Area-selective deposition is a promising technique for positional self-alignment of materials at a prepatterned surface. Critical to this is the development of molecular systems that have selective surface binding and can act as templates to material growth. This paper reports how end functionalized polymers can be used to create oxide films through a grafting method. Here, we detail a facile approach for rapid grafting (in seconds) of polymer brush films with complete coverage over large areas with high uniformity (pinhole free). Subsequent conversion to an oxide (∼3−4 nm thickness) is performed via liquid-phase metal ion infiltration. Exposing the covalently grafted polymer brush (P2VP-OH) to a metal salt-solvent solution (using the Al 3+ ion as a model species) swells the polymer, facilitating ion inclusion. Early results suggest that a solvent-mediated approach to polymer film infiltration can be used to develop inorganic films in a facile process. While data shows inclusion into both large-area and patterned films, the mechanism and understanding of these have been limited. In particular, the solution-mediated process described here shows the precise tailoring of nanometer-thin polymer films that are pinhole-free and that can be activated to create semiconductor-compatible oxide films that are parallel in quality to ALD-or CVD-derived processes. A surface deactivation strategy is also realized using a hydroxyl-terminated polystyrene (PS-OH) brush that prevents the deposition of ions. We consider this strategy as a means to prevent electromigration of ions as well as the possibility of coating ALD layers.

We describe a versatile bottom-up approach to covalently and rapidly graft hydroxyl terminated poly (2-vinyl pyridine) (P2VP-OH) polymers in 60 seconds that can subsequently be used to fabricate high quality TiO2 films on silicon substrates. A facile strategy based upon room temperature titanium vapor phase infiltration of the grafted P2VP-OH polymer brushes produces TiO2 nanofilms of 2-4 nm thickness. In order to fabricate coherent inorganic films with precise thickness control, it is critical to generate a high-quality polymer brush film i.e. a complete monolayer. Definition of precise and regular polymer monolayers is straightforwardly achieved for polymers which are weakly interacting with one another and the substrate (apart from the reactive terminal group used for grafting). However this is much more challenging for reactive systems. Crucial parameters are explored including molecular weight and solution concentration for grafting dense P2VP-OH monolayers from the liquid phase with very high coverage and uniformity across wafer scale areas. Additionally, we compare the P2VP-OH polymer system with another reactive polymer PMMA-OH and a relatively non-reactive polymer PS-OH, the latter we prove to be extremely effective for surface blocking and deactivation. Our methodology provides new insight into the grafting of polymer brushes and their ability to form dense TiO2 films. We believe the results described herein are important for further expanding the use of reactive and unreactive polymers for fields including area selective deposition, solar cell absorber layers and antimicrobial surface coatings.

In this work we present the results of a Hard X-ray Photoelectron Spectroscopy (HAXPES) study on the creation of metallic copper layers via metal-salt infiltration into a poly-2-vinylpyridine (P2VP) film. Metal salt inclusion is a wet chemistry process which allows for the fabrication of both metal and metal oxide films by means of infiltrating a receptive polymer thin film with metal salt precursors. A copper infiltrated P2VP film was subject to UV/Ozone treatment to form copper oxide and annealed in-vacuo to reduce the film to metallic copper. HAXPES and transmission electron microscope (TEM) measurements were used to study the polymer film before and after metal salt infiltration, along with analysis of the copper oxide created after UV/Ozone treatment. The results show successful infiltration of the metal salt into the polymer film, as well as complete conversion to copper oxide following UV/Ozone treatment and reduction to metallic copper with a subsequent in-situ anneal, which demonstrates the ability of the technique for the creation of several key integrated circuit features.

This work is motivated by the desire to develop a semiconductor device patterning technology based on precursor infiltration into block copolymer materials. Developing an understanding of the preferential infiltration of metal precursors into one of the polymer blocks is of critical importance to advance this patterning approach. In this study, metal salts were used as a means to diffuse metal ions into a poly 2-vinylpyridine (P2vP) polymer brush layer (~4 nm thick) which was deposited by spin coating on a silicon substrate. Thin P2vP films infused with aluminum nitrate and copper nitrate by a wet chemical process were analyzed with angle resolved hard x-ray photoelectron spectroscopy (AR HAXPES). From these photoemission measurements, significant information about the chemical compositional profile of the infiltrated films was obtained. The large sampling depth of HAXPES measurements (20–30 nm) enabled details of the chemical composition of the thin film to be characterized and subsequent angle-resolved HAXPES measurements offered a robust analysis of the interfaces and discrete layers that are present in the films. These measurements displayed evidence of bonding interactions between the elements in the polymer film and the infiltrated salts assisting in the development of an understanding of the infiltration process which needs to be optimized for device fabrication applications. Aluminum nitrate presented more evidence of infiltration into P2vP, while copper nitrate was more predominated at the surfaces into the P2vP.

Thin films of OH terminated poly-2-vinylpyridine (P2VP-OH), a polymer with potential for infiltration mediated thin film deposition, area selective deposition (ASD) and small feature size development via block copolymer (BCP) self-assembly, has been studied with hard X-Ray photoelectron spectroscopy (HAXPES). From the N 1s and C 1s core level spectra, accurate values for the binding energy positions of the species present in the films were obtained, providing clear evidence for signals associated to pyridine bonds. The aromatic ring on the P2VP side chain is clearly identified in the studied core levels. These observations allow for a complete understanding of the chemical environment of the polymer and provide evidence of the potential reactions that can occur with metal diffusion into P2VP. Transmission Electron Microscopy (TEM), Attenuated Total Reflection Infrared Spectroscopy (ATR IR) and Atomic Force Microscopy (AFM) measurements reveal high quality films and this work provides a reference base for this functional material in terms of its utility for ASD, BCP and subsequent atomic layer deposition (ALD) based polymer infiltration processes.

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This work identifies the critical factors when developing a polymer brush vapor phase infiltration process, while also demonstrating the use of novel pyridines for area selective purposes.

Oxygen plasma treatments for conversion of metal salt infiltrated polymer films to metal oxide films using an asymmetrical capacitively coupled plasma system were investigated. Hydroxylated Poly-2-Vinylpyridine (P2VP-OH) thin films grafted to silicon were exposed to metal salt-solvent solutions which swell the polymer enabling metal ion infiltration. Exposing the resulting film to oxygen plasma resulted in formation of polymer-free metal oxide films. Atomic oxygen and positive ions present in plasma can both influence the process outcome. A design of experiment approach was used to investigate the impact of RF power, gas pressure and process time on plasma composition and the resulting metal oxide films. A combination of Langmuir probe, retarding field energy analyser and optical emission spectroscopy measurements were used to monitor the plasma. The samples surfaces were examined using X-ray photoelectron spectroscopy, ellipsometry, transmission electron microscopy and energy dispersive X-ray analysis. Gas pressure and RF power were found to strongly influence both ion energy, and atomic oxygen to molecular ion ratios [O]/[O2 +] in the plasma which impacted the resulting surface layer. For the plasma conditions investigated conversion to a metal oxide was achieved in minutes. Sputter contamination was found to be significant in some cases.