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Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
Resist A and B (1/m)
1.5
1.2
A
0.9
0.6
B
0.3
0.0
300
340
380
420
460
500
Wavelength (nm)
Figure 5.1 Resist parameters A and B as a function of wavelength measured with
a UV spectrophotometer for a typical g-line resist (a 5-arylsulfonate DNQ).
1
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
O
N2
C=O
COOH
UV
+ N2
H 2O
SO2
SO2
SO2
R
R
R
Equation (5.21) – DNQ exposure mechanism
2
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
Relative PAC Concentration
Aerial Image Intensity
1.5
1.2
0.9
0.6
0.3
0.0
-500
-300
-100
100
300
500
1.0
0.8
0.6
0.4
0.2
0.0
-500
-300
-100
100
300
Horizontal Position (nm)
Horizontal Position (nm)
(a)
(b)
500
Figure 5.2 The exposure process takes an aerial image (a) and converts it into a
latent image (b).
3
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
O
N2
C=O

+
SO2
SO2
R
R
N2
X
Equation (5.36) – Thermal decomposition of DNQ
4
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
C=O
COOH
+ H 2O
SO2
SO2
R
R
CH3
CH3
CH3
C=O
R esin
OH
O
OH
CO
SO2
R
SO2
R
Equations (5.46) and (5.47) – DNQ thermal decomposition products
5
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
0.5
1.2
A (1/m)
1.0
0.8
0.6
0.4
0.0
80
-0.5
95
-1.0
Ln(A/ANB)
80 ºC
95 ºC
110 ºC
125 ºC
110
-1.5
125
-2.0
-2.5
-3.0
0.2
-3.5
-4.0
0.0
0
20
40
60
80
Bake Time (min)
(a)
100
120
-4.5
0
15
30
45
60
75
90
Bake Time (min)
(b)
Figure 5.3 The variation of the resist absorption parameter A with post-apply bake
time and temperature for Kodak 820 resist at 365 nm (a convection oven bake was
used): a) linear plot, and b) logarithmic plot.
6
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
0.12
Solvent Mass Faction
90 ºC
0.10
100 ºC
0.08
0.06
110 ºC
0.04
0.02
0.00
0
100
200
300
400
500
Depth into Resist (nm)
Figure 5.4 Predicted variation of solvent concentration as a function of depth into
the resist at the end of a 60 s post-apply bake.
7
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
15
Tg
14
ln(Diffusivity)
13
12
s = 0.10
11
10
9
8
s = 0.05
7
6
0.00245
0.0025
0.00255
0.0026
0.00265
0.0027
1/Absolute Temperature (K)
Figure 5.5 Temperature dependence of solvent diffusivity (using the parameters
from Table 5.1 and assuming a solvent mass fractions of 0.05 and 0.1) showing an
essentially fixed diffusivity below the glass transition temperature.
8
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
Figure 5.6 Lower solvent content at the top of this 248 nm resist leads to reduced
acid diffusion during PEB, and thus the presence of standing waves only at the top
of the resist (photo courtesy of John Petersen, used with permission).
9
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
(a)
(b)
(c)
Figure 5.7 Typical i-line photoresist profile simulations (using PROLITH) for resist
on silicon as a function of the PEB diffusion length: (a) 20nm, (b) 40nm, and (c)
60nm.
10
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
Resist Temperature (ºC)
100
80
60
40
20
Hotplate
Xfer
Chill plate
0
0
20
40
60
80
100
Time (sec)
Figure 5.8 Typical wafer bake profile (60 s bake followed by a 10 s transfer to a
chill plate).
11
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
Wafer
High Thermal Mass Hotplate
Figure 5.9 Proximity bake of a wafer on a hot plate showing (in a highly
exaggerated way) how wafer warpage leads to a variation in proximity gap
(drawing not to scale).
12
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
Resist Coated
Glass Substrate
Collimating
Lens
Light Meter
UP
A/D
Light Source
Bandpass
Filter
Figure 5.10. Experimental configuration for the measurement of the ABC
parameters.
13
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
1.0
0.9
Transmittance
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
200
400
600
800
1000
Exposure Dose
(mJ/cm2)
Figure 5.11. Typical transmittance curve of a positive g- or i-line bleaching
photoresist measured using an apparatus similar to that pictured in Figure 5.10.
14
Chris A. Mack, Fundamental Principles of Optical Lithography, (c) 2007
1.0
Transmittance
0.8
0.6
80 ºC
125 ºC
0.4
0.2
0.0
0
100
200
300
400
Exposure Dose (mJ/cm2)
Figure 5.12. Two transmittance curves for Kodak 820 resist at 365 nm. The curves
are for a convection oven post-apply bake of 30 minutes at the temperatures shown.
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