Illumination System

• US 20090091734A1
• Filed: 12/04/2008
• Published: 04/09/2009
• Est. Priority Date: 12/02/2005
• Status: Active Grant

• Current Assignee: ASML Holding NV, ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: VISSER, Huibert, Vink, Henri Johannes Petrus, Coston, Scott D., Ryzhikov, Lev, Joobeur, Adel, Shmarev, Yevgeniy Konstantinovich, Klinkhamer, Jacob Fredrik Friso
• Granted Patent: US 8,164,740 B2
• Time in Patent Office: Days
• US Class Current: 355/67
• CPC Class Codes: G02B 27/0905 Dividing and/or superposing multiple light beams
• CPC Class Codes: G03F 7/70075 Homogenization of illumination intensity in the mask plane by using an integrator, e.g. fly's eye lens, facet mirror or glass rod, by using a diffusing optical element or by beam deflection
• CPC Class Codes: G03F 7/70583 Speckle reduction, e.g. coherence control or amplitude/wavefront splitting

Abstract

A coherence remover is provided. In an embodiment the coherence remover includes a first mirror and a second mirror coupled to the first mirror. The coherence remover is configured to receive an input beam. Each of the first and second mirrors is configured to reflect a respective portion of the input beam to produce respective one or more intermediate beams. The intermediate beams collectively form an output beam that has a reduced coherence compared to the input beam.

Claims

1. A coherence remover, comprising:

a first mirror; and

a second mirror coupled to the first mirror;

wherein the coherence remover is configured to receive an input beam,

wherein each of the first and second mirrors is configured to reflect a respective portion of the input beam to produce respective one or more intermediate beams, and

wherein the intermediate beams collectively form an output beam that has a reduced coherence compared to the input beam.

2. The coherence remover of claim 1, further comprising:

a beam splitter configured to output the input beam at a first port such that the input beam is incident on the first and second mirrors, wherein the beam splitter is configured to receive the output beam and output the output beam at a second port that is different than the first port.

3. The coherence remover of claim 2, wherein the beam splitter is a polarizing beam splitter that is configured to direct beams having a first polarization to the first port and direct beams having a second polarization at the second port.

4. The coherence remover of claim 3, further comprising:

a wave plate configured to alter a polarization state of the output beam.

5. The coherence remover of claim 4, wherein the wave plate is a quarter wave plate.

6. The coherence remover of claim 1, further comprising:

a third mirror; and

a fourth mirror,

wherein each of the third and fourth mirrors is configured to reflect a respective portion of the output beam to produce respective one or more second intermediate beams;

wherein each the first and second mirrors substantially extends in a first direction, whereby the output beam has a reduced coherence compared to the input beam in the first direction;

wherein each the third and fourth mirrors substantially extends in a second direction that is perpendicular to the first direction; and

wherein second intermediate beams collectively form a second output beam that has a reduced coherence compared to the first output beam in the second direction.

7. The coherence remover of claim 6, further comprising:

a beam splitter configured to direct the first output beam to a first port, such that the first output beam is incident on the third and fourth mirrors, and to direct the second output beam to a second port that is different than the first port.

8. The coherence remover of claim 7, wherein the beam splitter is a polarizing beam splitter that is configured to direct beams having a first polarization to the first port and to direct beams having a second polarization to the second port.

9. The coherence remover of claim 8, further comprising:

a wave plate configured to alter a polarization state of the second output beam.

10. The coherence remover of claim 9, wherein the wave plate is a quarter wave plate.

11. The coherence remover of claim 1, wherein the first mirror comprises a substrate with opposing first and second surfaces, wherein the first surface is a reflective surface, and wherein the second mirror is coupled to the second surface.

12. The coherence remover of claim 11, wherein a thickness between the first surface and the second surface is larger than a coherence length of the input beam.

13. The coherence remover of claim 11, wherein the substrate has an angled edge.

14. The coherence remover of claim 1, further comprising third through sixth mirrors, wherein each of the third through sixth mirrors is coupled to another mirror.

15. The coherence remover of claim 1, wherein the output beam is received by a homogenizer or a patterning device.

16. A lithographic apparatus, comprising:

a coherence remover, comprising,

a first mirror, and

a second mirror coupled to the first mirror,

wherein the coherence remover is configured to receive an input beam, wherein each of the first and second mirrors is configured to reflect a respective portion of the input beam to produce respective one or more intermediate beams, and wherein the intermediate beams collectively form an output beam that has a reduced coherence compared to the input beam; and

homogenizer configured to convert the output beam into a plurality of beams.

17. The lithographic apparatus of claim 16, further comprising:

a patterning device configured to modulate the plurality of beams, such that a pattern is formed on a substrate that receives the modulated plurality of beams.

18. The lithographic apparatus of claim 16, wherein the homogenizer comprises first and second homogenizer plates that are angled relative to one another.

19. The lithographic apparatus of claim 18, wherein the first and second homogenizer plates are configured to be mounted so that an angular orientation between the first and second homogenizer plates is adjustable.

20. The lithographic apparatus of claim 16, wherein the homogenizer comprises:

a first homogenizer device configured to homogenize the output beam in a first direction to produce a first homogenized output beam; and

a second homogenizer device configured to homogenize the first homogenized output beam in a second direction to produce a second homogenized beam, wherein the first direction is perpendicular to the second direction.

21. The lithographic apparatus of claim 20, wherein at least one of the first homogenizer device and the second homogenizer device comprises at least one of a plate or two parallel mirrors.

22. The lithographic apparatus of claim 20, further comprising:

a lens configured to condense the output beam before it is received by the first homogenizer device.

23. The lithographic apparatus of claim 20, further comprising:

a first lens configured to received the second homogenized beam and to produce a collimated output therefrom; and

a second lens configured to condense the collimated output,

wherein an orientation of the first lens is perpendicular to an orientation of the second lens.