The mechanism of thin film Si nanomachining using femtosecond laser pulses

Femtosecond (fs) laser ablation has been the subject of intense recent research. The pulse time ('width') is shorter than the electronic relaxation time, resulting in a decoupling of the period of laser illumination and the melting of the substrate. Since the laser does not directly heat the substrate, and there has been no directly observed heat affected zone (HAZ) nor vaporization, fs laser ablation is sometimes considered to be a direct solid-vapor phenomenon. Recent research indicates that the phenomenon is not as straightforward as assumed. Time-of-flight spectroscopy used to measure the reflectivity indicates that molten material is present for a few hundred picoseconds, well after the laser pulse. A material-modification threshold has been observed that is below the ablation threshold. This indicates that the laser can affect the substrate without ablation occurring. However, many scanning electron microscopy (SEM) studies have been performed, but material change in the substrate have not been observed. Transmission electron microscope (TEM) studies have also been done, but they have all been carried out in plane-view, so that it is difficult to separately observe bulk and surface effects. In this study, cross-sectional TEM analysis of holes drilled in single crystal silicon films in silicon-on-insulator (SOI) structures have been carried out, and have allowed direct observation of the subsurface modified material. Samples were prepared using a focused ion beam (FIB) system, and a metal mask was applied to protect the surface from the ion beam. Through transmission electron microscopy,

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Jia, Jimmy Yi-Jie, 1980-

Advisor dc:contributor.advisor

• Carl V. Thompson II.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/35752
• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Identifier URI

http://dspace.mit.edu/handle/1721.1/35752

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/35752