Monday, August 14, 2017

University of Helsinki present a thermal ALD gold process

Some years ago Barry Lab presented their plasma enhanced gold ALD process (LINK). However, in order to coat 3D features and objects plasma activated processes have limitations so that is why it is now very cool to read about a thermally activated ALD process for gold from University of Helsinki. They have identified a precursor, Me2Au(S2CNEt2), with a quite broad thermal ALD process window (120–250 °C). Amazingly, as for the earlier breakthrough from Helsinki on Ruthenium ALD, the trick is to use a oxygen co reactant and for gold the Finns had to go all the way and use ozone. Read all about the details in the paper below.

Thermal Atomic Layer Deposition of Continuous and Highly Conducting Gold Thin Films
Maarit Mäkelä, Timo Hatanpää, Kenichiro Mizohata, Jyrki Räisänen, Mikko Ritala, and Markku Leskel

Five Au(III) compounds were synthesized and evaluated for atomic layer deposition of Au thin films. One of the compounds, Me2Au(S2CNEt2), showed optimal thermal characteristics while being volatile and thermally stable. In the growth experiments, this compound was applied with O3 at temperatures of 120–250 °C. Self-limiting growth was confirmed at 180 °C with a rate of 0.9 Å/cycle. The deposited Au thin films were uniform, polycrystalline, continuous, and conductive. Typical resistivity values of 40 nm thick films were 4–16 μΩ cm, which are low for chemically deposited thin films. The chemical composition of a Au thin film deposited at 180 °C was analyzed by time-of-flight elastic recoil detection analysis, proving the film was pure with small amounts of impurities. The detected impurities were O (2.9 atom %), H (0.9 atom %), C (0.2 atom %), and N (0.2 atom %).