Laser dicing, a technique that uses focused laser pulses to separate individual chips from a semiconductor wafer, is increasingly favored over mechanical blade cutting as it can process delicate, low-strength materials with minimal physical stress. However, achieving proper yield requires precise control over the process. If pulses fall short, they leave a wafer only partially cut, while excessive pulses can cause damage to the material or the tape used to hold it. While techniques for monitoring processing depth do exist, most of them are often too slow or too fragile to use on production lines.
Now, a team of researchers led by Professor Hirofumi Hidai from the Graduate School of Engineering, Chiba University , Japan, focused on a different signal: recoil force to address this challenge. Recoil force is the minute reaction force generated on a material's surface when it is rapidly heated and vaporized by a laser pulse. The team included Dr. Masataka Sato and Dr. Sho Itoh, both from the Graduate School of Science and Engineering, Chiba University; Dr. Mutsumi Horikoshi from KISTLER Japan GK., Japan; and Dr. Souta Matsusaka from the Graduate School of Engineering, Chiba University. The findings of the study were made available online on June 8, 2026, and will be published in Volume 203 of the Journal Optics and Laser Technology on November 1, 2026.
To test their idea, the researchers carried out laser drilling experiments on silicon samples using a laser that emits extremely short bursts of light lasting only 25 nanoseconds, which is 25 billionths of a second. While doing so, the researchers used a sensitive load cell (a device that converts mechanical force into a measurable signal) to record the recoil force generated as vaporized material was expelled from the sample with every laser pulse fired. They observed that this force increased in a predictable way with pulse energy and decreased with defocusing, or moving the laser focus away from the wafer surface. This suggested a mathematical relationship between the recoil force and the laser processing conditions.
"By directly measuring the recoil force, we could detect the processing depth and sample penetration, allowing us to observe the laser processing conditions in real time," explains Prof. Hidai.
Building on this relationship, the researchers used repeated laser pulses to drill deeper into a silicon wafer and tracked how the recoil force changed with depth. As the depth increased, the recoil force declined in a steady and predictable pattern. Finally, when the laser achieved full penetration through the wafer, the pattern showed a noticeable shift. This distinct signature showed that the method could flag the exact instant when a wafer was fully cut without the need for physical inspection of the sample. Using this model, they were also able to estimate processing depth with a relative error of 24.3%, demonstrating that recoil force measurements can provide practical, real-time information about laser machining.
Beyond demonstrating a new sensing technique, the researchers believe their work could significantly improve the manufacturing of semiconductor devices and other precision components. "By reducing under- or over-processing, we can minimize defective products, which is expected to lead to a stable supply and reduced costs for the electronic devices used in smartphones, automobiles, and medical equipment," claims Prof. Hidai. Looking ahead, the team envisions that combining this technology with laser processing systems could pave the way for smart manufacturing tools capable of automatically assessing and adjusting cutting conditions, ultimately leading to faster production of high-performance electronics.
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About Professor Hirofumi Hidai from Chiba University, Japan
Professor Hirofumi Hidai currently serves as a Professor in the Graduate School of Engineering at Chiba University, Japan, and is also affiliated with the university's Molecular Chirality Research Center. He received his Doctor of Engineering degree from the Tokyo Institute of Technology. His research focuses on laser processing, precision engineering, and manufacturing technologies, particularly laser machining of hard, brittle materials such as glass, silicon, and diamond for advanced manufacturing applications. Over the years, he has published more than 121 scientific papers, and his work has contributed to advances in laser-based microfabrication, semiconductor processing, and precision manufacturing.
Reference:
DOI: https://doi.org/10.1016/j.optlastec.2026.115604
