Mechanistic Study of Nucleation Enhancement in Atomic Layer Deposition by Pretreatment with Small Organometallic Molecules

Abstract

Thermal atomic layer deposition (ALD) of metals on metal oxide surfaces typically suffers from nucleation delays that result in poor-quality films. The poor nucleation may be caused by a lack of suitable chemisorption sites on the oxide surface, which are needed for metal nucleation to occur. In this work, we demonstrate that prefunctionalizing the surface with a single monolayer of small organometallic molecules from the vapor phase can lead to a significant increase in surface coverage of the metal deposited by ALD. This process is demonstrated for Pt ALD from (methylcyclopentadienyl)­trimethylplatinum (MeCpPtMe3) and O2, with nucleation enhanced almost 3-fold at 100 ALD cycles after the pretreatment. We hypothesize that the high coverage of the organometallic molecule provides an alternative chemisorption mechanism for the platinum precursor and thus leads to an increase in its uptake. The proposed chemisorption mechanism is robust across several organometallic molecule pretreatments and could potentially be exploited for other organometallic-based metal ALD processes. This chemisorption mechanism was probed using in situ quadrupole mass spectrometry (QMS). The growth of the platinum deposits was investigated in depth through scanning electron microscopy (SEM) and grazing incidence small-angle X-ray scattering (GISAXS). These studies show that the pretreatment also results in the improved wettability of Pt nanoparticles (NPs). The improved wettability is likely to affect the Pt diffusion properties, further contributing to the enhancement observed on the treated substrates. In addition, GISAXS and SEM studies indicate the growth of larger, denser, and more highly ordered Pt NPs at early cycle numbers, which subsequently coalesce into continuous and pinhole-free films. Surface pretreatment by organometallic molecules therefore introduces a potential route to achieve improved nucleation and growth of ultrathin films.

Surface mobility and impact of precursor dosing during atomic layer deposition of platinum:in situmonitoring of nucleation and island growth

“…21 Not only the ALD process conditions play a crucial role but the substrate itself and pre-treatment steps can significantly influence the nucleation of the noble metal nanoparticles. [22][23][24][25][26] Despite numerous reports on noble metal nanoparticle deposition by ALD, the mechanisms that govern the very initial stages of growth are still not fully understood. Surface processes such as diffusion of deposited atoms, 5,12,[27][28][29][30][31] adsorption of precursor ligands on the substrate, 5,23,26,[31][32][33] thermal decomposition of the metal precursor, 31,34,35 and reactions catalyzed by the deposited nanoparticles 5,31 are suggested to play a role.…”

“…5 Moreover, the nucleation and island growth mechanisms and kinetics are influenced by the choice of ALD process conditions, e.g., precursor/reactant type, exposure and deposition temperature, resulting in different incubation times and nanoparticles morphologies. Although some efforts have been made, 5,12,14,23,26,28,31,34,36 it is essential to further improve our understanding of the role of the different deposition parameters in order to enhance the control over the ALD technique for the tailored deposition of noble metal nanoparticles.…”

“…58 Besides monitoring the thin film growth, it is also possible to monitor the behaviour of a deposited film under several conditions, for example, sintering of Pt nanoparticles during annealing in different oxidizing atmospheres, 59 or the formation of bimetallic nanoparticles by annealing ALD deposited layers. 60 A few reports presented ex situ 26,27,[61][62][63] or in situ 12 GISAXS measurements during Pt ALD. In 2009, Christensen et al, investigated the morphology of Pt nanoparticles grown by 10, 20, 30 and 40 ALD cycles on SrTiO 3 surfaces.…”

The Importance of Decarbonylation Mechanisms in the Atomic Layer Deposition of High‐Quality Ru Films by Zero‐Oxidation State Ru(DMBD)(CO)3

“…[7][8][9][10] As vapor-phase deposition techniques, CVD and ALD rely heavily on the chemical interaction between precursors and substrates, [1] meaning surface chemical reactions are of particular importance. Surface reaction pathways have a significant impact on observed growth phenomena, [7,10,19,[11][12][13][14][15][16][17][18] and the coordination sphere of a precursor has been found to have a direct effect on various film properties, including crystallinity, [20][21][22] dielectric constant, [21] and impurity concentration, [23,24] among others. [22,25] Moreover, tuning precursor chemistry by altering the coordination sphere around the metal center has been shown to be a highly effective tool to enhance film nucleation, resulting in higher growth rates (GR) for CVD or growth per cycle (GPC) for ALD.…”

The Importance of Decarbonylation Mechanisms in the Atomic Layer Deposition of High-Quality Ru Films by Zero-Oxidation State Ru(DMBD)(CO)3

“…[7][8][9][10] As vapor-phase deposition techniques, CVD and ALD rely heavily on the chemical interaction between precursors and substrates, [1] meaning surface chemical reactions are of particular importance. Surface reaction pathways have a significant impact on observed growth phenomena, [7,10,19,[11][12][13][14][15][16][17][18] and the coordination sphere of a precursor has been found to have a direct effect on various film properties, including crystallinity, [20][21][22] dielectric constant, [21] and impurity concentration, [23,24] among others. [22,25] Moreover, tuning precursor chemistry by altering the coordination sphere around the metal center has been shown to be a highly effective tool to Across those previous studies, the reported temperatures at which constant GPCs were achieved differ by 60-80 °C, and the reported GPC value differ by 0.2-0.35 Å/cycle.…”