Measurements and Simulations of Temperatures in Polyimide during Excimer Laser Ablation
- PDF / 459,973 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 51 Downloads / 186 Views
MEASUREMENTS AND SIMULATIONS OF TEMPERATURES IN POLYIMIDE DURING EXCIMER LASER ABLATION D. P. Brunco*, Michael 0. Thompson*, C. E. Otis** and P. M. Goodwint Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853 "IBM T. J. Watson Research Center, Yorktown Heights, NY 10598 t Mail Stop M888, LANL, Los Alamos, NM 87545 ABSTRACT The temperature at the interface between a thin polyimide film and a quartz substrate was monitored as a function of time during KrF (248 nm) laser-induced heating and ablation using thin film NiSi thermistors. These experimental temperature measurements were coupled with heat flow simulations to obtain time-resolved temperature profiles in the polyimide. Thermal properties of the polyimide were estimated by requiring that the simulations reproduce experimental temperature profiles. The peak surface temperature in the polyimide at the onset of ablation was subsequently estimated from these simulations, producing a value of 1660 ± 100 K 2 at the observed ablation threshold fluence of 36 mJ/cm . Simulations were also used to explore the role of pulse duration on polyimide ablation. INTRODUCTION Since Srinivasan and Mayne-Banton's[1] observation in 1982 of direct etching of poly(ethylene terephthalate) by an ArF excimer laser (193 nm), the subject of pulsed excimer laser ablation of polymers has attracted a great deal of interest.J2-5] While considerable progress has been made in characterizing various aspects of the ablation process, convincing measurements of temperatures during ablation have been lacking. Yet temperature is perhaps the most important thermodynamic quantity characterizing the process, and its knowledge is a critical input for any comprehensive thermal model for polymer ablation. Experimentally, it is found that for moderate fluences above a threshold, the etch rate increases roughly as the logarithm of fluence. For fluences below "threshold", ablation may occur but only at very low rates and/or after repeated irradiation. Laser pulse durations ranging from 300 fs[6] to 500 ns[4] have been used for polymer ablation, and the relation of etch depth to pulse length for a fixed incident fluence has proven to be very interesting. Despite a range of nearly two orders of magnitude in incident intensity, the etch depth vs fluence for 7, 300, and 500 ns XeCI excimer laser (308 nm) ablation of polyimide is virtually identical.[4] The ablation threshold for 5 ps XeCl laser pulses is only about a factor of two lower, despite an intensity 1400 times greater than for 7 ns pulses. While little difference has been found for irradiations with pulse lengths in the ns regime, slightly different behavior has been observed for pulses
Data Loading...
