Research On The Surface Shape Accuracy And Damage Control Of Sapphire Wafer During Double-side Lapping

Light emitting diode(LED), as a solid state lighting devices, is usedwidely in indoor and outdoor lighting, automotive lighting, traffic indication lamp, military and other fields. Sapphire is one of the key materials for the Ga N epilayer growth, which has the excellent mechanical and physical properties. These applications have high requirements on the quality of sapphire wafer. But, due to its intrinsic nature(high hardness and chemical inertness), sapphire is difficult to be polished ideally.Expensive processing and material cost is an important factor to limit the futher development of this industry, as well as low processing efficiency. Therefore, the optimum process parameters have been study in this paper, which can not only reduce processing costs and improve processing efficiency for enterprises, but also promote the development of this industry.With the current production status of the enterprise where we practiced, the influence of different process parameters on the surface roughness and surface topography of sapphire wafer have been analyzed by detecting the surface shape precision and sub-surface damage during double-side polishing process. Moreover,the influence of annealing on shape accuracy has been analyzed at the same time. The process parameters have been optimized in the view of actual processing efficiency and processing costs. The following major conclusions could be drawn from this study.(1) During the coarse lapping processing with different removal amount, it can be concluded that the surface shape accuracy of sapphire wafer tends to be stable when the removal amount is 45μm. And at this time, the obtained machining accuracy can meet the requirements.(2) Through test the surface shape accuracy and the variation characteristics of surface morphologies after grinded by different lapping parameters, the good surface shape accuracy and high material removal rate can be acquired when the lapping pressure is 7.5 kpa, lapping speed is 15 r/min and the concentration of lapping liquid is 22.76%.(3) According to observe the thickiness of damage layers, the order of the crack depth generated during different process is coarse lapping(about 3.3μm), wire sawing(about 2.5μm) and fine lapping(about 2.2μm).(4) Compared with the existing technology, the optimized process can significantly improve the surface shape accuracy of the wafer while holding the same surface roughness Ra and sub-surface damage with that of existing technology. Meanwhile,which can reduce the consumables and material cost of about 11.99% and 2.36%repectively for the enterprise, and the annual production capacity can be increased10.2%.