Growth kinetics and microstructure of MOCVD iridium coating from iridium(III) acetylacetonate with hydrogen

- High purity iridium coatings were produced by metallo-organic chemical vapor deposition in the presence of hydrogen.
- The effect of hydrogen on deposition velocity has been studied and effectively explained by a Rideal-Elay model.
- The effect of hydrogen on microstructure evolution was studied.
- At ambient hydrogen, the effect of deposition temperature on growth kinetics and microstructure was studied.

Iridium coatings were produced by metallo-organic chemical vapor deposition (MOCVD) using iridium(III) acetylacetonate (Ir(acac)3) as precursor at 400-520 °C under atmospheric pressure in the presence of hydrogen. Three different deposition regions were obtained in the study: reaction-rate-limited regions at intermediate (460-500 °C), low (<460 °C), and high (520, and 540 °C) temperatures. The steady-state kinetics of iridium deposition was studied as functions of temperature and hydrogen pressure at intermediate temperatures, which could be described with the Rideal-Elay kinetic model. This model indicates that the hydrogen in the air is activated and reacts with the Ir(acac)3 molecules adsorbed on the surface. At high temperatures, growth velocity was changed into the relation dependent more on deposition temperature and hydrogen partial pressure, while at low temperatures stable deposition results could not be obtained in the system. The coating microstructure strongly depended on deposition temperature and hydrogen pressure. The coatings surfaces show an even topography in the reaction-limited regions and uneven ones at low or high deposition temperatures. The grain size increased with decreased temperature or decreased hydrogen pressure at 400-500 °C.