Abstract

The arrival of the femtosecond laser with a MHz repetition rate has provided the industry with a new tool to conduct submicron and nano scale machining. Several advantages such as high quality machining finish, good precision and high throughput can be obtained when using femtosecond laser to conduct nanomachining over lithography techniques currently in use. High repetition rate systems are preferred over low repetition rate femtosecond laser systems that have been studied by others due to their increased stability, speed, quality and discovery of new phenomena such as ripples and grains. This thesis proposes a high repetition rate fiber femtosecond laser system for meeting the above-mentioned conditions. The influence of the laser repetition rate and pulse energy on the size and quality of nano features fabricated on silicon wafers was investigated. Higher repetition rates led to smaller cutlines with uniform width. A 110 nm crater with a small heat affected zone of 0.79 µm was obtained at 13 MHz repetition rate and 2.042 J/cm² energy fluence. In terms of nanomachining below the ablation threshold (surface patterning), the influence of pulse width, repetition rate and pulse energy on the spacing of ripples, as well as diameter of grains created on silicon wafers, was examined. For the pulse width, repetition rate and pulse energy range used, the ripple spacing and grain diameter increased with laser pulse duration while other parameters did not play a significant role. These results show the capability of the proposed system in meeting the industry requirements.

Highlights

  • Even though the feasibility of using femtosecond lasers has been predicted for over a decade industrial application of this technique has not been fully realized due to the challenges faced in terms of laser parameters and inadequate experimental studies in this area

  • 4.4 SUMMARY Thin film laser micromachining has been utilized for repairing semiconductor masks, creating solar cells and fabricating MEMS devices

  • A unique high repetition rate femtosecond fiber laser system capable of variable repetition rates from 200 kHz to 25 MHz along with helium gas assist was used to study the effect of pulse repetition rate and pulse energy on femtosecond laser machining of gold-coated silicon wafer

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Summary

Introduction

1.1 INTRODUCTION TO NANO FABRICATION TECHNIQUESAccording to [1], micro and nanotechnology has immense impact on our daily lives due to our dependence on computers. The recent progress in laser systems, the chirped pulse amplification (CPA) technique, has allowed the systematic study of the laser/matter interaction using a broad range of laser parameters [4]. According to [38, 39], there are various micro-patterning techniques such as electron beam etching, photolithography, atomic force microscopy, soft lithography, laser micromachining and microsphere nanopatterning. Atomic force microscopy takes advantage of mechanical forces to etch the surface, but the procedure is slow and cannot conveniently etch large surface areas Soft lithography techniques such as microcontact printing, micromolding, microtransfer moulding and replica moulding, imprinting and injection molding can be used due to their low thermal effect, cost and the ability to scan a large area. The major disadvantages include difficulty in controlling the particle arrangement and the particles cannot be used repeatedly

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