperature can be used as the ones in subzero.3. Dispersion property of Nano α-Al2O3 suspension in water.The effect of dispersion properties of Nano α-Al2O3 suspension was studied by reasonable selection of milling time, ball abrasive ratio, rotation speed. Theoretical guidance of development of excellent performance nano α-Al2O3 slurries was provided by optimum dispersion conditions. And dispersion property was verified by particle size distribution of the slurry.4. Preparation of ice fixed abrasive polishing disc.Designed and produced a mold of ice fixed abrasive polishing disc with a thermal resistance layer. An ice fixed abrasive polishing disc was produced with dispersed slurry by layered spray and freezing. The frozen polishing disc was dense, uniform, flat and increasing service life. The wear characteristics of polishing disc was studied and proposed melting wear in addition to the traditional wear of the friction. A theoretical basis was provided for the thickness design of multi-layer ice fixed abrasive polishing disc.5. Simulation study on temperature field of ice fixed abrasive polishing.A finite element analysis(FEA) model of temperature field of ice fixed abrasive polishing ring disc was established by using ABAQUS software. The reliability of the model was verified by a temperature test equipment. The influence of polishing disc temperature was analyzed by the temperature field simulation model through ambient temperature, polishing time, cylinder pressure, rotation speed and eccentricity. Combining test results, the average rate of melting speed of ice fixed abrasive polishing disc was obtained. A theoretical basis was provided for a reasonable choice of the thickness of polishing disc and polishing time.6. Polishing material removal model based on the trajectory.The influence on the speed ratio between workpiece and polishing disc by eccentricity was simulation analyzed. An ice polishing material removal model was established. The influence on polishing material removal rate was analyzed through cylinder pressure, rotation speed, abrasives concentration. The average material removal rate of ice fixed abrasive polishing disc was obtained. A theoretical basis was provided for a reasonable choice of polishing time.7. Research on process of polishing single crystal germanium thin wafer with ice fixed abrasives.According to the simulation results of the temperature field, a new process of ice fixed abrasive polishing in subzero was invented, which was polishing with organic solution as auxiliary slurry under-10 ℃. Process optimization of ice fixed abrasive polishing single crystal germanium wafer was carried out by using Taguchi method and comprehensive evaluation method. Combined with the optimization results, a rough polishing- semi-fine polishing- fine polishing process was performed to polishing single crystal germanium wafer with multi-layer ice fixed abrasive polishing disc. The smoothness surface of Sa=1.45 nm was got. Actively exploring for practical use of IFAP was done.