Study On High Quality Surface Protection Of Single Crystal MgO Polishing Substrate

Single crystal MgO with excellent optical, mechanical, and electrical properties, chemical stability, heat conductivity and insulativity, has been widely used to grow high temperature conductors, ferroelectric pervoskites, colossal magnetoresistive and optical thin-films as the substrate materials.Surface quality of substrate materials has important influences on the properties of the grown thin-films. As single crystal MgO has the nature of absorption and deliquescence, the high quality single crystal MgO polishing substrate will react with CO₂ and moisture in the air, leading to the deliquescence or atomization, when it is placed in air or humid environment for a long time. For this case, the surface of the MgO substrate will become tough, and the quality of the grown thin-films will be seriously affected. At present, although the ultra precise manufacture efficiency of single crystal MgO has been greatly improved, sub-nanometer scale surface can be achieved, yet few efforts are taken on the absorption and deliquescence behaviors of single crystal MgO. Furthermore, there are no specific methods on the high quality surface protection of the substrate.Based on the absorption and deliquescence problems of single crystal MgO polishing substrate, systematic experiments are presented. The absorption and deliquescence reactions on the substrate surface are analyzed. Conclusions are drawn as follows:At different environments, such as air, hothouse, N₂, Ar and vacuum, the absorption and deliquescence cases of single crystal MgO (100) polishing substrate surface are diverse. The polished substrates placed in the air possess the fastest degration speed and the worst surface roughness; the ones placed in the hothouse possess the second fastest degration speed and worst surface roughness; the ones placed in N₂ and Ar have the third fastest degration speed and worst surface roughness, and the ones placed in the vacuum have the slowest degration speed and the best surface roughness.For one thing, both the humidity and temperature parameters in the air have a great importance on the absorption and deliquescence of the polished MgO substrate surface: the higher the humidity, the worse the absorption and deliquescence; in some scales, the higher the temperature, the worse the absorption and deliquescence; for another thing, the surface manufacture quality of the substrate also has a great importance on the absorption and deliquescence: the worse the surface manufacture quality, the worse the absorption and deliquescence.The absorption and deliquescence properties of single crystal MgO polishing substrate have a close relationship with its crystal orientation. MgO (111) degrades fastest and most seriously, compared with MgO (110) substrate. Furthermore, MgO (100) has the most stable property compared with MgO (111) and MgO (110) substrates at the same environment.Under different water coverage ratio or at different kinds of defects, the absorption and deliquescence properties of single crystal MgO polishing substrate are different, and they are determined by the coordination number of the microstructure.According to the above experiments and theoretical analysis, single crystal MgO polishing substrate with high quality polished surface and defect-free microstructure can be saved for a long time in dry and airtight environment.