Pulsed laser micro-processing of advanced electronic materials and related transport issues

As an emerging technology, pulsed laser materials processing holds great promises in microelectronics, micromechanics, and biomedical engineering. Unique advantages of pulsed laser materials processing lie in its capability to work in micro-dimensions due to the high energy density within the laser pulse and the laser light coherence. Optimization of the laser micro-processing needs thorough understanding of the process itself and the fundamental mechanisms involved in pulsed laser interactions with materials. This study is devoted to the coupling of new process development and understanding of heat and mass transport in pulsed laser micro-processing of advanced electronic materials.; Understanding of the transient heat and mass transport in pulsed laser processing requires accurate knowledge of thin film thermal properties. A novel experimental technique is developed to measure submicron thin film thermal conductivity, simultaneously with thermal diffusivity. Micro-heater and micro-sensor assemblies are designed and integrated on the free-standing SiN films. Measured SiN thermal properties are in good agreement with values obtained by two other independent methods. Influences of the microstructure of SiN thin films on the thermal properties are revealed.; This work explored two types of excimer laser processing of materials: non-ablative and ablative. As a new non-ablation process, formation of ultrashallow and box-like p+-junctions (30-400 nm) by excimer laser doping of silicon from spin-on-glass (SOG) is studied. It is demonstrated that it is possible to precisely control the diffusion depth and profile shape by confined diffusion in a thin surface liquid silicon layer melted by the excimer laser. Experimental dopant profiles are in reasonable agreement with transient heat and mass transfer simulation. A 50 nm-depth diode with excellent I-V characteristics is fabricated by this excimer laser doping technology.; Excimer laser ablation of two thin film systems, metallic and polymeric films is examined. In situ optical diagnostics and an ultra-sensitive mass removal detection system are developed. The ablation rate of thin gold film on a quartz substrate is found at least two orders larger than the numerical predictions by the surface thermal vaporization model. Surface morphology of gold films observed by SEM suggests that hydrodynamic motion is developed during laser melting. Hydrodynamic ablation mechanism is therefore proposed to explain this large discrepancy.; Excimer laser projection micromachining of polyimide thin films is achieved with micron lateral resolution and submicron depth resolution. Measured etch rate dependence on laser fluence supports the photo-chemical mechanism in excimer laser ablation of polyimide thin films. Estimated etch rates based on the measured optical absorption coefficient are in agreement with the experimental values within 15%.