Effects of ozone as an oxygen source on the properties of the Al2O3 thin films prepared by atomic layer deposition

The atomic layer deposition (ALD) technique has been used to grow ultra-thin and conformal aluminum oxide (Al2O3) thin films on patterned poly-Si (1 0 0) substrates using trimethylaluminum (TMA), Al(CH3)3, and ozone (O3) as the starting precursors for Al and O, respectively. The growth rate and the thickness uniformity have been studied, along with Auger depth profiling and Rutherford back scattering (RBS), to ascertain the quality of the films. The novel head-injector type ALD system used in this study produced highly uniform (with non-uniformity <2%) conformal Al2O3 films over a large deposition area of 8 in. diameter substrates. The growth rate was found to be about 0.85 Å per cycle under this experimental condition. It has been found that the use of O3 does not significantly alter the growth rate or the thickness uniformity when compared with H2O-based Al2O3 films. However, substrate temperature plays a crucial role on the film growth. In case of O3-based Al2O3 films, the growth rate and the step coverage were found to increase with increasing substrate temperature in our experimental range, unlike H2O-based Al2O3 films, where the growth rate drops beyond 350 °C. The increase in the deposition rate and the better step coverage with the increase in the substrate temperature confirms that the growth of O3-based Al2O3 films is controlled by the amount of the decomposed O3. An excellent step coverage and a large aspect ratio (∼ 40:1) prove a very good quality of the films with a very low (<1%) level of carbon contamination, as has been confirmed from Auger depth profile analysis. RBS analysis results confirm that the Al2O3 films are near stoichiometric (Al2.2O2.8). The XPS analysis of Al2O3 films grown revealed only an oxidized Al 2p peak.