Paper PS2-ThA3
An Analysis of the Deposition Mechanisms Involved During Self-limiting Growth of Metal Oxides by Pulsed PECVD

Thursday, October 23, 2008, 2:40 pm, Room 306

Self-limiting deposition (~ 1 Å/pulse) of several metal oxides (Al₂O₃, TiO₂, ZnO, TiO₂) has been achieved by pulsed plasma-enhanced chemical vapor deposition (PECVD). In this process a metal precursor and O₂ are delivered continuously to a PECVD reactor while the rf power is pulsed at low frequency (~ 1 Hz). With proper reactor design and operation the net deposition rate of pulsed PECVD exceeds that of continuous wave operation, and the quantity of impurities is dramatically attenuated. The growth mechanism of alumina from trimethyl aluminum (Al(CH₃)₃, 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 °C 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.