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Spie Press Book

Molecular Theory of Lithography
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Book Description

This book is a unified exposition of the molecular theory that underlies lithographic imaging. It explains with physical-chemical theories the molecular-level interactions involved in lithographic imaging. It also provides the theoretical basis for the main unit operations of the advanced lithographic process, as well as for advanced lithographic imaging mechanisms, including photochemical and radiochemical, imprint, and directed block copolymer self-assembly imaging mechanisms. The book is intended for students and professionals whose knowledge of lithography extends to the chemistry and physics underlying its various forms. A familiarity with chemical kinetics, thermodynamics, statistical mechanics, and quantum mechanics will be helpful, as will be familiarity with elementary concepts in physics such as energy, force, electrostatics, electrodynamics, and optics.


Book Details

Date Published: 17 December 2015
Pages: 488
ISBN: 9781628415513
Volume: PM255

Table of Contents
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Table of Contents

Preface

Acronyms and Abbreviations

Overview of Lithography
1.1 Introduction
1.2 The Lithographic Process
1.3 Advanced Lithographic Patterning Techniques and Imaging Mechanisms
     1.3.1 Optical lithography
     1.3.2 Extreme ultraviolet lithography
     1.3.3 Electron beam lithography
     1.3.4 Ion beam lithography
     1.3.5 Imprint lithography
     1.3.6 Molecular self-assembly lithography

2 Theory of the Lithographic Process
2.1 Introduction
2.2 Adhesion Promotion
2.3 Resist Coating
     2.3.1 Resist spin-coating process
     2.3.2 Characteristics of thin resist films
     2.3.3 Instabilities in UTR films
2.4 Soft Bake
2.5 Alignment
2.6 Exposure
     2.6.1 Basic imaging theory
     2.6.2 Aerial image formation
     2.6.3 Standing wave models
     2.6.4 Image formation in the resist
     2.6.5 Continuum modeling of latent image formation in the resist
     2.6.6 Stochastic modeling of latent image formation in resists
2.7 Development
     2.7.1 Resist development methods
     2.7.2 The nature of the development process
     2.7.3 Solubility switching approaches to realizing contrast between exposed and unexposed regions of the resist during
               development
     2.7.4 Types of development in resist processing
     2.7.5 Kinetics and mechanism of resist polymer dissolution
2.8 Postdevelopment Bake and Resist Stabilization Treatments
     2.8.1 Postdevelopment bake
     2.8.2 UV radiation curing
     2.8.3 Electron beam curing of resists

3 Theory of Molecular Interactions in Lithography
3.1 Introduction
3.2 Combining Relations and Interactions that Determine the Solubility Switch and Contrast in Lithographic Resist Systems
3.3 Molecular Solubility Modulation and Lithographic Contrast
     3.3.1 Molecular solubility modulation
     3.3.2 Lithographic contrast
3.4 Molecular Interactions in Lithography
     3.4.1 General van der Waals interactions operating during resist film PEB and development in the developer solution
               medium
     3.4.2 General electrostatic interaction forces operating in resist solvent development
     3.4.3 Van der Waals and double-layer electrostatic interactions between the resist and developer, and between charged
               species in the developer
     3.4.4 Hydrophobic interaction forces operating during resist solvent development
     3.4.5 Steric interactions
     3.4.6 Hydration interactions
     3.4.7 Acid–base interactions
     3.4.8 Hydrogen bonding interactions
3.5 Overall Developer–Resist Interaction Potential and the Dissolution Process
     3.5.1 Estimating the overall interaction energy of the developer–resist film system
3.6 Resist Dissolution Process
     3.6.1 Thermodynamics of resist polymer dissolution
3.7 Molecular Interactions Operating in Thermally Driven Diffusion of Photoacids During PEB of Resist Films
     3.7.1 Interactions between immiscible polymer–polymer interfaces of the exposed and unexposed parts of the resist
               polymer film
     3.7.2 Ambipolar diffusion of photoacid ions
     3.7.3 Acid evaporation at the resist–air interface
3.8 Dissolution Properties of Resist Polymers

4 Theory of Photochemical and Radiochemical Lithographic Imaging Mechanisms
4.1 Introduction
4.2 Preliminary Remarks on Resist Photochemistry and Photophysics
     4.2.1 Quenching processes of excited states
     4.2.2 Excited-state complexes
     4.2.3 Energy transfer
     4.2.4 Energy migration in resist polymers
     4.2.5 Spectral sensitization
     4.2.6 Radiation chemistry versus photochemistry of resists
     4.2.7 Radiation chemical yield and dosimetry
     4.2.8 Radiation chemistry of resist polymers
     4.2.9 Sensitivity and exposure radiation
     4.2.10 Exposure mechanisms of resists and exposure radiation
4.3 Negative-Resist Imaging Mechanisms
     4.3.1 Radiation-induced crosslinking imaging mechanisms
     4.3.2 Radiation-induced polarity-change imaging mechanism
     4.3.3 Radiation-initiated polymerization imaging mechanisms
     4.3.4 Photoinitiated cationic polymerization imaging mechanisms
4.4 Positive-Resist Imaging Mechanisms
     4.4.1 Photolysis and radiolysis imaging mechanisms
     4.4.2 Photo- and radiation-induced main-chain scissioning imaging mechanisms
     4.3.3 Photo- and radiation-induced depolymerization imaging mechanisms

5 Theory of Block Copolymer Self-assembly Lithographic Imaging Mechanisms
5.1 Introduction
5.2 Block Copolymer Synthesis
     5.2.1 Block copolymers via anionic polymerization
     5.2.2 Block copolymers via controlled radical polymerization
     5.2.3 Block copolymers via cationic polymerization
     5.2.4 Improving chemical and thermal stability of block copolymers
5.3 Physics of Micro- and Nanophase Separation in Block Copolymer Systems
     5.3.1 Phase formation and construction in a symmetric AB diblock copolymer melt
5.4 Domain Orientational Control and Long-Range Ordering
     5.4.1 Neutral brushes for perpendicular alignment
     5.4.2 Chemical patterning or chemo-epitaxy
     5.4.3 Topographical patterning with grapho-epitaxy
     5.4.4 Solvent annealing
     5.4.5 Other methods used in aligning the orientation of self-assembling block copolymers
5.5 Lithographic Patterning with Block Copolymers
     5.5.1 Block copolymers as lithographic etch masks
     5.5.2 Block copolymers as templates for patterning inorganic materials
     5.5.3 Block copolymers as templates for biomolecular patterning

6 Theory of Imprint Lithographic Imaging Mechanisms
6.1 Introduction
6.2 Imprint Resist Materials
6.3 Imprint Lithographic Imaging Mechanisms
     6.3.1 Thermal imprint lithographic imaging mechanism
     6.3.2 Photoimprint lithographic imaging mechanism
     6.3.3 Comparison of PIL and TIL
6.4 Theoretical Models of the Imprinting Process
     6.4.1 General considerations on the viscoelastic properties of polymers
     6.4.2 Squeezing flow theory of the imprint process

Index


Preface

The science and technology of lithography, especially advanced semiconductor lithography, have now reached such an advanced stage of development and promise such numerous applications (as evidenced by the numerous technologies that the field is now enabling—from electronics to photonics, catalysis to medicine, energy transduction and storage to sensing) that there is a need for a single, reasonably complete, unified exposition of the molecular theory that underlies lithographic imaging. This book is intended to fill this need. It attempts to systematically explain with physical-chemical theories the molecular-level interactions that underlie the essential aspects of lithographic imaging phenomena. The effects of such molecular-level interactions become all the more heightened in the regime of single-digit to a few tens of nanometer-patterned feature length scales, a regime that overlaps the radius of gyration of the resist polymers used in the patterning. In addition, the book will provide the theoretical basis for the main unit operations of the advanced lithographic process, as well as for advanced lithographic imaging mechanisms, including photochemical and radiochemical, imprint, and directed self-assembly imaging mechanisms.

The book is intended for students and professionals whose knowledge of lithography extends to the chemistry and physics underlying its various unit operations, and the imaging mechanisms of its various forms. The methods of physical chemistry are used as far as possible; therefore, a certain familiarity with chemical kinetics, thermodynamics, statistical mechanics, and quantum mechanics will be helpful, as will be familiarity with elementary concepts in physics such as energy, force, electrostatics, electrodynamics, and optics. For the rest, the book has also been written to be of service to readers who are not studying the above-named subjects; to this end an effort has been made to be particularly complete with bibliographic references in the text.

I am particularly grateful to Dr. Chris Mack, Editor of the Journal of Micro/Nanolithography, MEMS and MOEMS, who read and commented on the entire manuscript and provided numerous suggestions for improvement. I am also grateful to Dr. Manuel Thesen of micro resist technology GmbH, who read parts of the manuscript and provided suggestions for improvement.

I would also express my sincere appreciation to the editorial staff of SPIE Press, especially Dara Burrows and Tim Lamkins, who oversaw the production and publication of the book.

Uzodinma Okoroanyanwu
November 2015


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