Ozone Based Atomic Layer Deposition of Hafnium Oxide and Impact of Nitrogen Oxide Species

It has recently been reported that nitrogen oxide species (e.g., N 2 O 5 , NO 2 , NO 3 , and/or N 2 O) can have an impact on ozone based atomic layer deposition (ALD) of metal oxides when ozone is generated by dielectric barrier discharge (DBD) in O 2 /N 2 mixtures. In this work, we further investigate the effect of the O 2 /N 2 ratio in the DBD for HfO 2 ALD using HfCl 4 as metal precursor. Using O 3 in the absence of nitrogen oxides, uniform HfO 2 layers are obtained between 200 and 250°C in a hot wall cross flow reactor. The self-limiting nature of the O 3 and HfCl 4 reaction is demonstrated at 225°C and the growth-per-cycle is 0.12 nm. At higher temperature, O 3 decomposes at the HfO 2 coated reactor walls, resulting in a decreasing HfO 2 thickness over Si substrates in the direction of the gas flow. Using O 3 in combination with nitrogen oxides by DBD in N 2 /O 2 mixtures, we obtained uniform HfO 2 layers in the 200–300°C temperature range. At 300°C, the GPC is 0.14 nm and the HfO 2 films show a low impurity content. Both processes produce high quality dielectric layers in Pt gated capacitors.