EP3610222A1

EP3610222A1 - System and method for super-resolution full-field optical metrology on the far-field nanometre scale

Info

Publication number: EP3610222A1
Application number: EP18720128.0A
Authority: EP
Inventors: Paul Montgomery; Sylvain LECLER; Stéphane PERRIN; Audrey LEONG-HOI
Original assignee: Centre National de la Recherche Scientifique CNRS; Universite de Strasbourg
Current assignee: Centre National de la Recherche Scientifique CNRS; Universite de Strasbourg
Priority date: 2017-04-11
Filing date: 2018-04-11
Publication date: 2020-02-19
Also published as: CN110770534A; KR20190138788A; EP3388779A1; US20200103224A1; WO2018189250A1

Abstract

A system of super-resolution full-field optical metrology for delivering information on the surface topography of a sample or object (6) on the far-field nanometre scale, comprising a light source (2), an interferometer (1a, 1b, 1c, 1d) comprising a reference arm incorporating a microbead (9) and a mirror (10), an object arm including a microbead (7) similar to said microbead (9) and arranged in immediate proximity to the surface (22) of the object (6), receiving means (5) for capturing the interference figures, and means for processing these interference figures in such a way as to produce surface topography information. The light source (2) is temporally coherent or partially coherent. The interferometer and the means for processing interference figures are designed to reconstruct the surface of the object (6) by phase shifting interferometry.

Description

"Full-field optical metrology system and method in nanoscale super-resolution in far-field"

Technical area

The present invention relates to a super-resolution full-field optical metrology system and method for providing surface topography information of a nanoscale far-field sample. It is also aimed at a metrology method implemented in this system.

This system and this method particularly aim at super-resolution optical profilometry. His interest concerns the nanometric spatial resolution, beyond the diffraction limit, obtained in the three directions of space.

State of the art

An optical profilometer is a non-contact metrology instrument used to reconstruct the surface topography of an object. There are several optical profilometry techniques such as confocal microscopy, structured light projection and interferometric microscopy.

The principle of optical interferometry is similar to that of acoustic echography because it allows reconstructing the depth information of an object by measuring the flight time of a wave reflected by a junction between two materials of different indices. of this object. In other words, in ultrasound, the wave emitted by the transducer is reflected by a junction and is then collected by a receiver. The duration between transmission and reception is called flight time. By making the link between speed, time and distance, we can then find the relative position of the junction. In interferometry, it's the same idea; that is to say measure the flight time. On the other hand, the speed of the light being much higher than the speed of the sound, no sensor, at the moment, is able to measure this duration. This technique therefore requires a more complex configuration by adding for example a reference arm. In interferometry, the signal recorded by the receiver (an intensity image) is called an interference pattern that carries optical path difference information. The receiver is generally a CCD (Charge Coupled Device) or CMOS (English Complementary Metal Oxide Semiconductor) matrix. By measuring the optical path difference between the reference wave (which is reflected by a mirror) and the wave reflected by the junction of the object, we can then go back to the height information.

An interferometric profilometer therefore uses this principle to reconstruct the topography of an object. Interferometry brings together two main measurement methods based on their illumination. Also, to further diversify these two methods, there are multiple ways to interpret the results and reconstruct the topography.

The first profilometry method uses a temporally coherent illumination. It comprises two methods for reconstructing the topography which are digital holography and phase shift interferometry.

In digital holography (holography), the depth information (or optical path difference) on each pixel depends on the phase shift between the reference wave and the object wave. The detector collects the interference pattern. Then, by algorithms based on wave propagation and the Fourier transform, we find the phase shift between the object wave and the reference wave. The technique has the advantage of requiring only one acquisition. In contrast, unlike phase shift interferometry, it requires a spatially coherent source and a more complex algorithm method.

In phase shifting interferometry (phase shifting interferometry), the phase difference between the object wave and the reference wave is calculated from a series of phase-shifted interference patterns, allowing find the optical path difference on each pixel. The phase shift is applied by moving axially, by a known distance, the reference object or mirror. This technique allows a very high axial sensitivity, typically less than 1 nm. These two techniques in coherent optical metrology light are currently little used for optical profilometry because they are dependent on the coherence noise and the scab and speckle effects induced.

In coherent interferometry, the coherence function is approximated to 1. So the term optical path difference is therefore found in the phase term. On the other hand, the second profilometry method uses an incoherent or partially incoherent illumination temporally (that is to say a polychromatic light source, for example a halogen lamp or an LED light emitting diode). Here, the principle is based on the fact that the interaction between two incoherent or partially incoherent waves forms an interference signal carried by a signal which is called the coherence function which carries the optical path difference information on each pixel. Mathematically, this coherence function is expressed as a Fourier transform of the spectrum of the light source. The narrower the spectrum (in the case of a monochromatic source), the wider is the coherence function, and vice versa.

Here, the depth information does not come from the phase term but from the coherence term which also carries the optical path difference information on each pixel. The detector records the luminous irradiance on each pixel which is the sum of the magnitudes of the object and reference waves, squared. By axially moving the reference object or mirror, an interferogram is obtained on each pixel as a function of the position of the object. When the optical path difference between the plane of the mirror and the junction of the object is zero, the value of the envelope of the fringes is maximum on each pixel and a peak of intensity appears. In other words, by scanning the difference in optical path along the optical axis, the method detects this peak of the envelope per pixel and then goes back to the depth information of the object.

This technique is called white light interferometry or CSI (English Coherence Scanning Interferometry). It can be used both for surface reconstruction (topography) but also for volume (tomography). The half-height width of the source coherence function is called the coherence length and is an axial resolution criterion. The larger the spectrum, the better the axial resolution. The method makes it possible to obtain an axial sensitivity of less than one hundred nanometers per sampling step. Envelope interpolation methods improve the sensitivity to ten nanometers (using mathematical interpolation) up to a few nanometers (using phase interpolation) depending on the roughness of the surface.

However, the lateral resolution of an optical profilometer is limited by diffraction mainly from the microscope objective.

According to Abbe's criterion, the theoretical value of the resolution in incoherent imaging is · / (2/7 sin ·) where · is the wavelength, · is the half-angle of the detection cone of the system optics and n the refractive index of the medium. Since the value of sin · is less than 1, the resolution is greater than · / (2/7). Recently, new experimental methods have made it possible to exceed this limit in optics using the principle of stimulated emission or lenses with a negative refractive index. On the other hand, these methods can not be applied to full-field interferometry.

In 2010, Z. Wang et al. (Nature Communications !, 218 (2011)) proposed an incoherent imaging method that allows acquisition of a full-field image by placing a glass microbead on the sample. This projects a virtual and enlarged image of the object under the surface of the sample. The virtual image is then collected by a microscope objective. The microbead, transparent to the wavelength range of the source, collects the evanescent waves and converts them into propagative waves. Thus, it can be glass, silica, polystyrene, melamine formaldehyde, barium titanate (immersion case), etc. In addition, depending on its diameter (between 3 μm and 150 μm) and its refractive index contrast (between 1.2 and 2.0), the performance varies. The index contrast is defined as the ratio between the refractive index of the microbead and the refractive index of the environment. A resolution 50 nm lateral has been shown (Nature Communications !, 218 (2011)). Since then, the phenomenon of super lateral resolution has been the subject of numerous research and numerous scientific publications for 2D imaging.

This phenomenon applies to lateral resolution, that is to say 2D imaging. By placing a microbead in the object arm of a Linnik interferometer, it has been shown the possibility of reconstructing in 3D an object with a high axial and lateral resolution. We can notably cite the publication of F. Wang et al. (Scientific Reports6, 24703 (2016)) on super resolution applied to white light interferometry or CSI. In this publication, the consistency function is used to retrieve the depth information of the object. It is therefore necessary to use a light source with low temporal coherence, usually referred to as a white light source.

For the use of microbeads in metrology in super resolution at the nanoscale, mention may especially be made of the documents CN 103823353 "Sub wavelength super-resolution digital holography imaging system based on microspheres", WO2013043818 "Microsphere superlens based super resolution imaging platform" or CN 102735878 "Super resolution microscopic imaging method and system based on micro cantilever and microsphere combined probe".

The aim of the present invention is to propose a full-field optical profilometry system in super-resolution, in far-field and in coherent or partially coherent illumination which presents better performances than the current methods mentioned above, both in terms of axial resolution and terms of measurement sensitivity. The phase shift interferometry technique is used to find the optical path distribution of the sample. Presentation of the invention

This objective is achieved with a super-resolution full-field optical metrology system for delivering information on the surface topography of a nanoscale sample or object in the far field, including a coherent light source or partially coherent, an interferometer comprising an object arm incorporating a transparent microbead and disposed in close proximity to the surface of the object, a reference arm incorporating a mirror, receiving means for capturing interference patterns, and means for processing said interference patterns so as to produce said surface topography information, said interferometer and said interference figure processing means being arranged to reconstruct the topography of the object by phase shift interferometry.

The microbeads used in the profilometry system according to the invention promote the evanescent wave phenomenon and thus contribute to providing a full-field image in super-resolution, which the scanning profilometric systems of the prior art do not allow. not.

It is understood that the microbeads used in the profilometry system according to the invention may be spherical, elliptical, hemispherical and more generally convex. The temporally coherent or quasi-coherent light source may have a wavelength in the infra-red, the visible or the near ultraviolet.

In a first embodiment, the interferometer is arranged to provide measurements in reflective configuration and may be of a type selected from the group of interferometers Michelson (la), Twyman-Green (Ib), Mirau (le) and Mach Zehnder.

In another embodiment, the interferometer may be arranged to provide measurements in a transmissive configuration and may be Mach Zehnder (1d).

In the prior art, the microbeads are deposited on the surface of the object. This can damage the object in the case for example biological samples or when the material of the object has a lower coefficient of hardness than the material of the microbead. By positioning the microbead a few nanometers away from the surface of the object, a non-contact measurement can be provided. In an advantageous form of the invention, the microbead is thus kept out of contact with the surface of the the sample. The microbead is held by a support (for example mechanical tip type, optical clamp or pierced grid system).

This microbead can also be held above the surface of the sample by a piezoelectric displacement plate provided with means for holding said microbead.

This microbead can also be held above the surface of the sample by a micromanipulator arm provided with means for holding said microbead or by an optical clamp. In a particular embodiment of a system according to the invention, the microbead is placed in a micro-grid disposed above the surface of the sample and having holes of diameter substantially smaller than that of said microbead.

It may for example be placed in a gaseous medium, liquid or solid and of refractive index lower than that of said microbead, or in a transparent layer of refractive index lower than that of said microbead and disposed on the surface of the microbead. 'sample.

The microbead (spherical, elliptical, hemispherical, convex) can be advantageously arranged to concentrate a light beam (commonly known as the photonic jet) on the object.

In another particular embodiment, the reference arm also incorporates a microbead similar to the microbead of the object arm, said microbead of the reference arm being arranged to compensate for the dispersion.

It is also possible to provide an arrangement of the microbeads in a translatable matrix configuration making it possible to reconstruct a larger field of view.

According to another aspect of the invention, there is provided a super-resolution full-field optical profilometry method for providing surface topography information of a nanoscale sample in the far field, implemented in a system. optical metrology system according to the invention, said system incorporating an interferometer comprising an object arm provided with a microbead disposed in close proximity to the surface of the sample and arranged to provide interference patterns. The method according to the invention comprises:

an illumination of said surface via the microbead, for example of spherical, elliptical, hemispherical or convex shape, by a light source coherent or quasi-coherent temporally with a wavelength in the visible or the ultraviolet or the infrared, and

processing of said interference patterns to reconstruct the surface of the sample by phase shift interferometry.

It can also advantageously comprise a concentration of a light beam on the object (photonic jet), and be arranged to provide interferometric measurements in reflective configuration.

In a particular form of implementation of the optical metrology method according to the invention, the processing of the interference figures comprises:

A production, from interference patterns, of a raw signal of the measured phase modulo 2π,

A division of said raw phase signal into an area of interest of the sample so as to limit edge effects,

An unfolding of the modulo 2π phase image thus obtained in two dimensions,

An adjustment of said phase image thus unfolded, so as to eliminate effects of aberrations,

A conversion of said phase image thus unfolded and then adjusted, into a height distribution, and

- A treatment of said height distribution for drawing surface profiles of said sample.

Description of figures

Other advantages and particularities of the invention will appear on reading the detailed description of implementations and non-limiting embodiments, and the following appended drawings:

FIG. 1 diagrammatically illustrates four optical configurations used in reflection and an optical configuration used in transmission, for a metrology system according to the invention, FIG. 2 schematically illustrates a device for positioning a microbead with respect to the surface of a sample,

FIG. 3 schematically illustrates a matrix arrangement of microbeads (in this case of the hemispherical type),

FIG. 4 schematically illustrates a succession of steps implemented in the optical metrology method according to the invention, and

- Figure 5 schematically illustrates a variant of the positioning device of a microbead with respect to the surface of a sample, implementing a piezoelectric actuator.

Detailed embodiments

These embodiments being in no way limiting, it will be possible to consider variants of the invention comprising only a selection of characteristics described or illustrated subsequently isolated from the other characteristics described or illustrated (even if this selection is isolated within a phase comprising these other characteristics), if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art. This selection comprises at least one preferably functional characteristic without structural details, and / or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention from the state of the art. earlier.

Referring to FIG. 1, three variants of an optical metrology system operating in a reflective configuration respectively based on a Michelson I interferometer, a Twyman-Green I interferometer and a Mirau I interferometer, and a variant operating in a transmissive configuration. Based on a Mach Zehnder ld interferometer are described according to the invention.

The components common to these four embodiments are identified in the following with identical references.

The Michelson type configuration requires an illumination part comprising a source 2 which is coherent or partially temporally coherent, a collimator and a beam splitter 3, and an imaging part comprising the Michelson interferometer, a tube lens 4, a detector 5 and a device 8 for processing these interference patterns in order to generate profiles of surface of an object or sample 6.

An assembly (not shown in FIG. 1) of lenses and diaphragms makes it possible to obtain an illumination of the homogeneous object in intensity. In the Michelson interferometer, the reference and object arms are perpendicular to each other. The incident beam on a converging lens or a lens assembly 11 is separated into beam fractions by a beam splitter 12 and oriented in the reference arm and the object arm. The reference arm comprises a microbead or a matrix of microbeads 9 (spherical, elliptical, hemispherical, convex) and a mirror 10. The microbead is in contact or not on the mirror. The object arm comprises a microbead or a matrix of microbeads 7 similar to said microbead of the reference arm, and the object or sample 6 to be characterized in reflection mode.

The detector 5 captures interference patterns produced by the interference of an object beam from the object arm and a reference beam from the reference arm, and a device 8 processes these interference patterns to generate surface profiles of the sample 6.

The tube lens 4 is disposed at the output of the beam splitter 3 in order to converge the two measurement and reference beams in interference towards the detector 5, while the second lens 11 is arranged between the first separator device 3 and the second separator device 12 to converge the illumination beam to the object 6 to be measured.

The numerical aperture of the lens 11 is in practice limited by its working distance and therefore is generally less than 0.3. With a microbead diameter greater than 30 pm, this allows to obtain a large field of view.

The Twyman-Green configuration lb shown in FIG. 1 is a variant of the Linnik configuration which is itself an improvement of the Michelson configuration in that it provides better lateral resolution. This architecture requires an illumination part comprising a temporally coherent or partially coherent source 2 provided with a collimator, and an imaging part comprising a Twyman-Green interferometer, a tube lens 4, a detector 5 connected to a signal processing unit 8 in order to generate the topography of an object or sample 6. An assembly (not shown in FIG. 1) of lenses and diaphragms makes it possible to obtain an illumination of the homogeneous object in intensity.

In the Twyman-Green interferometer, the reference and object arms are perpendicular to each other and coupled by a beam splitter 12. The beam fractions are incident on two converging lenses or two lens assemblies (one in each arm). and 14. A portion of the beam is transmitted in the reference arm. The beam is then focused by the lens 14 and the microbead or a matrix of microbeads 9 (spherical, elliptical, hemispherical, convex) on the reference mirror 10 and reflected by the latter. The microbead 9 is in contact or not on the mirror 10. The reflected wave is collected by the microbead 9 and the lens 14. The second part of the beam is reflected by the separator 12 and then directed into the object arm of the interferometer. The second lens 13 focuses the beam on the surface of the object 6 to be characterized in reflection mode, via a microbead 7 similar to the microbead 9 of the reference arm and disposed in the immediate vicinity of this object. The wave is then reflected or diffused by the surface of the object 6 and then collected via the microbead 7 by the lens 13. Like the reference wave, the object wave is transmitted by the tube lens 4 and then imaged on the detector 5.

The detector 5 captures interference patterns produced by the interference of an object beam from the object arm and a reference beam from the reference arm, and a device 8 processes these interference patterns to generate surface profiles of the sample 6. The tube lens 4 is disposed at the output of the separator 12 in order to converge the two measurement and reference beams in interference towards the detector 5.

The numerical aperture of the two identical lenses 13 and 14 is in practice not limited by its working distance and therefore makes it possible to acquire with a high lateral resolution. The architecture of Twyman Green presents the interest of a compromise between lateral resolution and field of view.

The Mirau configuration shown in Figure 1 has an advantage over other architectures which is that of a reduction in size. Indeed, the reference arm is superimposed on the object arm and the optical axes of the reference and object arms are then merged. This architecture requires an illumination part comprising a temporally coherent or partially coherent source 2 provided with a collimator and a beam splitter 3, and an imaging part comprising the Mirau interferometer, a tube lens 4, a detector 5 and a device 8. processing these interference patterns. An assembly (not shown in FIG. 1) of lenses and diaphragms makes it possible to obtain an illumination of the homogeneous object in intensity.

In the Mirau interferometer, the reference and object arms are parallel to each other. The incident beam on a converging lens or a lens assembly 11 is separated into fractions by a beam splitter 12 and oriented in reference arm and the object arm. The reference arm comprises a microbead or a matrix of microbeads 9 (spherical, elliptical, hemispherical, convex) and a mirror 10. The microbead is in contact or not on the mirror. The object arm comprises a microbead or a matrix of microbeads 7 similar to the microbead of the reference arm, and the object 6 to be characterized in reflection mode.

The detector 5 captures interference patterns produced by the interference of an object beam from the object arm and a reference beam from the reference arm, and a device 8 processes these interference patterns to generate surface profiles of the sample 6. The tube lens 4 is disposed at the output of the beam splitter 3 in order to converge the two measurement and reference beams in interference towards the detector 5, while the second lens 11 is arranged between the first separator device 3 and the second separator device 12 to converge the illumination beam towards the object 6 to be measured and the reference mirror 10.

The numerical aperture of the lens 11 is in practice limited by its working distance and therefore is generally less than 0.5. With a microbead diameter greater than 30 μιτι, this allows to obtain a large field of view.

A configuration ld of an optical metrology system employing a Mach Zehnder type interferometer adapted for transmission measurements will now be described with reference to FIG. Transmission measurements are mainly used in biology because the samples are often transparent at the wavelength.

A measurement in transmission makes it possible to go back to the difference in optical path induced by the crossed object. Knowing the refractive index of the object, we find the geometric height of the object, and vice versa.

The light beam originating from a coherent or partially coherent source 2 is divided in two by a beam splitter 12. The beam transmitted by the separator 12, called the object beam, passes through an object or sample 6, after being possibly focused by an optional lens 15 which is provided to focus the energy of the light on the desired field of view and thus harvest more light thereafter.

A microbead 7 then a lens 11 collect the beam scattered by the object 6. A mirror 16 directs this object beam on a detector 5 by passing through a beam splitter 18 and a tube lens or relay lens 4.

The beam reflected by the beam splitter 12, referred to as the reference beam, is directed by a mirror 17 towards the beam splitter 18 where it is again directed on the detector 5 via the tube lens 4. The device 8 for processing the interference patterns then makes it possible to find the lateral distribution (that is to say according to X and Y) of the optical path of the object, in particular refractive index and geometric height information. .

In the four configurations 1a, 1b, 1c, and 1d just described, the reference mirror 10 may be attached to a piezoelectric device (not shown) which is controlled to provide lateral displacement of this mirror 10 around of a position of equilibrium, so as to obtain the phase shift. The microbeads 7 can be maintained at small distance from the object 6 by another device ^¬ piezo electrical connector (not shown).

It is important to note that, according to the invention, in the optical metrology systems which have just been described, it is possible to modify the polarization via polarisers and delay plates, the uniformity of the illumination of the object via a lighting system, and the angles of the rays incident on the sample.

The microbeads 7, 9, which are implemented in the systems 1a, 1b, 11d and 1d of optical metrology according to the invention described above with reference to FIG. 1, can be placed in the air or immersed in a transparent material of gaseous, liquid or solid type (for example, a polymer such as polydimethylsiloxane or PDMS).

In the various cases which have just been described, the measurable quantity in an optical metrology system according to the invention is a two-dimensional image or series of intensity images which is more commonly referred to as an interference figure. The information found is then the surface topography of the object via phase shift interferometry. This phase shift method is faster than the known method of detecting the peak of the coherence function because it requires fewer acquisitions, and provides better axial resolution. Four images are enough to reconstruct the surface topography of the object. The phase shift calculated between the reference wave and the object wave (interpreted as a delay of the wave) makes it possible to find the surface reliefs, that is to say the topography, via a conventional formula taking into account the dispersion of the microbead. For the different embodiments that have just been described, the light source 2 must provide a high degree of coherence. In addition, numerical simulations as well as experimental measurements have shown that the use of a light source with a short wavelength provides greater lateral resolution. For example, a blue and near UV light source brings greater lateral resolution.

The light source 2 can be:

coherent, for example a laser source with a coherence length of the meter,

quasi-coherent, for example a laser diode with a centimeter coherence length,

partially coherent, for example a superluminescent diode with a coherence length of about one hundred micrometers,

partially incoherent, for example an electroluminescent diode with a coherence length of about ten micrometers,

- narrowly filtered in wavelengths, for example a super-continuum and a filter,

in all cases, preferably with a short wavelength or with a spectrum centered on a short wavelength, in green, blue or even ultraviolet, for example a 450 nm blue LED .

The performance of a super resolution profilometer according to the invention depends on several parameters such as the combination between the lens or the assembly of collection lenses and the microbead, and the wavelength. It has been shown that a Twyman-Green configuration interferometer 1b described above with reference to FIG. 1 and comprising a near-low wavelength light source and a glass microbead having a diameter between 10 μm and 30 μm. , solves patterns of 100 nm in size. The microscope objective 13 placed in an immersion medium must have a numerical aperture of 0.9.

In the embodiment illustrated in FIG. 2, a microbead 7 intended to be arranged in a measurement beam 23 within one optical metrology systems shown in Figure 1, is included in a dipping layer 21. The refractive index of the medium constituting the layer 21 is less than that of the microbead 7. This dipping layer 21 is disposed on the surface 22 of the object 6 to be measured, for example a substrate, itself placed on a support 24. The microbead 7 then collects the reflected or diffused beam 25 by the surface 22 of the object 6.

In an alternative embodiment of the device of FIG. 2, illustrated in FIG. 5, on which components common to the two embodiments have common references, a lamella 27 transparent to the wavelength of the light source is disposed on the microbead. 7.

This plate 27 may be made of glass or another transparent material and have the same refractive index or not as the microbead 7 which can be glued, welded or held by a force to the strip 27. The strip 27 is attached to an actuator piezoelectric 28 which can control a vertical and / or horizontal movement.

The index contrast to be taken into account for the evaluation of the imaging performance is that between the microbead 7 and the layer 21. For example, the microbead 7 may be made of barium titanate and included in a layer 21 in PDMS. . It can also be provided that the microbead is placed in a micro-grid pierced to a diameter slightly smaller than the size of the microbeads to maintain them, or maintained by a micro manipulator arm with a clamp or other adhesion system, or still maintained by an optical clamp.

In addition, a matrix configuration of microbeads can be envisaged as illustrated in FIG. 3, in which, in this example, a matrix of hemispherical microbeads 26 is represented. The hemisphere matrix intended to be arranged in a measuring beam 23 in one of the optical metrology systems represented in FIG.

1, is included in an immersion medium 21. The refractive index of the medium 21 is less than that of the microbeads 26. This immersion layer 21 is disposed on the surface 22 of the object 6 to be measured, for example a substrate, itself placed on a support 24. The microbead 7 then collects the beam reflected or scattered 25 by the surface 22 of the object 6.

This matrix arrangement of microbeads is particularly suitable with the use of a matrix of Mirau interferometers due to the small footprint, and it allows to increase the field of view while maintaining a similar acquisition rate.

A practical example of a processing of the interference patterns obtained with the optical metrology method according to the invention will now be described with reference to FIG. Signal processing in phase shift interferometry requires phase unfolding.

The raw signal 30a of the measured phase modulo 2π is cut into an area of interest 30b of the object in order to limit the edge effects. The phase image is then unfolded 30c (unwrapping English) in two dimensions and then adjusted 30d (English surface fitting) to remove the effects of aberrations.

This image thus treated is then converted into a 30th height distribution. A dedicated program then makes it possible, from this distribution of height, to draw 30f profiles of the surface.

Of course, the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention. Of course, the various features, shapes, variants and embodiments of the invention can be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other. In particular all the variants and embodiments described above are combinable with each other.

Claims

A super-resolution full-field optical metrology system for providing information on the surface topography of a nanoscale far-field sample or object (6), comprising a coherent or partially coherent light source (2), an interferometer (1a, 1b, 1c, 1d) comprising an object arm incorporating a transparent microbead (7) and disposed in close proximity to the surface of the object (6), a reference arm incorporating a mirror (10), receiving means (5) for picking up interference patterns, and means (8) for processing said interference patterns to produce said surface topography information,

said interferometer (1a, 1b, 1c, 1d) and said interference pattern processing means (8) being arranged to reconstruct the topography of the object (6) by phase shift interferometry.

2. System according to claim 1, characterized in that the light source (2) is coherent or quasi-coherent temporally with a wavelength in the visible.

3. System according to claim 1, characterized in that the light source (2) is coherent or quasi-coherent temporally with a wavelength in the infrared.

4. System according to claim 1, characterized in that the light source (2) is coherent or quasi-coherent temporally with a wavelength in the ultraviolet.

5. System according to one of the preceding claims, characterized in that the interferometer is arranged to provide measurements in reflective configuration.

6. System according to claim 5, characterized in that the interferometer is of a type selected from the group of interferometers Michelson (la), Twyman-Green (Ib), Mirau (le) and Mach Zehnder (ld) .

7. System according to any one of claims 1 to 4, characterized in that the interferometer is arranged to provide measurements in transmissive configuration.

8. System according to claim 7, characterized in that the interferometer is Mach Zehnder type (ld).

9. System according to any one of the preceding claims, characterized in that the reference arm further comprises a microbead (9) similar to the microbead (7) of the object arm, said microbead (9) of the reference arm being arranged to compensate for the dispersion, and arranged in close proximity to the surface of the mirror (10).

10. System according to any one of the preceding claims, characterized in that it comprises, in the object arm and in the reference arm, a plurality of microbeads arranged in the form of a matrix of microbeads (26) translatable.

11. System according to any one of the preceding claims, characterized in that the microbead (s) (7, 9, 26) are spherical, elliptical, hemispherical or convex.

12. System according to any one of the preceding claims, characterized in that the one or more microbeads (7, 9, 26) are placed in contact with the surface (22) of the object (6) or the surface of the mirror of reference (10).

13. System according to any one of claims 1 to 11, characterized in that the or microbeads (26) are kept out of contact with the surface (22) of the object (6) or with the surface of the mirror of reference (10).

14. System according to claim 13, characterized in that the one or more microspheres (26) are placed in a transparent layer (21) disposed on the surface (22) of the object (6) and of index lower than that of said one or more microbeads (26).

15. System according to claim 13, characterized in that the microbead or microbeads are held above the surface of the object by a micromanipulator arm provided with means for holding said microbead or microbeads.

16. System according to claim 13, characterized in that the microbeads are held above the object by an optical clamp.

17. System according to claim 13, characterized in that the microbeads are held above the object by a piezoelectric system.

18. The system of claim 13, characterized in that the one or more microbeads are placed in a micro-grid disposed above the surface of the object and having holes of diameter substantially less than that of said one or more microbeads.

19. Super-resolution full-field optical metrology method for delivering information on the surface topography of an object (6) at the far-field nanoscale, implemented in an optical metrology system according to one any one of the preceding claims, said system incorporating an interferometer (1a, 1b, 1c, 1d) comprising an object arm provided with a microbead (7) disposed in close proximity to the surface of the object (6) and being arranged to provide interference figures,

this process comprising:

an illumination of the surface via said microbead (7), by a coherent or partially temporally coherent light source (2),

processing the interference patterns to reconstruct the surface of the object (6) by phase shift interferometry.

20. The method of claim 19, characterized in that it provides interferometric measurements in reflective configuration.

21. The method of claim 19, characterized in that it provides interferometric measurements in transmissive configuration.

22. Method according to one of claims 19 to 21, characterized in that it provides interferometric measurements in matrix configuration.

23. Method according to any one of claims 19 to 22, characterized in that the treatment (30) of the interference figures comprises:

a production (30a), from a phase measurement in images of interference patterns, of a raw signal of the measured phase modulo 2π,

- cutting (30b) of said raw phase signal into an area of interest of the object (6) so as to limit edge effects, - unfolding (30c) of the phase image thus obtained in two dimensions ,

an adjustment (30d) of said phase image thus unfolded, so as to eliminate effects of aberrations,

a conversion (30e) of said phase image thus unfolded and then adjusted, into a height distribution, and

- a treatment (30f) of said height distribution for drawing surface profiles of said object (6).

24. Method according to any one of claims 19 to 23, characterized in that the processing (30) interference figures comprises an optimization algorithm used to seek to reconcile the measurements of a simulation of the result describing the ball-object interaction.