Lithography Techniques

Piotr Matyba

Department of Physics

Umeå University

Outline

Motivation for micro and nanotechnology

Techniques for micro and nano patterning

Soft lithography

Photolitography

E-beam lithography

Ion-beam lithography

Future and possible development

Moore’s low

The complexity for minimum component costs has increased at a rate of roughly a factor of two per year ... Certainly over the short term this rate can be expected to continue, if not to increase. Over the longer term, the rate of increase is a bitmore uncertain, although there is no reason to believe it will not remain nearly constant for at least 10 years. That means by 1975, the number of components per integrated circuit for minimum cost will be 65,000. I believe that such a large circuit can be built on a single wafer. (Electronics Magazine, 19th April 1965)

Techniques for micro patterning

Add one more slide explain how it is done in practice

Typical flowchart for fabrication

substrate resist spinning

development

metal deposition

etchinglift off

exposure

electrolytic growth

Lithography

Reproduction of a pattern ↔ expose a resist to open windows in a controlled way

First planar technology (1957)

Photoresist

soluble

not soluble

Ideal photoresist

In contrary to photography one does not want any grayscale, the highest contrast is desired

Negative resist

Positive resist

Optical lithography by contact

Projection lithography

Evolution of projection lithography

Phase shifting masks (PSM)

The use of PSM techniques allows to go down to the Rayleight criterion, k=0.61 to k=0.4

85 nm gate with PSM

transmision phase shift

Resolution Enhanced Techniques

Nature, T. Ito & S. Okazaki

Film Thickness 60um, 10um posts6:1 aspect ratio structures

10µ line/space features 6:1 aspect ratio structures

193nm lithography

Extreme UV (EUV) lithography

EUV is absorbed by all materials, and gasses

vacuum required !Physikalisch-Technische Bundesanstalt, Annual Report 2002

Photons are not for ever !

reflection

refraction

Aberrations

- High surface figure

- Aspherization

Flare (contrast loss)

- Spatial frequency roughness

Reflectivity loss

- Graded multilayer thickness

Competition between immersion 157nm technology and EUV technology. The industry however seems to develop lens/immersion approach.

X-ray lithography

X-ray mask

Examples of X-ray lithography

+ Good resolution

- Complex and expensive

- Time demanding

3D X-ray lithography

Produces 3D structures, with potential application to photonic crystals

Electron beam lithography

Electron beam spot less than 10nm

Very small wavelength no diffraction limitation

Direct writing no mask needed

Resolution depends upon the photoresist, limitation ~1nm

Sequential writing, small throughput

Electron-resist interaction

Multilayer technique

E-beam writing

Schottky Emitter tip

Tungsten heating filament

Reservoir (ZrN)

Crystal W

Hard density track patterning on a real magnetic hard disk

Pitch ~60nm

50 nm gold dots on a silicon wafer

Ion beam litography

Holes in a silicone membrane

Trenching in GaAs

30kV Gallium ionsIon beam spot size <10nm

rapidly absorbed

Near field lithography (soft)

The pattern is reproduced by a mold or a stamp

Fast and efficient method

No scaling, 1:1 ratio

Future

Development of light based techniques for industrial applications (EUV range)

Further development of soft lithography techniques

Techniques based upon self assembling abilities of certain materials. Resolution below 1nm.

A huge effort put on a production of photo resistive materials with good properties for EUV lithography