IC lithography with Fr-TIR under different media

[Ramon]

Hi friends

The sample is anIntegrated Circuit. I am using an ilumination device for optical microscopes (trans illuminated) that illuminates the sample through a light guide and immersion oil. It works by Frustrated Total Internal Reflection (Fr-TIR). It allows for opaque samples interrogation with biological microscopes.

Normally, as index matching medium I use immersion oil (n=1.5) but as per request of Holger I tried water (n=1.33) and also glycerine (n=1.47) and parafine (n=1.47).

The band that contains the alphanumerics A3 changes colour upon the angle/distribution of incident light and the type of media that I use for Fr-TIR, which impacts the angle itself.

These differences are explained by a thin film and a diffraction grating in the band.

Notice that with glycerine (n=1.47) and parafine (n=1.47) we have a blue band. Exactly as it happens when I use immersion oil (n=1.5). But with water (n=1.33) the band goes dark.

My interpretation is that, with water as Fr-TIR medium, the diffracted light exiting the band does not reach the objective.

I would appreciate contributions to explain this phenomena. Holger??



Thks
Ramon