Engineering block copolymers for advanced lithography

Block copolymer (BCP) nanoimprint lithography is an attractive possible solution for manufacturing hard disk drives with information densities greater than 1 Tbit/in². At these densities, individual bits must be smaller than 10 nm, and BCPs can be engineered to spontaneously self-segregate into features on this size scale. In addition to small feature sizes, industrially relevant BCPs should have simple orientation strategies and possess good etch contrast and resistance. Several silicon-containing BCPs were investigated due to the increased etch contrast and resistance imparted by silicon. The synthesis, characterization, and thin film studies of three silicon-containing BCPs are detailed. Due to the surface energy mismatch between the silicon-containing block and the organic block, solvent annealing and top coats were needed to perpendicularly orient these materials. While these materials possess many advantages, they each have shortcomings that prevent them from being ideal industrial materials. A derivative of poly(styrene-block-methyl methacrylate) was engineered to take advantage of its simple orientation procedure while decreasing the smallest achievable feature size. The synthesis and characterization, including determination of the [chi] parameter, of this BCP are detailed. The thin film assembly of this BCP was also successfully demonstrated, and this dissertation concludes with several ideas for future studies.Chemical Engineerin

Channel detection on two-dimensional magnetic recording

Two-dimensional magnetic recording (TDMR) coupled with shingled-magnetic recording (SMR) is one of next generation techniques for increasing the hard disk drive (HDD) capacity up to 10 Tbit/in2 in order to meet the growing demand of mass storage.We focus on solving the tough problems and challenges on the detection end of TDMR. Since the reader works on the overlapped tracks, which are even narrower than the read head, the channel detector works in an environment of low signal-to-noise ratio (SNR), two-dimensional (2-D) inter-symbol interference (ISI) and colored noise, therefore it requires sophisticated detection techniques to provide reliable data recovery. Given that the complexity of optimal 2-D symbol detection is exponential on the data width, we had to choose suboptimal solutions.To build our research environment, we use an innovative Voronoi grain based channel model which captures the important features of SMR, such as squeezed tracks, tilted bit cells, 2-D ISI, electronic and media noise, etc. Then we take an in-depth exploration of channel detection techniques on the TDMR channel model. Our approaches extend the conventional 1-D detection techniques, by using a joint-track equalizer to optimize the 2-D partial-response (PR) target followed by the multi-track detector (MTD) for joint detection, or using the inter-track interference (ITI) canceller to estimate and cancel the ITI from side tracks, followed by a standard BCJR detector. We used the single-track detector (STD) for pre-detecting the side tracks to lower the overall complexity. Then we use pattern-dependent noise prediction (PDNP) techniques to linearly predict the noise sample, so as to improve the detection performance under colored media noise, and especially the data dependent jitter noise. The results show that our 2-D detectors provide significant performance gains against the conventional detectors with manageable complexity

ON REDUCING THE DECODING COMPLEXITY OF SHINGLED MAGNETIC RECORDING SYSTEM

Shingled Magnetic Recording (SMR) has been recognised as one of the alternative technologies to achieve an areal density beyond the limit of the perpendicular recording technique, 1 Tb/in2, which has an advantage of extending the use of the conventional method media and read/write head. This work presents SMR system subject to both Inter Symbol Interference (ISI) and Inter Track Interference (ITI) and investigates different equalisation/detection techniques in order to reduce the complexity of this system. To investigate the ITI in shingled systems, one-track one-head system model has been extended into two-track one-head system model to have two interfering tracks. Consequently, six novel decoding techniques have been applied to the new system in order to find the Maximum Likelihood (ML) sequence. The decoding complexity of the six techniques has been investigated and then measured. The results show that the complexity is reduced by more than three times with 0.5 dB loss in performance. To measure this complexity practically, perpendicular recording system has been implemented in hardware. Hardware architectures are designed for that system with successful Quartus II fitter which are: Perpendicular Magnetic Recording (PMR) channel, digital filter equaliser with and without Additive White Gaussian Noise (AWGN) and ideal channel architectures. Two different hardware designs are implemented for Viterbi Algorithm (VA), however, Quartus II fitter for both of them was unsuccessful. It is found that, Simulink/Digital Signal Processing (DSP) Builder based designs are not efficient for complex algorithms and the eligible solution for such designs is writing Hardware Description Language (HDL) codes for those algorithms.The Iraqi Governmen

Self assembly of block copolymers : applicability in microelectronics and gains for patterned media

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references (leaves 88-93).As device size decreases, conventional lithographic methods are finding it increasingly hard to keep up. Introduction of newer method such as E-beam, X-ray lithography etc. has demonstrated possibility of scaling to lower dimensions. However most of these methods are too expensive, too complex or too slow. Hence a method is required which can provide high resolutions at low cost, is easy to implement and can be integrated with current processing technologies. Block copolymer self assembly promises to do just that. An immiscible block copolymer will microphase separate into individual domains due to unfavorable mixing enthalpy. These microphase-separated blocks can have domain sizes of very low dimensions, to the order of 15-20 nms. By careful preparation, microphase-separated thin films of immiscible block copolymers can act as nanomasks for a variety of applications in electronic, optoelectronic and storage media fields. One such application is patterned media. With ever increasing areal densities, there is a limit to which the grain size within a bit can be decreased, for a conventional thin film media. Beyond a certain limit, which is dictated by the superparamagnetic effect, these grains will spontaneously reverse, resulting in undesired data loss. Patterned media has been proposed as an alternative to surpass this thermal instability criterion. In patterned media, lithographically defined nano-scale magnetic elements form single bits onto which the data is stored. Due to its unique structure in which each magnetic dots act as a single magnetic domain it can postpone the arrival of superparamagnetic effect beyond densities much higher than 10 Terabits/inch². However, very high resolutions and strict positioning control is required for its fabrication so as to attain a marketable 1Tb/inch² advantage.(cont.) Block Copolymer self assembly holds great promise in fabrication of such devices requiring periodic, high resolution pattern generation. If issues such as long range order, pattern uniformity and placement accuracy of magnetic dots can be effectively resolved, block copolymer self assembly enabled lithography can quickly become the main stay of the multimillion dollar hard disk industry.by Anay Chaube.M.Eng

Nanoshape imprint lithography : fabrication and modeling

Complex nanoshaped structures have been shown to enable emerging nanoscale applications in energy, electronics, photonics and medicine. Such nanoshaped fabrication at high throughput is well beyond the capabilities of advanced optical lithography. Even the highest resolution electron beam lithography processes (Gaussian beam tools with non-chemically amplified resists) can achieve only ~10nm resolution, but at very low throughputs. In this work, fabrication of precise diamond-like nanoshapes with ~3nm radius corners is demonstrated using nanoimprint lithography. An exemplary shaped silicon nanowire ultracapacitor device was fabricated with these nanoshaped structures, wherein the half pitch was 100nm. The device significantly exceeded standard nanowire capacitor performance (by 90%) due to relative increase in surface area per unit projected area, enabled by the nanoshape. In the process of further scaling these nanoshaped structures to 10nm half pitch and below, a new “shape retention” resolution limit is observed due to polymer relaxation in imprint resists, which cannot be predicted with a linear elastic continuum model. An all-atom molecular dynamics model of the nanoshape structure is developed to study this shape retention phenomenon and accurately predict the polymer relaxation. The atomistic framework has been used as a modeling and design tool to extend the capability of imprint lithography to sub 10nm nanoshapes. This framework can propose process refinements that maximize shape retention, and design template assist features (design for nanoshape retention) to achieve targeted nanoshapes.Mechanical Engineerin

A Study of Periodic and Aperiodic Ferromagnetic Antidot Lattices

This thesis reports our study of the effect of domain wall pinning by ferromagnetic (FM) metamaterials [1] in the form of periodic antidot lattices (ADL) on spin wave spectra in the reversible regime. This study was then extended to artificial quasicrystals in the form of Penrose P2 tilings (P2T). Our DC magnetization study of these metamaterials showed reproducible and temperature dependent knee anomalies in the hysteretic regime that are due to the isolated switching of the FM segments. Our dumbbell model analysis [2] of simulated magnetization maps indicates that FM switching in P2T is nonstochastic. We have also acquired the first direct, two-dimensional images of the magnetization of Permalloy films patterned into P2T using scanning electron microscopy with polarization analysis (SEMPA). Our SEMPA images demonstrate P2T behave as geometrically frustrated networks of narrow ferromagnetic film segments having near-uniform, bipolar (Ising-like) magnetization, similar to artificial spin ices (ASI). We find the unique aperiodic translational symmetry and diverse vertex coordination of multiply-connected P2T induce a more complex spin-ice behavior driven by exchange interactions in vertex domain walls, which differs markedly from the behavior of disconnected ASI governed only by dipolar interactions

Enabling control of matter at the atomic level: atomic layer deposition and fluorocarbon-based atomic layer etching

The diminishing size of devices has necessitated the development of new patterning, deposition and etch techniques at ever-finer resolution, now approaching the atomic scale. Current trends in device manufacturing impose stringent requirements on nanoscale processing techniques, in terms of material properties and dimensional control. At the required nanoscale dimensions, additionally, surface composition and damage will be as important as physical dimensions for the desired functionality. Ultimately, the deposition and removal of arbitrary materials with single atomic layer precision are required. In this work I will present the insights of my work into fabrication processes and characterization techniques needed in the era of controlling matter at the atomic level using atomic layer deposition (ALD) and atomic layer etching (ALE). To address the challenges in atomic scale manufacturing, a solid understanding of materials and their physical and chemical interactions is required. In this work, the synergy between materials and different fabrication processes is investigated. By studying how ALD performs on spacer defined double patterning (SDDP) I demonstrate the engineering of sub-10 nm features. SDDP is generally limited in resolution due to lack of nanoscale processes at sub-10 nm dimensions. Here, I establish how thermal ALD allows for conformal deposition of a titanium dioxide spacer layer without damaging or modifying any substrate. In conclusion, the first successful fabrication of 7.5 nm titanium oxide features using SDDP is made possible by atomic scaled processes. While ALD has become productive enough to become a mainstream technology, the etch counterpart ALE has been more challenging. Indeed, removing material one atomic layer at a time is a complex scientific problem, especially when directional etching is required. In my work, a major goal was to develop methodologies that would allow the use of existing plasma etching tools for ALE. In this context, this work establishes and evaluates a cyclic fluorocarbon (FC) based approach for ALE of silicon dioxide, characterizes the mechanisms involved, and evaluates the impact of processing parameters. Using a cyclical FC and argon plasma process it is possible to atomically etch silicon oxide in a conventional plasma etch tool with minimal modifications. Plasma-based ALE allows for the directional etching required for deep narrow structures. For the first time, using the FC-based ALE processes, aspect ratio independent etching and high fidelity pattern transfer have been achieved. This result is obtained through a detailed study of the impact of plasma parameters on the SiO2 etch performance and using this information to achieve self-limiting behavior. Overall, this work proves how new technology nodes are enabled by ALD and ALE as part of the increasing trend toward the atomic scale processing.Die fortschreitende Miniaturisierung von Halbleiterschaltkreisen erfordert die Entwicklung neuartiger Strukturierungs-, Abscheidungs- und Ätzmethoden. Die dafür erforderliche Auflösung nähert sich heutzutage atomaren Maßstäben. Die derzeitigen Trends in der Fabrikation von elektronischen Schaltkreisen stellen strenge Anforderungen an die verwendeten Nanostrukturierungsmethoden, in Bezug auf Kontrolle der Materialeigenschaften und der Strukturabmessungen. Für diese nanoskalige Strukturen sind außerdem Oberflächenzusammensetzung und Oberflächendefekte genauso wichtig wie die Strukturabmessungen, um die gewünschte Funktionalität zu erreichen. Letztendlich ist es daher notwendig beliebige Materialien mit der Präzision einzelner atomarer Lagen abzuscheiden und abzutragen. Die vorliegende Arbeit untersucht geeignete Fabrikations- und Charakterisierungsprozesse für die Ära der atomar genauen Materialstrukturierung mittels sogenannter Atomic Layer Deposition (ALD) und Atomic Layer Etching (ALE). Um die Herausforderungen atomar genauer Materialstrukturierung zu adressieren ist ein tiefgehendes Verständnis der Materialien und ihrer physikalisch-chemischen Wechselwirkungen von Nöten. In der vorliegenden Arbeit wird die Synergie verschiedener Materialien und Fabrikationsprozesse untersucht. Durch Anwendung von ALD für die Doppelstrukturierung mittels Spacer-Technik (spacer defined double patterning, SDDP) wird gezeigt wie sich Strukturen mit Dimensionen unterhalb von 10 nm herstellen lassen. Generell ist die Auflösung von SDDP durch das Fehlen geeigneter Nanofabrikationsprozesse für Strukturen unterhalb von 10 nm limitiert. Die Arbeit etabliert, dass thermische ALD eine konforme Abscheidung einer Titandioxid-Spacer-Schicht erlaubt, ohne dabei das darunterliegende Substrate zu beschädigen oder zu modifizieren. Zusammenfassen lässt sich sagen, dass die erste erfolgreiche Fabrikation von 7.5 nm breiten Titanoxidstrukturen mittels SDDP nur durch die Anwendung von Prozessen auf atomarem Maßstab ermöglicht wurde. Während ALD bereits zu einer produktiven Standardtechnologie geworden ist, erweist sich die Etablierung des korrespondieren Ätzprozesses, nämlich ALE, als ungleich schwieriger. Tatsächlich ist die kontrollierte Materialabtragung um jeweils eine Atomlage ein komplexes wissenschaftliches Problem. Dies gilt besonders für direktionales Ätzen. Ein Hauptziel der Arbeit besteht in der Entwicklung von Methoden, die es erlauben existierende Plasmaätzanlagen für ALE zu verwenden. In diesem Zusammenhand etabliert und evaluiert diese Arbeit einen zyklischen Prozess basierend auf Fluorcarbonen (FC) für ALE von Siliziumdioxid. Es werden die beteiligten Reaktionsmechanismen charakterisiert und der Einfluss der Prozessparameter evaluiert. Mittels eines zyklischen FC- und Argon-Plasmas ist es möglich Siliciumdioxid atomar genau in einer minimal modifizierten, konventionellen Plasmaätzanlage zu ätzen. Plasma-basiertes ALE erlaubt direktionales Ätzen, das für tiefe, schmale Strukturen erforderlich ist. Zum ersten Mal werden hier sowohl seitenverhältnisunabhängiges Ätzen als auch hohe Zuverlässigkeit beim Strukturtransfer mittels FC-basiertem ALE erreicht. Das Resultat wird durch eine detaillierte Untersuchung des Einflusses der Plasmaparameter auf das Ätzverhalten von Siliziumdioxid und Anwendung der gewonnenen Informationen auf ein selbstlimitierendes Verhalten ermöglicht. Zusammengefasst demonstriert die vorliegende Arbeit wie neue Technologieknoten, die Teil des zunehmenden Trends zu atomar genauer Halbleiterprozessierung sind, durch ALD und ALE ermöglicht werden

STRUCTURES, PROPERTIES AND FUNCTIONALITIES OF MAGNETIC DOMAIN WALLS IN THIN FILMS, NANOWIRES AND ATOMIC CHAINS: MICROMAGNETIC AND AB INITIO STUDIES

Structures, properties and functionalities of magnetic domain walls in thin film, nanowires and atomic chains are studied by micromagnetic simulations and ab initio calculations in this dissertation. For magnetic domain walls in thin films, we computationally investigated the dynamics of one-dimensional domain wall line in ultrathin ferromagnetic film, and the exponent α = 1.24 ± 0.05 is obtained in the creep regime near depinning force, indicating the washboard potential model is supported by our simulations. Furthermore, the roughness, creep, depinning and flow of domain wall line with commonly existed substructures driven by magnetic field are also studied. Our simulation results demonstrate that substructures will decrease the roughness exponent ζ, increase the critical depinning force, and reduce the effective creep energy barrier. Current induced domain-wall substructure motion is also studied, which is found quite different from current induced domain wall motion. For magnetic domain walls in nanowires, field and current induced domain wall motion is studied, and some relevant spintronic devices are proposed based on micromagnetic simulations. Novel nanometer transverse-domain-wall-based logic elements, 360° domain wall generator and shift register are proposed. When spinpolarized current is applied, the critical current for domain wall depinning can be substantially reduced and conveniently tuned by controlling domain wall number in the pile-up at pinning site, in analogy to dislocation pile-up responsible for Hall-Petch effect in mechanical strength. Furthermore, threshold currents for domain wall depinning and transportation through circular geometry in planar nanowire induced by spin transfer torques and spin-orbit torques are theoretically calculated. In addition, magnetic vortex racetrack memory which combines both conceptions of magnetic vortex domain walls and racetrack is also proposed using micromagnetic simulations. For magnetic domain walls in Ni atomic chains, a truly magnetic domain wall structure and the single domain switching process are investigated by both ab initio studies and spin dynamics simulations. Spin moment softening effect caused by the hybridization effect between two spin channels is considered. The atomic domain wall as narrow as 4 atom-distance with slight spin moment softening effect indicates a relatively evident ballistic magnetoresistance effect, and the large EB indicates the strong stability of single domain state