Monitoring of layer growth during metalorganic chemical vapor deposition (MOCVD) is restricted to optical methods such as reflectance measurements. We use the high sensitivity of the phase modulated infrared spectroscopic ellipsometer (IREL) to observe in situ the properties of growing aluminum layers on TiN and SiO2. The spectral range of the IREL is from 930 cm(-1) to 4500 cm(-1), the resolution is 8 cm(-1) and a typical measurement takes 30 s. In the case of aluminum deposition on SiO2, after a wetting treatment with TDMAT (tetrakisdimethylaminotitanium), the delta spectra rapidly change from the oxide spectrum to that of an aluminum layer. A time sequence of the delta values (Delta) chosen at a suitable wavenumber (e.g. 2600 cm(-1)) shows the typical growth behavior of incubation, nucleation, island growth, coalescence and increasing roughness for the aluminum layer on TiN layers. IREL is able to monitor the aluminum layer growth up to complete coalescence with high sensitivity. The maximum of delta Delta(max) is correlated with the thickness at which complete coalescence occurs. This is connected with low surface roughness and a resistivity of 3 mu Omega cm. The thickness at Delta(max) depends on partial pressure (0.5-60 mu bar) of DMAH (dimethylaluminumhydride) and on the wetting behavior of the bottom layer. Hydrogen remote plasma treatment gives improved wetting of TiN layers for Al MOCVD under our conditions and earlier coalescence during Al growth as detected by IREL.