Reflective optical element for ultraviolet radiation, projection optical system and projection exposure system therewith, and method for forming the same
AssigneeCarl Zeiss SMT GmbH
InventorChristoph Zaczek
Life of this patent
Estimating the term…
Abstract
A reflective optical element (1) for radiation with a wavelength λ in the ultraviolet wavelength range comprises a reflective surface (6), and a dielectric multilayer system (4) formed on the reflective surface (6) which comprises at least two successive pairs of layers (5.i, 5.i+1), each pair of layers (5.1 to 5.N) consisting of a high refractive index layer (H1 to HN) alternating with a low refractive index layer (L1 to LN), wherein the optical thicknesses (Hi, Hi+1) of the high refractive index layers (Hi, Hi+1) and the optical thicknesses (Li, Li+1) of the low refractive index layers (Li, Li+1) of each adjacent pair of layers (5.i, 5.i+1) are different from each other.
Claims16
Reflective optical element comprising:
- a reflective surface, and
- a dielectric multilayer system formed on said reflective surface,
- said dielectric multilayer system comprising at least four successive pairs of layers, each of said pairs of layers consisting of a high refractive index layer alternating with a low refractive index layer, said dielectric multilayer system being reflective for a wavelength λ in the ultraviolet wavelength range,
- wherein said optical thickness of said low refractive index layers increases at least on average with increasing distance from said reflective surface, and
- wherein the total optical thickness of said high refractive index layers of the three pairs of layers having the closest distance to said reflective surface and the total optical thickness of said low refractive index layers of the three pairs of layers having the largest distance from said reflective surface each is higher than 3 times λ/4, and
- wherein the total optical thickness of said low refractive index layers of said three pairs having the closest distance to the reflective surface and the total optical thickness of said high refractive index layers of said three pairs of layers having the largest distance from said reflective surface each is lower than 3 times λ/4.
Method for forming a reflective optical element for radiation with a wavelength λ in the ultraviolet wavelength range, said method comprising the steps of:
- forming a metal film on a substrate with a thickness below 100 nm, a surface of the metal film forming a reflective surface,
- forming a dielectric multilayer system on said reflective surface starting with a first low refractive index layer with an optical thickness between 0.1λ and 0.2λ superimposing over said first layer at least four successive pairs of layers, each pair of layers consisting of a high refractive index layer alternating with a low refractive index layer, wherein
- wherein said optical thickness of said low refractive index layers increases at least on average with increasing distance from said reflective surface, and
- wherein the total optical thickness of said high refractive index layers of the three pairs of layers having the closest distance to said reflective surface and the total optical thickness of said low refractive index layers of the three pairs of layers having the largest distance from said reflective surface each is higher than 3 times λ/4, and
- wherein the total optical thickness of said low refractive index layers of said three pairs of layers having the closest distance to the reflective surface and the total optical thickness of said high refractive index layers of said three pairs of layers having the largest distance from said reflective surface each is lower than 3 times λ/4.
Dependencies are inferred from the claim text.