Fast optical methods for real-time monitoring of pulsed laser processing of thin films

Abstract

Thin film materials have been attracted many new and promising applications in numerous technology fields from microelectronics to biosensors. Laser processing of those films is still explored to achieve targeted properties as optical and electrical, thermal or mechanical high properties. Fast optical methods were developed during the last decade for the monitoring of the real-time or the time-resolved processing by nano and sub-nanosecond pulsed lasers. More particularly pulsed photothermal (PPT) and real time reflectometry (RTR) were successfully used for the thermo-physical/themo-mechanical characterization of numerous thin samples such as Ti embedded vertically aligned carbon nanotube (CNT) carpets and/or mesoporous silicon (MeSi) membranes. Those characterizations were achieved using a homemade optical device based on picosecond time-detection in hemi-spherical vacuum chamber. Contribution of real-time RTR to laser induced processes is highlighted through several applications with Excimer and Nd:YAG laser beams processing a high number of materials (sc-Si, sc-ZnO, Fe-C…) related either to sensor fabrication or optical surface properties enhancement. In addition to the surface temperature monitoring, the PPT technique, with less than 2ns response time, allows the evaluation of thermal properties of a wide range of promising thin film materials used for the thermal management of microelectronic power devices. As reducing the size of active surfaces, laser-based nanostructuration of copper and titanium thin films as well as Me-Si substrates was also successfully monitored using RTR from nano to the picosecond scale. A comparative study of the incubation coefficient determined using the ‘Liu’ semi-empirical approach to the one determined by the RTR method would be also detailed.