motivation ic business requires a sub 100 nm next generation lithography tool. –(100 nm for...
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![Page 1: Motivation IC business requires a sub 100 nm Next Generation Lithography tool. –(100 nm for 16GDRAM) Any of the following 4 major candidates are not prevailing](https://reader035.vdocument.in/reader035/viewer/2022062517/56649ef15503460f94c022fe/html5/thumbnails/1.jpg)
Motivation
• IC business requires a sub 100 nm Next Generation Lithography tool. – (100 nm for 16GDRAM)
• Any of the following 4 major candidates are not prevailing.– EUV(Extreme UV)
– SCALPEL(SCattering with Angular Limitation in Projection Electron beam Lithography)
– X-ray with Synchrotron
– IPL(Ion Projection Lithography)
• Generally, it is assumed that due to the large lateral straggling of ions in the membrane mask, it is not possible to get high resolution with ion beam - which is not necessarily so.
• As a first step towards Ion beam lithography (IBL) using membrane mask, it is necessary to demonstrate the good spatial resolution
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Advantage and Disadvantage of IBL
Advantage• Good sensitivity for 0.1 um pattern
– X-ray : 375 mJ/cm2
– e-beam : 100 uC/cm2
– IBL : 4.5 uC/cm2 (720mJ)
• Good intrinsic resolution – 10 nm : limitation not from the wa
velength but from PR
Disadvantage• vacuum treatment• 1:1 membrane mask • lateral straggling• non familiar method - no extensive
study
Comparison of limiting resolutions
Line Width [m]
0.01 0.1 1
cont
rast
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
multilayer resistsingle layer resist
ION
X-RAY
OPTICS
E-BEAM
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Current Status of Ion Beam Lithography
IPL • IMS (Ionen Mikrofabikations System) and Vi
enna University since 1986
• ALG consortium in USA
• Siemens, ASM lithography, Leica and IMS-Stuttgart formulated $36M 3-year research program in 2000
• 0.1 um pre-production type stepper in 1999
IBL with membrane mask• No dominant study after the proximity IBL
by Hughes Research Laboratory
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Experiment
Proton Irradiation 220 - 500 keV
4 X 1013
/cm2
Development60% diethyleneglykol-monobutylether20% morpholine15% aqua regia 5% etanolamine
Developer
40oC 4 min. in ultrasonic bath
Mask Preparation2m LPCVD Si3N4 membraneon Si Wafer
Backside etch-off by KOH
Proton beam
Au wire
2m Si3N4
MembraneSi wafer
PMMA
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KIGAM Implantation System
1.7 MV tandem Van de Graaff
precollimator
injector
SNICS source
RF source
previewerbeam
electronsuppressor
water
holdertarget
cooling
scan freq
magnetanalyzing
collimator supplierelectron
= 64x517
ScannerX-Y
chamber
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Simulation of Dose distribution at PR
• Purpose : To see and understand the dose distribution at pattern edges which is directly responsible for the edge definition in the development process
• Simulation tool : TRIM (SRIM2000)
• Simulation Geometry : simple infinite slit
slit width = 1 or 10 m450 - 500 keVProtons
membrane :2m Si3N4
slit center
event distribution ofpassing-thru protonsat 2000A orinfinite thickPMMA
PMMA
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Factors affecting the line definition
Ion Beam quality• Parellelity and homogeniety• dose measurement
Mask Quality• mask production by e-beam writer
• problem : approx. 1 m thick PMMA should be used - Resolution worsening
• distortion during irradiation
e-beam writing
2 m Si3N4
Au 100A
PMMA 1m
Si waferdevelop
electroplating and etch off
backside etch
Development• precise temperature control - find the temperatur
e at which until the midde irradiated point is developed
• not controllable by develop time because of the statistical character of melting process
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Change of molecular weight by proton irradiation
• Molecular weight of PMMA changes drastically by proton irradiation which enables
the very well defined structure reproduction
Molecular weight [Da]
102 103 104 105 106
Rel
ativ
e yi
eld
0
2
4
6
8pristine7x1012 ions/cm2
5x1013 ions/cm2
3x1014 ions/cm2
Molecular weight distribution resulting from irradiation
depth [m]
0 200 400 600 800 1000
mol
ecul
ar w
eigh
t [ar
b. u
nit]
0
200
400
600
800
Syncrotron Radiation
Proton Beam
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Result of simulation - m slit
Position distribution of protons entering resist surface through a 1m width slit membrane maskMembrane : 2m Si3N4
PR : 200nm PMMA
Distance from Slit Center [nm]
-2000 -1500 -1000 -500 0 500 1000 1500 2000
Nu
mbe
r of
Eve
nts
[arb
itrar
y]
0
2000
4000
6000
8000
10000
12000
350 keV
400 keV
450 keV
500 keV
14 to 86 % width
440 nm
260 nm
190 nm
160 nm
Change of position distribution of protons passing through a 200nm PMMA resistafter 1m width slit membrane maskmembrane : 2m Si3N4Proton Energy : 450 keV
Distance from Slit Center [nm]
-2000 -1500 -1000 -500 0 500 1000 1500 2000
Num
ber
of E
vent
s [a
rbitr
ary]
0
1000
2000
3000
4000
5000
6000
7000
before PR
after PR
50% dose position = 505 nm14 to 86 % width = 220 nm
50 % dose position = 507 nm14 to 86 % width = 195 nm
Gaussian fit to the differentiated edge
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Result of simulation - m slit
Change of the 50% dose position and 14 - 86 % dose widthof protons through 200 nm PMMA resist.membrane mask : 2m Si3N4
Initial Proton Energy [keV]
350 400 450 500
Ch
ange
of 5
0 %
Do
se P
ositi
on
or 1
4 -
86 %
Dos
e W
idth
[nm
]
0
10
20
30
40
50
60
70
14 - 86 % dose width
50% dose position
Small conclusion
• Theoretically, the edge definition can be controlled within 20 nm if the development process can be performed very precisely
• Even taking into account the 14 - 86 % dose width, edge definition can be controlled at least within 50nm with rather rough develop condition
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Comparison of Simulation and Experiment- for the case of large mask to PR distance
Position distribution of protons along the penetration depthin a thick resist through a 10m width slit membrane maskwhen the mask to PR distance is large (35m)Proton Energy : 500keVMembrane : 2m Si3N4
PR : PMMAProton Range in PMMA : 3.8m
Distance from Slit Center [m]
-20 -15 -10 -5 0 5 10 15 20
Num
ber
of E
vent
s [a
rbitr
ary]
0
2000
4000
6000
8000
surface
1mm
m
m
m
Depth profile of PMMA after developmentProton Energy : 500keVMembrane : m Si3N4
shadow width : mMask to PR distance : 35m
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Extreme Cases
Depth profile of PMMA after developmentProton Energy : 500keVMembrane : m Si3N4
shadow width : m
Mask to PR distance = 0
Mask to PR distance = 530m
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AFM results
Edge configuration
500keV proton
Au wire mask w/o membrane
Edge configuration
800 keV proton
Au wire mask with
10 m mylar membrane
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SEM observations
500keV w/o membrane
tilt angle 50o
400keV with membrane
mask to sample : contact
tilt angle 50o
450keV with membrane
mask to sample : m
tilt angle 50o
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Conclusion
• Simulation results show the good possibility of employing IBL using membrane mask as the NGL tool.
• Well below 100nm pattern definition can be obtained if develop condition can be found at which only until the middle dose position at the pattern edge is developed.
• There are still, however, many basic works to be performed before real launch. They are :1. The relationship between proton dose, develop condition (Temperature, ti
me) and pattern edge (the position until which PR is developed)
2. Mask quality (e-beam writing)
3. Understanding the deviation of simulation result and the real measurement
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김영석 , 홍완 , 우형주 , 최한우한국자원연구소 이온빔응용연구그룹
김영석 , 홍완 , 우형주 , 최한우한국자원연구소 이온빔응용연구그룹
수백 keV 양성자를 이용한이온빔 리소그라피의 분해능 측정
수백 keV 양성자를 이용한이온빔 리소그라피의 분해능 측정