ee235 class presentation on lithography (spring 2007) fabrication of high-aspect-ratio silicon...

EE235 Class Presentation on Lithography (Spring 2007)

Fabrication of high-aspect-ratio siliconFabrication of high-aspect-ratio siliconnanostructures using near-field scanningnanostructures using near-field scanningoptical lithography and silicon anisotropicoptical lithography and silicon anisotropic

wet-etching processwet-etching process

by S. J. Kwon, Y. M. Jeong, and S. H. Jeong by S. J. Kwon, Y. M. Jeong, and S. H. Jeong Gwangju Institute of Science and Technology (Korea)Gwangju Institute of Science and Technology (Korea)Applied Phys. A – Material Science and Processing, vol. 86, pp. 11-18, Applied Phys. A – Material Science and Processing, vol. 86, pp. 11-18, 2007)2007)

Presented by Darsen Lu (3/19/2007)Presented by Darsen Lu (3/19/2007)

EE235 Class Presentation on Lithography (Spring 2007) UC Berkeley - 2

OutlineOutline

IntroductionIntroduction

Description of the tools and experimental Description of the tools and experimental setupsetup

Fabrication ResultsFabrication Results

ConclusionConclusion



Scanning probe lithography (SPL)Scanning probe lithography (SPL) SPL is a nanopatterning technique based on scanning probe microscSPL is a nanopatterning technique based on scanning probe microsc

ope technologiesope technologies

Various forms of SPL techniques includeVarious forms of SPL techniques include Atomic Force Microscope (AFM) LithographyAtomic Force Microscope (AFM) Lithography Dip-pen lithographyDip-pen lithography Near Field Scanning Optical lithographyNear Field Scanning Optical lithography

(NSOL)(NSOL)

As opposed to the electron beam (e-beam) lithography, SPLs can be As opposed to the electron beam (e-beam) lithography, SPLs can be exercised under ambient conditionsexercised under ambient conditions

This PaperThis Paper The The NSOLNSOL is used to pattern is used to pattern nanochannelnanochannels with high aspect ratio with high aspect ratio


Dip Pen Nanolithography

In near field scanning optical microscopy (NSOM) a very small light source very close to the sample is scanned. Light passes through a sub-wavelength diameter aperture and illuminates a sample that is placed within its near field, at a distance much less than the wavelength of the light. The resolution achieved is far better than that which is attainable in conventional optical microscopes.

Atomic Force Microscope

Near Field Scanning Optical Microscopy

http://stm2.nrl.navy.mil/how-afm/how-afm.html

http://www.nanoink.net/WhatisDPN.htm

http://en.wikipedia.org/wiki/Near-field_scanning_optical_microscope



The Near-field scanning optical The Near-field scanning optical lithography (NSOL) systemlithography (NSOL) system

442nm, 130mW, He-Cd Laser Source Shutter

Position Feedback System

Apertured Cantilever Nanoprobe

Power Meter

ND Filter

Fiber

Wafer + PR

Light goes through Light goes through the apertured cantithe apertured cantilever nanoprobe alever nanoprobe and expose the photnd expose the photoresist (PR).oresist (PR).

The nanoprobe moThe nanoprobe moves along a trajectves along a trajectory to pattern the ory to pattern the PRPR

Motorized Stage


Fabrication process Fabrication process

Goal: fabricate high-aspect-ratio (HAR) nanochannGoal: fabricate high-aspect-ratio (HAR) nanochannelsels

Procedure:Procedure:1. Start with a 110 wafer

2. Deposit 10nm nitride using LPCVD

3. A commercial photoresist is deposited on the wafer

4. The 111 direction of the wafer is aligned precisely to the y-axis of the microscope

5. The NSOL scans through the programmed trajectory

6. PR Development

7. RIE etch of PR and nitride in CF4/O2 Plasma

8. KOH wet etch


Results: After PR DevelopmentResults: After PR Development Good linewidth uniformity is achieved (Fig. 1, 2)Good linewidth uniformity is achieved (Fig. 1, 2) Reproducibility over the same sample has been pReproducibility over the same sample has been p

roved (Fig. 3)roved (Fig. 3)

Fig. 2 Fig. 4Fig. 1

Fig. 3

Reproducibility between different Reproducibility between different samples requires further study (Fig. 4)samples requires further study (Fig. 4)

Solid lines: first sampleSolid lines: first sample Dotted lines: second sampleDotted lines: second sample

13%

7.7%


Result: After KOH wet etchingResult: After KOH wet etching

Wet Etching ResultWet Etching Result1. Width 200nm / Depth 800nm1. Width 200nm / Depth 800nm2. Width 230nm / Depth 1560nm2. Width 230nm / Depth 1560nm

Compare with theoretical KOH Compare with theoretical KOH selectivityselectivity

Reason for width increase: Reason for width increase: Nonzero etching in the Nonzero etching in the

{111} plane{111} plane Thinning of SiThinning of Si33NN44 at the at the

edge of the channel during edge of the channel during the dry-etchingthe dry-etching

The. {111} : {110} = 1 : 600The. {111} : {110} = 1 : 600 Exp. {111} : {110} = 1 : 26Exp. {111} : {110} = 1 : 26

NSOL effect was proven by NSOL effect was proven by closing the shutter during the closing the shutter during the scanning process (see right scanning process (see right figure)figure)


SummarySummary

An NSOL system has been set up for nanofabricationAn NSOL system has been set up for nanofabrication

Lines have been patterned and good linewidth uniformity haLines have been patterned and good linewidth uniformity has been demonstrated. However, further study is needed to is been demonstrated. However, further study is needed to improve the reproducibility over different samples.mprove the reproducibility over different samples.

Nanochannel has been produced after wet etching. A linewiNanochannel has been produced after wet etching. A linewidth of ~200nm and an aspect ratio of 1:6.8 has been achieved.dth of ~200nm and an aspect ratio of 1:6.8 has been achieved.

This nanofabrication technology could be potentially applicaThis nanofabrication technology could be potentially applicable to the fabrication of micro/nanofluidic channels, substratble to the fabrication of micro/nanofluidic channels, substrates for biomolecular analysis, etc.es for biomolecular analysis, etc.

ee235 class presentation on lithography (spring 2007) fabrication of high-aspect-ratio silicon...

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