Nikon F2 Exposure Tool

Nikon F2 Exposure Tool
Soichi Owa, Naomasa Shiraishi, Issei Tanaka,
Yasuhiro Ohmura, Toshihiko Ozawa,
Teruki Kobayashi, Kazushi Nomura, Takashi Aoki,
and Takayuki Mizutani
Nikon Corporation
Nikon
Nikon NSR
157nm Data Review
December, 2001
1
Outline
1. F2 Exposure Tool Basic Specification
2. Optics design
3. Intrinsic birefringence
• Birefringence by axis direction
• Correction method
• Correction result
• Polishing
4. Coating
5. Purging
6. Pellicle
Nikon
Nikon NSR
157nm Data Review
December, 2001
2
Exposure Tool Basic Spec.
NA
> 0.8
Reduction ratio
4X
Field size
22mm x 33mm
Throughput
(300mm wafer)
> 90 wph
(10mJ/cm2 resist, 40W laser)
Optics
Off-axis catadioptric
Nikon
Nikon NSR
157nm Data Review
December, 2001
3
F2 Exposure Tool Imaging
By imaging simulations:
F2 (157nm) lithography with NA>0.8 can cover:
With binary mask:
80 - 70nm L/S
With attenuated PSM
70 - 60nm L/S
90 - 80nm contact hole
With alternating PSM
60 - 55nm L/S
35 - 25nm isolated line (double exposure)
Nikon
Nikon NSR
157nm Data Review
December, 2001
4
Projection Optics and Laser
•
Optics
Catadioptric Optics (off-axis)
•
Laser
Line selected laser
Spectrum bandwidth 1.0pm FWHM
2.5pm 95%width
Output power
40W
Nikon
Nikon NSR
157nm Data Review
December, 2001
5
Off-axis Catadioptric Optics
Type A
Type B
Type C
NA >0.8, Scanning slit length 22mm
Nikon
Nikon NSR
157nm Data Review
December, 2001
6
Intrinsic Birefringence (IB)
NIST report (May and July)
NIST
∆n (157.63nm) = 11.2 +- 0.5nm/cm
Nikon measurement
∆n (156.96nm) = 11.5 +- 0.8nm/cm
Data are consistent.
Nikon
Nikon NSR
157nm Data Review
December, 2001
7
Crystal structure and IB
CaF2 axes
[001]
[011]
[111]
[101]
Zero Birefringence
on [100] and [111] Axes.
Max. Birefringence
on [110] Axis.
[010]
[100]
[110]
Nikon
Nikon NSR
157nm Data Review
December, 2001
8
Intrinsic Birefringence of [111] axis
Distribution of Birefringence
[111]
[101]
[011]
[110]
CaF2 Plate
Nikon
Nikon NSR
157nm Data Review
December, 2001
9
Intrinsic Birefringence of [100] axis
Distribution of Birefringence
[100]
[110]
[-1-10]
[-10-1]
[101]
CaF2
Plate
Nikon
Nikon NSR
157nm Data Review
December, 2001
10
Intrinsic Birefringence of [110] axis
Distribution of Birefringence
[110]
[111]
[11-1]
[100]
[010]
CaF2 Plate
Nikon
Nikon NSR
157nm Data Review
December, 2001
11
Correction Methods
[111] Axis
[100] Axis
+ 60 deg. rotation
[110] Axis
+ 45 deg. rotation
+ 90 deg. rotation
( NIST mentioned )
[111] Axis
[100] Axis
[110] Axis
Nikon
Nikon NSR
157nm Data Review
December, 2001
12
Correction Software
•
At present, Nikon is using a combination of:
– In-house software
Evaluation and optimization
– Code-V (since Oct. 2001)
Automatic optimization
Nikon
Nikon NSR
157nm Data Review
December, 2001
13
Effect on Point Spread Function
No birefringence
Strehl Intensity ~ 1.00
With IB
before correction
Strehl Intensity = 0.56
Nikon
Nikon NSR
157nm Data Review
December, 2001
14
Correction Status
With
birefringence (11nm/cm)
after correction
Other than PSF, we are checking,
CD uniformity, line width
abnormality, etc.
We are in the final stage of
correction, but have not finished it.
S.I. = 0.96
Nikon
Nikon NSR
157nm Data Review
December, 2001
15
Polishing of New Surfaces
•
Hardness is different between [111], [100] and [110].
àPolishing speed is different.
•
Nikon is doing R&D, and is getting data:
1. By a modified polishing method, polishing speed
difference has become small enough.
2. Surface roughness became good in all [111], [100] and
[110] surfaces.
Nikon
Nikon NSR
157nm Data Review
December, 2001
16
Intrinsic birefringence status and Timing
•
Optics design is in the final stage, but is not completed.
•
Polishing R&D on new surfaces is ongoing, we are getting
good data.
•
Delay due to IB amounts to several months.
•
#1 exposure tool shipment is also delayed, but we are
trying to have the timing in 2004.
Nikon
Nikon NSR
157nm Data Review
December, 2001
17
Coating
Water-free process is expected to improve performance and durability.
Condition: AR-Coatings with Both sides of CaF2 substrate
100
Transmittance [%]
95
90
85
80
V-Coat
Water Free
Conventional
W-Coat
Water Free
Conventional
75
70
140
145
150
155
160
165
170
175
180
Wavelength [nm] ? Incident Angle
Nikon
Nikon NSR
157nm Data Review
December, 2001
18
Coating (Water-Free)
IR transmittance
Transmittance(%)
100
OH stretching vibration
98
Water free process Wide type
96
94
92
Conventional process V-type
Conventional process Wide type
90
1500
2000
2500
wavelength(nm)
3000
Nikon
Nikon NSR
157nm Data Review
December, 2001
19
Purging of closed space
Closed space purging shows steady progress.
1000000
Oxygen [ppm]
10000
1000
100
10
10
Concentration [ppm]
Diffusion model
Experiment
21%
100000
H2O
O2
1
0.1
0.01
1
0.1
0:00
5:00
10:00
15:00
0.001
0:00
0:30
1:00
Purging Time (Min:Sec)
[O2] < 1ppm
1:30
2:00
2:30
3:00
3:30
4:00
Purge Time [h:m]
[O2]
[H2O]
< 0.1ppm
< 1ppm
Nikon
Nikon NSR
157nm Data Review
December, 2001
20
Purging of closed space
Concentration [ppm]
1000
O2
H2O
100
10
1
0.1
0.01
0:00
0:10
0:20
0:30
0:40
0:50
1:00
Purge time [Hour:Min]
Recent experiment:
[O2]
[H2O]
~ 0.01ppm
~ 0.1ppm
Nikon
Nikon NSR
157nm Data Review
December, 2001
21
Purging of wafer and reticle space
•
Frequent exchange of wafer and reticle, and purging should
be attained at the same time.
•
Global purging (whole space purging surrounding W/R stages)
and local purging (limited space purging of optical path) are
being studied by Computational Fluid Dynamics simulations.
Nikon
Nikon NSR
157nm Data Review
December, 2001
22
Pellicle
•
Our primary preference is SOFT (or thin) pellicle.
• We expect the improvement of durability by 2004.
• Thin, inorganic pellicle seems to be better than hard pellicle
from the optical viewpoint.
•
Hard pellicle is the second choice.
• Distortion caused by mounted pellicle is the issue.
• Distortion pattern should be same for every mounted pellicles.
Because we cannot measure the distortion beforehand.
(Distortion correction parameter should be constant for all
pellicles)
•
Removable pellicle is a common subject with EUV, but it takes
time for R&D.
• It will not be in time for 2004 exposure tool shipment.
Nikon
Nikon NSR
157nm Data Review
December, 2001
23
Summary
•
Optics design correcting for IB is in the final stage, but is
not finished yet.
•
Polishing of [100], [110] seems to be feasible.
•
Coating performance and durability is being improved by
water-free process.
•
Purging development shows steady progress.
•
Delay due to IB will amount to several months. #1 Exposure
tool shipment is also delayed, but we are trying to have the
timing in 2004.
Nikon
Nikon NSR
157nm Data Review
December, 2001
24