Depth-resolution optical measurement system

Abstract

The present disclosure provides an optical measurement system comprising optics configured to project a pattern of radiation onto a top of a patterned object having microscopic patterns, a first detection sub-channel configured to receive first radiation comprising reflected radiation from the top of the patterned object, a second detection sub-channel configured to receive second radiation comprising smeared radiation scattered from a below top region of the patterned object, and a processing circuit configured to process signals from the first and second detection sub-channels to provide information regarding the patterned object. The system enables differentiation between top and below top features of the patterned object by analyzing the reflected and smeared radiation separately.

Description

DEPTH-RESOLUTION OPTICAL MEASUREMENT SYSTEM CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 652,667 filed May 28, 2024, which is hereby incorporated by reference in its entirety. BACKGROUND

[0002] Optical metrology plays a crucial role in characterizing and controlling processes throughout semiconductor fabrication. Of particular interest are Optical Critical Dimensions (OCD) metrology methods, commonly employed for dimensional metrology of fabricated nanostructures. OCD is typically implemented using techniques such as Spectral Reflectometry (SR), Spectral Ellipsometry (SE), Spectral Interferometry (SI), or combinations thereof. The non-destructive nature and rich information content of these techniques make them suitable for a diverse set of challenges in semiconductor manufacturing.

[0003] A recurring challenge in these methods is differentiating between sensitivities to structural properties originating from different regions of the measured structure. Often, only a subset of characteristics is of interest, such as the thickness of the top layer or dimensions of an etched nanostructure at the top of the measured object. Alternatively, information may be needed on different regions in a tall stack to identify deviations from intended characteristics. However, the scattered light is frequently affected by numerous aspects of the structure, including properties of regions that are not of interest to the metrology.

[0004] Existing approaches to address this challenge include using spectral ranges where different wavelengths have different penetration depths into the stack. This approach is limited to specific materials where such differentiation is applicable and restricts the usable bandwidth. For example, mid-IR spectral ranges are used for characterization of oxide-nitride multilayer stacks in 3D-NAND applications, as wavelengths in this spectral range have suitable penetration depth variations.

[0005] Another approach involves Spectral Interferometry, which offers vertically- resolved optical dimensional metrology. However, this technique is limited to normal- incidence reflectivity and has constraints such as small numerical aperture, preventing ultra-small spot size and sensitivity to vibrations.

[0006] There remains a need for improved optical metrology techniques that can provide depth-resolved information about patterned objects with microscopic features. Microscopic features have at least one dimension that ranges between a nanometer to tens of microns.

[0007] Such techniques could potentially enable more accurate characterization of complex, multi-layered structures, or patterned objects with features at different depths, without relying solely on wavelength-dependent penetration depths or being limited to specific measurement configurations. SUMMARY

[0008] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] According to an aspect of the present disclosure, an optical measurement system is provided. The optical measurement system includes optics configured to project a pattern of radiation onto a top of a patterned object having microscopic patterns. The system includes a first detection sub-channel configured to receive first radiation comprising reflected radiation from the top of the patterned object. The system includes a second detection sub-channel configured to receive second radiation comprising smeared radiation scattered from a below top region of the patterned object. The system includes a processing circuit configured to process signals from the first and second detection sub- channels to provide information regarding the patterned object.

[0010] According to other aspects of the present disclosure, the optical measurement system may include one or more of the following features. The optics may comprise a mask configured to create the pattern of radiation. The mask may be movable to adjust the pattern of radiation. The first detection sub-channel may comprise a first radiation sensor configured to generate a first detection signal indicative of the first radiation. The second detection sub-channel may comprise a second radiation sensor configured to generate a second detection signal indicative of the second radiation. The processing circuit may be configured to process the first detection signal and the second detection signal to extract information about both top and below top features of the patternedobject. The system may further comprise an optical parameter adjuster unit configured to change an optical parameter to obtain information about different depths within the patterned object.

[0011] According to another aspect of the present disclosure, a method for optical measurement is provided. The method includes projecting, by optics, a pattern of radiation onto a top of a patterned object having microscopic patterns. The method includes directing first radiation comprising reflected radiation from the top of the patterned object towards a first detection sub-channel. The method includes directing second radiation comprising smeared radiation scattered from a below top region of the patterned object towards a second detection sub-channel. The method includes generating a first detection signal indicative of the first radiation and a second detection signal indicative of the second radiation. The method includes processing the first detection signal and the second detection signal to provide information regarding the patterned object.

[0012] According to other aspects of the present disclosure, the method may include one or more of the following features. Projecting the pattern of radiation may comprise using a mask to create the pattern of radiation. The method may further comprise moving the mask to adjust the pattern of radiation. Directing the first radiation may comprise using a first radiation sensor to generate the first detection signal. Directing the second radiation may comprise using a second radiation sensor to generate the second detection signal. Processing the first detection signal and the second detection signal may comprise extracting information about both top and below top features of the patterned object. The method may further comprise adjusting an optical parameter to obtain information about different depths within the patterned object.

[0013] According to another aspect of the present disclosure, a non-transitory computer readable medium storing instructions for controlling an optical measurement system is provided. The instructions cause the optical measurement system to project a pattern of radiation onto a top of a patterned object having microscopic patterns. The instructions cause the optical measurement system to direct first radiation comprising reflected radiation from the top of the patterned object towards a first detection sub- channel. The instructions cause the optical measurement system to direct second radiationcomprising smeared radiation scattered from a below top region of the patterned object towards a second detection sub-channel. The instructions cause the optical measurement system to generate a first detection signal indicative of the first radiation and a second detection signal indicative of the second radiation. The instructions cause the optical measurement system to process the first detection signal and the second detection signal to provide information regarding the patterned object.

[0014] According to other aspects of the present disclosure, the non-transitory computer readable medium may include one or more of the following features. The instructions may further cause the optical measurement system to move a mask to adjust the pattern of radiation. The instructions may further cause the optical measurement system to scan the mask laterally while acquiring multiple measurements. Processing the first detection signal and the second detection signal may comprise analyzing partially coherent sums of the reflected radiation and the smeared radiation. The instructions may further cause the optical measurement system to adjust an optical parameter to obtain information about different depths within the patterned object. Adjusting the optical parameter may comprise changing a numerical aperture of an optical system used to project the pattern of radiation.

[0015] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive. BRIEF DESCRIPTION OF FIGURES

[0016] Non-limiting and non-exhaustive examples are described with reference to the following figures.

[0017] FIG.1 illustrates examples of radiation patterns interacting with a patterned object, according to aspects of the present disclosure.

[0018] FIG.2 depicts an optical measurement system with illumination and collection paths, according to an embodiment.

[0019] FIG.3 shows optical configurations of a measurement system with different radiation directing arrangements, according to aspects of the present disclosure.

[0020] FIG.4 illustrates examples of angled radiation patterns interacting with a patterned object, according to an embodiment.P0328

[0021] FIG.5 depicts a diagram of light propagation through an object structure, according to aspects of the present disclosure.

[0022] FIG.6 illustrates a flowchart of a method for optical measurement, according to an embodiment.

[0023] FIG.7 illustrates an example of sensors. DETAILED DESCRIPTION

[0024] The following description sets forth exemplary aspects of the present disclosure. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure. Rather, the description also encompasses combinations and modifications to those exemplary aspects described herein.

[0025] The present disclosure relates to an optical measurement system for evaluating patterned objects with microscopic features. This system may be used for characterizing and analyzing various types of objects, including but not limited to semiconductor devices, optical components, and other micro-structured materials.

[0026] The optical measurement system described herein utilizes a novel approach for obtaining depth-resolved information about a patterned object. In some cases, the system projects a specific pattern of radiation onto the top of the object being measured. This projected pattern interacts differently with various depths within the object, allowing for separation and analysis of radiation contributions from different regions.

[0027] The system may collect multiple types of radiation resulting from the interaction between the projected pattern and the patterned object. In some cases, this includes reflected radiation from the top of the object, which largely maintains the projected pattern structure. Additionally, the system may collect scattered or smeared radiation originating from below-top regions of the object, which exhibits different spatial characteristics compared to the top reflection.

[0028] By analyzing these different radiation components, the system may provide information about both top and below top features of the patterned object. This approach allows for depth-resolved measurements without relying solely on wavelength-dependent penetration depths or destructive testing methods.P0328

[0029] The optical measurement system described herein may offer advantages in terms of vertical resolution, flexibility in measurement configurations, and the ability to separate information from different depths within an object. These capabilities may be particularly useful in applications requiring non-destructive evaluation of complex, multi- layered structures, or patterned objects with features at different depths.

[0030] The optical measurement system may include various components arranged along an illumination path and a collection path. FIG.2 illustrates an example configuration of these optical components.

[0031] In the illumination path, the system may include a first relay lens 41 and a second relay lens 42. These relay lenses may be configured to project a pattern of radiation 11 onto the object. In some cases, the pattern of radiation 11 may be a dense set of lines. In other cases, the pattern of radiation 11 may be a dense set of points.

[0032] The illumination path may also include a beam splitter 51 positioned to receive radiation from the second relay lens 42. The beam splitter 51 may direct the radiation toward an objective lens 44. In some cases, the objective lens 44 may focus the radiation to form a pattern structure 31 on a microscopic pattern 20 of the object.

[0033] The illumination may be directed at the object in different ways. In some cases, the illumination may be at normal incidence to the object surface. In other cases, the illumination may be at oblique incidence to the object surface.

[0034] In the collection path, the system may include a first collection lens 45. The first collection lens 45 may be positioned to collect reflected radiation 32 from the microscopic pattern 20 and direct the reflected radiation 32 along the collection path.

[0035] The beam splitter 51 may serve a dual purpose in the optical system. In addition to directing illumination radiation, the beam splitter 51 may also separate the illumination path from the collection path, allowing the reflected radiation 32 to pass through to the collection optics.

[0036] The arrangement of these optical components may allow for precise projection of the radiation pattern onto the object and efficient collection of both reflected and scattered radiation for analysis. The specific configuration and properties of these components may be adjusted to optimize the system for different types of objects or measurement requirements.P0328

[0037] The optical measurement system may project a radiation pattern 11 onto a patterned object having a microscopic pattern 20. FIG.1 illustrates examples of how the radiation pattern 11 interacts with different depths of the patterned object.

[0038] In some cases, the radiation pattern 11 may comprise multiple spots of radiation projected onto a top 21 of the patterned object. FIG.1, example (A) shows a radiation pattern 11 with three spots 12a, 12b, and 12c arranged in a linear pattern. Each spot may form a line. Figure 1, being a cross sectional view illustrates only a portion of the line.

[0039] When the radiation pattern 11 interacts with the top 21, reflected radiation 16 may be produced. The reflected radiation 16 may maintain the pattern structure of the original radiation pattern 11. FIG.1, example (B) depicts the reflected radiation 16 from the top 21, which includes reflected spots 17a, 17b, and 17c corresponding to the locations of the original projected spots.

[0040] As the radiation pattern 11 propagates deeper into the patterned object, the radiation may become partially smeared. FIG.1, example (C) illustrates how the radiation pattern 11 becomes smeared as it travels toward a bottom surface 22 of the patterned object. The smeared pattern may include smeared spots 13a, 13b, and 13c that correspond to, but are broader than, the original projected spots.

[0041] After interacting with the bottom surface 22 and traveling back through the patterned object, smeared radiation 19 may be produced. FIG.1, example (D) shows the smeared radiation 19 appearing as a single combined spot 18, demonstrating how the original distinct pattern becomes diffused after multiple interactions within the patterned object.

[0042] In some cases, the radiation pattern 11 may be projected onto the patterned object at an angle. FIG.4 illustrates examples of oblique illumination and its interactions with the patterned object. FIG.4, example (A) shows a radiation pattern 11 comprising two spots 12a and 12b directed at an angle onto the patterned object.

[0043] The reflected radiation 16 from the top of the patterned object under oblique illumination may still maintain the pattern structure, as shown in FIG.4, example (B). The reflected radiation 16 includes reflected spots 17a and 17b corresponding to the original projected spots.

[0044] Under oblique illumination, the radiation pattern propagates to a below-top region of the patterned object under oblique illumination, and form spots 13a and 13b that may not be smeared or partially smeared but still represent the radiation pattern 11, as illustrated in FIG.4, example (C). The radiation output after interaction with the below-top region may produce output spots 81a and 81b, which maintain some of the original pattern structure while exhibiting effects of propagation through the patterned object, as shown in FIG.4, example (D).

[0045] The optical measurement system may be extended to analyze structures with more than two reflecting interfaces. In such cases, the system may collect and analyze radiation reflected or scattered from multiple depths within the patterned object. The radiation pattern 11 may interact differently with each interface, potentially producing multiple sets of reflected radiation 16 and smeared radiation 19 corresponding to different depths within the patterned object.

[0046] The optical measurement system may include various components for directing and detecting the reflected radiation and smeared radiation from the patterned object. FIG.3 illustrates different configurations for radiation directing and detection.

[0047] In some cases, the optical measurement system may include a radiation mask 60 positioned in the collection path. The radiation mask 60 may be configured to selectively direct the reflected radiation 32 and the smeared radiation 33 towards different detection sub-channels. The radiation mask 60 may have a pattern that corresponds to the radiation pattern 11 projected onto the patterned object. Different detection sub-channels may include different optical components, may share one or more optical components, or may use the same components but using a different configuration (for example the location of the radiation mask may change over time to provide different detection sub- channels).

[0048] A mask movement unit 79 may be coupled to the radiation mask 60. The mask movement unit 79 may be configured to move the radiation mask 60 between different positions. In some cases, the mask movement unit 79 may scan the radiation mask 60 laterally while acquiring multiple measurements. This scanning may allow for collection of different combinations of the reflected radiation 32 and the smeared radiation 33.

[0049] The optical measurement system may include a first radiation sensor 70 positioned to receive radiation that passes through the radiation mask 60. In some cases, the first radiation sensor 70 may detect a partially coherent sum of the reflected radiation 32 and the smeared radiation 33 - especially a portion of the smeared radiation that spatially overlaps the reflected radiation.

[0050] In some configurations, the optical measurement system may use interchangeable radiation masks or controlled apertures. These may allow for variable illuminated line width and pitch in the radiation pattern 11 projected onto the patterned object. The mask movement unit 79 may also be configured to shift the radiation mask 60 in a direction perpendicular to the top 21. This movement may create a defocus between the radiation mask 60 and the top 21, potentially altering the balance of collected reflected radiation 32 and smeared radiation 33.

[0051] In other cases, the optical measurement system may include a collection beam splitter 77 positioned in the collection path. The collection beam splitter 77 may be configured to split the collected radiation into multiple paths - for example to different detection sub-channels. For example, the collection beam splitter 77 may direct a portion of the collected radiation towards the first radiation sensor 70 and another portion towards a second radiation sensor 72.

[0052] According to an embodiment, a patterned mirror can be created with the same structure as the radiation mask proposed above. Such a mirror will split the aligned and counter-aligned contributions (passing one and reflecting the other), allowing concurrent collection of both contributions. Such implementation, which may be more complex in terms of the optical layout, offers faster acquisitions and avoids the need for moving parts.

[0053] The optical measurement system may, in some configurations, use an imaging spectrometer as one of the radiation sensors. The imaging spectrometer may provide a two-dimensional image where one axis represents a spectral breakdown of the collected radiation, and the other axis is conjugated to the top 21. See for example lines 181(1)-181(J) of imaging spectrometer – each line provides a spectrum related to one or more lines of the image. It should be noted that the imaging spectrometer may include a single line (for example only 181(1)) and a scanning mechanism provides different imageP0328 line segments to the imaging spectrometer at different points in time. Figure 7 also illustrates a 2D array of pixels of a 2D array of pixels of an image sensor – which also illustrated multiple pixel groups 171(1,1)- 171(J,K) and pixels regions 171(1)1, 171(2) and 171(3) corresponding to the locations of the pattern of radiation. In this case this mapping may allow not to use a mask.

[0054] Referring to figure 3 – example (A) – the radiation mask may be removed and the radiation (both smeared and reflected) will reach a two dimensions pixel array of the imaging spectrometer, whereas pixels associated with the pattern (for example when locating the imaging spectrometer at a conjugate plane to the top of the object – the pixels are located at locations that correspond to the locations of the pattern of radiation) will receive the first radiation.

[0055] In yet another configuration, the optical measurement system may use a collection fiber optic positioned at a plane conjugate to the top 21. The collection fiber optic may be scanned across the collected radiation pattern, alternately collecting signals from regions corresponding to the reflected radiation 32 and the smeared radiation 33.

[0056] These various configurations and components may allow the optical measurement system to detect one or more partially coherent sums of the reflected radiation 32 and the smeared radiation 33. By analyzing these different combinations, the system may extract information about both top and below top features of the microscopic pattern 20 on the patterned object.

[0057] The optical measurement system may utilize principles of light propagation through the patterned object to achieve depth-resolved measurements. FIG.5 illustrates a diagram showing how light propagates through different layers of an object structure.

[0058] In some cases, the radiation pattern may be projected onto the top of the patterned object. As the radiation propagates through the patterned object, the beam may diverge. The degree of beam divergence may be related to the numerical aperture (NA) of the optical system and the effective refractive index of the patterned object.

[0059] The diagram in FIG.5 depicts an object that includes a substrate 100 and patterned structures formed above the substrate. The substrate has a thickness that may represent the vertical distance through which the radiation propagates within theP0328 patterned object. As the radiation travels through the substrate thickness 100, the beam may spread laterally.

[0060] The optical measurement system may be designed to optimize vertical resolution by considering factors such as the numerical aperture of the objective lens, the wavelength range of the radiation, and the properties of the patterned object being measured. In some cases, using a higher numerical aperture objective lens may improve vertical resolution by increasing the beam divergence angle and reducing the minimum resolvable vertical separation.

[0061] The principles of light propagation through the patterned object may also affect how the smeared radiation is generated and collected. As the radiation propagates through the substrate thickness 100, the initially distinct pattern may become increasingly diffuse. This diffusion may result in the formation of the combined spot observed in the smeared radiation collected from deeper regions of the patterned object.

[0062] Understanding these light propagation principles may allow for the design of measurement configurations that effectively separate contributions from different depths within the patterned object. By carefully selecting the radiation pattern, optical system parameters, and collection strategies, the optical measurement system may achieve depth- resolved measurements of the microscopic pattern within the patterned object.

[0063] The optical measurement system may perform a method of optical measurement to evaluate patterned objects with microscopic features. FIG.6 illustrates a method 600 for optical measurement that may be implemented by the optical measurement system.

[0064] The method 600 may begin with a step 610 of projecting, by optics, the radiation pattern onto a top of a patterned object having the microscopic pattern. In some cases, the optics may include the first relay lens, the second relay lens, the beam splitter, and the objective lens to form and project the radiation pattern onto the top of the patterned object.

[0065] Following the projection of the radiation pattern, the method 600 may proceed to a step 620 of directing, by the optics, first radiation towards a first detection sub-channel. The first radiation may comprise the reflected radiation that was reflected from the top of the pattern due to the projection of the radiation pattern onto the top of theP0328 patterned object. In some cases, the first collection lens may collect the reflected radiation and direct the reflected radiation along the collection path.

[0066] The method 600 may continue with a step 630 of directing, by the optics, second radiation towards a second detection sub-channel. The second radiation may comprise the smeared radiation that was scattered from a below top region of the patterned object due to the projection of the radiation pattern onto the top of the patterned object. In some cases, the smeared radiation may result from interactions between the radiation pattern and the bottom surface of the patterned object.

[0067] After directing the first and second radiation, the method 600 may include a step 640 of generating a first detection signal that is indicative of the first radiation and a second detection signal that is indicative of the second radiation. In some cases, the first radiation sensor may generate the first detection signal, and the second radiation sensor may generate the second detection signal.

[0068] The method 600 may conclude with a step 650 of processing, by a processing circuit, the first detection signal and the second detection signal to provide information regarding the patterned object. In some cases, the processing may involve analyzing the partially coherent sums of the reflected radiation and the smeared radiation to extract information about both top and below top features of the microscopic pattern on the patterned object.

[0069] In some cases, the method 600 may include additional steps or variations. For example, the method 600 may include moving the radiation mask between different positions using the mask movement unit. This movement may allow for collection of different combinations of the reflected radiation and the smeared radiation.

[0070] The method 600 may also include adjusting optical parameters to obtain information about different depths within the patterned object. In some cases, this may involve changing the focal point of the illumination (for example by introducing a movement between the object and the illumination path) or adjusting the numerical aperture of the optical system to modify the beam divergence angle.

[0071] In some implementations of the method 600, the radiation pattern may be projected at an oblique angle onto the patterned object. This oblique illumination mayP0328 affect how the radiation interacts with different depths of the patterned object and may influence the characteristics of the reflected radiation and the smeared radiation.

[0072] The method 600 may be adapted for analyzing patterned objects with multiple reflecting interfaces. In such cases, the method 600 may include steps for collecting and analyzing radiation reflected or scattered from multiple depths within the patterned object.

[0073] By following the steps of the method 600, the optical measurement system may obtain depth-resolved information about the patterned object, allowing for characterization of both top and below top features of the microscopic pattern.

[0074] The optical measurement system may integrate various components to perform depth-resolved measurements of patterned objects with microscopic features. The system may combine illumination optics, collection optics, detection components, and processing elements to analyze both top and below top characteristics of the measured object.

[0075] In some cases, the illumination path of the system may project a specific pattern of radiation onto the top of the patterned object. This pattern may be created using relay lenses and a mask or other patterning element. The projected pattern may interact differently with various depths within the object, allowing for separation and analysis of radiation contributions from different regions.

[0076] The collection path of the system may gather multiple types of radiation resulting from the interaction between the projected pattern and the patterned object. In some cases, this may include reflected radiation from the top of the object, which largely maintains the projected pattern structure. Additionally, the system may collect scattered or smeared radiation originating from below-surface regions of the object, which may exhibit different spatial characteristics compared to the top reflection.

[0077] The system may employ various strategies to separate and analyze the different radiation components. In some cases, a movable mask in the collection path may selectively direct reflected radiation and smeared radiation towards different detection sub-channels. Alternatively, a beam splitter may be used to simultaneously direct different radiation components to separate detectors.P0328

[0078] Detection components in the system may generate signals corresponding to the collected radiation. In some cases, these may include spectral measurements of the reflected and smeared radiation. The system may use multiple detection configurations to obtain different combinations or partially coherent sums of the radiation components.

[0079] A processing circuit may analyze the detection signals to extract information about both top and below top features of the patterned object. The processing may involve comparing the signals from different detection configurations, analyzing spectral characteristics, or applying mathematical models of light propagation through the object.

[0080] The system may be adaptable to different measurement requirements. In some cases, the illumination pattern, collection optics, or detection parameters may be adjusted to optimize measurements for specific types of patterned objects or to focus on particular depth regions within the object.

[0081] By integrating these various components and functions, the optical measurement system may provide non-destructive, depth-resolved analysis of patterned objects with microscopic features. The system may offer advantages in terms of vertical resolution and the ability to separate information from different depths within an object, potentially enabling detailed characterization of complex, multi-layered structures, or patterned objects with features at different depths.

[0082] Interpretation

[0083] The proposed implementation provides (at least) two measured signals – aligned (reflected radiation related signal) and counter-aligned (smeared radiation related signal) with the illuminated pattern.

[0084] As explained, different layouts would provide different collection balances between the top and bottom regions. For example, using an illuminated pattern of 1:2 duty-cycle (meaning illuminated lines widths is half the illuminated pitch), reflections from the bottom are (roughly) attenuated by factor ½ compared to reflections from the top. Conversely, using a large-pitch array of narrow illuminated lines, reflections from underlayers will be spread across a much larger span reducing their relative contributions at the illuminated lines regions.

[0085] The measured signal at each such configuration is determined by a partially- coherent sum over contributions from the object bottom and top. Detailed quantitativeP0328 description of the resulting signal can be obtained based on partially-coherent field summation, as described in standard literature (for example, [M. Born and E. Wolf, Principles of Optics and J. W. Goodman, Introduction to Fourier Optics]). A general expression describing any such measurement is given by ^^^^^^ ൌ ^^^^௧^^^^^^ ^ ^^^^^^௧^^^^ ^^^ℜ^^^௧∗^^^^^^^^^^௧^^^^^. is the reflected spectrum, ^^௧^^^^^^ ൌ ห^^௧^^^^^^หଶ and ^^^^௧^^^^ ൌ|^^^^௧^^^^|ଶare the reflected intensities from thereflected (complex) fields. The term ℜ^^^௧∗^^^^^^^^^^௧^^^^^ describes interference betweenthe top and bottom reflected fields. ^^,^^ and ^^ represent the relative contributions between each term and depend on the measurement layout. Generally, these will also be wavelength-dependent, but for clarify we omit stating this dependence here (this has no impact on the proposed approach).

[0087] The factors ^^,^^ and ^^ can either be obtained theoretically or though calibrations using characterized structures.

[0088] Interpretation can be split in two situations (a) Negligible top-bottom interference, and (b) Non-negligible top-bottom interference.

[0089] Negligible top-bottom interference: The simplest situation for interpretation involves cases when the interference contribution is negligible (namely, ^^ ≪ ^^,^^). Undersuch conditions, the two measurements (aligned and counter-aligned) are ^^^^^^^ ൌ^^^^^௧^^^^^^ ^ ^^^^^^^௧^^^^ and ^^^^^^^ ൌ ^^^^^^^௧௧^^^^^^.and counter-aligned measurements correspondingly.

[0091] Top and bottom reflected contributions can be extracted by suitable linear combinations of the two measurements, namely ^^௧^^^^^^ ൌ ூೌ ^ఒ^െ ఉೌ⋅ூ^^ఒ^; ^^^^௧௧^^^^^^ ൌఈೌ^ூೌ ^ఒ^െ^^௧^^^^^^^.top-bottom interference: this situation can either be unavoidable due to the object characteristics, or intentional – by correctly choosing the measurement layout (see discussion below for more details). While interpretation is more complex in such a case, it provides additional valuable metrology information in the formP0328 of an additional phase spectrum, representing the phase difference between top and bottom contributions.

[0093] Interpretation in this case is based on (at least) three measurements withdifferent values of ^^, ^^ and ^^. For convenience, we rewrite the first equations as ^^^^^^ ൌ^^ห^^௧^^^^^^หଶ ^^^|^^^^௧^^^^|ଶ ^ ^^ห^^௧^^^^^^ห|^^^^௧^^^^| cos ^^^௧^^ି^^௧^^^^^, with ^^௧^^ି^^௧^^^^isstraightforward to solve for ห^^௧^^^^^^ห, |^^^^௧^^^^| and cos ^^^௧^^ି^^௧^^^^^.

[0095] Technical

[0096] can using various optical layouts and characteristics. However, there are important considerations determining the eventual performance and potential of the system, which are described below.

[0097] The presented description is approximate and simplified for clarity. It assumes illumination at normal incidence, disregards factors such as pupil apodization, obscurations etc. Extending this analysis is straightforward, but unnecessary for understanding the general considerations involved.

[0098] In addition, we describe light propagation inside the stack assuming an effective refractive index approximation. Under this approximation, light inside the structure behave similarly to propagation through a homogeneous medium with a refractive index determined by the structure. While this approximation is often inaccurate, it will serve to simplify the discussion and allow general conclusions. Commonly, when light propagation cannot be described using this approximation, its angular divergence is increased compared to the homogeneous case, making the proposed invention more efficient. Consequently, this assumption can be (roughly) assumed as a worst-case approximation.

[0099] The illuminated pattern directly determines the attainable vertical resolution. Figure 5 presents a high-level sketch defining the main parameters involved.

[0100] The illuminated pattern is assumed to have pitch ^. Non-periodic patterns are also possible but would typically not be advantageous. For a broadband optical systemP0328 with numerical aperture NA and maximal wavelength ^^^^௫, this pitch is limited by Λ ^^^^^௫ / ^^^^.

[0101] The angular span of the illuminated beam is described by divergence angle ^^ ൌ sinି^^^^^^^.

[0102] As light enters the measured structure, the beam is bent according to Fresnel laws. For normal incidence, beam divergence becomes ^^ ି^^^ ൌ sin ൫sin^^ / ^^^^^൯ ൌ sinି^൫^^^^ / ^^^^^൯, which we will approximate as ^^^^~^^^^ / ^^^^^. Again, thisapproximation imprecise for high-NA illumination, but can be used for this rough analysis.

[0103] After propagation to the bottom layer and back up towards the top , each beam is expanded by 2ℎ ⋅ tan ൬ே^ ^^^^ ^ which we again approximate as 2ℎ ⋅ே^ ^^^^. Thelines as they exit the object after reflection from the bottom is thus given by Δ ^ Λ െ 4ℎ ⋅ ൬ே^ ^^^^^.

[0104] to work, the pattern reflected from the objectbottom should be significantly spatially smeared. Such conditions are guaranteed when Δ^ 0.

[0105] Using the equations above, we find that efficient vertical separation is obtained when 0 ^ Δ ൌ ఒ^ೌ^ െ 4ℎ ⋅ ൬ே^ ^^^^^, or ℎఒ^ೌ^⋅^^^^^^^^^௩^ௗ^మ.

[0106] vertical separation between reflecting interfaces. For example, using a spectral bandwidth reaching IR (^^^^௫~1^^^^) and high numertical aperture of 0.9 to measure object with effectiveof ^^^^^~1.5 , the attainable vertical separation is roughly ℎ^^^^^௩^ௗ~0.5^^^^. Such capability if of high potential benefit for many semiconductor applications.

[0107] The last equation highlights the importance of using a high-NA system: the attainable vertical resolution is quadratically proportional to the numerical aperture.

[0108] Multi-layer objects

[0109] While the description above focused on structures comprised of (predominantly) two interfaces, the invention can be extended to more reflectingP0328 interfaces. Of course, these cannot be closer to each other than the attainable vertical resolution ℎ^^^^^௩^ௗ.

[0110] Given multiple interfaces reflection, it is possible to obtain multiple measurements when focus is directed to each interface. At each focus, few measurements (as described above) are taken, separating the reflections from the interface under focus and reflection from all other interfaces. Using the same approach as described above, reflections from each interface can be separated.

[0111] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

[0112] According to an embodiment there is provided an optical measurement system that includes (a) optics that is configured to: project a pattern of radiation onto a top of a patterned object having microscopic patterns; direct first radiation towards a first detection sub-channel , the first radiation includes reflected radiation that was reflected from the top of the pattern due to the projection of the pattern or radiation onto the top of the patterned object; direct second radiation towards a second detection sub-channel, the second radiation includes smeared radiation that was scattered from a below top region of the patterned object the due to the projection of the pattern or radiation onto the top of the patterned object; and generate a first detection signal that indicative of the first radiation and a second detection signal that is indicative of the second radiation; and (b) a processing circuit that is configured to process the first detection signal and the second detection signal to provide information regarding the patterned object.

[0113] According to an embodiment, the optics includes a radiation mask that is located within a collection path of the optics, the radiation mask is configured to direct the first radiation and direct the second radiation, wherein the radiation mask has a radiation mask pattern that corresponds to the pattern of radiation.

[0114] According to an embodiment, the optical measurement system further includes a radiation mask movement unit for moving the radiation mask between a first radiation transfer position and a second radiation transfer position.P0328

[0115] According to an embodiment, the optical measurement system further includes a radiation mask movement unit for moving the radiation mask to provide an additional first signal and an additional second signal.

[0116] According to an embodiment, the optical measurement system further includes a radiation mask movement unit for moving the radiation mask along an axis that is perpendicular to the radiation mask .

[0117] According to an embodiment, the optical measurement system further includes a radiation mask movement unit for moving the radiation mask upwards and downwards.

[0118] According to an embodiment, the optical measurement system further includes an optical parameter adjuster unit for changing an optical parameter that once applied provides information regarding another below top region of the patterned object.

[0119] According to an embodiment, the pattern of radiation is projected by illuminating the top with normal illumination.

[0120] According to an embodiment, the pattern of radiation is projected by illuminating the top with oblique illumination.

[0121] According to an embodiment, the processing circuit is configured to process the first detection signal and the second detection signal assuming that first detection signal represents a first partially coherent sum of the reflected radiation and the smeared radiation, and that the second detection signal represents a second partially coherent sum of the reflected radiation and the smeared radiation.

[0122] In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.

[0123] Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.P0328

[0124] Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks, circuit elements, or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality.

[0125] Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

[0126] Furthermore, those skilled in the art will recognize that boundaries between the above-described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.

[0127] However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

[0128] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true forP0328 the use of definite articles. Unless stated otherwise, terms such as “first" and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0129] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

P0328 CLAIMS 1. An optical measurement system, comprising: optics configured to project a pattern of radiation onto a top of a patterned object having microscopic patterns; a first detection sub-channel configured to receive first radiation comprising reflected radiation from the top of the patterned object; a second detection sub-channel configured to receive second radiation comprising smeared radiation scattered from a below top region of the patterned object; and a processing circuit configured to process signals from the first and second detection sub-channels to provide information regarding the patterned object.

2. The optical measurement system of claim 1, wherein the optics comprise a mask configured to create the pattern of radiation.

3. The optical measurement system of claim 2, wherein the mask is movable to adjust the pattern of radiation.

4. The optical measurement system of claim 1, wherein the first detection sub-channel comprises a first radiation sensor configured to generate a first detection signal indicative of the first radiation.

5. The optical measurement system of claim 4, wherein the second detection sub-channel comprises a second radiation sensor configured to generate a second detection signal indicative of the second radiation.

6. The optical measurement system of claim 5, wherein the processing circuit is configured to process the first detection signal and the second detection signal to extract information about both top and below top features of the patterned object.

7. The optical measurement system of claim 6, further comprising an optical parameter adjuster unit configured to change an optical parameter to obtain information about different depths within the patterned object.

8. The optical measurement system of claim 1, wherein the first detection sub-channel comprises an imaging spectrometer.

9. A method for optical measurement, comprising:P0328 projecting, by optics, a pattern of radiation onto a top of a patterned object having microscopic patterns; directing first radiation comprising reflected radiation from the top of the patterned object towards a first detection sub-channel; directing second radiation comprising smeared radiation scattered from a below top region of the patterned object towards a second detection sub-channel; generating a first detection signal indicative of the first radiation and a second detection signal indicative of the second radiation; and processing the first detection signal and the second detection signal to provide information regarding the patterned object.

10. The method of claim 9, wherein projecting the pattern of radiation comprises using a mask to create the pattern of radiation.

11. The method of claim 10, further comprising moving the mask to adjust the pattern of radiation.

12. The method of claim 9, wherein directing the first radiation comprises using a first radiation sensor to generate the first detection signal.

13. The method of claim 12, wherein directing the second radiation comprises using a second radiation sensor to generate the second detection signal.

14. The method of claim 13, wherein processing the first detection signal and the second detection signal comprises extracting information about both top and below top features of the patterned object.

15. The method of claim 14, further comprising adjusting an optical parameter to obtain information about different depths within the patterned object.

16. A non-transitory computer readable medium storing instructions for controlling an optical measurement system to: project a pattern of radiation onto a top of a patterned object having microscopic patterns; direct first radiation comprising reflected radiation from the top of the patterned object towards a first detection sub-channel; direct second radiation comprising smeared radiation scattered from a below top region of the patterned object towards a second detection sub-channel;P0328 generate a first detection signal indicative of the first radiation and a second detection signal indicative of the second radiation; and process the first detection signal and the second detection signal to provide information regarding the patterned object.

17. The non-transitory computer readable medium of claim 16, wherein the instructions further cause the optical measurement system to move a mask to adjust the pattern of radiation.

18. The non-transitory computer readable medium of claim 17, wherein the instructions further cause the optical measurement system to scan the mask laterally while acquiring multiple measurements.

19. The non-transitory computer readable medium of claim 16, wherein processing the first detection signal and the second detection signal comprises analyzing partially coherent sums of the reflected radiation and the smeared radiation.

20. The non-transitory computer readable medium of claim 19, wherein the instructions further cause the optical measurement system to adjust an optical parameter to obtain information about different depths within the patterned object.

21. The non-transitory computer readable medium of claim 20, wherein adjusting the optical parameter comprises changing a numerical aperture of an optical system used to project the pattern of radiation.

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