[Libre-silicon-devel] OK. That happened (Funding)

Ferenc Éger eegerferenc at gmail.com
Fri Dec 18 02:50:06 CET 2020

Hello Everyone,

I recently elaborated further on the optical considerations of the uLED 
reticle topic. I put the results into the maskless litho repo as usual:


Please find errors in it...

I plan to prepare a thermomechanical/thermohydraulic FEM simulation 
also, to study possible implementations of cooling.


Ferenc Éger

On 12/12/2020 00:29, Staf Verhaegen wrote:
> Éger Ferenc schreef op vr 11-12-2020 om 22:34 [+0100]:
>> To counter this, illumination systems in steppers contain a 
>> narrow-band filter (Bragg-filter or similar) to filter out exactly 
>> one narrow spectral line (hence I-line and G-line), and additional 
>> optics to eliminate off-axis components and increase coherence 
>> (therefore, what reaches the reticle is more or less "laser-like", 
>> highly coherent and monochromatic radiation with very narrow FWHM). 
>> Also, the projection optics in the stepper is usually a "narrow-band" 
>> system in terms of wavelength due to dispersion, and fine-tuned to 
>> work only at the wavelength of the line it is specified for.
> It is true that old steppers contain spectral line filters; more 
> recent steppers use monochromatic lasers.
> But what in lithography is actually done is to use off-axis 
> illumination for resolution enhancement. In the extreme one can reach 
> double the resolution over coherent illumination (0.25*λ/NA versus 
> 0.5*λ/NA). More info on off-axis illumination: 
> http://www.lithoguru.com/scientist/litho_tutor/TUTOR42%20(Aug%2003).pdf
> Off-axis illumination can be implemented by a second lens system 
> before the light reaches the reticle where a pupil plane is present 
> where one can insert the shape of the off-axis illumination one wants. 
> Actual scanners from ASML (which I am familiar with) use more complex 
> systems with so-called diffractive optical elements to optimize for 
> other effects like lens aberrations, light intensity uniformity, 
> minize effect of temperature expansion of materials, etc.
> greets,
> Staf.
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