High-resolution optical magnifying inspection device using non-collimated light beam for measuring changes in polarization state

Abstract

A high-resolution optical magnifying inspection device which uses non-collimated light beam (4) for examining small samples (2) measuring only a few mm2 is discussed. The device comprises at least one light source (1), the light source (1) being a real or a virtual light source configured to illuminate a given area of a surface of the sample (2) in at least one illumination plane non-perpendicularly with non-collimated beam (4) of light of selectable polarization state, the light source (1) having a size at least equal to the wavelength of said light, but at most one order of magnitude larger than the wavelength of the light applied. Said device further comprises at least one light receiving means (3) arranged in a light path of light reflected from said area of the sample (2) and / or of transmitted light passing through the sample in an entire thickness thereof in said area of the sample (2), the at least one light receiving means (3) is formed as a screen / position-sensitive detector system configured to detect light intensity distribution at least along a line and arranged in such a way that the light path between the sample (2) and the light receiving means (3) is free of optical elements that affect straight-line propagation of light. Here, a distance (t) between the light source (1) and the sample (2) measured along an optical axis (9) is smaller than a distance (t or t") between the sample (2) and the light receiving means (3) measured along said optical axis (9).

Description

[0001] HIGH-RESOLUTION OPTICAL MAGNIFYING INSPECTION DEVICE USING NON-COLLI ATED

[0002] LIGHT BEAM FOR MEASURING CHANGES IN POLARIZATION STATE

[0003] The present invention relates to a high-resolution optical inspection device. Specifically, the subject of the present invention is an optical magnifying inspection device (that is, an inspection polarimeter or ellipsometer) using non-collimated light beam without a lens, which is suitable for measuring changes in polarization state of light reflected from or passing through very small (~1 mm2, but at most a few mm2) surfaces or volumes of various materials in such a way that the resolution is on the order of microns, thus enabling the rapid and simultaneous mapping examination of these materials with high resolution.

[0004] The optical inspection device according to the present invention is particularly advantageous for the high-resolution, non-destructive, rapid, and simple optical mapping investigation of very small surfaces of various materials, e.g. thin layers deposited by physical or chemical means, or biological samples on a substrate. Specifically, the imaging optical magnifying device according to the invention is suitable for the simultaneous measurement of the local optical properties of very small surface portions of various samples, and based on the data obtained in this way, for the quick and reliable mapping of numerous physical and chemical properties of the samples examined.

[0005] It is well known that illuminated materials significantly change the properties of light reflected from them or passing through them. Vision is essentially based on this. The brain provides information about the surrounding world through the angle and spectrum-dependent, and less frequently, mainly in the animal kingdom, polarization-dependent processing of the reflected light intensity, which allows various components of the environment to become identifiable.

[0006] The "more scientific" version of vision, one of the most widespread types of optical examination methods, is reflectometry. Reflectometry determines the change in light intensity that is reflected from the surface of the sample being examined, often after interacting with the sample, as a function of the angle of incidence and reflection, and, in some cases, the spectrum of the light. Based on this data, it qualifies the sample itself. In certain cases, it may also be useful to examine the polarization state of the incident and reflected light relative to each other, which is the subject of polarimetry. A special case of polarimetry is ellipsometry, where the angular dependence of polarization is studied, while spectro-ellipsometers can also examine its wavelength dependence. All of this provides information that is characteristic of the composition of the examined sample, its surface quality, and in some cases even its subsurface properties.

[0007] Polarimetric / ellipsometric measurements are typically performed only locally, even with the most advanced equipment, meaning that at each step, only a single selected point on the sample is used, employing a collimated beam of light at a freely chosen but always single, specified angle of incidence (reflection). In these general solutions, the examined sample point typically represents an area of a few mm2, and the system integrates the polarization information coming from this area. Subsequently, the measurement can be repeated by changing, for example, the sample position or the angle of incidence [1, 2, 3],

[0008] If we want to obtain information from the sample surface with a resolution on the order of microns, a special optical solution is needed in every case, because the general designs of polarimeters / ellipsometers are not suitable for this task. There are so-called microspot solutions, but they do not provide better resolution than approximately 100 microns on the sample surface [4, 5, 6], Although it is possible to achieve a resolution of about 10 microns with a special optical arrangement, this can only be done at one sample point at a time using optical path-modifying elements, lenses, and mirrors placed between the sample and the detector [7],

[0009] Nowadays, there are position-sensitive, linear detector arrays and two-dimensional detector matrices that provide precision signals suitable for real-time measurement, formed from a multitude of independent light sensors. These allow for significantly more position-dependent simultaneous measurements of data than before. The known position of the elements in the detector matrix can be used to measure time (scanning), angle (rotation), spectrum (color separation), or sample topography (imaging).

[0010] The problems associated with local measurements that can be performed slowly with a single detector can be alleviated by the so-called mapping polarimetry / ellipsometry, which allows us to take measurements at thousands of sample points in a single step. One of the key elements of this solution is the mentioned detector array or matrix; however, the creation of an appropriate optical illumination system tailored to the given task is equally important. When creating a photograph or video recording, that is, a time-dependent series of images, we naturally take pictures of a sample surface and its portion that falls within the optical field of view. Therefore, in this approach, the 'optical imaging devices (reflectometers)' have existed for a long time. However, these devices utilize light path modifying tools, focusing systems, so-called lenses, and / or, in certain cases, non-flat mirrors for imaging. The essence of an imaging system based on refractive media with variable optical thickness and / or non-planar reflective surfaces is that - under ideal and geometrical optical considerations - it maps each individual point of the object plane to its corresponding point in the image plane separately. This imaging system increases light intensity by collecting light rays emerging from a single selected object point at different angles and then focusing them onto a single image point. Since light rays emerging from the image point toward the selected object point at various angles are integrated (summed), conventional optical systems that include path-altering elements are, in principle, unsuitable for angle-dependent analysis of reflected light, as they average out the angular information.

[0011] However, this strict criterion does not always pose an obstacle. For example, if we photograph the light of the Sun (which can be considered as an infinitely distant point source) reflected from the surface of the sea, we use a nearly flawless imaging reflectometer, as the diameter of the lens limits the collection angle of light arriving from a specific point of the nearly infinite object, namely the surface of the sea, to a very small field of view. In other words, the critical angle range for imaging detection is determined by the distance from the light source of the sample and the aperture of the imaging system.

[0012] In contrast, under laboratory and / or industrial conditions (where reflection measurements are preferably conducted), both the sample and the light source are close to the detector, meaning that imaging reflectometry with angular integrating optical imaging cannot be used. In some certain cases, relatively large, but only flat surfaces can yield well -evaluated images, which means that imaging reflectometry can function; however, in such cases, lighting requires the use of a large-diameter, perfectly collimated light beam. Such a measurement device is described in document [8], where a theoretically collimated beam illuminates a large (300 mm) sample surface, and a telephoto lens is then used to project a reduced image onto the detector. That is, an imaging element is used between the sample and the detector.

[0013] Hungarian patent application no. P0103248 teaches a true imaging reflectometer, which illuminates the sample with a point-like light source, and creates a non-focused image on a screen or directly on a detector matrix, maintaining the angular dependency of the divergent light projection. It is apparent, that the apparatus described in this document is suitable for measuring large area samples, which is explicitly stated multiple times in the description. For the skilled persons in the art, large area examination means measuring approximately 100 cm2of sample surface simultaneously. Although the apparatus operates with a point-like light source, for the expert, the point-like light source size is generally on the order of a few hundred microns, which is far larger than what would allow for micrometer resolution on the sample's surface. According to data available in scientific literature, the skilled persons in the art would recognize that the size of a point-like light source is typically -100 microns or larger [9], In the constructed form of the device described in document no. P0103248, both the size of the examined surface (-30 mm x 70 mm elliptical area) and the size of the light source (-800 microns) make it theoretically impossible to achieve a resolution of micron-level

[0010] ,

[0014] European patent no. EP-2,160,59 1B1 describes another imaging reflectometer using a pinhole camera. The essence of its operation is that it allows light reflected from the object to reach the screen, photo plate or detector in a strictly angle-dependent manner, but this solution specifically creates a reduced image of large-area samples with a resolution worse than 1 mm, and the imaging is performed by the pinhole [11, 12], meaning it uses an imaging element between the sample and the detector.

[0015] There is indeed a lensless imaging technique

[0013] , but in this solution, the sample is placed extremely close (1 micron - 1 mm) to the detector matrix, illuminated by a distant (several tens of cm) quasi-point-source diverging light beam with nominally perpendicular incidence, thus the magnification of the system is practically 1. In this device, the resolution of the sample is determined not by the size of the quasi-point source but much more by the pixel size of the applied detector, and the shadow image of the sample details is recorded, which is why it can only be used for the examination of transparent samples in transmission. The use of a polarized light source does not provide any advantages due to the nominally perpendicular illumination.

[0016] At present, only one solution is known to the skilled person in the art that enables polarimetric / ellipsometric analysis of multiple sample points simultaneously with micron-level resolution. This ellipsometric microscope is described in US patent no. US-5,754,296

[0014] , The system typically employs a collimated illuminating beam along with imaging optical elements and lenses to perform micron-resolution imaging of the sample, illuminating all measured sample points with light at an identical angle of incidence

[0015] , A similar optical approach is presented in publication

[0016] , which also describes an imaging ellipsometer. In this setup, a parallel beam illuminates the sample, and an imaging lens creates an image of the sample on the surface of the detector. The description focuses on the analysis of biological protein samples and indicates that the method can detect the presence of specific protein layers as well as the interactions of different protein layers on the substrate surface.

[0017] In the solution disclosed by U.S. patent no. US-4,655,595 A

[0020] , the incident light is successively directed onto the sample under investigation and a reference sample, which are rotated 90 degrees relative to each other. For this purpose, a narrow, collimated light beam is used, and an additional (reference) sample is placed in the optical path.

[0018] U.S. patent application no. US20150077750A1

[0021] describes an ellipsometric measurement method in which a deliberately wide-area light source is employed for the examination. This light source consistently emits a collimated light beam.

[0019] During our investigations, we concluded that an ideal solution for the implementation of a high-resolution optical magnifying device is to direct a non-collimated beam from a sufficiently small, point-like source located in close proximity to the sample onto the surface to be examined, and then to direct the light rays reflecting from or passing through that surface, without imaging optical elements, lenses, and pinholes, to a detector system located at a sufficient distance. As a result, each object point can be measured at only one incidence (reflection) angle in a single step, and each object point corresponds to a different angle. Thus, the single image detected as a recording provides angle -dependent reflection data for the range of angles corresponding to the system's field of view, with each sample point measured at a different incidence angle with a resolution on the order of microns.

[0020] Optical beam shaping solutions (e.g., imaging with large aperture optics) increase the brightness of imaging as a result of angular summation, and additionally - due to their focusing properties - can provide "sharper" and higher resolution images within a certain depth of field range. This dual advantage justified their introduction in photography and, for example, in astronomical observations. However, it should be noted that the term "imaging" can strictly be applied only to optical systems that modify light paths. The essence of the operation of the inventive device is that it only allows those light rays to reach a light receiving means, i.e. the screen / detector, that are unchanged in direction, that is, what are known as "straight" light rays. The device according to the present invention implements the linear projection of the object, resulting in an image. Consequently, the procedure performed by the device could even be interpreted as a mapping, but - as would be evident to the skilled persons in the art - such a solution fundamentally differs in principle from the usual imaging in optics. The essence of the difference lies precisely in one important requirement of the present invention, which is the absence of angle integration.

[0021] We have come to the conclusion that the applicability of a high-resolution optical magnifying device - designed to measure changes in polarization state using a non-collimated light beam from a point source (e.g., polarimeter or ellipsometer) - is subject to strict constraints regarding the design of the specialized, often task-specific light source used to illuminate the sample. Simple geometric considerations reveal that the desired magnification and resolution can be adjusted by varying the size of the light source and the relative distances between the light source, the sample, and the detector. Assuming an average pixel size of ~10 pm in modem digital cameras, a magnification factor of 20 x, and a resolution better than ~50 pm (which is considered good in micro-ellipsometry), it can be generally stated that the light source must be at least one order of magnitude smaller than the 100 pm size typically considered small in ellipsometry. Therefore, a light source larger than ~10 pm is not suitable. Another reason for requiring a specially miniaturized light source lies in the wave nature of light. If the size of the light source (e.g., optical fiber, pinhole) approaches the wavelength of the applied light, diffraction rings caused by edge diffraction appear on the illuminated sample (see Figure la). The position of these rings is temporally unstable, and certain regions exhibit low intensity, which can fundamentally compromise the measurement.

[0022] To ensure that, within the visible light spectrum, the diffraction pattern expands sufficiently and the sample is illuminated in a quasi-homogeneous manner by the so-called Airy disk, the light source must fall within the range of a few microns. That is, its size should be at most one order of magnitude larger than the wavelength of the applied electromagnetic radiation (see Figure lb), but ideally equal to the wavelength itself - otherwise, the intensity drops significantly.

[0023] In accordance with the above, the point-like light source used in the magnifying device according to the invention is subject to size constraints. Its dimensions may exceed the wavelength of the emitted light - considered as electromagnetic radiation - by no more than one order of magnitude, i.e., up to ten times the wavelength, in order to ensure the desired lateral (transverse) resolution. Under such conditions, physical optical phenomena arise that differ from the geometrical optics-based solution presented in Hungarian patent application no. P0103248. These include, for example, the sub-diffraction-limited core size of an optical fiber, or a suitably designed pinhole that generates a so-called Airy disk (see Figure 10).

[0024] We also determined that if we place a two-dimensional diffraction grating, also known as a mask, in the path of the light, then the system is suitable for creating a periodic beam system with a specific density, meaning structured illumination. The structure depends on the design of the mask, the shape of the holes, and their distances. The structured illumination is created by the interference of beams that diffract at the edges of the two-dimensional grating. The application of structured illumination ensures that by placing the sample in the appropriate geometric position - consistent with the grating period - only specific points of the sample are illuminated, thereby ensuring a predetermined resolution on the surface of the sample.

[0025] We also determined that if we create a periodic structure on the surface of a substrate, for example by placing small, few-micron thick layers in a checkerboard pattern on the substrate, then by positioning the detector correctly, the image of the periodic pattern formed on the substrate surface will also be created.

[0026] These masks are primarily used in the field of wavefront distortion detection [17, 18, 19], where their technical task is completely different from the current case, which involves creating structured illumination.

[0027] In light of the above, the goal of the present invention is to create an optical magnifying device (polarimeter, ellipsometer) suitable for measuring changes in a polarization state, which is capable of conducting polarimetric / ellipsometric mapping examinations of small-area samples with a resolution of micron-level at multiple points simultaneously. This enables a nondestructive measurement of local optical properties at various points on very small surface areas of different samples, and based on the data obtained, allows for a fast, reliable, and distinctly high (-micron) resolution mapping of the physical properties of the samples examined.

[0028] The basis of the invention lies in our realization that by simultaneously applying a specially small, point-like light source and the optical magnifying device according to the invention, and, if applicable, aperiodic two-dimensional mask, the aforementioned objectives can be achieved by measuring the polarization and / or wavelength dependence of reflection on a surface of the sample and / or transmission through the material of the sample. With this solution, multiple points of a very small surface can be investigated simultaneously at different angles of incidence in a single image, with a resolution on the order of microns.

[0029] The above objectives aimed at creating an optical magnifying device suitable for measuring changes in polarization state (polarimeter, ellipsometer) have been achieved with the device according to claim 1. Preferred further exemplary embodiments of said device according to the invention are defined by claims 2 to 18.

[0030] Preferably, the size of a real or virtual point-like light source creating non-collimated illumination is no larger than a few microns, and that the sample is illuminated with light of adjustable polarization state. By correctly setting the ratio of the extremely small light source to the light source-to-sample distance, micron resolution on the surface of the sample can be achieved.

[0031] It is preferred to create an extreme miniature real or virtual light source by focusing a collimated light beam to a focal point using lenses and mirrors, where the focal point can be located either in front of or behind the sample along the optical axis, thus allowing for the choice of whether the sample is illuminated with divergent or convergent beam.

[0032] It is preferred for the light source creating non-collimated illumination to be the end of a light guide fiber; in this case, the extreme small size of the light source can be precisely adjusted with the core size of the employed light guide fiber, and by appropriately selecting the physical properties of the light guide fiber, the divergence of the light cone coming from it can be controlled.

[0033] It is preferred to use a light guide fiber that preserves the polarization state when using a point-like light source provided by the light guide fiber, thus there is no need to place a polarization state generator between the end of the light guide fiber that provides point-like noncollimated illumination and the sample.

[0034] It is preferred to have an extreme miniature pinhole provided by a collimated laser beam placed in the path of the point-like light source, allowing for precise adjustment of the light source size and the divergence of the expanding laser cone after the pinhole with the size of the pinhole.

[0035] It is preferred to generate the point-like light source by focusing a collimated laser beam into an extremely small pinhole, as this allows for significant noise reduction in the intensity distribution of the beam profile through the use of the pinhole.

[0036] It is preferred to have an arbitrarily adjustable polarizer installed between the sample and the detector system, allowing for ellipsometric measurements to be conducted simultaneously at multiple sample points with micron resolution, instead of polarimetric measurements. In a significant number of cases, it is worthwhile to perform a complete ellipsometric measurement.

[0037] Preferably, the detector system is sensitive to polarization states, as this allows for the construction of a device capable of full ellipsometric measurement at multiple sampling points simultaneously, with micron resolution, without moving parts, enabling shorter measurement times and simpler construction.

[0038] It is preferred to use a detector system that is sensitive to both polarization state and wavelength, which allows for spectro-ellipsometric measurements at multiple sampling points in a single measurement, even with micron resolution.

[0039] Preferably, the light source is a variable wavelength light source or it is capable of being switched between wavelength ranges, enabling polarimetric or ellipsometric measurements at one or more wavelengths or even across different wavelength ranges, which allows for much more precise sample analysis. In many cases, it is worth performing measurements at multiple wavelengths.

[0040] It is preferred for the plane of the detector system surface to be aligned parallel to the plane of the sample, as this solution minimizes the perspective distortion effect.

[0041] It is preferred to place an adjustable compensator between the light source and the sample, as this can significantly increase the measurement accuracy.

[0042] Preferably, the mechanics holding the light source and the detector system allows for the adjustability of the distances between the light source and the sample, as well as the sample and detector, thus enabling the desired resolution and magnification to be easily set.

[0043] Preferably, the angle between the optical axis of the light source / sample and the normal to the sample, as well as the angle between the optical axis of the sample / detector and the normal to the sample, are adjustable.

[0044] Preferably, the sample can be displaced along at least one straight line parallel to the plane of its own surface, allowing for a larger sample area to be examined with multiple measurements.

[0045] It is preferred to place a mask with an arbitrary number, shape, and size of holes in the light path between the light source and the sample, arranged in a test layout, allowing the given sized and positioned points of the sample to be examined simultaneously.

[0046] The invention will now be described in more detail with reference to the attached drawings, in which

[0047] Figure 1 illustrates light diffraction at the edges of a light source for (a) a source size large compared to the wavelength, and (b) a relatively small source size;

[0048] Figure 2a shows an exemplary embodiment of the optical inspection device according to the invention, designed for rapid quality assessment of materials under examination;

[0049] Figure 2b presents a thickness map of a sol-gel layer deposited with vertically oscillating thickness on a c-Si substrate, measured with ~5 micron resolution using the device outlined in Figure 2a;

[0050] Figure 3a illustrates another possible embodiment of the optical inspection device according to the invention, enabling rapid quality assessment of materials, where a mask placed in front of the sample provides structured illumination;

[0051] Figure 3b shows a thickness map of an Si Oz layer on a c-Si substrate, measured with ~5 micron resolution using the device illustrated in Figure 3a;

[0052] Figure 4a depicts a further possible embodiment of the optical inspection device according to the invention, where illumination is provided by a sample placed in the beam path, arranged in a checkerboard pattern in the plane of the sample, with square holes of 5 micron side length; Figure 4b presents a thickness map of a chromium layer on a checkerboard-patterned chrome-on-glass sample, measured using the device shown in Figure 4a;

[0053] Figure 5 illustrates another possible embodiment of the optical inspection device according to the invention;

[0054] Figure 6a shows one possible variation of the embodiment illustrated in Figure 5;

[0055] Figure 6b presents another possible variation of the embodiment illustrated in Figure 5;

[0056] Figure 7 depicts a further possible variation of the embodiments shown in Figures 6a and 6b.

[0057] Figure 8 illustrates a further variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention;

[0058] Figure 9 illustrates another possible variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention;

[0059] Figure 10 illustrates yet another possible variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention;

[0060] Figure 11 illustrates an additional variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention;

[0061] Figure 12 illustrates one possible variation of the embodiments of the optical inspection device shown in Figures 5 to 11 according to the invention;

[0062] Figure 13 illustrates another possible variation of the embodiments of the optical inspection device shown in Figures 5 to 11 according to the invention;

[0063] Figure 14 illustrates a further possible variation of the embodiments of the optical inspection device shown in Figures 5 to 11 according to the invention; finally,

[0064] Figure 15 illustrates a variation of the embodiments of the optical inspection device shown in Figures 5-14 according to the invention.

[0065] Further advantages of the solution according to the invention, as well as additional technical problems that can be addressed through its application, will become apparent from the following description and the accompanying drawings, which illustrate preferred exemplary embodiments of the invention. In the figures, identical reference numerals indicate corresponding structural elements.

[0066] Figure 2a illustrates a possible simple embodiment of the imaging optical inspection device according to the invention, suitable for rapid quality assessment of materials under examination, i.e., a sample (2). In this embodiment, the primary illuminating light source (23) is a three-color RGB laser source (465 nm, 520 nm, 635 nm), whose collimated beam (6) is focused into a pinhole (5) by an optical lens (7) of positive focal length, thereby creating a point-like light source (1). Polarization state of a resulting divergent beam (4) is adjusted by a polarization-state generator (10) placed between the pinhole (5) and the sample (2). In this case, the generator (10) is a linear film polarizer, although other types of polarizers can also be used. The sample (2) under investigation is mounted on a suitably designed sample holder (not shown in the figure). The surface of the sample (2), considered to be reflective, is illuminated by the divergent, linearly polarized light emerging from the pinhole (5). The light (4) reflected from the sample (2) is captured by an appropriate light receiving means, i.e., a position- and polarization-sensitive detector system (3), which in this embodiment is a computer-controlled Sony Polarsens digital CMOS monochrome camera. Based on the ratio of the pinhole-to-sample distance (t) and the sample-to-camera distance (t') along an optical axis (9), the magnification is 25 x. The detector system (3) is preferably composed of a CCD matrix, wherein each 2x2 pixel block is equipped with micro-polarizers oriented at 0°, 45°, 90°, and 135°. Each individual pixel measures 3.45 microns, and each 2x2 pixel block (or "superpixel") measures 7x7 microns. Noise reduction and measurement accuracy were enhanced by combining 4x4 superpixels and cooling the detector system (3). After superpixel aggregation, the detector (3) consisted of 255x306 combined pixels. From the intensity ratios of the detector (3) pixels, the change in polarization state caused by reflection from the sample (2) can be determined, as is well known to the skilled persons in the art. The sample (2) can be moved along at least one straight line within its own plane - for example, by mounting the inspection setup shown in Figure 2a onto a continuously moving production line. This movement ensures that every point of the sample (2) passes at least once through every possible angle within the detection cone defined by the size and relative distance of the pinhole (5) and the position- and polarization-sensitive detector system (3). In this configuration, ellipsometric measurement of tens of thousands of points on the sample (2) at three wavelengths with 5-micron linear resolution takes approximately 3 minutes - several orders of magnitude faster than what is achievable by means of point-by-point measurement systems capable of similar resolution.

[0067] Figure 2b shows a thickness map of a small section of a sol-gel coating deposited by dipcoating onto a c-Si substrate. The nominal thickness of 125 nm varies periodically along the withdrawal direction, with an amplitude of approximately 6 to 8 nm and a period of about 80 to 90 microns. The measurement was performed using the setup illustrated in Figure 2a, at all three wavelengths.

[0068] Figure 3a illustrates another possible simple embodiment of the optical inspection device according to the invention, suitable for rapid quality assessment of materials under examination. In this embodiment, the primary illuminating light source (1) is a three-color RGB laser source (465 nm, 520 nm, 635 nm), whose collimated beam (6) is focused into a pinhole (5) by an optical lens (7) of positive focal length. The polarization state of the resulting divergent beam (4) is adjusted by a polarization-state generator (10) placed between the pinhole (5) and the sample (2). In this case, the generator is a linear film polarizer, although other types of polarizers may also be used. After the polarization-state generator (10), a two-dimensional diffraction grating (hereinafter referred to as the mask) (8) is placed in the optical path, producing structured illumination. The mask consists of a checkerboard pattern of square elements with 5-micron side lengths, coated with chromium. The light diffracted at the edges of these squares interferes to create a structured illumination pattern, so that only specific surface elements of the sample (2) - in this case, a 64 nm thick SiOa layer on a c-Si substrate - are illuminated. By combining the geometry of the divergent beam (4) and the design of the mask (8), a structured illumination pattern is easily achieved on the sample (2), allowing simultaneous inspection of surface elements approximately 5 microns in size. The light (4) reflected from the sample (2) is captured by the light receiving means, that is, the position- and polarization-sensitive detector system (3), which in this embodiment is a computer-controlled Sony Polarsens digital CMOS monochrome camera. Based on the ratio of the pinhole-to-sample distance (t) and the sample-to-camera distance (t'), the magnification is 25 x . The detector system (3) preferably consists of a specialized CCD matrix, where each 2x2 pixel block is equipped with micro-polarizers oriented at 0°, 45°, 90°, and 135°. Each individual pixel measures 3.45 microns, and each 2x2 pixel block (or "superpixel") measures 7x7 microns. Noise reduction and measurement accuracy were enhanced by combining 4x4 superpixels and cooling the detector system (3). After superpixel aggregation, the detector system (3) consisted of 255x306 combined pixels. From the intensity ratios of the detector pixels, the change in polarization state caused by reflection from the sample (2) can be determined, as is well known to the skilled persons in the art. The sample (2) can be moved along at least one straight line within its own plane - for example, by mounting the inspection setup shown in Figure 3a onto a continuously moving production line. This movement ensures that every point of the sample (2) passes at least once through every possible angle within the detection cone defined by the size and relative distance of the pinhole (5) and the position- and polarization-sensitive detector system (3). Using this device, ellipsometric measurement of tens of thousands of points on the sample (2) at three wavelengths with ~5-micron linear resolution takes approximately 3 minutes - several orders of magnitude faster than what is achievable by means of point-by-point measurement systems capable of similar resolution.

[0069] In Figure 3b, the thickness map of the Si CU layer applied to a c-Si substrate, created with structured illumination by placing a mask with chessboard-like arrangement of square 'holes' of 5 microns side length into a beam path, is shown at a resolution of ~ 5 microns.

[0070] Figure 4a illustrates another possible simple embodiment of the optical inspection device according to the invention, suitable for rapid quality assessment of materials under examination. In this embodiment, the primary illuminating light source (1) is a three-color RGB laser source (465 nm, 520 nm, 635 nm), whose collimated beam (6) is focused into a pinhole (5) by an optical lens (7) of positive focal length. The polarization state of the resulting divergent beam (4) is adjusted by a polarization-state generator (10) placed between the pinhole (5) and the sample (2). In this case, the generator is a linear film polarizer, although other types of polarizers may also be used. Following the polarization-state generator (10), the sample (2) is placed in the optical path. The sample features a checkerboard pattern of square elements with 5-micron side lengths, coated with chromium. Due to diffraction at the edges of these squares, interference occurs, forming an image of the sample (2) on the detector. This enables simultaneous inspection of surface elements approximately 5 microns in size. The light (4) reflected from the sample (2) is captured by the position- and polarization-sensitive detector system (3), which in this embodiment is a computer-controlled Sony Polarsens digital CMOS monochrome camera. Based on the ratio of the pinhole-to-sample distance (t) and the sample -to-camera distance (t'), the magnification is 25 x. The detector system (3) preferably consists of a specialized CCD matrix, where each 2x2 pixel block is equipped with micro-polarizers oriented at 0°, 45°, 90°, and 135°. Each individual pixel measures 3.45 microns, and each 2x2 pixel block (or "superpixel") measures 7x7 microns. Noise reduction and measurement accuracy were enhanced by combining 4x4 superpixels and cooling the detector (3). After superpixel aggregation, the detector system (3) consisted of 255 x 306 combined pixels. From the intensity ratios of the detector pixels, the change in polarization state caused by reflection from the sample (2) can be determined, as is well known to the skilled persons in the art. The sample (2) can be moved along at least one straight line within its own plane - for example, by mounting the inspection setup shown in Figure 4a onto a continuously moving production line. This movement ensures that every point of the sample (2) passes at least once through every possible angle within the detection cone defined by the size and relative distance of the pinhole (5) and the position- and polarization-sensitive detector system (3). Using this device, ellipsometric measurement of tens of thousands of points on the sample (2) at three wavelengths with ~5-micron linear resolution takes approximately 3 minutes - several orders of magnitude faster than what is achievable by means of point-by-point measurement systems capable of similar resolution.

[0071] Figure 4b shows the thickness map of the chromium layer obtained by placing a mask with chessboard-like arranged square 'holes' of approximately 5 microns side length in the sample position, with a resolution of about 5 microns.

[0072] Figure 5 illustrates a possible further embodiment of the optical inspection device according to the invention. In this configuration, the small-sized sample (2), measuring only a few mm2, is illuminated in at least one illumination plane by a non-collimated beam (4) of light with selectable polarization state, incident at a non-perpendicular angle. The system includes at least one virtual or real light source (1), whose size exceeds the wavelength of the applied electromagnetic radiation, i.e., of the illuminating light, by no more than one order of magnitude. Additionally, the device comprises at least one light receiving means, preferentially provided as at least one screen and / or at least one position-sensitive detector system (3) capable of capturing light reflected from the sample and / or light transmitted through the full thickness of the sample. These components are arranged in an optical path in such a way that there are no optical elements between the sample and the detector system (3) which would alter the straight-line propagation of light. Furthermore, the distance (t) between the light source and the sample, measured along an optical axis (9), is smaller than the distance (t' or t") between the sample and the detector, also measured along the optical axis.

[0073] Figure 6a illustrates a variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention. In this configuration, a light source (13) illuminates the sample (2) with convergent beam (11) in at least one illumination plane. The focal point of the converging beam, acting as the point-like light source ( 1 ), may be positioned in front of the sample (2) along the optical axis (9). Even in this case, the non-collimated beam (4) reaches a positionsensitive detector system (3), with the light path between the sample and the detector system being free of any optical elements that would alter the straight-line propagation of light.

[0074] Figure 6b illustrates a further variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention, in which the light source (13) illuminates the sample (2) with convergent beam (11) in at least one illumination plane. In this configuration, the focal point of the converging beam - acting as the point-like light source (I) - may be positioned after the sample (2) along the optical axis (9).

[0075] Even in this case, the non-collimated beam (4) reaches a position-sensitive detector system (3), with the light path between the sample and the detector system being free of any optical elements that would alter the straight-line propagation of light.

[0076] Figure 7 illustrates a yet further variation of the embodiments of the optical inspection device shown in Figures 6a and 6b according to the invention. In this configuration, the convergent light beam and the point-like light source (1) are realized by focusing a collimated beam (6), originating from a light source (14), into a point (1) using an optical lens (7) of positive focal length. Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches a position-sensitive detector system (3), with the light path between the sample and the detector system remaining free of any optical elements that would alter the straight-line propagation of light.

[0077] Figure 8 illustrates a yet variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention. In this configuration, the divergent light beam (4) and the virtual point-like light source (1) are generated by defocusing (dispersing) a collimated beam (6), originating from a light source (14), using an optical lens (15) of negative focal length. Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches a position-sensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0078] Figure 9 illustrates another variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention. In this configuration, the point-like light source (1) is formed by the end of an optical fiber (16), and the divergent illuminating beam (4) is generated by a polarization-state generator (10). Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches a position-sensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0079] Figure 10 illustrates a further possible variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention. In this configuration, the pointlike light source (1) is formed by placing a pinhole (5) in the path of a collimated light beam (6) originating from the light source (14). The divergent beam (4) is generated by the phenomenon of light diffraction, resulting in an Airy disk (see Figure 1). Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches a position-sensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0080] Figure 11 illustrates a further possible variation of the embodiment of the optical inspection device shown in Figure 5 according to the invention. In this configuration, the pointlike light source ( 1) is generated by focusing a collimated beam (6), originating from a light source (14), into a pinhole (5) using an optical lens (7) of positive focal length. Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches a position-sensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0081] Figure 12 illustrates a possible variation of the embodiments of the optical inspection device shown in Figures 5 to 11 according to the invention. In this configuration, a polarizer (17) is inserted into the non-collimated light path (4) extending from the sample (2) to the positionsensitive detector system (3). Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches the position-sensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0082] Figure 13 illustrates another possible variation of the embodiments of the optical inspection device shown in Figures 5 to 11 according to the invention. In this configuration, the light receiving means, i.e., the at least one screen and / or the at least one position-sensitive detector system (3) is arranged essentially parallel to the sample (2) under examination. Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches the positionsensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0083] Figure 14 illustrates a further possible variation of the embodiments of the optical inspection device shown in Figures 5 to 11 according to the invention. In this configuration, a compensator ( 18) is placed in the light path between the light source (1) and the sample (2). Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches a position-sensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0084] Figure 15 illustrates a variation of the embodiments of the optical inspection device shown in Figures 5 to 14 according to the invention, in which an angle (a) enclosed between the optical axis (9) and the normal incidence direction (20) of the sample (2) is adjustable. Even in this case, the non-collimated beam (4), after being reflected from the sample (2), reaches a position-sensitive detector system (3), with the light path between the sample (2) and the detector system (3) remaining free of any optical elements that would alter the straight-line propagation of light.

[0085] The optical magnifying inspection device according to the invention (in particular, the inspection polarimeter or ellipsometer) has advantageous effects that are mainly manifested in the visual representability of the measured data. The distortion-free inspection device allows for simultaneous high-resolution measurements over a wide range of angles, covering the small surface area of the sample examined. Visual representability means simultaneous measurement of many points of the sample, thus the inspection device according to the invention reduces the measurement time by at least two orders of magnitude. The reduction in measurement time also enables the application of the inspection device in a production line (thus not in a laboratory) and in real-time (thus not merely based on sampling), which has significant practical economic advantages. It should be noted that the size and resolution of the generated image on the detector / screen can be simply regulated by changing the applied geometry.

[0086] The optical magnifying inspection device according to the invention is particularly advantageous for the rapid, precise, and high-resolution measurement of the quality of thin films applied to a substrate, as well as various physical / chemical parameters. The arrangement in question is thus particularly suitable for examining the thickness / thicknesses of the applied layer(s) and their optical refractive index(es) (and thereby their composition and / or structure), as well as the changes in the aforementioned parameters.

[0087] The optical magnifying inspection device according to the invention is particularly advantageous for the temporal examination of the properties of biological samples, such as the presence and quantity of bacteria, proteins, or even tumor markers, the temporal examination, the determination of growth / reproduction rates, and due to its mapping capability, the execution of these examinations on a "large scale."

[0088] It is obvious to the skilled persons in the art that various modifications can be made to the arrangement of the optical inspection device according to the invention without exceeding the scope of protection claimed hereby. List of references

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Claims

1. CLAIMS1. A high-resolution optical magnifying inspection device using non-collimated light beam for examining small samples (2) measuring only a few mm2, characterized in that the device comprises: at least one light source (1), the light source (1) being a real or a virtual light source configured to illuminate a given area of a surface of the sample (2) in at least one illumination plane non-perpendicularly with non-collimated beam (4) of light of selectable polarization state, the light source (1) having a size at least equal to the wavelength of said light, but at most one order of magnitude larger than the wavelength of the light applied, at least one light receiving means (3) arranged in a light path of light reflected from said area of the sample (2) and / or of transmitted light passing through the sample in an entire thickness thereof in said area of the sample (2), the at least one light receiving means (3) is formed as a screen / position-sensitive detector system configured to detect light intensity distribution at least along a line and arranged in such a way that the light path between the sample (2) and the light receiving means (3) is free of optical elements that affect straight- line propagation of light, wherein a distance (t) between the light source (1) and the sample (2) measured along an optical axis (9) is smaller than a distance (f or t") between the sample (2) and the light receiving means (3) measured along said optical axis (9).

2. The optical inspection device according to claim 1, characterized in that the light source (1), as a point-like light source, is arranged on the optical axis (9) defined by the point-like light source, a center of the surface of the sample (2) examined, and a center of an image appearing on the light receiving means (3) either in front of or behind the sample (2) in the form of a focal point of a convergent beam (11) of a light source (13) illuminating the sample with convergent beam in at least one illumination plane.

3. The optical inspection device according to any of claims 1 to 2, characterized in that a convergent illumination beam and the point-like light source (1) are formed by focusing a collimated beam (6) from a light source (14) into a point by means of a positive optical lens (7).

4. The optical inspection device according to claim 1, characterized in that a divergent illumination beam (4) and the point-like virtual light source (1) are formed by defocusing a collimated beam (6) from a light source (14) by means of a negative optical lens (15).

5. The optical inspection device according to claim 1, characterized in that a divergent illumination beam (4) is formed by a point-like light source (1) of an exit end of an optical fiber (16) and a polarization-state generator (10).

6. The optical inspection device according to claim 1, characterized in that the light source (1) is formed by a pinhole (5) arranged in a light path of collimated light beam (6) from a light source (14), and a divergent illumination beam (4) is generated by the phenomenon of light diffraction.

7. The optical inspection device according to claim 1, characterized in that the light source (1) is formed by focusing collimated beam (6) from a light source (14) into a pinhole (5) by means of a positive optical lens (7).

8. The optical inspection device according to any of claims 1 to 7, characterized in that a polarizer (17) is inserted into the light path of non-collimated light beam extending from the sample (2) to the light receiving means (3).

9. The optical inspection device according to any of claims 1 to 7, characterized in that the detector system (3) is a polarization-sensitive detector system.

10. The optical inspection device according to any of claims 1 to 9, characterized in that the detector system (3) is a spectrally sensitive detector system.

11. The optical inspection device according to any of claims 1 to 10, characterized in that the light source (1) is a variable wavelength light source.

12. The optical inspection device according to any of claims 1 to 11, characterized in that said light receiving means (3) is arranged substantially parallel to the sample (2) examined.

13. The optical inspection device according to any of claims 1 to 12, characterized in that a compensator (18) is arranged in a light path between the light source (1) and the sample (2).

14. The optical inspection device according to any of claims 1 to 13, characterized in that the distance (t) between the light source (1) and the sample (2) is adjustable, and the distance ( , t") between the sample (2) and the light receiving means (3) is adjustable.

15. The optical inspection device according to any of claims 1 to 14, characterized in that an angle (a) formed by the optical axis (9) and the direction (20) of normal incidence to the sample (2) is adjustable.

16. The optical inspection device according to any of claims 1 to 15, characterized in that the sample (2) is arranged so as to be displaceable along at least a straight line in a plane of said sample (2).

17. The optical inspection device according to any of claims 1 to 16, characterized in that a mask (8) is inserted into the light path of non-collimated light beam (4) between the light source(1) and the sample (2), said mask formed with a plurality of holes of arbitrary shape and size in a periodic pattern.

18. The optical inspection device according to any of claims 1 to 16, characterized in that parts of the sample (2) to be examined are formed on the surface of said sample (2) in any number, shape, and size, in a periodic pattern.

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