Toru Umeda
1, a
, Makoto Momota
2
, Naoya Iguchi
2
, Shuichi Tsuzuki
1
1
Nihon Pall Ltd. Scientific & Laboratory Services Division
46 Kasuminosato, Ami-machi, Inashiki-gun, Ibaraki 300-0315 Japan
2
FUJIFILM ELECTRONIC MATERIALS CO., LTD. Technology Dept. No.1
ABSTRACT
4000,Kawashiri,Yoshida-cho, Haibara-gun, Shizuoka 421-0302 Japan a
Toru_Umeda@pall.com
filter membranes seems to be reaching a
We varied aging term of ArF photoresist from 0 to 24 weeks as well as membrane material of Point-of Use filtration to find appropriate membrane for reducing bridging defects, then found that bridge defect count on ArF photoresist pattern did not increase if Point-of-use filtration was utilized even though the photoresist had been aged for 24 weeks, also found that the most appropriate filter material to reduce bridging defect was Nylon 6,6 and the mechanism thought to be responsible was its hydrophilicity. Additionally, we limitation due to smaller pore size, in other words, the finer the pore size, the higher the differential pressure, and this causes problems such as pump overloading.
Alternative filter designs are required to keep up with the rapid progress of micro lithography. Pall Corporation has developed two alternative design solutions to deal with the above problems.
One is utilizing the adsorptive effect of the membrane surface with defect precursors in lieu of utilizing a smaller pore size. Nylon
6,6 is thought to be one of those filter confirmed that newly developed 0.02 m rated nylon 6,6 asymmetric pore membrane is capable in photoresist spin-coat process without any sacrifices of lithographic performance.
1. INTRODUCTION
As microlithography patterning continues in size reduction, defects in the thin films become more apparent. Bridging defect in materials because it has hydrophilic amide bond in its formula while conventional
High Density Poly Ethylene (HDPE) or
Poly Tetra Fluoro Ethylene (PTFE) has no such polar group. (Figure 1)
The other one is utilizing an asymmetric pore construction of the filter membrane to reduce differential pressure of the membrane. Figure 2 is a Scanning Electron
Microscopy (SEM) image of Pall resist patterns is one of the defectivity problems that has appeared in 248nm lithography. Particularly in 193nm lithography, this defect has been getting asymmetric nylon 6,6 membrane which shows coarse to fine pore size change from upstream side to downstream side and
Figure 3 is a flow rate improvement data of more serious due to the continuous CD reduction. To reduce these bridging defects, asymmetric construction compared with isotropic construction. implementation of improved FUJIFILM ELECTRONIC MATERIALS micro-filtration in both the photoresist CO., LTD. and Nihon Pall Ltd. have been manufacturing process and in the
Point-Of-Use spin-coating process at the coater-developer has been shown to be effective. [1]
However, development of finer and finer working together to explore the appropriate filter membrane using the above methods to reduce bridging defects in ArF lithography and report the obtained results in this paper.
Interface 2005 Page 1

Hydrophilic group
O
C
O H
CH
2
4
C N
H
CH
2
6
N
Nylon6,6 n
CH
2
CH
2
Polyethylene n
CF
2
CF
2 n
Polytetrafluoroethylene (PTFE)
Figure 1 Chemical formula of filter membrane materials
Coarse
Upstream
Fine
Downstream
Figure 2 SEM image of the cross section of the asymmetric nylon6,6 membrane.
250
Asymmetric 0.02um Nylon6,6
Isotropic 0.02um Nylon6,6
200
150
100
50
15
10
0
10
5
35
30
25
20
0
0 2 4 6
Flow rate(mL/sec.,1cP)
8
Figure 3 Flow - differential pressure of the asymmetric nylon6,6 filter and the isotropic nylon6,6 filter
Interface 2005 Page 2

2. TEST METHODS
2.1 Confirming the filtration effect for intentionally produced bridging defect by aging the resist.
In order to increase bridging defectivity,
ArF photoresist was filtered by a 0.1 m rated filter (this is coarser then is standard for ArF lithography). Then the photoresist was aged at room temperature for 0, 4,
8,10,16 and 24weeks. (Figure 4) The test process from BARC coating through pattern inspection is described in Table 1.
Photoresist was patterned in 110nm line and space on 8 inch Si wafer using coater-developer varying the Point-Of-Use filter membrane. (Figure 5) The tested filter membranes were HDPE 0.05 m, Nylon
6,6 0.04 m, Nylon 6,6 0.02 m asymmetric pore structure and a Dummy capsule (capsule without filter membrane).
(Table 2) Then, inspection and analysis of defects using High Resolution Imaging
Inspection System and SEM on the patterned wafers was performed. Bridging defects which bridge only between 1 line to line were categorized as “Micro bridge”
Mixing
0.1um Filtration and those more than two spaces were categorized as “Large bridge”. (Figure 6)
2.2 Research of appropriate filter membrane for intentionally produced bridging defect.
for 4 weeks.
ArF photoresist was prepared in the same way as described above except for the aging time, which was not varied and only aged
ArF photoresist was patterned by spin coating the ArF photoresist while varying the Point-Of-Use filter membrane including HDPE, Nylon
6,6 and Poly Tetra Fluoro Ethylene (PTFE) as well as a surface modified PTFE. (Table
3) Then, inspection and analysis of defects using High Resolution Imaging Inspection
System and SEM on the pattern wafer was performed.
2.3 Adaptability of new nylon 6,6 asymmetric pore media to spin-coat system.
Newly developed 0.02 m rated nylon 6,6 asymmetric pore membrane was also tested in trials as described above.
Stored at room temperature for
0, 4, 8, 10, 16, 24 weeks
Figure 4 Photoresist preparation for increasing defectivity
Interface 2005 Page 3

ArF PR
Point-of-Use Test filter
KOGANEI
CT pump
Process
Table 1 Test process
Equipment
Spin-coat
8 inch Wafer
Figure 5 Set up of each components in spin-coat system.
Organic BARC
ArF PR
TEL ACT8/ HDPE filter
TEL ACT8/ Filter testing
Exposure
Develop
ASML PAS 5500/1100
TEL ACT8
Inspection
SEM
KT 2360
HHT S-8840
Table 2 Test filters for confirming the filtration effect for intentionally produced bridging defect by aging the resist
No.
Media material
Removal rating
/micron
Pore structure Part number
1
High density polyethylene (HDPE)
0.05
Isotropic PHD11UG005EH11
2 Nylon 6,6 0.04
Isotropic PHD11UNDEH11
3
4
Nylon 6,6 0.02
Dummy capsule
Asymmetric PHD11ANMEH11
PHDC11HC
Interface 2005 Page 4

Table 3 Test filters for research of appropriate filter membrane for intentionally produced bridging defect
No.
1
2
Media material
High density polyethylene (HDPE)
High density polyethylene (HDPE)
Removal rating
/micron
0.05
0.03
Pore structure
Isotropic
Isotropic
Part number
PHD11UG005EH11
PHD11UG003EH11
3
4
5
6
7
Nylon 6,6
Nylon 6,6
Polytetrafluoroethyle ne (PTFE)
Hydrophilic Surface modified PTFE
0.04
0.02
0.03
0.03
Dummy capsule
Isotropic
Asymmetric
Isotropic
Isotropic
PHD11UNDEH11
PHD11ANMEH11
PHD11UFQEH11
PHD11GPQEH11
PHDC11HC
(a) “Micro bridge” (b) “Large bridge”
Figure 6 Examples of bridging defects. Defects that bridge only between 1 line to line (a) were categorized as “Micro bridge” and those more than two spaces (b) were categorized as “Large bridge”
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3. RESULTS AND DISCUSSIONS
3.1 Confirming the filtration effect for intentionally produced bridging defect by aging the resist.
The results were shown in Figure 7 and
Figure 8. As a result, in both micro bridge and large bridge, many these defects were observed when the dummy capsule was used, i.e., no Point-Of-Use filtration.
Coarse filtration before aging, aging, and room temperature conditions were believed to increase these defects. There seemed tendency that the number of micro bridge varies time to time while the number of large bridge is rather even as well. It was also clear that these defects were reduced by Point-of-use filtration, especially by
Nylon 6,6 0.02 m asymmetric membrane.
3.2 Research of appropriate filter membrane for intentionally produced bridging defect.
The results in Figure 9 and Figure 10 showed the trend that filters constructed with Nylon 6,6 and surface modified PTFE membranes had the lowest generation of bridging defects, followed by HDPE and
PTFE membranes. Also observed was that membranes with hydrophilic surfaces generate lower defectivity. Based on these results, it can be said that utilizing the adsorptive effect in filtration can reduce bridging defects on ArF lithography.
3.3 Adaptability of new nylon 6,6 asymmetric pore media to spin-coat system.
The results in Figure 11 and Figure 12 showed that there seemed no difference between conventional HDPE 0.05 m membrane and new nylon 6,6 0.02 m asymmetric pore media in terms of photoresist thickness uniformity. Also,
Figure 13 showed that Critical Dimension
(CD) of these two membranes were almost the same value. These results conclude that there seemed to be no issues for standard operation in photo resist coating process.
Interface 2005 Page 6

0.250
0.200
0.150
0.100
0.050
HDPE 0.05
N66 0.04
N66 Asym 0.02
Dummy capsule
0.000
0 4 8 12 16 20
Aged term of photoresist (Weeks)
24 28
Figure 7 Micro bridge defect density on ArF photo resist pattern on 8 inch Si wafer versus preserved term of the
ArF photo resist. Each point is average of 3 wafers. Intentionally, the ArF photo resist was preliminary filtered by
0.1um rated filter (coarser than standard process) then aged for 0,4,8,10,16 and 24weeks at room temperature in order to gain numbers of bridging defects.
HDPE 0.05
0.250
N66 0.04
N66 Asym 0.02
Dummy capsule
0.200
0.150
0.100
0.050
0.000
0 4 8 12 16 20
Aged term of photoresist (Weeks)
24 28
Figure 8 Large bridge defect density on ArF photo resist pattern on 8 inch Si wafer versus preserved term of the
ArF photo resist. Each point is average of 3 wafers. Intentionally, the ArF photo resist was preliminary filtered by
0.1um rated filter (coarser than standard process) then aged for 0,4,8,10,16 and 24weeks at room temperature in order to gain numbers of bridging defects.
Interface 2005 Page 7

0.300
0.250
0.200
0.201
These membranes have
0.150
hydrophilic group.
0.100
0.050
0.000
0.035
HDPE
0.05um
HDPE
0.03um
0.007
0
N66
0.04um
0
N66
Asym.
0.02um
PTFE
0.021
PTFE
0
0.03um
Surf.mod.
Dummy
Capsule
Figure 9 Micro bridge defect density on ArF photo resist pattern on 8inch Si wafer among various Point-of-use filter material. Points are averaged value in 3 wafers. Error bar is standard deviation. Intentionally, the ArF photo resist was preliminary filtered by 0.1
µ m rated (coarser than standard process) filter then aged for 4weeks at room temperature in order to gain numbers of bridging defects.
0.300
0.250
0.200
0.150
0.100
0.050
0.042
0.000
HDPE
0.05um
0
HDPE
0.03um
0
N66
0.04um
0
N66
Asym.
0.02um
0
PTFE
0.03um
0 0
PTFE
Surf.mod.
Dummy
Capsule
Figure 10 Large bridge defect density on ArF photo resist pattern on 8inch Si wafer among various Point-of-use filter material. Points are averaged value in 3 wafers. Error bar is standard deviation. Intentionally, the ArF photo resist was preliminary filtered by 0.1
µ m rated (coarser than standard process) filter then aged for 4weeks at room temperature in order to gain numbers of bridging defects.
Interface 2005 Page 8

2750
2730
2710
Filter: HDPE 0.05um
N=1
N=2
N=3
2690
2670
2650
-100 -50 0
Radius (mm)
50 100
Figure 11 ArF photoresist thickness uniformity in using HDPE 0.05
µ m filter at Point-of-Use filtration in photoresist spin-coat system.
2750
2730
2710
2690
Filter: N66 asym. 0.02um
N=1
N=2
N=3
2670
2650
-100 -50 0
Radius (mm)
50 100
Figure 12 ArF photoresist thickness uniformity in using Nylon6,6 0.02
µ m asymmetric filter at Point-of-Use filtration in photoresist spin-coat system.
0.12
0.11
0.1
0.09
0.08
0.07
0.06
0.05
0.107
0.106
HDPE 0.05
N66 0.02 asym.
Interface 2005
0.02
µ m asymmetric filter used at Point-of-Use filtration in photoresist spin-coat system. ArF photoresist, 110nm line and space pattern.
Page 9

4. CONCLUSION
It was found that bridge defect count on
ArF photoresist pattern did not increase if
Point-of-use filtration was utilized even though the photoresist had been aged for 24 weeks. Also, it was found that the most appropriate filter material to reduce bridging defect in ArF lithography was
Nylon 6,6 and the mechanism thought to be responsible was its hydrophilicity.
Additionally, it was confirmed that newly developed 0.02 m rated nylon 6,6 asymmetric pore membrane had an advantage of good flow rate capability as a
0.02 m rated filter in photoresist spin-coat process without any sacrifices of lithographic performance.
ACKNOWLEDGEMENTS
Nihon Pall Ltd. scientific and laboratory services would like to thank FUJIFILM
ELECTRONIC MATERIALS CO., LTD. for this valuable opportunity of co-working.
The authors also would like to thank
KOGANEI CORPORATION for providing
Coaxial Tubephragm (CT) pump for photoresist dispense system.
REFERENCES
[1] D. Hall, B. Gotlinsky, M. Mesawich,
"The Effectiveness of sub 50nm Filtration on Reduced Defectivity in Advance
Lithography Applications," ARCH Interface,
Sept. 2003.
Interface 2005 Page 10