| Abstract [eng] |
Because of its unique mechanical, chemical and electrical characteristics sapphire single crystals are widely used in various industries, especially in electronics. The latest trends of sapphire usage are for high-brightness light emitting diode (LED) devices as a substrate for GaN layer growing. So, the volume of sapphire wafer production is growing and in the nearest future trends are not going to change. Because of parameters getting stricter for electronic devices any surface defect in wafer have more influence in product application. Making Al2O3 wafers with low surface roughness and optimization of polishing process is a challenge for researchers. The treatment process could be optimized by choosing the relevant processing parameters and materials. Researches shows that CMP method is the most acceptable for making high surface quality wafers. However, this method needs more investigation because of unique sapphire properties. Influence of polishing time, top load, different size of abrasive particles in slurry to surface roughness of C-plane sapphire wafer, material removal rate, geometrical parameters and axis tilt orientation were analyzed. AFM, high resolution profilometer and XRD were used to analyze wafer surface area, roughness, crystal size and orientation. Optical device was used to measure changes in thickness of the samples before and after polishing. Given results were used to calculate removal rate. Surface analysis shows that there is linear dependent of removal rate to top load and better distribution of surface roughness in wafer is obtained by increasing top load. The lowest roughness values were found at top load of 600 N. There was noticed that by increasing polishing time lower roughness values could be achieved, but it affects in decreasing material removal rate. Geometric orientation and tilt parameters are significantly dependent on polishing. Smaller abrasive particles in polishing slurry takes more time to get same roughness as bigger particles, but with increased polish time lower roughness could be reached using smaller abrasive particles. |
