Angularly resolved scatterometer, inspection method, lithographic apparatus, lithographic processing cell device manufacturing method and alignment sensor

• US 20080239265A1
• Filed: 03/30/2007
• Published: 10/02/2008
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Den Boef, Arie Jeffrey
• Granted Patent: US 7,570,358 B2
• Time in Patent Office: Days
• US Class Current: 355/53
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01N 21/956 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 H01L22/10
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• CPC Class Codes: G03F 7/70633 Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching
• CPC Class Codes: G03F 9/7065 Production of alignment light, e.g. light source, control of coherence, polarization, pulse length, wavelength

Abstract

An angularly resolved scatterometer uses a broadband radiation source and an acousto-optical tunable filter to select one or more narrowband components from the broadband beam emitted by the source for use in measurements. A feedback loop can be used to control the intensity of the selected narrowband components to reduce noise.

Claims

1. An angularly resolved scatterometer configured to determine a value related to a parameter of a target pattern printed on a substrate by a lithographic process used to manufacture a device layer on the substrate, the apparatus comprising:

a broadband radiation source arranged to emit a first beam of radiation having a first wavelength range;

an acousto-optical tunable filter comprising

an acousto-optical crystal arranged to receive the first beam of radiation,

a transducer coupled to the acousto-optical filter and arranged to excite acoustic waves therein, and

a beam selecting device arranged to select as an output beam one of a plurality of beams, output by the acousto-optical crystal in response to the first beam and the acoustic waves, as a second beam of radiation having a second wavelength range, the second wavelength range being narrower than the first wavelength range;

an optical system comprising a high-NA objective lens arranged to direct the second beam of radiation onto the target pattern and to project radiation reflected or scattered by the target pattern onto a detector to obtain a scatterometric spectrum; and

a driver circuit electrically coupled to the transducer and arranged to generate a drive signal therefor, the driver circuit being adapted to control a frequency of the drive signal so as to control the second wavelength range.

2. An angularly resolved scatterometer according to claim 1, wherein the second beam of radiation has a bandwidth of less than about 20 nm.

3. An angularly resolved scatterometer according to claim 2, wherein the second beam of radiation has a bandwidth of less than about less than about 10 nm.

4. An angularly resolved scatterometer according to claim 3, wherein the second beam of radiation has a bandwidth of less than about 5 nm.

5. An angularly resolved scatterometer according to claim 1, further comprising a detector;

and a beam splitter arranged to divert a predetermined portion of the second beam of radiation to the detector, wherein the detector is arranged to detect an intensity of the diverted portion of the second beam of radiation and to generate an intensity measurement signal, the driver circuit being responsive to the intensity measurement signal to control an amplitude of the drive signal and thereby an amplitude of the second beam of radiation.

6. An angularly resolved scatterometer according to claim 1, wherein the drive circuit is arranged to generate a drive signal having a plurality of different frequency components, wherein the acousto-optical tunable filter is configured to output simultaneously a plurality of second beams of radiation having respectively different wavelength ranges.

7. An angularly resolved scatterometer according to claim 6, further comprising a detector;

and a beam splitter arranged to divert a predetermined portion of the second beams of radiation to the detector, wherein the detector is arranged to detect the intensity of the diverted portion of the second beams of radiation and to generate an intensity measurement signal, the driver circuit being responsive to the intensity measurement signal to control an amplitude of the drive signal and thereby an amplitude of the second beam.

8. An angularly resolved scatterometer according to claim 7, wherein the beam splitter is a dichroic beam splitter arranged to divert a predetermined portion of a specific one of the second beams of radiation to the detector.

9. An angularly resolved scatterometer according to claim 6, further comprising a plurality of detectors;

and a plurality of dichroic beam splitters each arranged to divert a predetermined portion of a respective one of the second beams of radiation to a respective one of the detectors, wherein each of the detectors is arranged to detect an intensity of the diverted portion of the respective second beam and to generate a respective intensity measurement signal, the driver circuit being responsive to the intensity measurement signal to control the amplitude of the respective frequency component of the drive signal and thereby the amplitude of the respective second beam of radiation.

10. An angularly resolved scatterometer according to claim 1, wherein the broadband radiation source is a supercontinuum laser.

11. An angularly resolved scatterometer according to claim 1, wherein the broadband radiation source is a xenon lamp.

13. A lithographic cell comprising:

a coater arranged to coat substrates with a radiation sensitive layer;

a lithographic apparatus arranged to expose images onto the radiation sensitive layer of the substrates coated by the coater;

a developer arranged to develop images exposed by the lithographic apparatus; and

an angularly resolved scatterometer according to claim 1.

12. A lithographic apparatus comprising:

an illumination optical system arranged to illuminate a pattern;

a projection optical system arranged to project an image of the pattern onto a substrate; and

an angularly resolved scatterometer including

a broadband radiation source arranged to emit a first beam of radiation having a first wavelength range;

an acousto-optical tunable filter comprising

an acousto-optical crystal arranged to receive the first beam of radiation,

a transducer coupled to the acousto-optical filter and arranged to excite acoustic waves therein, and

a beam selecting device arranged to select as an output beam one of a plurality of beams, output by the acousto-optical crystal in response to the first beam and the acoustic waves, as a second beam of radiation having a second wavelength range, the second wavelength range being narrower than the first wavelength range;

an optical system comprising a high-NA objective lens arranged to direct the second beam of radiation onto a target pattern and to project radiation reflected or scattered by the target pattern onto a detector to obtain a scatterometric spectrum; and

a driver circuit electrically coupled to the transducer and arranged to generate a drive signal therefor, the driver circuit being adapted to control the frequency of the drive signal so as to control the second wavelength range.

14. An inspection method to determine a value related to a parameter of a target pattern printed on a substrate by a lithographic process used to manufacture a device layer on the substrate, the method comprising:

emitting a first beam of radiation having a first wavelength range using a broadband radiation source;

directing the first beam of radiation to an acousto-optical tunable filter comprising an acousto-optical crystal arranged to receive the first beam of radiation, a transducer coupled to the acousto-optical filter and arranged to excite acoustic waves therein and a beam selecting device arranged to select as an output beam one of a plurality of beams, output by the acousto-optical crystal in response to the first beam and the acoustic waves, as a second beam of radiation having a second wavelength range, the second wavelength range being narrower than the first wavelength range;

directing the second beam of radiation onto the target pattern using an optical system comprising a high-NA objective lens and projecting radiation reflected or scattered by the target pattern onto a detector to obtain a scatterometric spectrum; and

providing a drive signal to the transducer, the drive signal having a frequency determined to control the second wavelength range.

15. A device manufacturing method comprising:

forming a pattern on a substrate using a lithographic apparatus; and

determining a value related to a parameter of the pattern formed on the substrate by;

emitting a first beam of radiation having a first wavelength range using a broadband radiation source;

directing the first beam of radiation to an acousto-optical tunable filter comprising an acousto-optical crystal arranged to receive the first beam of radiation, a transducer coupled to the acousto-optical filter and arranged to excite acoustic waves therein and a beam selecting device arranged to select as an output beam one of a plurality of beams, output by the acousto-optical crystal in response to the first beam and the acoustic waves, as a second beam of radiation having a second wavelength range, the second wavelength range being narrower than the first wavelength range;

directing the second beam of radiation onto the target pattern using an optical system comprising a high-NA objective lens and projecting radiation reflected or scattered by the target pattern onto a detector to obtain a scatterometric spectrum;

providing a drive signal to the transducer, the drive signal having a frequency determined to control the second wavelength range.

16. An alignment sensor configured to determine a position of a target pattern printed on a substrate by a lithographic process used to manufacture a device layer on a substrate, the sensor comprising:

a broadband radiation source arranged to emit a first beam of radiation having a first wavelength range;

an acousto-optical tunable filter comprising

an acousto-optical crystal arranged to receive the first beam of radiation,

a transducer coupled to the acousto-optical filter and arranged to excite acoustic waves therein, and

a beam selecting device arranged to select as an output beam one of a plurality of beams, output by the acousto-optical crystal in response to the first beam and the acoustic waves, as a second beam of radiation having a second wavelength range, the second wavelength range being narrower than the first wavelength range;

an optical system comprising a self-referencing interferometer and arranged to direct the second beam of radiation onto the target pattern and to project radiation reflected or scattered by the target pattern onto a detector; and

a driver circuit electrically coupled to the transducer and arranged to generate a drive signal therefor, the driver circuit being adapted to control the frequency of the drive signal so as to control the second wavelength range.

17. An alignment sensor according to claim 16, further comprising a detector;

and a beam splitter arranged to divert a predetermined portion of the second beam to the detector, wherein the detector is arranged to detect the intensity of the diverted portion of the second beam and to generate an intensity measurement signal, the driver circuit being responsive to the intensity measurement signal to control the amplitude of the drive signal and thereby the amplitude of the second beam.

18. An alignment sensor according to claim 16, wherein the drive circuit is arranged to generate a drive signal having a plurality of different frequency components so that the acousto-optical tunable filter is configured to output simultaneously a plurality of second beams of radiation having respectively different wavelength ranges.

19. An alignment sensor according to claim 18, further comprising a detector;

and a beam splitter arranged to divert a predetermined portion of the second beams to the detector, wherein the detector is arranged to detect the intensity of the diverted portion of the second beams of radiation and to generate an intensity measurement signal, the driver circuit being responsive to an intensity measurement signal to control an amplitude of the drive signal and thereby the amplitude of the second beam.

20. An alignment sensor according to claim 19, wherein the beam splitter is a dichroic beam splitter arranged to divert a predetermined portion of a specific one of the second beams of radiation to the detector.

21. An alignment sensor according to claim 18, further comprising a plurality of detectors;

and a plurality of dichroic beam splitters each arranged to divert a predetermined portion of a respective one of the second beams of radiation to a respective one of the detectors, wherein each of the detectors is arranged to detect an intensity of the diverted portion of the respective second beam of radiation and to generate a respective intensity measurement signal, the driver circuit being responsive to the intensity measurement signal to control the amplitude of the respective frequency component of the drive signal and thereby the amplitude of the respective second beam of radiation.