| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a polycrystalline substrate having a concentration of impurities except Y, Al and O of 3,000 ppm or less in terms of an element, having a pore volume of less than 100 ppm, having a mathematical surface roughness Ra of less than 1 nm, not having a flaw whose width is 5 μm or more, not having a dent whose diameter is 5 μm or more, having a height difference between unit crystal particles constituting of a polycrystal of 5 nm or less and being flat and smooth and to provide a method for polishing the same. <P>SOLUTION: A YAG polycrystal having a concentration of impurities except Y, Al and O of 3,000 ppm or less in terms of an element and a pore volume of less than 100 ppm is polished by using a surface plate having a Brinell hardness of 40 or less and alumina or diamond-mixed abrasive grains whose main component is alumina as an abrasive material. The surface of the YAG polycrystalline substrate has a mathematical surface roughness Ra of less than 1 nm, has no flaw whose width is 5 μm or more, has no dent whose diameter is 5 μm or more, has a height difference between the unit crystal particles constituting a polycrystal of 5 nm or less, is flat and smooth and has a flatness of less than 100 nm. The flat and smooth YAG polycrystal substrate with high flatness and the method for polishing the same are provided. <P>COPYRIGHT: (C)2010,JPO&INPIT |
