Method of producing aspherical optical surfaces
View Patent ↗In the case of a method of producing aspherical optical surfaces of optical elements ( 1 ), in particular for use in microlithography for producing semiconductor elements, the optical element ( 1 ) is ground for example in the form of a meniscus. In a first method step, the optical element ( 1 ) is introduced into a basic form ( 2 ), which has a spherical form bed and is being held at a distance over the form bed ( 3 ). After that, an intermediate medium ( 6 ) is introduced in the basic form ( 2 ) between the optical element ( 1 ) and the form bed ( 3 ) and, subsequently the optical element ( 1 ) being removed together with the intermediate medium ( 6 ) from the basic form. Then, the spherical form bed ( 3 ) of the basic form ( 2 ) or a second basic form is transformed into an aspherical form bed ( 3 ′) computationally determined in advance. The optical element ( 1 ) is then re-introduced with the intermediate medium ( 6 ) into the basic form ( 2 ) or the second basic form, the intermediate medium ( 6 ) being sucked against the form bed ( 3 ′) by applying a vacuum. Subsequently, the optical element ( 1 ) deformed by the vacuum applied is spherically machined on a surface ( 7 ). Finally, after removing the vacuum, the surface ( 7 ′) assumes the form of an aspherical surface.
1. A method of producing aspherical optical surfaces of optical elements, wherein said optical element is pre-ground, wherein
a) in a first method step, said optical element is introduced into a basic form, which has a spherical form bed and is being held at a distance over the form bed, after which
b) an intermediate medium is introduced in said basic form between said optical element and said form bed and, subsequently, said optical element is removed together with said intermediate medium from said basic form, after which
c) said spherical form bed of said basic form or a second basic form is transformed into an aspherical form bed computationally determined In advance, after which
d) said optical element is re-introduced with said intermediate medium into said basic form or said second basic form and said intermediate medium is sucked against said form bed by applying a vacuum, after which
e) said optical element deformed by the vacuum applied is spherically machined on a free surface and
f) finally, after removing the vacuum, the free surface assumes the form of an aspherical surface.
2. The method as claimed in claim 1 , wherein said optical element is brought in the form of a meniscus.
3. The method as claimed in claim 1 , wherein a curable material is used as said intermediate medium.
4. The method as claimed in claim 3 , wherein silicone rubber is used as said intermediate medium.
5. The method as claimed in claim 1 , wherein said aspherical surface contains a radius term, a coma term and an astigmatism term.
6. The method as claimed in claim 1 , wherein said aspherical surface is produced axially.
7. The method as claimed in claim 1 , wherein said aspherical surface is produced off-axially.
8. The method as claimed in claim 1 , wherein said optical element is introduced into said basic form onto spacers, after which said intermediate medium is introduced.
9. The method as claimed in claim 1 wherein the dimensioning of said intermediate medium and the geometry of said form bed are determined by model simulation based on finite element methods.
10. The method as claimed in claim 1 , wherein said free surface is spherically machined by lapping and polishing processes.
11. The method as claimed in claim 1 , wherein a fine machining of said aspherical surface is performed by an ion-beam etching process.
12. The method as claimed in claim 1 , wherein the intermediate medium is brought into the basic form in the form of an opening.
13. The method as claimed in claim 1 , wherein a mirror is used as said optical element.
14. The method as claimed in claim 13 , wherein said mirror is formed from glass-ceramics with an edge form and an edge course as desired.
15. The method as claimed in claim 1 , wherein a lens is used as said optical element.