COMSOL Multiphyisics® based simulation of DPSS laser dicing in wide-gap thin substrate

Abstract

Diode-pumped solid-state (DPSS) ultraviolet lasers have been proven to be effective for dicing various types of glass in various applications and mainly thin substrates for microelectronics. The main varieties of glass are transparent to wavelengths above 300–350 nm. However, GW/cm2 intensities can be produced by tightly focusing short pulses (nanosecond to femtosecond) that will enable nonlinear interaction phenomena. High thermal stress induces cracks that might be prohibitive for precision engineering. As glass becomes absorptive below 300 nm, linear absorption and thermal ablation will occur without cracks by setting the right laser parameters (beam fluence, scanning speed, defocus, wavelength, and pulse width). In this paper we demonstrate the possibility of the crack-free laser dicing of borosilicate glass. The effect of a polymer layer is analysed on the laser (diode-pumped solid-state, 355 nm, nanosecond) dicing capability of a commercial glass (BorofloatO33) for backend packaging. The main drawbacks concerned the brittleness of glass and photothermal ablation, which induces thermal stresses responsible for chipping or cracks. It was assumed that a thick enough polymer would enhance the energy coupling between the beam and the target. The effect of pulse energy and speed on the scribing depth is provided in the present article. A numerical simulation using COMSOL Multiphysics® was performed in order to analyse the volume temperature distribution. It revealed that the temperature remained higher than the working point of glass (1500 K) between two pulses. The viscosity is thus low between two pulses, and thermal stresses are diminished compared to the processing of raw glass samples. A comparative study between SEM images and COMSOL based surface and in volume temperature will be finally discussed for the simulation validation according to the laser parameters.