Using an Interferometer as a High Speed Variable Attenuator

• US 20080106717A1
• Filed: 10/03/2007
• Published: 05/08/2008
• Est. Priority Date: 10/17/2006
• Status: Active Grant

• Current Assignee: ASML Holding NV, ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Holding NV, ASML Netherlands BV (ASML Holding NV)
• Inventors: Van Den Dool, Teunis, Calero, Daniel, Vink, Henri, NOORDMAN, Oscar, Kreuzer, Justin
• Granted Patent: US 7,898,646 B2
• Time in Patent Office: Days
• US Class Current: 355/66
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G03F 7/70041 by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control
• CPC Class Codes: G03F 7/70558 Dose control, i.e. achievement of a desired dose

Abstract

A system and method provides high speed variable attenuators. The attenuators can be used within a lithographic apparatus to control intensity of radiation in one or more correction pulses used to correct a dose of the radiation following an initial pulse of radiation.

Claims

1. A variable attenuator suitable for use in a lithographic apparatus and configured to adjust its level of transmission of an input beam of radiation in response to an input control signal that represents a desired level of transmission of the variable attenuator to the beam of radiation, comprising:

first and second semi-transparent reflectors, arranged substantially mutually parallel and such that the beam of radiation successively passes through the first and second semi-transparent reflectors; and

an actuator system configured to control the separation of the first and second semi-transparent reflectors in response to the input control signal.

2. The variable attenuator of claim 1, wherein the beam of radiation is incident on the first semi-transparent reflector at an oblique angle.

3. The variable attenuator of claim 1, further comprising a controller configured to provide control signals to the actuator system in order to control the actuator system in response to the input control signal.

4. The variable attenuator of claim 3, wherein:

the controller comprises a memory configured to store calibration data corresponding to a relationship between the level of transmission of the attenuator and the control signals; and

the controller is configured to generate the control signals for the actuator system in response to the input control signal and based on the calibration data.

5. The variable attenuator of claim 3, further comprising:

a position sensor system configured to measure a relative position of the first and second semi-transparent reflectors,

wherein the controller is configured to generate the control signals for the actuator system in response to the input control signal and based on the measured relative position of the first and second semi-transparent reflectors.

6. The variable attenuator of claim 5, wherein:

the controller is configured to determine a desired relative position of the first and second semi-transparent reflectors based on the input control signal and to generate the control signals for the actuator system based on the difference between the desired and measured relative position of the first and second semi-transparent reflectors.

7. The variable attenuator of claim 5, wherein:

the actuator system is further configured to control a relative angular position of the first and second semi-transparent reflectors; and

the controller is configured such that it provides control signals to the actuator system to control the relative angular position of the first and second semi-transparent reflectors based on the measured relative position of the first and second semi-transparent reflectors.

8. The variable attenuator of claim 3, further comprising:

a source of radiation configured to generate a second beam of radiation that is incident on one of the first and second semi-transparent reflectors at a different angle from that at which the first beam of radiation is incident on the first semi-transparent reflector; and

a detector system that is configured to inspect the second beam of radiation after it has passed through the first and second semi-transparent reflectors,

wherein the detector system is configured to measure an intensity of the second beam of radiation passing through the variable attenuator, and

wherein the controller is configured to generate the control signals for the actuator system in response to the input control signal based on the measured intensity of the second beam of radiation.

9. The variable attenuator of claim 8, wherein:

the detector system is further configured to measure the uniformity of the radiation intensity across a cross section of the second beam of radiation;

the actuator system is further configured to control the relative angular position of the first and second semi-transparent reflectors; and

the controller is configured such that it provides control signals to the actuator system to control the relative angular position of the first and second semi-transparent reflectors based on the measured uniformity of the radiation intensity across the cross section of the second beam of radiation.

10. A variable attenuator suitable for use in a lithographic apparatus and configured to adjust its level of transmission to an input beam of radiation in response to an input control signal that represents a desired level of transmission of the variable attenuator to the beam of radiation, comprising:

a radiation beam splitter that divides the beam of radiation into first and second radiation beam paths;

a radiation beam combiner that re-combines radiation from the first and second radiation beam paths, such the re-combined radiation interferes and produces an output beam of radiation; and

a radiation beam pathlength controller configured to control a pathlength of the first radiation beam path in response to the input control signal in order to control the interference of the radiation from the first and second radiation beam paths.

11. The variable attenuator of claim 10, wherein the radiation beam pathlength controller comprises a reflector and an actuator system configured to control a position of the reflector, such that the radiation beam pathlength controller can alter the pathlength of the first radiation beam path.

12. The variable attenuator of claim 11, further comprising a controller configured to provide control signals to the actuator system in order to control the actuator system in response to the input control signal.

13. The variable attenuator of claim 12, wherein:

the controller comprises a memory configured to store calibration data corresponding to a relationship between the level of transmission of the attenuator and the control signals, and

the controller is configured to generate the control signals for the actuator system in response to the input control signal based on the calibration data.

14. The variable attenuator of claim 12, further comprising:

a source of radiation configured to generate a second beam of radiation and to direct it to the radiation beam splitter, such that the second beam of radiation is divided into the first and second beam paths and re-combined by the radiation beam combiner; and

a detector system that is configured to inspect the second beam of radiation once it has been re-combined by the radiation beam combiner,

wherein the detector system is configured to measure an intensity of the second beam of radiation, and

wherein the controller is configured to generate the control signals for the actuator system in response to the input control signal based on the measured intensity of the second beam of radiation.

15. The variable attenuator of claim 14, wherein:

the detector system is configured to measure a uniformity of the radiation intensity across the cross section of the second beam of radiation;

the actuator system is configured such that it can control an angle of the reflector of the radiation beam pathlength controller relative to a beam of radiation propagating through the first radiation beam path which, in turn, controls a relative angle of incidence of the radiation from the first and second radiation beam paths in the radiation beam combiner; and

the controller is configured such that it provides control signals to the actuator system to control the angle of the reflector of the radiation beam pathlength controller based on the measured uniformity of the radiation intensity across the cross section of the second beam of radiation.

16. The variable attenuator of claim 10, wherein the radiation beam pathlength controller comprises:

first and second parallel reflectors; and

an actuator system configured to control the separation of the first and second reflectors,

wherein the first radiation beam path is arranged such that the radiation is reflected a plurality of times between the first and second reflectors, and

wherein the actuator system controls the separation of the first and second reflectors in response to the input control signal.

17. A variable attenuator suitable for use in a lithographic apparatus and configured to adjust its level of transmission to an input beam of radiation in response to an input control signal that represents a desired level of transmission of the variable attenuator to the beam of radiation, comprising:

first and second phase gratings; and

an actuator system,

wherein the first and second phase gratings are arranged substantially mutually parallel and so that the beam of radiation is initially incident on the first phase grating and then is incident on the second phase grating,

wherein each of the phase gratings comprises a plurality of regions of a first type and a plurality of regions of a second type,

wherein the phase gratings are constructed such that, for each phase grating, a phase shift introduced to the beam of radiation passing through the regions of the first type is a quarter of a wavelength of the beam of radiation input to the variable attenuator greater than for the regions of the second type, and

wherein the actuator system is configured to adjust the relative positions of the first and second phase gratings in response to the input control signal between at least a first position, in which radiation passing through regions of the first and second type of the first phase grating subsequently passes through regions of the first and second type, respectively, of the second phase grating, and a second position, in which radiation passing through regions of the first and second type of the first grating subsequently passes through regions of the second and first type, respectively, of the second phase grating.

18. The variable attenuator of claim 17, wherein:

zero order radiation that has passed through the first and second phase gratings is directed as an output of the variable attenuator; and

the variable attenuator comprises at least one radiation dump to which higher positive or higher negative orders, or both, of radiation that has passed through the first and second phase gratings are directed.

19. The variable attenuator of claim 17, further comprising a controller that is configured to provide control signals to the actuator system in order to control the actuator system in response to the input control signal.

20. The variable attenuator of claim 19, wherein:

the controller includes a memory configured to store calibration data corresponding to the relationship between the transmission level of the attenuator and the control signals; and

the controller is configured to generate the control signals for the actuator system in response to the input control signal and based on the calibration data.

21. The variable attenuator of claim 19, further comprising:

a position sensor system configured to measure a relative position of the first and second phase gratings,

wherein the controller is configured to generate the control signals for the actuator system in response to the input control signal and based on the measured relative position of the first and second phase gratings.

22. The variable attenuator of claim 21, wherein the controller is configured to determine a desired relative position of the first and second phase gratings based on the input control signal and to generate the control signals for the actuator system based on the difference between the desired and measured relative position of the first and second phase gratings.

23. The variable attenuator of claim 21, wherein:

the actuator system is further configured to control a relative angular position of the first and second phase gratings; and

the controller is configured such that it provides control signals to the actuator system to control the relative angular position of the first and second phase gratings based on the measured relative position of the first and second phase gratings.

24. The variable attenuator of claim 19, further comprising:

a source of radiation configured to generate a second beam of radiation that is directed to pass through the first and second phase gratings at a location different from the first beam of radiation; and

a radiation detector configured to detect intensity of zero order radiation derived from the second beam of radiation that has passed through the first and second phase gratings,

wherein the controller is configured to generate the control signals for the actuator system in response to the input control signal based on the intensity measured by the radiation detector.

25. The variable attenuator of claim 24, wherein:

the source of radiation and the radiation detector form a first sensor for providing information to the controller related to the relative position of the first and second phase gratings;

the variable attenuator comprises at least one further sensor corresponding to the first sensor generating a corresponding beam of radiation that passes through the first and second phase gratings at a location different from the first and second beams of radiation; and

the controller is configured to generate the control signals for the actuator system in response to the input control signal based on the information provided by the sensors.

26. The variable attenuator of claim 17, wherein the second phase grating is separated from the first phase grating and lies in a Talbot plane of the first grating or a half-Talbot plane of the first grating.

27. A radiation dose controller, comprising:

a detector configured to determine an energy within pulses of radiation received by the radiation dose controller;

a variable attenuator configured to attenuate an intensity of at least one pulse of radiation, wherein the variable attenuator comprises one of;

(a) first and second semi-transparent reflectors;

(b) a radiation beam splitter, a radiation beam combiner, and a radiation beam path length controller;

or

(c) first and second phase gratings; and

a controller configured to determine, from the energy in a first pulse determined by the detector, a required energy in a second pulse to provide a required total radiation dose and to provide a control signal to the variable attenuator in order to set a level of transmission of the variable attenuator such that it attenuates the second pulse to the required level.

28. A radiation dose controller, comprising:

a detector configured to measure an energy of radiation within a pulse of radiation received by the radiation dose controller;

a variable attenuator configured to attenuate the energy of radiation within at least one pulse of radiation, wherein the variable attenuator comprises one of;

(a) first and second semi-transparent reflectors;

(b) a radiation beam splitter, a radiation beam combiner, and a radiation beam path length controller;

or

(c) first and second phase gratings;

an optical delay configured to provide a time delay before a pulse of radiation is input to the variable attenuator; and

a triggering unit configured to send a control signal to the variable attenuator in response to the energy of the radiation within a pulse of radiation measured by the detector, such that the variable attenuator is set to attenuate the energy in the pulse of radiation to a desired radiation dose when the pulse of radiation is input to the variable attenuator.

29. A radiation dose controller, comprising:

a detector configured to measure an intensity of radiation within a pulse of radiation received by the radiation dose controller;

a variable attenuator configured to attenuate an energy of radiation within at least one pulse of radiation, wherein the variable attenuator comprises one of;

(a) first and second semi-transparent reflectors;

(b) a radiation beam splitter, a radiation beam combiner, and a radiation beam path length controller;

or

(c) first and second phase gratings;

an optical delay configured to provide a time delay before a pulse of radiation is input to the variable attenuator; and

a triggering unit configured to send a control signal to the variable attenuator in response to the intensity of a pulse of radiation measured by the detector, such that the variable attenuator switches from a state of maximum transmissivity to a state of minimum transmissivity at a time required to trim the energy of the pulse of radiation to a desired radiation dose.

30. A lithographic apparatus, comprising:

an illumination system configured to condition a pulsed beam of radiation;

a variable attenuator configured such that it attenuates the intensity of at least one pulse of the pulsed beam of radiation, wherein the variable attenuator comprises one of;

(a) first and second semi-transparent reflectors;

(b) a radiation beam splitter, a radiation beam combiner, and a radiation beam path length controller;

or

(c) first and second phase gratings; and

a control system configured to determine a desired intensity of a pulse of radiation and to provide a control signal to the variable attenuator, corresponding to a desired level of transmission of the variable attenuator to the beam of radiation, necessary to attenuate the pulse to the desired intensity.

31. The lithographic apparatus of claim 30, comprising a plurality of the variable attenuators according arranged in series.

32. A device manufacturing method, comprising:

forming a variable attenuator using first and second semi-transparent reflectors that are arranged substantially mutually parallel, such that a pulsed beam of radiation successively passes through the first and second semi-transparent reflectors;

controlling a separation of the first and second semi-transparent reflectors in response to the input control signal;

attenuating an intensity of at least one pulse of the pulsed beam of radiation using the variable attenuator configured to adjust its level of transmission to an input beam of radiation in response to an input control signal, which represents a desired level of transmission of the variable attenuator to the beam of radiation;

modulating the pulsed beam of radiation; and

projecting the modulated beam onto a substrate.

35. A flat panel display manufactured according to the method of claim 32.

36. An integrated circuit device manufactured according to the method of claim 32.

33. A device manufacturing method, comprising:

forming a variable attenuator using a radiation beam splitter that divides a pulsed beam of radiation into first and second radiation beam paths and a radiation beam combiner that re-combines radiation from the first and second radiation beam paths such that it interferes and produces an output beam of radiation;

using a radiation beam pathlength controller to control the pathlength of the first radiation beam path in response to an input control signal in order to control the interference of the radiation from the first and second radiation beam paths;

attenuating an intensity of at least one pulse of the pulsed beam of radiation is using the variable attenuator configured to adjust its level of transmission to an input beam of radiation in response to the input control signal, which represents a desired level of transmission of the variable attenuator to the beam of radiation;

modulating the pulsed beam of radiation; and

projecting the modulated beam onto a substrate.

37. A flat panel display manufactured according to the method of claim 33.

38. An integrated circuit device manufactured according to the method of claim 33.

34. A device manufacturing method, comprising:

forming a variable attenuator from first and second phase gratings that are arranged substantially mutually parallel, such that the pulsed beam of radiation is initially incident on the first phase grating and, having passed through the first phase grating, is incident on the second phase grating;

forming a plurality of regions of a first type and a plurality of regions of a second type on each of the phase gratings;

constructing the phase gratings such that, for each phase grating, the phase shift introduced to the pulsed beam of radiation passing through the regions of the first type is a quarter of the wavelength of the beam of radiation input to the variable attenuator greater than for the regions of the second type;

adjusting relative positions of the first and second phase gratings in response to an input control signal between at least a first position, in which the radiation passing through regions of the first and second type of the first phase grating subsequently passes through regions of the first and second type, respectively, of the second phase grating, and a second position, in which radiation passing through regions of the first and second type of the first grating subsequently passes through regions of the second and first type, respectively, of the second phase grating;

attenuating an intensity of at least one pulse of the pulsed beam of radiation using the variable attenuator configured to adjust its level of transmission to an input beam of radiation in response to an input control signal which represents a desired level of transmission of the variable attenuator to the beam of radiation;

modulating the pulsed beam of radiation; and

projecting the modulated beam onto a substrate.

39. A flat panel display manufactured according to the method of claim 34.

40. An integrated circuit device manufactured according to the method of claim 34.