Study on the Lapping Characteristics of Sapphire Wafer by using a Fixed Abrasive Plate

Abstract

− Diamond mechanical polishing (DMP) is a crucial process in a sapphire wafering process to improve flatness and achieve the target thickness by using free abrasives. In a DMP process, material removal rate (MRR) is a key factor to reduce process time and cost. Controlling mechanical parameters, such as velocity and pressure, can increase the MRR in a DMP process. However, there are limitations of using high velocities and pressures for achieving a high MRR owing to their side effects. In this paper, we present the lapping characteristics and improvement of MRR by using a fixed abrasive plate through an experimental study. The change in MRR as a function of velocity and pressure follows Preston's equation. The surface roughness of a wafer decreases as the plate velocity and pressure increases. We observe a sharp decrease in MRR over the lapping time at a high velocity and pressure in the velocity and pressure test. An analysis of surface roughness (Rq and Rpk) indicates that wear of abrasives decreases the MRR sharply. In order to investigate the effect of abrasive wear on the MRR, we utilize a cutting fluid and a rough wafer. The cutting fluid delays the wear of abrasives resulting in improvement of MRR drop. The rough wafer maintains the MRR at a stable rate by self-dressing. DMP 공정은 정반에 다이아몬드 연마 입자를 공급하 면서 기판을 가압하여 정반과 기판의 상대 운동을 이 용하여 기판을 가공하는 공정이다 (Fig. 1). 이때 입자는 자유 입자(free abrasive)로 기판과 정반 사이에서 구르 거나(three-body) 정반에 박혀 긁으면서(two-body) 기판