This work reports on the initial growth of atomic layer deposited titanium nitride thin films on SiO2 substrate at temperatures of 350–425◦C and process pressures of 2.6–3.2×10−2 mbar. We used spectroscopic ellipsometry for in situ monitoring the growth, atomic force microscopy and electrical measurements for further film characterization. We demonstrate that the growth obeys Stranski – Krastanov mode with an initial 2D growth followed by a 3D island formation. The growth of the islands eventually leads to coalescence. We found the 2D–3D transition to be independent of temperature whereas the coalescence of the 3D islands is strongly affected by temperature. The former takes place as the film thickness reaches 0.69 ± 0.1 nm, which is equivalent to 3 monolayers of TiN. The latter occurs at a thickness of 2.5 ± 0.1 nm for 350◦C and at a thickness of 3.5 ± 0.1 nm for 425◦C.