Multi-spot laser lock-in thermography for real-time imaging of cracks in semiconductor chips during a manufacturing process

This article proposes a new multi-spot laser lock-in thermography (MLLT) system for real-time imaging of cracks in semiconductor chips. The proposed MLLT system is able to inspect a semiconductor chip in real-time during its manufacturing process by simultaneously generating thermal waves on multiple points of the target semiconductor chip surface using multi-spot pulsed laser beams and measuring the corresponding thermal responses using a high-speed infrared (IR) camera. In particular, the MLLT system offers the following advantages for the semiconductor chip inspection: (1) complete non-contact, non-destructive and non-intrusive inspection, (2) real-time crack inspection with fast data acquisition and processing, (3) baseline-free crack visualization using only current-state data, making it possible to avoid false alarms caused by operational and environmental variations and (4) high detectability of cracks. To realize the MLLT system, optical components for multi-spot thermal wave generation are designed through an optical analysis and integrated with the high-speed IR camera, a close-up lens and a personal computer. The developed MLLT system is then experimentally demonstrated using actual semiconductor chips with real cracks produced during the manufacturing process. The experimental results reveal that the total inspection time including the data acquisition and processing takes less than 1 s for each semiconductor chip, and cracks in the range of 20 μm are successfully detected.