A hot-wall Picosun R-200 Advanced ALD reactor was used for depositions. The reactor operated at a pressure of 4 mbar with a continuous flow of 400 sccm of high-purity N2 (99.999 %, further dried using a getter filter), which served as purge gas. The reactor walls were heated to 350 °C and the substrate table was heated to 350 °C for all depositions. Trimethylaluminum (TMA), Aluminum precursor, (Epivalence, electronic grade) was kept at 22 °C, and vapor was drawn by opening a valve to the reactor, which is at a lower pressure. The processes used NH3 (AGA/Linde, 99.999 %, further purified by a getter filter) as the nitrogen precursor. From our previous study on this ALD process, in the same reactor, 10 we used 0.1 s TMA pulse and 12 s NH3 pulse. The purge time after both the TMA and NH3 pulses was 10 s. Depositions were conducted both without and with a diffusion additive. In the latter case, Kr (99.999 %) with a flow of 15 sccm was used as diffusion additive during the whole process, i.e., not pulsed in with the precursors. Prior to deposition, Si(100) substrates with 55 µm deep and 3 µm wide, i.e., 18:1 aspect ratio, trench structures or lateral high aspect ratio (LHAR) Pillar Hall chips from Chipmetrics were used as substrates. The LHAR chips have an 0.5 µm opening to a 150 µm or 75 µm deep hall, enabling studies of up to 300:1 or 150:1 aspect ratio structures. The Si trench structures were cleaned with acetone and isopropanol for 3 minutes each and subsequently blow-dried with N2 gas, the LHAR chips were used as received.