jeol jbx-9300fs electron beam lithography system training

6/17/09, revision 11

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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

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







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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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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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• Pattern Preparation– CAD file preparation– linkCAD conversion– file transfer– JBXFiler– Job Deck & Schedule File– Schd and Array check




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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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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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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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Website

•http://nanolithography.gatech.edu

jeol jbx-9300fs electron beam lithography system training

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