Illumination source for an inspection apparatus, inspection apparatus and inspection method

• US 10,642,172 B2
• Filed: 04/30/2019
• Issued: 05/05/2020
• Est. Priority Date: 05/14/2018
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: O Dwyer, David, Smorenburg, Petrus Wilhelmus, Brussaard, Gerrit Jacobus Hendrik
• Primary Examiner(s): Iacoletti, Michelle M
• Application Number:
  US16/399,372
• Publication Number:
  US 20190346776A1
• Time in Patent Office: 371 Days
• Field of Search: None
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G01N 21/4788 Diffraction for sizing particles G01N15/0205
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• 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: G02B 27/095 Refractive optical elements
• CPC Class Codes: G02B 27/0955 Lenses lenses per se G02B3/00
• CPC Class Codes: G02B 5/001 Axicons, waxicons, reflaxicons
• CPC Class Codes: G02F 1/0102 Constructional details, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/3503 Structural association of optical elements, e.g. lenses, with the non-linear optical device
• CPC Class Codes: G02F 1/353 Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
• CPC Class Codes: G02F 1/354 Third or higher harmonic generation
• CPC Class Codes: G03F 7/70025 by lasers
• CPC Class Codes: G03F 7/70033 by plasma extreme ultraviolet [EUV] sources
• CPC Class Codes: G03F 7/7015 Details of optical elements
• CPC Class Codes: G03F 7/70158 Diffractive optical elements
• CPC Class Codes: G03F 7/70616 Monitoring the printed patterns
• 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 7/70641 Focus
• CPC Class Codes: G03F 7/7065 Defects, e.g. optical inspection of patterned layer for defects
• CPC Class Codes: G03F 9/7065 : Production of alignment light, e.g. light source, control of coherence, polarization, pulse length, wavelength
• CPC Class Codes: H01S 3/0092 : Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H05G 2/003 : being produced from a liquid or gas

Abstract

An illumination source apparatus (500), suitable for use in a metrology apparatus for the characterization of a structure on a substrate, the illumination source apparatus comprising: a high harmonic generation, HHG, medium (502); a pump radiation source (506) operable to emit a beam of pump radiation (508); and adjustable transformation optics (510) configured to adjustably transform the transverse spatial profile of the beam of pump radiation to produce a transformed beam (518) such that relative to the centre axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the centre axis of the transformed beam has a non-zero intensity, wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation (540), wherein the location of said outer region is dependent on an adjustment setting of the adjustable transformation optics.

Claims

1. An illumination source apparatus, suitable for use in a metrology apparatus for characterization of a structure on a substrate, the illumination source apparatus comprising:

a high harmonic generation, HHG, medium;

a pump radiation source operable to emit a beam of pump radiation; and

adjustable transformation optics configured to adjustably transform a transverse spatial profile of the beam of pump radiation to produce a transformed beam such that relative to a center axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the center axis of the transformed beam has a non-zero intensity,

wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation,

wherein the location of the outer region is dependent on an adjustment setting of the adjustable transformation optics,

wherein the transformed beam is a collimated annular beam having an inner ring radius R₁ and an outer ring radius R₂ , and

wherein the adjustment setting of the adjustable transformation optics is configured to independently tune the inner ring radius R₁ and the outer ring radius R₂.

2. The illumination source apparatus of claim 1, further comprising:

a focussing element positioned between the adjustable transformation optics and the HHG medium, the focussing element configured to focus the transformed beam into the HHG medium, and wherein the focussing element is a lens.

3. The illumination source apparatus of claim 2, wherein the focal plane of the focussing element is positioned substantially in the HHG medium.

4. The illumination source apparatus of claim 1, wherein the adjustable transformation optics comprise at least one diffractive optical element or conical optical element.

5. The illumination source apparatus of claim 4, wherein the at least one diffractive optical element or conical optical element is an axicon element.

6. The illumination source apparatus of claim 1, wherein:

the adjustable transformation optics comprise a pair of axicon elements consisting of a first axicon element and a second axicon element;

the first axicon element precedes the second axicon element relative to the propagation direction of the beam of pump radiation; and

an axial separation between the first axicon element and the second axicon element controls the adjustment setting of the adjustable transformation optics.

7. The illumination source apparatus of claim 6, wherein:

the pair of axicon elements consists of one negative axicon element and one positive axicon element; and

at least one of the axicon elements is a reflective axicon element, a refractive axicon element, or a diffractive axicon element.

8. The illumination source apparatus of claim 6, wherein:

each axicon of the pair of axicon elements has substantially the same apex angle,τ

, or the same divergence angle, β

, and the axicon elements are mounted on one or more movable mounts such that the axial separation, D₁, between the axicon elements is adjustable in use to control the adjustment setting.

9. The illumination source apparatus of claim 8, further comprising:

a blocking element positioned after the HHG medium, the blocking element configured to suppress the residual transformed beam remaining after high harmonic generation, whilst substantially transmitting the generated high harmonic radiation, and

wherein the blocking element is an output aperture aligned with a center axis of the generated high harmonic radiation.

10. The illumination source apparatus of claim 9, wherein in use the axial separation of the axicons, D₁, is selected by the one or more movable mounts in order to optimize, for a given axicon apex angle τ

or a given divergence angle β

;

(A) the conversion efficiency of the high harmonic generation process; and

/or

(B) the suppression of the residual transformed beam.

11. The illumination source apparatus of claim 10, wherein:

the adjustable transformation optics further comprise a variable beam expander/contractor configured to adjust the input waist size, w₀, of the beam of pump radiation, and

in use w₀ is selected in order to further optimize (A) and (B).

12. The illumination source apparatus of claim 11, wherein:

R₁=D₁ tan(γ

); and

R₂=R₁+w₀,

where γ

is the deflection angle (as defined herein) of the axicon,

the adjustable transformation optics further comprise an input aperture located on the center axis of the beam of pump radiation,

the input aperture is positioned after the axicon elements and prior to the HHG medium with respect to the direction of propagation of the beam of pump radiation,

the focussing element is configured to image the input aperture onto the blocking element,

in use the aperture size of the input aperture is selected in order to further optimize (A) and (B), and

the input aperture is configured to adjust the outer ring radius R₂.

13. A method of operating an illumination source apparatus, suitable for use in a metrology apparatus for the characterization of a structure on a substrate, the method comprising:

providing a high harmonic generation, HHG, medium;

operating a pump radiation source to emit a beam of pump radiation; and

transforming, by adjustable transformation optics, a transverse spatial profile of the beam of pump radiation to produce a transformed beam such that relative to a center axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the center axis of the transformed beam has a non-zero intensity,

wherein the transformed beam excites the HHG medium so as to generate high harmonic radiation,

wherein the location of the outer region is dependent on an adjustment setting of the adjustable transformation optics,

wherein the transformed beam is a collimated annular beam having an inner ring radius R₁ and an outer ring radius R₂, and

wherein the inner ring radius R₁ and the outer ring radius R₂ are independently tuned by the adjustment setting of the adjustable transformation optics.

14. A lithographic apparatus comprising:

an illumination source apparatus, suitable for use in a metrology apparatus for characterization of a structure on a substrate, the illumination source apparatus comprising;

a high harmonic generation, HHG, medium;

a pump radiation source operable to emit a beam of pump radiation; and

adjustable transformation optics configured to adjustably transform a transverse spatial profile of the beam of pump radiation to produce a transformed beam such that relative to a center axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the center axis of the transformed beam has a non-zero intensity,

wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation,

wherein the location of the outer region is dependent on an adjustment setting of the adjustable transformation optics,

wherein the transformed beam is a collimated annular beam having an inner ring radius R₁ and an outer ring radius R₂,and

wherein the adjustment setting of the adjustable transformation optics is configured to independently tune the inner ring radius R₁ and the outer ring radius R₂.

15. A metrology apparatus comprising:

an illumination source apparatus, suitable for use in a metrology apparatus for characterization of a structure on a substrate, the illumination source apparatus comprising;

a high harmonic generation, HHG, medium;

a pump radiation source operable to emit a beam of pump radiation;

adjustable transformation optics configured to adjustably transform a transverse spatial profile of the beam of pump radiation to produce a transformed beam such that relative to a center axis of the transformed beam, a central region of the transformed beam has substantially zero intensity and an outer region which is radially outwards from the center axis of the transformed beam has a non-zero intensity; and

an output aperture positioned after the HHG medium and aligned with a center axis of generated high harmonic radiation from the HHG medium, the output aperture configured to suppress a residual transformed beam remaining after high harmonic generation and substantially transmit the generated high harmonic radiation,

wherein the transformed beam is arranged to excite the HHG medium so as to generate high harmonic radiation,

wherein the location of the outer region is dependent on an adjustment setting of the adjustable transformation optics.

16. The metrology apparatus of claim 15, wherein:

the adjustable transformation optics comprise a pair of axicon elements consisting of a first axicon element and a second axicon element;

the first axicon element precedes the second axicon element relative to the propagation direction of the beam of pump radiation; and

an axial separation between the first axicon element and the second axicon element controls the adjustment setting of the adjustable transformation optics.

17. The metrology apparatus of claim 16, wherein:

each axicon of the pair of axicon elements has substantially the same apex angle, τ

, or the same divergence angle, β

, and the axicon elements are mounted on one or more movable mounts such that the axial separation, D₁, between the axicon elements is adjustable in use to control the adjustment setting.

18. The metrology apparatus of claim 17, wherein in use the axial separation of the axicons, D₁, is selected by the one or more movable mounts in order to optimize, for a given axicon apex angle τ

or a given divergence angle β

;

(A) the conversion efficiency of the high harmonic generation process; and

/or

(B) the suppression of the residual transformed beam.

19. The metrology apparatus of claim 18, wherein:

the adjustable transformation optics further comprise a variable beam expander/contractor configured to adjust the input waist size, w₀, of the beam of pump radiation, and

in use w₀ is selected in order to further optimize (A) and (B).

20. The metrology apparatus of claim 19, wherein:

the transformed beam is a collimated annular beam having an annulus radius R₁ and a ring width R₂, wherein;

R₁=D₁ tan(γ

); and

R₂=R₁+w₀,

where γ

is the deflection angle (as defined herein) of the axicon,

the adjustable transformation optics further comprise an input aperture located on the center axis of the beam of pump radiation,

the input aperture is positioned after the axicon elements and prior to the HHG medium with respect to the direction of propagation of the beam of pump radiation,

the focussing element is configured to image the input aperture onto the blocking element,

in use the aperture size of the input aperture is selected in order to further optimize (A) and (B), and

the input aperture is configured to adjust the ring width R₂.