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Integrated CD Metrology forPoly Si Etching
G.P. Kota, V.Venugopal and R.A. GottschoLam Research Corporation
T.G. Dziura, U.Whitney and A. LevyKLA-Tencor
Plasma Etch Users Group MeetingJan 17, 2002
Outline
s Motivations Scatterometer concepts Results
; comparison to CD-SEM, x-SEM and AFM; different profiles; repeatability measurements; 193nm PR measurements
s Summary
What Does CD Mean?What Does CD Mean?s For smaller design rules, corner rounding, notching etc
can make up a significant fraction of the line shape; Examples:
s Where do we measure CD?; Not clear using CDSEM; Can measure CD at any height using SCD since the entire profile
information is available
Pre etch Post etch and clean
?
?
? ?
?
?
Demand For Profile MeasurementDemand For Profile Measurements For most processes, dimensional measurements
are required at specific locations on the features Example: STI application
STI line
Nitride bottom CD
Silicon top CD
Silicon
Nitride
Trench wall angle
Trench depth
SCD Measurement ProcessSCD Measurement Process
• 240-780nmEllipsometer• Amplitudeand phase areacquired•Best matchdeterminestargetparameters
Offline:Library generation
Online:Film measurementProfile measurement
Film 1Film 2
θ
Model
Best Fit
CD, HT, SWA etc.
Library
Wafer
Measureddata
ProcessInfo
GratingInfo
On-Tool
Off-Line
s Integrated metrology uses Low cost of ownerships High throughput
; 100 wafers per hour with 5 measurement points for eachwafer
s CD as well as profile informations Non-destructive technique
; prevent shrinkage of 193nm PR
s Average profile of the grating area inspected
Advantages of SCD
Disadvantages of SCDs Creation of off-line spectral librariess Library needs to be re-created if any of the grating parameters
are changeds Test structures (grating) required
; Current minimum grating size ~ 50µm x 50µm
50µm
50µm
Applications of SCD
s Integrated CD measurement (iCD) tool can beused in real time for; Feed forward control
» measure pre etch CD/profile and adjust process recipe for desiredpost etch CD/profile
; Feed back control» measure post etch CD/profile and adjust process recipe for
desired CD/profile
; Fault detection» measure post etch CD/profile to detect any process excursions
and avoid further mis-processing of wafers
Stacks and FeaturesStacks and Features
s Stack: resist / organic ARC / a-Si / gate oxide / Si
l CD: 50, 55, 60, 65, 70, 75,80, 85, 90, 95, 100, 120, 140,160 nm
l L/S ratio: 1:1, 1:2, 1:3, 1:5
s Process step: pre etch, post-BARC etch, post a-Si etch,post a-Si etch and clean
l a-Si etch: “nominal”,“tapered”, “bowed”
ProcessesProcesses
Sampling PlanSampling Plan
s 49 sites across the wafer
l Measurements made atdifferent process steps weremade on sister wafers
Post etch
Postclean
Preetch
Pre etch Results: XSEM & SCDPre etch Results: XSEM & SCD
XSEM – SCD comparison SCD model match to data
s Good match to XSEM & spectral data
160 1:1
SCD profileresult
resist
BARC
a-Si
SCD profileresult
resist
BARC
a-Si
Pre Etch Wafer Maps (160 nm 1:1)Pre Etch Wafer Maps (160 nm 1:1)s wafer map data can be rapidly
collected at many sites acrossthe wafer, providing the processtool signature
s limited sampling plans (5-site)would not extract thisinformation
Mid CD
height
wallangle
SCD compares well with AFM measurement
Measurement Technique PR thickness (nm)
SCD 396x-SEM 390AFM 396
Pre etch wafer: PR thickness measurements
Post Etch Results: XSEM & SCDPost Etch Results: XSEM & SCDs 160 nm 1:5 L:Ss Mask erosion, a-Si profile are correctly measured
XSEM – SCD comparison SCD model match to data
resist
BARC
underlyinga-Si profile
etchresidue
resist
BARC
underlyinga-Si profile
etchresidue
Post Etch & Clean Results: XSEM & SCDPost Etch & Clean Results: XSEM & SCD
s 160 nm 1:1 L:S, tapered etch
XSEM – SCD comparison SCD model match to data
scatterometry profile result
a-Si
gate oxide
scatterometry profile result
a-Si
gate oxide
Post Clean Wafer Bottom CD and Profile MapsPost Clean Wafer Bottom CD and Profile Maps
s 160 nm 1:1 L:S; tapered etchs cross wafer profile uniformity is excellent
0
50
100
150
200
250
300
350
400
-200 -150 -100 -50 0 50 100 150 200
X (nm)
Y (
nm
)
Post Clean Wafer Sidewall Angle MapPost Clean Wafer Sidewall Angle Map
s 160 1:1 tapered etchs sidewall angle distribution is tight
0
5
10
15
20
25
8585
.25 85.585
.75 8686
.25 86.5
86.75 87
87.25 87
.587
.75 88
Gate sidewall angle (deg)
Fre
qu
ency
0%
20%
40%
60%
80%
100%
120%
Cu
mu
lativ
e p
erce
nta
ge
(%)
FrequencyCumulative %
Post Clean Wafer Results: XSEM & SCDPost Clean Wafer Results: XSEM & SCDs 160 nm 1:1 L:S, bowed etchs sidewall profiles are accurately measured
XSEM – SCD comparison SCD model match to data
SCD profileSCD profile
Good Correlation between CD-SEM and SCDCD-SEM SCD
0.9
0.95
1
1.05
1.1
0.9 0.95 1 1.05 1.1
normalized CD-SEM
no
rmal
ized
SC
D
SCD
CDSEM
Pre etch wafer
SCD: Static and Dynamic Repeatability <0.02nm
149.2
149.22
149.24
149.26
149.28
149.3
0 10 20 30
measurement #
MC
D (
nm
)
static
dynamic
MCD Static Dynamicaverage (nm) 149.25 149.253*std dev (nm) 0.0152 0.0195range (nm) 0.0227 0.0219
CD
@ m
id-h
eig
ht
(nm
)
Post clean wafer
CD-SEM Measurement Issues of 193nm PR
s 193nm PR is known to shrink ~ 10nm duringCD-SEM measurements (e-beam exposure); This can be minimized by using SCD
s 193nm PR typically has rough sidewalls whichlead to ambiguity in CD measurements; This can be minimized by using a non-localized
measurement technique» SCD averages over the beam spot area» CD-SEM is a very localized measurement
Localized CD-SEM measurement can result inunrepeatable CD measurements
CD measurement = 131.9 CD measurement = 125.5
CD measurements on the same die
193nm PR: Static Repeatability on pre etch wafer
CD drift after 5 measurements:CD-SEM, 800V = 8.8 nmCD-SEM, 300V = 8.1 nmSCD = 0.16nm
170
180
190
200
210
220
230
240
0 1 2 3 4 5 6
measurement #
Lin
e C
D CD-SEM, 800VCD-SEM, 300VSCD
Summarys SCD provides accurate CD and profile
information; low 3sigma dynamic and static repeatability
s SCD shows good correlation to CDSEMand x-SEM
s SCD enables process control; integrated on to the etch platform; feed forward, feed back and fault detection
s SCD better for measuring 193nm PR thanCD-SEM due to PR shrinkage