Nucleation Enhancement and Area-Selective ... - ACS Publications

Subscriber access provided by Macquarie University

Article

Nucleation Enhancement and Area-Selective Atomic Layer Deposition of Ruthenium using RuO# and H#-gas Matthias M. Minjauw, Hannes Rijckaert, Isabel Van Driessche, Christophe Detavernier, and Jolien Dendooven Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b03852 • Publication Date (Web): 20 Feb 2019 Downloaded from http://pubs.acs.org on February 23, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemistry of Materials

Nucleation Enhancement and Area-Selective Atomic Layer Deposition of Ruthenium using RuO₄ and H₂-gas Matthias M. Minjauw,a Hannes Rijckaert,b Isabel Van Driessche,b Christophe Detavernier,a Jolien Dendoovena Ghent University, Conformal Coating of Nanostructures (CoCooN), Department of Solid State Sciences, Krijgslaan 281 (S1), 9000 Ghent, Belgium. b Ghent University, Sol-gel Centre for Research on Inorganic Powders and Thin films Synthesis (SCRIPTS), Department of Chemistry, Krijgslaan 281 (S3), 9000 Ghent, Belgium. a

ABSTRACT: Inherent substrate selectivity is reported for the thermal RuO₄ (ToRuSTM)/H₂-gas atomic layer deposition process (ALD) on H-terminated Si (Si-H) versus SiO₂. In situ spectroscopic ellipsometry (SE) detected Ru growth from the first cycle on blanket Si-H, while on blanket SiO2 60 cycles were needed to detect growth. Area-selective growth was evaluated on a patterned substrate with 1-10 µm wide Si-H lines separated by 10 µm wide SiO₂ regions. Ex situ planar scanning electron microscopy and cross-section high resolution transmission electron microscopy measurements showed that a smooth, continuous Ru film of 4.5 nm could be deposited on the Si-H, with no Ru detected on the SiO₂. The proposed mechanism behind the inherent substrate selectivity is the oxidation of the Si-H surface by RuO₄, which was confirmed by in vacuo X-ray photoelectron spectroscopy (XPS) experiments. A methodology to enhance the nucleation of the RuO₄/H₂-gas process on oxide substrates is also reported. In situ SE and in vacuo XPS experiments show that the nucleation delay on SiO2 can be completely removed by exposing the surface to trimethylaluminum (TMA) just before the start of the ALD process. We found evidence that the TMA pulse makes the oxide surface reactive towards RuO₄, by introduction of surface methyl groups which can be combusted by RuO₄. As TMA is known to be reactive towards many oxide substrates, this methodology presents a way to achieve Ru metallization of virtually any surface. Therefore one can either (i) use the RuO₄/H₂-gas process to coat non-oxidized surfaces selectively with Ru, or (ii) by using a TMA-priming one can bypass the selectivity and coat a wide variety of surfaces non-selectively with Ru.

INTRODUCTION Ruthenium is a candidate to replace copper in future sub-10 nm interconnects. Although Ru has a higher bulk resistivity, it shows a better electromigration behavior, and most likely Ru interconnects will not need a barrier and liner.1-10 Atomic layer deposition (ALD) is a thin film deposition method in which the growing film is alternately exposed to a series of chemical precursors, each reacting with the surface in a self-limited way. This enables the deposition of thin films with precise thickness control and excellent conformality.11-13 By now, ALD of compounds has proven to be a key enabling technology for semiconductor device manufacturing. However, ALD blanket layers still need to be patterned by lithography, and for future technology nodes it will be increasingly difficult to align subsequent lithography steps, such that bottom-up fabrication of patterned structures becomes desirable. Therefore areaselective ALD, in which ALD film growth is achieved only on selected areas of the substrate, is of high interest.14-17 Areaselective ALD is also of interest for applications in catalysis.1821

For ALD of metals, and in particular for ALD of Ru, most processes show significant nucleation delays on a wide range of surfaces.13 When ALD of blanket Ru films is required, the long nucleation delays reported for most Ru ALD processes lead to increased process times, waste of expensive precursor, and layer closure when the thickness of the film exceeds 5-10 nm, which limits the applicability of such processes. If the length of

the nucleation delay depends on the nature of the surface, this can be exploited to achieve area-selective deposition, which has been reported for several Ru ALD processes.22-29 Only in one of these reports, selective deposition of Ru is acquired directly onto the underlying patterned structure, which is called inherent substrate selectivity.26 The other approaches are using additional process steps to either block or activate Ru growth onto specific areas of the underlying structure. As these blocking or activation layers need to be deposited and aligned onto the patterned structure, this complicates fabrication and therefore makes most of these approaches less desirable. It must be noted that one of the more recent approaches uses the selective adsorption of a Si ALD precursor to inhibit Ru growth on SiO2, and therefore displays more application potential.28 For the inherently selective Ru ALD process reported by Zyulkov et al., the observed selectivity window corresponds to a layer of 3.2 nm of Ru on SiCN with respect to amorphous C, and the continuity of the layer was not reported.26 In a previous publication, we reported a thermal Ru ALD process using the inorganic RuO4-precursor (ToRuSTM, Air Liquide) in combination with H2-gas.30 The ALD process was shown to have a narrow temperature window near 100°C, where high quality, low-resistivity Ru films can be deposited with a high growth rate of 0.1 nm/cycle. The following half-reactions were proposed for the process in steady growth conditions (linear ALD growth):

Ru (s) + RuO4 (g)  2RuO2 (s)

ACS Paragon Plus Environment

(1)

Chemistry of Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

RuO2 (s) + 2H2 (g)  Ru (s) + 2H2O (g)

(2)

As soon as the Ru surface is fully oxidized, half-reaction (1) stops, while half-reaction (2) stops as soon as the RuO2 surface is fully reduced to Ru. This explains the self-limiting nature of the process. At higher temperatures, thermal decomposition of RuO4 occurs:

RuO4 (g)  RuO2 (s) + O2 (g)

(3)

Such that half-reaction (1) is not self-limiting, and this determines the upper limit of the temperature window. Halfreaction (2) is inefficient at temperatures below 100°C, which determines the lower limit of the temperature window. Based on this last observation, we developed a plasma-enhanced Ru ALD process using RuO4 and H2-plasma at 50°C.31 As halfreaction (1) stops as soon as the Ru surface is fully oxidized, one could expect that an oxidizable surface is needed to nucleate Ru.30,32 In this paper we report strong inherent selectivity of the RuO4/H2-gas process on H-terminated Si (SiH) vs. SiO2, as a result of the difficult Ru nucleation on SiO2 compared to Si-H. Although the difficult nucleation on oxides is beneficial for achieving area-selective Ru growth, some applications might require Ru metallization of an oxide surface. In this case, using the RuO4/H2-process would be problematic, as the large nucleation delay leads to a loss of precursor and Ru films with a high roughness. Therefore we developed a method to enhance the nucleation on oxides. In this paper we show that the Ru nucleation delay on SiO2 can be completely removed by pretreatment of the surface with trimethylaluminum (TMA). Therefore one can either (i) use the RuO4/H2-gas process to coat non-oxidized surfaces selectively with Ru, or (ii) by using a TMA-priming one can bypass the selectivity and coat a wide variety of surfaces non-selectively with Ru and without potential nucleation difficulties. EXPERIMENTAL SECTION Deposition System. The ALD depositions were performed in an experimental high vacuum ALD reactor with a base pressure of 10-7 mbar. This pressure is achieved by using a turbomolecular pump in combination with a rotary vane backing pump. Samples were resistively heated inside the reactor chamber to a temperature of 125°C, and it was verified that RuO4 did not thermally decompose at this temperature. The walls of the reactor were heated to 80°C. Precursors are evaporated in stainless steel containers, and delivered to the reactor through stainless steel tubing and pneumatically controlled inlets. Both the RuO4 (ToRuSTM, Air Liquide) and TMA (STREM CHEMICALS, min. 98%) precursors were at room temperature, with stainless steel tubing heated to 35°C. The reactor is equipped with a remote inductively coupled RF plasma source (13.56 MHz). Deposition Process. Ru ALD was achieved using the RuO4/H2-gas process.30 RuO4 was supplied to the reactor by using the ToRuSTM-precursor, which is a solution of RuO4 in a methyl-ethyl fluorinated solvent developed and produced by Air Liquide. H2-gas was supplied by using a 20% mixture of H2 in Ar. Both ToRuS and H2 pulses were of a static nature. This means that the valve between the chamber and the turbo pump was closed to allow the pressure to build up by injecting the gas over a time ti, after which the pneumatic inlet was closed and the chamber was held at a constant pressure Ps for a time ts. After this, the chamber was evacuated again by first using the

Page 2 of 17

backing pump, which is bypassed to the reactor to allow pumping down to roughing vacuum, and afterwards using the turbomolecular pump to pump down to base pressure. {Ps , ti , ts} for ToRuS and H2-gas pulses were {1.8 mbar , 8s , 10s} and {5 mbar , 8s , 20s} respectively. Substrate Preparation. Planar SiO2 substrates were 100 nm SiO2 films grown on Si by plasma-enhanced chemical vapour deposition. Air storage lead to carbonaceous contamination of the SiO2 surface, which was removed by in situ O2 plasma (O2*) cleaning before Ru deposition. The plasma cleaning involved 5 pulses of 10s O2-plasma using 99.999% pure O2-gas at 0.005 mbar pressure and with a power of 250W. Successful removal of carbon was verified by in vacuo XPS. For an SiO2 surface treated with TMA this standard O2* cleaning was followed by a single 10s pulse of TMA at a pressure of 0.008 mbar. For TMA-treatment followed by an O2-plasma, the standard O2* cleaning was followed by a single 10s pulse of TMA at a pressure of 0.008 mbar and a single 10s O2* pulse (250W) at 0.005 mbar pressure. Patterned Si/SiO2 substrates were prepared by first sputtering a 100 nm blanket SiO2-layer on lowdoped 2-inch Si wafers. Next, the circular pattern was defined by contact printing of an image reversal resist mask (LOR1A + IX845) on the SiO2, which is resistant to a buffered oxide etch (BOE). Finally, the non-covered SiO2 was removed down to the Si substrate with BOE, and the mask was removed using acetone and isopropyl alcohol. Prior to deposition, planar Si and patterned Si/SiO2 substrates were cleaned by a hydrofluoric acid (HF) dip using a 2% HF in H2O solution for 60s. After this the substrates were rinsed in DI water and blown dry using pure nitrogen. The transfer time to the ALD reactor after this procedure was less than 10 minutes. Materials and Process Characterization. In situ spectroscopic ellipsometry (SE) was performed in between ALD cycles using a Woollam M-2000 spectrometer fitted directly onto the ALD reactor. For thin metallic films, a strong statistical correlation exists between the thickness and optical constants when fitting an optical model to the ellipsometric Ψ and Δ data.33 A typical approach is to determine the film thickness of a reference ex situ sample by using a different technique, and then fit an optical model to the ellipsometric Ψ and Δ data. This model can then be used to fit a thickness to the in situ data after every ALD cycle.34 However, metal ALD films typically nucleate as particles, such that the same optical model cannot be used during the nucleation regime (this is defined here as the growth regime before linear, steady ALD growth takes place, and is different from the nucleation delay, during which no appreciable growth is observed).13, 35-37 Furthermore, even after film coalescence, the optical constants might depend on the cycle number or process conditions, as metal ALD films are polycrystalline.12, 38, 39 Therefore, in this work we followed a more qualitative approach by using the ellipsometric Ψ and Δ data to monitor metal growth.37, 39, 40 The in situ ellipsometric Ψ and Δ data were analyzed over the entire wavelength range for each experiment, however the amplitude ratio Ψ at 515 nm was selected for presentation. In vacuo X-ray Photoelectron Spectroscopy (XPS) measurements were performed using a Thermo ScientificTM Theta Probe X-ray Photoelectron Spectrometer System, which is directly attached to the ALD reactor through an UHV connection. This setup allows through-vacuum sample transfer times below 60s from the ALD chamber (10-7 mbar) to the XPS analysis chamber (10-10 mbar). For most types of surfaces, this


Page 3 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is sufficiently fast to avoid carbon contamination or desorption of surface species. As the Ru3d region overlaps with C1s, we used Ru3p as a means to detect ruthenium on the surface. This overlap also prevented us from detecting small carbon contaminations (< 10 at. %) when Ru was present. The energy axis of the spectra was calibrated using either the Si2p position for SiO2 substrates (103.5 eV) or the Si2p3/2 (99.8eV) position for Si-H substrates.41 Area-selective Ru deposition on patterned substrates was evaluated by Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM). SEM was performed using a FEI Quanta 200F instrument, combined with an EDAX silicon drift detector to perform Energydispersive X-ray spectroscopy (EDX). (S)TEM was performed using a JEOL JEM 2200-FS instrument. Samples for (S)TEM were prepared by cutting a cross-sectional lamella via the Focused Ion Beam (FIB) technique in a FEI Nova 600 Nanolab Dual Beam FIB-SEM. The lamella were extracted using the in situ lift out procedure with an Omniprobe extraction needle.42 The thickness of blanket Ru films was determined by X-ray Reflectivity (XRR) measurements, using a Bruker D8 diffractometer (CuKα source). For some of these samples, Xray Fluorescence (XRF) was used to determine the thickness, as the films were too rough for XRR. This was done by first constructing a calibration curve of the integrated XRF Ru L peak intensity versus the XRR thickness of smooth Ru films, and afterwards calibrating the XRF data of rough films using this curve. The root mean square (RMS) roughness was determined by Atomic Force Microscopy, using a Bruker Dimension Edge system. The electrical resistivity of blanket Ru films was determined by using the 4-point probes method. RESULTS AND DISCUSSION Area-Selective Ru ALD. The RuO4/H2-gas process was monitored by in situ SE on blanket SiO2 and Si-H substrates (Figure 1). At cycle 0, the amplitude ratio Ψ(515 nm) has a value which corresponds to the substrate in question, and is therefore different for both cases. The real difference between both cases is that the value of Ψ(515 nm) changes from the first cycle for Si-H, while for SiO2 the change is observed after ~ 60 cycles. Hence, Ru growth is detected from the first cycle on SiH, while for SiO2 this is only after 60 cycles. This does not mean that the Ru growth discretely onsets at 60 cycles, most likely minor amounts of Ru are deposited on the surface from the initial cycles, which SE is not able to detect.15, 43 In view of the established submonolayer sensitivity of SE however, these changes will be negligible.40, 44-47 Moreover, this is in agreement with our previous results obtained using in situ synchrotron Xray Fluorescence spectroscopy measurements.32 The amount of material that can be allowed on SiO2 will depend on the targeted application. Figure 1. In situ spectroscopic ellipsometry data for the RuO4/H2gas process on blanket Si-H and SiO2 substrates.

Area-selective ALD was evaluated on a patterned Si-H/SiO2 substrate. As we were aiming for a Ru layer with a thickness below 10 nm, the RuO4/H2-gas process was run for 20 cycles. The sample was analyzed by ex situ planar SEM-EDX and cross-section TEM. In Figure 2, the ex situ planar SEM-EDX analysis results are shown. No sign of Ru was detected by EDX in the SiO2-regions, while a clear RuL peak was present on the Si-H lines.

Figure 2. Planar view SEM analysis of patterned Si-H lines (3 µm width, and 10 µm separation) on SiO2 which were exposed to 20 cycles of the RuO4/H2-gas process. The SEM micrograph was acquired after the EDX line scan perpendicular to the Si lines. The carbon track left by the electron beam can be seen on the micrograph, and is overlaid with the corresponding integrated EDX data for the Ru, O and Si-peaks.

In Figure 3, ex situ cross-section (S)TEM images are shown. From the overview TEM image it is clear that Ru was only deposited on the Si-H lines, and not on the SiO2. Also, the thickness uniformity of the Ru film on Si-H is good. The thick Pt overlayer is present due to the FIB preparation. From Figure 3 (b), a thickness of 4.5 nm was extracted for the Ru film. In addition, an interface is visible between the Ru film and the Si, for which a thickness of 2.7 nm was found. From Figure 3 (c), it is clear that the edge of the Ru film near the transition of Si to SiO2 is well-defined. The Ru film is slightly overhanging the SiO2 slope due to the conformality of the ALD-process. This result is similar to what Kalanyan et al. found for area-selective ALD of tungsten using the SiH4/(WF6+H2)-process.16 The interface between Ru and Si has a similar contrast as the SiO2 region, and therefore we expect that the interface is a layer of oxidized Si. Figure 3. Cross section (S)TEM analysis of patterned Si-H lines (7.2 µm width) on SiO2 which were exposed to 20 cycles of the RuO4/H2-gas process. (a) Overview TEM image. The Pt on top is deriving from the FIB preparation. (b) HRTEM image of the Ru film deposited on the Si-H. (c) HRTEM image near the edge of the Si-H with the SiO2.

We propose that the mechanism behind the instant nucleation of Ru on Si-H is the oxidation of Si-H to SiO2 by RuO4. During this oxidation, RuO2 is deposited on the surface. In the case of SiO2 the surface is already fully oxidized, such that a large nucleation delay is present (Figure 4). To support this hypothesis, in vacuo XPS experiments were conducted. From Figure 5 (a) it is clear that a single precursor pulse on SiO2 does not lead to a detectable amount of Ru on the surface by XPS, due to the absence of the Ru3p peaks. For Si-H on the other hand (Figure 5 (b)), a single RuO4 pulse leads to deposition of Ru on the surface. The Si2p peak (Si2p3/2 at 99.2 eV and Si2p1/2 at 99.8eV) for the pristine Si-H substrate is at a lower binding energy compared to the one for pristine SiO2 (103.5 eV). After exposing Si-H to RuO4 an additional broad peak at higher binding energy (102.3 eV) appears in the Si2p spectrum. This proves that the Si surface is oxidized by RuO4. As the Si2p peak for bulk SiO2 is expected at a higher binding energy (103.5 eV), most likely a sub-oxide is formed at the surface.48 In the O1s spectrum, two peaks can be distinguished. The one at higher binding energy (531.6 eV) can be assigned to oxygen atoms bound to Si,41 while the one at lower energy (529.7 eV) can be assigned to oxygen bound to Ru.49 The positions and shapes of the Ru3d peaks (data not shown), corresponded to anhydrous RuO2, as an acceptable fit was found using the peak models reported by Morgan et al.49 Figure 4. The proposed surface reactions occurring during the very first half-cycle of the RuO4/H2-gas process, explaining the observed selectivity between SiO2 and Si-H. (a) The fully oxidized SiO2-surface is unlikely to react with the RuO4-precursor. (b) The Si-H surface can be oxidized by RuO4 resulting in the deposition of a thin RuO2 layer.



Page 4 of 17

Figure 5. In vacuo XPS data showing the effect of a single RuO4-pulse on (a) SiO2 and (b) Si-H. The pass energy setting of the XPSspectrometer used to acquire each spectrum is shown in the upper left corner. In the case of Si-H we are able to resolve the spin-orbit split components Si2p3/2 and Si2p1/2 of the Si2p peak, by using a low pass energy (high resolution).

Nucleation Enhancement on Oxides. The large nucleation delay observed on SiO2 was explained by the inability of RuO4 to react with the fully oxidized SiO2 surface. RuO4 is known as a strong oxidizing agent in organic chemistry.50, 51 Therefore we developed the idea to enhance the Ru nucleation by introducing hydrocarbon functional groups on the SiO2 surface. It is established that TMA functionalizes the SiO2-surface with methyl groups.11 In Figure 6 it can be seen that by giving a single pulse of TMA before the RuO4/H2-gas process, the nucleation delay on SiO2 is completely removed. When an O2*-pulse is given after the TMA-pulse, a nucleation delay is introduced again. Figure 6. In situ spectroscopic ellipsometry data for the RuO4/H2gas process performed on SiO2, with different in situ surface pretreatments. For the curve indicated by “SiO2”, the surface received the standard in situ O2* pretreatment discussed in the experimental section. For the curve indicated by “TMA”, this O2* pretreatment was followed by a single TMA-pulse, while for “TMA + O2*” it was followed by one TMA pulse and one final O2* pulse.

We propose that the mechanism behind the prompt Ru nucleation on TMA-treated SiO2 is due to the reaction of RuO4 with the surface -CH3 groups introduced by TMA (Figure 7). Note that these methyl groups can either be bound to Al or they can be directly bound to Si atoms from the substrate.11 In vacuo XPS experiments were performed to support this hypothesis. From Figure 8 (a) and (b) it can be seen that a single TMA pulse leads to a detectable amount of Al and C atoms on the SiO2surface by XPS. This illustrates that XPS is sufficiently surfacesensitive to detect a monolayer of adsorbed TMA molecules, which has been shown previously by Geidel et al.52 From Figure 8 (c) it can be seen that O2-plasma removes all the carbon from the surface. The Al2p signal is still visible, so most likely the O2-plasma oxidizes the surface, removing the methyl groups and leaving behind oxidized Al atoms (Figure 7). If we now expose each of these three surfaces to RuO4 (Figure 8), this

leads to a detectable amount of Ru only in the case where methyl groups are initially present. Again, the deposited Ru had oxidation state +IV, as evidenced by the Ru3d peak positions and shapes (data not shown).49 These results are in agreement with our proposed hypothesis. An important remark is that the Al2p peak is still visible after the exposure to RuO4 (data not shown). This means that most likely Al impurities will be present at the interface between the final Ru film and the SiO2 substrate, which may influence the application. The use of TMA to enhance the Ru nucleation on SiO2 merely serves as a proof of concept however, and we believe that similar results can be achieved by using alternative functionalizations on any type of oxide surface, the main condition being that the functional groups can be oxidized by RuO4. For example, in the case of SiO2, one could try to functionalize the oxide surface by using a silylation agent to avoid the Al-impurities at the interface.28, 53 Finally we would like to note that although previous works have reported the nucleation enhancement of Pd54, 55 and Pt56 ALD by TMA treatments, the mechanism is different compared to our work. The Pd and Pt ALD processes are using metalorganic precursors, and this can lead to surface poisoning by adsorbed precursor fragments.13, 57 Treatment with TMA was shown to remove this surface poisoning in the case of Pd ALD, leading to an enhancement of the nucleation.55 In our case, the nucleation is enhanced by combustion of surface methyl groups by RuO4. Figure 7. The proposed surface reactions during the very first halfcycle of the RuO4/H2-gas process on SiO2, following different surface pretreatments. (a) The fully oxidized SiO2-surface is unlikely to react with the RuO4-precursor. (b) Exposure of the SiO2-surface to TMA leads to adsorbed methyl groups, which can be oxidized by RuO4, and leads to deposition of RuO2 on the surface. (c) When the surface methyl groups introduced by TMA are removed by O2-plasma, the surface is again unlikely to react with the RuO4-precursor.

Figure 8. In vacuo XPS data showing the effect of a single RuO4-pulse on (a) SiO2, (b) SiO2 + TMA and (c) SiO2 + TMA + O2*. The pass energy setting of the XPS-spectrometer used to acquire each spectrum was 200 eV.

Ru Thin Film Properties. The thickness, RMS roughness, resistivity and impurity content of four thick Ru films deposited on planar Si-H and SiO2 substrates with different pretreatments are presented in Table 1. Comparing the thickness of these films, it can be seen that 200 cycles of RuO4/H2 are needed on SiO2 to achieve the same Ru film thickness as is obtained on SiH after 75 cycles. We know that TMA treatment of SiO2 leads to an enhancement of the nucleation. However, if we compare the thickness of the Ru films deposited on SiO2 + TMA and SiH for the same number of cycles, we can conclude that the nucleation must still be better on Si-H. If TMA treatment of SiO2 is followed by O2-plasma, the thickness of the Ru film is slightly higher compared to that on plain SiO2 for the same

number of cycles. As the nucleation delay on SiO2 + TMA + O2* is longer, this suggests that the initial Ru growth rate after the nucleation delay on SiO2 + TMA + O2* must be higher compared to SiO2. A similar observation was made by Soethoudt et al.43 In that study the initial stages of Ru ALD were investigated using Rutherford backscattering spectrometry (RBS) on a variety of substrates. Ru growth on CH3-terminated Si was detected after a 100 cycle nucleation delay, and on OHterminated SiO2 after 7 cycles. In the former case, steady growth was achieved after 400 cycles, and the growth rate was twice as high between 300 and 400 cycles. In the latter case, steady growth was achieved after 7 cycles, without any enhanced initial growth. The higher initial growth rate could be due to a


Page 5 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


rougher surface morphology during the nucleation regime.58 Next, if we compare the RMS roughness of these four Ru films, the films that nucleate most easily, Si-H and SiO2 + TMA, have the lowest roughness. The resistivities of all Ru films are similar, and have a sufficiently low value.4 Ex situ XPS depth profiling was used to determine the impurity content of the Ru films. In the bulk of the films, the only detected impurity was oxygen. From Table 1 it is evident that the bulk oxygen impurity content was low and does not depend on the nature of the starting surface. At the surface of all Ru films, fluorine was detected. Fluorine was also detected during the in vacuo XPS experiments which studied the nucleation regime. As no fluorine was detected in the bulk of the Ru films, this suggests that the fluorine remains at the top of the Ru film during growth. The fluorine is most likely deriving from the ToRuS solvent, and therefore the solvent might be involved in some way in the surface reactions.59 However, this needs further investigation. We can conclude that for thick Ru films deposited by the RuO4 / H2 process, the material properties are the same for all starting surfaces, except for the roughness. The lowest roughness is found for films that nucleate most easily: Si-H and TMA-treated SiO2. Table 1. Thickness d, RMS roughness R, electrical resistivity ρ and bulk atomic concentration of oxygen relative to ruthenium O of Ru thin films deposited on different surfaces.a Substrate

Cycles

d (nm)

R (nm)

ρ (µΩ.cm)

O (%)

Si-H

75

18.5

0.3

36

4

SiO2

200

17.3

2.2

35

5

SiO2 + TMA

75

13.3

0.4

37

4

SiO2 + TMA + O2*

200

20

2.2

40

5

aThese Ru films were obtained during the in situ SE experiments of which the data are shown in Figure 1 and Figure 6.

In view of the potential application of Ru films in sub-10 nm interconnects, the resistivity of Ru films deposited on Si-H and TMA-treated SiO2 was also determined as a function of thickness (Figure 9). On Si-H no real trend can be observed with decreasing Ru film thickness, and a resistivity of ~35 µΩ.cm is obtained for a film with a thickness of only 2.7 nm. This result suggests that the Ru films are continuous early on during deposition, which is promising for applications and in agreement with our previous results.32 The resistivity values and their low dependence on film thickness is also compatible with the report by Dutta et al., in which the resistivity dependence on thickness was studied for sub-10 nm Ru films sputtered onto SiO2.4 The authors suggested that this results from the short mean free path of conduction electrons in Ru, based on simulations within the Mayadas-Shatzkes model. When depositing on TMA-treated SiO2, the resistivity increases with decreasing Ru film thickness below 5 nm. Most likely this is caused by the more difficult nucleation on SiO2 + TMA compared to Si-H. Although this larger resistivity might limit the applicability of this approach for sub-10 nm interconnects, the Ru films are still continuous and one could try to improve the resistivity by optimizing the deposition conditions or performing post deposition annealing.4 In summary, Ru films with a resistivity below 40 µΩ.cm were obtained on Si-H and

SiO2 + TMA for a thickness exceeding 2.5 nm and 7.5 nm respectively. These values are of the same magnitude as the results obtained by other Ru ALD processes reported in the literature, as can be seen in Figure 9.60-62 Figure 9. Resistivity as a function of thickness for Ru films deposited by RuO4/H2 on Si-H (blue symbols) and TMA-treated SiO2 (red symbols) substrates. Resistivity values found in literature, using different Ru ALD processes, are also shown (green symbols).

CONCLUSIONS The RuO4/H2 process shows inherent substrate selectivity, which allows us to grow Ru on Si-H while limiting growth on SiO2. In vacuo XPS experiments suggest that this derives from the strong oxidative nature of the RuO4-precursor, which allows reaction with the Si-H surface during the first half-cycle, but not with SiO2. Using this inherent substrate selectivity, areaselective ALD was demonstrated on a Si/SiO2 patterned substrate. Based on these results and the established strong oxidative nature of RuO4, we expect that area-selective ALD with the RuO4/H2 process can be achieved more generally with other material systems, e.g. to achieve selective metal-on-metal growth on metal/dielectric patterned structures.30, 15 Fully oxidized regions can be used to inhibit Ru growth, while Ru growth is achieved on regions which can be oxidized by RuO4. Although the substrate selectivity is crucial for achieving area-selective ALD, some applications might require ALD deposition of a good quality, continuous Ru film on an oxide surface. We showed by in situ SE experiments that the Ru nucleation delay on SiO2 can be eliminated by first exposing the surface to TMA. In vacuo XPS experiments suggest that the methyl functional groups on the TMA-exposed SiO2 surface are responsible for this enhanced nucleation, most likely through combustion by RuO4. As TMA reacts similarly with most oxide substrates, it is likely that this methodology presents a way to perform Ru metallization of virtually any oxide surface. In addition, we expect that this methodology can be extended to the use of other molecules to functionalize the surface, that is, if the functional groups can be oxidized by RuO4. For example, in the case of SiO2, this will be necessary if one wants to avoid the Al impurities which were observed at the SiO2/Ru interface, and could be achieved by silylation of the SiO2 surface.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]

Author Contributions M.M.M. designed the experiments, performed the ALD depositions, performed the in vacuo XPS and in situ SE measurements, and analyzed the experimental results. H.R. performed the FIB sample preparation and TEM measurements. C.D. assisted in designing the experiments. C.D. and J.D assisted in analyzing the results. M.M.M. prepared the manuscript. All authors contributed in revising the manuscript. All authors have given approval to the final version of the manuscript.

Funding Sources This research was funded by Fonds Wetenschappelijk Onderzoek Vlaanderen (FWO Vlaanderen), the special research fund BOF at Ghent University (GOA 01G01513) and the Flemish Government (Medium-scale research infrastructure funding, Hercules funding). M.M.M and J.D. received financial support through a personal



FWO research grant. J.D. also received funding through the FWO “Krediet aan Navorsers” (1527916N).

ACKNOWLEDGMENT The authors acknowledge: Lode Tassignon, Davy Deduytsche and Stefaan Broekaert for technical assistance with the construction of the in vacuo ALD-XPS setup; Lin-Lin Wang and Marc Schaekers for providing the patterned Si/SiO2 substrates; and Olivier Janssens for performing SEM-EDX measurements.

REFERENCES (1) Adelmann, C.; Wen, L. G.; Peter, A. P.; Siew, Y. K.; Croes, K.; Swerts, J.; Popovici, M.; Sankaran, K.; Pourtois, G.; Van Elshocht, S.; et al. Alternative Metals for Advanced Interconnects. 2014 IEEE Int. Interconnect Technol. Conf. / Adv. Met. Conf. IITC/AMC 2014 2014, 173–176. (2) Wen, L. G.; Adelmann, C.; Pedreira, O. V.; Dutta, S.; Popovici, M.; Briggs, B.; Heylen, N.; Vanstreels, K.; Wilson, C. J.; Van Elshocht, S.; et al. Ruthenium Metallization for Advanced Interconnects. 2016 IEEE Int. Interconnect Technol. Conf. / Adv. Met. Conf. IITC/AMC 2016 2016, 34–36. (3) Wen, L. G.; Roussel, P.; Pedreira, O. V.; Briggs, B.; Groven, B.; Dutta, S.; Popovici, M. I.; Heylen, N.; Ciofi, I.; Vanstreels, K.; et al. Atomic Layer Deposition of Ruthenium with TiN Interface for Sub-10 Nm Advanced Interconnects beyond Copper. ACS Appl. Mater. Interfaces 2016, 8, 26119–26125. (4) Dutta, S.; Sankaran, K.; Moors, K.; Pourtois, G.; Van Elshocht, S.; Bömmels, J.; Vandervorst, W.; Tokei, Z.; Adelmann, C. Thickness Dependence of the Resistivity of Platinum-Group Metal Thin Films. J. Appl. Phys. 2017, 122, 025107, 1-11. (5) Varela Pedreira, O.; Croes, K.; Lesniewska, A.; Wu, C.; Van Der Veen, M. H.; De Messemaeker, J.; Vandersmissen, K.; Jourdan, N.; Wen, L. G.; Adelmann, C.; et al. Reliability Study on Cobalt and Ruthenium as Alternative Metals for Advanced Interconnects. IEEE Int. Reliab. Phys. Symp. Proc. 2017, 6B2.1-6B2.8. (6) Dutta, S.; Kundu, S.; Wen, L.; Jamieson, G.; Croes, K.; Gupta, A.; Bommels, J.; Wilson, C. J.; Adelmann, C.; Tokei, Z. Ruthenium Interconnects with 58 nm2 Cross-Section Area Using a Metal-Spacer Process. 2017 IEEE International Interconnect Technology Conference (IITC) 2017, 1–3. (7) Dutta, S.; Kundu, S.; Gupta, A.; Jamieson, G.; Gomez Granados, J. F.; Boemmels, J.; Wilson, C. J.; Tokei, Z.; Adelmann, C. Highly Scaled Ruthenium Interconnects. IEEE Electron Device Lett. 2017, 38, 949-951. (8) Dutta, S.; Moors, K.; Vandemaele, M.; Adelmann, C. Finite Size Effects in Highly Scaled Ruthenium Interconnects. IEEE Electron Device Lett. 2018, 39, 268–271. (9) Beyne, S.; Dutta, S.; Pedreira, O. V.; Bosman, N.; Adelmann, C.; De Wolf, I.; Tokei, Z.; Croes, K. The First Observation of P-Type Electromigration Failure in Full Ruthenium Interconnects. IEEE Int. Reliab. Phys. Symp. Proc. 2018, 2018–March, 6D.71-6D.79. (10) Hu, C. K.; Kelly, J.; Huang, H.; Motoyama, K.; Shobha, H.; Ostrovski, Y.; Chen, J. H. C.; Patlolla, R.; Peethala, B.; Adusumilli, P.; et al. Future On-Chip Interconnect Metallization and Electromigration. IEEE Int. Reliab. Phys. Symp. Proc. 2018, 2018–March, 4F.11-4F.16. (11) Puurunen, R. L. Surface Chemistry of Atomic Layer Deposition: A Case Study for the Trimethylaluminum/Water Process. J. Appl. Phys. 2005, 97, 121301, 1-52. (12) Miikkulainen, V.; Leskelä, M.; Ritala, M.; Puurunen, R. L. Crystallinity of Inorganic Films Grown by Atomic Layer Deposition: Overview and General Trends. J. Appl. Phys. 2013, 113, 021301, 1101. (13) Hämäläinen, J.; Ritala, M.; Leskelä, M. Atomic Layer Deposition of Noble Metals and Their Oxides. Chem. Mater. 2014, 26, 786–801. (14) Mackus, A. J. M.; Bol, A. A.; Kessels, W. M. M. The Use of Atomic Layer Deposition in Advanced Nanopatterning. Nanoscale 2014, 6, 10941-10960.

Page 6 of 17

(15) Mackus, A. J. M.; Merkx, M. J. M.; Kessels, W. M. M. From the Bottom-Up: Toward Area-Selective Atomic Layer Deposition with High Selectivity. Chem. Mater. 2019, 31, 2–12. (16) Kalanyan, B.; Lemaire, P. C.; Atanasov, S. E.; Ritz, M. J.; Parsons, G. N. Using Hydrogen To Expand the Inherent Substrate Selectivity Window During Tungsten Atomic Layer Deposition. Chem. Mater. 2016, 28, 117–126. (17) Lemaire, P. C.; King, M.; Parsons, G. N. Understanding Inherent Substrate Selectivity during Atomic Layer Deposition: Effect of Surface Preparation, Hydroxyl Density, and Metal Oxide Composition on Nucleation Mechanisms during Tungsten ALD. J. Chem. Phys. 2017, 146, 052811, 1-9. (18) Lu, J.; Elam, J. W.; Stair, P. C. Synthesis and Stabilization of Supported Metal Catalysts by Atomic Layer Deposition. Acc. Chem. Res. 2013, 46, 1806–1815. (19) Lu, J.; Low, K.-B.; Lei, Y.; Libera, J. A.; Nicholls, A.; Stair, P. C.; Elam, J. W. Toward Atomically-Precise Synthesis of Supported Bimetallic Nanoparticles Using Atomic Layer Deposition. Nat. Commun. 2014, 5, 3264, 1-9. (20) Lu, J.; Elam, J. W.; Stair, P. C. Atomic Layer Deposition Sequential Self-Limiting Surface Reactions for Advanced Catalyst “Bottom-up” Synthesis. Surf. Sci. Rep. 2016, 71, 410–472. (21) Cao, K.; Cai, J.; Liu, X.; Chen, R. Review Article: Catalysts Design and Synthesis via Selective Atomic Layer Deposition. J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 2018, 36, 010801, 1-12. (22) Park, K. J.; Doub, J. M.; Gougousi, T.; Parsons, G. N. Microcontact Patterning of Ruthenium Gate Electrodes by Selective Area Atomic Layer Deposition. Appl. Phys. Lett. 2005, 86 , 051903, 13. (23) Färm, E.; Kemell, M.; Ritala, M.; Leskela, M. Selective-Area Atomic Layer Deposition Using Poly ( Methyl Methacrylate ) Films as Mask Layers. J. Phys. Chem. 2008, 112, 15791–15795. (24) Färm, E.; Kemell, M.; Santala, E.; Ritala, M.; Leskelä, M. Selective-Area Atomic Layer Deposition Using Poly(Vinyl Pyrrolidone) as a Passivation Layer. J. Electrochem. Soc. 2010, 157, K10-K14. (25) Färm, E.; Lindroos, S.; Ritala, M.; Leskelä, M. Microcontact Printed RuO x Film as an Activation Layer for Selective-Area Atomic Layer Deposition of Ruthenium. Chem. Mater. 2012, 24, 275–278. (26) Zyulkov, I.; Krishtab, M.; De Gendt, S.; Armini, S. Selective Ru ALD as a Catalyst for Sub-Seven-Nanometer Bottom-Up Metal Interconnects. ACS Appl. Mater. Interfaces 2017, 9, 31031–31041. (27) Junige, M.; Löffler, M.; Geidel, M.; Albert, M.; Bartha, J. W.; Zschech, E.; Rellinghaus, B.; van Dorp, W. F. Area-Selective Atomic Layer Deposition of Ru on Electron-Beam-Written Pt(C) Patterns versus SiO2 Substratum. Nanotechnology 2017, 28, 395301, 1-10. (28) Khan, R.; Shong, B.; Ko, B. G.; Lee, J. K.; Lee, H.; Park, J. Y.; Oh, I.-K.; Raya, S. S.; Hong, H. M.; Chung, K.-B.; et al. Area-Selective Atomic Layer Deposition Using Si Precursors as Inhibitors. Chem. Mater. 2018, 30, 7603–7610. (29) Bobb-Semple, D.; Nardi, K. L.; Draeger, N.; Hausmann, D. M; Bent, S. F. Area Selective Atomic Layer Deposition Assisted by SelfAssembled Monolayers: A Comparison of Cu, Co, W and Ru. Chem. Mater. 2019, DOI: 10.1021/acs.chemmater.8b04926. (30) Minjauw, M. M.; Dendooven, J.; Capon, B.; Schaekers, M.; Detavernier, C. Atomic Layer Deposition of Ruthenium at 100 °C Using the RuO4-Precursor and H2. J. Mater. Chem. C 2015, 3, 132– 137. (31) Minjauw, M. M.; Dendooven, J.; Capon, B.; Schaekers, M.; Detavernier, C. Near Room Temperature Plasma-Enhanced Atomic Layer Deposition of Ruthenium Using the RuO4-Precursor and H2Plasma. J. Mater. Chem. C 2015, 3, 4848–4851. (32) Dendooven, J.; Solano, E.; Minjauw, M. M.; Van de Kerckhove, K.; Coati, A.; Fonda, E.; Portale, G.; Garreau, Y.; Detavernier, C. Mobile Setup for Synchrotron Based in Situ Characterization during Thermal and Plasma-Enhanced Atomic Layer Deposition. Rev. Sci. Instrum. 2016, 87, 113905, 1-10. (33) McGahan, W. A.; Johs, B.; Woollam, J. A. Techniques for Ellipsometric Measurement of the Thickness and Optical Constants of Thin Absorbing Films. Thin Solid Films 1993, 234, 443–446.


Page 7 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(34) Knaut, M.; Junige, M.; Albert, M.; Bartha, J. W. In-Situ RealTime Ellipsometric Investigations during the Atomic Layer Deposition of Ruthenium: A Process Development from [(Ethylcyclopentadienyl)(Pyrrolyl)Ruthenium] and Molecular Oxygen. J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 2012, 30, 01A151, 1-9. (35) Nguyen, H. V.; An, I.; Collins, R. W. Evolution of the Optical Functions of Aluminum Films during Nucleation and Growth Determined by Real-Time Spectroscopic Ellipsometry. Phys. Rev. Lett. 1992, 68, 994–997. (36) Norrman, S.; Andersson, T.; Granqvist, C. G.; Hunderi, O. Optical Properties of Discontinuous Gold Films. Phys. Rev. B 1978, 18, 674–695. (37) Lee, S.; Hong, J.; Oh, S. Real-Time Ellipsometry Studies of Gold Thin-Film Growth. Jpn. J. Appl. Phys. 1997, 36, 3662–3668. (38) Yano, M.; Fukui, M.; Haraguchi, M.; Shintani, Y. In Situ and Real-Time Observation of Optical Constants of Metal Films during Growth. Surf. Sci. 1990, 227, 129–137. (39) Tompkins, H. G.; Tasic, S.; Baker, J.; Convey, D. Spectroscopic Ellipsometry Measurements of Thin Metal Films. Surf. Interface Anal. 2000, 29, 179–187. (40) Jiang, X.; Wang, H.; Qi, J.; Willis, B. G. In-Situ Spectroscopic Ellipsometry Study of Copper Selective-Area Atomic Layer Deposition on Palladium. J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 2014, 32, 041513, 1-10. (41) NIST X-ray Photoelectron Spectroscopy Database, NIST Standard Reference Database Number 20, National Institute of Standards and Technology, Gaithersburg MD, 20899 (2000), doi: 10.18434/T4T88K, (retrieved 26th june 2018). (42) Rijckaert, H.; Pollefeyt, G.; Sieger, M.; Hänisch, J.; Bennewitz, J.; De Keukeleere, K.; De Roo, J.; Hühne, R.; Bäcker, M.; Paturi, P.; et al. Optimizing Nanocomposites through Nanocrystal Surface Chemistry: Superconducting YBa2Cu3O7 Thin Films via LowFluorine Metal Organic Deposition and Preformed Metal Oxide Nanocrystals. Chem. Mater. 2017, 29, 6104–6113. (43) Soethoudt, J.; Grillo, F.; Marques, E. A.; van Ommen, J. R.; Tomczak, Y.; Nyns, L.; Van Elshocht, S.; Delabie, A. DiffusionMediated Growth and Size-Dependent Nanoparticle Reactivity during Ruthenium Atomic Layer Deposition on Dielectric Substrates. Adv. Mater. Interfaces 2018, 5, 1800870, 1-11. (44) Langereis, E.; Heil, S. B. S.; Knoops, H. C. M.; Keuning, W.; van de Sanden, M. C. M.; Kessels, W. M. M. In Situ Spectroscopic Ellipsometry as a Versatile Tool for Studying Atomic Layer Deposition. J. Phys. D. Appl. Phys. 2009, 42, 073001, 1-19. (45) Wang, H.; Jiang, X.; Willis, B. G. Real-Time Spectroscopic Ellipsometric Investigation of Adsorption and Desorption in Atomic Layer Deposition: A Case Study for the Strontium Bis(TriIsopropylcyclopentadienyl)/Water Process. J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 2012, 30, 01A133, 1-5. (46) Wang, H.; Fu, K. Nucleation and Growth of MgO Atomic Layer Deposition: A Real-Time Spectroscopic Ellipsometry Study. J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 2013, 31, 06F101, 1-4. (47) Muneshwar, T.; Cadien, K. Probing Initial-Stages of ALD Growth with Dynamic in Situ Spectroscopic Ellipsometry. Appl. Surf. Sci. 2015, 328, 344–348.

(48) Hattori, T. High Resolution X-Ray Photoemission Spectroscopy Studies of Thin SiO2 and Si/SiO2 Interfaces. J. Vac. Sci. Technol. B Microelectron. Nanom. Struct. 1993, 11, 1528-1532. (49) Morgan, D. J. Resolving Ruthenium: XPS Studies of Common Ruthenium Materials. Surf. Interface Anal. 2015, 47, 1072–1079. (50) Plietker, B. Selectivity versus Reactivity - Recent Advances in RuO4-Catalyzed Oxidations. ChemInform 2006, 37, 2453–2472. (51) Piccialli, V. Ruthenium Tetroxide and Perruthenate Chemistry. Recent Advances and Related Transformations Mediated by Other Transition Metal Oxo-Species. Molecules 2014, 19, 6534–6582. (52) Geidel, M.; Knaut, M.; Albert, M.; Bartha, J. W. In Situ XPS Investigation of the Chemical Surface Composition during the ALD of Ultra-Thin Aluminum Oxide Films. IEEE 2011 Semiconductor Conference Dresden, 2011, 1–4. (53) Van Der Voort, P.; Vansant, E. F. Silylation of the Silica Surface A Review. J. Liq. Chromatogr. Relat. Technol. 1996, 19, 2723–2752. (54) Goldstein, D. N.; George, S. M. Enhancing the Nucleation of Palladium Atomic Layer Deposition on Al2O3 Using Trimethylaluminum to Prevent Surface Poisoning by Reaction Products. Appl. Phys. Lett. 2009, 95, 143106, 1-3. (55) Goldstein, D. N.; George, S. M. Surface Poisoning in the Nucleation and Growth of Palladium Atomic Layer Deposition with Pd(Hfac)2 and Formalin. Thin Solid Films 2011, 519, 5339–5347. (56) Hwang, Y.; Nguyen, B.-M.; Dayeh, S. A. Atomic Layer Deposition of Platinum with Enhanced Nucleation and Coalescence by Trimethylaluminum Pre-Pulsing. Appl. Phys. Lett. 2013, 103, 263115, 1-5. (57) Van Daele, M.; Detavernier, C.; Dendooven, J. Phys. Chem. Chem. Phys. 2018, 20, 25343-25356. (58) Puurunen, R. L.; Vandervorst, W. Island Growth as a Growth Mode in Atomic Layer Deposition: A Phenomenological Model. J. Appl. Phys. 2004, 96, 7686–7695. (59) Gatineau, J.; Yanagita, K.; Dussarrat, C. A New RuO4 Solvent Solution for Pure Ruthenium Film Depositions. Microelectron. Eng. 2006, 83, 2248–2252. (60) Kukli, K.; Ritala, M.; Kemell, M.; Leskelä, M. High Temperature Atomic Layer Deposition of Ruthenium from N,NDimethyl-1-Ruthenocenylethylamine. J. Electrochem. Soc. 2010, 157, D35-D40. (61) Kukli, K.; Kemell, M.; Puukilainen, E.; Aarik, J.; Aidla, A.; Sajavaara, T.; Laitinen, M.; Tallarida, M.; Sundqvist, J.; Ritala, M.; et al. Atomic Layer Deposition of Ruthenium Films from (Ethylcyclopentadienyl)(Pyrrolyl)Ruthenium and Oxygen. J. Electrochem. Soc. 2011, 158, D158-D165. (62) Kukli, K.; Aarik, J.; Aidla, A.; Jõgi, I.; Arroval, T.; Lu, J.; Sajavaara, T.; Laitinen, M.; Kiisler, A.-A.; Ritala, M.; et al. Atomic Layer Deposition of Ru Films from Bis(2,5Dimethylpyrrolyl)Ruthenium and Oxygen. Thin Solid Films 2012, 520, 2756–2763.


Ψ (515 nm)

80


PageSiO 8 of2 17 Si-H

60

1 2 40 3 4 20 5 6 0 7 0 8 9

ACS Paragon Plus Environment 50

100

# cycles

150

200

EDX 9integrated peak intensity Page of 17 Chemistry of Materials

1 2 3 4 5 6 7 8 9 10 11 12 13

RuL OK SiK Electron beam track

Si

SiO2

ACS Paragon Plus Environment 50 µm

(a)

Chemistry of Materials Page 10 of 17 Pt SiO2

Ru 1 2 3 4 (b) 5 6 7 8 9 10 11 12 13

Si

100 nm

(c)

Ru

Ru

SiO2

ACS Paragon Plus Environment Si

10 nm

Si

10 nm

(a)

no deposition

Page 11 of 17 Chemistry of Materials SiO2

1 2 (b) 3 4 5 6

O

O Si

O

RuO4

SiO2

O

O

O

Si

O O H HACS H HParagon Plus Environment SiO2 RuO4 Si Si

O

RuO2


Si2p

O1s

Si2p

O1s

Ru3p

110

105

100

95

540

535

530

525

110

Binding energy (eV)

Binding energy (eV)

200eV

105

100

95

200eV

540

Binding energy (eV)

535

CPS (a.u.)

RuO4

CPS (a.u.)

200eV

CPS (a.u.)

200eV

CPS (a.u.)

CPS (a.u.)

(a)

530

525

200eV

500 490 480 470 460 450

Binding energy (eV)

Binding energy (eV)

110

105

100

95

Binding energy (eV)

RuO4

540

535

530

525

Binding energy (eV)

20eV

110

105

100

95

Binding energy (eV)


20eV

540

535

CPS (a.u.)

20eV

CPS (a.u.)

CPS (a.u.)

20eV

CPS (a.u.)

(b) CPS (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 17

530

525

Binding energy (eV)

200eV

500 490 480 470 460 450

Binding energy (eV)

Ψ (515 nm)

Page 8013 of 17 Chemistry of Materials 60

1 2 40 3 4 20 5 6 0 7 0 8 9

SiO₂ TMA TMA + O2*

ACS Paragon Plus Environment 50

100

# cycles

150

200

(a)

no deposition Chemistry of Materials Page 14 of 17

SiO2

1 2 3 4 (b) 5 6 H3C 7SiO2 8 9 10 (c) 11 12 13SiO 2 14

Si

RuO4

SiO2

RuO4

SiO2

Si

TMA

CH3 CH3 Al CH3 Al Si

RuO2 Si

O2 * no deposition


O Al Si

RuO4

SiO2

O Al Si

Page 15 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30



Chemistry of Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Page 16 of 17

ref. [60] ref. [61] Si-H ref. [61] SiO2 ref. [62]


{

O

}

ALD

Page 17 of 17OChemistry Ru O + H2 of Materials O

SiO2

SiO2 Si

"Area-selective Ru ALD"

1 SiO2 SiO2 Si 2 3 4 SiO2 ACS Paragon Plus Environment H5 CH3 O 3C Si ALD Al 6 CH + O Ru O + H2 3

{

O

}

SiO2

"Ru on everything"

Nucleation Enhancement and Area-Selective ... - ACS Publications

Recommend Documents