An Analysis of the Deposition Mechanisms Involved during Self-Limiting Growth of Metal Oxides by Pulsed PECVD
Michael T. Seman1, David N. Richards2, and Colin A. Wolden2. (1) CMD Research LLC, 400 Corporate Circle, Unit B, Golden, CO 80401, (2) Chemical Engineering, Colorado School of Mines, 1500 Illinois, Golden, CO 80401
Self-limiting deposition (~ Å/pulse) of several metal oxides (Al2O3, TiO2, ZnO, TiO2) has been achieved by pulsed plasma-enhanced chemical vapor deposition (PECVD). In this process the metal precursor and O2 are delivered continuously to a PECVD reactor while the rf power is pulsed at low frequency ( ~ 1 Hz). The net deposition rate of pulsed PECVD can exceed that of continuous wave operation, and the quantity of impurities was dramatically attenuated. The growth mechanism of alumina synthesis from trimethyl aluminum (TMA) was investigated by comparing the results from pulsed PECVD with those of plasma-enhanced atomic layer deposition (PE-ALD). For both processes the rate/cycle saturated with ~200 L of TMA exposure. At 165 ºC a rate of 1.37 Å/cycle was obtained using PE-ALD. For pulsed PECVD the rate scaled linearly with the TMA partial pressure, and its extrapolation was in good agreement with PE-ALD. The results suggest that deposition in pulsed PECVD involves an ALD component which is supplemented by PECVD growth, and that the contribution of the latter may be tuned using the TMA partial pressure. Experiments using patterned wafers supported this hypothesis. Conformal coatings were observed within 10:1 aspect ratio trenches using pulsed PECVD, however the deposition rate on the surface of these substrates was greater than within the trench. The ratio between the two corresponds well to the ratio of rates obtained from pulsed PECVD and PE-ALD on planar substrates. With cycle times < 1 s, net rates > 30 nm/min were obtained by pulsed PECVD while retaining high quality and digital control.