The effects of ultra-smooth surface atomic step morphology on CMP performances of sapphire and SiC wafers
Whether sapphire or SiC wafer, clear and regular atomic step morphology could be observed all over the ultra-smooth wafer surface via atomic force microscopy (AFM) using our CMP technology. However, towards sapphire and SiC wafers, the variations of atomic step widths and step directions on the whole of wafer surface are different. The step widths and step directions on the different positions of sapphire wafer are uniform, while that on SiC wafer are distinct. Thus, the effects of atomic step width on CMP removal rate of sapphire and SiC wafers were studied. On the other side, the CMP removal model of super-hard hexagonal crystalline wafer to realize atomically ultra-smooth surface is proposed. The variations of atomic step morphology towards different defects on sapphire and SiC wafers surface are analyzed, and the formation mechanism of the defects is discussed.
Extended study of the atomic step-terrace structure on hexagonal SiC (0 0 0 1) by chemical-mechanical planarization
The atomic step-terrace structure on hexagonal silicon carbide (0 0 0 1) surface is significant in that it guides the improvement of chemical-mechanical planarization (CMP) and epitaxial technique. The final state of atomic step-terrace structure can be used as a feedback for improving the CMP process, the formula of slurry and the epitaxial technique. In this paper an extended study of the atomic step-terrace structure on 4H- and 6H-SiC (0 0 0 1) planarized by CMP is presented. Surface topography of the (0 0 0 1) facet plane of 4H- and 6H-SiC wafers during CMP process was studied by atomic force microscopy (AFM). The results demonstrate that high-definition atomic step-terrace structure of the (0 0 0 1) facet plane of both 4H- and 6H-SiC can be obtained by appropriate CMP process, and during CMP process, the formation of step-terrace structure had a certain rule. We studied the relationship between the CMP process and the characteristics of the atomic step-terrace structure, and analyzed the possible impact of the CMP process on the status of terraces. We studied the distribution of terraces in different areas of the wafer, and the origin of this distribution was discussed briefly. We also describe the formation of dislocations in hexagonal SiC. The results of this paper may provide some ideas and suggestions for CMP, crystal growth and epitaxy research.
Traceability strategy for gear-pitch-measuring instruments: development and calibration of a multiball artifact
There is a strong demand to ensure the traceability of gear-measuring instruments (GMIs). We propose a multiball artifact (MBA) for the evaluation of pitch-measuring accuracy. The aim of the MBA is to transfer the minimum uncertainty from a calibrated value at the National Metrology Institute of Japan (NMIJ) to a measured value of GMIs at a shop floor. The MBA is composed of equally spaced high-accuracy balls around an axis. The pitch-measuring accuracy of GMIs is evaluated by measuring the angular pitch deviation of the balls instead of the angular pitch deviation of a gear. We calibrated the angular pitch deviation using a coordinate measuring instrument (CMM) at the NMIJ and adapting a multiple-orientation technique. We proposed a calibration strategy of the angular pitch deviation. The calibration value of the pitch deviation for the MBA at the NMIJ was obtained with a measurement uncertainty (U95) of 0.2 µm. We evaluated the pitch-measuring accuracy of a GMI using the calibrated MBA. Each value of U95 for the cumulative and single pitch deviations for the left and right flanks was less than or equal to 0.5 µm. The small uncertainty was transferred from the NMIJ to the GMI.