IMPROVED GROWTH AND THERMAL-STABILITY OF PARYLENE FILMS

Experimental results for the deposition of low dielectric constant Par ylene-N and Parylene-F films are explained by a mechanism based on bul k phase diffusion reaction in the firn. The deposition rate of Parylen e-F decreases significantly as time increases and ultimately achieves steady state, Very favorable agreement with experiments at a substrate temperature of -10 degrees C is obtained for parylene-F with a rate c onstant of k(f)=5X10(-5)/s, and a diffusion coefficient D-f=1.3X10(-8) cm(2)/s. In contrast, the much higher rate constant at room temperatu re for Parylene-N films is k(f)=0.16/s and the predicted deposition ra te is constant after a very small period of time (t(ss)<4/k(f)=25 s). This prediction is confirmed by the experiments. The model predicts co rrectly that low deposition temperatures improve both the deposition r ate and thermal stability of Parylene films, Our experiments confirm t his prediction and one obtains both high growth rates and high molecul ar weight films at lower deposition temperatures, Furthermore, experim ents show that the longer chains formed at low temperatures significan tly improve the thermal stability of the films, The deposition rate al so can be improved by using higher reactor pressures, However, the pre ssure that can be employed is limited to about 100 mTorr to maintain h igh quality films, At liquid nitrogen temperature (77 K), the depositi on rate is three orders of magnitude larger than the film deposition r ate at room temperature. The increased monomer concentration on the su bstrate due to higher condensation leads to this increased deposition rate. (C) 1997 American Vacuum Society. [S0734-2101(97)00206-6].