Magnifying imaging optical unit and EUV mask inspection system with such an imaging optical unit

Patent metadata

Field	Value
Publication number	US-10408765-B2
Application number	US-201514835308-A
Country	US
Kind code	B2
Filing date	Aug 25, 2015
Priority date	Mar 14, 2013
Publication date	Sep 10, 2019
Grant date	Sep 10, 2019

Abstract

A magnifying imaging optical unit serves for inspecting lithography masks which are used in EUV projection exposure. The imaging optical unit comprises at least two mirrors (M 1 to M 4 ) which can be displaced relative to one another for changing a magnification value. According to a further aspect, a magnifying imaging optical unit comprises at least one mirror (M 1 to M 4 ) and a magnification value, which can be changed by displacement of at least two mirrors (M 1 to M 4 ) relative to one another. Here, the magnification value can be changed between a minimum magnification value, which is greater than 100, and a maximum magnification value, which is greater than 200. An imaging optical unit emerges, which can be adapted to, in particular, mask structures with different sizes.

First claim

The invention claimed is:

1. An imaging optical unit, comprising:
a first mirror; and
a second mirror,
wherein:
the first and second mirrors are displaceable relative to each other to change a magnification value of the imaging optical unit;
a size of an image field of the imaging optical unit is independent of the magnification value of the imaging optical unit;
a position of the image field of the imaging optical unit is independent of the magnification value of the imaging optical unit;
a distance between an object field of the imaging optical unit and the first mirror is finite; and
a distance between the object field of the imaging optical unit and the second mirror is finite.

2. The imaging optical unit of claim 1 , wherein only one of the first and second mirrors is displaceable to change the magnification value of the imaging optical unit.

3. The imaging optical unit of claim 1 , wherein each of the first and second mirrors is displaceable to change the magnification value of the imaging optical unit.

4. The imaging optical unit of claim 1 , further comprising an aperture stop, wherein:
during use of the imaging optical unit, light passes along a path through the imaging optical unit from the object field to the image field; and
the aperture stop is in the path between the object field and the first mirror.

5. The imaging optical unit of claim 1 , wherein:
during use of the imaging optical unit, light passes along a path through the imaging optical unit from the object field to the image field; and
the imaging optical unit has an intermediate image in the path between the first and second mirrors.

6. The imaging optical unit of claim 1 , wherein the imaging optical unit is a catoptric imaging optical unit.

7. The imaging optical unit of claim 1 , wherein no mirror of the imaging optical unit has a central passage opening configured to pass light during use of the imaging optical unit.

8. The imaging optical unit of claim 1 , wherein:
the imaging optical unit has an object-side numerical aperture which is changeable between a minimum value and a maximum value by displacing the first and second mirrors relative to each other;
the minimum value of the object-side numerical aperture is 0.1; and
the maximum object-side numerical aperture is 0.25.

9. A system, comprising:
an imaging optical unit according claim 1 ; and
a spatially resolving detector configured to detect the image field,
wherein the system is an EUV mask inspection system.

10. An imaging optical unit, comprising:
at least two mirrors which are displaceable relative to each other to change a magnification value of the imaging optical unit,
wherein:
the magnification value of the imaging optical unit has a minimum value which is greater than 100; and
the magnification value of the imaging optical unit has a maximum value which is greater than 200.

11. The imaging optical unit of claim 10 , wherein:
a size of an image field of the imaging optical unit is independent of the magnification value of the imaging optical unit;
a position of the image field of the imaging optical unit is independent of the magnification value of the imaging optical unit.

12. The imaging optical unit of claim 10 , wherein only one of the first and second mirrors is displaceable to change the magnification value of the imaging optical unit.

13. The imaging optical unit of claim 10 , wherein each of the first and second mirrors is displaceable to change the magnification value of the imaging optical unit.

14. The imaging optical unit of claim 10 , further comprising an aperture stop, wherein:
during use of the imaging optical unit, light passes along a path through the imaging optical unit from the object field to the image field; and
the aperture stop is in the path between the object field and the first mirror.

15. The imaging optical unit of claim 10 , wherein:
during use of the imaging optical unit, light passes along a path through the imaging optical unit from the object field to the image field; and
the imaging optical unit has an intermediate image in the path between the first and second mirrors.

16. The imaging optical unit of claim 10 , wherein the imaging optical unit is a catoptric imaging optical unit.

17. The imaging optical unit of claim 10 , wherein no mirror of the imaging optical unit has a central passage opening configured to pass light during use of the imaging optical unit.

18. The imaging optical unit of claim 10 , wherein:
the imaging optical unit has an object-side numerical aperture which is changeable between a minimum value and a maximum value by displacing the first and second mirrors relative to each other;
the minimum value of the object-side numerical aperture is 0.1; and
the maximum object-side numerical aperture is 0.25.

19. The imaging optical unit of claim 10 , wherein the imaging optical unit comprises precisely four mirrors.

20. A system, comprising:
an imaging optical unit according claim 10 ; and
a spatially resolving detector configured to detect the image field;
wherein the system is an EUV mask inspection system.

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Mann Hans-Juergen

Classifications

• G02B17/0694

  with variable magnification or multiple imaging planes, including multispectral systems (systems with only refractive elements G02B15/14) · CPC title

• G02B17/0663

  off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements · CPC title

• G02B17/0657 Primary

  off-axis or unobscured systems in which all of the mirrors share a common axis of rotational symmetry · CPC title

• G01N21/95

  characterised by the material or shape of the object to be examined (G01N21/89 - G01N21/91, G01N21/94 take precedence) · CPC title

• G01N2201/068

  Optics, miscellaneous · CPC title