NIST programs in photoresistoutgassing and optics damage

C. Tarrio, S. B. Hill, S. Grantham, N Faradzhev, T. B. Lucatorto

National Institute of Standards and Technology

Outline

• Resist outgassing measurements

• Optics lifetime testing

• Witness sample testing

• Results from initial witness-plate tests

• Summary

Semi-quantitative method: Combining resist data to rank damage potential

Measure resist outgassing and composition

Measure carbon growth for all significant constituent molecules

Assume partial pressure proportional to amount of each constituent

Assume total carbon growth is sum of growth expected from each component

Weaknesses:

Extrapolation of growth rates to stepper conditions is problematic

Assumes each molecule acts independently from other molecules and background water vapor

Outgassing measurements

5

An example of 6 resist compositional analyses

Total outgas

Significant components

observed

Isobutene Diethyl hexaneBenzene Diphenyl sulfideAcetone HexaneToluene Tert-butylbenzene

6

NIST optics damage facility

Load lockBe filter

Sample

• Average, in-band (13.5 nm ± 2%) intensity 4-8 mW/mm2 at sample• Expose in controlled partial pressure of admitted gases• Bake to 150º C• Base pressure ~2×10-10 Torr• C-deposition measured by XPS and spectroscopic ellipsometry

• Logarithmic pressure dependence continues down to 10-10 Torr

• Surface coverage: Yakshinskiy, et al, Proc. SPIE 7271-36 (2009).

carbon growth rate

Both surface coverage and carbon growth are logarithmic with pressure

8

Extrapolation to lower pressures: potential errors

• More recent work shows mitigation by ambient water vapor must also be considered at very low contaminant partial pressures.

• Intensity scaling also less likely to be linear at lower pressures…

Langmuir

Pure lin

ear

log(p/p0)

px

linear

Extrapolation from only 1 decade of high-pressure data

tert-butylbenzene

C10H14

tert-butylbenzene

C10H14

~p/(1

+a×p)

Witness-plate facility (BL-1B)

•Incorporates grazing incidence broadband (6 - 18 nm) mirror to demagnifyEUV beam on witness plate.

• Sufficient intensity to provide mass limited deposition rates.

• In situ power measurement to ensure accurate resist dose.

• Single-wavelength, Null-field Ellipsometric Imaging System (NEIS) monitors deposition in real-time during exposure.

• Wafer translation and rotation and spot oversampling to insure uniform wafer exposure.

• Narrow band 13.5 nm radiation to expose 200 mm wafer in <1hr.

• Integrated glovebox permits rapid cycle time for samples.

• Base pressure of the vacuum ~ 10-9 Torr.

Witness-plate facility (BL-1B)

Witness-plate

MirrorLight from SURF III

SamplechamberGlovebox

Witness-plate facility (BL-1B)Cut away view of the exposure chamber

Wafer

Witness plate is at intersection of focused EUV beam from synchrotron and NEIS laser beam. Second mirror of focused beam path relays narrow band EUV to the resist.

Witness plate

Relay mirror

Test sequence flow chart

Transport to SURF

H-atom clean WS

Co-expose resist and WS

Transport to SE

SE for carbon thickness

(1)

Post-expH-atom clean

XPS on WSCorrelate at%

to DR/R(2)

Measure Eo of resist

(1) Post exposure DR/R must be ≤2% as determined by carbon thickness measured by spectroscopic ellipsometry(2) Post cleaning (non-cleanable) DR/R ≤0.16% determined by

XPS at%

transport to XPS

EUV spot and spectra for BL1B witness-plate facility

1 mm

50 W/cm2

25 W/cm2

0 W/cm2

Witness-plate

2 mm

17 mW/cm2

8.5 mW/cm2

0 mW/cm2

Wafer plane

0

0.05

0.1

0.15

0.2

0.25

0.3

0

0.015

0.03

0.045

0.06

0.075

0.09

5 10 15 20

Witness-plate Relay mirrorWafer

Po

wer

(m

W/n

m @

300

mA

)

wavelength (nm)

Incident power

NEIS system provides real-time measurement of carbon contamination

Time evolution of line profile

Time evolution of center thickness

•The null-field ellipsometric imaging system (NEIS) thickness monitor provides a real-time measurement of carbon accumulation on the irradiated sample.

•Center thickness evolution normalized to ex situ spectral ellipsometry.

Dose-to-Clear (E0) measurement

•E0 measurement necessary for a proper wafer exposure.

•Turntable action of wafer motion provides simple method for E0 determination.

•Resist processing and thickness measurement provided by Center for Nanoscale Science and Technology (CNST)

0

5

10

15

20

25

30

35

40

2.5 3 3.5 4 4.5 5

E0 run

Thi

ckne

ss (

nm)

Dose (mJ/cm2)

Pre- and post- processing facilities for witness-plate testing at NIST

•Atomic hydrogen cleaning facility for pre- and post- exposure cleaning of witness-plates.

•Scanning spectroscopic ellipsometer for evaluation post-exposure contamination thickness.

•X-ray photoelectron spectroscopy system for post-exposure elemental analysis of contamination from witness-plate test.

•EUV reflectometer available for reflectivity pre- and post-exposure scans of witness-plates.

Three types of metrology correlate WS results

SE

2 4 6 8

1

2

3

4

5

2 4 6 8

XPS

EUVReflectometry

60.6

60.8

61

61.2

61.4

61.6

4 6 8 10 12Position (mm)

Position (mm)

Pos

ition

(m

m)

Pos

ition

(m

m)

Pos

ition

(m

m)

Position (mm)

Position (mm)

Position (mm)

R (

%)

Thi

ckne

ss (

nm)

Thi

ckne

ss (

nm)

Witness plate results show acceptable reproducibility

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

A B C D

Thi

ckne

ss (

nm)

Resist

4 resists for qualification tests:

•Repeatability adequate for qualification purposes.

• Rates varied over a factor of three from the least to the most contaminating.

•No elements other than carbon detected above the ~ 1% atomic concentration level.

Summary

• NIST has constructed a witness plate testing facility with the goal to meet the requirements for resist outgas testing for the ASML NXE

• In situ ellipsometric imaging provides the first real-time measurement of evolution of contaminant across EUV intensity distribution

• On-campus wafer processing, XPS, SE and EUV reflectometry available at NIST

• The NIST facility will soon be available to provide testing on selected key resist for resist developers pending qualification of post-exposure cleaning

• Multiple tests on several resists show good repeatability with sufficient process control

• Comparison between NIST and ASML results indicate that there is good correlation between EUV and electron beam witness-plate tests