Applied Surface Science 302 (2014) 163–168 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc A novel patterning effect during high frequency laser micro-cutting of hard ceramics for microelectronics applications Guillaume Savriama a,b,∗ , Vincent Jarry b , Laurent Barreau b , Chantal Boulmer-Leborgne a , Nadjib Semmar a a GREMI-UMR 7344, CNRS/Univ-Orléans, 14 rue d’Issoudun, BP 6744, F-45067 Orléans, France b STMicroelectronics, 10 rue Thalès de Milet, CS 97155, 37071 Tours Cedex 2, France a r t i c l e i n f o Article history: Received 24 June 2013 Received in revised form 13 February 2014 Accepted 15 February 2014 Available online 24 February 2014 Keywords: Laser micromachining Sapphire Glass Phase explosion Microelectronics industry a b s t r a c t This paper investigates the laser micro-cutting of wide band gap materials for microelectronics industry purposes. An ultraviolet (355 nm) diode-pumped solid-state (DPSS) nanosecond laser was used in this investigation. The laser energy varied from 7 to 140 J/pulse with typical frequencies from 40 to 200 kHz. The effect of pulse energy and scanning speed on the depth of the cutting street of -Al 2 O 3 and glass was studied. Typical depths of 200 m were achieved on -Al 2 O 3 for 140 J/pulse, 40 kHz at 13 mm/s. SEM images showed periodic patterns produced by periodic explosive boiling that can influence the achieved depth. The shape, size and periodicity of the recast material depended on the feed rate and the laser beam frequency. This periodic removal mechanism seems to be specific to dielectrics since it was not observed for semiconductors such as silicon or silicon carbide. © 2014 Elsevier B.V. All rights reserved. 1. Introduction For nanosecond lasers, damage usually occurs via conventional heating in transparent dielectrics [1]. The electrons are located in the valence band and are separated from the conduction band by an optical band gap. The photon energy of the present system was 3.5 eV and was not sufficient to promote an electron from the valence to the conduction band. It was shown in Ref. [2] that the -Al 2 O 3 used here contained impurities, defects and inter-band transitions. This is responsible for non-linear absorption of the inci- dent light and initiates the transfer of energy to the matter. In such a case, the ablation mechanism will likely be similar to that of a metal [3–5]. The main issue is that this ablation regime depends on the seed electrons and the laser intensity. The impurities absorb the incident radiation and transfer the heat energy to the lattice by carrier-phonon coupling. The material is then heated until its melt- ing point. The surface of the liquid is then vaporized, and the vapour exerts a recoil pressure which ejects part of the remaining liquid. The phenomenon of phase explosion or explosive boiling has also been reported in the literature [6,7]. This mechanism occurs as the ∗ Corresponding author at: GREMI-UMR 7344, CNRS/Univ-Orléans, 14 rue d’Issoudun, BP 6744, F-45067 Orléans, France. Tel.: +33 247428112. E-mail addresses: guillaume.savriama@gmail.com, guillaume.savriama@st.com (G. Savriama). superheated liquid reaches 0.8–0.9 times the thermodynamic crit- ical temperature “T c ” which is around 5335 K for -Al 2 O 3 [8] and 4000 K for CB6 red glass variety [9]. The system is then a mixture of vapour and superheated liquid droplets (nuclei). On reaching a certain density, they are ejected explosively. Phase explosion thus occurs, provided that both thermodynamic (temperature ∼ 0.8–0.9 “T c ”) and kinetic (sufficient time “ c ” to allow the nuclei to reach a critical size “dc”) conditions are met. Refs. [10,11] suggested that a high power density of 10 10 W/cm 2 is required. However, Han et al. [9], using a lower power density of 10 8 W/cm 2 at 355 nm, indicated that the high repetition frequency has a role to play for glass. Stoian et al. [12] also mentioned the effect of multi-shots on the occurrence of phase explosion for -Al 2 O 3. A previous paper [2] revealed that for high overlap ratios, periodic explosive boiling could occur, leading to an undesirable larger Heat Affected Zone (HAZ). Reducing the cutting width is critical in the microelectron- ics industry to increase the gross die (number of chips per wafer), as this increases the throughput and reduces the production steps and material consumption. The present study aims at extending our knowledge of the parameters that influence explosive boiling in ceramic substrates. 2. Experimental details The processing source was a DPSS Nd:YAG laser that is part of an industrial machine built to manage several wafers, and com- http://dx.doi.org/10.1016/j.apsusc.2014.02.077 0169-4332/© 2014 Elsevier B.V. All rights reserved.