motivation ic business requires a sub 100 nm next generation lithography tool. –(100 nm for...
TRANSCRIPT
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
김영석 , 홍완 , 우형주 , 최한우한국자원연구소 이온빔응용연구그룹
김영석 , 홍완 , 우형주 , 최한우한국자원연구소 이온빔응용연구그룹
수백 keV 양성자를 이용한이온빔 리소그라피의 분해능 측정
수백 keV 양성자를 이용한이온빔 리소그라피의 분해능 측정