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

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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