Preparation And Characterization Of Polished SiC Single Crystal Wafer

Owing to high hardness and brittleness of SiC single crystal which has a good chemical stability, it is the critical issue that must be solved in its extensive application to obtain a wafer surface which is super smooth and free of scratch. Therefor, it has higher practical value to research the processing and characterization techniques for polished SiC single crystal wafer. On the basis of its machine mechanism, the cause of formation for scratches and pits are analysed. Then parameters of processes are optimized which include wire sawing, lapping and polishing. By molten alkaline etching techniques and AFM, subsurface damage is removed; its thickness is measured as well. The efficiency and machined quality are improved.The main research contents and conclusions are as following:1. The infeed velocity whose upper limit is affected by diameter and repeating use of diamond wire, decides the actual removal rate that is in the direct ratio to the wire sawing efficiency of SiC single crystal ingot. Selections of diamond wire diameter are: 0.21mm, 0.26mm and 0.31mm. The results of experiments demonstrate that the higher removal rate and larger sawing area can be ensured by the diamond wire with 0.31mm diameter. In order to lessen wear of diamond wire, decrease of the infeed velocity is required when the diamond wire is repeating used.2. The lapping removal rate is in the direct ratio to the diamond particle concentration of lapping liquid for sawed SiC single crystal wafer. When the W14 diamond particle concentration is 2%, the lapping removal rate reaches saturation. According to the wafer figure and machine purpose, plate rotating speed and load are needed to be arranged in pairs or groups.3. The WIWNU of mechanical polishing can be reduced by using improved slurry supply and polyurethane polishing pad with thickness of 2mm for lapped SiC single crystal wafer. The polishing removal thickness can be enhanced by increase polishing time, whose plate rotating speed is higher than 100rpm and polishing time is 16 hours.4. The most important influence factor is the PH of slurry. According to using range of temperature and the PH of colloidal silica slurry in CMP process, increasing the values is beneficial to enhance the chemical removal for mechanical polished SiC single crystal wafer. The RMS of surface can equal to 4nm, under the process parameter: the PH between 11-12 and the temperature less than 50℃.5. In order to decrease and measure the subsurface damage of polished SiC single crystal wafer, molten alkali etch technique was used, the optimal etch process is: 430℃/10min. The AFM results showed: the thickness of subsurface damage is less than 10nm, RMS is 1.7nm.