Exposure method
An exposure method includes forming a resist film on a substrate to be processed, forming a top anti-reflection coating on the resist film, and irradiating the resist film with exposure light through the top anti-reflection coating. Forming the top anti-reflection coating includes adjusting refractive index and thickness of the top anti-reflection coating to increase a ratio of s-polarized light to p-polarized light in the exposure light entering the resist film.
1 . An exposure method comprising:
forming a resist film on a substrate to be processed;
forming a top anti-reflection coating on the resist film; and
irradiating the resist film with exposure light through the top anti-reflection coating, wherein forming the top anti-reflection coating includes adjusting refractive index and thickness of the top anti-reflection coating to increase ratio of s-polarized light to p-polarized light in the exposure light entering the resist film.
2 . The exposure method as claimed in claim 1 , wherein forming the top anti-reflection coating includes adjusting the refractive index and the thickness of the top anti-reflection coating such that the ratio of the s-polarized light to the p-polarized light in the exposure light entering the resist film is more than 10% higher than when the top anti-reflection coating is not present.
3 . The exposure method as claimed in claim 1 , wherein forming the top anti-reflection coating includes adjusting the refractive index and the thickness of the top anti-reflection coating to maximize the ratio of the s-polarized light to the p-polarized light in the exposure light entering the resist film.
4 . The exposure method as claimed in claim 1 , wherein:
the top anti-reflection coating is a material having a first refractive index; and
forming the top anti-reflection coating includes adjusting the thickness of the top anti-reflection coating to increase the ratio of the s-polarized light to the p-polarized light in the exposure light entering the resist film.
5 . The exposure method as claimed in claim 1 , wherein the exposure light enters the top anti-reflection coating at an oblique angle.
6 . The exposure method as claimed in claim 5 , further comprising:
calculating relationships between the refractive index of the top anti-reflection coating and energy of the s-polarized light and the p-polarized light in reflected light reflected from a surface of the top anti-reflection coating, wherein
incident angle of the exposure light incident on the top anti-reflection coating is calculated according to the equation:
θ i =arc sin( NA )
where θ i is the incident angle of the exposure light incident on the top anti-reflection coating, and NA is the numerical aperture of an aligner, and
the thickness of the top anti-reflection coating is calculated according to the equation:
d =λ/(4 n cos θ t )
where d is the thickness of the top anti-reflection coating, λ is a wavelength of the exposure light, n is the refractive index of the top anti-reflection coating, and θ t is the incident angle of the exposure light within the top anti-reflection coating;
determining, based on the relationships calculated, a refractive index of the top anti-reflection coating reducing the ratio of the energy of the s-polarized light to the energy of the p-polarized light in the reflected light; and
determining, based on the refractive index determined, a thickness for the top anti-reflection coating according to the equation: d=λ/(4n cos θ t ), wherein forming the top anti-reflection coating includes forming the top anti-reflection coating to have the refractive index determined and the thickness determined.
7 . The exposure method as claimed in claim 6 , further comprising:
calculating, based on the refractive index determined and the thickness determined for the top anti-reflection coating, a proportion of the energy of the s-polarized light in the energy of the exposure light absorbed into the resist film for each incident angle of the exposure light incident on the top anti-reflection coating, with the thickness of the resist film used as a parameter; and
determining, based on the proportion calculated, a thickness for the resist film with respect to the numerical aperture of the aligner to increase the proportion of the energy of the s-polarized light, wherein forming the resist film includes forming the resist film to have the thickness determined for the resist film.
8 . The exposure method as claimed in claim 1 , further comprising forming an antireflective film between the substrate to be processed and the resist film.
9 . The exposure method as claimed in claim 1 , wherein the exposure light has a wavelength of no more than 193 nm.
10 . The exposure method as claimed in claim 1 , including irradiating the resist film with the exposure light through an aligner having a numerical aperture of at least 0.68.