Study Of Desorption And Machining Induced By Femtosecond Pulse Laser In MEMS' Fabrication

Since the birth of femtosecond pulse laser, new technologies based on the new ultra-strong and ultra-short pulse laser are developing rapidly. Femtosecond pulse laser provides many amazing tools and insights into the fields of scientific research, experimental technique and engineering application.Due to its following advantages, such as very high peak laser pulse intensity with low pulse energy, a very small heat diffusion penetration depth, availability of manipulating matter at atomic and molecular scale, capability in modifying and processing in the microscopic areas of matter, femtosecond pulse laser has a good prospect in the fabrication of MEMS and other micro or nano-systems.With the rapid shrink size of the semiconductor devices, desorption of impurity molecules and residue water adsorbed on a solid thin film becomes very important in the MEMS'fabrication process. This paper proposes a novel technique–applying femtosecond pulse laser to remove impurity molecules on the substrate. Based on the microscopic mechanism of heat transfer in solid and the energy transfer mechanism of desorption on a metal surface induced by short pulse laser, comparison is made between femtosecond and nanosecond pulse laser. The Brownian motion also is employed in the study and a new model based on the stochastic process is established for elucidating desorption induced by short pulse laser.Further discussions are made on the numerical calculation and the related program design for stimulation of desorption process. The results reveal the electron and phonon temperature profiles on the surface of substrate, a time-varying probability of adsorbed molecules and heating effects on the lattice of substrate. It is shown that as a light source, femtosecond pulse laser is a better tool for impurity desorption.In order to optimize the desorption process induced by femtosecond pulse laser, some interesting results are presented, which indicate that laser parameters, e.g. incident laser energy flux, wavelength of laser, pulse duration, play an important role in improving the desorption probability. Another useful information obtained in the study is that pairs of femtosecond pulse laser which are delayed from each other can be introduced into the desorption. It not only leads to a better performance of desorption probability, but also effectively prevent the over-heating of the substrate lattice.In the last part of the paper, study on micro-machining with femtosecond pulse laser is discussed briefly. Based on the none-equilibrium heating, the temperature profiles in lattice obtained demonstrate that the physical parameters of matter is a key factor in determining the heating effects on metal film. The dependence of the depth of melting range on laser energy flux is also defined and stimulated in this paper.