Study on Surface Control of Polished Germanium Wafer with Ice-fixed Abrasive Polishing Tool

The uniformity of the material removal directly affects the polished surface of the workpiece. In order to improve the uniformity of the material removal and to achieve high flattening polishing for the chemical mechanical polishing (CMP) of the single crystal Germanium wafer, based on the Preston equation, the motion law of the ice pad and the workpiece is numerically analyzed in the whole contact condition. The results show that the average relative velocity has the edge effect which increases with the radius. The closer the velocity ratio k is to 1 and the greater the eccentricity e is, the more uniform the material removal will be. The contact stress distribution between the polishing pad and the workpiece under different loading conditions is simulated and analyzed. It was found that the stress distribution has the stress concentration effect and the edge effect, and the stress distribution under three loading conditions were verified by experiments; when the velocity distribution and stress distribution is more uniform, the flatness of the polished wafer is effectively improved. Introduction With the development of aerospace technology, the demand for photoelectric conversion efficiency of solar cells is becoming higher and higher. The excellent match between germanium single crystal and gallium arsenide (GaAs) makes it a suitable substrate material, and germanium substrate GaAs/Ge thin film battery made with MOCVD process has better resistance to radiation, longer service life and more than 30% of the energy conversion efficiency . As a germanium monocrystalline wafer for solar cell substrates, it has higher requirements on the shape accuracy, surface roughness, surface uniformity and processing efficiency. Chemical mechanical polishing (CMP) technology provides an almost unique planarization technique by means of an organic combination of the grinding action of micro-nanoparticles and the corrosion of oxidants; fixed abrasive polishing technology is based on two-body wear principle and has a high excellent flattening capacity ; low temperature polishing technology causes less damage to the surface and sub-surface of the machined workpiece . Based on the characteristics of these three polishing technologies, an ice-fixed abrasive tool with uniform abrasive distribution is proposed and applied to polish germanium monocrystalline wafer. One of the key technical issues is how to remove the surface material uniformly in order to obtain ultra-flat and ultra-clean surface. Macroscopic studies show that the relative velocity and average pressure have a significant effect on the removal of the material , but only explain the average effect of the polishing process and cannot explain and control the change of the workpiece surface after polishing. In order to achieve high flattening processing and to get a better surface of the workpiece, it is necessary to analyze the contact state and the motion of each point in the workpiece during the polishing process and to make their distribution uniform. Theoretical background 714 Advances in Abrasive Technology XX