Question

Among the most important top-down techniques of nanofabrication, we mention the photolithography. To pattern a part on thin films, a student uses an UV light with a wavelength λ=193nm. For far field resolution, he utilizes a lens with focal length f=21cm and refractive index n=1.2. The maximal half-angle of the cone of light that can enter the lens is θmax=38º . Find: 1. The numerical aperture NA. 2. The resolution R. 3. The Depth focus σ.

Answer 1

given: wavelength of UV light = 193nm; n= 1.2; maximal half-angle of the cone of light = 38 degree

Numerical aperture NA = index of refraction of the medium* sin()

where is half of the angular aperture of the lens.

NA = 1.2* sin(38) =0.73879.

the resolution = 0.61* (wavelength/ NA).

R =( .61*193 ) / 0.73879

R = 159.355 nm

depth focus σ = wavelength /(2* NA2)

= 193 / (2 * 0.738792)

= 176.801 nm