Abstract
<p>The general objective of this thesis is to introduce ultrafast "Laser Induced Reverse Transfer" (LIRT) as a technique for material transfer in micro-fabrication. LIRT is performed using femtosecond laser radiation of wavelength 515 nm with gold coated silicon wafers under ambient conditions. The material transfer process is explained by the dynamics of a laser ablated plasma plume. The influence of processing parameters such as laser pulse energy, pulse width and scan speed on the width of transferred material is also investigated. The width of the deposition increases with the increase in pulse energy while it decreases with scan speed. Also, the width increases with laser pulse width ranging from femtosecond to picosecond range. In general the transferred material size is determined by the amount of material present in the plasma plume which depends on the energy deposited in the bulk material by laser irradiation. In the femtosecond pulse width range, the increase in pulse energy at constant pulse width transfers more energy in a short time with minimal heating effect to the surrounding material. Hence, the efficiency of material removal increases. This in turn enhances the feature size. On the other hand, as the laser pulse width increases from femtoseconds to picoseconds, the interaction time of laser radiation with material increases. This leads to an increase in the amount of material removed, thereby increasing the transferred material size. However, thermal damage to the surrounding material increases. An increase in scan speed at constant pulse energy decreases the laser interaction time, which results in a decrease in amount of material in the plasma plume. This in tum decreases the width of the deposited material. In general, femtosecond laser induced reverse material transfer is an efficient technique for microfabrication and can be used for device manufacturing.</p>
Highlights
Introduction toMicro-fabrication through depositionThe ability to produce a wide variety of material structures, spots and lines with high resolution at micro and submicro scales is desirable in many fields from the fabrication of biodevices, microelectronics and integrated optics to biological microarrays
The significant difference between femtosecond and nanosecond laser-matter interaction in terms of transferring . laser energy into thermal energy of the target is that electrons and ions are not in equilibrium during the laser pulse in the Femtosecond laser ablation case
In using short laser pulses as an alternative for silicon material transfer, laser parameters including wavelength, pulse energy and beam shape must be optimized to satisfy the requirements of specific tasks and to maximize the efficiency of laser power usage
Summary
I hereby declare that I am the sole author of this thesis report. I authorize Ryerson University to lend this thesis to other institutions or individuals for the purpose of scholarly research. Gurinder Department of Mechanical and Industrial Engineering Ryerson University I further authorize Ryerson University to reproduce this project by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. Gurinderpal Singh Dhami, Master of Applied Science, 2009 Mechanical Engineering, Ryerson University
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