Nanometers and Picometers:
Keys to Success with
5 Terabit/in2 Patterned Media
Donald A. Chernoff
Advanced Surface Microscopy Inc.
Indianapolis, IN USA
www.ASMICRO.COM
2/10/2009
IDEMA Technical Symposium Dec. 11, 2008
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525 G dot/in2 pattern (35 nm pitch, 2D array)
-Measure size, shape and position of the marks
is the most basic position parameter
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IDEMA Technical Symposium Dec. 11, 2008
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Measure Pitch for Consecutive Pairs of Columns
Raw Pitch
34.4
Mean
Std.Dev.
34.19
0.084
Pitch (nm)
34.3
34.2
34.1
34.0
33.9
-1000
-500
0
500
Position (nm)
SEM - Zeiss Supra 55VP
σ = 84 pm
Pitch σ / Mean = 0.25%
(uncorrected, raw data)
u
u
u
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IDEMA Technical Symposium Dec. 11, 2008
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1000
Bump Widths and Lengths
Width2 at Middle Length2 at Middle
(nm)
(nm)
Count
1958
1958
Mean
20.44
19.68
Standard Deviation
1.09
0.90
Standard Error of
Mean
0.02
0.02
Maximum
23.72
22.36
Minimum
17.14
17.36
Range
6.58
5.00
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IDEMA Technical Symposium Dec. 11, 2008
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Track Pitch Metrology for Patterned Media
Media Type
Track Pitch (nm)
Removable?
Magnetic
25-50
No
Track Pitch Variation
(% of Pitch, 1 σ)
3-6%
Gauge Precision
(% of Pitch, 1 σ)
1-2%
Example Gauge Test
(Pitch / 1 σ) (nm)
50 / 0.5-1
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IDEMA Technical Symposium Dec. 11, 2008
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Optical
100-150
Yes
1-1.5%
0.33-0.5%
150 / 0.75
Picometer Accuracy
u Comparative
study with PTB, the
German national standards lab.
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IDEMA Technical Symposium Dec. 11, 2008
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Materials and Methods—Test Specimens
292 nm Pitch, 1D, Ti on Si
(Height: 36 nm)
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IDEMA Technical Symposium Dec. 11, 2008
144 nm Pitch, 2D, Al on Si
(Height: 88 nm,
column average height 52 nm)
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Materials and Methods—Traceability Path
uPhysikalisch-Technische
Bundesanstalt (PTB) used
optical diffraction (OD) to
measure the mean pitch of
the gratings.
uAt Advanced Surface
Microscopy (ASM) we
used atomic force
microscopy (AFM) to
measure individual pitch
values, which led to mean
values and standard
deviation.
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IDEMA Technical Symposium Dec. 11, 2008
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AFM Data Capture and Analysis
u
u
u
2/10/2009
NanoScope® IIIA, Dimension 3100, open-loop AFM
(Veeco Metrology/Digital Instruments).
We alternated scans of the calibration and test specimen.
We analyzed height images using Advanced Surface
Microscopy’s DiscTrack Plus™ software.
IDEMA Technical Symposium Dec. 11, 2008
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AFM Measurement of Individual Pitch values
292 nm Standard (2 images)
300
Data set has 3 images:
Pitch (nm)
298
- Calibration Standard
- Test Sample
- Calibration Standard
296
Raw Pitch
294
Border
292
“Bookend calibration”
corrects for short term
magnification drift.
290
288
0
1000
2000
3000
4000
5000
Position (nm)
Raw
Calibrated
Mean
144.91
143.98
St.Dev.
1.30
0.40
150
Data exclusion
zone
Pitch (nm)
148
146
Raw Pitch
Border
Calibrated
144
142
140
0
1000
2000
3000
Position (nm)
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IDEMA Technical Symposium Dec. 11, 2008
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4000
5000
144 nm Grating (1 image)
AFM Results at 10 spots on Test Specimen (X Axis pitch)
Data
Set
Count
1
30
2
30
3
30
4
30
5
31
6
31
7
31
8
30
9
31
10
30
Overall AFM
Results
143.895
0.55
144.1
Mean Pitch (nm)
Mean
Standard
Pitch Standard Deviation
(nm) Deviation of Mean
143.85
0.42
0.08
143.98
0.40
0.07
143.83
0.55
0.10
143.98
0.64
0.12
144.05
0.69
0.12
143.86
0.58
0.10
143.89
0.50
0.09
143.81
0.55
0.10
143.92
0.55
0.10
143.77
0.59
0.11
144.0
143.9
143.8
143.7
0.032
0
2
143.8950
4
6
Data Set
There was no significant variation in mean pitch from spot to spot.
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IDEMA Technical Symposium Dec. 11, 2008
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8
10
Optical Diffraction (OD) Proves AFM Accuracy
X direction
Y direction
Uncertainty of
mean(1 σ)
Uncertainty of
single pitch
values (1 σ)
Optical Diffraction (nm) AFM Analysis (nm) Difference (nm)
143.928
143.895
0.033
33 pm WOW!
143.931
0.007 (0.005%)
0.039 (0.027%)
N/A
0.55 (0.38%)
Optical Diffraction and AFM results agree within the 95% confidence limits,
and the difference is mainly due to random error in individual pitch measurements.
Difference in precision could be related to the number of lines measured:
7000 in 1 mm spot for OD
304 for AFM
Sqrt(7000/304) = ca. 5. Ratio of uncertainties = ca. 5
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IDEMA Technical Symposium Dec. 11, 2008
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Picometer Precision
u To
qualify microscopes and prospective
calibration standards:
u Measure pitch in 1 or a few images using
self-calibration.
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IDEMA Technical Symposium Dec. 11, 2008
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SEM Pitch Measurements of 144 nm Grid - Precision
SEM: Hitachi S4700 at 5 kV.
σ = 0.43 nm.
Relative σ = σ / mean = 0.30%
Field Emission SEM and AFM have similar precision for pitch measurements.
Pitch (nm)
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IDEMA Technical Symposium Dec. 11, 2008
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Count Mean Std.Deviation
35 143.90
0.43
SEM of 76 nm 1-D Grating
u
u
SEM - Zeiss Supra 55VP
Relative σ = 0.21%
200 kX raw Pitch (nm)
Raw and Calibrated Pitch for 1 image
79.5
78.0
77.5
77.0
76.5
78.0
77.5
Raw
Cal
77.0
76.5
76.0
75.5
76.0
75.5
75.0
-1000
Raw
Raw Calibrated
Calibrated
Mean
75.94
76.03
Mean
75.94
76.03
Std.Dev.
0.47
0.16
Std.Dev.
0.47
0.16
79.0
78.5
Pitch (nm)
78.5
Pitch
79.5
The raw pitch
results from 9
different images
show consistent
distortion in the
SEM scan.
79.0
-500
0
500
1000
75.0
-1000
-500
Position (nm)
Position
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IDEMA Technical Symposium Dec. 11, 2008
0
15
500
1000
Precision of Single Pitch Measurements
for Grating Pitch 35-2000 nm
Measured results
Relative Standard
Deviation (%)
0.5%
0.4%
0.3%
0.2%
0.1%
0.0%
10
100
1000
10000
Pitch (nm)
The relative Standard Deviation was in the range 0.22-0.43% for all pitch values
from 35 to 2000 nm. At 0.5% relative Standard Deviation for single Pitch values,
it is practical to get relative uncertainty of mean < 0.05% in a short data run.
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IDEMA Technical Symposium Dec. 11, 2008
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A Chain of Traceable Pitch Calibration Specimens with
Mean Accuracy better than 0.1% (10 pm) at 10 nm.
144 calibrates 76
76 à 35
35 à 20
20 à 10
10 à 5 nm
Uncertainty
u
Relative Pitch Uncertainty (1 σ)
0.6%
0.5%
0.4%
0.3%
0.2%
0.1%
0.0%
N=300
0
50
100
Single Value
Mean
150
200
Pitch (nm)
u
The uncertainty of mean for “76” depends mainly on the
uncertainty of mean of “144”, the uncertainty of single values of
“76”, and the number of pitch measurements (N).
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IDEMA Technical Symposium Dec. 11, 2008
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Summary
u
u
u
Measurement of size and position parameters.
Picometer Accuracy and Precision
--with “Ordinary” AFMs and SEMs.
Certification of Traceable Calibration Standards
--A path exists to 10 nm pitch (5 Tb/in2) and beyond.
Copyright (c) 2008 Advanced Surface Microscopy, Inc. All rights
reserved. IDEMA is hereby granted a non-exclusive world-wide
license to reproduce this presentation in hard copy and PDF form.
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IDEMA Technical Symposium Dec. 11, 2008
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