Graduation Year

2022

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemical Engineering

Major Professor

Clifford L. Henderson, Ph.D.

Committee Member

David S. Simmons, Ph.D.

Committee Member

Ryan Toomey, Ph.D.

Committee Member

Michael Cai Wang, Ph.D.

Committee Member

Peter J. Ludovice, Ph.D.

Keywords

Advanced Lithography, Defectivity, Functional polymers, Molecular Dynamics, Organic Nanotechnology

Abstract

Over the course of the past 80 years, semiconductor devices have become increasingly ubiquitous in everyday life.From constructing mainframes that encompassed entire rooms during the 1940s, to inventing personal computers in the 1980s, to developing progressively faster smartphones and wearable technology in the 2010s, the primary driving force behind the Digital Revolution has been increasing transistor counts, and thus computing power, via incremental improvements in optical lithography. In 1965, Intel co-founder Gordon Moore boldly predicted that the transistor density of semiconductor devices would double approximately every 18-24 months. While this prediction -- now colloquially referred to as Moore's Law -- was largely realized for the better part of five decades, progress has slowed as feature sizes have shrunk below 20 nm and device fabricators have begun to approach the theoretical resolution limit of optical lithography.

In order to continue feature scaling at the rate Moore predicted, several potential extensions to optical lithography have been presented, including extreme ultraviolet (EUV) lithography, ion-beam lithography, electron-beam lithography, nano-imprint lithography, and block copolymer (BCP) directed self-assembly (DSA).Block copolymer DSA is a particularly intriguing approach because existing fabrication equipment can largely be retrofitted to accommodate device patterning with DSA; on the other hand, EUV, electron-beam, and ion-beam lithography either require cost-prohibitive instrumentation or have significant throughput limitations. DSA technology exploits a unique feature of block copolymers in which they can microphase separate into various nanoscale morphologies such as spheres, cylinders, gyroids, and lamellae. Cylinders and lamellae are of particular interest to the microelectronics community because of their direct applications in contact-hole patterning and line-space patterning, respectively. Although the nanostructures found in bulk block copolymer materials are naturally unaligned, directed self-assembly techniques such as graphoepitaxy and chemoepitaxy use a pre-patterned underlayer to guide the BCP features into the desired orientation.

Despite the promising qualities that block copolymer directed self-assembly provides, several issues must be addressed before DSA can become viable in high-volume semiconductor manufacturing applications.The Semiconductor Research Corporation (SRC) identified three critical research needs for advancing DSA in its May 2020 Call for Research. These high priority research needs include defect improvement through material synthesis, multi-pitch patterning using a single block copolymer, and implementing vertical orientation. The work proposed here aims to address these issues by investigating the following questions:

  1. Is homopolymer an effective additive for modulating block copolymer pitch? If so, what are the effects of homopolymer blending on line edge roughness and line width roughness?
  2. Can two or more block copolymers with discrete molecular weights be effectively blended in order to tune pitch? Does blending multiple BCP populations increase the measured line edge roughness and line width roughness?
  3. What are the root causes of bridge defects found in thin-film block copolymers? Can structural or energetic properties of either the underlayer or the thin-film block copolymer be tuned in order to limit the frequency of bridge defects?
  4. Can enhanced polymer simulation algorithms be implemented to increase the efficiency of simulations while maintaining overall thermodynamic and structural fidelity?

By designing molecular dynamics simulation routines that target these currently unsolved questions, this work will shed further light into the feasibility of incorporating block copolymer directed self-assembly into high-volume semiconductor manufacturing.

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