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Advanced technology: Photolithography

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Sahil Mehta

on 17 March 2014

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Transcript of Advanced technology: Photolithography

Advanced Photolithography
Current state-of-the-art photolithography tools use deep ultraviolet (DUV) light from excimer lasers with wavelengths of 248 and 193 nm (the dominant lithography technology today is thus also called "excimer laser lithography"), which allow minimum feature sizes down to 50 nm. Excimer laser lithography has thus played a critical role in the continued advance of the so-called Moore’s Law for the last 20 years
SiO2 strongly absorbs UV when l < 180 nm
Silica lenses and masks can’t be used 157 nm F2 laser photolithography
Fused silica with low OH concentration, fluorine doped silica, and calcium fluoride (CaF2), With phase-shift mask, even 0.035 mm is possible
Further, relay on next generation lithography.
Extreme ultraviolet lithography (also known as EUV or EUVL) is a next-generation lithography technology using an extreme ultraviolet (EUV) wavelength, currently expected to be 13.5 nm.
When an EUV photon is absorbed, photoelectrons and secondary electrons are generated by ionization, much like what happens when X-rays or electron beams are absorbed by matter.It has been estimated that about 4 secondary electrons on average are generated for every EUV photon, although the generation volume is not definite.These secondary electrons have energies of a few to tens of eV and travel tens of nanometers inside photoresist before initiating the desired chemical reaction. This is very similar to the photoelectron migration for the latent image formation in silver halide photographic films. A contributing factor for this rather large distance is the fact that polymers have significant amounts of free volume. In a recent actual EUV print test,it was found 30 nm spaces could not be resolved, even though the optical resolution and the photoresist composition were not the limiting factor.
Similar to traditional photolithography (or
ultraviolet lithography)
The pattern is written directly onto the electron-sensitive resist (no mask is used)
• More precise than photolithography or XRay lithography
• Used to make high-resolution masks for photolithography and X-Ray lithography
• Beats the diffraction limit of light, minimum feature size around 5 nm
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. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate.
Next-generation lithography or NGL is a term used in integrated circuit manufacturing to describe the lithography technologies slated to replace photolithography. As of 2009 the most advanced form of photolithography is immersion lithography, in which water is used as an immersion medium for the final lens.
Next-generation lithography
Extreme ultraviolet lithography
Deep ultraviolet lithography
X-ray lithography
Electron beam lithography
X-Ray Lithography - Pros
Shorter wavelength (0.4 –4nm) than UV light
High penetration, high resolution
•Minimum feature size around 10–20 nm
Simple process–can use both positive and
negative resists
•Essentially negligible diffraction
•Longer mask lifetime than with
•Very costly (compared to photolithography)
•Requires special masks and resists
X-ray absorbers: gold and tungsten
X-ray membrane: silicon carbide or diamond
•X-rays cannot be focused -> prevents the use of lenses
X-Ray Lithography - Cons
E-Beam Lithography - Cons
Very slow. Takes over 10 hours to scan
across the entire surface of a wafer
• Very costly. One e-beam system costs
upwards of 5 to 10 MILLION dollars
• Potential problems with electron
– Electron energy: 100eV -> very slow,
inefficient, damage the substrate
– Electron energy: 10eV -> lower
penetration depth and lower resolution
BY Sahil Mehta
and Vidya Mene

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