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6/17/09, revision 11
1
JEOL JBX-9300FS Electron Beam Lithography System
Training
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Course Outline• Explain hardware– column, lenses, amplifiers– field, chip, subfield– shot pitch, beam diameter– D = (I * t)/A
• Calibration– AE & BE marks– INITAE, INITBE, PDEFBE, SUBDEFBE, DISTBE– HEIMAP
• Substrate– various cassettes– global & chip mark alignment– virtual chip mark height detection
• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check– ALD & Exposure
• Resist Exposure & development– positive & negative resists– contrast– liftoff, etching
• Proximity Effect• Website
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Why E-beam Lithography?
• exceeds patterning capability of optical lithography– easily pattern sub-micron features– MiRC has demonstrated 6.5nm features
• patterns rapidly created from CAD file– no mask necessary like optical lithography– rapid turn around on design modifications,
ideal for research
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JBX-9300FS key features• 4nm diameter Gaussian spot electron beam• 50kV/100kV accelerating voltage• 50pA – 100nA current range• 50MHz scan speed• +/- 100um vertical range automatic focus• +/- 2mm vertical range manual focus• ZrO/W thermal field emission source• vector scan for beam deflection• max 300mm (12") wafers with 9" of writing area• < 20nm line width writing at 100kV• < 20nm field stitching accuracy at 100kV• < 25nm overlay accuracy at 100kV
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Generic Block Diagram
Gun Control
Blanking Control
Deflection Control
Electron Optics Control
Pattern Proc.and control
StageControl
Computer
x-interferometer
y-in
terf
erom
eter
stage
stagemotor
stagemotor
Gun
Ele
ctro
n O
pics
referencemarks
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ColumnElectron gun
ZrO/W emitterSuppressor
First anode
Second anode
Acceleration electrodes
Ground anode
First alignment coil
Second alignment coil
Blanking electrode
Blanking aperture
Secondlens
Thirdlens
Zoom lensesDynamic focus correction electrode
Third alignment coil
Dynamic astigmatism correction electrode
Subsidiary deflector (SUBDEF)
Electromagnetism astigmatism correction electrode
Main deflector (PDEF)
Backscattered electron detector
Objective aperture
Objectivelens
Workpiece surface
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Beam & Stage Position
Stage position accuracy = λ / 1024 = 0.62nm
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PDEF & SUBDEF
50
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Top View of Stage
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Side View
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Stage w/o Cassette
cassette goes here
laser mirrors
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Wafer Cassette
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Field Stitching
500 µm (100kV)
500 µm(100kV)
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Within Field Writing
Vector scan
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4” Wafer with Chips
2mm
2mm
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Example “Chip”
Chip
Field
500um
500um
4um
4um
Subfields
beamdiameter
shot pitch
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Objective Aperture
larger aperture = larger beam diameter, more currentsmaller aperture = higher resolution
aperture beam diameter min resolution current range3,4,5 4 – 9nm < 20nm 50pA – 2nA6 8 – 14nm 30nm 2nA – 7nA7 30nm 60nm 10nA
Most of the time, the 9300 will be set to aperture #3 and 2nA beam current.
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Beam diameter as a function of current & aperture
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Dose Equation
AtID /)*(whereD = dose (µC/cm2)I = current (A)t = time (sec)A = exposure area (cm2)
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Job Time Estimate
IADt /)*(if D = 200 µC/cm2
A = 1 cm2 I = 2nA
then t = 27 hours 46 min
time calculator at http://nanolithography.gatech.edu/tcalc.php
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Shot Pitch
• Shot pitch is equivalent to pixel value – the smaller the shot pitch, the better the feature definition
• Shot pitch is limited by scanning frequency of the SUBDEF (max = 50MHz)
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Effect of Shot PitchEnergy deposited in resist
x
Consider a line is exposedwith 200uC/cm^2 dose. Dependingon the number of pixels thatthe line-width is divided into, the line edge roughness (LER)and line-width will vary.
The graph at right shows the cross-section of energydeposition profile of a line with1,2,4 and n pixels.
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Minimum Shot Pitch Calculation
• t = D.A/I• A = area of pixel = a2
• t = 1/fclk where fclk is the maximum scanning frequency of the amplifier
a = √I/(fclk.D)
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Faraday Cup
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• Explain hardware– column, lenses, amplifiers– field, chip, subfield– shot pitch, beam diameter– D = (I * t)/A
• Calibration– AE & BE marks– INITAE, INITBE, PDEFBE, SUBDEFBE, DISTBE– HEIMAP
• Substrate– various cassettes– global & chip mark alignment– virtual chip mark height detection
• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check– ALD & Exposure
• Resist Exposure & development– positive & negative resists– contrast– liftoff, etching
• Proximity Effect• Website
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Stage
faraday cupAE, BE markSEM sample
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Absorbed Electron Detection
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INITAE
x - scan y - scan
ds/dx ds/dy
mark center position
y-scan
metal grid
x-scan
pn junction
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Backscattered Electron Detection
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INITBE
x - scan y - scan
ds/dx ds/dy
Au cross on Si substrate
x-scan
y-scan
mark center position
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PDEFBE, SUBDEFBE, DISTBE mark detection
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PDEFBE & SUBDEFBE500 um
500 um
top
bottom
left right
482um
482um
4 um
4 um
1 2 3
54 6
7 8 9
PDEFBE4 points measured
x & y gain correctionx & y rotation correction
SUBDEFBE9 points measured
x & y gain correctionx & y rotation correction
gain
rotation
shift
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DISTBE Field Distortion Correction
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Height Detection
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HEIMAP
• measures height across wafer on defined array positions (adjustable by user)
• takes average height and uses that for focus value for writing everywhere
• appropriate for 100pA & 1nA current
• not appropriate for 10nA – use virtual chip mark height detection
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• Explain hardware– column, lenses, amplifiers– field, chip, subfield– shot pitch, beam diameter– D = (I * t)/A
• Calibration– AE & BE marks– INITAE, INITBE, PDEFBE, SUBDEFBE, DISTBE– HEIMAP
• Substrate– various cassettes– global & chip mark alignment– virtual chip mark height detection
• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check– ALD & Exposure
• Resist Exposure & development– positive & negative resists– contrast– liftoff, etching
• Proximity Effect• Website
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Available Cassettes
• Wafer– 75mm, 100mm, 150mm, 200mm diameter– 300mm can be purchased for up to 9” square
writing area
• Masks– 5” mask, 6” mask
• Pieces– minimum 3 x 5mm piece
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4” Wafer Cassette
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Backside of Wafer Cassette
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Global & Chip Mark Detection
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• Explain hardware– column, lenses, amplifiers– field, chip, subfield– shot pitch, beam diameter– D = (I * t)/A
• Calibration– AE & BE marks– INITAE, INITBE, PDEFBE, SUBDEFBE, DISTBE– HEIMAP
• Substrate– various cassettes– global & chip mark alignment– virtual chip mark height detection
• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check
• Resist Exposure & development– positive & negative resists– contrast– liftoff, etching
• Proximity Effect• Website
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CAD file conversion
CADENCEfile
AutoCAD.DXF file
linkCAD
GDSII file
JEOL01file JBXFILER
JEOL52 v3.0 file
or
or
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SCHD execution
specifies1. JEOL52 v3.0 pattern file2. how to arrange on wafer3. shot modulation4. type of calibration 5. beam current
specifies1. wafer cassette window2. calibration file3. base dose4. job deck file(s) to use 5. shot pitch
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Pattern Preparation
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JBXFILER Pattern Preparation
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• Explain hardware– column, lenses, amplifiers– field, chip, subfield– shot pitch, beam diameter– D = (I * t)/A
• Calibration– AE & BE marks– INITAE, INITBE, PDEFBE, SUBDEFBE, DISTBE– HEIMAP
• Substrate– various cassettes– global & chip mark alignment– virtual chip mark height detection
• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check
• Resist Exposure & development– positive & negative resists– contrast– liftoff, etching
• Proximity Effect• Website
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Negative/Positive Resist
substrate
exposing e-beam exposing e-beam
NEGATIVE POSITIVE
select appropriate resist for process and to minimize writing time
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resist vs. dose curves
dose
resist thickness
positive negative
dose
resist thickness
lesssensitive
moresensitive
dose
resist thickness
lesscontrast
morecontrast
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Resists on hand at MiRC• Positive resists
– ZEP520A+ good etch resistance
+ fast
+ good resolution (~ 10nm)
- expensive ($3/mL)
– PMMA+ cheap ($1/mL)
+ good for liftoff
+ high resolution (< 10nm)
- poor etch resistance
- slow
• Negative resist– XR-1541 (HSQ)
+ good etch resistance (HSQ is basically SiO2)
+ excellent resolution (6.5nm)- slow- expensive ($4/mL)
– ma-N 2403 (Novolak)+ good etch resistance+ optical DUV exposable+ faster than HSQ± moderately priced ($2/mL)- poor adhesion to quartz
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Resist Comparison
-0.2
0
0.2
0.4
0.6
0.8
1
1.2n
orm
aliz
ed
re
sis
t th
ick
ne
ss
100 1000 800 600 500 400 300 200 2000 3000
dose (uC/cm2)
HSQ
PMMA
ZEP
resist200 480 1280
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Metal Liftoff
evaporate metal ontopatterned resist
strip resist
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• Explain hardware– column, lenses, amplifiers– field, chip, subfield– shot pitch, beam diameter– D = (I * t)/A
• Calibration– AE & BE marks– INITAE, INITBE, PDEFBE, SUBDEFBE, DISTBE– HEIMAP
• Substrate– various cassettes– global & chip mark alignment– virtual chip mark height detection
• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check
• Resist Exposure & development– positive & negative resists– contrast– liftoff, etching
• Proximity Effect• Website
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Electron Solid Interactions
• electrons forward scatter in resist (alpha)
• electrons backscatter off substrate (beta)
• Causes dose to spread away from where you want it to go, and expose areas you don’t want to be exposed
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Forward Scattering (α)
• as electrons enter resist, they experience small angle scattering, effectively broadening the initial beam diameter
• forward scattering is minimized by using the thinnest possible resist and highest accelerating voltage
5.1)/(9.0 btf VRd df = effective beam diameter (nm)Rt = resist thickness (nm)Vb = acceleration voltage (kV)
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Backscattering (β)
• as electrons pass thru resist and enter substrate, many will undergo large angle scattering events
• these electrons may return back into the resist at a significant distance from the incident beam, causing additional resist exposure → this is called the proximity effect
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Electron Solid Interaction
Source: SPIE Handbook of Microlithography, Section 2.3 Electron-Solid Interactions
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Simulated Electron Energy Profile
Source: SPIE Handbook of Microlithography, Section 2.3 Electron-Solid Interactions
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Alpha & Beta(for 0.5um resist on Si substrate)
Beam energy (keV)
α (um) β (um) η
5 1.33 [0.18] [0.74]
10 0.39 [0.60] [0.74]
20 0.12 2.0 0.74
50 0.024 9.5 0.74
100 0.007 31.2 0.74
backscattered electrons have large range at 100kV!!!
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Influence of Proximity Effect on Pattern Generation
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Line Edge Deviations due to Proximity Effect
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Proximity Effect Correction by Dose Modulation
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Proximity Effect Correction by Shape Modulation
original CAD pattern
simulated doseprofile
calculated shape modification to achieve desired
line
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Dose Dependencies
pattern size
pattern density
required dose
required dose
resist thickness required dose
acceleration voltage required dose
substrate AMU required dose
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Example of Proximity Effectlarge exposed area next to small lines
causes overexposure
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How to correct in my CAD file?
• separate small features from large features by placing on different layers in AutoCAD
• then assign a different datatype to each layer in linkCAD
• then assign different doses (shot modulation) to each datatype– try a wide range of doses on your first exposure
• use SEM image to make careful dimension measurements
• adjust dose as necessary and repeat exposure
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Test Pattern
1000nm
500nm
200nm
100nm
50nm
20nm
10nm
2nm
50 x 50um
1 x line 2 x line 10 x line 10um 20um 30um 40um 50um
line width
space width(exception: 2nm line group has same spacing as 10nm line group)
3 x line 4 x line 5 x line
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1um lines in ZEP at various pitch
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
line
wid
th (
um
)
100 200 300 400 500 600 700 800 900 1000 1100
actual dose (uC/cm2)
"1:01"
"1:02"
"1:03"
"1:04"
"1:05"
"1:10"
"1:20"
"1:30"
"1:40"
"1:50"
line:space ratio
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Required dose for 1um line in ZEPas a function of grating
0
1000
2000
3000
4000
50001
um
do
se
(u
C/c
m2
)
0 10 20 30 40 50 60
space/line ratio
1um dose (uC/cm2) = 98.318479 + 85.290888 space/line ratio
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• Explain hardware– column, lenses, amplifiers– field, chip, subfield– shot pitch, beam diameter– D = (I * t)/A
• Calibration– AE & BE marks– INITAE, INITBE, PDEFBE, SUBDEFBE, DISTBE– HEIMAP
• Substrate– various cassettes– global & chip mark alignment– virtual chip mark height detection
• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check
• Resist Exposure & development– positive & negative resists– contrast– liftoff, etching
• Proximity Effect• Website
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Website
•http://nanolithography.gatech.edu