Weir PSFM Fixed Focus Analysis Dataset:blanketfocmon.XLS Features:Full-wafer exposure, fixed focus Sections: Comparison of PSFM 180, 160 and PGM response

Weir PSFMWeir PSFMWeir PSFMWeir PSFM

Fixed Focus AnalysisDataset: blanketfocmon.XLS

Features: Full-wafer exposure, fixed focus

Sections:

• Comparison of PSFM 180, 160 and PGM response

• PGM whole-wafer focus model

• Reticle Scan-stage analysis (Up/Down scan comparison)

• Up-Scan analysis

• Down-Scan analysis of image

• Average Field

• Astigmatic behaviorTEA Systems Corp.

65 Schlossburg St.Alburtis, PA 18011

610 682 [email protected]

0304 Weir PSFM - Fixed Focus Analysis Page -2-TEA Systems Corp. Confidential

Project Summary• Candidate slides for Paper

Comparison of PSFM 180, 160 and PGM response• All 3 features present a lens-characteristic signature response• 3 features can be used to replicate focus behavior of features with increasing density.

– PSFM 180 = isolated– PGM = dense-packed feature performance.

PGM whole-wafer focus model • Modeled focus across wafer shows high-point in central area.• X-Slit (lens) and Y-scan (reticle stage travel) characteristics• Methods of plotting lens signature and reticle scan characteristics are shown

Reticle Scan-stage analysis (Up/Down scan comparison)• While being well balanced, stage is shown to contribute more noise in down-scan• Scan tilt is present and shown• Scan-speed nonlinearity shown to be greater in down-scan• Sensitivity of direction and wafer-edge on field tilt • Plate bowing during scan can be seen• Astigmatism across slit is shown to have a directional component.

– Consistent with the concept of scan-averaging of y-direction aberrations

• Background slides with in-depth analysis Up-Scan analysis Down-Scan analysis of image Average Field Astigmatic behavior


PSFM 180 – data conversion

• Data converted to focus errors


PSFM 180 Raw Focus Data

• Mean Focus contour shown

• Note the high focus errors located at left/right edges & in lower left edge. “7 o’clock” location

Reticle stage scan direction


PSFM 180 – raw Astigmatism

• Data is before conversion to focus

• Used to determine data culling limits Use a cull = 0.013 um base on

quartiles.

• A total of 24 points were removed using this method.


PSFM 160 Raw Focus


PGM Raw Focus Data

• Lens fingerprint is obvious


Comparison PSFM 180, 160 & PGM

• Ranges change

• Field signatures are very similar

• PGM and PSFM replication is very close.


Comparison PSFM 180, 160 & PGM

• Mean Linear change from –93 to 0 to +25 nm for mean focus Represents progressively increased density in feature packing.

• Range Approximately the same with PSFM 160 being slightly higher Recall that PSFM data used some data culling

• Standard Deviation. Same for PSFM 180,160 Lower for PGM

• Astigmatism Follows mean focus trend

PGMPSFM 160PSFM 180


Comparison; PGM & PSFM 180• Average field was removed.

• Note ranges are about the same.


Comparison; PGM & PSFM 180

• PSFM 180 Focus behavior replicates isolated

line performance

• PGM Responds to focus like dense-

packed features

• Differences Range of PSFM 180 is about

150nm greater Astigmatic behavior is different

• Pgm = -29nm, PSFM = 4 nm

Standard deviation about the same

TEA Systems Corp. Confidential

PGM Whole-wafer Analysis


PGM Focus modeled data

• Sites at lower-left exhibit greatest errors on wafer

• Wafer Model X-tilt is equivalent to Field

Slit-tilt and will add


Wafer-based focus variation

• Wafer contributes a total of 39 nm focus error Systematic variations mostly lie with the +5, -7 nm

range. Note high points at top and center as well as tilt.


New Algorithm


New Algorithm, Residuals


X-slit flight characteristics

• Objective: View X-slit pitch, roll and dip

• Aberrations removed Wafer aberrations Average row X-focus Average column X-focus

• View variation in X-slit focus across wafer up-scan

• tendency to bow the field down-scan

• Greater problems with scan-direction tilt

Down- scan

Up- scan

Down- scan

Up- scan


Y-Scan focus, Modeled field piston

• Y-scan focus• Modeled focus piston (offset) for

each row.• Objective:

View focus-signature across lens-slit


Slit Signature – using Y-scan focus piston

• Note circled row on right All down-scan Alternating field left & right edges

• Field tilt resulting from direction of travel-to-the-field


X-slit roll

• Only the modeled X-slit Tilt is shown Illustrates the roll of the slit as it is scanned

• Majority of tilt lies within the +/- 25 nm range (max=261 nm, min =-56 nm)• Note large tilt on right side of wafer.

Reticle-stageScan direction


Scan Direction Analysis

• Examine the contribution of the reticle-stage scan to the focus-error budget Results in:

• Loss of process window

• Overlay errors in registration

• Asymmetric errors in critical feature size

• Analyze Raw-focus data Variations in modeled field performance


Reticle-Stage Scan Direction

Reticle-stageScan direction


Scan Direction Contours • Mean-focus plotted


Scan Direction Statistics

• Astigmatism Same

• Mean focus Same

• Standard Deviation same

• Range Up scan < Down 194 nm < 328 nm

• Down scan exhibits greater range than UP! We’ll see why in the

next few slides

Up Scan Down Scan


Radial-location Dependence

• Mean-focus and wafer-radial position

• Performance very similar

• Wafer-edge noise increases slightly for both distributions


Modeled Field and scan

• Field Model Every row/column

modeled separately

• Best Focus (BF) Same

• Tilt Down-scan > up

• Curvature Up-scan > down

• Residuals St.Dev. residuals Random variation of

down-scan > up

Down-Scan, Modeled Field

Up-Scan, Modeled Field


Comparison, Scan-stage flight path

• “Stable” fields values are plotted

• Note the increased “noise” of down-scan in 3rd & 4th rows

Down-Scan, X-slit Piston

Up-Scan, X-slit Piston


Comparison, Scan-stage flight path

• “Stable” fields values are plotted

• Note the increased “noise” of down-scan in 3rd & 4th rows

Down-Scan, X-slit Piston

Up-Scan, X-slit Piston


Comparison, X-slit signature

• All fields are collapsed onto one graph

• Plot modeled Y-scan Piston (focus offset) against position in slit

• Fluctuation at edges of lens “flutter” of slit height


Comparison, X-slit focus signature stability

• Down-scan tilts seem to drop toward outer edge of wafer. Auto-leveling

limitation?

• Slit-signature is maintained in most fields

Up Scan

DownScan

Comparison, X-slit focus signature stability

• Down-scan tilts seem to drop toward outer edge of wafer. Auto-leveling

limitation?

• Slit-signature is maintained in most fields

Up Scan

DownScan


Astigmatism – Scan-stage flight comparison• Astigmatism = (Y-X) focus• Y-Focus

Errors are averaged by scan of the slit Sensitive to:

• scan-speed• Pitch (y-tilt) of reticle-scan path

• X-focus Sensitive to:

• lens focus aberrations• Roll (X-tilt) of slit from auto-leveling

• Up-scan (upper graph) Center-field is near-zero

• Constant velocity of scan Scan-start (left side)

• Requires 7 mm of scan to settle Scan stop (right side)

• Last 2 mm exhibit acceleration

• Down-scan (lower graph) Shown to be “noisier” scan direction Scanning top (right side) to bottom (left side) Acceleration is non-zero at only one point

• –7mm from field bottom• Shown to be a point in field where curvature and field tilt

change anomalously Source of down-scan noise!

Same sign, velocity change

Opposite sign, velocity change

Astigmatism – Scan-stage flight comparison

• Astigmatism = (Y-X) focus• Y-Focus

Errors are averaged by scan of the slit Sensitive to:

• scan-speed• Pitch (y-tilt) of reticle-scan path

• X-focus Sensitive to:

• lens focus aberrations• Roll (X-tilt) of slit from auto-leveling

• Up-scan (upper graph) Center-field is near-zero

• Constant velocity of scan Scan-start (left side)

• Requires 7 mm of scan to settle Scan stop (right side)

• Last 2 mm exhibit acceleration

• Down-scan (lower graph) Shown to be “noisier” scan direction Scanning top (right side) to bottom (left side) Acceleration is non-zero at only one point

• –7mm from field bottom• Shown to be a point in field where curvature and field

tilt change anomalously Source of down-scan noise!

Same sign, velocity change

Opposite sign, velocity change


Astigmatism – Across slit Comparison

• Signatures appear “Balanced”

• Up scan signature is mirror image of down-scan. Reason: unknown

• Suggestions?

Up-scan

Down-scan

Z5

-10

-8

-6

-4

-2

0

2

4

6

8

10

-15 -10 -5 0 5 10 15


Up-Scan analysis

Detailed analysis of focus performance of exposure tool during the Up-scan stage of exposure


Wafer aberrations – Up-scan

• Mean focus plotted

• Objective: Examine and remove wafer aberrations. Obtain clearer picture of field variations


Modeled Field Aberrations

• Wafer Aberrations removed

• Mean Focus plotted Piston, tilt, curvature

• Model fitted to each field independently


Up-Scan, piston X-slit focus • Objective: View reticle flight-path in up-scan direction

• Wafer aberrations removed.

• Display modeled focus-piston (offset) of each row Illustrates the variation in scan uniformity

across wafer.

• Range of 50 nm seen in the plot of stable fields shown


Up-Scan, Y-scan focus Piston

• Modeled focus piston (offset) of each column.

• Objective: Observe slit-focus signature

• Graph is average of all fields Excluding top field at 12 o’clock


Up-Scan, Y-scan focus Piston

• Modeled focus piston (offset) of each column.

• Objective: Observe slit-focus signature

• Note retention of signature in all but the 4th column Reticle bowing?

• Variation is in the average offset of each field and tilt.


Up-Scan, Modeled X-slit Tilt

• Objective Observe “Roll” of slit along it’s

glide path during scan.

• Slit tilt varies by 54 nm across wafer

• Note behavior of tilt at left and right edges of wafer Equivalent to the “Roll” of the

reticle Platen.


Up-Scan, modeled Y-scan Tilt • Horizontal feature focus Wafer aberrations removed

• Pitch-variation of reticle scan-stage

• Objective: View pitch of scan stage as it

travels from bottom to top Tilt modeled for each column

of each field.

• Exhibits a 68 nm focus range contribution


Up-Scan, Y-scan flutter

• Y-scan curvature variation

• Objective: View 2nd order, curvature, stability

of each column Reticle is “flexed” as it scans

• This is a measure of the variation in focus at the start/stop of scan.

• Note the “flutter” at the extreme edges of the slit


Up-Scan – X slit curvature variation

• Variation in curvature of slit. Measured for each row of each

field.

• Objective: Direct measure of 2nd order

flexure of reticle during scan

• Caused by bowing of the reticle during the scan?


Up-Scan, Residuals to modeled wafer & field

• Wafer aberrations are removed

• Field Piston, tilt and 2nd order systematics are removed

• Residuals contain: Higher-order focus variations (systematic errors) Random noise


Up-Scan, Mean - Focus

• Note presence of higher –order scan signature.

• High-point “bumps” in scan center Viewed earlier in slit profile box-plots


Up-Scan, Residuals to Wafer & Field

• Y-scan Sensitive to noise during scan-travel

• Bearing chatter, stage flex

• X-slit Sensitive to lens aberrations

Y-Scan Focus – Horizontal Features X-slit Focus – Vertical Features


X-Slit Focus, across slit residuals

• High-order focus errors due to lens aberrations.


Down-scan focus behavior


Down-scan, raw data analysis


Down-Scan, Wafer aberrations


Down-scan, Wafer aberrations removed


Down-Scan, X-slit piston


X-Slit focus, Down-scan

• Objective: View reticle flight-path in up-scan

direction

• Field Piston plotted

• Analysis and up-scan comparison in next slide


Down-Scan, Scan flight path using X-slit piston

• Modeled X-focus piston (offset) for each row

• Graph (above) summarizes five (5) fields shown

• Illustrates average path of reticle-scan table


Down Scan, Slit Signature• Display of Modeled Y-scan piston

(offset) One model for each column of each field

• Results in focus signature across lens-slit

• Slit signature (below) is average of all fields Note large variation at field edges


Down-scan, Y-scan Focus piston


Down-Scan, X-slit focus tilt


Down-Scan, X-slit curvature

• Note that the lower-left corner of the wafer is typically the location of the greatest focus errors.


Down-scan, Y-scan focus Tilt


Down-scan, Y-scan focus Curvature


Average Field Analysis

• Fields across the wafer are “collapsed” or overlaid.

• Metrology for each field-site is averaged

• Objective: View average performance of field Attempt to estimate the aberrations of the aerial scan image.


Mean Field & Scan DirectionUp-scan Scan glide-path

Lens-slit


Up-Scan – Wafer & Field tilt/piston removed

• Aberrations removed Wafer Field tilt Field piston

• Focus-error contributors Lens-aberrations Higher-order scan

errors


Up-Scan Direction piston

• View modeled piston variation Top: for each column

• Focus errors across lens-slit

Bottom: for each row• Focus errors caused by scan-

travel of slit

• Up-scan only

• Lens slit errors (top) Characteristic lens signature. On average, very level

• Bottom: scan glide-path Up-Scan exhibits a tilt Field-center point

• “bump” in scan

• This noise seen in earlier slides.

Scan glide-path

Lens-slit focus


Up-Scan – Field Tilt

• Vertical Features (left) X-slit tilt Note abrupt change in tilt at field center

Vertical Features Horizontal Features Mean Focus


Astigmatic Behavior• (Y-X) Focus behavior

• The net-effect of this variation is to reduce the process window for this tool

• Objective: Analysis validation by comparison of values with those calculated

from an Artemis Zernike study.


Astigmatism – Up Scan

• Residuals to wafer aberrations• Y-scan focus

Primarily contributed by the scan-stage

• X-scan focus From lens focus errors From stage-scan errors


Astigmatism – Up ScanZ5

-10

-8

-6

-4

-2

0

2

4

6

8

10

-15 -10 -5 0 5 10 15

Artemis Astigmatic Zernike

Scan glide-path

Lens-slit

• Slit-astigmatic behavior (upper left) Tracks Z5 coefficient Note:

• Zernike analysis is from fy 2002 using a ring-aperture Estimated magnitude of Z5 errors is much less than

measured.

• Scan-glide path (bottom left) Scanning averages & removes errors Errors at scan-start and end

• Caused by scan-speed nonlinearity.– Acceleration errors in scan stabilize out in frist 7 to 12 mm– Acceleration errors at end of scan indicate start of turn-

around


Astigmatism – Up Scan

• No wafer removal Wafer aberrations previously also

included piston

• Otherwise, calculations same as in previous analysis.


Astigmatism – Down Scan

• Wafer aberrations removed


Astigmatism – Down Scan

• Slit signature (top) Classic lens signature at center Wings vary from up-scan

• Scan signature (bottom) Fairly level Scan now moving down

• Right to left on graph

Non-flat performance suggest acceleration component present

After the 3rd row (from left), acceleration component again rises.


Astigmatism

• Wafer aberrations were removed

• Edge-field data culled

• Up and Down scans Up/down averaging removes signature resemblance to Z5 Zernike (upper right)

Z5

-10

-8

-6

-4

-2

0

2

4

6

8

10

-15 -10 -5 0 5 10 15

Documents

Weir PSFM Fixed Focus Analysis Dataset:blanketfocmon.XLS Features:Full-wafer exposure, fixed focus Sections: Comparison of PSFM 180, 160 and PGM response