Gas-Phase Electron-Impact Activation of Atomic Layer Deposition (ALD) Precursors: MeCpPtMe₃

Abstract

The use of gas-phase electron-impact activation of metalorganic complexes to facilitate atomic layer depositions (ALD) was tested for the case of (methylcyclopentadienyl)Pt(IV) trimethyl (MeCpPtMe) on silicon oxide films. Uptake enhancements of more than 1 order of magnitude were calculated from X-ray photoelectron spectroscopy (XPS) data. On the basis of the measured C:Pt ratios, the surface species were estimated to mainly consist of MeCpPt moieties, likely because of the prevalent formation of [MeCpPtMe - nH] ions after gas-phase ionization (as determined by mass spectrometry). Counterintuitively, more extensive adsorption was observed on thick SiO films than on the native thin SiO film that forms on Si(100) wafers, despite the former having virtually no surface OH groups. The adsorption of MeCpPt fragments on silicon oxide surfaces was determined by density functional theory (DFT) calculations to be highly exothermic and to favor attachment to Si-O-Si bridge sites.

Thermal Chemistry of Metal Organic Compounds Adsorbed on Oxide Surfaces

“…Indeed, DFT calculations with 6 have identified adsorption geometries such as that shown in Figure 2, where bonding occurs via the interaction of silanol surface groups with the aromatic ring. 62,133 The calculated energies for such molecular adsorption were estimated to be on the order of only about 70 kJ/mol, which means that molecular desorption is facile and competes favorably with dissociative adsorption and decomposition. Consequently, thermal film deposition processes with these precursors is quite inefficient.…”

“…135,138,139 With 6, more than 90% of all the ions made in the electron-impact ionizer correspond to MeCpPtMe x−nH + , and less than 1% corresponds to products from MeCp decomposition. 62,140 The lack of extensive cracking and the preservation of the MeCp moiety upon electron-impact excitation in these cases may reflect the high stability of the original precursors and may not be general, applicable to other compounds, but this can be checked easily by simply acquiring the appropriate mass spectra. Finally, it is interesting to point out that while the interaction and activation of metal organic compounds with oxide surfaces is believed to almost always occur at individual OH surface groups, silanols in the case of silicon oxide films, there may be cases where this is not the case.…”

“…Here we point to our recent results from quantum mechanics calculation probing the nature of the bonding of MeCpPt moieties on simulated silicon oxide surfaces once the methyl ligands have been stripped from the initial 6 precursor. 62 Bonding to the oxygen atom in silanol groups was calculated to be strong, with a bond energy of approximately 115 kJ/mol, but attachment to a Si−O−Si bridging oxygen was found to be even more stable, releasing an energy of ΔE = −136.5 kJ/mol. The nature of the bonding in the initial adsorbed species is expected to affect their subsequent thermal chemistry, so the change in adsorption site may lead to the opening of new surface chemistry.…”

“…The main vessel is equipped with a Leybold EA11 semispherical electron energy analyzer with multichannel detection and a nonmonochromatized dual Mg Kα/Al Kα X-ray excitation source for the XPS data acquisition. 62,147 Gas-phase electron-impact excitation was performed during dosing in the ALD reactor by using a nonline-of-sight nude Bayard−Alpert-type ion gauge (IG) operated at an ionization potential of 150 eV. The SSIMS analysis was done ex situ using a time-of-flight (ToF)-SIMS instrument (ToF-SIMS IV, ION-TOF, Munster, Germany) and a 25 keV monoisotopic Bi 3+ ion beam.…”

Thermal Decomposition In Situ Monitoring System of the Gas Phase Cyclopentadienyl Tris(dimethylamino) Zirconium (CpZr(NMe2)3) Based on FT-IR and QMS for Atomic Layer Deposition

“…FT-IR and QMS are used to understand the reaction of precursors. Mostly studies on decomposition mechanisms of precursor using FT-IR and QMS have been used to understand reaction mechanisms on the deposition substrates [23,24]. FT-IR quickly provides information on the precise data of precursor or its chemical reaction [12], and QMS make know the gaseous species that relate to surface reaction [25,26].…”