Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
3/27/03 12003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
In-Situ Metrology: the Path to Real-Time Advanced Process Control
Gary W. RubloffProfessor, Materials Science and Engineering, Institute for Systems Research,
and Electrical and Computer EngineeringUniversity of Maryland
www.isr.umd.edu/gwrubloff, [email protected]
Department of MaterialsScience and Engineering
3/27/03 22003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Synopsis• Advanced process control (APC) has become pervasive
• In-situ metrology is key to extending this to real-time APC
• In-situ chemical sensors provide viable quantitative real-time metrology– Multiple sensors deliver <1% precision– Real-time end point control demonstrated– Course correction as well as fault detection– Application to CVD, PECVD, etch, spin-cast, …
• New opportunities– Uniformity control spatially programmable reactor design– Precursor delivery control solid & low pvapor sources
ready for tech transfer & evaluation in manufacturing environment
3/27/03 32003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Advanced Process Control (APC)
deposition pattern generation etching metrologymetrology
Advanced ProcessControl (APC)
Course correctionCompensate for variationsto maintain process targets
Fault managementIdentify and repair
equipment problemsSensor-drivenModel-based
run-to-runfeedback control
run-to-runfeedforward
control
Run-to-run controlFeedback & feedforward
Fault classification & responseOptimize management of faults
fault classification& response
Real-time controlEnd point and instantaneous
real-timecontrol
sensor
Real-time fault detectionKnown failure modes and signatures
real-time faultdetection
sensor
3/27/03 42003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
APC Hierarchy
supervisory
regulatory
Factory Control System
In-line & other metrologyMulti-step process controlMulti-scale time response
Run-to-runcourse correction-feedback-feedforward
Course correction
Tool maintenance- fault diagnosis- PM scheduling
Fault management
In-situ, real-time process sensorsUnit process control Real-time response
Real-timefault detection
Real-timecourse correction
quantitative metrologyin-situ, real-timeRealReal--Time APCTime APC
Real-time equipment sensorsEquipment component controlReal-time response
Regulatory tool control- equipment state
Tool Control System
3/27/03 52003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
In-Situ Sensors for Quantitative Process Metrology
REQUIREMENTS• In-situ, real-time• Quantitative precision (~1%)
– Required for course correction
• Process state• Wafer state• Preferably multi-use
– Indicators of process & wafer state
– Simultaneous application for fault detection
• Rich information– Chemically specific
• Robust, integratable
TECHNIQUES• Plasma optical emission
spectroscopy (OES)• Laser/optical interferometry• Mass spectrometry• Acoustic sensing• Fourier transform infrared
spectroscopy (FTIR)• Plasma impedance• Optical
thermometry/pyrometry• Ellipsometry• Optical scatterometry• …
3/27/03 62003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Mass Spectrometry for Real-Time APC
PROCESS CHAMBER
Chemical vapor depositionchamber for tungsten metal
H2SiH4/WF6
BP
Reactor exhaust
Turbo pump50 l/s
QMS
Ion gauge
to drag stage
orificeorificeorifice
Pressurecontrolvalve
Baratron
PROCESSGAS FLOW
SENSORGAS FLOW
Ulvac multi-chamber“cluster” tool CHEMICAL SENSORS
InficonComposer
acoustic sensor
Inficon Transpectormass spec
chemical sensor
Pressure transductionto low pressure
3/27/03 72003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Real-Time Mass Spec in W CVD
2 WF (g) + 3 SiH (g) 2 W (s) + 3 SiF (g) + 6 H (g)6 4 4 2WF6 (g) + SiH4 (g) W (s) + 2 SiHF3 (g) + 3 H2 (g)
2 WF6 (g) + 3 SiH4 (g) 2 W (s) + 3 SiF4 (g) + 6 H2 (g)
WF6 (g) + SiH4 (g) W (s) + 2 SiHF3• W CVD by SiH4reduction of WF6 in 0.5 torr thermal CVD
• Monitor process state as gas concentrations in reactor
• Product generation and reactant depletion reveal wafer state changes in real time
(g) + 3 H2 (g)
3/27/03 82003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Real-Time Thickness Metrology
• Reasonable Conversion Rate of WF6 reactant (~20%)
• Metrology established from weight vs. integrated mass spec signal– Linear regression
standard deviation 1.09%
• Viable for manufacturing process control
SiH4 reduction of WF60.5 torr, 250°C
SiH4 reduction of WF60.5 torr, 250°C
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0H2 Integration Signal (arb unit)
W F
ilm W
eigh
t (g)
7/14/00, y = 89069 x + 0.0004, R2 = 0.99977/07/00, y = 90876 x - 0.0002, R2 = 0.99896/28/00, y = 90830 x – 0.0005, R2 = 0.99936/20/00, y = 87682 x + 0.0004, R2 = 0.9944
3/27/03 92003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Real-Time Thickness Control
W F
ilm W
eigh
t (g)
H2
Inte
grat
ion
Sign
al
target H2 value
no control (experimental)
with control
Wafer Number Wafer Number
no control (experimental)
with control
0.0E+00
1.0E-07
2.0E-07
3.0E-07
4.0E-07
5.0E-07
0 1 2 3 4 5 6 7 8 9 100.000
0.010
0.020
0.030
0.040
0 1 2 3 4 5 6 7 8 9 10
Mass specMass spec Film thicknessFilm thickness
• Open-loop wafer-to-wafer thickness variation ~ 10%• Real-time end-point control of thickness to ~ 3%• Real-time course correction to compensate for BOTH:
– Random short-term variability– Systematic longer-term drift
3/27/03 102003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Mass Spec Thickness Metrology
H reduction of WF2 6WF (g) + 3 H (g) W(s) + 6 HF(g)6 2
Fixed process condition: 10 torr, 500°C, 640 sec
H2 reduction of WF6WF6(g) + 3 H2(g) W(s) + 6 HF(g)
Fixed process condition: 10 torr, 500°C, 640 sec
0.02.0x10-5 2.1x10-5 2.2x10-5 2.3x10-5 2.4x10-5 2.5x10-5 2.6x10-5 2.7x10-5 2.8x10-50
230
240
250
260
270
280
3
24
51
67
89
10
W F
ilm W
eigh
t (m
g)
Integrated HF Signal (Amps-sec)
0
15500
16000
16500
17000
17500
18000
Linear RegressionAverage Uncertainty +/- 0.56%
Standard Deviation 0.67%
0 0 0
4%
Estim
ated
Ave
rage
Film
Thi
ckne
ss (A
)
0 1 2 3 4 5 6 7 8 9 10 110
230
240
250
260
270
280
W F
ilm W
eigh
t (m
g)
Wafer (or Run) Number
0
15500
16000
16500
17000
17500
18000
10 wafer average drift +/- 1.18%(extreme case +/- 3.99%)
255.7
0 0 Estim
ated
Ave
rage
Film
Thi
ckne
ss (A
)
Run-to-run thickness driftAverage 1.18%Extreme 3.99%
Mass spec thickness metrologyAverage uncertainty 0.56%Standard deviation 0.67%
3/27/03 112003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Mass Spec Thickness Metrology: Intentional Temperature Drift
Intentional Run-to-Run Temperature DriftFixed Deposition Time 618 sec
Intentional RunIntentional Run--toto--Run Temperature DriftRun Temperature DriftFixed Deposition Time 618 sec• Introduce significant
temperature drift to test robustness of metrology
• Substantial change in thickness (4X)
– Much larger than expected in manufacturing
0 5000 10000 15000 200000
1x10-10
2x10-10
3x10-10
4x10-10
400'C
WF6
Sig
nal (
Amps
)
0
2x10-8
4x10-8
6x10-8
18171615
14131211
10987654321
HF S
igna
l (Am
ps)
340350360370380390400
340'C350'C360'C
370'C380'C385'C390'C395'C
Tem
pera
ture
('C)
Time (sec)
3/27/03 122003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Mass Spec Thickness Metrology: Intentional Temperature Drift
Moderate non-linearity over broad temperature rangeDeposition on showerhead, adsorption on chamber walls, …
Metrology precision ~ 0.6% near local process setpoint
0.01.0x10 -5 1.5x10 -5 2.0x10 -5 2.5x10 -5 3.0x10 -5 3.5x10 -5 4.0x10 -5
0
50
100
150
200
250
300
350
Wafer #2-#10 (400'C-380'C)Linear Regression
average uncertainty +/- 0.55%standard deviation 0.62%
Wafer #9-#18 (380'C-340'C)Linear Regression
average uncertainty +/- 0.57%standard deviation 0.69%
W fi
lm w
eigh
t (m
g)
Integrated HF signal (amp-sec)
0
5000
10000
15000
20000
Estim
ated
ave
rage
film
thic
knes
s (A
)
3/27/03 132003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Mass Spec Thickness Metrology: Intentional Process Time Drift
0.0 1.0 2.0 3.0 4.0 5.0 6.00
50
100
150
200
250
300
350
400
W F
ilm W
eigh
t (m
g)
HF Integration Signal (10-5 Amps-sec)
0
5000
10000
15000
20000
25000
Estim
ated
Film
Thi
ckne
ss (A
)
H reduction of WF2 6WF6(g) + 3 H (g) W(s) + 6 HF(g)2
10 torr, 390°C
H2 reduction of WF6WF6(g) + 3 H2(g) W(s) + 6 HF(g)
10 torr, 390°C
• Introduce significant process time drift to test robustness of metrology
• Substantial change in thickness (4X)
– Much larger than expected in manufacturing
• Linear regression fit– Average uncertainty 1.19%– Standard deviation 1.59%
• Quadratic regression fit– Average uncertainty 0.48%– Standard deviation 0.57%
3/27/03 142003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Acoustic Sensing for Real-Time APC
• Acoustic wave propagation and resonance
P > 50 torr
• Resonant frequency depends on average molecular weight, specific heat, and temperature of gas mixture
C = speed of sound
Gas compression(0.5 cfm diaphragm pump)
acousticsensor100 torr
Capacitancegauge
Pressure ctrl.valve
WF6 H2
4” wafer
Pressure controllerto process pumps
CVD process10 torr
Needle valve
Pressure transductionto higher pressure
Transmitter
InletAcoustic chamber Heater
Outlet Receiver
avg
avg
MRTγ
Cwith2LCF ==
3/27/03 152003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Acoustic Sensor Thickness Metrology
H reduction of WF2 6WF (g) + 3 H (g) W(s) + 6 HF(g)6 2
Fixed process condition: 10 torr, 490°C, 640 sec
H2 reduction of WF6WF6(g) + 3 H2
Run-to-run thickness driftAverage 4% over 10 runs
Acoustic sensor thickness metrology
0.5% average uncertainty from linear regression fit
(g) W(s) + 6 HF(g)Fixed process condition: 10 torr, 490°C, 640 sec
+/- 1 % weight error
01000 84000 88000 92000 960000.00
0.01
0.02
0.20
0.21
0.22
0.23
0.24
0.25
0.26
0.27
Wafer 203 to 212Linear Fit of Data2_B
W fi
lm w
eigh
t (g)
Frequency integrated signal (Hz.s)
0
1000
14000
15000
16000
17000
Estim
ated
film
thic
knes
s (A
)
3/27/03 162003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
FTIR Sensing for Real-Time APC• Implementation like acoustic sensor
P > 50 torr• Sense molecular vibrations (infrared) for product generation, reactant
depletion• WF6 product depletion thickness metrology precision ~0.5%
0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21580
600
620
640
660
680
410oC
410oC
405oC400oC400oC
395oC395oC
390oC390oC WF6 absorption at 712.5 cm-1
R=-0.99672
Inte
grat
ed W
F 6Si
gnal
Mass of deposited tungsten (g)
H2 reduction of WF6WF6(g) + 3 H2(g) W(s) + 6 HF(g)Intentional temperature drift: 10 torr, 390-450°C
H2 reduction of WF6WF6(g) + 3 H2(g) W(s) + 6 HF(g)Intentional temperature drift: 10 torr, 390-450°CWF6
3/27/03 172003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Sensor Integration
real-time control
equipment stateLabView
sensorcontrol
process & wafer state metrology
sensor
Brooks
toolcontrol
Pumpsystem
W CVD Reactor
Centralwafer
handler
W CVD Reactor
Loadlock Ulvac ERA-1000
W CVD cluster tool
VisSim
dynsimul dynamic system
simulation
3/27/03 182003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Interface and Thin Layer Sensitivity
SiF4 product of Si reduction reaction3 Si (s) + 2 WF6(g) 2 W(s) + 3 SiF4(g)
SiF4 product of Si reduction reaction3 Si (s) + 2 WF6(g) 2 W(s) + 3 SiF4(g)
1.0 1.5 2.0 2.5 3.00.0
1.0x10-12
2.0x10-12
3.0x10-12
4.0x10-12
5.0x10-12
6.0x10-12
Mas
s sp
ec s
igna
l (A
)
time (min)
“cold” waferHF signal
HF production “hot” waferHF signal
H reduction of WF :2 6WF6(g) + 3 H2(g) W(s) + 6 HF(g)
H2 reduction of WF6:WF6(g) + 3 H2
Initial reaction dominated by WF6 - Si nucleation
~30 nm W formedReadily observed
(g) W(s) + 6 HF(g)
Implications:Fault detection
assure oxide-free contacts)
Metrology for ultrathinCVD layers
3/27/03 192003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Ready for Technology Transfer• In-situ sensors deliver metrology for real-time APC
– Quantitative precision for real-time course correction– Dual-use sensors to drive both course correction and fault
management (e.g., mass spec)• Research underpinnings in place
– Multiple sensors with metrology at 1% or better– Real-time end point control demonstrated– Sensor-tool integration
• Ready for implementation in manufacturing environment – Compatible with existing/installed real-time sensors for fault detection– UMD anxious to assist, collaborate, … –– Prediction: further improvement in metrology precisionPrediction: further improvement in metrology precision
• High throughput enhances sensor & tool conditioning
3/27/03 202003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Across-Wafer Uniformity
• Key manufacturing metric for yield
• In-situ sensor capability to date– Spatially resolved optical (OES) –
process state– Full-wafer interferometry – wafer
state
• No mechanism for real-time uniformity adjustment
• Currently, process optimization involves tradeoff between material quality metrics and uniformity
Material quality
Uniformity
Recipe 1
Recipe 2
Recipe 3
Choose compromise as process design to balance uniformity and material quality for fixed reactor configuration
3/27/03 212003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Programmable Uniformityto Optimize Quality & Manufacturability
Choose process design point for optimal material
and device performance
Choose process design point for optimal material
and device performance
Uniformity unacceptable
Retune spatial conditions in programmable reactor
Retune spatial conditions in programmable reactor
Uniformity unacceptable
Produce high uniformity with optimal material
and device performance
Produce high uniformity with optimal material
and device performance
3/27/03 222003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Spatially Programmable CVD Uniformity through a Smart Showerhead
Sensors - integrated into the showerhead
Spatially resolved, multizonewafer and process state measurements
Actuators - multizone, gas inlet
Gas flow rates and compositions controlled within each showerhead segment
Supplementary pumping through the showerhead
Reduced inter-segment gas mixing, precise composition control, gas sampling for chemical sensing
Simulation and reduced-order models
Support for process equipment design and control
Multipoint OpticalSensing
(e.g., full-waferinterferometry)
Heated SusceptorWafer
Gas Exhaust toProcess Pumps
Reactor
MultisectorGas Inlet
and Showerhead
IlluminationSource
Multipoint GasPumping & Sensing
(e.g., mass spec)
3/27/03 232003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Experimental Testbed:Spatially Programmable CVD Showerhead
inlet
exhaust
3-segment prototypeExhaust and inlet in each segmentAdjustable spacings to wafer
intersegment vs. intrasegmentmixing
Extensive coupling to modeling
3-segment prototypeExhaust and inlet in each segmentAdjustable spacings to wafer
intersegment vs. intrasegmentmixing
Extensive coupling to modeling
individual segment :quasi-independent mini-showerhead incorporating gas inlet, exhaust, sensing, and model-based control of actuation
3/27/03 242003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Experimental Testbed:Spatially Programmable CVD Showerhead
• Ulvac ERA-1000 W CVD cluster tool• W CVD process using WF6 + H2
Segmented showerhead
Gas management(inlets and exhaust)
3/27/03 252003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Programmable Nonuniformityfor Rapid Materials & Process Development
One-wafer DOE process optimizationOne-wafer DOE process optimization
Combinatorial CVD new materials discovery and development Combinatorial CVD new materials discovery and development
3/27/03 262003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Precursor Delivery Challenges
• Solid & low vapor pressure sources increasingly critical for new materials
• Precursor delivery control remains problematic
– Changing morphology with time and usage
– Adsorption on walls– Complex chemical precursors
• Options limited for both chemical precursor and delivery system design
Example: Cp2Mg temperature decrease 40 32°C reduces vapor pressure & composition 2X
Simulates “aging” effects
3/27/03 272003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Real-Time Precursor Delivery Control
• Acoustic sensor for composition metrology
• Source and dilution gas flow control
Carrier gas flow set point
MFC
H2
H2 dilution
H2 carrier
P
Compositionmeasurement
Dilution flow set point
Composer controller
MFC
Composeracoustic
transducer50 g. Cp2Mgsolid source
precursordelivery
Source temperature varied from 4032oC
Σ (H2 flows) = 150 sccm, P = 300 torrCp2Mg target = 0.01 mol%
Cp2Mg composition controlled to 1% of target (0.0001 mol %)
3/27/03 282003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
MOCVD Precursor Delivery Line Control
T(source) = 40oC
60 ± 1.5oC
0 20 40 60
0.0092
0.0096
0.0100
0.0104
0.0108
Time (min)
20
40
60
80
100
120
Cp 2
Mg
com
posi
tion
(mol
%) Closed loop Open loop
H2
flow
rate
s (s
ccm
)0 20 40 60
0.0092
0.0096
0.0100
0.0104
0.0108
Time (min)
20
40
60
80
100
120Closed loop Open loop
Acoustic sensor reveals wall adsorption fluctuations optimize wall temperature
Control system suppresses delivery fluctuations
50 ± 1.5oCT (feed line) =
H2
flow
rate
s (s
ccm
)
3/27/03 292003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
• In-situ metrology is key to achieving real-time APC– Benefits in rapid feedback at unit process (tool) level– Implementation within hierarchical control framework
• In-situ chemical sensors provide quantitative real-time metrology– Multiple sensors with <1% precision– Real-time end point control demonstrated– Course correction synergistic with fault detection– Broad applications - CVD, PECVD, etch, spin-cast, …
• Ready for tech transfer, evaluation in manufacturing environment
• New opportunities– Uniformity control – Precursor delivery control
Conclusions
3/27/03 302003 Int'l. Conf. Characterization & Metrology for ULSI TechnologyG. W. Rubloff © 2003
Acknowledgements• Research group
– L. Henn-Lecordier, J. N. Kidder, T. Gougousi, Y. Xu, S. Cho, R. A. Adomaitis, J. Choo, Y. Liu, R. Sreenivasan, L. Tedder, G.-Q. Lu, A. Singhal
• NIST– J. Whetstone, A. Lee, C. Tilford
• Inficon– R. Ellefson, L. Frees, C. Gogol, A. Wajid, J. Kushneir
• Other colleagues– Metrology TWG, AEC/APC, AVS MSTG
• Support