Source multiplexing illumination for mask inspection

Patent metadata

Field	Value
Publication number	US-9625810-B2
Application number	US-201213419157-A
Country	US
Kind code	B2
Filing date	Mar 13, 2012
Priority date	Mar 16, 2011
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

Methods and systems for source multiplexing illumination for mask inspection are disclosed. Such illumination systems enable EUV sources of small brightness to be used for EUV mask defect inspection at nodes below the 22 nm. Utilizing the multiple plane or conic mirrors that are either attached to a continuously rotating base with different angles or individually rotating to position for each pulse, the reflected beams may be directed through a common optical path. The light may then be focused by a condenser to an EUV mask. The reflected and scattered light from the mask may then be imaged by some imaging optics onto some sensors. The mask image may be subsequently processed for defect information.

First claim

What is claimed is:

1. An illumination system, comprising:
a base member rotatable about a rotation axis, the base member having a generally truncated conical shape defining at least an outer surface, an inner surface and an end surface;
at least two of:
a first set of mirrors distributed around the outer surface of the base member, each one of the first set of mirrors having a mirror surface generally facing away from the rotation axis and tilted away from the rotation axis by a first predetermined angle;
a second set of mirrors distributed around the inner surface of the base member, each one of the second set of mirrors having a mirror surface generally facing toward the rotation axis and tilted toward the rotation axis by a second predetermined angle; and
a third set of mirrors distributed around the end surface of the base member, each one of the third set of mirrors having a mirror surface tilted by a third predetermined angle with respect to an axis perpendicular to the rotation axis;
wherein the first set of mirrors, the second set of mirrors and the third set of mirrors are configured for reflecting radiations from a plurality of illumination sources and merging the radiations from the plurality of illumination sources so that the radiations are directed to traverse along a common optical path.

2. The illumination system of claim 1 , wherein the illumination system comprises the first set of mirrors, the second set of mirrors, and the third set of mirrors.

3. The illumination system of claim 1 , wherein at least one of the first set of mirrors or the second set of mirrors is configured for reflecting radiations from a corresponding illumination source at grazing incidence.

4. The illumination system of claim 1 , wherein the third set of mirrors is configured for reflecting radiations from a corresponding illumination source at near-normal incidence.

5. The illumination system of claim 1 , wherein each of the plurality of illumination sources is a pulsed EUV source.

6. The illumination system of claim 1 , further comprising:
at least one aperture positioned on the common optical path.

7. The illumination system of claim 1 , further comprising:
an additional set of mirrors mounted to the outer surface of the base member, the additional set of mirrors positioned to be interleaved with the first set of mirrors, each one of the additional set of mirrors having a mirror surface generally facing away from the rotation axis and tilted away from the rotation axis by a predetermined angle different from the first predetermined angle, wherein the additional set of mirrors is configured for reflecting radiations from an illumination source to the common optical path.

8. The illumination system of claim 1 , further comprising:
an additional set of mirrors mounted to the inner surface of the base member, the additional set of mirrors positioned to be interleaved with the second set of mirrors, each one of the additional set of mirrors having a mirror surface generally facing toward the rotation axis and tilted toward the rotation axis by a predetermined angle different from the second predetermined angle, wherein the additional set of mirrors is configured for reflecting radiations from an illumination source to the common optical path.

9. The illumination system of claim 1 , further comprising:
an additional set of mirrors mounted to the end surface of the base member, the additional set of mirrors positioned to be interleaved with the third set of mirrors, each one of the additional set of mirrors having a mirror surface tilted by a predetermined angle with respect to the axis perpendicular to the rotation axis, wherein the predetermined angle is different from the third predetermined angle, and wherein the additional set of mirrors is configured for reflecting radiations from an illumination source to the common optical path.

10. An illumination system, comprising:
a plurality of illumination sources, wherein the illumination sources include collection modules configured for providing emission collection for the illumination sources;
a base member rotatable about a rotation axis; and
a conic mirror positioned on an outer surface of the base member, wherein a center of axis of the conic mirror is configured to coincide with the rotation axis, wherein the base member is configured to support rotation of the conic mirror about the rotation axis independently with respect to the plurality of illumination sources, and wherein the conic mirror is configured to receive light from the plurality of illumination sources at grazing incidence angles between approximately 0° and 15° with respect to a surface of the conic mirror and reflect the light from the plurality of illumination sources to traverse along a common optical path.

11. The illumination system of claim 10 , wherein at least one of the collection modules is an ellipsoidal shaped module and the conic mirror is at least one of: a hyperbolical mirror or an ellipsoidal mirror.

12. The illumination system of claim 10 , wherein at least one of the collection modules is a parabolic shaped module and the conic mirror is a parabolic mirror.

13. The illumination system of claim 10 , wherein the plurality of illumination sources includes a pulsed EUV source.

14. The illumination system of claim 10 , further comprising: at least one aperture positioned on the common optical path.

15. An illumination system, comprising:
an array of individually rotatable mirrors placed in a single file along a common optical axis;
an array of light sources corresponding to the array of individually rotatable mirrors; and
a control mechanism in communication with the array of individually rotatable mirrors, the control mechanism configured for rotating the array of individually rotatable mirrors into reflecting positions for the corresponding array of light sources wherein the array of individually rotatable mirrors are configured to direct light emitted by the array of light sources to traverse along the common optical axis,
wherein the array of light sources include an array of pulsed light sources, and
wherein each particular individual mirror of the array of individually rotatable mirrors has an oscillation frequency the same as the pulse rate of its corresponding light source.

16. The illumination system of claim 15 , wherein each particular individual mirror of the array of individually rotatable mirrors has a duty cycle no less than a reciprocal of the number of mirrors in the array.

17. The illumination system of claim 15 , wherein each particular individual mirror of the array of individually rotatable mirrors includes at least one of: a MEMS type mirror or a resonant mirror.

Assignees

• Wang Daimian
• Wack Daniel
• Kvamme Damon F
• Fu Tao-Yi
• Kla Tencor Corp

Inventors

• Wang Daimian
• Wack Daniel
• Kvamme Damon F
• Fu Tao-Yi

Classifications

• G03F1/84 Primary

  Inspecting · CPC title