Focused Electron Beam-Induced Deposition and Post-Growth

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Functional Nanostructured Materials (including low-D carbon)

Focused Electron Beam Induced Deposition (FEBID) and Post-Growth Purification Using the Heteroleptic Ru Complex (#-CH)Ru(CO)Br 3

3

5

3

Jakub Jurczyk, Christopher R Brewer, Olivia Morgan Hawkins, Mikhail Polyakov, Czes#aw Kapusta, Lisa McElwee-White, and Ivo Utke ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b07634 • Publication Date (Web): 16 Jul 2019 Downloaded from pubs.acs.org on July 22, 2019

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ACS Applied Materials & Interfaces

Focused Electron Beam Induced Deposition (FEBID) and Post-Growth Purification Using the Heteroleptic Ru Complex (η3-C3H5)Ru(CO)3Br Jakub Jurczyk,1,2 Christopher R. Brewer,3 Olivia M. Hawkins,3 Mikhail N.Polyakov,1,† Czeslaw Kapusta,2 Lisa McElwee-White,3,* and Ivo Utke1,*

1. Empa - Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkerstrasse 39, CH - 3602 Thun, Switzerland

2. AGH University of Science and Technology Krakow, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Kraków, Poland

3. Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA

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KEYWORDS: focused electron beam induced deposition, ruthenium, precursor compounds, mask repair, post-growth purification.


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ABSTRACT

Focused electron beam induced deposition using the heteroleptic complex (η3C3H5)Ru(CO)3Br as a precursor resulted in deposition of material with Ru content of 23 at%. TEM images indicated a nanogranular structure of pure Ru nanocrystals, embedded into a matrix containing carbon, oxygen and bromine. The deposits were purified by annealing in a reactive 98% N2 / 2% H2 atmosphere at 300 ºC, resulting in a reduction of contaminants and an increase of Ru content to 83 at%. Although a significant volume loss of 79% was found, the shrinkage was observed mostly for vertical thickness (around 75%). The lateral dimensions decreased much less significantly (around 9%).

Deposition

results, in conjunction with previous gas phase and condensed phase surface studies on the electron-induced reactions of (η3-C3H5)Ru(CO)3Br, provide insight into the behavior of allyl, carbonyl and bromide ligands under identical electron beam irradiation.

INTRODUCTION Focused Electron Beam Induced Deposition (FEBID) is a powerful technique to create three-dimensional structures on the nanometer scale on almost any conductive substrate 3 ACS Paragon Plus Environment


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within the vacuum chamber of a standard scanning electron microscope (SEM).1-3 Among the advantages, the most important are its simplicity and maskless approach, allowing one to directly create or modify structures of a desired shape. The applications include creating samples for fundamental research in fields such as nanoelectronics,4 nanomagnetics,5,

6

nano-optics and plasmonics,2,

7

or even superconductors.8,

9

Other

applications, including creating sensing devices,10-12 fabricating tips for MFM13 and repairing photolithographic masks,14 with potential applications in extreme UV lithography (EUVL) masks, have also been reported. For the latter, deposition of ruthenium is especially important, as this metal was chosen as a capping layer for EUVL masks.15 The concept of FEBID is simple. The gas injection system (GIS) delivers organometallic molecules in the gas phase to the sample surface, where they adsorb and are locally dissociated by a focused electron beam, creating a deposit of desired shape. Ideally, dissociation of the adsorbate leaves only the metal atoms on the surface, while the organic ligands desorb and are pumped out of the chamber.16 Dissociation of metal–ligand bonds has been demonstrated for a few precursors: WF6,17 AuClPF3,18 AuCl(CO),19 HFeCo3(CO)12,20 Co2(CO)8,21,

22

C2F5CO2Ag,23,

24

AgO2Me2Bu,25 Fe(CO)526 and 4

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neopentasilane,27 although in some cases, concomitant decomposition of the ligand resulted in incorporation of inpurities into the deposits. High purity deposits were obtained: 94-100 at% for Au, Co, Fe, Si, around 75 at% for Ag and 66 at% for W. For more standard commercial FEBID precursors such as MeCpPtMe3,28, 29 W(CO)6,30 Cu(hfac)2,31 TEOS,32 and Me2Au(tfac)33 the deposition process presently results in high carbon content due to incomplete dissociation of precursor or ligand co-deposition. Typical metal contents inside the deposits are approximately 15-20 at%. In-situ reactive gas addition during FEBID has also been carried out for deposition of Me2Au(tfac) assisted with H2O,34 MeCpPtMe335 assisted with O2 and Pt(PF3) assisted with XeF2,36 but these examples are confined to the noble metals Pt and Au. Liquid phase FEBID37, 38 has also been explored and produces high purity deposits, but control of the deposit shape is problematic. Post-FEBID purification procedures were developed recently for MeCpPtMe3,29,

39, 40

Co2(CO)8,41-43 Pt(PF3),44 and Pt(CO)2Cl245 and work predominantly for thin deposits. In conjunction with post-FEBID purification, a large metal content is desirable for threedimensional shape fidelity. Forming gas (5% H2 in N2) has previously been used for



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purification of Pt deposits from MeCpPtMe3, but even though the annealing temperature was high (500 ºC), the purity increased only from 15-25 at% to 40 at% of Pt.46 While FEBID is developing as a 3D nanomanufacturing method, researchers are trying to identify precursors that are optimal for this type of process.47-49 One route to avoid high carbon content in the deposits is to use short chain organic ligands in the organometallic precursor. Another requirement is sufficient precursor volatility at room or moderately elevated temperature (vapor pressure above 1 x 10-4 mbar at temperatures between 25 and 200 ºC). Homoleptic precursors have typically been employed for FEBID (see above) while the use of heteroleptic precursors is confined to MeCpPtMe3, (hfac)Cu(VTMS),50 Co(CO)3NO51 and Me2Au(acac)28. One metal that has still not been deposited with high purity is Ru. Ruthenium containing structures have been deposited by FEBID using two homoleptic precursors, Ru3(CO)1252 and EtCp2Ru.53 For FEBID with Ru3(CO)12 the exact metal content was not reported. For EtCp2Ru, the Ru:C ratio in the as-deposited material was roughly 1:9. Post-growth curing of the deposits caused a significant decrease of the C signal in the EDX spectra, but


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probably also oxidation of ruthenium.

However, no quantitative data on the atomic

composition of purified structures was provided. We now report a study of a heteroleptic Ru precursor to determine how efficiently the three different ligand types dissociate under typical and identical FEBID conditions with the goal to obtain a pure metal deposit. The heteroleptic compound (η3-C3H5)Ru(CO)3Br contains three different ligands: allyl (η3-C3H5), carbonyl (CO) and halide (bromide). With this precursor we obtained an as-deposited Ru:C ratio of 1:2, which was significantly enhanced using a post-growth forming gas-based purification procedure. The experiments allow comparison of FEB-induced dissociation pathways to the electroninduced reactions of (η3-C3H5)Ru(CO)3Br in previous gas phase54 and surface science experiments.55

RESULTS AND DISCUSSION Deposition and Characterization.

FEBID 3 µm x 3 µm square deposits from (η3-

C3H5)Ru(CO)3Br are presented in Figure 1a. The small non-circular light feature close to the center is probably a lithography artifact, as it was present on all square deposits 7 ACS Paragon Plus Environment


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prepared with a spiral pattering strategy.56 The bright, circular halo visible around the deposit is a well-known proximity effect, resulting from the interaction between backscattered electrons with the adsorbed precursor molecules.16 The as-deposited ruthenium content, shown in Figure 1b, was approximately 23 at.%, which is double the value reported for EtCp2Ru53. Figure 1c presents the three dimensional visualization of an atomic force microscope (AFM) map.

The observed triangular substructure can be

explained by the mutual orientations of the gas flux vector with the slow and fast patterning directions of the square deposit.56 The center of the deposit is around 75 ± 15 nm lower than the edges. There are two contributions which may explain the central pit. First, as the beam encircles the center, it depletes mobile adsorbates from the center which diffuse to the outer spiral arms being written. It also hinders mobile adsorbates from the outside from diffusing into the center. The second contribution is the effective dwell time, which in the center is about 14 times larger and may lead to a denser deposit.57 The density of the deposit was around 5.43 ± 0.26 g/cm3, based on AFM measurements and StrataGEM thin film correction software (see Experimental Section and Supporting Information). As can be seen in Figure 1d, the width of the deposit is larger than the nominal 3 µm and reaches 8 ACS Paragon Plus Environment

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3.34 µm at FWHM. Considering that the AFM tip has a pyramidal shape with a side angle of 17.5 ± 2º, the maximum lateral broadening of the deposit resulting from the tip geometry is around 112 nm on each side at the FWHM deposit height (see Experimental Section). Deconvoluting the AFM tip geometry reveals the true FWHM of the deposit to be 3.11 µm. The remaining difference of 110 nm to the nominal 3 µm can be attributed to the FWHM of the electron beam, which was measured independently with the knife edge method to be around 90 nm.



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Figure 1. a) Top view scanning electron micrograph of typical 3x3 µm deposit on native oxide Si substrate with the red circle symbolizing the EDX and WDS measurement area, with excitation range b) Average composition of the deposit (in at%, with uncertainty approximately 3 at%) c) AFM 3D measurement of the shape of the deposit with marked line profile positions. d) AFM profiles measured through the center of the deposit.


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TEM analysis showed a nanogranular structure of deposited material. Figure 2a presents a bright field scanning transmission electron microscope (STEM) micrograph of a deposited pillar. The average grain size is around 2-3 nm. Electron diffraction patterns were captured for the pillars and resulted in a visibly nanocrystalline pattern, with diffraction rings matching those of a pure Ru crystals (Figure 2b). Thus, the deposited material contains pure ruthenium nanocrystals embedded in an amorphous carbon-halide matrix.

Figure 2. a) Bright Field STEM of pillar, b) Electron diffraction pattern of deposit matching the simulated pure Ru pattern (green lines).



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Normalizing the deposit composition from Figure 1b to ruthenium and comparing to the stoichiometry of the precursor, it is clear that that nearly all of the oxygen was removed, while one third of the carbon and all of the bromine were incorporated into the deposit (Table 1).


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Table 1. Normalized atomic ratios of the (η3-C3H5)Ru(CO)3Br precursor (stoichiometry neglecting hydrogen) versus the measured compositions of squares deposited by FEBID and of electron-irradiated condensed (η3-C3H5)Ru(CO)3Br films.55

aThe

bThe

Condensed phase

Stoichiometry

studies55

(intact precursor)

1

1

1

C

2.0

3

6

O

0.3

0

3

Br

1.0

1 (0.5)b

1

Element

FEBID (this work)a

Ru

maximum

uncertainty

has

been

estimated

as

±0.3

atoms.

Br content in the condensed phase studies decreased to 0.5 atoms after 50 hours of

electron irradiation after warming to room temperature.

Table 1 compares the results of FEBID, where delivery of the volatile precursor continuously replenishes dissociated adsorbates and covers the deposit surface, with results of surface science experiments on a condensed (frozen) precursor film.55 In the surface science study, a 2-3 nanometer thick layer of (η3-C3H5)Ru(CO)3Br molecules was



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condensed on amorphous C and polycrystalline Au substrates at –168 °C in ultra high vacuum (UHV) and irradiated with a broad electron beam of 500eV. In that study, loss of all CO groups was observed as a decrease of intensity for both the O(1s) and C(1s) peaks in X-ray photoelectron spectroscopy (XPS) spectra, while bromine and amount of carbon equivalent to the allyl ligand remained on the surface. Desorption of Br was observed only after an additional 50 hour e-beam exposure of the irradiated condensed layers at room temperature. In our FEBID deposits we observed removal of four carbon atoms together with about three (2.7 ± 0.3) oxygen atoms. This is consistent with dissociation of all three CO ligands from Ru and desorption of the volatile carbonyl groups. The disappearance of the fourth carbon atom is more speculative and could be attributed to dissociation of some of the Ru-(η3-C3H5) bonds and their subsequent desorption, or the cleavage of volatile CHx moieties from the allyl group. Loss of carbonyl ligands was also identified as the most probable pathway for both dissociative electron attachment (DEA) and dissociative ionization (DI) in gas phase experiments on this molecule.54 Carbonyl compounds, such as Co2(CO)822 and Fe(CO)5,26, 58 also gave high-purity deposits, so it is highly probable that during FEB induced deposition of (η3-C3H5)Ru(CO)3Br the carbonyl groups are 14 ACS Paragon Plus Environment

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cleaved off the adsorbate and desorb from the deposit. The remaining carbon atoms in the FEBID deposit most likely are derived from the allyl group of the precursor. In condensed phase studies, the allyl group was not detected as one of the leaving fragments, and a strong carbon signal was still present in the XPS spectrum of irradiated thin films of condensed precursor. Gas phase studies54 showed the possibility of breaking C3H5 – Ru bonds due to both DEA and DI, although the process was less probable than cleavage of carbonyl groups (0.9 CO loss per molecule vs 0.2 allyl group loss for DEA and 2.1 CO loss versus 0.3 allyl loss for DI).54 Considering the TEM results in Figure 2 showing Ru nanocrystals embedded into a C-Br matrix, it is possible that the (η3-C3H5)– Ru bonds were also dissociated by electrons, allowing the Ru atoms to cluster. However, the allyl groups seem to desorb with much lower efficiency than carbonyls, instead forming a polymerized non-volatile carbon network under electron beam irradiation, as has been shown for some volatile purely organic precursors.59 Condensed phase studies55 did not detect any [C3H5]+ in the mass spectrum, but these studies were performed at -168°C stage temperature, where desorption of the allyl group would be significantly decreased. Bromine did not desorb during our FEBID experiments and remained in the deposit at its 15 ACS Paragon Plus Environment


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original stoichiometry, yet not bond to Ru. In contrast, in the gas phase studies, dissociation of the halide was observed via DI but had a significantly lower cross section than cleavage of carbonyl (0.4 Br vs. 2.1 CO were lost54 per molecule per incident electron). We attribute the bromine content in our as-grown FEBID material to the continuous precursor refreshment by new volatile molecules, leading to a continuous growth of material which can embed volatile species that form and/or desorb at a slower rate. Bromine could also be reacting with the byproducts from the decomposition of other ligands, which would result in its incorporation into an amorphous matrix containing C, O and Br. Post-Growth Purification. In order to decrease the amount of the carbon- and brominecontaining matrix embedding the ruthenium nanocrystals, post-growth purification with forming gas was applied. The sample was heated in a 2% H2/98% N2 atmosphere (see Experimental Section) to avoid oxidation of the ruthenium. The maximum temperature of the process was 300 ºC. Heating provides energy for reaction with the environmental gases, mobility of volatile species to diffuse out of the deposit volume, and desorption into the gas phase. 16 ACS Paragon Plus Environment

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Figure 3. a) 45º tilt view SEM of a typical square deposit purified with forming gas at 300 ºC. b) Results of EDX + WDS quantification c) AFM 3D measurement of the shape of the deposit after purification. The red line marks the position of the line profile in part d. d) AFM profile measured before (black) and after (red) purification. Figure 3a shows a scanning electron micrograph of a typical deposit purified in forming gas at 300 ºC. Figure 3b presents results of EDS and WDS quantitative analysis. As can 17 ACS Paragon Plus Environment


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be seen in Figure 3b, bromine was successfully removed from the sample, while the oxygen content was reduced to 4 at%. The carbon content was decreased significantly, from around 46 at.% to 13 at.%. Removal of the majority of the embedding C-Br matrix caused around 79 ± 2% volume reduction of the deposit. The observed lateral shrinkage was approximately 9 ± 5%, while the thickness decreased by 75 ± 1%. The lateral shrinkage values were calculated considering edge broadening in AFM profiles due to tip dimensions (see Experimental Section). Slightly lower volume losses of 69-77% were reported for Pt-C structures purified using electron beam irradiation in the presence of water vapor39 and approximately 60 ± 5% for Pt-C structures purified in O2 atmosphere.29 The measured deposit density after post growth purification was 10.8 ± 1.2 g/cm3 (see Supporting Information). Increasing the heating temperature to 450 ºC resulted in even higher Ru content (up to 89 at%), but caused cracking of the deposit surface and delamination of the structure from the substrate, likely due to a thermal expansion mismatch (see Supporting Information). The most probable volatile reaction products with hydrogen are HBr,61 CHx, and halogenated hydrocarbons, which can all evaporate at


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these temperatures. Although we cannot detect the actual compounds leaving the sample surface, the postulated process is depicted in Figure 4c.

Figure 4. Schematic of a) physisorbed precursor molecules covering the surface in an adsorption-desorption equilibrium surface concentration, b) electron beam dissociated material and desorbing carbonyl and allyl species, and c) material obtained after heating in reducing forming gas atmosphere creating volatile HBr and CHx species, leaving ruthenium on the surface.

CONCLUSIONS Ruthenium-containing structures were deposited with a focused electron beam, using (η3-C3H5)Ru(CO)3Br as precursor. The ruthenium content of as-deposited material reached 23 at% and increased to 83 at% after a forming-gas purification protocol. The



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results are consistent with a dissociation mechanism in which all the ligand groups are dissociated from the metal atom due to the electron interaction with the adsorbed molecule, followed by desorption of the carbonyls and some of the allyls (1 per every 3 dissociated molecules) from the substrate surface. The bromide and the rest of the allyl ligands are converted to the embedding matrix for Ru nanocrystals, decreasing the metal content of the structures. The proposed pathways are based on the results of our FEBID experiments, as well as gas phase54 and surface condensed film55 investigations in the literature. However, differences with respect to the gas phase and surface science experiments were found in the halogen incorporation into the FEBID material. Our results confirm that carbonyl ligands are good candidates for FEBID precursors, since they dissociate from the metal atom and desorb from the substrate before they can be incorporated into the deposit. The allyl group was partially incorporated into the deposit, probably due to its tendency to oligomerize to less volatile compounds upon electron irradiation. The halide ligand was completely incorporated into the deposited material under our experimental conditions.


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A forming gas based purification protocol was demonstrated. Annealing the sample in a reducing H2/N2 gas atmosphere avoided the oxidation of the non-noble metal ruthenium and successfully removed all of the bromine and most of the carbon from the deposited material. The metal content achieved after purification was 83 at.%. Although the volume loss was 79%, it was mostly caused by a decrease in thickness of the deposit while the lateral dimensions were less affected. Annealing in H2/N2 gas is a promising method for purification of FEB material containing non-noble metals.

EXPERIMENTAL SECTION Precursor synthesis. Synthesis was carried out under an inert atmosphere (N2) using standard Schlenk techniques. Reagents were purchased from Acros Organics, Oakwood Chemical, or Fisher Scientific and used without further purification. 1H NMR spectra were obtained on either a 300 MHz Mercury or 300 MHz Gemini instrument. Peaks were referenced to the residual protons of CDCl3. IR spectroscopy was performed on a PerkinElmer Spectrum One FT-IR Spectrometer using a solution cell equipped with NaCl windows and a path length of 1.0 mm. Synthesis and purification of (η3-C3H5)Ru(CO)3Br 21 ACS Paragon Plus Environment


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was carried out using a literature procedure.62 The compound was characterized by comparison to literature data.62, 63 FEBID experiments. All deposition experiments were performed using a Hitachi S3600 SEM. The electron gun was a tungsten cathode, working with thermionic emission of electrons. The SEM was equipped with a home-built heated stage, stainless steel of type 1.4445 in-chamber gas injection system (GIS) and a patterning system from Xenos. The GIS was attached to a 3-axis stage holder allowing precise positioning over the sample substrate. The silicon substrates, p-doped with boron to avoid charging effects, with native oxide on top, were kept at room temperature, whereas the gas injection system was heated to 35 °C to maintain sufficient precursor delivery rate. The precursor flux at the nozzle exit with a 780 µm inner diameter, calculated from the mass loss during the process, was 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠

3.54 ⋅ 1017 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑠 ⋅ 𝑐𝑚2

𝑠 ⋅ 𝑐𝑚2

. Using GIS Simulator software64, 65 this translated to around 7.6 ⋅ 1016

impinging at the electron beam irradiated sample surface. The geometry and other

details of simulation are in Supporting Information. The acceleration voltage was set to 20 kV and the beam current, measured on the silicon surface, was around 0.65 nA, which 22 ACS Paragon Plus Environment

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𝑒―

resulted in an electron flux of 1.4 ⋅ 1019𝑐𝑚2 ⋅ 𝑠 average within the FWHM area. The deposition site was scanned with a spiral strategy from outside to center with a point pitch (PoP) of 6 nm and a 10 us pixel dwell time (td). Each square was repeated 800 times. As the FWHM of our FEB is 182 nm, the effective dwell time per pixel is 𝑡𝑑 ⋅

𝐹𝑊𝐻𝑀 𝑃𝑜𝑃

= 303 𝜇𝑠

along the lines, while at the corners and in the center it becomes 606 𝜇𝑠 and 4600 𝜇𝑠, respectively. Morphology and composition analysis. To analyze morphology, a Hitachi S4800 SEM was used. Composition was measured using a Dual Beam Tescan Lyra equipped with EDAX Energy Dispersive X-ray Spectrometer (EDX) and Wavelength Dispersive Spectrometer (WDS) detectors. The composition was measured close to the center of the square deposit. EDX and WDS spectra were acquired with around 1 nA of beam current, measured in Faraday cup. All spectra were taken at 10 kV, which entails a 1 um radius area of generated X-rays (estimated for electron interaction with Si, using the Anderson and Hasler formula).66 EDX spectra were acquired for 10 seconds per spot and each WDS spectrum was acquired with 5 s per bin and 555 s of total acquisition time. For all elements except carbon, quantification results come from a standardless analysis of the Energy 23 ACS Paragon Plus Environment


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Dispersive Spectrum. As carbon K and ruthenium M spectral lines cannot be distinguished using only EDX, WDS was applied. Prior to quantification, WDS spectra for both the standard and the sample were normalized to the total number of electrons in the primary beam to reduce the influence of beam current variations. Background subtraction and peak integrations were done using Peak Analyzer in Origin TM software. All composition results were corrected for thin film geometry using SAMx StrataGEM software.67, 68 The deposit density was obtained from the SAMx StrataGEMGem software by adjusting it to match the calculated thickness with the measured average thickness of the deposit by AFM. The density range was estimated by matching the calculated thickness to both minimum

and

maximum

thickness.

The

difference

between

average

maximum/minimum density was chosen as the density uncertainty.

and

Details of

quantification procedures are described in Supporting Information. AFM measurements. Atomic force microscopy measurements were performed using an NT-MDT NTEGRA SPECTRA AFM, equipped with an optical microscope. The measurements were done in semi-contact, tapping mode, using Si cantilevers, covered with reflective Al layer. Full width at half maximum of the deposit thickness was used as a 24 ACS Paragon Plus Environment

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measure of width for each square structure. The value was corrected for the edge broadening due to tip dimensions. The tip had a pyramidal shape, with 17.5 ± 2º. Using the tangent function of this value the maximum lateral broadening of the deposit resulting from the tip geometry is around 112 nm for as-deposited and around 21 nm for purified structure, from each side. The correction values for each structure were subtracted from the measured FWHM, to obtain the real deposit width. Purification experiments. Purification experiments were performed using an Advance Riko MILA-5050 furnace. The reactive atmosphere consisted of forming gas (2% H2 / 98% of N2). The purification temperature was set to 300 ºC, which was reached after 14 minutes of heating with a ramp of 20 K/min. TEM measurements. TEM analysis was performed using a JEM 2200FS TEM (JEOL, Japan). During TEM imaging, diffraction patterns were collected prior to subsequent imaging, in order to avoid changing the crystal structure with a concentrated scanning TEM beam. Diffraction data were analyzed using CSpot software for crystal structure analysis of electron diffraction results.



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To fabricate samples for TEM observations, a series of Ru pillars were grown on the edge of a copper TEM grid. In order to grow very thin pillars, the acceleration voltage was set to 25 kV and the smallest aperture was used, which resulted in a beam current of 0.15 nA. Exposure time was 20 min per pillar. The as-grown pillars were covered with protective Pt layers from Me3PtCpMe (first using an electron beam to avoid damage, and then another layer with an ion beam). The Pt-protected pillars were then thinned to electron transparency using a Ga+ Focused Ion Beam (FIB).

ASSOCIATED CONTENT Supporting information

WDS and EDX combined quantification procedure, TEM diffraction patterns of RuO2 and RuBr3, Purification experiments at 450 ºC, Calculation of impinging molecular flux.

AUTHOR INFORMATION Corresponding Authors Ivo Utke


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[email protected] Lisa McElwee-White [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding sources The research was conducted with the financial support of EU Horizon 2020 Marie CurieSklodowska Innovative Training Network “ELENA”, grant agreement No 722149. LMW, CRB and OMH gratefully acknowledge the support from the US National Science Foundation (Grant CHE-1607547).

ACKNOWLEDGEMENTS The authors thank L. Berger and C. Vicente Manzano for help with purification.



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Figure 1. a) Top view scanning electron micrograph of typical 3x3 µm deposit on native oxide Si substrate with the red circle symbolizing the EDX and WDS measurement area, with excitation range b) Average composition of the deposit (in at%, with uncertainty approximately 3 at%) c) AFM 3D measurement of the shape of the deposit with marked line profile positions. d) AFM profiles measured through the center of the deposit.



Figure 2. a) Bright Field STEM of pillar, b) Electron diffraction pattern of deposit matching the simulated pure Ru pattern (green lines).


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Figure 3. a) 45º tilt view SEM of a typical square deposit purified with forming gas at 300 ºC. b) Results of EDX + WDS quantification c) AFM 3D measurement of the shape of the deposit after purification. The red line marks the position of the line profile in part d. d) AFM profile measured before (black) and after (red) purification.



Figure 4. Schematic of a) physisorbed precursor molecules covering the surface in an adsorption-desorption equilibrium surface concentration, b) electron beam dissociated material and desorbing carbonyl and allyl species, and c) material obtained after heating in reducing forming gas atmosphere creating volatile HBr and CHx species, leaving ruthenium on the surface.


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Focused Electron Beam-Induced Deposition and Post-Growth

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