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

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

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

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

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

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

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)

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

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

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)

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

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.

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

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. 141-149, 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. 297-304, 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

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.