A Study On UV Laser Micro-machining Single-crystal Silicon

Now, micro-machining has become one of the most active research directions in manufactory area. There are many methods to do micro-machining, and the UV laser micro-machining is one of the most promising ones, which has been widely used in the aerospace, electronics, MEMS, and many other fields due to the advantages of its no mechanical stress,good micro-machining precision and quality, low cost, flexible method, higher efficiency, less pollution and so on. The capacity of UV laser micro-machining is developing from 2D extension to complex 3D, and its precision is also improved from micron to mill micron in the international level. However, at home, 3D structure achieved by the laser micro-machining, is still in its infancy.This thesis expounds the basic principle of UV pulse laser micro-machining based on the mechanism of interaction between laser and material.. The basic structure of UV pulse laser micro-machining is percussion drilling or etching drilling process and the patterns or structures are achieved by a series of coupling pulse beam spot superposition .The experiments of percussion drilling and line etching processes were carried out on Si materials by using UV pulse laser with the wavelength of 355 nm. The effects of average power density, laser frequency, processing times, beam defocus and scanning speed on the drilling hole diameter and the etching entrance width as well as depth of the straight line were analyzed. There are two new methods proposed to improve the micro-machining quality in multiple layer laser etching processing. One is increasing the delay time after one layer laser etching processing is finished in order to reduce the accumulation of the thermal effect; another is the focal plane moving down with the depth of process progression so that laser power density remains the same. The effects of average power density, beam defocus, scan spacing, scanning speed and other process parameters on the etching quality of percussion drilling and straight line etching were also researched and analyzed in this thesis.Some planar structures were processed on the Si surface by the optimal parameters. And then, 3D structures such as quadrangular frustum pyramid and hemisphere were manufactured by using new methods. The results showed that 2D and 3D structures on the Si surface could be achieved by 355 nm UV laser etched processing, however, some better parameters combination and method should be researched further in order to reduce the roughness on the 3D structures.