STOCHASTIC LIMITATIONS FOR EUV RESIST
KINETICS TOWARDS THE 16 nm NODE
ALESSANDRO VAGLIO PRET, KONSTANTINOS GARIDIS, ROEL GRONHEID (IMEC)
JOHN BIAFORE (KLA-TENCOR)
VARIABILITY ROOT CAUSES
1. Mask Uniformity
2. Photon distributions
3. Acid generation
Diffraction Orders
0.5
0.4
0.3
0.2
Row…
Row…
Row…
Row…
Row…
Row…
Row…
Row…
Row…
Row 6
Row 1
0.1
0
1 6
11
16
21
26
31
36
41
46
4. Deprotection variability
51
EUV Point Spread Function
0.7
5. Development Uniformity
0.6
0.5
0.4
Row 41
Row 36
Row 31
Row 26
Row 21
Row 16
0.3
0.2
0.1
0
1 4
7 10
13
Row 11
16 19
22 25
28 31
34 37
40
© IMEC 2011
Row 6
Row 1
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
3
OUTLINE
1. Shot Noise: from photons to acids
2. Stochastic Prolith: going towards 16 nm hp

ADT EUV exposure data-set

Variability root cause(s): from mask to wafer
3. Available knobs
4. Conclusion
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
4
SHOT NOISE: THEORETICAL
APPROACH
Wavelength (nm)
k (α µm-1)
QY
Available # Ph/CH area
Available # Ph/nm2
Ph lost
13.5
0.0068 (6.3)
5.00
4931
~10
78%
193
0.0347 (2.3)
0.25
70488
~146
91%
Shot Noise for 22nm CH @ 15mJ/cm^2
40
20
# Ph absorbed/generated Acids
60
80
100
120
140
160
180
0
Resist Top
Resist depth - z (nm)
5
10
15
20
25
30
35
40
Resist Bottom
45
EUV Ph absorbed
© IMEC 2011
EUV Ph absorbed
ArF Ph absorbed
EUV Ph absorbed
EUV generated acids
ArF Ph absorbed
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
ArF generated acids
5
200
OUTLINE
1. Shot Noise: from photons to acids
2. Stochastic Prolith: going towards 16 nm hp

ADT EUV exposure data-set

Variability root cause(s): from mask to wafer
3. Available knobs
4. Conclusion
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
6
ADT EXPOSURE DATA SET
CH, L/S FEMs of different
structures @ different PEB were
considered for the calibration
model
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
80°C PEB
85°C PEB
95°C PEB
110°C PEB
7
ADT EXPOSURE DATA SET
CH, L/S FEMs of different
structures @ different PEB were
considered for the calibration
model
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
80°C PEB
85°C PEB
95°C PEB
110°C PEB
8
TOWARDS 16nm: NXE 3100/3300
ADT
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
9
TOWARDS 16nm: NXE 3100/3300
ADT
NXE: 3100
NXE:3300
1. 22 nm hp CH barely printable on NXE:3100
2. 16 nm hp CH barely printable on NXE:3300
NXE:3300ADV.
3. Aerial image plays a fundamental role, but only @ high k1
4. Chemical contrast needed for CDU trends
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
10
VARIABILITY ROOT CAUSES: MASK
CONTRIBUTION
Mask CD-SEM image
Prolith Mask modeling
Ideal case
9 CHs
25 CHs
CH-CDU mask impact
Mask contribution was evaluated simulating
85
95
4
1.
1 “real” CH (ideal case) * 250
2.
9 “real” CHs * 28
3.
25 “real” CHs * 10
for 85°and 95°PEB
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
CDU (nm)
3
+11%
+7%
2
+2%
+3%
1
0
Single Contact
9 Contacts
25 Contacts
11
VARIABILITY ROOT CAUSES:
PHOTON DISTRIBUTION
Single
contact
25 contacts
average
© IMEC 2011
Photons
Gaussian σ distribution CD variability
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
12
VARIABILITY ROOT CAUSES: ACID
DISTRIBUTION
Single
contact
Acids
25 contacts
average
Photons
Rectifying effect due
to high QY for EUV
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
13
VARIABILITY ROOT CAUSES:
DEPROTECTION VARIABILITY
Photons
Acids
Latent Image
Latent Image: Higher variability in Gaussian
profile compared to Acid distributions
Poor Gaussian Fit  variability evaluated
directly on latent image CD
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
14
VARIABILITY ROOT CAUSES:
DEPROTECTION VARIABILITY
Photons
Acids
Latent Image
Latent Image: Higher variability in Gaussian
profile compared to Acid distributions
Poor Gaussian Fit  variability evaluated
directly on latent image CD
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
15
VARIABILITY (%) FOR SEVR140 - 22nm
CH ON NXE: 3300
20
Variability (%) = 100*σ/<x>
18
19
16
14
1
12
10
11
10
8
8
6
4
2
0
Absorbed Photons
Generated Acids
Polymer Deprotection
Resist CDU (+ Mask)
1. Mask contribution for CH: negligible
2. PSN contribution can be smoothed by high QY
3. Deprotection step increases CD variability
4. Development partially reduces deprotection variability
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
16
OUTLINE
1. Shot Noise: from photons to acids
2. Stochastic Prolith: going towards 16 nm hp

ADT EUV exposure data-set

Variability root cause(s): from mask to wafer
3. Available knobs
4. Conclusion
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
17
RESIST OPTIMIZATION
SEVR140
Alex-1
Alex-6
Alex-9
Dose (Sensitivity)
17.9
20.6
8.2
34.0
CDU (LWR)
1.11
0.97
1.11
0.78
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
18
RESIST OPTIMIZATION
SEVR140
Alex-1
Alex-6
Alex-9
Dose (Sensitivity)
17.9
20.6
8.2
34.0
CDU (LWR)
1.11
0.97
1.11
0.78
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
19
NEGATIVE TONE DEVELOPMENT:
...JUST A TIP...
POSITIVE
...just imagine a
NTD as
performing as
SEVR140
(Alex-0)
NEGATIVE
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
20
OUTLINE
1. Shot Noise: from photons to acids
2. Stochastic Prolith: going towards 16 nm hp

ADT EUV exposure data-set

Variability root cause(s): from mask to wafer
3. Available knobs
4. Conclusion
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
21
SUMMARY
1.
Mask CDU impact is negligible for CH
2.
Photon Shot Noise impact on pattern variability is inevitable, going
towards smaller features/lower doses/higher photons energy,
however:
3.
1.
Resist Absorbance can be still increased to improve the photon spatial
distribution density with small impact on SWA
2.
High Quantum Yield smoothen the PSN effect (high acid generation
means lower Acid Shot Noise)
3.
Deprotection variability can be improved tuning Mth
Negative Tone Development platforms may be used to increase
sensitivity/reduce pattern variability
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
22
Thank you for your attention
OBJECTIVE EXPERIENCE IS DISCRETE BUT THE WORLD
HANGS TOGETHER BY THE GRACE OF CONTINUITY
ZENO
© IMEC 2011
A. VAGLIO PRET, K. GARIDIS, R. GRONHEID, J. BIAFORE
23