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