Electron Beam Lithography in Nanoscale FabricationRecent DevelopmentBY: TEJASRI SALADI

Agenda

Nanoscale Fabrication Conventional Photolithography techniques Electron Beam Lithography Projection Printing Direct Writing E-beam Resists Recent techniques in electron beam lithography Challenges in e beam lithography and ways to overcome Future scope Conclusion

Nanoscale Fabrication

Nanofabrication is the design and manufacture of devices with dimensions measured in nanometers. One nanometer is 10 -9 meter, or a millionth of a millimeter.

Techniques used earlier in Nanoscale Fabrication

There are several ways that nanofabrication might be done. One method involves scaling down integrated-circuit fabrication that has been standard since the 1970s, removing one atom at a time until the desired structure emerges. A more sophisticated hypothetical scheme involves the assembly of a chip atom-by-atom.

One such conventional technique used in nanoscale fabrication is “Photolithography”

Photolithography

Photolithography, also termed optical lithography or UV lithography, is a process used in microfabrication to pattern parts of a thin film or the bulk of a substrate.

Because of its diffraction limit, conventional optical or ultraviolet photolithography is becoming increasingly inadequate.

Electron Beam Lithography

Electron-beam lithography (often abbreviated as e-beam lithography) is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist ("exposing").

The main advantages of e-beam lithography over the conventional photolithograph techniques include very high resolution and versatile pattern formation.

It is the most powerful technique for fabricating the features as small as 3 to 5 nm.

Electron beam lithography process

EBL SystemElectron source:Electrons may be emitted from a conducting material either by heating or by applying an electric field.Stigmators:A stigmator is a special type of lens used for the alignment of e-beam. Stigmators may be either electrostatic or magnetic and consist of four or more poles.Electron Lenses: Electron lenses can be made only to converge, not diverge. Electrons can be focused either by electrostatic forces or magnetic forces. Apertures:Apertures are small holes through which the beam passes on its way down the column. Blanking Plates:Blanking plates are use to modify the e-beam, these are simple electrostatic deflector.

Electron-beam lithography system

Schemes used in e-beam Lithography

Two distinct schemes used in electron beam lithography are1. Projection Printing2. Direct writing In projection printing, a relatively large sized electron-beam pattern is

projected in parallel through the mask onto a resist-coated substrate by using a high-precision lens system;

In direct writing, a small spot of the electron beam is written directly onto a resist-coated substrate, eliminating the expensive and time-consuming production of masks.

Direct Writing and Projection Printing

Projection Printing

Projection EBL development further proceeds with the techniques Scattering with angular limitation in projection electron-beam

lithography (SCALPEL) system projection reduction exposure with variable axis immersion lenses

(PREVAIL)technology

Direct Writing

It is the most common EBL approach which uses finely focused Guassian round beam.

The another technique which is carried out in direct writing EBL is Lift-off process. It is an additive process that adds material to the substrate.

E-beam Resists

Electron beam resists are the resists which are normally coated on the substrate to record the image of the pattern to be transferred.

Electron beam resists are of two types. They are1) Positive Resists2) Negative Resists

Types of E-beam resists

Electron beam lithography benefits

Print complex patterns directly on wafers Eliminates the diffraction problem High resolution up to 20 nm(photolithography ~50nm) Flexible technique

Defects in e-beam lithography and challenges faced

Despite the high resolution of electron-beam lithography, the generation of defects during electron-beam lithography is often not considered by users. Defects may be classified into two categories:

1. Data-related defects2. Physical defects.This is Expensive and complicated technoloogy

Proximity effect

Recent techniques and their comparison with e-beam lithography

Nano imprint lithography X-ray lithography Dip-Pen (DPN) nanolithography

Nano-imprint lithography(recent technique)

Nano-imprint lithography (NIL) is a lithography technique that combines the speed of optical lithography with the resolution of EBL, we use NIL to make nanostructured substrates.

When compared to e-beam lithography, it is a simple nanolithography process with low cost, high throughput and high resolution

Comparison of various lithography techniques

Applications

1. Fabrication of very high density molds for nano-imprint lithography (NIL) and for the 2. Fabrication of Multiple Tunnel Junction devices that can be used for single electron device applications or for the connection of small molecules.3. In X-ray lithography techniques and DPN techniques.

Conclusion

The current development of electron beam lithography in nanofabrication has been reviewed.

Both the technologies of direct writing and projection printing are examined and compared.

Challenges faced in e-beam technology were overcome by various other recent techniques and these were compared to the e-beam lithography.

Thus lithography techniques helps in fabrication processes of nanoscale devices their scope continues in future.

REFERENCES

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Queries

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