Effect of scanning speed on continuous wave laser scribing of metal thin films: theory and experiment

Abstract

In this paper continuous wave laser scribing of the metal thin films have been investigated theoretically and experimentally. A formulation is presented based on parameters like beam power, spot size, scanning speed and fluence thresholds. The role of speed on the transient temperature and tracks width is studied numerically. By using two frameworks of pulsed laser ablation of thin films and laser printing on paper, the relation between ablation width and scanning speed has been derived. Furthermore, various speeds of the focused 450 nm continuous laser diode with an elliptical beam spot applied to a 290 nm copper thin film coated on glass, experimentally. The beam power was 150 mW after spatial filtering. By fitting the theoretical formulation to the experimental data, the threshold fluence and energy were obtained to be 13.2 J mm −2 and 414 µJ respectively. An anticipated theoretical parameter named equilibrium border was verified experimentally. It shows that in the scribing of the 290 nm copper thin film, at a distance where the intensity reaches about 1/e of its maximum value, the absorbed fluence on the surface is equal to zero. Therefore the application of continuous laser in metal thin film ablation has different mechanism from pulsed laser drilling and beam scanning in printers.

Direct Laser Writing: From Materials Synthesis and Conversion to Electronic Device Processing

“…For CW lasers, writing speed dictates the fluence (J cm −2 ) or irradiance (W cm −2 ), since it directly establishes the dwell time of the beam over a unit of area. [ 112 ] For pulsed lasers, writing speed is also crucial to determine the overlapping rate of subsequent pulses, playing a critical role in many synthesis and conversion processes, as well as in patterning resolution. [ 113 ] As such, writing speed is usually used in conjunction with laser power, to control the energy dose subjected to the irradiated material and its areal distribution, as well as the resulting heat accumulation and dissipation effects.…”