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Optical Emission Analysis of BCl3/Cl2 Plasma Etch of W,
Al, and Ti Thin Films
Anushka Walia
Irvington High School
1
Centura MET (ICP chamber)
• 2 Power sources
• Inductively coupled source power through chamber wall
• Platen Bias Power
• Independent power sources allow lower pressure inside the chamber
• More control of system
ICPPlaten
2
Mechanism
Standard etch recipe (MET_AL_ME)
Metal (M)
Si
Cl ions MClx
1. RF power causes molecules to dissociate and form ions
2. Ions are accelerated downwards by bias power
3. Ions/Activated neutrals adsorbed onto surface of substrate, where reaction occurs
4. Product molecules are desorbed from the surface of the substrate and removed from the chamber (by bias power) 3
OES Technique
• Technique used to determine elemental composition of samples
• Utilizes unique emission spectra
• Wavelength range: 160 – 770 nm
4
Mechanism1. Electrons stripped by RF power, ionizing gas
species
2. As electrons recombine with the ions, light emitted at specific wavelengths
3. Diffraction grating splits light
4. Detectors measure light intensity
at different wavelengths – emission
spectrum of atom/molecule
Emission spectrum used to identify
species present, intensity of light is used
to measure relative concentrations5
Multi-wavelength OES
• Multi-wavelength OES can monitor multiple wavelengths instead of only 1-2
• Allows for investigation of secondary lines to confirm species
• Can choose lines to maximize signal to noise ratio
• Endpoint detection
• Contaminant detection
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Experimental Plan
Goal: Optical emission analysis of species present in plasma etches of various materials
• W/Si, W/SiO2, Ti/Si, Ti/SiO2, Al/Si, Al/SiO2
• Bare Si before and after each wafer
• Monitor etch conditions using OES
• Analysis of data• Baseline fingerprint of materials relevant to the etch
• Identify useful wavelengths
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MET setup• x2 2-meter Fiber Patch Cables from Thorlabs with
range 200-1200 nm
• Spectrophotometer
• OceanView software
MET Chamber C
Computer
Cable #1 Cable #2
Spectrometer
USB
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Species Wavelength
AlCl3 (AlCl) 261, 265, 268
BCl3 (BCl) 272, 267
Cl2 309
SiCl4 (SiCl) 281,282,287
W 272 201 407 430
Ti 335 365 400
TiCl 419
Relevant Wavelength Data
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Cl2 on Bare Si
SiCl Band
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BCl3 on Bare Si
BCl3 Band
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Al/Si
Al / AlCl peaks
SiCl Band
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Al/Si
Endpoint
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Al/SiO2
Al peaks
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Al/SiO2
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Why SiCl with Si but not SiO2?
• Si-O bond stronger than Si-Cl bond
• B-O bond stronger than B-Cl bond
Al/SiO2 Al/Si
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Ti/Si
Ti peaksSiCl band
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Ti/Si
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Ti/SiO2
Ti peaks
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Ti/SiO2
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W/Si
W peaksW peaksSiCl band
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W/Si
W etch does not have clear endpoint
>4 minutes to endpoint
0
200
400
600
800
1000
1200
1400
1600
1800
00
:00
.0
00
:06
.6
00
:13
.2
00
:20
.0
00
:26
.6
00
:33
.2
00
:39
.8
00
:46
.4
00
:53
.0
00
:59
.6
01
:06
.2
01
:12
.8
01
:19
.4
01
:26
.0
01
:32
.6
01
:39
.2
01
:45
.8
01
:52
.4
01
:59
.0
02
:05
.6
02
:12
.2
02
:18
.8
02
:25
.4
02
:32
.0
02
:38
.6
02
:45
.2
02
:51
.8
02
:58
.4
03
:05
.0
03
:11
.6
03
:18
.2
03
:24
.8
03
:31
.4
03
:38
.0
03
:44
.6
03
:51
.2
03
:57
.8
04
:04
.4
04
:11
.0
04
:17
.6
04
:24
.2
04
:30
.8
04
:37
.4
04
:44
.0
W/Si Timeseries
506.999 (W)
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W/SiO2
W peaks
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W/SiO2
W etch does not have clear endpoint
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Bare Si
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W endpoints
WCl4 Extremely high (solid at rt)
WCl5 275.6 °C
WCl6 346.7°C
Boiling points of W chlorides
Species with boiling points under ~300°C at standard pressure will be removed, but some W chlorides have bp above that
W
Si
Cl ions
WClxWClx WClx
W chlorides do not get removed, act like a block => slow endpoints
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Recommendations
• Wavelengths recommended for various etches:
Al: 264, 311, 397
Ti: 418, 431, 455, 469, 502, 521
W: 507
• Do not run Cl based etch on W wafers
• SF6 + O2 based etch for W
• Check for cross contamination of S byproducts
Future testing
27
Works Cited
• “Stationary Metal Analyzers”, Ametek Materials Analysis Division
• P5000 Endpoint Manual
28
Acknowledgements
• Ryan Rivers
• Jayss
• Jesse
• Cheryl
• Marilyn
• Bill Flounders
29
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