We have investigated metallorganic chemical vapor deposition (MOCVD) of Al layers on sputtered TIN, CVD TiCN, and SiO2 using DMAH (Dimethylaluminiumhydride). We have used the high sensitivity of a phase modulated infrared spectroscopic ellipsometer (IREL) to observe the early stages of Al growth. The spectral range of the IREL is from 930 to 4500 cm(-1), the resolution 8 cm(-1) and a typical measuring period takes 30 s. Our results demonstrate the value of IREL measurements for the investigation of early stages of thin Al layer growth. The time sequences of the IREL delta values at a suitable wave number (e.g., 2600 cm(-1)) show characteristic features during deposition, which correspond to the surface structure at different growth stages (incubation, nucleation, island growth, coalescence, and growing roughness). The IREL data helped identify the strong effect of growth temperature (150 degrees C to 250 degrees C) on the nucleation behavior of Al growth, while DMAH partial pressure (1 to 10 mu bar) also influences the layer thickness needed for coalescence. Al growth is very sensitive to substrate conditions. The Al layer quality can be improved by using CVD TiCN barrier layer from TDMAT (Tetrakisdimethylaminotitanium) on Si substrates.