Illumination system and projection objective of a mask inspection apparatus

Patent metadata

Field	Value
Publication number	US-10114293-B2
Application number	US-201213587077-A
Country	US
Kind code	B2
Filing date	Aug 16, 2012
Priority date	Feb 22, 2010
Publication date	Oct 30, 2018
Grant date	Oct 30, 2018

Abstract

An illumination system and a projection objective of a mask inspection apparatus are provided. During operation of the mask inspection apparatus, the illumination system illuminates a mask with an illumination bundle of rays having a centroid ray that has a direction dependent on the location of the incidence of the illumination bundle of rays on the mask.

First claim

The invention claimed is:

1. An illumination system of a mask inspection apparatus,
wherein the illumination system is configured to, in operation of the mask inspection apparatus, illuminate a mask with an illumination bundle of rays which has a centroid ray; and
wherein the illumination system is further configured such that, during the operation of the mask inspection apparatus, said centroid ray has a direction dependent on the location of the incidence of the illumination bundle of rays on the mask, in which the centroid ray has at least two different directions for different locations of the incidence of the illumination bundle of rays on the mask, and there is a predetermined relationship between the direction of the centroid ray and the location of incidence of the illumination bundle of rays on the mask, such that the centroid ray has a first direction for a first location of incidence of the illumination bundle of rays on the mask, and the centroid ray has a second direction different from the first direction for a second location different from the first location of incidence of the illumination bundle of rays on the mask.

2. The illumination system of claim 1 in which the maximum angle between the planes of incidence of two bundles of rays incident on different locations of the mask is at least 3°.

3. The illumination system of claim 1 in which the maximum angle between the centroid rays of two bundles of rays incident on different locations of the mask is at least 3 °.

4. The illumination system of claim 1 in which the mask that is analyzed in the operation of the mask inspection apparatus is designed for use with an illumination region in the form of a segment of a ring in a projection exposure apparatus.

5. The illumination system as of claim 4 in which the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask, complies with the condition:

sin
⁡

(
α
)

=

y
R

wherein:
y denotes the co-ordinate of the mask plane,
R denotes the radius of the ring field, and
α denotes the angle between the plane of incidence, formed by the centroid ray which is incident on the mask from the illumination system and that which is reflected by the mask, with the y =0 plane.

6. The illumination system of claim 1 in which the illumination system is designed for operation in an extreme ultra-violet (EUV) mode.

7. The illumination system of claim 1 in which the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask, is such that the magnitude of the angle between the centroid ray and the surface normal on the mask is maintained.

8. The illumination system of claim 1 in which there is provided at least one blade movable in a predetermined plane of movement for adjustment of the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask.

9. The illumination system of claim 1 in which the illumination system comprises at least one blade movable for adjustment of the variation in the direction of the centroid ray during the operation of the mask inspection apparatus, wherein the illumination system is configured such that when the at least one blade is at a first location, the incidence of the illumination bundle of rays is at the first location on the mask and the centroid ray has the first direction, and when the same at least one blade is at a second location, the incidence of the illumination bundle of rays is at the second location on the mask and the centroid ray has the second direction.

10. The illumination system of claim 1 in which a magnitude of an angle between the incident centroid ray and a surface normal of the mask remains constant when the direction of the centroid ray changes from the first direction to the second direction.

11. The illumination system of claim 10 in which the constant magnitude of the angle between the incident centroid ray and the surface normal of the mask defines a cone of directions of incidence, and a variation of the direction of the centroid ray takes place along the cone of directions of incidence.

12. The illumination system of claim 1 in which for at least a portion of the mask, the direction of the centroid ray varies continuously as the location of incidence of the illumination bundle of rays on the mask varies continuously.

13. The illumination system of claim 1 , wherein an object field is in a shape of a segment of a ring that extends concentrically around an optical axis, and wherein when the incidence of the illumination bundle of rays is at the first location on the mask, the incident centroid ray propagates along a first plane of incidence, when the incidence of the illumination bundle of rays is at the second location on the mask, the incident centroid ray propagates along a second plane of incidence, and the first plane of incidence intersects the second plane of incidence at the optical axis.

14. The illumination system of claim 1 in which the direction of the centroid ray is a function of the location of the incidence of the illumination bundle of rays on the mask.

15. An illumination system of a mask inspection apparatus,
wherein the illumination system is configured to, in operation of the mask inspection apparatus, illuminate a mask with an illumination bundle of rays which has a centroid ray;
wherein the illumination system is further configured such that, during the operation of the mask inspection apparatus, said centroid ray has a direction dependent on the location of the incidence of the illumination bundle of rays on the mask, in which the centroid ray has at least two different directions for different locations of the incidence of the illumination bundle of rays on the mask, and there is a predetermined relationship between the direction of the centroid ray and the location of incidence of the illumination bundle of rays on the mask, such that the centroid ray has a first direction for a first location of incidence of the illumination bundle of rays on the mask, and the centroid ray has a second direction different from the first direction for a second location different from the first location of incidence of the illumination bundle of rays on the mask;
wherein the illumination system comprises at least one blade movable in a predetermined plane of movement for adjustment of the variation in the direction of the centroid ray during the operation of the mask inspection apparatus, dependent on the location of incidence of the illumination bundle of rays on the mask.

16. The illumination system of claim 15 in which said plane of movement extends in substantially coplanar relationship with the mask plane.

17. The illumination system of claim 15 in which a region of the plane of movement, over which the blade is movable for adjustment in the variation in the direction of the centroid ray, that is dependent on the location of incidence of the illumination bundle of rays on the mask, has a substantially reniform contour.

18. The illumination system of claim 15 in which the blade is adapted

Assignees

• Feldmann Heiko
• Sohmen Erik Matthias
• Stuehler Joachim
• Gromer Oswald
• Mueller Ulrich
• Layh Michael
• Schwab Markus
• Zeiss Carl Smt Gmbh

Inventors

• Feldmann Heiko
• Sohmen Erik Matthias
• Stuehler Joachim
• Gromer Oswald
• Mueller Ulrich
• Layh Michael
• Schwab Markus

Classifications

• G03F1/84

  Inspecting · CPC title

• G01N2021/95676

  Masks, reticles, shadow masks · CPC title

• G03F7/70091 Primary

  Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA] · CPC title

• G01N21/956

  Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} · CPC title

• G01N21/00

  Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light (G01N3/00 - G01N19/00 take precedence) · CPC title