Mechanics of laser-assisted debonding of films

Films of GaN and ZnO can be separated from the substrates on which they are grown by the use of a laser-assisted debonding process in which a pulsed laser is shone through the substrate and absorbed in the film. Experience shows that the success in separating the films intact and damage free depends sensitively on the laser parameters used and the physical and geometric properties of the films. In this contribution, the mechanics of the laser-assisted debonding of GaN films are presented and used to construct process maps that delineate the conditions for damage-free film separation. The key variable is the nondimensional group ${\mathrm{\Omega E}}_p{\mathrm{/(d}}_p^2\sqrt{\tau }\mathrm{),}$ where $\Omega$ is a lumped material constant, $E_p$ is the laser pulse energy, $d_p$ is the diameter of the illuminated area and $\tau$ is the laser pulse length. Experimental observations of UV/excimer laser assisted debonding of GaN films from sapphire substrates are used to illustrate the types of deformations and cracking modes on which the process maps are based.