Femtosecond Laser Machining At Submicron And Nano Scale

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.