無変形冷凍ピンチヤツクの開発（第1報）: 冷凍液特性に基づく冷凍ピンチヤツクの設計

摘要

液晶テレビやコンピュータディスプレイは大型化が進み，第10世代2.85×3.5mのマザーガラスが使用さ れつつある．このマザーガラスに微細パターンを光学的に転写するためのマスク基板も大型化し，現在 ，0.85×1.2mの石英基板が使用されている1）．現状の石英基板は，数1叫m～10叫mの大きな反りを有し ，これらは微細パターン転写に悪影響を及ぼす．このため反りと平坦度を含めて10μm以下に向上させる ことが求められている．マスク基板は，現在，水貼り法により緩く拘束して軟らかいパッドで片面研磨 されている．そのため，高い平坦度に研磨することは難しく，とくに反りを除去することは短時間の研 磨では不可能に近い．%Polishing is commonly used to attain high flatness and smoothness for silicon wafers and rectangular glasses. A flatness of better than 10 μm is required for large quartz masks to transfer fine patterns. A backing pad is usually used to hold the workpiece during one-sided polishing. However, it is difficult to fabricate a nonwarped mask by this method. Therefore, a nondeforming freezing pin chuck has been developed. This paper describes the principles of the nondeforming chuck and the process used to manufacture a nonwarped substrate. The temperature distribution in the chuck, the droplet profile and the shear peeling strength of the freezing liquid are investigated. The temperature distribution of the freezing pin chuck is calculated by the finite element method using an axisymmetric model. The results reveal that, for a polishing temperature of less than 30℃, use of a coolant at 5℃ with a heat transfer coefficient of 1000 W/(m~2 K) can reduce the temperature on the back surface of a quartz substrate to below 15℃ for a substrate that is over 2 mm thick. The freezing liquid has a contact angle from 20° to 40°, which is much smaller than that of water. Consequently, the pin must have a diameter of over 0.73 mm. The average shear peeling strength of the freezing liquid is improved from 37 to 80 kPa by lapping the pin top. Based on these results, a freezing pin chuck with a pitch of 2 mm and a pin diameter of 0.8 mm was designed for polishing applications.