Activation of Metal–Organic Precursors by Electron Bombardment in the Gas Phase for Enhanced Deposition of Solid Films

Abstract

The incorporation of gas-phase electron-impact ionization and activation of metal-organic compounds into atomic layer deposition (ALD) processes is reported as a way to enhance film growth with stable precursors. Specifically, it is shown here that gas-phase activation of methylcyclopentadienylmanganese tricarbonyl, MeCpMn(CO)3, which was accomplished by using a typical nude ion gauge employed in many ultrahigh-vacuum (UHV) studies, enhances its dissociative adsorption on silicon surfaces, affording the design of ALD cycles with more extensive Mn deposition and at lower temperatures. Significantly higher Mn uptakes were demonstrated by X-ray photoelectron spectroscopy (XPS) on both silicon dioxide films and on Si(100) wafers Ar(+)-sputtered to remove their native oxide layer. The effectiveness of this electron-impact activation approach in ALD is explained in terms of the cracking patterns seen in mass spectrometry for the metal-organic precursor used.

Thermal Chemistry of Metal Organic Compounds Adsorbed on Oxide Surfaces

“…We have in the past shown the viability of this approach by using electron-impact activation of both 5 and 6 precursors for their adsorption on silicon oxide surfaces. Figure reports both XPS (left panel) ,,, and static secondary ion mass spectrometry (SSIMS; right) data from surfaces prepared using this approach to illustrate the significant gains in uptake that take place in both cases, of up to an order of magnitude in some instances, upon gas-phase activation, which was done by using the stray electrons from a nude ion gauge (hence the labeling of the tests as “ion gauge off” versus “ion gauge on”). One particularly remarkable result from this study is that a clear peak was detected in the SSIMS traces for the MeCp ligand on the surface in ex situ experiments that required mailing of the samples from the laboratory were they were prepared (Riverside, CA) to the laboratory were they were characterized (Newark, DE).…”

“…In both cases, two traces are displayed, for experiments with the chamber’s ion gauge, used for gas-phase electron-impact precursor activation, off (blue) or on (red). The left panel was adapted from ref . Copyright 2012 American Chemical Society.…”

“…Luckily, in the case of Cp metal organics, the main reaction pathway is the loss of the ancillary ligands and the formation of CpM + ions (MeCpM + , Me = methyl substitution in the Cp ring, with 5 and 6 ). For instance, with 5 , the cracking pattern is dominated by MeCpMn­(CO) x + ions ( x = 0–3), with MeCpMn + alone accounting for 35% of all the ions produced, and with the sum of all species only missing carbonyl ligands amounting to approximately two-thirds of the total mass spectra signal. ,, With 6 , more than 90% of all the ions made in the electron-impact ionizer correspond to MeCpPtMe x – n H + , and less than 1% corresponds to products from MeCp decomposition. , 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.…”

ToF-SIMS Investigation of the Initial Stages of MeCpPt(CH3)3 Adsorption and Decomposition on Nickel Oxide Surfaces: Exploring the Role and Location of the Ligands

“…The temperature of the surface was monitored using a K-type thermocouple inserted between the sample and the metallic clip that holds the sample in place. An ionization gauge is coupled to the UHV system for two purposes, to monitor the pressure of the gases during dosing and as a gas-phase electron-impact activating source for the organometallic Pt compound, as we have discussed before. , The MeCpPt­(CH 3 ) 3 precursor (purchased from Sigma-Aldrich 98% purity) was purified in situ via repeated freeze–pump–thaw cycles before introduction to the side chamber for surface dosing. This auxiliary chamber has a base pressure of 1 × 10 –8 Torr, maintained by using a turbomolecular pump.…”

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

“…We have recently reported an alternative where electron excitation is carried out in the gas phase, prior to adsorption on the surface. 35 We showed that with (methylcyclopentadienyl)-Mn(I) tricarbonyl (MeCpMn(CO) 3 ) the carbonyl groups are easily removed this way, and that the remaining MeCpMn fragment is easily adsorbed and activated cleanly once adsorbed on the substrate of interest. The question remains of how general this approach may be.…”