Selective Atomic Layer Deposition Research Articles

Atomic Layer Deposition of Pt on the Surface Deactivated by Fluorocarbon Implantation: Investigation of the Growth Mechanism

Selective atomic layer deposition (ALD) using surface-controlled reactivity is attracting a great deal of attention as a simple bottom-up patterning process that can provide both continued dimensio...

Selective ALD of SiN using SiI4 and NH3: The effect of temperature, plasma treatment, and oxide underlayer

The initial growth of silicon nitride (SiN) thin films was studied during thermal atomic layer deposition (ALD) using silicon tetraiodide (SiI4) and ammonia (NH3) onto various oxide underlayers (native SiO2, sapphire, ALD Al2O3, and ALD ZrO2) at two deposition temperatures (200 and 350 °C). We found that the SiI4/NH3 process shows earlier nucleation on high-k oxide underlayers (sapphire, ALD Al2O3, and ALD ZrO2) compared with SiO2 at 200 °C. Interestingly, an NH3-plasma treatment reverses the selectivity between high-k oxides and SiO2: SiN growth has no nucleation delay on NH3-plasma-treated SiO2 but is severely delayed on NH3-plasma-treated high-k oxides at both temperatures (an incubation period of at least 300 cycles at 200 °C and 50 cycles at 350 °C).

Cu–Cu Bonding Using Selective Cobalt Atomic Layer Deposition for 2.5-D/3-D Chip Integration Technologies

The feasibility of using selective thermal cobalt metal (Co) atomic layer deposition (ALD) as high density Cu–Cu interconnect bonding is demonstrated at a low temperature (200 °C) and with minimal surface pretreatment. A Cu/Gap/Cu structure, which emulates 3-D ICs stacking is fabricated. Cobalt ALD showing seamless interconnection between copper (Cu) pads with 30- $\mu \text{m}$ pitch is demonstrated with greater than 90% yield through electrical measurements, SEM inspection, EDS, and focused ion beam (FIB) cross section.

Substrate-Dependent Study of Chain Orientation and Order in Alkylphosphonic Acid Self-Assembled Monolayers for ALD Blocking.

For years, many efforts in area selective atomic layer deposition (AS-ALD) have focused on trying to achieve high-quality self-assembled monolayers (SAMs), which have been shown by a number of studies to be effective for blocking deposition. Herein, we show that in some cases where a densely packed SAM is not formed, significant ALD inhibition may still be realized. The formation of octadecylphosphonic acid (ODPA) SAMs was evaluated on four metal substrates: Cu, Co, W, and Ru. The molecular orientation, chain packing, and relative surface coverage were evaluated using near-edge X-ray absorption fine structure (NEXAFS), Fourier transform infrared (FTIR) spectroscopy, and electrochemical impedance spectroscopy (EIS). ODPA SAMs formed on Co, Cu, and W showed strong angular dependence of the NEXAFS signal whereas ODPA on Ru did not, suggesting a disordered layer was formed on Ru. Additionally, EIS and FTIR spectroscopy confirmed that Co and Cu form densely packed, "crystal-like" SAMs whereas Ru and W form less dense monolayers, a surprising result since W-ODPA was previously shown to inhibit the ALD of ZnO and Al2O3 best among all the substrates. This work suggests that multiple factors play a role in SAM-based AS-ALD, not just the SAM quality. Therefore, metrological averaging techniques (e.g., WCA and FTIR spectroscopy) commonly used for evaluating SAMs to predict their suitability for ALD inhibition should be supplemented by more atomically sensitive methods. Finally, it highlights important considerations for describing the mechanism of SAM-based selective ALD.

Substrate protection and deprotection with salt films to prevent surface contamination and enable selective atomic layer deposition

Surface contamination can decrease surface reactivity, and removal of surface contaminants adds additional steps to a process. Here we demonstrate surface protection from contamination and one-sided atomic layer deposition (ALD) by means of protective, sacrificial, thermally evaporated NaCl layers. This approach allows clean silicon surfaces to be stored under ambient conditions for extended periods of time in a pristine state, and ALD to be performed selectively on one side of a planar material. For the ALD depositions, planar substrates are (i) selectively coated on one side with ca. 100 nm of NaCl by thermal evaporation, (ii) non-selectively coated using traditional ALD, and (c) rinsed with water to remove the NaCl layer. Water treatment removes the salt film and any ALD deposition on top of it. Salt film deposition, surface protection, and selective ALD are confirmed by X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Selective, thermal ALD of alumina and ZnO are demonstrated, and protective salt films of different thicknesses (10, 50, and 100 nm) are investigated.

Passivation of Defects in Macroscopic Graphene Sheets Via Selective Atomic Layer Deposition of Metal Oxides

Graphene, with its high conductivity, specific surface area, and overall chemical inertness, has been heavily researched for applications in batteries, supercapacitors, and water-splitting devices. While graphene films can be synthesized over large areas (>1 cm2) through chemical vapor deposition, graphene generated through this route exhibits a high defect density that can inhibit performance and stability in electrochemical systems. Considerable effort has been devoted to passivating, repairing, and remediating these defects for graphene-based devices to match their theoretical potential.To this end, we have developed new atomic layer deposition (ALD) processes designed to selectively passivate high energy defect sites with metal oxides. This deposition chemistry targets dangling bonds and oxidized regions on the graphene sheet based on their higher reactivity relative to the pristine basal plane. We have also demonstrated analogous chemistry on bulk highly-ordered pyrolytic graphite as well as exfoliated few-layer graphene. The efficacy of the deposition process was examined as a function of precursor dose and temperature. The selectivity of this process and metal-oxide layer thicknesses was assessed using several electron microscopy techniques. This work further illustrates an effective scheme to ameliorate the interfacial chemistry of large-area graphene and demonstrate how targeted passivation can improve device performance.

Simple masking method for selective atomic layer deposition of thin films

A simple physical masking method is presented for selective atomic layer deposition (ALD). Iron powder and a magnet are used as a masking pair. This method is easy and efficient for depositing patterned thin films with feature sizes estimated 0.3 mm or larger on any substrate. In this work, using iron powder held in place by a magnet would mask part of the silicon wafer substrate, while no iron powder is on the unmasked part. A silver particulated thin film was deposited on the masked Si wafer. X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy were used for silver characterization on the masked and unmasked parts of the sample. Results indicated that an ALD-like surface growth of a silver thin film occurred on the unmasked Si wafer, and no growth was detected on the masked portion of the Si wafer.

Inherently Selective Atomic Layer Deposition and Applications

The chemical approaches enabling selective atomic layer deposition (ALD) are gaining growing interest. The selective ALD has unlocked attractive avenues for the development of novel nanostructures ...

Selective Atomic Layer Deposition of Metals on Graphene for Transparent Conducting Electrode Application.

Although graphene has considerable potential as a next-generation transparent conducting electrode (TCE) material owing to its excellent optical transparency and flexibility, its electrical properties require further improvement for industrial application. This study reports a pathway of doping graphene by selective atomic layer deposition (ALD) of metals to elevate the electrical conductivity of graphene. Introduction of a novel Pt precursor [dimethyl(N,N-dimethyl-3-butene-1-amine-N)platinum(II); C8H19NPt; DDAP] facilitates a low-temperature (165 °C) process. The sheet resistance (Rs) of graphene is reduced significantly from 471 to 86.8 Ω sq-1 after 200 cycles of Pt ALD, while the optical transmittance at 550 nm (T) is maintained above 90% up to 200 cycles due to the selective growth of Pt on the defects of graphene. Furthermore, comprehensive analysis, including metal (Ru, Pt, and Ni) ALD on graphene, metal (Ru, Pt, Ni, Au, and Co) evaporation on graphene, and change in the ALD chemicals, demonstrates that ALD allows efficient graphene doping and the oxygen affinity of the metal is one of the key properties for efficient graphene doping. Finally, Pt ALD is applied to a multilayer graphene to further reduce Rs down to 75.8 Ω sq-1 yet to be highly transparent (T: 87.3%) after 200 cycles. In summary, the selective ALD of metals opens a way of improving the electrical properties of graphene to a level required for the industrial TCE application and has the potential to promote development of other types of functional metal-graphene composites.

‘Cleanroom’ in SEM

To allow researchers to fabricate micro- and nano-devices on a small scale, without having to use complex cleanroom facilities, a single tool is proposed in which a variety of typical cleanroom techniques and processes is combined. This ‘cleanroom’ in SEM tool, based on a scanning electron microscope (SEM), integrates several add-on tools, such as a miniature plasma source for sputtering and cleaning purposes, a miniature thermal evaporator for metal deposition, and facilities to enable in-situ selective atomic layer deposition. The cleanroom techniques and processes selected for integration in the ‘cleanroom’ in SEM tool are discussed, and the design and fabrication of the add-on tools are presented. Finally the proofs of principle of the plasma source, evaporator and in-situ selective ALD process are experimentally demonstrated.

Dense Organosilane Monolayer Resist That Directs Highly Selective Atomic Layer Deposition

Organosilane monolayers are part of many process flows in nanoelectronics and biotechnology because of their versatility. Monolayers that inhibit reactions on silicon/silicon oxide surfaces are nee...

Highly dispersed Pt studded on CoOx nanoclusters for CO preferential oxidation in H2

Highly dispersed Pt studded on CoOx catalysts are designed and fabricated by selective atomic layer deposition method for enhanced CO preferential oxidation performance.

Next generation of extreme-resolution electron beam lithography

In top down nanofabrication research facilities around the world, the direct-write high-resolution patterning tool of choice is overwhelmingly electron beam lithography. Remarkably small features can be written in a variety of polymeric resists [V. R. Manfrinato et al., Nano Lett. 14, 4406 (2014); V. R. Manfrinato, A. Stein, L. Zhang, Y. Nam, K. G. Yager, E. A. Stach, and C. T. Black, Nano Lett. 17, 4562 (2017)]. However, this technology, which in this article the authors will refer to as conventional electron beam lithography (CEBL), is reaching its practical resolution and precision limits [V. R. Manfrinato et al., Nano Lett. 14, 4406 (2014)]. Hydrogen depassivation lithography (HDL) [J. N. Randall, J. W. Lyding, S. Schmucker, J. R. Von Ehr, J. Ballard, R. Saini, and Y. Ding, J. Vac. Sci. Technol. B 27, 2764 (2009); J. N. Randall, J. B. Ballard, J. W. Lyding, S. Schmucker, J. R. Von Ehr, R. Saini, H. Xu, and Y. Ding, Microelectron. Eng. 87, 955 (2010)] is a different version of electron beam lithography that is not limited in resolution and precision in the way that CEBL is. It uses a cold field emitter, a scanning tunneling microscope (STM) tip, to deliver a small spot of electrons on a Si (100) 2 × 1 H-passivated surface to expose a self-developing resist that is a monolayer of H adsorbed to the Si surface. Subnanometer features [S. Chen, H. Xu, K. E. J. Goh, L. Liu, and J. N. Randall, Nanotechnology 23, 275301 (2012)], and even the removal of single H atoms can be routinely accomplished [M. A. Walsh and M. C. Hersam, Annu. Rev. Phys. Chem. 60, 193 (2009)]. It is known that the H desorption process at low biases is a multielectron process [E. Foley, A. Kam, J. Lyding, and P. Avouris, Phys. Rev. Lett. 80, 1336 (1998)], but the tunneling distribution of the electrons from the STM tip to the Si surface lattice is not known. The authors have developed a simple model that demonstrates that the combination of two highly nonlinear processes creates a much higher contrast exposure mechanism than CEBL. Currently, HDL has been used almost exclusively on the Si (100) surface and has a limited number of pattern transfer techniques including Si and Ge patterned epitaxy, selective atomic layer deposition of TiO2 followed by reactive ion etching [J. B. Ballard, T. W. Sisson, J. H. G. Owen, W. R. Owen, E. Fuchs, J. Alexander, J. N. Randall, and J. R. Von Ehr, J. Vac. Sci. Technol. B 31, 06FC01 (2013)], and selective deposition of dopant atoms for quantum devices and materials [Workshop on 2D Quantum MetaMaterials held at NIST, Gaithersburg, MD, April 25–26, 2018, edited by J. Owen and W. P. Kirk]. While the throughput of HDL is very low, going parallel in a big way appears promising [J. N. Randall, J. H. G. Owen, J. Lake, R. Saini, E. Fuchs, M. Mahdavi, S. O. R. Moheimani, and B. C. Schaefer, J. Vac. Sci. Technol. B 36, 6 (2018)]. However, the most exciting aspect of HDL is its atomic-scale resolution and precision, which is key to nanoscale research. The authors see HDL emerging as the ultimate high-resolution patterning tool in top down nanofabrication research facilities.

Highly selective atomic layer deposition of MoSiOx using inherently substrate-dependent processes

A resistive MoSiOx film was deposited with high selectivity on Si in preference to SiO2 and SiN using MoF6, Si2H6 and O2 as reactants. Two different approaches were demonstrated via thermal atomic layer deposition (ALD). First, ALD of MoSiOx by sequential dosing of MoF6, Si2H6 and O2 (ABC-type) at 200 °C followed by an ex-situ post-deposition anneal (PDA) in O2 at 350 °C was performed. The growth of the film using the ABC-type deposition was limited to ~5.25 ± 0.5 nm because the insulating film inhibits the MoF6 and Si2H6 ALD reaction. The second method was to grow MoSix at 120 °C and employ a post-deposition anneal in O2/He at 350 °C (AB + C-type) to form MoSiOx. The selectivity of this process on Si versus SiO2 was perfect for 10 nm of deposition on Si, as there were no nuclei or particle formation observed on the SiO2 surface by atomic force microscopy (AFM). The high selectivity can be obtained due to the inherent inability of MoF6 to react SiO2 and SiN surfaces. Transmission electron microscopy (TEM) of a nanoscale-patterned sample demonstrated that the highly selective MoSiOx can be achieved and be integrated into three-dimensional nanoscale structures.

(Invited) Selective Atomic Layer Deposition Strategies for Catalytic Applications

Atomic layer deposition (ALD) is a mainstay of the semiconductor industry since it allows depositing nanometer thin layers of a desired material onto a substrate in a very controlled and uniform manner. Recently, ALD has been adapted to design and synthesize composite catalysts that allow them to enhance multiple chemical reactions. In fabrication of composite catalysts, the selective approaches of ALD are of great importance to exert spatial control of deposition to fabricate three dimensional nanostructures. In this talk, strategies for selective ALD and enabled nanostructures for catalytic applications will be discussed. The atomically ccomposite nanostructures allows motivations of selective-ALD enable directionally and precisely tailoring of the structural parameters, interfaces, and active sites, that is of great significance for advanced catalysis. Both metal and oxide selectively decorated nanoparticle catalysts will be discussed. With these methods, core shell structures, oxide overcoating structures, facet selective structures are fabricated. The DFT calculations for precursors’ chemisorption and binding energies are carried out to verify the results. These strategies of selective ALD have demonstrated unique advantages to design and fabricate highly active and thermal stable catalysts in atomic scale, and also provided insights to understand the structure–activity relationship.

(Invited) Selective Area Growth of Deactivating Polymers

As the semiconductor community continues scaling, area selective atomic layer deposition (ASD) offers the potential to relax down-stream processing steps by enabling self-aligned processes (e.g. self-aligned via). ASD can be achieved under a variety of conditions and, with the use of organic inhibiting materials, exhibit some of the highest levels of selectivity. However, the organic materials exploited are generally relegated to small molecules and may require multiple cycles of etch-back processes followed by renewal of the surface protection coating. The chemical composition of polymeric materials offers significant potential to broaden the number and film compositions that can be selectively deposited as they draw from such a vast number of chemical functionalities that can be exploited to tailor surface properties [1,2]. There are two approaches to exploiting polymers for ASD, (i) grafting to a substrate with polymer brushes or (ii) growing polymers from a surface. Grafting polymer brushes, with materials shown to inhibit ALD film growth and functionalized with metal binding ligands, exhibited poor selectivity to surfaces and resulted in high defectivity on patterned surfaces where polymer particles were observed on both a metal and dielectric. Growing polymers from a substrate is an attractive strategy, though difficult to realize experimentally. Using a facile synthetic route, a surface binding monomer was engineered that maintained high activity for surface polymerizations and which selectively adheres to a nanoscale metal features, in a field of dielectric material. The resulting surface afforded the ability to produce polymers in an area selective manner and chemically engineer the surface, as desired. The resulting surface polymers were both thermal and chemically stable under ALD conditions and highly selective at guiding the ALD of several films including TiO2 and ZnO for extended periods of time that allow the growth of film thicknesses greater than 48nm, relevant in a number of device applications. This method was also found to be scalable where initial experiments were carried out on laboratory scale experiments and could be scaled to a full 300mm wafer. Furthermore, the mechanism of inhibition was shown where ALD films inhibition is the result of precursor solubility in the polymer film. This unique strategy of growing polymers in an area selective manner and the inhibiting mechanism, present a set of design rules for engineering surfaces to direct the formation of inorganic films.

(Invited) Area Selective Atomic Layer Deposition As an Emerging Process for Advanced Nanofabrication

The rapid growth of technologies such as artificial intelligence and autonomous vehicles is fueling a need for more powerful electronic chips, which the semiconductor industry is working to meet with ever-more complex nanoscale device structures. With this growing need for nanostructure fabrication, selective deposition is gaining much attention as an important process to achieve pattern features at the ~10 nm length scale. Both two-dimensional planar geometries and three-dimensional structures will benefit from selective deposition processes, with bottom-up growth strategies providing advantages in reduced process complexity and improved pattern fidelity. In this presentation, we will describe how control over surface chemistry using molecular monolayers can achieve area selective atomic layer deposition (ALD). ALD is a good choice for selective deposition because its chemical specificity provides a means to achieve selectivity on a spatially patterned substrate. In particular, inhibitory layers such as self-assembled monolayers (SAMs) can alter the native surface reactivity, allowing ALD selectivity to be achieved. We will show that this process provides good selectivity for thin deposited films, and demonstrate selective deposition on different materials, including dielectrics and metals such as Cu, Co, W and Ru. Because area selective ALD processes often break down after more than a few nanometers of material is deposited, strategies to overcome the undesired ALD nucleation on the inhibitory layer and achieve significantly higher selectivity in area selective ALD are also important. Two such strategies that improve the final selectivity will be described, including SAM repair between ALD cycles and a self-correcting process in which selective deposition is combined with selective etching. With both approaches, selective ALD of more than 60 nm of metal oxide dielectric material can be achieved. Directions toward new area selective deposition processes will also be described.

Extending the compositional diversity of films in area selective atomic layer deposition through chemical functionalities

As the semiconductor community continues scaling, area selective atomic layer deposition (ASD) offers the potential to relax down stream processing steps by enabling self-aligned processes (e.g., self-aligned vias). Otherwise, conventional means of lithography face increasingly difficult challenges such as patterning and overlay errors as resolution improves. ASD can be achieved under a variety of conditions, and with the use of organic inhibiting materials, it can exhibit some of the highest levels of selectivity. However, the structure property relationship of these inhibiting materials is not completely understood, and therefore the relationship between a materials chemical functionality and its inhibiting properties remains largely unexplored. This was explored with polymeric materials that served as a versatile materials platform allowing a broad variation of chemical functional groups and physical properties that may then enable the ASD community to extend the number and types of films that can be selectively deposited. Initially, hydrophobic polymers including polystyrene (PS) and polyvinyl chloride (PVC), as well as an oleophobic polymer, poly[difluoro-bis(trifluoromethyo)-dioxole-co-tetrafluoroethylene] (PTFE-AF), were surveyed for their inhibitory properties toward the atomic layer deposition of industry relevant metal oxides such as Al2O3 and TiO2, which heavily feature as etch masks and other functional nanostructures. Despite blanket deposition of Al2O3 being observed, even when using an oleophobic polymer such as PTFE-AF, TiO2 deposition was notably inhibited by blanket films of PVC, PS, and PTFE-AF. In light of these results, the functionalization of PVC and PS with selective area substrate anchoring groups such as phosphonic acids (targeting copper oxide surfaces) was conducted to investigate whether grafting selectivity of these polymer films to their intended surface could be inhibited, thereby achieving film growth in the proximal uninhibited area. Two methods of polymer functionalization were evaluated: phosphonic acid groups distributed randomly throughout the polymer backbone of PVC and a single phosphonic acid group localized at the chain end of PS. Notably, the PVC multidentate derivatives and the PS monodentate type polymers exhibited effective inhibition of TiO2.

First Principles Studies of Solid-Solid Interfaces between LiMn2O4 and Protective Coatings

Numerous studies have shown that protective surface coatings are effective in reducing the well-documented problem of Mn ion dissolution from the surface of the spinel LiMn2O4 (LMO) Li-ion battery cathode.[1] Although recent computational work has identified many promising coating chemistries based on bulk thermochemical properties,[2,3] there remains much to be understood regarding the interface formed between protective coatings and the LMO electrode and how such interfacial properties may influence electrochemical performance. In this work, first principles density functional theory calculations are performed on models for both oxide and metallic coatings on the LMO surface. First, we elucidate the mechanism for the onset of Al2O3 film growth by atomic layer deposition (ALD) and show that precursor decomposition in early ALD pulses leads to adsorption site blocking and sub-monolayer film growth.[4] During ALD, the trimethylaluminum [Al(CH3)3] precursor loses its -CH3 groups to the LMO surface, where the Al(CH3)x* and CH3* surface adsorbates each behave as Lewis bases (electron donors), where near-surface Mn ions are the Lewis acidic adduct (electron acceptor). These studies are extended to various thermodynamically stable low- and high-index LMO surface models,[5] demonstrating that ALD on LMO is structure-sensitive toward stepped sites, which are more electron accepting as suggested by calculated oxygen vacancy formation energies. Moreover, we find that the thermodynamics of decomposed intermediates are linearly related to the corresponding oxygen vacancy formation energy, or the relative Lewis acidity of near-surface Mn ions, of each given surface facet and termination. We propose that selective ALD leads to partial coatings formed at defect sites which may be particularly vulnerable to Mn dissolution. Next, we model the process of delithiation near the surface of an LMO coated with metallic Au, which effectively mitigates Mn dissolution. Moreover, Au coatings have been shown to improve kinetics and do not strip under the potentials where LMO electrochemistry occurs.[6] DFT calculations show that a Li+-deficient near-surface is thermodynamically favored for Au-coated LMO. We demonstrate through local density of states and chemical bonding analyses that Au hybridizes with LMO upon delithiation, leading to partial oxidation on Au electronic states rather than full localization of holes on Mn ions. The Au coating has a lower work function than LMO, driving electron transfer from Au to LMO. This is also associated with downward bending of the LMO conduction band in response to Fermi level pinning at the LMO/Au interface. Operando X-ray diffraction experiments show that these interfacial effects may translate to a reduction in the amount of Li+ that can intercalate into the bulk of Au-coated LMO. These studies help elucidate the structure-property relationships of protective coatings at the LMO surface. In particular, this work highlights the driving forces for nucleation and growth of protective coatings by ALD, as well as the influence of interfacial electronic structure on intercalation chemistry of coated electrode materials. This research is supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

MnO2–Graphene-oxide-scroll–TiO2 composite catalyst for low-temperature NH3-SCR of NO with good steam and SO2 resistance obtained by low-temperature carbon-coating and selective atomic layer deposition

Coating GO at low temperature and selectively depositing TiO2 on oxygen-containing functional groups on GO.