Advanced Lithography methods Flashcards
Describe Extreme UV Lithography: What type of imaging to does it use?
EUVL uses wavelengths in 10-14 nm to carry out projection imaging. It’s perhaps the most natural extension of optical projection lithography as in principle it only differs in terms of the wavelength. This type of radiation is also referred to as soft-x-ray radiation or vacuum UV.
What are the limitations in EUVL?
EUV is strongly absorbed in virtually all materials and consequently imaging must be carried out in a vacuum (bc if not, ozone is geneated), makes it a more expensive process. ALSO All camera optics as well as masks used must be reflective rather than refractive.Would need to develop new resists and processing techniques.
What are pro and con of EUVL reflective mask requirements?
Advantage: no thin membranes are needed as in the case of x-ray lithography, just a solid substrate coated with reflective coating and petterned EUV absorber; and because of the 4:1 reduction, mask making is also easier than with x-rays. Disadvantage: the defect density in the reflective coating needs to be made so small that there are few techniques available yet.
Compare x-ray lithography to ion and elcton beam lith.
unlike ion and e beam, x-ray does not require charged beams, so no vacuum. another advantage is that this can be in large exposure, not beam, so can do more area in same time. xray lithography essentially has no optics involved.
What are the 3 sources of x-ray lithography?
electron impact tubes, laser-based plasmas, and synchrotrons.
What are the big advantages of x-ray diffraction?
it’s immune to low atomic number partical contamination (Z), i.e. dust. That’s a big perk. it also uses shoerter wavelengths and acheives large DOF (good). Additionaly, its independent of substrate type, surface reflections, and wafer topography.Diffraction is negligable.can be used in general exposure, i.e. not beam, can acheive good resolution, do not require a lense or NA
What is a big disadvantage of x ray lithography?
no image reduction is possible do to 1:1 shadow printing. this leads to complicated mask production.
In LIGA, what type of printing is done on the mask? (contact,prox, proj?)
This is proximity printing, about 10 microns btwn the wafer and the mask.
Using LIGA, how much can a mask cost?
13,000
What limits the resolution of a mask in LIGA?
blurring of the image. this is represented by lower case delta, which should be controlled within 0.1 micron
How does exposure time of LIGA compare to others?
because of the much higher flux of usable collimated x-rays, shorter exposure times become more possible.
What is limitting the implimentation of LIGA lithography?
The cost of implementing and creating new machinery ofr LIGA is very expensive, and want to use the existing infrastructure for photoliithography. Photolithography is pushed more and more to get better resolution, like phase shifting to increase resolution. ADITIONALLY, x-ray resists are required to have high sensitivity to x-rays while high resistance to chemical, ion and/or plasma etching while maintaining resolution, such material have yet to be fully developed.
What material is typically used in LIGA for photoresist?
PMMA- poly(methylmethacrylate) i.e. Plexiglass or Lucite or acrylics. this has a relatively low sensitivity for x-rays, implying a small throughput, so things like chemical amplification of PMMA resists are being looked at.
How are x-rays generatred?
in a synchrotron, electrons are pulled around in a circle (building is a circle, so this circle has a large diameter), being held in by magnets, and this generates dissapated x-rays
What is the general feeilng about implementing world wide the use of EUV lithogrpahy?
It’s desireable because it can use the existing infrastructure
