Performance Evaluation and Comparison between Direct and Chemical-Assisted Picosecond Laser Micro-Trepanning of Single Crystalline Silicon

Abstract

The fabrication of micro-holes in silicon substrates that have a proper taper, higher depth-to-diameter ratio, and better surface quality has been attracting intense interest for a long time due to its importance in the semiconductor and MEMS (Micro-Electro-Mechanical System) industry. In this paper, an experimental investigation of the machining performance of the direct and chemical-assisted picosecond laser trepanning of single crystalline silicon is conducted, with a view to assess the two machining methods. The relevant parameters affecting the trepanning process are considered, employing the orthogonal experimental design scheme. It is found that the direct laser trepanning results are associated with evident thermal defects, while the chemical-assisted method is capable of machining micro-holes with negligible thermal damage. Range analysis is then carried out, and the effects of the processing parameters on the hole characteristics are amply discussed to obtain the recommended parameters. Finally, the material removal mechanisms that are involved in the two machining methods are adequately analyzed. For the chemical-assisted trepanning case, the enhanced material removal rate may be attributed to the serious mechanical effects caused by the liquid-confined plasma and cavitation bubbles, and the chemical etching effect provided by NaOH solution.

An Investigation into Picosecond Laser Micro-Trepanning of Alumina Ceramics Employing a Semi-Water-Immersed Scheme

“…This leads to a plasma zone that is in a high-pressure and high-temperature state, which may enhance the removal of the molten material. The material removal can therefore be attributed to evaporation, melt expulsion and phase explosion [16,24,29]. During pulse intervals, the residual liquid material on the ablated surface re-solidifies, leading to sub-micron humps on the sidewall surface.…”

“…( a ) Repeated hole diameter measurement method at entrances and exits, and ( b ) estimation scheme of the hole tapering [24]. …”

Fabrication of Taper Free Micro-Holes Utilizing a Combined Rotating Helical Electrode and Short Voltage Pulse by ECM

“…Wu et al developed a low-cost desktop micro electro-chemical machining (ECM) and fabricated micro-holes in the tungsten cemented carbide (WC-Co) workpiece with spindle electrode [22]. In addition, to machine micro-holes on silicon materials, various electrochemical composite machining methods have been studied [23,24,25,26,27,28].…”

Optimization of Processing Parameters for Water-Jet-Assisted Laser Etching of Polycrystalline Silicon

“…The absorption of laser light by the water, the formation of laser-induced plasma in water, the formation of bubbles, and the laser refraction at the air-water interface were discussed. To evaluate two machining methods, Hao Zhu et al [18] compared the direct and chemical-assisted picosecond laser trepanning of single crystalline silicon. In their study, an orthogonal test design scheme was adopted to consider the relevant parameters affecting the trepanning process.…”