Feature Size Dependence Research Articles

(Invited) Introduction and Overview of Area-Selective Thin Film Deposition

Low temperature Area-Selective Deposition (ASD) is becoming an important need in semiconductor manufacturing to augment photolithography for improved resolution and alignment of printed features. Area-selective deposition is used routinely at temperature in excess of 800°C to form epitaxial transistor contacts, but for back-end applications, new ASD processes are needed that work at <400°C. This tutorial will introduce the challenges of low temperature ASD, and summarize recent advances in this field, including ASD via Atomic Layer Deposition (ALD) and Chemical Vapor Deposition (CVD), and understanding of feature size dependence and lateral “mushroom” growth. We will review approaches using surface passivation, including self-assembled monolayers and small molecule inhibitors, as well as approaches based on inherent differences in nucleation on different clean surfaces. Further, we will present emerging approaches that achieve patterning by taking advantage of native selectivity in nucleation and etching reactions, for example, where ALD and Atomic Layer Etching (ALE) can be combined, either in sequence or in parallel, to achieve desired outcomes. We will also review current modeling efforts, including methods to quantitatively analyze ASD and compare results for different materials and different processes, highlighting the challenges of understanding reactions for initial nucleation and nucleus removal.

Site-selective assembly of quantum dots on patterned self-assembled monolayers fabricated by laser direct-writing

A simple and efficient route for quantum dot (QDs) patterning using self-assembled monolayers (SAMs) as templates is described. By means of a laser direct-writing (LDW) technique, SAMs of octadecylphosphonic acid formed by adsorption on native oxide layer of titanium film were patterned through laser-induced ablation of the SAM molecules. This technique allows the creation of chemical-specific patterns accompanied by slight change in the topography. Using atomic force microscopy and friction force microscopy, the dependence of feature size and characteristics on the irradiation dose was demonstrated. Upon immersion of a substrate with patterned SAMs bearing thiol as the terminal group into a dispersion of QDs resulted in the assembly of QDs on the specific thiol-terminated areas. Patterns of QDs with different photoluminescent wavelength were generated. The LDW technique, which is convenient and flexible due to its path-directed and maskless fabrication process, provided a new powerful approach for patterning materials on surfaces for various applications.

Three-dimensional micro-/nano-structuring via direct write polymerization with picosecond laser pulses

We demonstrate capability to structure photo-polymers with sub-wavelength resolution, ∼200-500 nm, and retrieve three-dimensional (3D) structures using a picosecond laser exposure. This alternative to commonly used ultra-short femtosecond lasers extends accessibility of 3D direct write. A popular hybrid sol-gel resist SZ2080 was used for quantitative determination of structuring resolution at 1064 nm and 532 nm wavelengths and for pulses of 8-25 ps duration at the repetition rates of 0.2-1 MHz. Systematic study of feature size dependence of 3D suspended nano-rods shows that linear power dependence of photopolymerization on the dose-per-pulse becomes dominant at higher repetition rates (≥0.5 MHz) while the two-photon nonlinear absorption is still distinguishable at rates lower than 0.2 MHz and shorter pulses (≤8 ps). Thermal accumulation defines polymerization when cooling time of the focal volume is larger than separation between pulses. Photopolymerization and its scaling mechanisms, quality, and fidelity at tight focusing of fs-, ps-, and cw-laser radiation are revealed and explained. 3D scaffolds for biomedicine and microlenses for optical applications are fabricated by the ps-laser direct write.

Annealing of Heavy-Ion Induced Floating Gate Errors: LET and Feature Size Dependence

We discuss the room temperature annealing of Floating Gate errors in Flash memories with NAND and NOR architecture after heavy-ion irradiation. We present the evolution of rough bit errors as a function of time after the exposure, examining the annealing dependence on the particle LET, cell feature size, and for Multi Level Cells, on the program level. The results are explained based on the statistical properties of the cell threshold voltage distributions before and after heavy-ion strikes.

Impact of feature-size dependent etching on the optical properties of photonic crystal devices

Feature size dependence in Ar/Cl2 chemically assisted ion beam etching of InP-based photonic crystals (PhCs) and its influence on the optical properties of PhC devices operating in the band gap are investigated. The analysis of the measured quality factors, the determined mirror reflectivities, and losses of one-dimensional Fabry–Pérot cavities clearly demonstrates the importance of feature-size dependent etching. The optical properties show a dramatic improvement up to a hole depth of about 3.5 μm that is primarily due to a significant reduction in extrinsic losses. However, beyond this hole depth, the improvement is at a lower rate, which suggests that extrinsic losses, although present, are not dominant.

Feature size dependence on hysteresis due to relative humidity ramping and patterning order in dip-pen nanolithography

The water meniscus that forms between an atomic force microscope (AFM) tip and the substrate has been shown to have variable height and width due to relative humidity (RH) hysteresis. The current study investigates the effect of this variability in meniscus shape due to RH on the feature size of patterns written with mercaptohexadecanoic acid on a gold substrate, using dip-pen nanolithography (DPN). The patterns were written under conditions of increasing and decreasing RH cycles with different tip dwell times. The variation in resulting dot sizes during the RH ramping (up and down) cycles was then measured. DPN patterning was also performed with increasing and decreasing order of dwell times at constant RH, in order to quantify whether the order of patterning has an effect on feature size. Significant differences were observed in dot areas patterned over many RH ramping cycles; whereas the order of patterning was observed to have an effect only for dwell times ≤5 s.

SPM local oxidation nanolithography with active control of cantilever dynamics

Local oxidation nanolithography using scanning probe microscope (SPM) has enabled us to fabricate nanometer-scale oxide wires on material surfaces. Here, we study tapping mode SPM local oxidation experiments for silicon by controlling the dynamic properties of the cantilever. Dependence of feature size of fabricated oxide wires on the amplitude of the cantilever was precisely investigated. The quality factor (Q) was fixed at a natural value of ∼500. By enhancing the amplitude of the cantilever, both width and height of fabricated Si oxide wires were decreased. With the variation of the amplitude of the cantilever from 0.5 V to 3.0 V (DC voltage = 22.5 V, scanning speed = 20 nm/s), the feature size of Si oxide wires was well controlled, ranging from 40 nm to 18 nm in width and 2.3 nm to 0.6 nm in height. Standard deviation of width on Si oxide wires formed by tapping mode SPM is around 2.0 nm, which is smaller than that of contact mode Si oxide wires. Furthermore, the variation of the oscillation amplitude of the cantilever does not affect the size uniformity of the wires. These results imply that the SPM local oxidation nanolithography with active control of cantilever dynamics is a useful technique for producing higher controllability on the nanometer-scale fabrication of Si oxide wires.

Directed Immobilization of Protein-Coated Nanospheres to Nanometer-Scale Patterns Fabricated by Electron Beam Lithography of Poly(ethylene glycol) Self-Assembled Monolayers

Controlling the spatial organization of biomolecules on solid supports with high resolution is important for a wide range of scientific and technological problems. Here we report a study of electron beam lithography (EBL) patterning of a self-assembled monolayer (SAM) of the amide-containing poly(ethylene glycol) (PEG) thiol CH(3)O(CH(2)CH(2)O)(17)NHCO(CH(2))(2)SH on Au and demonstrate the patterning of biomolecular features with dimensions approaching 40 nm. The electron dose dependence of feature size and pattern resolution is studied in detail by atomic force microscopy (AFM), which reveals two distinct patterning mechanisms. At low doses, the pattern formation occurs by SAM ablation in a self-developing process where the feature size is directly dose-dependent. At higher doses, electron beam-induced deposition of material, so-called contamination writing, is seen in the ablated areas of the SAM. The balance between these two mechanisms is shown to depend on the geometry of the pattern. The patterned SAMs were backfilled with fluorescent 40-nm spheres coated with NeutrAvidin. These protein-coated spheres adhered to exposed areas in the SAM with high selectivity. This direct writing approach for patterning bioactive surfaces is a fast and efficient way to produce patterns with a resolution approaching that of single proteins.

Gray Level and DMA Estimation in Monocomponent Development Systems

In our companion paper, we introduced a novel field calculation technique for obtaining the electric field in the developer gap. In this paper, we demonstrate how normal and horizontal fields obtained from this method can be used to estimate gray level and developed mass per unit area (DMA) of a given pattern. The estimation procedure is phenomenological, but it exploits the physics governing toner movement in the development nip to account for observed feature size dependence of toner development. Estimated DMA specifies developed mass at each point in the calculation grid (3 &#x3BC;m cell). Thus, for any input bitmap, DMA at the subpixel level can be accurately predicted over the entire image. Using two different print engines and various bitmaps, we present simulation results and measurements, which are in good agreement. DMA measurements are collected from measured average toner mass data and scanned images using video microscopy. We calibrated microscopic grayscale data to the toner mass measurements, so that DMA can be obtained directly from scanned gray values.

Effect of radio frequency bias power on SiO2 feature etching in inductively coupled fluorocarbon plasmas

We present and discuss results obtained in studies of the mechanisms underlying various feature size dependencies of SiO2 etching in inductively coupled fluorocarbon plasmas. The variation of the fluorocarbon deposition rate and the SiO2 etch rate with both feature size and rf bias power has been measured in a variety of constant aspect ratio features for both an etch stop (C3F6/H2) and a nonetch stop (CHF3) feedgas chemistry.

Pattern shape effects and artefacts in deep silicon etching

Deep silicon etching in an inductively coupled plasma (ICP) reactor offers a high etch rate (7 μm/min), nearly vertical profile with simple oxide masking. Test structures with patterns of different sizes (from a few microns to over 100 μm) and shapes (square and circular holes and trenches of variable width/length) have been etched to depths up to 500 μm. Long narrow features are etched faster than wide short features, indicating the three-dimensional nature of the reactive ion etching lag. Experiments have been done for many different etch times in order to understand aspect ratio dependence of deep etching. Simple flow conductance model explains most of the observed aspect ratio and feature size dependence.

Diagnostics of patterning mechanisms in chemically amplified resists from bake dependencies of images

Measurement and analysis of bake dependencies of resist profiles are used to establish the critical role of diffusion and acid loss in lithographic performance. Imaging experiments carried out with APEX-E with postexposure bake temperatures above and below its glass transition temperature evidence widely dissimilar feature size dependencies attributable to different acid diffusion mechanisms in the glassy and the rubbery polymer, respectively. Examination of the mechanisms determining e-beam exposed resist image stability show that, when an acid loss mechanism is present, the initial amount of acid generated the reaction rate, and the diffusion mechanisms are essential in predicting feature size dependence on postexposure bake conditions.

The dependence of nanostructure etch rates on feature size

The feature size dependence of plasma etch rates has been the focus of recent theoretical and experimental study [1–3]. The effect, already problematic at submicron dimensions, can limit attainable structures and is expected to increase in importance as lateral dimensions are further reduced. In this paper, the models previously reported are developed further and a new nanostructure trench sectioning technique is used to extend etch rate measurements to features with lateral dimensions below 100 nm. The experimental results are compared to the new models.