Understanding EUV resist stochastic effects through...

transcript

Greg Denbeaux gdenbeaux@sunypoly.edu 1

Understanding EUV resist stochastic effects

through surface roughness measurements

SUNY Polytechnic Institute – Colleges of Nanoscale Science and Engineering

257 Fuller Rd. Albany, NY, USA 12203

February 23, 2020

IEUVI Resist TWG meeting

Greg Denbeaux, Eric Liu, Amir Hegazy, Hyeonseon Choi, Cole

Gregory, Belle Antonovich, Steven Grzeskowiak, Mueen

Mattoo, Robert Brainard

This work is funded by SRC

Chemically amplified resists have multiple components

Multiple components

- Current issues with distribution of components

- Upcoming issues with limited number of photoactive (PAG) molecules that can

fit within smaller features

Secondary electron interactions in EUV lithography

Incident photon

hν ≈ 92 eV

p+ = hole

e- = electron

References1S. Grzeskowiak, et al., J. Micro/Nanolith. MEMS MOEMS 17 (3), 033501 (2018).2T. Kozawa and S. Tagawa, Jpn. J. Appl.Phys., 49 (3) (2010) 030001.3A. Narasimhan, S. Grzeskowiak, et al., Proc. SPIE, 9779 (2016) 97790F.4J. Torok, et al., J. Photopolym. Sci. and Technol., 26 (5) (2013) 625–634.5P. de Schepper, et al., Proc. SPIE, 9425 (2015) 942507.6T. H. Fedynyshyn, et al., Proc. SPIE, 5039 (2003) 310.

• Photons liberate electrons in the resist and

possibly cause chemistry to occur in the process.

• Further chemistry due to electron-resist

interactions.

• These electron travel away from the EUV

absorption site resulting in blur.

Photoresist Exposure Tools

Substrate

Photoresist

Spin Coat

EUV (~ 92 eV) light

Expose

5-80 eV Electrons

Expose

ERIC (Electron Resist Interaction Chamber)ROX (Resist Outgassing Exposure Chamber)

Outline

1. Resist stochastics

2. Homogeneity measurements for PMMA and a chemically

amplified open source resist

3. Intentionally segregated resists

Failure rate for contacts (and other features)

is too large!

Peter De Bisschop,

“stochastic printing failures in

EUV lithography”, JM3 vol 17,

no 4 2018

For this resist and process,

41 nm pitch contacts with

dose 30-40 mJ/cm2

The failure rate is ~ 10-6 !!!

How to measure local chemical inhomogeneity on

the ~ 10-50 nm scale?

• We can’t find any suitable metrology technique to measure local

chemical variations

• Would need spatial resolution of 10’s of nm

• Would need speed to make millions or billions of

measurements

• Our goal is to measure the effect of the chemical inhomogeneity

Prior work (SPIE 2019) has shown the electron range – for

PMMA at 80 eV to be about 2 nm

0 2 4 6 8 10 12

PMMA – 80 eV

Depth [nm]

Blur = 1.8 [nm]

where Blur represents the

depth reactions have a 67%

probability of being induced

within this value.

Dose [µC/cm2]

y = 1.4565ln(x) - 0.3716R² = 0.9966

0.01 0.1 1 10 100 1000

PMMA – 80 eV

Use fit of data to generate

probability distribution of reactions.

exposed unexposed

Partial exposure

Conventional aerial imageOur top-down “aerial image”

Using low energy electrons

exposed

unexposed

Can tune the range of

partial exposure – MUCH

sharper than available

conventional exposures

Resulting line edge roughness

(LER) is a combination of aerial

image contrast, photon

stochastics, with fundamental

material inhomogeneities and

deprotection stochastics

With a dramatically sharper exposure

contrast, and better metrology across

large areas, we can measure the resist

non-uniform response over large areas

for statistics far beyond 3s

Resist measurements

Top down exposures provide much sharper contrast

to separate exposure contrast and statistics from material

response

0 5 10 15 20

distance (nm)

0.3 NA EUV imaging(lateral aerial image)

0.5 NA EUV imaging(lateral aerial image)

80 eV electrons(top down)

Slope can be

adjusted by varying

electron energy

Cartoon of exposure and sample for measurement

Low energy electron exposure to limit range,

increase vertical contrast and to provide the

same chemical response as EUV photons

Pits and bumps should occur due to

local resist sensitivity or solubility

variations

After exposure and development there are

multiple sources of roughness

A. Original roughness after spin coating

B. Added roughness due to development – local dissolution rate variations

C.Added roughness due to exposure (electron) statistics

D.Added roughness due to acid statistics and range (for chemically amplified

resists)

E. Final result of local variations in sensitivity due to local resist chemical

inhomogeneity

Outline

0 10 20 30 40 50 60 70

Position

Measurement Position vs RMS

2.60μC/cm2 7.79μC/cm2

Avg. RMS = 0.63nm Avg. RMS = 0.84nmNX

Avg. RMS = 0.54nm

Each data point is the result

of an AFM scan

Electron exposure spots

causing roughness

change are about 1 cm

Roughness variations across the exposure spot

(PMMA resist – not chemically amplified)

• Exposure times are a few

seconds with 80 eV

electrons

• Typical electron spacing at

these doses is about 2 nm

apart (~ 1013 electrons/cm2

incident)

Post PAB

Post PAB +

DevelopedPost PAB + Exposure + Developed

Si Substrate

Photoresist

Dose (2.60μC/cm2) Dose (7.79μC/cm2)

PMMA Resist AFM scans

0 10 20 30 40 50 60

Position

Measurement Position vs Nor. RMS3.46μC/cm2 7.79μC/cm2

Avg. RMS = 1.75 nm Avg. RMS = 1.80nm

Avg. RMS = 1.07nm

Roughness variations across the exposure spot (OS2 resist – chemically amplified)

Post PAB

Post PAB +

Developed

Post PAB + Exposure + Developed

Si Substrate

Photoresist

Dose (3.46μC/cm2) Dose (7.79μC/cm2)

OS2 Resist AFM scans

PAB No dose Low dose High dose

oughness (

C. Added roughness due to exposure (electron) statistics

D. Added roughness due to acid statistics and range (for chemically amplified

resists)

inhomogeneity

A+B+C+E

Roughness increases through development and exposurePMMA results

PAB No dose Low dose High dose

oughness (

resists)

inhomogeneity

A+B+C+D+E

Roughness increases through development and exposureComparing CAR to PMMA

Outline

Separating the multiple effects is a challenge

resists)

inhomogeneity

So, we started formulating resists to intentionally segregate to see the effects

Copolymer (PHS/TBA)

Standard Intentionally mix in

homopolymers

Polyhydroxystyrene

Polystyrene

First test – varying the polystyrene

homopolymer content

- A-4 sample (4% PS)

29% PHS/TBA (60/40)

15% PAG

52% PHS

29% PHS/TBA(60/40)

15% PAG

48% PHS

29% PHS/TBA (60/40)

15% PAG

12% PS

44% PHS

Large segregation effects,

possibly related to the

polystyrene content

~ 100-200 nm features!

Much bigger than the desired

rate of segregation effects

Why does segregation occur –

vary thermal processingHigher dose -> -> -> -> -> -> -> -> -> -> lower dose No dose

100C PAB

100C PEB

120C PAB

120C PEB

140C PAB

140C PEB

No PAB

120C PEB

Understanding EUV resist stochastic effects through...

Documents