Time-resolved imaging of microscale dynamics in laser drying of silicon wafers

Abstract

Surface drying plays a critical role in wafer fabrication in microelectronics, primarily on eliminating watermarks. Spin drying, isopropanol alcohol (IPA) drying, and Marangoni drying are the most commonly used methods, but they have drawbacks such as high risk of water stains, safety hazards, environmental concerns, and energy inefficiency. Hence, there is a continuous demand for fast, efficient, chemical-free, and energy-efficient wafer drying processes. This study explored the use of nanosecond (ns) laser pulses for laser-induced sub-surface evaporation as a promising alternative for surface drying. By adjusting the laser fluence, clean and dry silicon (Si) substrates can be obtained without any stain or damage. Large-area laser drying was also demonstrated. Time-resolved imaging was employed to investigate the drying dynamics after the interaction between the laser pulses and the substrates. It was observed that the deposited water droplet films expand, detach from the substrates, and eject into the air after excimer laser pulses. Moreover, the study examined the influence of substrate conditions on laser drying, including surface roughness and hydrophilicity. The effectiveness of laser drying was evaluated on various substrates, including stainless steels (polished/mirror polished) and glasses. Pulsed lasers demonstrate the ability to dry chemical solutions, such as 35 g/L NaCl, in addition to pure water. These findings show the potential of using ns pulsed lasers as a versatile and environmentally friendly drying tool for various solution and substrate types.