Optical Emission Analysis of BCl3/Cl2 Plasma Etch of W,

Al, and Ti Thin Films

Anushka Walia

Irvington High School

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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

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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

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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

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Works Cited

• “Stationary Metal Analyzers”, Ametek Materials Analysis Division

• P5000 Endpoint Manual

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Acknowledgements

• Ryan Rivers

• Jayss

• Jesse

• Cheryl

• Marilyn

• Bill Flounders

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