Substrate‐Independent Palladium Atomic Layer Deposition

Abstract

A novel method is presented for the atomic layer deposition (ALD) of palladium on a tetrasulfide self-assembled monolayer functionalized SiO 2 surface. Additionally, a novel reducing agent (glyoxylic acid) was used to remove the organic ligands from the chemisorbed palladium(II) hexafluoroacetylacetonate metallorganic. Glyoxylic acid is an effective reducing agent above 200 C, which is not optimal for palladium but it is effective enough to show proof-of-concept and deposit a Pd ªseedº layer. Palladium was also deposited on iridium at 80 C and 130 C via a hydrogen process or on the Pd seed layer at 80 C. The 60 Pd film grown on the tetrasulfide self-assembled monolayer (SAM) showed nearly random texture and higher carbon and fluorine contamination levels compared to the one grown on Ir. The 55 film grown on Ir at 80 C is highly (111) textured with a grain size of~60 , as shown by reflection high energy electron diffraction (RHEED). The higher contamination levels of the Pd film deposited on the tetrasulfide SAM, as measured by X-ray photoelectron spectroscopy (XPS), is attributed to the high temperatures needed to deposit the Pd seed layer. The higher deposition temperatures cause more dissociation of the hfac ligand and a higher metallorganic desorption rate. These equate to less Pd being deposited and with higher contamination levels.

Atomic Layer Deposition of Noble Metals – New Developments in Nanostructured Catalysts

“…10 Senkevich et al demonstrated Pd ALD at 80 °C on Ir metal surfaces, where atomic hydrogen, formed from the dissociation of H 2 on the Ir surface, served as the reducing reagent. 11 To increase the substrate generality, Ten Eyck et al used a remote hydrogen plasma for Pd ALD on Ir, W, and Si surfaces. 12 However, plasmas are not well suited to catalyst synthesis because they require line-of-site between the plasma and the substrate surface which is impractical for nanoporous catalyst templates.…”

Plasma-Assisted Atomic Layer Deposition of Palladium

“…[6] To date, Pd ALD has not achieved success on oxideterminated surfaces primarily due to the lack of chemisorption of palladium(II) hexafluoroacetylacetonate, Pd II -(hfac) 2 . [12,13] Additionally, there has been a lack of suitable reducing agents. Senkevich et al [12] successfully demonstrated the use of thermally cleaved glyoxylic acid as a reducing agent for Pd ALD, but this technique required substrate temperatures in excess of 200 C, which only yielded a monolayer seed' layer whereupon hydrogen could be used at 80 C. Hydrogen can only be utilized with thermal ALD when a catalytic surface is present for the dissociation of molecular hydrogen to atomic hydrogen.…”

In Situ Reflective High-Energy Electron Diffraction Analysis During the Initial Stage of a Trimethylaluminum/Water ALD Process

“…RHEED is widely used for in situ analysis of (crystalline) growth in pulsed laser deposition (PLD) and molecular-beam epitaxy (MBE) systems. Several ALD layers have been studied using ex situ RHEED, [6][7][8] although the photographs of the diffraction patterns are only presented to show (non)crystallinity of the deposited layers. A beam of high energy electrons (5-35 keV) is reflected off the sample surface at grazing incident angles, usually 1°-3°w ith respect to the wafer surface.…”