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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

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Motivation

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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 wavelength but from PR

Disadvantage

  • vacuum treatment

  • 1:1 membrane mask

  • lateral straggling

  • non familiar method - no extensive study


Current Status of Ion Beam Lithography

IPL

  • IMS (Ionen Mikrofabikations System) and Vienna 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


KIGAM Implantation System


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


Ion Beam quality

Parellelity and homogeniety

dose measurement

Mask Quality

mask production by e-beam writer

problem : approx. 1 mm thick PMMA should be used - Resolution worsening

distortion during irradiation

Factors affecting the line definition

Development

  • precise temperature control - find the temperature 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


Result of simulation - 1mm slit


Result of simulation - 1mm slit

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

Depth profile of PMMA after development

Proton Energy : 500keV

Membrane : 2mm Si3N4

shadow width : 100mm

Mask to PR distance : 35mm


Extreme Cases

Depth profile of PMMA after development

Proton Energy : 500keV

Membrane : 2mm Si3N4

shadow width : 100mm

Mask to PR distance = 0

Mask to PR distance = 530mm


AFM results

Edge configuration

500keV proton

Au wire mask w/o membrane

Edge configuration

800 keV proton

Au wire mask with

10 mm mylar membrane


SEM observations

400keV with membrane

mask to sample : contact

tilt angle 50o

500keV w/o membrane

tilt angle 50o

450keV with membrane

mask to sample : 25mm

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, time) 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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