Atomic Layer Deposition of High-k Dielectrics Using Supercritical CO$_2$

Atomic layer deposition (ALD) of high-$\kappa $dielectric was performed in supercritical CO$_{2}$ (SCCO$_{2})$, using a two-step reaction sequence.~~ In step one, tetraethoxy silane (TEOS) precursor was injected in SCCO$_{2}$ at 80-100\r{ }C and 50 MPa pressure to obtain a chemisorbed surface monolayer, which was then oxidized into SiO$_{2 }$using peroxide entrained in SCCO$_{2}$. ALD process was controlled by estimating precursor solubility and its mass transport with respect to the density of SCCO$_{2, }$and~correlating these parameters with precursor injection volume. In the ALD process, 7 pulses of precursor were used anticipating deposition of one atomic layer in each of~the pulses. The thickness of the SiO$_{2}$ atomic layers deposited using SCCO$_{2}$ was measured by variable angle spectroscopic ellipsometry (VASE), and the $C-V$ measurements were also performed. The result obtained using VASE indicates that there were 7 monolayers of SiO$_{2}$ with total thickness of 35 \textit{{\AA}}, and the dielectric constant of the deposited layers was 4.0$\pm $0.1. Our initial findings clearly demonstrate that SCCO$_{2}$ is capable of atomic layer deposition of high quality dielectric films at very low process temperatures preventing interface reaction.~~~More research is in progress to achieve ALD of HfO$_{2}$ and TiO$_{2}$ in SCCO$_{2}$.