1. Vicki Bourget & Vinson Gee April 23, 2014
Nanometer Scale Lithography Also Known as Nanolithography. It is the making of semiconductor devices on an atomic scale level to no more than 100 nm by transferring patterns to one medium to another. There are multiple techniques which include photolithography, x-ray nanolithography, electron beam direct-write lithography, extreme ultraviolet lithography, and ion beam lithography.
Vicki Bourget & Vinson Gee
April 23, 2014

2. Outline Basic Components Photolithography X-ray nanolithography
Electron Beam Direct-Write Lithography
Extreme Ultraviolet Lithography
Charged Particle Lithography

3. Optical Lithography Basic Components
Source
Condenser
Collects the source radiation and directs it onto the mask
Mask
Contains the pattern to be printed on the wafer
Reduction imaging lens
Projects an image of the mask onto the silicon wafer

4. Photolithography
Uses light to transfer a pattern from photomask to a photoresist chemical on the substrate
Chemical treatments engraves the exposure pattern into the material under the photoresist
Most cost effective
Requires a flat substrate
Used to pattern parts of a thin film or the bulk of a substrate
In an integrated circuit, a CMOS wafer will go through this cycle up to 50 times
Image From: Lin

5. X-Ray Nanolithography
Selectively remove parts of a thin film
Uses x-rays to transfer pattern from mask to photoresist on the substrate
Requires special mask sensitive to x-rays
Used for batch processing
Common mask material is gold or materials with a high atomic number.
Allows for structures to be created with great height compared to optical, used to be 1mm in newer photoresists but now larger as time progresses.
Image From: Antony

6. Electron Beam Direct Write Lithography
Electron beam Lithography has the ability to fabricate patterns that have nanometer feature sizes
Short wavelength and reasonable energy densities
Direct writing is the most common approach for electron beam lithography
Most often used in mask making, prototyping, fabrication of special small volume products, and research and development for advanced applications
Not often used in mass production due to a speed limitation
Can be used for extremely fine patterns with critical dimensions as small as 10 nm

7. Electron Beam Direct Write Lithography
Direct writing consists of a source of electrons, a focusing optics set, a blanker to turn the beam on and off, a deflection system for moving the beam and a stage for holding the substrate
(Image from Ampere)

8. Electron Beam Direct Write Lithography
It is the most desirable process because it is capable of superior resolution and requires no expansive projection optics or time consuming mask production
Two types of beams used
Gaussian round beam that moves with the wafer to expose the wafer one pixel at a time
Can be classified as vector scans
Variable shaped beam uses parallel electron beams to write a primitive shape in one shot
More speed is gained but the resolution is sacrificed
Speed vs detail

9. Extreme Ultra Violet Lithography
Uses a laser-produced plasma source of radiation, a reflective mask and a 4x all reflective imaging system
Ideal for creating a high volume of integrated circuits using wavelengths below 100 nm
EUVL manufacturing must be done in a vacuum using reflective mirrors and masks since all materials strongly absorb ultraviolet light

10. Extreme Ultra Violet Lithography
This image shows a simple EUVL process where the radiation from the laser-produced plasma illuminates a mask onto the silicon wafer substrate where the IC’s are built
(Image from Stulen)

11. Ion Beam Lithography
Similar to electron beam lithography, but the key difference is that ion lithography uses heavier, charged ions
Heavier ion particles have more momentum and offers high resolution patterning than UV, x-ray, or electron beam lithography
Uses include nanometer pattern fabrication and direct doping of the substrate
Boron and Phosphorus ions are commonly used

12. Ion Beam Lithography There are several methods of ion beam lithography
Focused ion beam lithography (FIB)
Masked ion beam lithography (MIB)
Ion beam projection lithography (IBP)
MIB is a faster method than FIB. MIB and IBP require masks.

13. Summary
Nanolithography is the making of semiconductor devices on an atomic level to no more that 100 nm
Used to create small integrated circuits and printed circuit boards
They are still improving the techniques

14. References
Ampere A. Tseng, Kuan Chen, Chii D. Chen, Kung J. Ma, “Electron Beam Lithography in Nanoscale Fabrication: Recent Development,” IEEE Transactions on Electronics Packaging Manufacturing, Vol. 26, No. 2, April 2003, p , PDF
Antony Bourdillon and Yuli Vladimirsky, “X-ray Lithography on the Sweet Spot”, UHRL, San Jose, (2006)
Lin, B. J., "Optical Lithography", SPIE Press, Bellingham, WA, 2009, p. 136.
Okazaki, Shinji, “Comparison of Optical, X-ray, Electron and Ion Beam Lithography,” Microelectronic Engineering 9 (1989), p , North-Holland, PDF.
Stulen, Richard H. and Donald W. Sweeney, “Extreme Ultraviolet Lithography,” IEEE Journal of Quantum Electronics, Vol. 35, No. 5, May 1999, p. 694 – 699, PDF

15. Key Concepts
Basic components for lithography are source, condenser, mask, and reduction imaging lens.
Photolithography is the most cost effective technique.
Most common application is integrated circuits.
Electron beam uses either round beam or variable shaped beam.
EUV is ideal for creating a high volume of integrated circuits using wavelengths below 100 nm.