Fabrication and characterisation of polymer brushes for the use in area selective deposition

With the constant increasing demand for faster and more efficient electronic devices, the requirement for smaller integrated circuits has grown exponentially. The current method of fabrication for these devices, known as photolithography, employs a ‘top-down’ approach using light and masks for the patterning of substrate surfaces. This method, however, is reaching its size limits and has become extremely costly to carry out. Research into the fabrication of polymer brushes for the use in area selective deposition is vital for the understanding of ‘bottom up’ lithography techniques, such as block copolymer lithography. Such methods rely on the self-assembly of polymers containing active and inactive regions and are being proposed as an alternative to the current ‘top-down’ methods used for the manufacturing of electronic devices. These self-assembled polymer patterns can be exposed to infiltrating materials via a vapour phase process thus allowing for the infiltration of the active regions while blocking deposition in the inactive areas. A major part of these fields is investigating the polymer materials that will either accept or block infiltration by different species such as metals. This work looks at developing fabrication techniques of polymer brushes with a focus on increasing the overall thickness. It then goes on to investigate the infiltration of different polymers as well as looking at the effect that thickness has on a polymers infiltration and blocking mechanisms using hard X-Ray photoelectron spectroscopy as the core analysis method alongside techniques such as ellipsometry, atomic force microscopy and X-Ray reflectivity

Thermal and plasma enhanced atomic layer deposition of ultrathin TiO2 on silicon from amide and alkoxide precursors: growth chemistry and photoelectrochemical performance

Due to its low cost and suitable band gap, silicon has been studied as a photoanode material for some time. However, as a result of poor stability during the oxygen evolution reaction (OER), Si still remains unsuitable for any extended use. Ultra-thin titanium dioxide (TiO2) films have been used as protective coatings and are shown to enhance Si photoanode lifetime with added solar to hydrogen performance improvements through distancing the oxidation reaction away from the Si photoanode surface and improved charge transport through the anode. This study details the nucleation, growth chemistry, and performance of TiO2 thin films prepared via thermal and plasma enhanced atomic layer deposition (ALD) using both titanium isopropoxide and tetrakis(dimethylamido)titanium as the precursor material. The effect of post ALD treatments of plasma and air annealing was also studied. Films were investigated using photoelectrochemical cell testing to evaluate photoelectrochemical performance, and in-vacuum cycle-by-cycle x-ray photoelectron spectroscopy was used as the primary characterisation technique to study nucleation mechanisms and film properties contributing to improvements in cell performance. TiO2 grown by plasma enhanced ALD results in cleaner films with reduced carbon incorporation. However, despite increased carbon incorporation, thermally grown films showed improved photocurrent as a result of oxygen vacancies in these films. Post deposition annealing in a H2 ambient is shown to further improve photocurrent in all cases, while annealing in atmosphere leads to uniform film chemistry and enhanced photocurrent stability in all cases

Analysing trimethylaluminum infiltration intopolymer brushes using a scalable area selectivevapor phase process

Developing vapor phase infiltration (VPI) processes for area selective polymer nanopatterning requires substantial advancement in understanding precursor infiltration, precursor–polymer interaction and process parameters. In this work, infiltration receptive poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP) brushes were exposed to a trimethylaluminum (TMA) VPI process and compared toa non-receptive polystyrene (PS) system. The interaction that takes place between TMA and P2VP/P4VPwas analysed in detail and we report on notable advantages in the use of P4VP, arising from the difference in position of the pyridinic nitrogen. The VPI process was performed in a commercial atomic layer deposition reactor and the effects of the fundamental process parameters on the three polymer brushes were investigated to ensure optimal area selectivity. In situX-ray photoelectron spectroscopy (XPS) measurements were supported by grazing angle Fourier transform infrared spectroscopy (GA-FTIR)and hard X-ray photoelectron spectroscopy (HAXPES). The report identifies several important factors when developing a VPI process to ensure area selectivity, while also demonstrating the use of novel pyridine containing polymers for VPI area selective purposes

Fabrication of sub-5 nm uniform zirconium oxide films on corrugated copper substrates by a scalable polymer brush assisted deposition method

We demonstrate a polymer brush assisted approach for the fabrication of continuous zirconium oxide (ZrO2) films over large areas with high uniformity (pin-hole free) on copper (Cu) substrates. This approach involves the use of a thiol-terminated polymethyl methacrylate brush (PMMA-SH) as the template layer for the selective infiltration of zirconium oxynitrate (ZrN2O7). The preparation of a highly uniform covalently grafted polymer monolayer on the Cu substrate is the critical factor in fabricating a metal oxide film of uniform thickness across the surface. Infiltration is reliant on the chemical interactions between the polymer functional group and the metal precursor. A following reductive H2 plasma treatment process results in ZrO2 film formation whilst the surface Cu2O passive oxide layer was reduced to a Cu/Cu2O interface. Fundamental analysis of the infiltration process and the resulting ZrO2 film was determined by XPS, and GA-FTIR. Results derived from these techniques confirm the inclusion of the ZrN2O7 into the polymer films. Cross-sectional transmission electron microscopy and energy dispersive X-ray mapping analysis corroborate the formation of ZrO2 layer at Cu substrate. We believe that this quick and facile methodology to prepare ZrO2 films is potentially scalable to other high-κ dielectric materials of high interest in microelectronic applications

Growth chemistry and electrical performance of ultrathin alumina formed by area selective vapor phase infiltration

The growth chemistry and electrical performance of 5 nm alumina films, fabricated via the area-selective vapor phase infiltration (VPI) of trimethylaluminum into poly(2-vinylpyridine), are compared to a conventional plasma enhanced atomic layer deposition (PEALD) process. The chemical properties are assessed via energy dispersive X-ray spectroscopy and hard X-ray photoelectron spectroscopy measurements, while current – voltage dielectric breakdown and capacitance – voltage analysis is undertaken to provide electrical information of these films for the first time. The success and challenges in dielectric formation via polymer VPI, the compatibility of pyridine in such a role, and the ability of the unique and rapid grafting-to polymer brush method in forming coherent metal oxides is evaluated. It was found that VPI made alumina fabricated at temperatures between 200 and 250 °C had a consistent breakdown electrical field, with the best performing devices possessing a к value of 5.9. The results indicate that the VPI approach allows for the creation of alumina films that display dielectric properties of a comparable quality to conventional PEALD grown films

Titanium infiltration into ultrathin PMMA brushes

Vapor phase infiltration (VPI) is a bottom-up process that involves the infiltration of polymers, often using atomic layer deposition compatible precursors. By exposing a polymer to an organo-metallic precursor, area selective material formation is achieved where the precursor reacts with regions covered by an infiltration-receptive polymer brush. Combining receptive and rejecting polymers that have the capability of forming complex nanopatterns could potentially allow for the creation of nanofeatures, offering a route to area selective deposition. This work is concerned with the creation and characterization of titanium-infiltrated films with a VPI process. Thin films of poly(methyl methacrylate) (PMMA) were infused with titanium isopropoxide and subsequently analyzed with angular resolved x-ray photoelectron spectroscopy. All XPS analysis and VPI treatments were completed without breaking vacuum in an integrated

Rapid area deactivation for blocking atomic layer deposition processes using polystyrene brush layers

Research into the fabrication of polymer brushes for use in Area Selective Deposition (ASD) is vital for the understanding of ‘bottom up’ lithographic techniques such as block copolymer (BCP) lithography. Polystyrene has been extensively studied as a blocking material and has been shown to reject both liquid and vapour phase precursors in block copolymer structures. In this work, we demonstrate that thin polystyrene brushes can effectively block atomic layer deposition processes (ALD), offering a route to area deactivation. The effect of varying the molecular weight and fabricating solution concentration of polystyrene (PS) on the overall brush thickness using the grafting-to method is presented in detail. Ellipsometry shows that an increase in molecular weight and solution concentration yields an increase in brush thickness. We demonstarte that PS brush thickness has a significant impact on the blocking efficacy of a HfO2 ALD process, using X-ray photoelectron spectroscopy as the primary characterisation technique. Results show that the thickest brushes fabricated in this work successfully blocked a process that would result in 19 nm of HfO2 on native oxide covered Si. Due to the significantly faster fabrication times of PS brushes, this process is deemed a highly competitive alternative to the more widely used ASD methodologies such as self-assembled monolayers (SAMs)

Analysing trimethylaluminum infiltration into polymer brushes using a scalable area selective vapor phase process

Developing vapor phase infiltration (VPI) processes for area selective polymer nanopatterning requires substantial advancement in understanding precursor infiltration, precursor–polymer interaction and process parameters. In this work, infiltration receptive poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP) brushes were exposed to a trimethylaluminum (TMA) VPI process and compared to a non-receptive polystyrene (PS) system. The interaction that takes place between TMA and P2VP/P4VP was analysed in detail and we report on notable advantages in the use of P4VP, arising from the difference in position of the pyridinic nitrogen. The VPI process was performed in a commercial atomic layer deposition reactor and the effects of the fundamental process parameters on the three polymer brushes were investigated to ensure optimal area selectivity. In situ X-ray photoelectron spectroscopy (XPS) measurements were supported by grazing angle Fourier transform infrared spectroscopy (GA-FTIR) and hard X-ray photoelectron spectroscopy (HAXPES). The report identifies several important factors when developing a VPI process to ensure area selectivity, while also demonstrating the use of novel pyridine containing polymers for VPI area selective purposes

Aluminium oxide formation via atomic layer deposition using a polymer brush mediated selective infiltration approach

Area selective deposition (ASD) is an emerging method for the patterning of electronic devices as it can significantly reduce processing steps in the industry. A potential ASD methodology uses infiltration of metal precursors into patterned polymer materials. The work presented within demonstrates this potential by examining hydroxy terminated poly(2-vinylpyridine) (P2VP-OH) as the \u27receiving\u27 polymer and trimethylaluminium (TMA) and H2O as the material precursors in a conventional atomic layer deposition (ALD) process. Fundamental understanding of the surface process was achieved using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) mapping via transmission electron microscopy (TEM). The resulting analysis confirms aluminium inclusion within the polymer film. Spectroscopic and microscopic characterisation show metal infiltration throughout the polymer to the underlying silicon dioxide interface. Exposing the infiltrated film to an oxygen plasma results in the removal of the organic component and resultant fabrication of a sub 5 nm aluminium oxide layer

Fabrication of high-κ dielectric metal oxide films on topographically patterned substrates: polymer brush mediated depositions

Fabrication of ultrathin films of dielectric (with particular reference to materials with high dielectric constants) materials has significance in many advanced technological applications including hard protective coatings, sensors, and next generation logic devices. Current state-of-the-art in microelectronics for fabricating these thin films is a combination of atomic layer deposition and photolithography. As feature size decreases and aspect ratios increase, conformality of the films becomes paramount. Here, we show a polymer brush template assisted deposition of highly conformal, ultrathin (sub 5 nm) high-κ dielectric metal oxide films (hafnium oxide and zirconium oxide) on topographically patterned silicon nitride substrates. This technique, using hydroxyl terminated poly-4-vinyl pyridine (P4VP-OH) as the polymer brush, allows for conformal deposition with uniform thickness along the trenches and sidewalls of the substrate. Metal salts are infiltrated into the grafted monolayer polymer brush films via solution deposition. Tailoring specific polymer interfacial chemistries for ion infiltration combined with subsequent oxygen plasma treatment enabled the fabrication of high-quality sub 5 nm metal oxide films