The Critical Role of Metrology in Nanofabrication - Space ...

The Critical Role of Metrology in Nanofabrication
Mark L. Schattenburg
Space Nanotechnology Laboratory
~
Center for Space Research
~
Massachusetts Institute of Technology
Microlunch Seminar
MIT Microsystems Technology Laboratories
April 8, 2003
Massachusetts Institute of Technology

MLS-2001-05-11.01eps
NASA Chandra X-ray Observatory
High Energy Transmission Grating Spectrometer (HETGS)
HETGS instrument.
1.1 meter
Invar grating frame.
3 cm
Scanning electron micrograph of gold grating.
100 nm
550 nm

Metrology Frames
• Metrology frames underpin all planar dimensional metrology.
• A key set of semiconductor manufacturing tools depend on metrology frames:
Coordinate measuring tools.
Diamond turning machines
Lithography mask (reticle) writers.
Lithography scanners/steppers.
CD metrology tools.
Pattern placement and overlay metrology tools.
Circuit and mask repair tools.
• A metrology frame consists of three components:
Stable structure.
Length scale (e.g., wavelength of light).
Means to compare workpiece with length scale (e.g., microscope).
• The heterodyne laser interferometer is the de facto length scale.
Massachusetts Institute of Technology

MLS-2001-03-23.01.eps
Computer
Traditional Heterodyne
Displacement Measuring Interferometer (DMI)
Laser
Fiber-optic
Cables
RS-232 / GBIP
50%
Beamsplitter
Fiber-optic
Pickup
Electronics
Two-axis
Stage with
Mirrors
Interferometer
Head
DMI Limitations
Moving arms create
time-dependant cosine,
Abbe, diffraction
& other path errors.
Air paths introduce large
errors due to atmospheric
disturbances:
-> Temperature, Pressure
-> Humidity, Turbulence
System is bulky
and expensive.
Heavy stage mirrors
limit stage scanning
speed & accuracy.

Zygo-Interferometer.eps
Wafer
Reticle
Lens
Measurement
Beams
Lithography Scanner
Substrate and Reticle Stages
Collimated UV
Light Beam
Reticle Stage
Mirrors
Wafer Stage
Mirrors
Laser Head
Scanner Mechanics
Reticle is imaged onto wafer
with ~4x reduction.
Reticle and wafer stages
are synchronously scanned
during exposure.
Tight pattern overlay (~30% CD)
requires extremely high
stage performance.
Interferometer is significant
drag on stage accuracy and
performance.

MLS-1997-05-01.01.eps
Diode
Laser
Diffraction
Grating Region of
Interference
Collimating
Lens
+1
-1
Principal of Optical Encoder
Sinusoidal
Fringes Detector
Array
4-Bin
Output
Encoder Advantages
Short, balanced arms are
immune to atmosphere.
Arms have constant length.
Eliminates path errors.
Grating can be patterned on
stiff, low-CTE substrate.
Eliminates moving
interferometer mirrors.
Problem
Accurate encoder plates
unavailable.

Encoder-Stage.eps
Reticle
Encoder
Plate
Reticle
Lens
Wafer
Encoder
Plate
Wafer
Lithography Scanner
With Optical Encoder Metrology
Reticle
Encoder
Plate
Wafer
Encoder
Plate
Wafer
Stage
Reticle
Stage
Read
Head
Stage Metrology with
Grid Optical Encoder
Stationary encoder plates.
Read heads fixed to stage.
Lighter stage has higher speed,
increased accuracy.
Encoder essentially
immune to atmosphere.

MLS-1997-01-20.08.eps
Resist
Left
Beam
Interference Lithography
2
Substrate
Grating Period p=/(2sin)
Right
Beam

MLS-2000-04-03.01.eps
Spherical waves cause
hyperbolic distortion.
Hyperbolic Phase
Traditional Interference Lithography
laser
Optics figure & defects
limit grating accuracy.
Linear Phase
laser

MLS-1999-05-26.03.eps
Variable
Attenuator
Mirror
Beamsplitter
p = λ
2sinθ
Interference Lithography
Beamsplitter
Spatial Filters
2θ
Pockels Cell
Substrate
Laser Beam
λ = 351.1 nm
Phase Error
Sensor
Mirror

MLS-2000-04-04.02.eps
Optical
Bench
Interferometer
Scanning-Beam Interference Lithography
Laser
XY Stage
Air Bearing Granite Block
Substrate
Y Direction
Y Direction
X Direction
Parallel Scanning
X Direction
Doppler Scanning
Scanning
Grating
Image
Air-Bearing
X-Y Stage
Resist-
Coated
Substrate
Scanning
Grating
Image

PTK-99-01-09-1
Y Direction
X Direction
(a) Scanning Scheme
Intensity
Scan
1
Grating Scanning Method
Grating
Image
Air-Bearing
Stage
Substrate
Summed Intensity
of Scans 1-6
Scan
2 Scan
3
Scan
4
Scan
5
Intensity
Scan
6
(b) Image Intensity Profile
(c) Overlapping Scans
Closely Approximate
a Uniform Intensity
Distribution
X
Grating
Period
p=λ/(2sinθ)
X

RKH-01-01-02.3
(a) Writing Mode
SBIL Reading and Writing Modes
DSP/
Frequency
Comparator Synthesizer
AOM1
DSP/
Comparator
Stage
Control
f L
AOM2
PM1
Wafer
X-Y Stage
PM2
AOM3
f R
f H
Stage
Control
PM4
AOM2
f L
Frequency
Synthesizer
PM3
Grating
X-Y Stage
AOM3
f R
(b) Reading Mode
CCD

RKH-2000-04-06
D
L
f 0 f 0 +F C
θ B
Principle of
Acousto-Optic Diffraction
Λ
RF Transducer
Quartz
v
F C
Sound Wave
λ
2θB = −
Λ
f 0

Metrology block with
phase measurement
optics
Wafer
Chuck
X-Y air bearing
stage
Front of System
Receiving tower
for UV laser
(λ = 351.1 nm)
MIT Space Nanotechnology Laboratory
ptk-frontsystem-032703.eps
Optical bench with
interference lithography
optics
Refractometer
interferometer
X-axis interferometer
Granite base
Isolation system

Super invar chuck
flexure mounted
to stage
Super invar
mounts for optics
Zerodur mirrors
bonded to chuck
Metrology Frames
Zerodur metrology block flexure
mounted to bench, super invar
inserts
ptk-metrologyframes-032903.eps
Refractometer
cavity, bonded
mirrors
x-axis column
reference mirror
MIT Space Nanotechnology Laboratory

SBIL Environmental Enclosure
Environmental parameters: Temperature
Pressure
Humidity
Particles
Acoustics
Air Handlers
Chamber
MIT Space Nanotechnology Laboratory
ptk-enclosure-032903.eps

Analog Input:
Power Sensors.
Sensors, general.
D/A PMC
A/D PMC
IXC6 Master/
DSP/Power PC
Analog Output:
Stage Linear Amplifiers
Vibration Isolation Feedforward.
Analog Test Points.
PC
Host
ZMI 2002
VME Bus
ZMI 2002
Control Architecture
Realtime Control Platform LabVIEW-Based I/O
ZMI 2002
ZMI 2002
VME Rack
Digital Change
of State Board
TTL Digital
Input/Output
TTL Digital
Input/Output
ZMI 2001
Refractometer.
Lithography
Interferometers
Stage
Interferometers
Power
Supply
Stage Position Limits
Air-bearing Pressure Limit
LabVIEW PC Control Lines
Digital Frequency
Sythesizer
Reference clock from Zygo laser
Comm. to LabVIEW PC
Acousto-Optic
Modulators
NI IMAQ 1424
Frame Grabber
NI PCI-DIO-96
Digital I/O
NI 6034E
Analog I/O
NI 6034E
Analog I/O
MIT Space Nanotechnology Laboratory
PC
Internal PCI Bus
Position Sensing
Detectors
Picomotor Driver
Communication to
IXC6.
Picomotors
ptk-controlarch-040103.eps
Wavefront
Metrology
CCD

VMIVME-1181-000,
32bit digital change-of-state
input board.
VMIVME-2510B,
64bit TTL digital output I/O
VMIVME-2510B,
64bit TTL digital output I/O
ZMI 2001, Interferometer
Card, 1 axis
ZMI 2002, Interferometer
Card, 2 axes
ZMI 2002, Interferometer
Card, 2 axes
ZMI 2002, Interferometer
Card, 2 axes
ZMI 2002, Interferometer
Card, 2 axes
SBIL Realtime Control Platform
PC with Windows NT 4.0, Micron
400 Mhz, Pentium II. 128 Mb DRAM
Development tools: Code Composer
Studio (TI), IXCtools (Ixthos),
Tornado II (Wind River Systems).
512 Kbytes
SBSRAM
83 Mhz
PMC
Site #1
Ethernet
Port
DSP A
C6701, 167 Mhz
16 Mbytes
SDRAM
83MHz
IXStar
PCI - DSP
Serial
Port
DSP B
C6701, 167 Mhz
512 Kbytes
SBSRAM
83 Mhz
16 bit Host Port Bus
Host Port
Interface
4 Mbytes
Flash
MPC 8240
IOPlus
250 Mhz
64 Mbytes
SDRAM
100 Mhz
32 Bit 32 Bit 32 Bit 32 Bit
64 Bit PCI - PCI 64 Bit 66 MHz PCI - PCI
64 Bit
66 MHz Bridge
Bridge 66 MHz
PMC-16AO-12-2022,
12 Channel, 16bit DA
64 Bit, User
Defined I/O
to P0*
16 Mbytes
SDRAM
83MHz
XDS510
ISA-JTAG emulator
JTAG to
DSP Chain
64 Bit
PCI - PCI
Bridge
33 MHz
Universe II
PCI-VMEbus
VME64x Backplane
(11 Mbytes/s)
DSP C
C6701, 167 Mhz
512 Kbytes
SBSRAM
83 Mhz
IXC6 Quad DSP Board
16 Mbytes
SDRAM
83MHz
IXStar
PCI - DSP
MIT Space Nanotechnology Laboratory
ptk-052601-control.eps
512 Kbytes
SBSRAM
83 Mhz
PMC-16AIO-88-31,
8 Channel, 16bit DA and
8 Channel, 16bit AD
DSP D
C6701, 167 Mhz
64 Bit, User
Defined I/O
to P2
16 Mbytes
SDRAM
83MHz
PMC
Site #2

x ue (nm)
Unobservable error over 56 seconds
5
4
3
2
1
0
-1
-2
-3
-4
x ue raw, 3σ=3.12 nm
x ue , 3σ=2.12 nm, d/v=20 ms
-5
0 10 20 30 40 50
Time (s), Resampled timer period=0.7 ms.
Data bandlimited from 0 to 714 Hz
MIT Space Nanotechnology Laboratory
ptk-midtermxue-033103.eps

ptk-xuepsd-033103.eps
Power Spectral Density of the Unobservable Error
Power spectrum of x ue (nm/sqrt(Hz))
10 0
10 -1
10 -2
60 Hz electrical, 3σ=1.1 nm
for 59.5 Hz to 60.5 Hz.
3σ=1.8 nm for 100 Hz to 714 Hz.
Thermal expansion, 0 to ≈0.04 Hz.
Vibrations
x ue raw, 3σ=3.12 nm
x ue , 3σ=2.12 nm, d/v=20 ms
Air index nonuniformity, 3σ=2.3 nm for 0 Hz to 59.5 Hz.
10
0 100 200 300 400 500 600 700
-3
Frequency (Hz), resolution=0.35 Hz
MIT Space Nanotechnology Laboratory

x fle (nm)
4
3
2
1
0
-1
-2
-3
Fringe locking error (x fle)
Raw data, µ = -0.01, 3 σ=2.45 nm.
Dose phase error µ = -0.01, 3 σ =0.35 nm, d/v = 10 ms.
-4
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
time(s)
ptk-fle-040103.eps
MIT Space Nanotechnology Laboratory

y (mm)
y (mm)
25
24
23
22
21
20
19
18
17
16
15
-5
-5
-10
-10
-15
-15
-20
-5
Errors Caused by Particles Between
the Wafer and the Chuck
-5
-20
-10
-10
-5
-15
-5
43 44 45 46 47 48 49 50 51
42 52
x (mm)
Calculated out-of-plane distortion (nm)
25
24
23
22
21
20
19
18
17
16
15
0
0
0
0
0
42
Grating nonlinearity (nm)
0
0
50
0
100
50
150
50
200
100
0
150
250
200
0
0
5
0 0
100
250
10
0
5
0
20
43 44 45 46 47 48 49 50 51
200
150
x (mm)
150
50
15
15
100
0
10
10
5
0
-5
5
100
0
100
150
50
0
0
-5
0
0
52
ptk-particles-040103.eps
White light interferogram formed between
a quartz wafer and the chuck
Rings around a particle
MIT Space Nanotechnology Laboratory

Acknowledgements
Students
Mireille Akilian, Graduate Research Assistant, Mechanical Engineering
Chih-Hao Chang, Graduate Research Assistant, Mechanical Engineering
Carl G. Chen, Graduate Research Assistant, Electrical Engineering
Craig Forest, Graduate Research Assistant, Mechanical Engineering
Chulmin Joo, Graduate Research Assistant, Mechanical Engineering
Paul T. Konkola, Graduate Research Assistant, Mechanical Engineering
Juan Montoya, Graduate Research Assistant, Electrical Engineering
Yanxia Sun, Graduate Research Assistant, Mechanical Engineering
Jenny You, Engineering (UROP)
Research Staff
James M. Carter, Research Specialist, RLE
Robert C. Fleming, Semiconductor Process Engineer, CSR (Lab Manager)
Dr. Ralf K. Heilmann, Research Scientist, CSR (Lab Assistant Director)
Dr. Michael McGuirk, Sponsored Research Technical Staff, CSR
Edward Murphy, Project Technician, CSR
Lab Web Site
http://snl.mit.edu
We are grateful to DARPA and NASA for support of this research.
Massachusetts Institute of Technology

SIA-Roadmap-2001.eps
2001
INTERNATIONAL TECHNOLOGY ROADMAP FOR SEMICONDUCTORS
LITHOGRAPHY
YEAR 2001 2002 2003 2004 2005 2006 2007 2010 2013 2016
CD (nm) 130 115 100 90 80 70 65 45 32 22
OVERLAY (nm, mean+3 sigma) 45 40 35 32 28 25 23 18 13 9
MASK IMAGE PLACEMENT (nm) 27 24 21 19 17 15 14 11 8 6
Solutions Solutions Being No Known
Exist Pursued Solutions
METROLOGY FRAME ERROR (nm) 11 10 8.8 8.0 7.0 6.3 5.8 4.5 3.3 2.3
LENGTH SCALE ERROR (nm) 2.8 2.5 2.2 2.0 1.8 1.6 1.4 1.1 0.8 0.6
MIT Effort

MLS-2002-02-28.02.eps
Many nanophotonic structures
depend on the coherent superpostion
of scattering from sub-wavelength features.
• Integrated Optical Bragg Grating Devices
• Photonic Crystals
• DFB Lasers
>1 mm
Nanoaccuracy in Nanophotonics
Bragg Waveguide Channel Add-Drop Filter
Accuracy Calculus
Grating period = 244.4 nm
period/50 ~5 nm placement accuracy
~ 1 nm metrology frame accuracy
Best-available e-beam tools
have ~20 nm accuracy.
244.4 nm
InGaAsP Waveguide
(Hermann Haus and Henry Smith, MIT)

MLS-2002-02-28.01.eps
Nickel
Pillars
Read/Write
Head
Nanoaccuracy in Patterned Nanomagnetic Media
Nanomagnets beat the "superparamagnetic limit."
100 nm
Electron Micrograph Magnetic Force Topograph
Patterned
Nanomagnets
Patterned Magnetic Disk
(Caroline Ross and Henry Smith, MIT)
Mag Field
Up
Mag Field
Down
Accuracy Calculus
25 nm nanomagnets (200 Gbit/in 2 )
~5 nm magnet placement accuracy
~1 nm metrology frame accuracy