Effect of initial deflection of diamond wire on thickness variation of sapphire wafer in multi-wire saw

Abstract

Sapphire wafers are widely used as substrates for fabricating gallium nitride light-emitting diodes. The quality of light-emitting diodes depends on the total thickness variation and BOW of the wafers. The multi-wire saw process is critical in determining post-processing times for steps such as diamond mechanical polishing and chemical mechanical polishing. In particular, thickness variation is affected by wear of diamond wires, which in turn is controlled by cutting conditions including wire speed, feed rate, initial contact condition between ingot and wire, and new wire consumption. Thickness variation shows a marked change from the initial to final feeding location during the multi-wire sawing process. A wire is not worn when it is initially contacted by an ingot. Hence, the initial kerf loss is greater than the kerf loss at the final feeding location. This study focused on minimizing the thickness variation between the initial and final contact points of the wafer. Experiments were conducted with different initial wire deflection conditions. The experimental results showed that increasing the wire deflection increased the cutting load, which in turn caused severe wear of the wire. Consequently, the thickness variation of the wafer in the multi-wire sawing process was controlled by adjusting the wire deflection.