BY SURAJ MENON S7,EEE,61

OUTLINE Lithography Introduction to EUVL Basic concepts Why do we need EUVL? EUVL Process Basic technology for EUV EUV masks All Reflective Optics Advantages Disadvantages Conclusion

WHAT IS LITHOGRAPHY

Lithography is akin to photography in that it uses light to transfer images onto a substrate

The term lithography is derived from the words ‘lithos’ meaning stone and ‘graphy’ meaning write.

Our stone is silicon wafer and writing is done using a photo sensitive polymer.

INTRODUCTION

Extreme ultraviolet lithography is an advanced technology for making microprocessors a hundred times more powerful than those made today.

Optical projection lithography has been the lithographic technique used in the high-volume manufacture of integrated circuits.

The key to creating more powerful microprocessors is the size of the light's wavelength.

BASIC CONCEPT BEHIND EUVMinimum lithographic feature size =

k1: “Process complexity factor”

λ: Exposure wavelength

NA: Numerical aperture of the lens.Higher NA means smaller depth of focus.

k1*λ

NA

WHY EUVL

EUVL is required for the continuity of Moore’s law

The number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years.

EUVL is a next generation lithography technique.

Glass lens replaced by mirrors….

λ= 13.5nm…Reflective masks are to

be used.more power…faster mp

This wafer was patterned on a prototype device using extreme-ultraviolet lithography (EUVL).

EUVL

EUVL PROCESSLaser is directed to a jet of xenon gas to produce plasma

To create the IC, light is directed to a mask.

Light reflects from the mask then through a series of mirrors that shrinks the image down.

Projected to wafer covered with photoresistLight hardens the photoresist.

Region not exposed remain gooey and the remaining is hardened photoresist and exposed silicon wafer.

All solids, liquids, and gases absorb 13.5nm – so system is under vacuum

Mask must be reflective and exceptionally defect-free

13.5nm photons generated by plasma source

All-reflective optics

(all lens materials are opaque)

BASIC TECHNOLOGY FOR EUV

EUV MASKS

All solids, liquids, and gases absorb 13.5nm photons

- So fused silica lenses are OUT …

- Indeed, all refracting lenses are OUT

Making EUV mirrors is no cakewalk, either … 50 or more alternating Mo/Si layers give the

mirror its reflectivity Each layer is 6.7nm thick and requires atomic

precision Since the angle of incidence changes across

the mirror, so do the required Si layer thicknesses

Net reflectance: ~70%

All-Reflective Optics

IMAGE FORMATION

Top: EUV multilayer and absorber constituting mask pattern for imaging a line.

Bottom: EUV radiation reflected from the mask pattern is absorbed in the resist and substrate, producing photoelectrons and secondary electrons.

These electrons increase the extent of chemical reactions in the resist.

EUVL ADVANTAGESMicroprocessors made by euvl are up to to 100 times faster than today's most powerful chips

Decrease in size of chip but the speed increases.

EUVL technology achieves good depth of focus and linearity for both dense and isolated lines with low NA. Increase in storage capacity.

The low thermal expansion substrates provide good image placement.

EUVL DEFECTSPositive charging, due to ejection of

photoelectrons

Contamination deposition on the resist from out gassed hydrocarbons, which results from EUV- or electron-driven reactions.

No known method for repairing defects in a ML coating.

Entire process has to be carried out in vacuum.

Mirrors used are only 70% reflective.

CONCLUSION

EUVL will opens a new chapter in semiconductor technology.

Successful implementation of EUVL would enable projection lithography to remain semiconductor industry’s pattern technology of choice for years to come.

Much work is to be done in order to determine whether EUVL is ready for large scale production.

REFERENCES

Sang Hun Lee, Yashesh Shroff, Manish Chandhok. Flare and Lens Aberration Requirements for EUV Lithographic Tools. Proceedings of SPIE, Volume 5751, Emerging Lithographic Technologies IX, May 2005. Pages 707–714.

Euv lithography- vivek bakshi A complete course of lithography by Alois.

www.howstuffwork.comwww.sandia.comwww.euvl.com www.lasers.llnl.gov/lasers/IST/euvl.html