Study Of The Mechanism Of The Ultra Precision Grinding On Single Crystal Silicon

Single crystal silicon wafer has been widely used in the semiconductor industry as the basic substrate material for the integrated circuits. Wafer manufactures are always under tremendous pressure to meet the ever increasing demand for lower cost and better quality. The pressure leads to the demand of the development of the ultra precision grinding technology which is regarded as the ideal technology for the planarization and backside thinning of the substrates of the ICs. However, the ultra precision grinding technology studied in this thesis is quite different from the traditional grinding technology in terms of the grinding motion and the material removal mechanism.The goal of this research was to provide new knowledge of silicon wafer grinding necessary for the further improvement of the surface quality and reduction of manufacturing cost of the silicon wafer. It not only provided new models and theory of the material machining mechanism, but also gave us a lot of experimental results.(1) First of all, this thesis analyzed the mechanism of the ultra precision grinding machine based on the self-rotating technology. By use of the 2D and 3D computer simulation, the mechanism of the surface formation was investigated. Self rotating grinding experiment were also undertaken to verify the analytical results.(2) Second, the models of the grinding force and stress distribution of the silicon wafer under diamond grinding wheel were studied as well as the mechanism of the brittle and ductile material removal. From the research, it was found that there was ductile deformation and micro cracks inside the silicon. The critical ductile stress and brittle stress were σP-N and σcr respectively which had significant affects on the properties of the single crystal silicon wafer. It was shown that the ductile deformation of the silicon material was the reason of the increase of the cutting stress τP-N, which leaded to the changes of the mechanical characteristics. The strength of the silicon wafer became smaller, which was the result of the micro cracks in brittle removal.(3) Third, with micro diamond grinding wheel and large diamond grinding wheel, grinding experiments was conducted to the study of the grinding force and grinding mechanism:① it was found in micro grinding that the silicon material was largely removed in ductile model. With small grinding force, plastic flow was found. The silicon material was removed in ductile model without any micro cracks. While with large grinding force, lots of micro cracks was shown on the edge of the grinding area due to the large stress applied by the abrasive. The threshold values of the moral grinding force for ductile and brittle model of micro grinding were 200mN and 300mN respectively. ② it was found in large diamond grinding that there were four different stage of the grinding force. They were the beginning stage, the stable grinding stage, the no-feed grinding stage and the ending stage. It was also found that:with 600# grinding wheel, if the grinding force was small (50N-70N), the silicon material was largely ductile removed and lots of ductile chips were found on the surface of the silicon. When the grinding force was large enough (more than 70N), brittle mechanism became the major material removal mechanism, and lot of brittle chips were found. With 2000# grinding wheel, if the grinding force was small (35-60N), the silicon was largely removed in ductile. When the grinding force was more than 80N, ductile removal mechanism became the bigger player. In the grinding experiment, the threshold values of the grinding force were 120N and 60N with 600# and 2000# diamond grinding respectively.(4) At last, in order to study the basic mechanism of the ultra precision grinding technology on silicon wafer, single diamond abrasive scratching and self rotating grinding experiment were conducted on the micro/nano force testing machine and the ultra precision grinding machine. It was found in the single diamond scratching experiment that the critical ductile machining force and critical brittle machining force are lOmN and 120mN with 5μm diamond abrasive. While for the 2μm diamond abrasive, the critical ductile machining force and critical brittle machining force were 5mN and 30mN respectively. It was also shown in the self rotating grinding experiment that the material removed by the 600# grinding wheel was largely in brittle model and the material removed by 2000# grinding wheel was largely in ductile model.The theses focus on the study of the ultra precision grinding mechanism on single crystal silicon. The results of the theory analysis and grinding experiments are consistent. The findings in this research filled the blanks in research literature, and provided the oretical guidance for wafer manufacturing. The results will also be valuable to the development of the ultra precision grinding machine and the wafer manufacturing of other semiconductor materials.