Bare wafer metrology challenges in microlithography at 45 nm node
and beyond
Chunsheng Huang, Ph.D.
KLA-Tencor Corporation
ADE Division
3470 Universal Way
Tucson, AZ 85706
Abstract
The shrinking depth of focus (100-150 nm) of high numerical aperture immersion microlithography optics dictates a
tight wafer flatness budget. Wafer flatness nanotopography (NT), and edge roll off (ERO) are critical parts of the
equation in immersion microlithographic technology at the 45 nm node and beyond. Wafer features at the nanometer
level could result not only in focus variation of the litho process, or thin film thickness variation in CMP process, but
also in structural defects of the devices. Therefore, the metrology to measure nanometer level features and to control the
quality of wafer geometry is a key to the success of IC production at the 45 nm node and beyond.
Key words: Bare wafer metrology, interferometer, wafer nanotopography, wafer edge roll off.
1. Introduction
Bare wafer surface topography variation is a significant part of focus budget of microlithography. As the IC line-width
shrinks, the depth of focus (DOF) is also reduced. The wafer surface flatness variation can take as much as 40% to 50%
of total DOF of the microlithographic project optical scanner with a dynamic tilt adjustment on each exposure according
to International Technology Roadmap for Semiconductors (ITRS).¹ Thus, as the wafer surface quality becomes
increasingly important, the metrology to control the surface quality is increasingly challenged.
This paper will present the technological challenges with a focus on nanometer level precision, accuracy, and tool
matching. It will also analyze bare wafer flatness, shape, ERO, and NT impact on the immersion lithographic focus
budget. The paper will describe and characterize the current state-of-the-art bare wafer metrology tool that has subnanometer precision. Data from multiple tools will be compared to demonstrate the tool-to-tool matching that will
overcome emerging microlithographic technology challenges.
2. Wafer flatness impact on Lithographic Focus Budget
Immersion technology increases the effective NA of the optical lithography and thus increases the printing solution and
makes it possible using ArF laser (193 nm) to resolve a 45 nm line-width. However, because NA increases, the DOF is
reduced. The half pitch of optical resolution or line-width L can be expressed² as
L= K1
λ0
(1)
NA
NA = n ⋅ sin(θ )
(2)
Quantum Optics, Optical Data Storage, and Advanced Microlithography, edited by Guangcan Guo,
Songhao Liu, Guofan Jin, Kees A. Schouhamer Immink, Keiji Shono, Chris A. Mack, Jinfeng Kang, Jun-en Yao,
Proc. of SPIE Vol. 6827, 682723, (2007) · 0277-786X/07/$18 · doi: 10.1117/12.759738
Proc. of SPIE Vol. 6827 682723-1
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Where K 1 is a processing related factor and NA is numerical aperture of the optical system and
wavelength in the air and n is the refractive index of immersion media and
θ
λ0 ⋅ n
is the exposing
is the marginal angle of the lithographic
lens at the wafer plane. The depth of focus (DOF) of the scale equation approximation
DOF= K 2
λ0
2
is
(3)
NA 2
Where K 2 is a processing related factor. As NA increases, L is inversely reduced with NA, and DOF is quadratically
inversely reduced. The DOF reduces faster than the line-width does as NA increases in the air. However, if the
effective NA increases by refractive index of the immersion media, the L and DOF have the same reduction rate as the
refractive index increases or it is proportional to
1
. Figure 1a. is the estimation of DOF calculated based on ITRS
n
roadmap. Using K1 range specified in ITRS roadmap and equation (2) to calculate NAs shown in Figure 1b. Then using
equation (2) and refractive indices of immersion medium obtain the DOF. Of course DOF may vary with the tools and
processing factor such as optical proximate correction (OPC), illumination schemes, and double pattern print.
Production worthy immersion scanner technology currently uses water as an immersion media which has a refractive
index of 1.43 at 193 nm wavelength. The effective NA of 1.2 to 1.35 has been reported. To achieve 45 nm line-width,
K1 of 0.28 to 0.31 is needed. A K 2 of 0.7 will result in the DOF of 106 nm to 134 nm range. For high refractive index
of the immersion media, the NA could be even higher, and DOF will be further reduced.
The process focus window is reduced to 26 to 34 nm after taking consideration of wafer flatness, wafer stage focus
accuracy and repeatability, wafer chuck flatness, and others factors, such as thermal stability. The focus accuracy of the
state of the art of scanning wafer stage technology has been reported by Mulkens³ to be as small as 25 nm. Chuck
4 ,11
(a Peak-to-Valley within a 26mm
flatness can be as small as 10 nm. According to ITRS, the wafer flatness of SFQR
x 8mm wafer surface area, after removing the tilt) is 45 nm for 45 nm node design and 32 nm for 32 nm node design.
Figure 2 shows a wafer flatness example of SFQR magnitude and distribution over a 300 nm wafer. This wafer has a
site with maximum value of 54 nm. In the case, the wafer site (or die) may go out of the process window and cause the
critical dimension (CD) out of specification.
The wafer flatness can take as much as 32 to 45% DOF for 45 nm and 32 nm design node depending on the scanners and
process factor. The primary focus budget allocation is to wafer flatness. To improve wafer flatness, the metrology of
wafer flatness is the key technology to be addressed.
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DOF vs Wafer Flatness
350
300
DOF (nm)
250
200
DOF (Dry)
DOF(wet)
150
ITRS Wafer Flatness
100
50
0
150 130 115 100 90
80
70
65
57
50
45
38
32
26
1999 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
ITRS Roadmap 1/2 pitch in nm
Figure 1 a. ITRS Roadmap vs. DOF and Wafer Flatness. K2 of 0.7, NAs and refractive indices in Figure 1 b are used to estimate the
DOF.
K1, NA, and refrative index used for calculate for DOF
2
1.5
K1
NA
1
Refractive Index of medium
0.5
0
150 130 115 100 90
80
70
65
57
50
45
38
32
26
19992001200220032004200520062007200820092010201120122013
ITRS Roadmap 1/2 pitch in nm
Figure 1 b. ITRS Roadmap vs. k1, NA, and refractive index of immersion medium that meet the roadmap
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Figure 2. A 300 mm SFQR map (peak-to-valley value after removal of tilt within the site. The site size is 26mm x 8mm.) There is a
site in which SFQR is as large as 54 nm.
3. Edge Roll Off (ERO) effect on the edge of wafer focus.
ERO is defined as occurring within a distance from the edge of 1mm to 5 mm, as shown in the Figure 3. If it is not
controlled, the amount of topography variation within the edge roll off of a wafer can cause the scanner to go out of
focus, thus reducing the area of a wafer that can be used. The ERO can be characterized with variety of parameters such
5
6
as radius of curvatures (ZDD), edge profile, or ESFQR (peak to valley value of a wafer edge radial section after
removing tilt) as shown in Figure 4. The ESFQR shown in Figure 4 has 72 sections and has a large maximum value of
197 nm. This amount of edge roll off is out of DOF for 45 nm node design. The wafer manufacturer is clearly
challenged to reduce ERO in the bare wafer process. For this surface area to be usable for 45 nm node, ERO should be
smaller than 60 nm, or less than 60% of DOF. To accurately measure the edge of wafer as close as 1 mm to the edge is
difficult, because it is close the edge of bevel and the edge roll off is very fast. Any sub-pixel data dropped off or added
in at the very edge can be a significant measurement variation. The repeatability and accuracy of the metrology is
challenged.
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ERO region
Edge
Bevel
5
4
2
3
Distance from edge (mm)
1
0
Figure 3. The edge roll off is defined as from 1mm to 5 mm.
Figure 4. ESFQR map with 1mm edge exclusion and 5 degrees per section has a maximum value of 197 nm.
4. Wafer nanotopography (NT) impact on litho.
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7
The wafer NT represents the nanometer level wafer flatness variation (bumps or trenches) of a bare wafer with the
spatial periods of 0.2 to 20mm over a 2x2mm square or a circle, 2 mm in diameter. NT defects at the bare wafer can
cause photoresist, thin film or metal layer thickness variations and result in defects of IC devices in the CMP process
reported by D. Boning et al.
8
Because of photoresist thickness variations due to NT defects, it is inevitable to have CD
9
variations in the litho-etching process. NT defects has corrected with CD variations by A. Grenville et al at Intel . It is
not clear what correlation the defects in nanometer level of a bare wafer with periods over 0.2mm and 20mm range have
with immersion litho defects such as bubbles. It is clear that NT impacts not only CD but also thin films such as gate
oxide (typical thickness <3 nm) or metal layers.
ITRS roadmap 2006 added NT as a part of bare wafer metrics. It recommends that NT be smaller than 11 nm for 45 nm
node and 8 nm for 32 nm node. NT requirements pose significant challenges for metrology equipment, to perform with
very high precision and accuracy at a nanometer level. In particular for optical metrology, very high quality optical
components, insensitivity to vibration and acoustic noise, and higher spatial resolution are a must.
NT values are calculated as follows: a) application of high pass filter to the wafer thickness map; b) find PV of the
filtered data within 2x2 square mm sliding over an entire wafer for TH2 metrics and 10x10 square mm for TH4; c)
7
calculate PV value distribution over percentage of the area. SEMI standard metrics uses 0.05% of the Full Qualified
Area (FQA) (full wafer excluding 2 mm edge) as a wafer NT value. Figure 5 shows an example of a wafer NT map
before and after filtering. Figure 6 shows a cumulative defective area versus NT value which indicates at each height, the
percentage of FQA present. For this particular wafer, TH2 is 8 nm which meets the ITRS roadmap requirement for 32
nm node. But it may be questionable for TH4. An example of an NT defect of 20 nm is shown in Figure 7
4 um
High Pass
Spatial
Filtering
20 nm
-20 nm
-4 um
Raw Surface Height Map
Nanotopography Map
Figure 5. A wafer flatness map produces the NT map after applying a high pass spatial filter.
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100
TH2(WS-NT)
%Defective A
10
TH4(WS-NT)
1
TH2
8 nm
0.1
TH4
16 nm
0.01
0
10
TH2---ITRS Roadmap 45 nm node
20
30
40
50
60
Threshold Height(nm)
Figure 6. Cumulative defect area vs height value. The steep one is TH2 and the other is TH4.
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A-'
2U.U
Figure 7. 20 nm NT feature is shown in both 2-d and 3-d plots.
5. The State-of-the Art Metrology to meet the challenges
KLA-Tencor’s newly developed WaferSight™ 2 product is designed and developed to meet the bare wafer metrology
requirements for 45 nm node and 32 nm node. The state-of the art technology is based on a dual Fizeau interferometer
design. Figure 9 shows an optical schematic of the wafer interferometer tool, where two Fizeau interferometer channels
are combined to look at the two wafer sides. Light from a single tunable laser diode is fiber-coupled to each
interferometer channel. In each channel, a polarization beam splitter (PBS) directs the beam through a quarter-wave
plate (λ/4) to the collimator lens. The collimated beam propagates to the reference flat, whose last surface is the
reference surface of the interferometer. The wafer is placed between the reference flats of the two interferometer
channels, such that both surfaces can be measured simultaneously. The beams reflected at the wafer surface and at the
reference surface propagate back to the collimator lens, and then on to the wave plate and beam splitter. The beam
splitter acts as an optical valve, now transmitting the light to the relay objective, which images the wafer surface onto the
camera, where the interferograms are detected. For the data acquisition, the wavelength of the laser is varied to create a
linear phase shift in the interferograms. Several camera frames with phase-shifted fringe patterns are digitized and
processed in the computer, where high-performance phase algorithms are employed to convert at each camera pixel the
fringe-phase to surface height.
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Reference
Flat
λ/4
PBS
Relay
Camera
Wafer
Collimator
Fibers
Channel
B
Illuminator
Illuminato
r
Computer
Channel
A
Figure 9. Dual channel Fizau interferometer for measuring wafer geometry.
Figure 10. Illustration of wafer flatness and shape derivation.
According to the Semi-standard M14, wafer flatness f(x,y) is defined as the thickness variation across the wafer, see Fig.
10. The wafer shape s(x,y) is defined as the deviation from a best fitting plane of the median surface between the front
and back surface of the wafer in a force-free state. The wafer flatness f ( x, y ) and shape s ( x, y ) can be calculated
from the measurements as
f ( x , y ) = d A ( x , y ) + d B ( x, y ) − c ( x , y )
s ( x, y ) ≈
(4)
1
(d A ( x, y ) − d B ( x, y )) − tilt
2
(5)
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Where d A ( x, y ) and d B ( x, y ) are single side distance from the wafer to cavity and c(x,y) is the distance (without
wafer) between two reference flat shown in Figure 10. Tilt is the wafer tilt.
The details of interferometric computation are described by Freischlad el al.
10
6. Tool performance and characterization
11
Wafer geometry metrics can be characterized by flatness metrics , edge metrics, NT, and shape metrics, industry
standards as described in the table 1. The performance is characterized against those metrics.
Flatness metrics
Peak-to-valley (PV, or range) of the total global flatness. This is equivalent to the total thickness
variation over the FQA.
GBIR
Peak-to-valley of the total site flatness. This is equivalent to the total thickness variation over
SBIR
the site.
Peak-to-valley of the site flatness after removing a best fitting plane over the site. This is
equivalent to the thickness variation over the site without any local wedge component.
SFQR
ERO metrics
ESFQR
ESBIR
ZDD
NT
TH2
Peak-to-valley of the site flatness after removing a best fitting plane over the site. The site is
defined as an angular sector sliced over 360 degrees. The radial length from the edge is from 1
mm to 5 mm. This is equivalent to the thickness variation over the site without any local wedge
component.
Peak-to-valley of the site flatness without removing a best fitting plane over the site. The site is
defined as an angular sector sliced over 360 degrees. The radial length from the edge is from 1
mm to 5 mm. This is equivalent to the thickness variation over the site containing any local
wedge component.
This radius curvatures as a function of radius over 1mm to 5mm from the edge averaged over
the sector which is radially sliced over 360 degrees.
Peak-to-valley (PV, or range) over 2x2 mmxmm sliding window after passing the high pass
filter over the thickness map.
Peak-to-valley (PV, or range) over 10x10 mmxmm sliding window after passing the high pass
filter over the thickness map.
TH4
Shape metrics
Warp
Peak-to-valley of the total shape over the FQA.
Peak-to-valley of the power term of the shape over the FQA. The power term is determined by a
Bow
best fit of a quadratic, or be a 4-point sag calculation.
Table 1. Bare wafer SEMI standard metrics.
7. Tool repeatability and reproducibility
It is important that the tool can repeat and reproduce the measurement results. If the tool has a large variability, the
confidence of the measurement results is reduced. The tolerance to precision ratio of a wafer metrology needs to be at
11
lease larger than 3. SEMI M49 specifies the geometry metrology tool performance only to 65nm node. Table 2
summarizes recommended specifications and data examples of the state-of-the art technology performance for 45 nm
and possibly 32 nm node in Figure 11 to 17.
The data was taken within a 3 day gauge repeatability and reproducibility (GRR) test. There are a total 25 wafers in one
cassette. Wafers were measured on WaferSight 2 with one repeat for each cycle and total of 5 cycles for each day. The
precision is calculated for each site of each wafer of each day and then averaged over all sites and all wafers and all days.
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The precisions (1 σ) for SFQR and SBIR are 0.26 and 0.42 nm respectively, and plotted in Figure 11 and Figure 12.
ERO precision (1 σ) for ESFQR is 0.32 nm shown in Figure 13. NT precisions for TH2 and TH4 are 0.04 and 0.11 nm,
respectively, shown in Figure 14.
65 nm node (Semi M49)
The state-of-the art technology
Matching
Reproducibility tolerance/bias
(nm)
(1 σ) nm
Flatness metrics
4.2
6.3
1.5
2.3
ERO metrics
N/A
N/A
NT metrics
0.3
0.5
1.2
1.8
SBIR
SFQR
ESFQR
TH2
TH4
Reproducibility
(1 σ) nm
Matching
tolerance/bias
(nm)
0.42
0.26
0.4
0.2
0.32
0.38
0.04
0.11
0.04
0.078
Table 2. Summary for SEMI M49 specifications for 65 nm node and data examples of the state-of-the art technology performance
from Figure 11 to 17.
[Variability Chart for SFQR Value (nm)
60
10
40
30
20
10
Site Number
Day
4
6
7
8
9
10
11
12
13
14
15
16
17
18
19
21
20
22
23
24
25
Source Slot
2.0
>1.6
1.2
B 0.8
0.4
0.0•
ite Number
1
2
3
4
rHrrn I
5
6
1111111111111111111iii
7
8
9
10
11
12
13
14
11
16
17
18
19
20
21
22
23
24 21 Source Slot
[Variance Components
Component
Source Slot
Day Ilource Slot1
Site NuniberSource Slot,Day]
Within
Total
Var Component % of Total 20406080
0.738214
0.8782
0 .000000
0.0
83. 2 64112
99.0
0. 061203
0.0776
84. 06 7609
100.0
Sqrt(Var Comp)
0. 8192
0 .0000
9. 1249
0. 2113
σ = 0.26nm
9. 168 8
Figure11. SFQR Precision plot. 1 sigma is 0.26 nm.
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p
C
P
P
σ = 0.42nm
Figure 12 SBIR precision plot. 1 sigma precision is 0.42 nm.
Variability Chart for ESFOR Value (nm)
110-
I 130
110-
90-
70
10
ESFQR Angle (deg)
t
4.0
>3.0
Day
10
11 12j1314 15
16 17j9 20
21 22j2324 28 Source Slot
02.0
S10
SFQR Angle (deg)
>>>3Day
1
2
3
4
S
67
0
9
10
11
12 13 14
11
le
17 18 19 20 21
22
23
24 21 Source Slot
Variance Components
Component
Source Slot
Day[Source SlotS
ESFQR Angle (deg)[Source Slot,Day]
within
Total
VarComponent * of Total 20408080
174.82914
0.00000
343.81301
0.08808
118.74184
33.7
0.0
ee.3
0.0191
100.0
oqrt(Var Comp)
13. 22 2
0.000
10. 142
0.3 11
22. 778
σ = 0.32nm
Figure 13 ESFQR precision (1 sigma) is 0.32 nm.
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THA2 Precision
VurlubHItyChurt foFront_1HA4mmiu ng.)6 % (nm)
9.0
* 8.0
P8.0
THA4 Precision
I
Lvarab11' Chart for Front mA (10 mm Square Range) g 0.05% (nm)
18
I Ji
I
7.0
1
17
3
18
11
14
I
13
12
oo
678
=
1
1
1
124 8 7 8
2.0
>0.8
0.6
>1.8
1.2
B 0.8
B 0.4
000.2
010.4
o o >__>__>;__>__a.a._-C_a_ >__;0__>__>;_>_;1__>__;0_>
0.0
878
Variance Components
Component Var Component * of Total 20406080 Oqrt(Var Comp)
Oourte hot
0.0942978
99.9
0.0928
within
0.0016041
0.0407
0.1383
Total
0.0909009
000.0
0.0936
Variance Components
Component Var Component * of Total 20408080
Source Slot
within
Total
3.1224313
0.0118321
3.0342834
σ = 0.04nm
99.7
0.334e
100.0
Sqrt(Var Comp)
1.8788
0.1088
1.8800
σ = 0.11nm
Figure 14. NT precisions (1 sigma) are 0.04 and 0.11 nm, THA2 and THA4 respectively.
8. Tool Matching
It is very important to tool users to have tools that can match results, so that the measurement is not tool dependent.
Tool matching first establishes a baseline by averaging the measurement results of multiple tools and then characterizes
the difference of the measurement of the same wafers from the tool against the baseline. Tool matching is a
measurement combination of tool accuracy plus tool variability. Figure 15 a) and b) show examples of site flatness
SFQR and SBIR as measured by WaferSight 2. The vertical axis is the difference and horizontal axis is the mean value
of two tools. The individual point is the corresponding site difference. Within the data, the worst site matching is 6 nm
for SFQR and 10 nm for SBIR. Average bias of all sites is 0.2 nm for SFQR and 0.4 nm for SBIR. Figure 16 shows
ERO metrics, ESFQR matching. The worst site matching is 8 nm for ESFQR and 20 nm for ESBIR. The mean bias is
0.39 nm for ESFQR and 0.69 nm for ESBOR. Figure 17 a) and b) show TH2 and TH4 of NT metrics matching results.
The worst wafer matching is 0.18 nm for TH2 and 0.6 nm for TH4. The mean bias is 0.04 nm for TH2 and 0.078 nm for
TH4. The results are summarized in Table 2.
9. Conclusions
Wafer site flatness, ERO and NT impact on litho processing window. The site flatness reduces the focus budget for litho
tool. Wafer ERO metrics affects the edge die yield. NT defects cause photoresist, thin films thickness to vary and thus
impact on etching process and CD variation. As line-width decreases to 45 nm or 32 nm, bare wafer specifications for
wafer flatness, ERO, and NT become increasingly tighter. Therefore, the metrology for the bare wafer measurement is
critical to achieve those specifications. ITRS roadmap requires the site flatness of SFQR to be less than 45 nm and 32
nm for 45 nm and 32 nm node design and NT of TH2 to be less than 11 nm and 8 nm for 45 nm and 32 nm node design,
respectively. The stage-of-the are technology has demonstrated that the wafer site flatness (SFQR) precision is 0.26 nm
and worst site matching 6 nm of 100% FQA. NT precision of TH2 is 0.04 nm and worst wafer matching is 0.18 nm.
The newly developed technology has demonstrated performance required to enable bare wafer specifications
that support shrinking DOF for 45 nm and 32 nodes.
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SFQR
SBIR
Loifference: SFQR(beta)BSdb-SFQR(alpha)
Loifference: SBIR(beta)BSdb-SBIR(alpha)
30
20
20
cr
10
4
10
_______
0
-10
10
0
0
10
20
30
40
60
10
70
100
110
200
210
300
80
Mean: (IBIR(beta)8ldb+IBIR(alphaD/2
Mean: (SFQR(beta)8ldb+SFQR(alphaD/2
SFQR(beta)8ldb 08.6074
SFQR(alpha)
18.8207
Mean Difference -0.2032
ltd Error
0.01008
-0.1831
Upperll%
LowerRl%
-0.223
N
Correlation
t- Ratio
-20. 16R3
0711
DF
Prob
ItI
<.0001
1.0000
<.0001
Prob t
Prob < t
1712
0.11718
71.9811
72.3798
t-Ratio
Mean Difference
-0.3987
Prob < ItI
ltd Error
0.03381
Prob t
Upperll%
Lowerls%
-0.3324
-0.4811
Prob < t
N
1712
0. 99818
IBIR(beta)8ldb
IBIR(alpha)
Correlation
Figure 15 a) SFQR site flatness matching.
DF
-11.7791
1711
<.0001
1.0000
<.0001
b) SBIR site flatness matching
ESFQR
Lofference: ESFQR(beta)85db-ESFQR(WSNT)alpha J
20
16
12
4
-4
12
16
-20
0 10 20 30 40 80 60 70 80 90 100 110
Mean: (E6FQR(beta)8Sdb+ESFQR(WSNT)alpha)/2
48.0948
ESFQR(beta)lldb
ESFQR(WSNT)alpha 47.7073
t- Ratio
Mean Difference
Std Error
9mb
Uppercl%
Lowemgs%
Correlation
0.38741
0.04821
0.48203
0.29286
1139
0.99613
8.037307
1138
DF
ItI
9mb t
<.0001
<.0001
9mb < t
1.0000
Figure 16 a) ERO: ESFQR matching
Proc. of SPIE Vol. 6827 682723-14
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THA 2 SQMM
THA 4 SQMM
LOfference: ThA2(beta)88db-THA2(WSNT)alpha 1
LDIffBrBnCB: THA4(Beta)85db-THA4(WSNT)alpha
1.00-
z
I
P 1.6
0.80
z
0.60
1.2
0.40
0.8
0.20
- 1.4
0.0
0.00
-
0.20
0.40
6-0.600.80
9
4.1 1.0 1.1 6.0 6.1 7.0 7.1 8.0 8.1 9.0
11 12 13 14 13 16 17
10
Mean:
Mean: (THA4(Beta)8ldb+THA4(WSNT)alpha)/2
(THA2(beta)88db+THA2(WSNT)alpha)/2
6.71706
THA2(beta)88db
THA2(WSNT)alpha 6.78937
Mean Difference
-0.0423
Std Error
0.01878
-0.0026
Uppercl%
Lowergl%
-0.0821
N
b
Correlat:on
DF
9mb
9mb
13.3642
THA4(Beta)8ldb
THA4(WSNT)alpha 114421
Mean Difference
-0.0783
Std Error
0.06301
0.01124
UpperRl%
Lowergs%
-0.2118
-2.28368
t- Rat:o
ItI
t
9mb Ct
16
0.0386
0.9807
0.0193
17
0.99869
Figure 17 a) TH2 of NT matching.
Correlation
-1.24321
t- Ratio
DF
Prob
Prob
Prob
16
ItI
t
t
0.2317
0.8841
0.1188
17
0.88102
b) TH4 of NT matching.
10. References:
1.
2.
ITRS 2006 Update “Front End Processes”.
B.J. Lin “New λ /NA scaling equations for resolution and depth-of-focus”, Proceedings of SPIE Vol. 4000
(2000).
3. J. Mulkens et al “Defects, Overlay and Focus Performance Improvements with Five Generations of Immersion
Exposure Systems,” Optical Microlithography xx, Proc. Of SPIE Vol. 6529, 652005, (2007).
4. SEMI M1-0600, “Specifications for polished monocrystalline silicon wafers”, SEMI 2000.
5. SEMI M68-0307 (Preliminary), “Practice for determining wafer near-edge geometry from a measured height
data array using a curvature metric, ZDD”, SEMI 2007.
6. SEMI M67-1106 (Preliminary), “Practice for determining wafer near-edge geometry from a measured thickness
data array using the ESFQR and ESFQD metrics”, SEMI 2006.
7. SEMI M43-0301, “Guide for reporting wafer nanotopography”, SEMI 2001.
8. D. Boning et al “Characterization and Modeling of Nanotopography Effects on
CMP”, MIT, International CMP Symposium, 2000.
9. A. Grenville et al “Electrical Critical Dimension Metrology for 100-nm Line-widths and Below,” Proc. Of SPIE
Vol 4000 (2000).
10. K. Freischlad et al “Interferometry for Wafer Dimensional Metrology,” Proc. of SPIE San Diego (2007).
11. SEMI M49-0307, “Guide for specifying geometry measurement systems for silicon wafers for the 130-nm to
65-nm technology generations”, SEMI 2007.
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