Wave-front aberration metrology of extreme ultraviolet mask inspection systems

Abstract

This invention discloses a measurement system for measuring wavefront aberrations in an extreme ultraviolet (EUV) photomask testing system. The test photomask includes: a substrate formed of a material substantially non-reflective to EUV illumination; and one or more patterns, or the like, formed on the substrate, the one or more patterns having a reflective portion configured to reflect EUV illumination, the reflective portion and an absorptive portion substantially non-reflective to EUV illumination being positioned in a common plane on or above the substrate.

Description

[Technical Field] This invention relates generally to wavefront aberration measurement, and more specifically to wavefront aberration measurement using an extreme ultraviolet (EUV) mask detection system incorporated into a test mask. [Previous Technology] Generally speaking, nanocircuits and their components have become increasingly sensitive to defects. These defects can impair the operation of nanocircuits or adversely affect their yield. Defect detection on nanocircuits is typically performed using an EUV inspection system that illuminates a photomask containing the pattern on which the nanocircuit is fabricated. However, EUV inspection systems rely on an array of optical instruments that use wavefront aberrations that frequently distort the image through the photomask to eliminate defects. Existing methods for measuring and mitigating wavefront aberrations introduced by the optical instruments of EUV inspection systems rely on diagnostic test masks. However, existing diagnostic test masks are susceptible to failures and undesirable performance due to manufacturing processes. For example, existing diagnostic patterns on test masks can introduce shadows or other undesirable reflective effects into the image. Furthermore, existing diagnostic test patterns suffer from a short lifespan due to oxidation. Furthermore, existing methods for measuring and mitigating wavefront aberrations introduced by the optical instruments of EUV inspection systems involve identifying aberrations using systems and procedures separate from the EUV inspection system. These methods do not allow for the quantification and mitigation of wavefront aberrations within the EUV inspection system itself, thereby reducing measurement efficiency. Therefore, it is expected to provide an improved system for in-situ measurement of wavefront aberrations for EUV mask inspection systems. [Summary of the Invention] According to one or more embodiments of the present invention, a test mask for measuring wavefront aberrations of an EUV mask inspection system is disclosed. In one embodiment, the test mask includes a substrate formed of a material that is substantially non-reflective to EUV illumination. In another embodiment, the test mask includes one or more patterns formed on the substrate, wherein the one or more patterns include an absorbing portion configured to absorb EUV illumination and a reflective portion configured to reflect EUV illumination, wherein the reflective portion and the absorbing portion are positioned in a common plane on or above the substrate. According to one or more embodiments of the present invention, an EUV photomask inspection system is disclosed. In one embodiment, the system includes an EUV illumination source. In another embodiment, the system includes one or more EUV illumination optics configured to guide an EUV beam from the EUV illumination source to one or more EUV illumination optics on a test photomask, the test photomask including a substrate formed of a material substantially non-reflective to EUV illumination, one or more test photomasks formed on the substrate, wherein the one or more patterns include an absorbing portion configured to absorb EUV illumination and a reflecting portion configured to reflect EUV illumination, wherein the absorbing portion and the reflecting portion are positioned in a common plane above the substrate, and one or more caps are disposed on at least one of the absorbing portion or the reflecting portion, the one or more caps being formed of a material suitable for reducing oxidation of one or more portions of the test photomask. In another embodiment, the system includes one or more detectors. In another embodiment, the system includes EUV illumination configured to collect reflected EUV illumination from the test diaphragm and direct the EUV illumination to one or more EUV projection optics on one or more detectors. In another embodiment, the system includes one or more controllers having processors communicatively coupled to the one or more detectors, wherein the one or more processors are configured to execute a set of program instructions maintained in memory, and wherein the set of program instructions are configured to cause the one or more processors to receive from the one or more detectors one or more signals indicating the EUV illumination reflected from the test diaphragm, and to identify one or more wavefront aberrations across the EUV beam based on the one or more signals indicating the EUV illumination received from the test diaphragm from the one or more detectors. According to one or more embodiments of the present invention, a method for using an EUV photomask inspection system is disclosed. In one embodiment, the method includes illuminating a test photomask comprising a substrate formed of a material substantially non-reflective to EUV illumination, one or more patterns formed on the substrate, wherein the one or more patterns include an absorbing portion configured to absorb EUV illumination and a reflecting portion configured to reflect EUV illumination, wherein the absorbing portion and the reflecting portion are positioned in a common plane above the substrate, and one or more caps are disposed on at least one of the absorbing portion or the reflecting portion, the one or more caps being formed of a material suitable for reducing oxidation of one or more portions of the test photomask. In another embodiment, the method includes detecting a reflected light beam. In another embodiment, the method includes generating one or more images based on the reflected light beam. In another embodiment, the method includes identifying one or more wavefront aberrations across the one or more images. In another embodiment, the method includes providing adjustments for adjusting one or more components of the EUV photomask inspection system. It should be understood that the above overview and the following detailed description are merely illustrative and not intended to limit the invention as claimed. The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with the overview, serve to explain the principles of the invention.

Implementation Method

Claims

1. A test mask for measuring wavefront aberrations in an extreme ultraviolet (EUV) mask inspection system, comprising: A substrate formed of a material that is substantially non-reflective to EUV illumination; One or more patterns, or the like, are formed on the substrate, wherein the one or more patterns include: an absorbing portion configured to absorb EUV illumination, wherein the absorbing portion includes one or more absorbers and one or more pinholes configured to expose one or more portions of the substrate; a reflecting portion configured to reflect EUV illumination, wherein the reflecting portion and the absorbing portion are positioned in a common plane on or above the substrate, wherein the reflecting portion includes one or more multilayer pillars formed by a plurality of periodically repeating double layers of molybdenum and silicon, wherein the thickness of each layer of the periodically repeating double layers and the periodicity of the periodically repeating double layers are configured to reflect EUV illumination, wherein the one or more multilayer pillars are embedded in the one or more absorbers, wherein the one or more pinholes are disposed between the one or more multilayer pillars; An antireflective coating disposed on one or more absorbers, wherein the antireflective coating is formed of a material substantially nonreflective to EUV illumination, and wherein the antireflective coating is formed of a transition metal nitride complex; and one or more caps disposed on at least one of the absorbing portion or the reflecting portion, the one or more caps being formed of a material suitable for reducing oxidation of one or more portions of the test mask, wherein the antireflective coating can be configured such that the height of the one or more absorbers together with the antireflective coating is equal to the height of the reflecting portion; wherein the thickness of each of the periodically repeating double layers is between approximately 7.0 nm and approximately 7.5 nm; and wherein the one or more multilayer pillars comprise between approximately five and approximately fifteen periodically repeating double layers.

2. The test photomask as requested in claim 1, wherein the substrate is formed of silicon dioxide.

3. The test mask as requested in claim 1, wherein the one or more multilayer pillars have a thickness equal to that of one or more absorbers.

4. The test mask as requested in item 1, wherein the one or more caps are formed of ruthenium.

5. An extreme ultraviolet (EUV) photomask inspection system, comprising: One EUV light source; One or more EUV illumination optics, or the like, configured to guide an EUV beam from the EUV illumination source onto a test mask, the test mask comprising a substrate formed of a material substantially non-reflective to EUV illumination, one or more patterns formed on the substrate, wherein the one or more patterns include: an absorption portion configured to absorb EUV illumination and including one or more absorbers and one or more pinholes configured to expose one or more portions of the substrate; a reflective portion configured to reflect EUV illumination, wherein the absorption portion and the reflective portion are positioned in a common plane on or above the substrate, wherein the reflective portion comprises one or more multilayer pillars formed of a plurality of periodically repeating double layers of molybdenum and silicon, wherein each layer of the periodically repeating double layers... The thickness and periodicity of the periodically repeating double layers are configured for reflecting EUV illumination, wherein one or more multilayer pillars are embedded in one or more absorbers, wherein one or more pinholes are disposed between one or more multilayer pillars; an anti-reflective coating is disposed on one or more absorbers, wherein the anti-reflective coating is formed of a material that is substantially non-reflective to EUV illumination, and wherein the anti-reflective coating is formed of a transition metal nitride complex; and one or more caps are disposed on at least one of the absorbing portion or the reflecting portion, wherein the one or more caps are formed of a material suitable for reducing oxidation of one or more portions of the test mask, wherein the anti-reflective coating can be configured such that the height of the one or more absorbers together with the anti-reflective coating is equal to the height of the reflecting portion; One or more detectors; one or more EUV projection optics, or the like, configured to collect EUV illumination reflected from the test diaphragm and direct the EUV illumination onto the one or more detectors; and one or more controllers, wherein the one or more controllers include one or more processors communicatively coupled to the one or more detectors, wherein the one or more processors are configured to execute a set of program instructions maintained in memory, wherein the set of program instructions are configured to cause the one or more processors to: receive from the one or more detectors one or more signals indicating the EUV illumination reflected from the test diaphragm; and identify one or more wavefront aberrations across the EUV beam based on the one or more signals indicating the EUV illumination reflected from the test diaphragm from the one or more detectors; wherein the thickness of each of the periodically repeating double layers is between approximately 7.0 nm and approximately 7.5 nm; and wherein the one or more multilayer pillars comprise between approximately five and approximately fifteen periodically repeating double layers.

6. The system of claim 5, wherein the substrate is formed of silicon dioxide.

7. The system of claim 5, wherein the absorbing portion and the reflecting portion are disposed on the substrate.

8. The system of claim 7, wherein the one or more absorbers are coated with a material that is substantially non-reflective to EUV illumination.

9. The system of claim 5, wherein the one or more multi-layer columns have a thickness equal to the thickness of the one or more absorbers.

10. The system of claim 5, wherein the one or more multi-layer pillars are embedded in the one or more absorbers.

11. The system of claim 5, wherein the one or more processors are configured to provide adjustments for adjusting at least one of the EUV illumination source, one or more EUV illumination optics, or one or more EUV projection optics to compensate for one or more of the identified wavefront aberrations in the EUV beam.

12. A method for detecting using an extreme ultraviolet (EUV) photomask system, comprising: The illumination includes a test mask formed from a substrate of a material substantially non-reflective to EUV illumination, with one or more patterns formed on the substrate, wherein the one or more patterns include: an absorbing portion configured to absorb EUV illumination and including one or more absorbers and one or more pinholes configured to expose one or more portions of the substrate; and a reflective portion configured to reflect EUV illumination, wherein the absorbing portion and the reflective portion are positioned in a common plane on or above the substrate, wherein the reflective portion includes one or more multilayer pillars formed from a plurality of periodically repeating double layers of molybdenum and silicon, wherein the thickness of each layer of the periodically repeating double layers and the periodicity of the periodically repeating double layers are configured for reflection. The test mask is equipped with EUV illumination, wherein one or more multilayer pillars are embedded in one or more absorbers, wherein one or more pinholes are disposed between the one or more multilayer pillars; one or more caps are disposed on at least one of the absorbing portion or the reflecting portion; and an anti-reflective coating is disposed on the one or more absorbers, wherein the anti-reflective coating is formed of a material that is substantially non-reflective to EUV illumination, and wherein the anti-reflective coating is formed of a transition metal nitride complex, the one or more caps are formed of a material suitable for reducing oxidation of one or more portions of the test mask, and wherein the anti-reflective coating can be configured such that the height of the one or more absorbers together with the anti-reflective coating is equal to the height of the reflecting portion; Detect a reflected light beam; generate one or more images based on the reflected light beam; identify one or more wavefront aberrations across the one or more images; and provide adjustments for adjusting one or more components of the EUV detection system; wherein the thickness of each of the periodically repeating double layers is between approximately 7.0 nm and approximately 7.5 nm; and wherein the one or more multilayer pillars comprise between approximately five and approximately fifteen periodically repeating double layers.

13. The method of claim 12, wherein the substrate is formed of silicon dioxide.

14. The method of claim 12, wherein the absorbing portion and the reflecting portion are disposed on the substrate.

15. The method of claim 14, wherein the one or more absorbers are coated with a material that is substantially non-reflective to EUV illumination.

16. The method of claim 12, wherein the one or more multilayer columns have a thickness equal to the thickness of the one or more absorbers.

17. The method of claim 12, wherein illuminating a test hood includes directing an EUV incident beam onto the test hood.

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