NA of 193i lens at the photomask?

[Tanj]

A Starlith 1900i will have an NA of 1.35 at the wafer under water. However, at the input to the lens, focus on the photomask, what is the NA there? I found one mention of 0.75 but it was just an example, and that would seem to be a difficult number since it was state of the art at the wafer end not long before immersion was introduced. Something more like 0.6 would seem to be enough?

 

[Fred Chen]

The photomask is 4x demagnified, an aerial inspection tool like AIMS that emulates the 1.35 NA system would have to support an NA of 1/4 of that, i.e., 0.3375.

 

[Tanj]

The photomask is 4x demagnified, an aerial inspection tool like AIMS that emulates the 1.35 NA system would have to support an NA of 1/4 of that, i.e., 0.3375.

Thanks, Fred. I was assuming the input NA would exceed that since it is cheap and would avoid adding input blur to the overall losses.

The reason it matters to me is understanding the angular separation in the illumination pupil, for some work on a photomask material. I found a reference to the ASML 193i machines having a sigma up to 1 in illuminator, which means they can go to the edge of the input NA for the projector. But I could not find any actual angles cited for either, just that dimensionless ratio.