Nanosecond Dynamics of Excimer Laser Induced Thermal Decompositon of Thin Polymer Films
- PDF / 313,243 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 61 Downloads / 233 Views
NANOSECOND DYNAMICS OF EXCIMER LASER INDUCED THERMAL DECOMPOSITON OF THIN POLYMER FILMS X.D. WU* D. DIJKKAMP, A.S. GOZDZ and T. VENKATESAN Bell Communications Research, Inc., Red Bank, NJ 07701 Physics Department, Rutgers University, Piscataway, NJ 08854
ABSTRACT A novel method to study the effect of rapid heating on polymers is presented. Nanosecond time resolved reflectivity measurements of thermal decomposition of poly(3-butenyltrimethylsilane sulfone) (PBTMSS) and polymethylmetacrylate (PMMA) films spun on silicon wafers and irradiated by a pulsed excimer laser at 248 nm are reported. It was found that there exists a critical temperature for effective decomposition. The time scale for thermal decomposition is comparable with the time scales determined for photoablation processes. The results indicate that thermal effects are very important in the interaction between polymers and pulsed UV-lasers.
INTRODUCTION Etching of thin organic polymer films by pulsed excimer irradiation has been extensively studied [1] because of its potential applications in microfabrication [2] and in microsurgery [3]. A variety of techniques, such as calorimetry [4], photo-acoustic and optical spectroscopy [5,6], time of flight [7] and time resolved temperature measurements [8] have been used to study the laser-polymer interaction mechanisms. It is now widely believed that there are two distinct polymer decomposition processes: photodissociation and thermal dissociation. It is still not clear which one governs the "laser ablation" processes because of the difficulty of separating them, although photo-dissociation is generally favoured in the theoretical models to date [9,10]. In this paper we report the results of nanosecond time resolved reflectivity (TRR) measurements following excimer laser irradiation of poly(3butenyltrimethylsilane sulfone) (PBTMSS) [11] and PMMA, which both have great potential in micro-electronics fabrication. Also, both polymers are known to decompose cleanly into their respective monomers upon heating to a temperature of about 250 °C.
EXPERIMENT A Lambda Physik EMG-200 excimer laser (248 nm, 30 ns) with a maximum energy output of 0.8 J/shot was used. To assure a homogeneous energy density, only the central •art of the beam was focused with a quartz lens to a spot of about 2 x 3 mm . Using quartz plates as attenuators, the energy density 2 could be varied between 0.1 and 2.5 J/cm . The conventional TRR technique [12] was employed in the experiments. An Ar-ion laser beam (514 nm) was used as probe beam, with an angle of incidence of 150, unless stated
Mat. Res. Soc. Symp. Proc. Vol. 74. -1987 Materials Research Society
276
otherwise. The probe beam was chopped to protect the polymer film from excessive heating. The signal was collected by a fast silicon photodiode connected with a waveform digitizer (LeCroy 6880, 1.3 GHz sampling rate). The time resolution of the whole system was about 1 ns. All data were stored in an IBM-PC computer. The polymer films, ranging in thickness from 100 nm to 1000 nm, were sp
Data Loading...
