Asymmetric fluid-structure dynamics in nanoscale imprint lithography

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Asymmetric Fluid-Structure Dynamics in Nanoscale Imprint LithographybyAnh Quoc Nguyen, M.S.E.The University of Texas at Austin, 2001Supervisor: S.V. SreenivasanThis thesis investigates the effect of the fluid mechanics of a lowviscosity, UV curable liquid film on the system dynamics of an imprinting systemused in a patterning process known as Step and Flash Imprint Lithography(SFIL). SFIL is a novel, low-cost, high-throughput alternative approach topatterning nanoscale features for semiconductor applications. This research isessential to the practical development of the SFIL process and is applicable to thedevelopment of a real-time control scheme for SFIL.The thesis starts with an introduction to optical lithography, establishednext generation lithography (NGL) research efforts, and SFIL. A theoreticalanalysis of the template-fluid-wafer (TFW) system shows that the imprintingpressures are proportional to the approach velocity of the template towards thewafer and the inverse of the cube of the film thickness, h 3 . Analytic solutions tothe pressure distribution due to the etch barrier fluid are applied to numericalsimulations, which are benchmarked by experiments using an active stageprototype. The development of an active stage prototype is detailed and a realtimegap sensing system for sub-micron films based on the FFT of spectralreflectivity is discussed. The experiments and simulation show that the TFWsystem is overdamped. An asymmetric squeeze film pressure distributionprovides a corrective torque in the presence of orientation misalignments.vi
Table of ContentsList of Tables .........................................................................................................xList of Figures.......................................................................................................xiChapter 1: Background and Motivation.............................................................11.1 INTRODUCTION ........................................................................................11.2 OPTICAL LITHOGRAPHY ..........................................................................31.2.1 Optical Lithography Process Overview ..........................................41.2.2 Limitations of Optical Lithography ................................................51.3 STEP AND FLASH IMPRINT LITHOGRAPHY ...............................................81.3.1 Step and Flash Imprint Lithography Process Overview .................81.3.2 Challenges to Step and Flash Imprint Lithography.......................111.4 THESIS...................................................................................................15Chapter 2: Theoretical Analysis ........................................................................172.1 INTRODUCTION ......................................................................................172.2 THE INCOMPRESSIBLE REYNOLDS EQUATION........................................202.3 THE TWO-DIMENSIONAL REYNOLDS EQUATION ...................................262.3.1 Derivation of the Two-Dimensional Reynolds Equation..............262.3.2 Squeeze Film Due to a Parallel Surface of Infinite Width............282.3.3 Squeeze Film Due to an Inclined Surface of Infinite Width.........292.4 THREE-DIMENSIONAL PROBLEM ...........................................................352.4.1 3D Pressure Distribution for Parallel, Rectangular Plates ............352.4.2 3D Pressure Distribution for Parallel, Circular Plates ..................382.5 TOPOGRAPHY EFFECTS..........................................................................39Chapter 3: Active Stage Design .........................................................................413.1 OPTIMIZING BASE LAYER THICKNESS, ORIENTATION ALIGNMENT, ANDTHROUGHPUT.................................................................................41vii
Page 3 and 4: Asymmetric Fluid-StructureDynamics
Page 5: AcknowledgementsFirst of all, I wou
Page 9 and 10: 6.2.3 Control Software ............
Page 11 and 12: List of FiguresFigure 1.1 Optical m
Page 13 and 14: Figure 6.9 Force due to fluid press
Page 15 and 16: The exponential escalation in the c
Page 17 and 18: 1.2.1 Optical Lithography Process O
Page 19 and 20: patterns to the desired specificati
Page 21 and 22: 1.3 STEP AND FLASH IMPRINT LITHOGRA
Page 23 and 24: transferlayerwaferStep 1: Spin-coat
Page 25 and 26: the etch barrier fluid has an infin
Page 27 and 28: Researchers at the University of Te
Page 29 and 30: stage development. Design requireme
Page 31 and 32: minimum and maximum base layer thic
Page 33 and 34: square plate with fluid completely
Page 35 and 36: 7. The fluid is assumed incompressi
Page 37 and 38: ⎛ ∂ ⎞⎜τdz ⎟dxdy⎝+ τ
Page 39 and 40: where V 1 and V 2 correspond to U 1
Page 41 and 42: ddx⎛⎜h⎝3dp ⎞ ∂h⎟ = 12µ
Page 43 and 44: dhdtLzhθh αh βxx αx = 0 x βFig
Page 45 and 46: C2hhtanθ2 21= αxαxβxαxβ( ) (
Page 47 and 48: ⎛⎜ hD⎜⎝6C ⎞1tanθ⎟24µh
Page 49 and 50: at the plate edges. Freeland obtain
Page 51 and 52: For the case of 10 psi of pressure,
Page 53 and 54: are the same as the width of the tr
Page 55 and 56: orientation stages relative to the
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Wafer ChuckAir SolenoidMounting Pla
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The one degree-of-freedom template
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Figure 3.7 Initial and final desire
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7645321Figure 3.8 Active stage prot
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Chapter 4: Real-Time Gap Sensing Vi
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R( λ)( 4πnd/ λ)2 2 −2αd−αd
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Rate Monitoring and is adapted for
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10090807060PSD504030201000 500 1000
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the multi-imprint and active stage
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5.2.2 Composite Stiffness and Dampi
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( )2πR−1.5clamping length of 1.5
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65actuator height, micron432100 0.1
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time marching is required to minimi
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5.4 SQUEEZE FILM DYNAMICS OF INCLIN
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force, lb504540353025201510500 0.05
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improve upon these results by tunin
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Again, Figure 5.12 shows that a bas
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optically flat quartz plate coated
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optic probe was illuminated with a
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Figure 6.3 Screenshot of control so
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6.3 EXPERIMENTAL PROCEDUREExperimen
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film thickness, nm40003800360034003
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Figure 6.6 shows that the force due
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similar. In Figures 6.7 and 6.8, th
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500045004000film thickness, nm35003
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Figure 6.13 shows the force-time pl
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⎛ n ⎞in the FFT that is not ind
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when measuring thin layers in the r
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is a major milestone. The next step
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7.2.4 Control schemeThe ultimate go
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Assuming the liquid perfectly wets
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ase h (for a semi-circular notch,h
Page 121 and 122:
Chou, S. Y., P .R. Krauss, and P. J
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Tripp, J. H. 1983. Surface roughnes
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