Lithographic apparatus and device manufacturing method

• US 20050024609A1
• Filed: 06/04/2004
• Published: 02/03/2005
• Est. Priority Date: 06/11/2003
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Banine, Vadim Yevgenyevich, De Smit, Joannes Theodoor, Dierichs, Marcel Mathijs Theodore Marie, Modderman, Theodorus Marinus, Josephus Bisschops, Theodorus Hubertus
• Granted Patent: US 7,684,008 B2
• Time in Patent Office: Days
• US Class Current: 355/18
• CPC Class Codes: G03F 7/70341 Details of immersion lithography aspects, e.g. exposure media or control of immersion liquid supply chemical composition of immersion liquids G03F7/2041
• CPC Class Codes: G03F 7/708 Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
• CPC Class Codes: G03F 7/70858 Environment aspects, e.g. pressure of beam-path gas, temperature pollution aspects G03F7/70916

Abstract

A lithographic apparatus and device manufacturing method makes use of a liquid confined in a reservoir between the projection system and the substrate. Bubbles forming in the liquid from dissolved atmospheric gases or from out-gassing from apparatus elements exposed to the liquid are detected and/or removed so that they do not interfere with exposure and lead to printing defects on the substrate. Detection may be carried out by measuring the frequency dependence of ultrasonic attenuation in the liquid and bubble removal may be implemented by degassing and pressurizing the liquid, isolating the liquid from the atmosphere, using liquids of low surface tension, providing a continuous flow of liquid through the imaging field, and/or phase shifting ultrasonic standing-wave node patterns.

Claims

1. A lithographic projection apparatus comprising:

an illumination system arranged to condition a radiation beam;

a support structure configured to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section;

a substrate table configured to hold a substrate;

a projection system arranged to project the patterned radiation beam onto a target portion of the substrate;

a liquid supply system configured to at least partly fill a space between the projection system and the substrate with a liquid; and

a bubble reduction device configured to reduce a size, a concentration, or both of bubbles in the liquid, the bubble reduction device comprising a bubble detector configured to detect bubbles in the liquid.

2. An apparatus according to claim 1, wherein the bubble detector comprises an ultrasonic transducer configured to measure attenuation of ultrasonic waves in the liquid so as to obtain information about bubbles present in the liquid.

3. An apparatus according to claim 2, wherein the ultrasonic transducer is configured to measure ultrasonic attenuation as a function of frequency.

4. An apparatus according to claim 2, wherein an ultrasonic transducer is arranged in a pulse-echo configuration, the transducer acting both to transmit ultrasonic waves and, after reflection, to receive ultrasonic waves that have been attenuated during propagation along a path through the liquid.

5. An apparatus according to claim 2, wherein the bubble detector comprises two spatially separated ultrasonic transducers, the first arranged to transmit ultrasonic waves, and the second to receive ultrasonic waves that have been attenuated during propagation along a path through the liquid between the two transducers.

6. An apparatus according to claim 1, wherein the bubble reduction device comprises a bubble removal device.

7. An apparatus according to claim 6, wherein the bubble removal device comprises a degassing device, the degassing device comprising an isolation chamber, wherein a space above liquid in the isolation chamber is maintained at a pressure below atmospheric pressure to encourage previously dissolved gases in the liquid to come out of solution and be pumped away.

8. An apparatus according to claim 6, wherein the bubble removal device is configured to provide a continuous flow of liquid over the projection system and the substrate to transport bubbles in the liquid out of the space between the projection system and the substrate.

9. An apparatus according to claim 6, wherein the bubble removal device includes two spatially separated ultrasonic transducers, arranged to produce ultrasonic standing-wave patterns within the liquid which trap bubbles within nodal regions, the bubble removal device being arranged to displace the bubbles through the use of a phase-adjusting device linked with the transducers, the phase-adjusting device causing spatial shift of nodal regions and bubbles trapped therein.

10. An apparatus according to claim 6, wherein the bubble removal device comprises an electric field generator configured to apply an electric field to the liquid, the electric field being capable of dislodging bubbles attached to the substrate.

11. An apparatus according to claim 6, wherein the bubble removal device comprises a heater configured to selectively control the temperature and therefore size of bubbles of a particular composition.

12. An apparatus according to claim 11, wherein the heater comprises a microwave source.

13. An apparatus according to claim 6, wherein the bubble removal device comprises a particle input device configured to introduce particles into the liquid, and a particle removal device configured to remove the particles from the liquid.

14. An apparatus according to claim 13, wherein the particles comprise a surface with characteristics that encourage bubbles to attach thereto.

15. An apparatus according to claim 1, wherein the bubble reduction device comprises a liquid pressurization device configured to pressurize the liquid above atmospheric pressure to minimize the size of bubbles and encourage bubble-forming gases to dissolve into the liquid.

16. An apparatus according to claim 1, wherein the composition of the liquid is chosen to have a lower surface tension than water.

17. An apparatus according to claim 1, wherein the bubble reduction device is configured to treat the liquid before it is supplied to the space between the projection system and the substrate.

18. An apparatus according to claim 17, wherein the treated liquid is kept in a sealed container, excess space in the sealed container comprising one or more of the following:

nitrogen gas, argon gas, helium gas or a vacuum.

19. An apparatus according to claim 1, wherein the bubble detector comprises a light source, a light detector and a light comparator, the light source and the light detector being arranged so that light emitted by the source propagates between the source and the detector through a portion of the liquid, the comparator being arranged to detect changes in the proportion of the emitted light that arrives at the detector after propagation through a portion of the liquid.

20. A lithographic projection apparatus comprising:

an illumination system arranged to condition a radiation beam;

a support structure configured to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section;

a substrate table configured to hold a substrate;

a projection system arranged to project the patterned radiation beam onto a target portion of the substrate;

a liquid supply system configured to at least partly fill a space between the projection system and the substrate with a liquid; and

a detection system configured to detect impurities in the liquid, including a light source, a light detector and a light comparator, the light source and the light detector being arranged so that light emitted by the source propagates between the source and the detector through a portion of the liquid, the comparator being arranged to detect changes in the proportion of the emitted light that arrives at the detector after propagation through a portion of the liquid.

21. An apparatus according to claim 20, wherein the detection system is configured to detect particles in the liquid between the projection system and the substrate.

22. A device manufacturing method comprising:

providing a liquid to a space between a projection system of a lithographic apparatus and a substrate;

projecting a patterned radiation beam using the projection system, through the liquid, onto a target portion of a substrate; and

detecting and reducing bubbles in the liquid.

23. A method according to claim 22, comprising measuring attenuation of ultrasonic waves in the liquid so as to obtain information about bubbles present in the liquid.

24. A method according to claim 23, wherein ultrasonic attenuation is measured as a function of frequency.

25. A method according to claim 22, comprising removing bubbles from the liquid.

26. A method according to claim 25, wherein removing bubbles from the liquid comprises degassing the liquid by maintaining a space of the liquid at a pressure below atmospheric pressure to encourage previously dissolved gases in the liquid to come out of solution and be pumped away.

27. A method according to claim 25, wherein removing bubbles comprises providing a continuous flow of liquid over the projection system and the substrate to transport bubbles in the liquid out of the space between the projection system and the substrate.

28. A method according to claim 25, wherein removing bubbles comprises producing ultrasonic standing-wave patterns within the liquid which trap bubbles within nodal regions and displacing the bubbles through a spatial shift of the nodal regions and bubbles trapped therein.

29. A method according to claim 25, wherein removing bubbles comprises applying an electric field to the liquid, the electric field being capable of dislodging bubbles attached to the substrate.

30. A method according to claim 25, wherein removing bubbles comprises selectively controlling the temperature and therefore size of bubbles of a particular composition.

31. A method according to claim 30, wherein the temperature is controlled using microwave radiation.

32. A method according to claim 25, wherein removing bubbles comprises introducing particles into the liquid and removing the particles from the liquid.

33. A method according to claim 32, wherein the particles comprise a surface with characteristics that encourage bubbles to attach thereto.

34. A method according to claim 22, wherein reducing bubbles comprises pressurizing the liquid above atmospheric pressure to minimize the size of bubbles and encourage bubble-forming gases to dissolve into the liquid.

35. A method according to claim 22, wherein the composition of the liquid is chosen to have a lower surface tension than water.

36. A method according to claim 22, wherein reducing bubbles, detecting bubbles or both occurs prior to the liquid is provided to the space between the projection system and the substrate.

37. A method according to claim 36, wherein the treated liquid is kept in a sealed container, excess space in the sealed container comprising one or more of the following:

nitrogen gas, argon gas, helium gas or a vacuum.

38. A method according to claim 22, wherein reducing bubbles, detecting bubbles or both occurs as the liquid is provided to or while the liquid is in the space between the projection system and the substrate.

39. A method according to claim 22, wherein detecting bubbles comprises propagating light through a portion of the liquid and detecting changes in the proportion of emitted light that arrives at a detector after propagation through a portion of the liquid.

40. A lithographic projection apparatus comprising:

an illumination system arranged to condition a radiation beam;

a support structure configured to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section;

a substrate table configured to hold a substrate;

a projection system arranged to project the patterned radiation beam onto a target portion of the substrate;

a liquid supply system configured to at least partly fill a space between the projection system and the substrate with a liquid; and

a liquid quality monitor capable of switching the operational state of the projection apparatus between an active state and a suspended state, the active state being selected when the liquid quality is determined to be above a predefined threshold and the suspended state being selected when the liquid quality is determined to be below a predefined threshold state.