Water-assisted femtosecond laser drilling of 4H-SiC to eliminate cracks and surface material shedding
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ORIGINAL ARTICLE
Water-assisted femtosecond laser drilling of 4H-SiC to eliminate cracks and surface material shedding Wenjun Wang 1,2
&
Hongwei Song 1,2 & Kai Liao 1,2 & Xuesong Mei 1,2
Received: 17 February 2020 / Revised: 1 September 2020 / Accepted: 15 October 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract This study adopted femtosecond laser with a wavelength of 515 nm to drill high-aspect-ratio micro through holes on a 500-μm thickness single-crystal SI-type 4H-SiC wafer. Firstly, through holes with a high aspect ratio of 20 were fabricated in air. However, the heat affect zone (HAZ), cracks, and surface material shedding around entrances and exits of the holes are inevitable in air even after chemical corrosion post-processing. In order to remove these defects, the water-assisted femtosecond laser drilling of 4H-SiC was investigated. The high-quality through holes free of cracks, surface material shedding, and HAZ were obtained under the action of internal scour and heat diffusion of water. Besides, the water layer thickness and the laser repetition frequency have a great influence on the processing quality and efficiency of the micro-holes. Finally, high-quality high-ratio-rate through micro-hole arrays on 4H-SiC were fabricated with the optimal process parameters, which is significant for the development of SiC electronic devices and the high-quality micro-fabrication of other hard and brittle materials. Keywords Femtosecond laser drilling . 4H-SiC . High-aspect-ratio through holes . Water-assisted laser processing . Cracks . Surface material shedding
1 Introduction Silicon carbide (SiC) single crystal is the third-generation semiconductor material developed after silicon (Si) and gallium arsenide (GaAs), which is mainly used to fabricate electromechanical system (EMS) and micro electro-mechanical system (MEMS) substrates. Due to its specific physical and chemical properties such as wider band gap, higher saturation drift velocity, higher thermal stability, higher thermal conductivity, lower diffusion rate, and chemical inertness compared with Si and GaAs, SiC is an attractive semiconductor material for high density interconnector (HDI) devices capable of functioning in high speed, high voltage, high temperature, highpower, high repetition rate, and intense radiation environments [1, 2]. To achieve high-density interconnector and
* Wenjun Wang [email protected] 1
State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
2
Shaanxi Key Laboratory of Intelligent Robots, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China
integrated packaging of the circuit layers, it is necessary to drill through micro-holes with high aspect ratio on singlecrystal SiC substrates and fill them. Unfortunately, it is difficult to drill high-quality through micro-holes on a SiC crystal due to its difficult-to-cut properties such as extremely high hardness (between diamond and corundum), high chemic
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