The present application pertains to the field of vapour phase deposition.
Self-assembled monolayers (SAMs) on metals have potential application in sensing, electrochemistry, drug delivery, surface protection, microelectronics and microelectromechanical systems. SAMs of carbon-based ligands known as N-heterocyclic carbenes (NHCs) have been studied (see Crudden, C. M., et al., Nature Chemistry 2014, 6, 409).
NHCs have played a significant role in the field of transition metal complexes. Unlike most carbenes, which are reactive with limited stability, NHCs typically have one or two heteroatoms adjacent to a carbene carbon. These heteroatoms increase NHCs' stability such that they can usually be prepared on a gram scale, crystallized or distilled, and stored for long periods of time (4 years, when stored under N2 in a freezer). An Au—NHC bond is estimated to be on an order of 90 kJ/mol stronger than a corresponding Au-phosphine bond, and twice as strong as metal sulfide bonds in molecular complexes [P. Pyykkö, et al. Chem. Asian J. 1, 623 (2006)]. As such, NHCs have potential to be valuable ligands for protecting and functionalizing gold and other metal substrates and/or surfaces.
Mobile phones, computers and all modern communications infrastructure derive function from microprocessors manufactured with integrated circuits containing thousands to billions of transistors. As device size decreases, so must the size of microprocessors, creating extreme manufacturing and design challenges. Modern integrated circuits are manufactured in three dimensions by depositing alternating conducting and insulating layers in a 3D arrangement to achieve maximum function in minimum size. Complex masking, depositing, and etching steps are needed to generate these 3D patterns. As sizes become smaller, mask misalignment and pinhole defects lead to significant performance losses. Area selective atomic layer deposition (AS-ALD) is a promising alternative for device construction, in which molecules are employed to mask substrates and/or surfaces. Molecular arrangement is achieved through the principles of self-assembly and preferential binding (i.e., the use of molecules that bind selectively to metals or to insulators). This technique allows patterning over large areas. It can theoretically produce patterns with molecular-level precision if sufficiently selective binding is achieved and the patterns are stable during the manufacturing process (Franzen, S., Chemical Physics Letters 2003, 381, 315, and Vericat, C., et al. Physical Chemistry Chemical Physics 2005, 7, 3258). Ligands that bind to metals and survive harsh manufacturing conditions are challenging to find.
In one aspect the invention provides a method of selective deposition, comprising disposing a patterned substrate in a deposition chamber, wherein the patterned substrate comprises a metal surface, and a non-metal or metal oxide surface, and wherein the deposition chamber comprises a valve-controlled inlet for a carrier gas, a furnace, wherein the carrier gas has valve-controlled access to a bubbler that contains an NHC precursor, heating and maintaining the bubbler at a sufficiently high temperature to generate gaseous free carbene that collects in a headspace of the bubbler, intermittently pulsing carrier gas that includes gaseous NHC into the heated deposition chamber and purging the deposition chamber with carrier gas, and wherein the NHC selectively chemisorbs onto the metal surface, and substantially no NHC chemisorbs onto the non-metal or metal oxide surface.
In one aspect, the invention provides a method of deposition, comprising disposing a substrate in a deposition chamber, wherein the substrate comprises at least a metal surface, and wherein the deposition chamber comprises a valve-controlled inlet for a carrier gas, and wherein the carrier gas has valve-controlled access to a bubbler that contains an NHC precursor, heating and maintaining the bubbler at a sufficiently high temperature to generate gaseous free carbene that collects in a headspace of the bubbler, intermittently pulsing carrier gas that includes gaseous NHC into the deposition chamber and purging the deposition chamber with carrier gas, and wherein the NHC chemisorbs onto the metal surface.
In one embodiment of the above aspects, the pulsing is opening the gas inlet valve for a selected time for a selected number of cycles. In one embodiment the number of cycles is about 100. In one embodiment the cleaning the metal surface comprises exposing it to hot plasma. In one embodiment, the hot plasma is a plasma of H2 at about 400° C. In one embodiment, the metal surface is a monolayer. In one embodiment, the metal surface is thick enough to exhibit bulk properties. In one embodiment, the metal is thick enough to exhibit bulk properties. In one embodiment, the metal surface is between 0.5 to 1 000 nm thick. In one embodiment, the metal is between 0.5 to 1 000 nm thick. In one embodiment, the metal surface is between 25 and 150 nm thick. In one embodiment, the metal is between 25 and 150 nm thick. In one embodiment, the metal surface is about 100 nm thick. In one embodiment, the metal is about 100 nm thick. In one embodiment the selected deposition temperature is in a range of about room temperature to about 500° C. In one embodiment, the selected deposition temperature is in a range of about 30 to about 200° C. In one embodiment, the deposition chamber is suitable for holding wafers. In one embodiment, the deposition chamber maintains a vacuum in a range of about 0.1 torr to about 5 torr. In one embodiment, the deposition chamber maintains a vacuum of about 3 torr. In one embodiment, the carrier gas is nitrogen or argon. In one embodiment, the nitrogen is 99% pure. In one embodiment, the nitrogen is 99.999% pure. In one embodiment, the purging the deposition chamber with carrier gas is performed for about 20 seconds. In one embodiment, the NHC chemisorbs onto the metal surface as a monolayer. In one embodiment, the NHC chemisorbs onto the metal surface as a bilayer. In one embodiment, the NHC chemisorbs onto the metal surface as a multilayer. In one embodiment, the method includes a step of cooling the deposition chamber to room temperature while continuously purging the deposition chamber with carrier gas. In one embodiment, the cooling and purging are conducted for 1 hour. In one embodiment, the method further comprises purging the deposition chamber with carrier gas. In one embodiment, the non-metal or metal oxide is a dielectric. In one embodiment, the non-metal or metal oxide comprises SiO2, Si3N4, Al2O3, SiwOxNy wherein w is 0 to 3, x is 0 to 2 and y is 0 to 4, HfO2, or any combination thereof.
In one embodiment, the method further includes removal of the NHC by thermal desorption to regenerate a pristine metal surface. In one embodiment, the NHC is 1,3-dialkylbenzimidazol-2-ylidene, where the alkyl is a C1-C6 aliphatic moiety that is branched or linear. Non-limiting examples of such NHCs include: 1,3-diisopropylbenzimidazol-2-ylidene (1iPr), 1,3-diisopropyl-5-(trifluoromethyl)benzimidazol-2-ylidene (1iPr-CF3); 1,3-ditertbutylbenzimidazol-2-ylidene (2tBu); and 1,3-diethylbenzimidazol-2-ylidene (3Et), see Table 1. In one embodiment, the metal surface comprises Au, Cu, Ag, Ru, W, Ni, Fe, Mo, Co, Pt, Pd, or alloys such as bronze and steel. In one embodiment, the metal surface of a patterned substrate comprises Au, Cu, Ag, Ru, W, Ni, Fe, Mo, Co, Pt, Pd, or alloys such as bronze and steel. In one embodiment, the metal surface of the substrate comprises Au, Cu, Ag, Ru, W, Ni, Fe, Mo, Co, Pt, Pd, or alloys such as bronze and steel. In one embodiment, the NHC precursor is a salt of NHC. In one embodiment, the NHC precursor is a bicarbonate salt. In one embodiment, the NHC precursor is a carbonate salt of NHC. In one embodiment, the NHC precursor is an azolium carboxylate zwitterion. In one embodiment, the NHC precursor is an alkylcarboxylate salt of NHC. where alkyl is an aliphatic moiety (e.g, methyl, ethyl, propyl). In one embodiment, the NHC precursor is an arylcarboxylate salt of NHC, where aryl is an aromatic moiety (e.g, phenyl, tolyl, etc.). In one embodiment, the NHC precursor is a salt of NHC that comprises an anion selected from the group consisting of bicarbonate, carbonate, halide, triflate, pseudohalide, cyanide, and azide. In one embodiment, the method further includes a step of treating the substrate to refine the interface between the metal surfaces, and the non-metal or metal oxide surfaces. In one embodiment, the treating the substrate comprises thermal annealing or plasma treatment. In one embodiment, the NHC precursor is a salt of 1iPr; a salt of 1iPr-CF3; a salt of 2tBu; or a salt of 3Et.
In one embodiment, the method further includes cleaning the substrate prior to the deposition of NHC. In one embodiment, the method further includes modifying the temperature of the deposition chamber to a selected deposition temperature if the deposition temperature differs from a temperature of cleaning. In one embodiment, the method further includes evacuating the deposition chamber such that it is under vacuum prior to the deposition of NHC. In one embodiment, the method further comprises annealing the substrate after NHC deposition.
For a better understanding of the invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, wherein:
As used herein, a “metal” is any of a class of substances characterized by high electrical and thermal conductivity as well as by malleability, ductility, and high reflectivity of light.
As used herein, the terms “physisorb” “physisorption” or “physical adsorption” mean adsorption in which the forces involved are intermolecular forces (e.g., van der Waals forces).
As used herein, the terms “chemisorb” or “chemical adsorption” mean adsorption in which the forces involved are valence forces of the same kind as those operating in the formation of chemical compounds.
As used herein, the term “dielectric material” means a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic fields (i.e., insulator).
Organic ligands called N-heterocyclic carbenes (NHCs) have been investigated in AS-ALD processes described herein. NHCs have been shown to form strong bonds to many metal surfaces, including Au, Cu, Ag, Ru, W, Ni, Fe, Mo, Co, Pt and Pd, and alloys such as bronze and steel (see Crudden, C. M., et al., Nature Chemistry 2014, 6, 409, and Crudden, C. M., et al., U.S. Patent Application Publication No. 20160199875). These robust molecules protect metal surfaces and provide a solution to the challenges of electronic device manufacturing.
A metal surface refers to a metallic portion of a substrate, that is accessible to vapor deposition. The metallic portion may be the accessible layer of a bulk metal, or it may be a metallic coating that is located on a support. The support can be made of another substance such as a different metal than the metal of the metallic coating, or a non-metal such as silicon, indium tin oxide (ITO), alumina (Al2O3), glass, etc.
NHCs can be used as removable small molecule masks (i.e., films, coatings) and inhibitors to prevent deposition of other materials. As described herein, NHCs have been shown to bind selectively to metal surfaces in the presence of non-metal or metal oxide materials. Examples of metals include, but are not limited to Au, Cu, Ag, Ru, W, Ni, Fe, Mo, Co, Pt and Pd, and alloys such as bronze and steel. Examples of non-metal surfaces or metal oxide surfaces include SiO2, Si3N4, Al2O3, SiwOxNy wherein w is 0 to 3, x is 0 to 2 and y is 0 to 4, HfO2, or any combination thereof.
Among methods for device fabrication, organic molecules that chemisorb selectively to metal surfaces have led to the development of this method of small molecule inhibitors for selective area deposition. In this approach, the small molecule coating acts as protecting groups such that the metal is protected from reaction with unwanted entities. Examples of reactive entities that have been used to test the durability of the NHC coating, are trimethylaluminum (TMA), triethylaluminium (TEA) and diethylzinc (DEZ), which were used to deposit aluminum oxide or zinc oxide on metal after exposure to water as a co-reactant. In the absence of a protective surface film, these species and water react with metal to form a metal oxide coating. In selective area deposition, an organic surface species (i.e., surfactant) acts as an inhibition layer during dielectric deposition and growth. This technique is functionally simple, allows patterning over large areas, and can maintain the picometer scale resolution that atomic layer deposition (ALD) is known for.
A method of deposition is provided that includes placing a substrate, which had at least a metal surface, in a deposition chamber. The deposition chamber includes a valve-controlled inlet for carrier gas. The carrier gas had valve-controlled access to a bubbler that contained an NHC precursor (e.g., a salt of NHC). The salt of NHC has an anionic counterion that can be selected from the group consisting of bicarbonate, carbonate, alkylcarboxylate, arylcarboxylate, carboxylate, halide, triflate, pseudohalide (e.g., cyanide, azide), etc. Such salts form a stable precursor form of the NHC. In the examples herein, a description is provided of thermolysis of shelf stable benzimidazolium or imidazolium bicarbonate salts to generate a carboxylate adduct through a dehydration reaction, and then generation of a free carbene through a decarboxylation reaction (see Table 1 for structural formulae).
In some embodiments, the substrate was cleaned (e.g., by hot plasma) before deposition of the small molecule layer. If necessary, the temperature of the deposition chamber can be modified from a cleaning temperature to a selected deposition temperature. The bubbler containing the NHC precursor was then heated and maintained at a sufficiently high temperature to generate gaseous free carbene that collected in a headspace of the bubbler. At this point, intermittently and repeatedly, carrier gas, which included gaseous NHC, was pulsed into the deposition chamber (e.g., for about 60 seconds). After each pulse, the deposition chamber was purged with carrier gas (e.g., for about 20 seconds). Once approximately 100 pulses had been performed, the deposition chamber was allowed to cool to room temperature while being continuously purged with carrier gas. Purging the deposition chamber with carrier gas was performed to substantially remove physisorbed species. Using this method, NHC chemisorbed onto the metal surface in a self-saturating manner.
In a selective deposition process, a method of deposition is provided that includes disposing a patterned substrate in a deposition chamber, the patterned substrate has a metal surface, and a non-metal or metal oxide surface. The deposition chamber included a valve-controlled inlet for carrier gas. The carrier gas had valve-controlled access to a bubbler that contained an NHC precursor (e.g., a bicarbonate salt of NHC, alkylcarboxylate salt of NHC, an arylcarboxylate salt of NHC, or a carboxylate salt of NHC). In some embodiments, the substrate had been cleaned (e.g., by hot plasma) prior to exposure to NHC vapors. If necessary, the temperature of the deposition chamber can be modified from a cleaning temperature to a selected deposition temperature. The bubbler containing the NHC precursor was then heated and maintained at a sufficiently high temperature to generate gaseous free carbene that collected in a headspace of the bubbler. At this point, intermittently and repeatedly, carrier gas, which included gaseous NHC, was pulsed into the deposition chamber (e.g., for about 60 seconds). After each pulse, the deposition chamber was purged with carrier gas (e.g., for about 20 seconds). Once approximately 100 pulses had been performed, the deposition chamber was allowed to cool to room temperature while being continuously purged with carrier gas. Purging the deposition chamber with carrier gas was performed to remove physisorbed species. Using this method, NHC chemisorbed onto the metal surface in a self-saturating manner and substantially no NHC chemisorbed onto the non-metal or metal oxide surface.
Designing metallic patterns on integrated circuits could change the way semiconductors are manufactured. Such patterns would enable smaller features and better performance.
Traditional device fabrication techniques involve top-down strategies composed of multiple cycles of etching and lithographic steps. As device miniaturization progresses, the errors associated with top-down fabrication methods become problematic and new strategies are needed. Area-selective atomic layer deposition (AS-ALD) is a promising fabrication technique which relies on differences in local surface environment.
In one embodiment, a further step was performed of treating the substrate to refine the interface between the metal surfaces, and the non-metal or metal oxide surfaces. Examples of such treating include thermal annealing, and plasma treatment. See
NHCs can be cleanly removed after use by thermal desorption to afford pristine metallic surfaces. Therefore, NHCs are ideal candidates for passivating patterned substrates in AS-ALD.
As described herein, exemplary NHCs, 1,3-diisopropylbenzimidazolylidene (1iPr) and 1,3-ditertbutyllbenzimidazolylidenes (2tBu), were deposited on Ag, Cu, Co, W, Fe, Mo and Ru in an ALD Tool (see the Working Examples). Film quality of the resultant film was assessed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectrometry (ToF-SIMS) experiments. Further studies on patterned substrates found that it was possible to deposit NHCs on metal surfaces selectively, in the presence of non-metal, metal oxide, or dielectric surfaces. Specifically, 1iPr and 2tBu were successfully selectively deposited on the metal areas of patterned substrates bearing side-by-side areas of exemplary metals (e.g, Cu, Ru, or Co), and exemplary dielectric (e.g., SiO2 or Al2O3) surfaces. Successful deposition of 1iPr and 2tBu was determined by XPS and ToF-SIMS analyses. The patterned substrates had alternating lines of metal surface (Cu, Co or Ru) and dielectric surface. Separate substrates were used for each of these three metals. This method of selective deposition of patterned substrates is described herein.
A series of experiments utilizing a tube furnace reactor equipped with a quartz crystal microbalance (QCM) was performed to help probe the optimal conditions for various NHCs to be deposited, using crystals coated with optically-polished Au films as a standard (see
Parameters, such as the pulse time for introducing the NHC and the “soak” time to help ensure full coverage were optimized. However, these experiments, while useful in determining essential parameters in tandem with XPS, were often qualitative in their determination of full surface coverage. Analysis by ToF-SIMS was used to optimize the deposition parameters.
Referring to
Referring to
Deposition properties were analyzed by changing the wingtips to ethyl groups, resulting in 1,3-diethylbenzimidazolylidene (3Et). It was previously shown that NHC ligands with ligands bearing primary wing groups tend to lie flat on surfaces (C. R. Larrea, Chem Phys Chem., 2017, 18, 3536-3539). This is in contrast to NHCs having secondary or tertiary wingtip groups such as 1iPr and 2tB which have been shown to stand in upright positions on surfaces (C. R. Larrea, Chem Phys Chem., 2017, 18, 3536-3539). This upright coverage has use in specific surface applications, including selective area deposition as described here, and in all kinds of device manufacturing and sensing (I. Singh, et al., 2021, Chem. Comm. 57, 8421-8424).
Referring to
For both 1iPr and 2tBu, plateaus or changed in growth behaviour were observed partway through their saturation experiments. Changes in growth behaviour may be responsible due to changes in NHC packing structure as the surface became more populated by surfactants.
To understand selective deposition of the NHCs on patterned metal surfaces, ToF-SIMS imaging was employed. ToF-SIMS provides mass spectrometry. Masses can be correlated to species within the system. After functionalizing patterned substrates with NHCs, surfaces were imaged by probing for different possible ions that could be observed. These images show ejected Si+ from areas that were expected to be composed of SiO2, and M+ ions in samples (Co, Cu, or Ru) in metal areas. Referring to
The ToF-SIMS data confirmed that substrate patterning was obtained and that the NHC preferentially chemisorbed to the Ru, Co and Cu metal surfaces in the presence of the silicon oxide dielectric layer, and substantially no NHC was present on the dielectric surface of each sample.
Evidence of NHC deposition on metallic regions was provided by the presence of the molecular ion of the NHC ligand on the ToF-SIMS images shown by the far-right of
With Cu, the NHC was more distributed, which may be related to the pre-cleaning process since the Cu to Si distribution was less well defined, suggesting migration of the metal to Si during cleaning.
To enhance visualization of where the NHC was deposited, a synthesis was developed of a modified NHC, which was readily detectable by XPS. Namely, 1iPr-CF3 was synthesized, wherein a CF3 group is located on the aromatic backbone of the NHC. Referring to
To further examine the effect of the NHC on patterned surfaces, a mixed SiO2/Co sample was prepared, exposed to NHC as described herein, and then was annealed at 170° C. for 12 hours. As shown in
Referring to
In the case of 2tBu (
In the case of the 3Et TMA durability test (
Referring to
Referring to
Referring to
Referring to
Referring to
Vapour pressure and thermal stability of NHCs 1iPr and 2tBu have been measured and found to be low enough to be introduced into the ALD chamber at room temperature. This facilitates deposition, and lowers cost. NHC monolayers of 1iPr have been prepared on copper substrates by room temperature pulses of 10 seconds each, delivering up to 240 μg of NHC/s, which is considerably more than required for industry processes.
The following working examples further illustrate the invention and are not intended to be limiting in any respect.
All synthetic reactions were conducted under air unless otherwise stated. Solvents were used without purification except where stated. Unless otherwise noted, chemicals were purchased from chemical suppliers at highest purity and used as received. N2 was 99.999% pure unless stated otherwise and was available from Praxair. Amberlyst A26 hydroxide resin was activated by sparging a solution with CO2 for 30 minutes before use as the HCO3 resin. 1H and 13C{1H} NMR spectra were recorded at Queen's University using Bruker Avance-400 or 700 MHz spectrometers at 298 K. Chemical shifts (δ) are reported in parts per million (ppm) and are internally referenced to residual protonated (1H) or deuterated (13C{1H}) solvent signals, which are themselves set relative to Si(CH3)4. Chemical shifts of known solvent impurities were referenced to the literature. Coupling constants (J) are reported in Hz as absolute values. All NMR data were processed and displayed using Bruker TopSpin or MestReNova software programs. Elemental analyses were performed at Queen's University using Flash 2000 CHNS—O analyzer. Electrospray ionization mass spectra (ESI-MS) of small molecules were recorded at Queen's University using a Thermo Fisher Orbitrap VelosPro mass spectrometer with a heated-electrospray ionization probe.
XPS spectra were recorded on a Kratos Nova AXIS spectrometer equipped with AIN X-ray source. Samples were mounted on an aluminum sample holder using double-sided adhesive copper tape and kept under high vacuum (10−8 Torr) overnight inside the preparation chamber before being transferred to the analysis chamber (ultra-high vacuum, 10−10 Torr).
Data were collected using Al Kα radiation operating at 1486.69 eV (150 W, 15 kV), charge neutralizer and a delay-line detector (DLD) consisting of three multichannel plates. Acquired data were processed using CasaXPS software following reference handbooks. Processed data were plotted in Python using Matplotlib package. Elemental compositions of samples were evaluated by running widescan at 160 eV pass energy. After peak identification, high resolution scans were performed for O 1 s, C 1 s, N 1 s, and substrate of interest regions. These scans were performed at 20 eV pass energy. C 1 s spectra were peak fitted following guidelines from reference handbooks and C—C/C—H peak was charge corrected to 248.8 eV. Unless otherwise mentioned, a Shirley type background correction was used for all spectra shown here.
Deposition and characterization studies of the resultant films (e.g., XPS, ToF-SIMS) were conducted. Depositions were carried out in a standard Picosun R200 thermal ALD tool. Depositions were standard pulse-purge cycles (e.g, 100 cycles; 10 s pulse NHC, 10 s N2 purge, with various substrates. Durability studies of monolayer deposition films were conducted a custom thermal ALD tool (see
5-(Trifluoromethyl)-1H-benzimidazolylidene: Synthesis of 5-(trifluoromethyl)-1H-benzimidazolylidene was modified from a published procedure of a similar compound.7 2-nitro-4-trifluoromethylaniline (5.000 g, 24.25 mol, 1 eq.) and ammonium chloride (12.97 g, 242.5 mol, 10 eq.) were dissolved in 2-propanol (160 mL). Iron powder (13.54 g, 242.5 mol, 10 eq) was added followed slow addition of Formic acid (190 mL). The reaction mixture was heated to 80° C. for 3 hours. Following, the reaction mixture was then filtered and concentrated to dryness. Saturated sodium bicarbonate solution was added to the flask until a pH of 6 was reached. Aqueous solution was extracted with ethyl acetate (3×50 mL) and the organic layers were dried over sodium sulfate. The organic layer was filtered, and volatiles removed by rotatory evaporation. An off-white solid was obtained after drying under vacuum. (78%, 3.450 g)
1H NMR (CDCl3, 300 MHz): δ 8.4 (s, 1H) 8.2 (s, 1H), 7.9 (s, 1H), 7.7 (d, J=8.1 Hz, 1H), 7.5 (d, J=8.2 Hz, 1H). 19F NMR (CDCl3, 500 MHz): δ −60.2.
1,3-Diisopropyl-5-(trifluoromethyl)-1H-benzimidazolium iodide: Synthesis of 1,3-diisopropyl-5-(trifluoromethyl)-1H-benzimidazolium iodide was modified from a published procedure of a similar compound (Crudden, C. M., et al., U.S. Patent Application Publication No. 20160199875). Cesium carbonate (1.925 g, 26.86 mol, 1.1 eq) and 5-(trifluoromethyl)-1H-benzimidazolylidene (1.000 g, 5.373 mol, 1 eq.) were stirred in acetonitrile (25 mL) under argon atmosphere. 2-Iodopropane (4.566 g, 26.86 mol, 5 eq.) was added via syringe and the reaction was heated to 90° C. for 2 days. After the reaction mixture was allowed to cool and volatiles were removed by rotary evaporation. The solid was then dissolved in dichloromethane (30 mL) and filtered through Celite pad. The solvent was removed by rotary evaporation, yielding a white powder (70%, 1.536 g) of 1,3-Diisopropyl-5-(trifluoromethyl)-1H-benzimidazolium iodide.
1H NMR (CDCl3, 300 MHz): δ 11.2 (s, 1H), 8.0 (s, 1H), 7.9 (d, J=9.1 Hz, 1H), 7.9 (d, J=8.7 Hz, 1H), 5.2 (m, 2H), 1.9 (dd, J=6.7, 4.1 Hz, 12H). 19F NMR (CDCl3, 500 MHz): δ −61.1.
1,3-Diisopropyl-5-(trifluoromethyl)-1H-benzoimidazolium bicarbonate: The synthesis of 1,3-diisopropyl-5-(trifluoromethyl)-1H-benzimidazolium bicarbonate was modified from a published procedure of a similar compound (Crudden, C. M., et al., U.S. Patent Application Publication No. 20160199875). To a 20 mL scintillation vial, 1,3-diisopropyl-5-(trifluoromethyl)-1H-benzimidazolium iodide (0.50 g, 1.26 mmol, 1 eq.) was dissolved in methanol (4 mL). This solution was added to activated HCO3 resin in another 20 mL scintillation vial. The reaction mixture was stirred for 1 hour. Following this, the resulting suspension was filtered through a cotton plug, and concentrated under air to dryness. An obtained solid was then dissolved in acetone (4 mL) and added dropwise to diethyl ether (6 mL). Sonication precipitated out a solid, which was filtered and washed with diethyl ether (4 mL), yielding 1,3-Diisopropyl-5-(trifluoromethyl)-1H-benzoimidazolium bicarbonate (1iPr-CF3·HCO3) as a white powder (64%, 0.2769 g).
1H NMR (CD3OD, 300 MHz): δ 8.5 (s, 1H), 8.2 (d, J=8.7, 1H), 8.0 (d, J=8.8, 1H), 5.16 (m, 2H), 1.7 (dd, J=6.7, 3.2, 12H). 19F NMR (CD3OD, 500 MHz): δ −62.4.
where R is Et, iPr, tBu.
Depositions were performed using a Picosun R200 Advanced Plasma Enhanced Atomic Layer Deposition (PE-ALD) tool (Masala, Finland). Substrates for deposition were placed in the deposition chamber. The chamber was flushed three times with nitrogen gas, wherein the chamber's pressure was raised to 100 hPa then reduced to the deposition pressure of 7 hPa. The deposition chamber was then allowed a 20 min delay once the deposition temperature of 150° C. has been reached, to ensure uniform temperature distribution. A plasma of 5% H2 in Ar mixture was generated at a power of 850 W to prepare and clean the surfaces. The plasma process used 100 cycles of a 12 s plasma pulse and 2 s “rest” pulse where the plasma was turned off. These 100 cycles were immediately followed by 600 cycles of a 0.1 s NHC vapor pulse and 10 s “purge” pulse of nitrogen. The reservoir of NHC precursor was maintained at 90° C. throughout the process. Roughly 50 mg of NHC material was delivered over the course of the 600 cycles. NHC precursor was selected from 1,3-diisopropyl-1H-benzimidazolium bicarbonate (1iPr·HCO3); 1,3-diisopropyl-5-(trifluoromethyl)-1H-benzimidazolium bicarbonate (1iPr-CF3·HCO3); 1,3-ditertButyl-1H-benzimidazolium bicarbonate (2tBu·HCO3); 1,3-diethyl-1H-benzimidazolium bicarbonate (3Et·HCO3). These precurors underwent thermolysis and NHC bicarbonate salts converted to NHC carboxylate adducts during heating. After decarboxylation, free NHC in vapor form was obtained: 1,3-diisopropylbenzimidazol-2-ylidene (1iPr);
All QCM experiments were conducted on a custom low pressure hot walled ALD tool (see
NHC precursor was delivered using a pass-through style bubbler to maximize volatilization. The bubbler was loaded in a glovebox with approximately 300 mg of precursor in a 10 mL open-ended beaker and sealed using a 2.75″ ConFlat (CF) copper gasket. Bubblers were attached using silver-plated VCR (vacuum coupling radiation) gaskets, and had headspaces evacuated under no-flow (0 sccm), room temperature conditions to control delivery of precursor to the QCM crystal surface.
For saturation experiments, QCM crystals that had equilibrated were exposed to 100 long doses (60 s pulse) of precursor with short (20 s) purge steps using a high (50 sccm) flow rate.
Durability experiments were conducted using the same temperature and flow conditions. Micro-pulses (0.1 s) of room temperature trimethyl aluminum (TMA) were exposed to the NHC coated crystal to test any inhibition on the growth of a TMA coating.
A standard Al2O3 deposition (0.1 s TMA, 0.1 s H2O, 15 s purges) was completed to test any prolonged inhibition on an industry standard deposition process, and to passivate the chamber interior for future experiments.
Adsorbed areal mass density was derived from the Sauerbrey equation, as follows:
wherein density of a quartz crystal (ρq) was 2.648 g cm−3, shear modulus of an AT-cut crystal (μAT) was 2.947*1011 g cm−1 s−2, and resonant frequency (ƒ0 of 6 MHz.
These values provided a conversion factor of −12.27 ng cm−2 Hz−1. QCM studies determined that saturative growth behaviour was seen in the NHC depositions described herein.
ToF-SIMS samples were examined using an ION-TOF (GmbH) ToF-SIMS IV equipped with a Bi cluster liquid metal ion source. A pulsed 25 keV Bi3+ cluster primary ion beam was used to bombard the sample surface to generate secondary ions with a current of 1 μA. The positive (or negative) secondary ions were extracted from the sample surface, mass separated, and detected via a reflectron-type of time-of-flight analyser. Reflector values for the positive and negative mode were +14V and −38V, respectively. Sample charging was neutralised with a pulsed, low energy electron flood. Ion mass spectra were collected in an area of 500 μm×500 μm at 128×128 pixels with 20 scans. High-resolution imaging spectra were processed on ION-TOF software and normalized to the total yield by a division normalization factor.
The ToF-SIMS data confirmed that substrate selectivity for metals was obtained (see
Vacuum annealing was carried out using a VWR Symphony Vacuum Oven (VWR, Edmonton, Canada) equipped with an Edwards RV12 Rotary Vane Vacuum Pump. NHC coated patterned substrates (e.g., Ru and SiO2, Co and SiO2, and Cu and SiO2) were placed on a glass dish and introduced into the pre-heated vacuum oven at 170° C. for 12 hours. The heating and cooling cycles were set to 0.5° C./min with a working pressure of 15 Torr. After vacuum annealing, samples were removed from the oven and placed in storage under atmospheric conditions until analysis was conducted.
In
In
These results show the increased binding selectivity of the NHC to metal substrates.
It will be understood by those skilled in the art that this description is made with reference to certain embodiments and that it is possible to make other embodiments employing the principles of the invention which fall within its spirit and scope.
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 63/333,190, filed on Apr. 21, 2022, the content of which are incorporated herein by reference in its entirety.
Number | Date | Country | |
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63333190 | Apr 2022 | US |