Dual-beam stealth laser dicing based on electrically tunable lens

Abstract

In this paper, we present the development of a high-speed dual-beam stealth laser dicing (D-SLD) method for processing semiconductor wafers based on electrically tunable lenses (ETLs). An SLD system utilizes a laser beam to dice a wafer by inducing interior defects without modifying the surface characteristics of a wafer, thereby presenting significant advantages over conventional dicing methods, e.g., blade dicing or laser ablation. Currently, the throughput of SLD is limited by the serial scanning process; in addition, wafer misalignment and the warpage effects together deteriorate the dicing quality and yield and demand high-cost multi-axis precision stages. To address the issue, we parallelize the dicing process by splitting the laser focus into two foci, where the laser intensity at different depths are automatically adjusted to achieve optimal dicing condition. By combining the height sensor and ETLs, each laser focus, i.e., laser scan lines, can be rapidly controlled axially to compensate the wafer curvature and misalignment errors in real time, leading to substantially improved precision (kerf width < 2 μm) and speed, demonstrated by our experimental results. The new dual-beam laser dicing system presents an effective solution for high-speed wafer dicing as well as other important engineering applications, e.g., fabrication of micro-devices and optical components.