Grayscale Laser
Lithography withHeidelberg Instruments
DWL Series

Hideo Jotaki
Heidelberg Instruments KK

Product Overview

Heidelberg Instruments Product LinesOverview
DWL Series

VPG Series

VPG+ 200 / 400

MLA Series

MLA100Nano Frazor Series

NanoFrazor Scholar

DWL 66+

MLA150DWL 2000/ 4000

VPG+ 800 / 1100 / 1400
MLA300

NanoFrazor ExploreDWL 2000 and 4000
High Resolution Pattern
Generators

DWL 66+
Ultimate Lithography
Research Tool

Our systems for
direct writing andlow volume mask
making –the DWL series

Acousto-optic modulator and deflector
AOM

Acousto-optic deflector
AOD0. orderscan
φ
1. ordersin j =RF-Voltage
f [MHz]RF-Voltage
f [MHz]t [µs]

Acousto-optic modulatort [µs]

l2d=lf2cs

Exposure strategy: The raster scan

Advantages:• Design independent
write time••High position
accuracy
Structure fidelity

Exposure strategy: The raster scanyStage Positionx

ULTRA
Semiconductor Laser
Mask Writer

VPG+Small Area
Volume Pattern
Generators
Large Area
Volume Pattern
Generators

architecture that supports column rates up to 350
kHz in AMP mode (1024 amplitude levels for eachpixels). Higher column rates can be achieved when
downloading a subset of pixels.
x The GLV module is separated from the controlelectronics with a flex cable to allow smaller opticalhead designs and facilitates optical alignment.
x Available in UV, Visible, Violet, or IR versions.

The Grating Light Valve1088 Channel High-Speed GLV Module Specifications
NominalMaximum

Number of Pixels

Minimum

1080

1088

Pixel Pitch

25.5µm355nm

UV version

405nm

Violet version

Operating WavelengthNotes

450543658nm

Visible version

800808825nm

IR version

80WIR version

Laser PowerOptical Rise Time

500

nsec

0th-order operation

Optical Fall Time

700

nsec

0th-order operation

Image Data Resolution

10bits350

Column Rate
March 4, 2016

>6000 ribbons
1088 pixelUnit■

KHz

Silicon Light Machines, 820 Kifer Road, Sunnyvale, CA 94086

Full 10-bit operation■www.siliconlight.com

GLV: The Grating Light Valve:
A 1D-spatial light modulator:
Ribbons of silicon-nitride on silicon chip; upand-down-position changed by voltage
à Groups of ribbons form a diffractive gratingà 3 variable and 3 fixed ribbons per pixelà Modulating laser light as per design data

Exposure strategy VPG+:
Raster scan, continuous scrollingLaserlightsource

Designdata
Spatial Light
Modulator - GLVMirror

Focusing lens
Scan width

Design andoperating
softwareScan direction
Writing
Process

Stage motion

Exposure strategy VPG+:
Raster scan, continuous scrolling
yStage PositionxµMLA
MLA150
MLA300

Maskless Aligners

The DMDTMDMD™ = digital multimirror device• MEMS device• Each pixel consists of••••an aluminum
micromirror
Two bias electrodes
tilt the mirror either to+10°or -10°
ON (+10°): Mirrorreflects light into lens,pixel is brightOFF (-10°): No
reflection, pixel isdark
DMD contains morethan 442,000
micromirrors-10°+10°

Simplified representation of twotilted mirrors (i.e. two pixels) in a
Texas Instruments DMD™
Schematic adapted from Marc J. Madou,
Fundamentals of Microfabrication andNanotechnology, Volume II, © CRC Press 2012

Exposure strategy MLA series

Bidirectional writing
processSPEED

The DMDTM

Exposure strategy MLA seriesNanoFrazor lithography

Heidelberg Instruments Nano
SwissLitho AG
16 February 2021

Technoparkstrasse 18005 Zurich, Switzerland

NanoFrazor Thermal Cantilevers
Key features» Ultra-sharp tip (silicon)» Integrated tip heater (resistive, up to 1100°C with 1 K resolution)» Integrated actuation (electrostatic for fast and accurate deflection)» Integrated topography sensor (unique AFM mode based on thermal distance sensor)
Tip with < 2 nm radius

5 µm
NanoFrazor Cantilever made of Si
Smart cantilever holder» Exchange within 1 min» Access almost any sample

2 µm

Glowing tip heater

Closed-Loop Lithography: Patterning & Imaging

1.
4.

2.

3.
Every few milliseconds:
1.

Patterning one linewith hot tip

2.

Cool down tip in few
microseconds

3.

Image topography ofwritten line

• No separate metrology necessary after lithography

4.

Feedback algorithm toadapt patterningÞDecrease total fabrication time5.

Patterning of next line

• “What You See Is What You Get”
• Check and online adaption of patterning every few msÞIncrease accuracy and reliability

www.heidelberg-instruments.com

Principle of NanoFrazor
Writing

Reading

Thermal probe

in-situ high-speed AFM» 10 nm sharp tip» Inspection» fast and accuratedeflection» Metrology

Laser sublimation

unique distance sensor» micrometerresolution» Level plane & Autofocus» 100x faster» Overlay & Stitching» Drift corrections» Other calibrations

Product Overview

The Basic Principle•

Binary Exposure
LightExposure

Development

ResistSubstrate•

Gray scale Exposure
LightExposure

ResistSubstrate

Development

Exposure strategy in DWL systems
AOM(acousto-opticModulator)

U ~ Intensity
f ~ Deflection angle
AOD(acousto-opticdeflector)

MirrorFocusing lens
Scan width

ScanWidth

Substrate motion

Acousto-optic modulator and deflector
AOM

Acousto-optic deflector
AOD

0. orderscan
φ1. order

sin j =

RF-Voltage
f [MHz]RF-Voltage
f [MHz]t [µs]

Acousto-optic modulatort [µs]

l2d=lf2cs

Exposure strategy in DWL systems
AOM
RF-Voltage
U [V]

1. ordert [µs]

Pattern definition… in design coordinates(STL, XYZ-ASCII)… in bitmap grayvalues(BMP,PNG)… in design layers(DXF)(x1,y1,z1)
Layer 0Layer 1(x2,y2,z2)(x3,y3,z3)
zyLayer nx

HIMT CONVERSION SOFTWARE
Coordinates(xi,yi)

Exposure DoseGV = {0,1024}

CAD data

Gray valuedata

Challenges in grayscale lithography...
Stitching & other defects

Resist non-linearity

Proximity & process effects

Design Layout

UV light distribution

Exposure Result

Depth in resist [µm]Maximum structure depth
0-10-20-30-40-50-60

Light intensity... and our solutions

Stitching optimization• Small intensity variations at the border
between stripes•

Instead of spreading structures across multiple stripes…

• Not visible in binary exposures

Stripe 1•

Stripe 2… place them inside a single stripe and optimize the stripe position
Stripe 2

StripewidthScan
WidthStripe 1
Stripe 1

Stripe 2

Stitching optimization
Idea: Smoothen stitching by averaging multiple exposures

n-Over 4

n-Over 10

n-Over 40

CI-Over 4

CI-Over 10

CI-Over 40“n-Over:“ n-times overlapping

1/2 stripe width -> “n-Over 2“Up to n-Over 40 possible

Non-linearity & proximity effects
Design Layout

Design Layout

UV light distribution

UV light distribution

Exposure ResultExposure Result

Creating linear
topographies usuallyrequires a non-linear lightintensity distributionDepth in resist [µm]Intensity ( % of maximumenergy)

Shape Optimization:
Linearization

Gray value• Resist does not respond linearly• Minimum energy needed forphotoreaction• Exposure proximity effect• Lateral development effectGray value

Withoutlinearization→ Geometry dependent32

GRAY SCALE OPTIMIZATION METHODS
Gray Value Table (GVT)

Automatic Intensity Correction(AIC)!

•••

Maps design gray value tocustomized gray value
Transformation at conversion level
Decrease of gray level resolution•••

Assigns design gray value to energylevel
Transformation at exposure level
Keeps gray level resolution

Large Area Gray Scale Lithography

Depth in resist [µm]Intensity ( % of maximumenergy)

Shape Optimization:
Linearization

Gray value• Use of a non-linear
relation between GVand energy:• One of 65000
energy levels
can beassigned toeach grayvalue

Gray value
AOMWi
thRF-Voltage
U [V]

255
35

255

170

129

90
10

135
t [µs]

linearization

Non-linearity & proximity effects
GVD approach
CHOOSE INITIAL GV
DISTRIBUTIONEXPOSURENon-linearity & proximity effects
GVD approach
CHOOSE INITIAL GV
DISTRIBUTIONEXPOSURE

MEASURE GEOMETRY AND
COMPARE TO TARGETHeightOK?

X

Non-linearity & proximity effects
GVD approach
CHOOSE INITIAL GV
DISTRIBUTIONEXPOSURE

MODIFY GRAY VALUE

MEASURE GEOMETRY AND

DISTRIBUTION OR DESIGNCOMPARE TO TARGETOK?

HeightNOX

Non-linearity & proximity effects
GVD approach
CHOOSE INITIAL GV
DISTRIBUTIONEXPOSURE

MODIFY GRAY VALUE

MEASURE GEOMETRY AND

DISTRIBUTION OR DESIGNCOMPARE TO TARGETOK?
YESHeightNO

FINAL EXPOSUREX

Why we need 1024 Grey Levels
ABWhy we need 1024 Grey Levels

1024 levels

256 levels

BA

D

C

256 levels

256 levels

B

256 levels

DCABCD︕

Works quite well, but...
• ... can be very time consuming• ... requires compromises• ... fails for irregular designs

Target Cross
SectionNon-linearity & proximity effects
GVD approach

Hexagonal microlens array

Top view

Courtesy of IGI

Positions with same theoretical depth, butdifferent local environmentÞ Same dose assignment leads todifferent resulting depth!

Non-linearity & proximity effects
BEAMER 3D-PEC

Shape Optimization:
Genisys Beamer 3D PEC
norm. height [a.u.]

exemplary contrast
curve

d0 d20 d40 d60 d80 d100

Resist pattern cross section(defined by layout)

Dose [uC/cm2]

28%

100%

92%

60%
60%

80%

35%

0%

Including
proximityeffects

35%

Adjusted dose distribution(top view)

100%

Resist height [nm]Process chain for multilevel resist pattern

Laser imaging modelNon-linearity & proximity effects
BEAMER 3D-PEC
Example: DOE

Maximum structure depth
So far: Limited to ~ 55 µm due to high absorption inupper resist layers
0Depth in resist [µm]-10-20-30-40-50-60

Light intensity

Now: Novel grayscale resist
ma-P 1200 G

RESIST
Ideal resist for Binary Lithography

Resist Thickness

Dose

Ideal resist for Greyscale Lithography

Resist Thickness

DoseRESISTTypical reaction ofresist for Binary Lithography

Resist Thickness

Dose

Typical reaction ofresist for Greyscale Lithography

Resist Thickness

DoseRESISTNCX GDX-002
30

Depth (um)

25
20
15
10
50050

100

150

200

measurement point
Try 2

MATERIAL IS IMPORTANT!

250

Maximum structure depth
Very recent results:

Heidelberg Instruments Nano (SwissLitho AG)
discrete levels (1.5 nm)

error (1σ): 0.69 nm

3 µm
Rawlings et al, Sci. Rep., 2017

NanoFrazor Explore

NanoFrazor Scholar

Ristic et al, OSA Tech Digest, 2015

Kulmala et al, SPIE Adv. Litho., 2018

Heidelberg Instruments Nano (SwissLitho AG)
Thermal Scanning Probe Lithography
5 µm

5 nm

3D patterning with vertical resolution < 1 nm
continous sine wave

discrete levels (1.5 nm)
error (1σ): 0.69 nm

error (1σ): 0.85 nm

2 µm

3 µm

Published examples for 3D grayscale
SiO2200 nm

2 µm

Hologram in Si (700 nm deep)

Phase Plates in SiN membranesKulmala et al., SPIE, 2018

Hettler et al., Micron, 2019

Optical Fourier Surfaces

Lassaline et al., submitted to Nature, 2020

Nanofluidic Brownian Motors

Topographies for stem cells

Photonic molecules

Skaug et al., Science, 2018

Tang et al., ACS Appl. Mat., 2019

Rawlings et al., Scientific Reports, 2017

3D Nanofluidics» Ratchets with nm accuracy» Nanoparticles sorting using Brownian Motors• Mastertextformat bearbeiten» Particles with 1 nm size difference move in
opposite directions• Zweite Ebene• Dritte Ebene• Vierte Ebene• Fünfte Ebene

Skaug et al., Science, 2018

Thank you foryour attention!
Heidelberg Instruments
Mikrotechnik GmbH
Tullastr. 269126 Heidelberg
Germany
Phone +49 6221 3430-0
www.himt.de
www.thelithographer.com

The power of direct writing