Apparatus for Characteristic Evaluation of a Substrate and a Film

Abstract

Various embodiments include an apparatus for characterizing the substrate thickness and film thickness of a substrate and a film formed thereon. The apparatus interrogates the substrate using one or more wavelengths of light from a light source (e.g., a swept laser). The light is directed substantially perpendicular to the upper surface of the substrate. A polarizer and an analyzer element are coupled between the light source and the substrate. Thus, both the polarizer and the analyzer are located in the beam propagation path from the light source to the substrate. An optical detector is disposed substantially perpendicular to the upper surface of the substrate. The optical detector receives the light returned from the substrate. The apparatus can determine the thickness of the substrate and one or more films contained thereon, regardless of whether the substrate has optical anisotropy, such as chiral properties, or a stress-induced film. Other apparatuses and methods are also disclosed.

Description

Technical Field

[0001] (Priority Claim) This patent application claims priority to U.S. Utility Patent Application No. 17 / 871,384, filed on July 22, 2022, entitled "APPARATUS TO CHARACTERIZE SUBSTRATES AND FILMS", the entire disclosure of which is incorporated herein by reference.

[0002] (Field of the Invention) The disclosed subject matter generally relates to the field of metrology tools used in the semiconductor and related industries (e.g., flat panel display and solar cell manufacturing facilities). More specifically, in various embodiments, the disclosed subject matter relates to the measurement of substrates (e.g., silicon wafers, etc.) and films formed on the substrates.

Background Art

[0003] One aspect of semiconductor manufacturing is the measurement of substrate thickness. Current techniques for measuring substrate thickness include, for example, capacitance sensors that measure the capacitance of the substrate, height sensor techniques that utilize two sensors with one sensor above the substrate and one sensor below the substrate, and reflectometers. The use of capacitance sensors typically requires detailed knowledge about the material constituting the substrate. Furthermore, capacitance sensors generally can only function correctly with a single substrate material and may not function correctly with substrates composed of multiple layers of different materials such as silicon-on-insulator (SOI) substrates, substrates supported by a carrier, or handle substrates. In addition, capacitance sensors have a thickness lower limit of approximately 200 microns and are limited to small material samples.

[0004] Height sensor technology and technology based on reflectivity measurement are similarly limited. For example, height sensor technology detects the physical surface of a wafer, so generally it can function with thinner samples and can accommodate multilayer wafer stacks made of substantially any material. However, height sensor technology requires precise alignment in all three axes and calibration to teach the sensor how far apart the axes are in space. Such calibration requirements are the lower limit of the accuracy of the measurements performed.

[0005] Current reflectometers do not adjust the polarization state of the incident light source (e.g., laser) on the substrate. Further, current reflectometers do not analyze the light returned from the substrate. As a result, current reflectometers cannot be used to accurately measure substrates having optical anisotropies such as chiral properties or stress-induced films.

[0006] In addition, substrates having multiple layers or substrates having chiral properties can currently only be measured by methods such as polarization analysis methods. However, polarization analysis techniques require specialized training and can be time-consuming and costly. Therefore, there is a need for an apparatus for accurately and precisely measuring substrate thickness and the films formed thereon. Ideally, such an apparatus should be relatively easy, inexpensive, and quick to use. SUMMARY OF THE INVENTION

[0007] This document describes, among other things, an apparatus for characterizing, inter alia, substrate thickness and film thickness, as well as other measurement criteria of a substrate and a film formed thereon. The apparatus interrogates a substrate using one or more wavelengths of light from a light source (e.g., a swept laser). The light is directed substantially perpendicular to the upper surface of the substrate. A polarizer and an analyzer element are both coupled between the light source and the substrate. In various embodiments, the polarizer and the analyzer may comprise a single element. Thus, both the polarizer and the analyzer are located in the beam propagation path from the light source to the substrate. An optical detector is disposed substantially perpendicular to the upper surface of the substrate. The optical detector receives the light returned from the substrate. The apparatus can determine the thickness of the substrate and one or more films contained thereon, regardless of whether the substrate has a chiral property or a stress-induced film.

[0008] In various embodiments, the disclosed subject matter is a metrology apparatus for measuring the thickness of a substrate. The metrology apparatus includes an illumination source directed substantially perpendicular to the upper surface of the substrate, and a polarizer coupled between the illumination source and the substrate. The substrate is for receiving light from the illumination source after the light has passed through the polarizer in a predetermined polarization state. An optical detector is for receiving the light returned from the substrate, and the optical detector is disposed substantially perpendicular to the upper surface of the substrate and between the illumination source and the substrate. An analyzer is coupled between the substrate and the optical detector. The analyzer is configured to determine an angle within the rotated polarization plane of the light received from the substrate due to an optical property of at least one of the substrate and a film formed on the substrate.

[0009] In various embodiments, the disclosed subject matter is a method for measuring the thickness of a substrate. The method includes setting a polarization state of a light source, selecting at least one wavelength from the light source, setting components of an analyzer based on a return light signal from the substrate, impinging a light beam from the light source substantially perpendicular onto the substrate, and calculating the thickness of the substrate based on the return light signal from the substrate.

[0010] In various embodiments, the disclosed subject matter is a metrology apparatus for measuring the thickness of a substrate having chiral properties. The metrology apparatus includes an illumination source directed substantially perpendicular to the upper surface of the substrate, and a polarizer coupled between the illumination source and the substrate. The substrate is for receiving light after the light from the illumination source passes through the polarizer within a predetermined plane of polarization. An optical detector is for receiving the light returned from the substrate, and the optical detector is disposed substantially perpendicular to the upper surface of the substrate. An analyzer is coupled between the substrate and the optical detector. The analyzer is for determining the angle within the rotated plane of polarization of the light received from the substrate due to the chiral properties of the substrate, and each of the polarizer and the analyzer is located in a common optical path. At least one optical compensator is for determining the optical path difference between the illumination source and the received light returned from the substrate.

[0011] The various figures of the accompanying drawings merely illustrate exemplary implementations of the present disclosure and should not be considered as limiting its scope.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Figure 5A

Figure 5B

Figure 6A

Figure 6B

Figure 7

[0013] The disclosed subject matter is directed to a polarization control sensor that can characterize the stack thickness of one or more optically anisotropic materials, such as a chiral object and a film having at least a portion of a stress - inducible film. In a normal incidence reflectometer, currently, there is no adjustment of the polarization state of the incident light source (e.g., a laser used as the light source). Further, there is no analysis of the light returned from the interrogated (measured) object, such as a substrate or a substrate with a film formed thereon.

[0014] Optical anisotropies such as chirality mislead standard measurement tools such as standard reflectometers about the actual thickness of various materials. When linearly polarized light passes through a sample with optical anisotropy properties, it rotates either to the left (counterclockwise) or to the right (clockwise). The amount by which the light rotates is known as the rotation angle. The direction (clockwise or counterclockwise) and magnitude of the rotation reveal information about the optical anisotropy properties of the sample, such as, in the case of chirality, the relative concentration of optical isomers present in the sample.

[0015] Generally, chirality, a type of optical anisotropy, is an optical structure or property, such as the configuration of a molecule or the spin of a particle, that makes the structure or property distinguishable from its mirror image or symmetric opposite. A molecule or ion is considered chiral if it cannot be superimposed on its mirror image by any combination of rotation, translation, and some structural changes. Chiral molecules or ions exist as two stereoisomers that are mirror images of each other, called optical isomers. Optical isomers are often distinguished as either "right-handed" or "left-handed" by their absolute configuration or some other criterion. The two optical isomers have the same physical properties except that they often have opposite optical properties. As a result, substrates with chiral properties often cannot be easily or accurately measured by optical-based measurement tools.

[0016] In various embodiments, the disclosed subject matter is a metrology tool that uses a light source having an angle of incidence with respect to the upper surface of a substrate that is set to approximately 0 degrees (i.e., substantially perpendicular to the substrate). Polarization control is provided in the interrogation beam path and between the sensor device and the substrate. Additionally, an analyzer component is provided between the substrate and the sensor device within the return beam path. In various embodiments, the polarization control can also serve the purpose of an analyzer. In an embodiment, the light source is set to a polarization state that matches the eigenmode of the substrate (e.g., the eigenmode of silicon if the substrate includes a silicon wafer). In an embodiment, specific information regarding one or more film layers can be input into the sensor device to determine the refractive index and thickness of the layer. The refractive index and thickness of the layer can be determined regardless of the optical anisotropy of the material. In an embodiment, the disclosed subject matter is a metrology tool that can characterize a thinned substrate, such as a thinned silicon wafer. The characterization can include measuring the thickness of the substrate and determining the anisotropy introduced into the substrate by the thinning process.

[0017] Generally, a standard reflectometer measures the thickness of a transparent layer of a wafer by measuring the wavelength dependence of Fabry - Perot interference that occurs in reflected or transmitted light. When the layer is illuminated with a spatially coherent light beam, both the upper and lower surfaces of the substrate and / or the film cause reflections. These reflections interfere with each other, and the amplitude of the reflected light can become larger or smaller depending on whether the interference is constructive or destructive. The interference depends on the layer thickness, its refractive index, and the wavelength of the light. The layer is defined as any homogeneous medium with substantially parallel upper and lower surfaces. Examples are a film deposited on a substrate and the substrate itself, such as a silicon wafer. These interference patterns are considered in more detail below.

[0018] For example, the reflection intensity of a single layer is as follows:

Equation

[0019] where r1 is the reflection coefficient at the first surface and r2 is the reflection coefficient at the second surface, [Number] where n is the refractive index, l is the thickness, and λ is the wavelength. Due to the complex exponential function, the reflection intensity is periodic in ∂. Since ∂ is proportional to the optical frequency (c / λ), the reflection intensity is periodic at the optical frequency with a period of c / 2nl, where n is the refractive index, l is the layer thickness, and c is the speed of light in vacuum.

[0020] As described below, the advanced measurement tool of the disclosed subject matter incorporates a light source consisting of a single-wavelength light source, multiple wavelengths, or a light source that sweeps through multiple wavelengths over time. The reflected light is then analyzed for its wavelength dependence. By determining the period of the reflection intensity in terms of the optical frequency (which is inversely proportional to the wavelength), the thickness of the substrate and / or layer can be determined if the refractive index is also known. A reflectometer can be used to measure the thickness or refractive index of a transparent layer when other factors are known. When the light source uses infrared wavelengths, specifically wavelengths longer than, for example, 1.4 μm, the thickness of a silicon substrate, for example, can be measured with a reflectometer. Also, as described below, the advanced reflectometer of the disclosed subject matter can also be used to measure structures with optical anisotropy, or stress-induced substrates and / or film layers.

[0021] When the object to be measured consists of multiple layers, the equation for the reflection intensity includes terms that combine various combinations of thicknesses. As described above, the resulting reflection spectrum includes several periodicities, such as the period corresponding to the optical thickness of each individual layer and the period corresponding to the total optical thickness.

[0022] To generate a sufficient interference signal, as observed through the fringe visibility of the reflected signal, the reflections from the top and bottom surfaces of the substrate include similar beam divergence. For example, when the beam on the substrate is collimated, the reflected beams from the front and bottom surfaces are collimated, the interference is enhanced, and the fringe visibility is increased.

[0023] When the substrate consists of multiple layers, Fabry - Perot interference causes the reflected signal to consist of multiple periodicities at the optical frequency. The reflected signal can be analyzed to extract the thickness of the substrate and the thicknesses of other layers on the substrate. However, as described above, a standard reflectometer cannot accurately measure a chiral substrate or film with induced stress.

[0024] Referring now to FIG. 1, a high - level example of a measurement system 100 for characterizing substrate thickness, film thickness, and other measurement criteria of a substrate and a film formed thereon, according to various embodiments of the disclosed subject matter, is shown. The measurement system 100 is shown to include a hardware - based processor 101 coupled to firmware and / or software components 103 for control and analysis of signals received from the measurement system 100. The hardware - based processor 101 and the firmware / software components 103 are electrically coupled to supply signals to, and receive signals from, an analog - to - digital converter (ADC) 107 through a bidirectional communication path 105. The analog signal converted by the ADC 107 is received from a polarimeter - type reflectometer 113 through a communication path 109. The ADC 107 further supplies a signal for controlling the polarimeter - type reflectometer 113 through a communication path 111.

[0025] The ellipsometric reflectometer 113 provides an interrogating light source 115 that is substantially perpendicular to the surface of the substrate 119. The substrate 119 can be, for example, a bare silicon wafer with or without one or more layers of a film formed thereon. Signals 117 in the form of reflected light, refracted light, and scattered light are received by the ellipsometric reflectometer 113 from the substrate 119. The signals received from and supplied to the ellipsometric reflectometer 113 are described in more detail below. For example, a hardware-based processor 101 coupled to firmware and / or software components 103 can be used for controlling and analyzing the signals received from the ellipsometric reflectometer 113. In embodiments, the firmware and / or software components 103 can also be at least partially hardware-based, including a special-purpose processor such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC) programmed to perform one or more aspects related to the disclosed subject matter described herein, for example, in software, in firmware, or as a hardware implementation.

[0026] In various embodiments, the hardware-based processor 101 and the firmware and / or software components 103 can be used to determine the thickness of the substrate and the substrate on which a film is formed by performing a Fourier analysis of the signal 117 initially received by the ellipsometric reflectometer 113 from the substrate 119. For example, the hardware-based processor 101 and the firmware and / or software components 103 can receive a digital signal from the ADC 107 through the bidirectional communication path 105 and then perform operations including (1) a Fourier transform of the digital signal, (2) finding the peak amplitude from the digital signal, and (3) calculating the thickness of the substrate and the film contained thereon. Each of these operations is described in more detail below.

[0027] The substrate 119 can comprise various types of substrates, such as, for example, a wafer comprising an elemental semiconductor (e.g., silicon or germanium), a wafer comprising a compound semiconductor (e.g., gallium arsenide (GaAs) or gallium nitride (GaN)), or various other types of substrates known in the art, including conductive, semiconductive, and non - conductive substrates. As a result, the substrate 119 can include, for example, circular substrates (e.g., wafers) of 400 mm, 300 mm, 200 mm, 150 mm, 125 mm, and 100 mm, or any one or more of other shapes and / or dimensions, including, for example, opaque, transparent, and bonded substrates (e.g., at visible wavelengths).

[0028] FIG. 2 shows additional exemplary details of a portion 200 of the measurement system 100 of FIG. 1, according to various embodiments of the disclosed subject matter. FIG. 2 is shown to include a light source 201, components 203 of a photonic circuit, an optical element 205, and a substrate 211. The combination of the light source 201, components 203 of the photonic circuit, and the optical element 205 can be the same as or similar to the polarimeter - type reflectometer 113 of FIG. 1. Further, while the portion 200 of the measurement system 100 is shown to include three separate elements (the light source 201, components 203 of the photonic circuit, and the optical element 205), the three elements are shown only to assist one of ordinary skill in the art in recognizing and understanding the relevant portions of the disclosed subject matter. For example, some or all of the separate elements can be combined into a single component.

[0029] In various embodiments, the light source 201 can be an illumination source that includes a swept laser. The swept laser is a type of laser where the output wavelength of the laser is adjustable over a wide range of wavelengths. The selected wavelength and the rate at which the wavelength is changed can be set by its own controller, a remote controller, or can be predetermined by a combination of the hardware-based processor 101 and the firmware / software components 103 of FIG. 1 that supply an appropriate signal to the spectrophotometric reflectometer 113 through the ADC107. In other embodiments, the light source 201 can comprise a broadband source, such as a broadband incoherent infrared or ultraviolet light source, or a broadband incoherent visible light source.

[0030] The components 203 of the photonic circuit can include several different photonic devices. For example, the photonic devices can include components for generating, manipulating, and / or detecting light. These components can include laser diodes, light emitting diodes, optical amplifiers, and other components for generating, detecting, or manipulating light (e.g., splitting, recombining, and / or circulating it). In various embodiments, the components 203 of the photonic circuit can also include an optical detector for receiving the light returned from the substrate. The optical detector is arranged to receive light substantially perpendicular to the upper surface of the substrate 211. The optical detector can comprise, for example, a photodetector or a spectrometer. The choice of using a photodetector or a spectrometer can be determined at least in part based on the configuration of the light source 201.

[0031] In various embodiments, the optical element 205 may comprise a collimator and an objective lens. The collimator may be used to convert the divergent light or other radiation emitted by the light source 201 into parallel light rays that impinge substantially perpendicularly to the upper surface of the substrate 211. In various embodiments, the objective lens can be used to focus the light rays on the substrate 211. The objective lens is also used to collect the light returned from the substrate 211. The optical element 205 may also comprise an optical detector such as a photodetector or a spectrometer, as described above. As a result, in various embodiments, the photodetector or spectrometer may be included within the component 203 of the photonic circuit.

[0032] Either the component 203 of the photonic circuit or the optical element 205 may also include a polarizer, an analyzer, a wave plate (e.g., a quarter-wave plate), and at least one optical compensator plate. The substrate 211 receives the light from the light source 201 after the light has passed through a polarizer within a predefined polarization plane. For example, the light from the light source 201 can be rotated to a polarization state such that the light incident on the sample matches the eigenmode of the sample.

[0033] The analyzer is used to determine the angle within the rotated polarization plane of the light received from the substrate 211 due to the optical properties of the substrate 211 and the film. For example, the optical properties of the substrate can include light rotated within the polarization plane due to the chiral properties of the substrate.

[0034] The at least one optical compensator plate can be used to determine the optical path difference between the light source 201 and the received light returned from the substrate 211. The optical path difference can be used to determine the phase of the light, which can be used to determine the interference and diffraction of the light as it propagates, as will be described in more detail below.

[0035] The substrate 211 can be, for example, a bare silicon wafer with or without one or more layers of a film formed thereon. As a result, the substrate 211 can be the same as or similar to the substrate 119 of FIG. 1.

[0036] Figure 3 shows an exemplary graph 300 of a signal 301 received from a silicon wafer having a nominal thickness of approximately 780 μm. The received signal is shown as a function of the frequency of the interrogating laser. Signal 301 forms an envelope of the fringe pattern received from the substrate. The vertical axis (y-axis, or vertical axis) is an arbitrary detector voltage 303 received by the systems of FIGS. 1 and 2.

[0037] Figures 4A - 4D show examples of graphs 400, 410, 420, 430 of signals received from a silicon wafer having a nominal thickness of approximately 780 μm as a function of the wavelength of the interrogating laser in various polarization states.

[0038] Figure 4A shows an exemplary graph 400 having a signal 401 received from a silicon wafer with a thickness of approximately 780 μm. Signal 401 forms an envelope of the fringe pattern received from the substrate. The interrogating laser is set to a polarization state of approximately 0 degrees (in this example, the silicon wafer includes a notch defined as -90 degrees). The vertical axis is an arbitrary detector voltage 403 received by the systems of FIGS. 1 and 2.

[0039] Figure 4B shows an exemplary graph 410 having a signal 411 received from a silicon wafer with a thickness of approximately 780 μm. Signal 411 forms an envelope of the fringe pattern received from the substrate. The interrogating laser is set to a polarization state of approximately 45 degrees (in this example, the silicon wafer includes a notch defined as -90 degrees). The vertical axis is an arbitrary detector voltage 413 received by the systems of FIGS. 1 and 2.

[0040] Figure 4C shows an exemplary graph 420 having a signal 421 received from a silicon wafer approximately 780 μm thick. The signal 421 forms an envelope of the fringe pattern received from the substrate. The interrogating laser is set to a polarization state of approximately 90 degrees (in this example, the silicon wafer includes a notch defined as -90 degrees). The vertical axis is an arbitrary detector voltage 423 received by the systems of FIGS. 1 and 2.

[0041] Figure 4D shows an exemplary graph 430 having a signal 431 received from a silicon wafer approximately 780 μm thick. The signal 431 forms an envelope of the fringe pattern received from the substrate. The interrogating laser is set to a polarization state of approximately 135 degrees (in this example, the silicon wafer includes a notch defined as -90 degrees). The vertical axis is an arbitrary detector voltage 433 received by the systems of FIGS. 1 and 2.

[0042] FIGS. 5A and 5B show examples of graphs of Fourier transform amplitude versus thickness (in micrometers, μm) for the received signals of FIGS. 4A-4D. Each of the graphs shows the polarization state of the interrogating light beam at approximately 0 degrees (501), approximately 45 degrees (503), approximately 90 degrees (505), and approximately 135 degrees (507).

[0043] Figure 5A shows an exemplary graph 500 showing any unit (e.g., the square of a Fourier component) on the vertical axis 509 and micron units on the horizontal axis 511 (x-axis, or horizontal axis). Graph 500 shows two distinct peaks. One peak is centered at approximately 5 μm and the other peak is centered at approximately 25 μm. The two peaks are caused by the reflection and / or scattering of the laser light from the surface of the metal chuck holding the silicon wafer. During the measurement process, a vacuum was applied to push down the wafer. Typically, there is a small air gap between the wafer and the metal chuck. The two traces are the result of the gap and are caused by the roughness of the underlying metal surface. The thickness of the air gap is approximately 3.5 times the value, as shown in the graph. In other words, the measured value of the sample includes not only silicon, but also metal, air, and silicon. However, the presence of these gaps does not change the measured thickness of the silicon, but they introduce side peaks near the main peak (as also described in Figure 5B below).

[0044] Figure 5B shows an exemplary graph 520 showing any unit on the vertical axis 521 and micron units on the horizontal axis 523. Graph 520 shows a distinct peak centered at approximately 780 μm. The test silicon wafers in Figures 4A - 4D had a thickness of approximately 780 μm. As a result, the thickness of the silicon wafer can be determined using the apparatus illustrated and described in Figures 1 and 2 above.

[0045] Figure 6A shows an exemplary graph 600 of the signal 601 received from a thinned silicon wafer having a nominal thickness of approximately 70 μm as a function of the wavelength of the interrogating laser. In this example, no polarization was applied to the interrogating beam. The received signal 601 is shown as a function of the wavelength of the interrogating laser. The vertical axis is any detector voltage 603 received by the system of Figures 1 and 2.

[0046] FIG. 6B shows an exemplary graph 620 of Fourier transform amplitude versus thickness for the received signal of FIG. 6A. Each of the transformed signals shows the polarization state of the interrogating light ray at no polarization (621), approximately 0 degrees (623), approximately 45 degrees (625), and approximately 135 degrees (627). Graph 620 shows a distinct peak centered slightly less than approximately 70 μm. The test silicon wafer in FIG. 6A had a thickness of approximately 70 μm. As a result, the determination of the thickness of the thinned silicon wafer can be determined using the apparatus illustrated and described in FIGS. 1 and 2 above.

[0047] FIG. 7 shows a generalized example of a method 700 for measuring the thickness of a substrate and a film using the disclosed subject matter's system, if present, according to various embodiments. However, not all of the steps shown may be required for a given operation. The exemplary steps can include at least some of the following steps discussed below. Also, the exemplary steps can be performed in an order different from that shown in method 700 of FIG. 7. Thus, method 700 is provided as an example of how the apparatus of FIGS. 1 and 2 can be used to determine the thickness of a substrate that includes a substrate having a film formed thereon. For example, if it is known that the substrate does not have chiral properties or the film does not have induced stress, thereby potentially changing their optical properties, the step of setting the polarization state of the light source of the apparatus or the step of setting the components of the analyzer may not be required.

[0048] In various embodiments, in operation 701, the polarization state of a light source (e.g., light source 201 of FIG. 2) is set. In operation 703, at least one wavelength of the light source is set. For example, if a swept laser is used as the light source, multiple wavelengths can be used to set it to sequentially interrogate the substrate.

[0049] In operation 705, the components of the analyzer can be set, if necessary, to determine the state of the signal received back from the substrate. Those skilled in the art will recognize that the setting of the components of the analyzer can be set later in method 700. Next, in operation 707, the light source impinges substantially perpendicular to the substrate under test. In an embodiment, the operation of setting the polarization state of the light source in operation 701 and the operation of setting the components of the analyzer in operation 705 can consist of the same operation if the polarizer and the analyzer comprise the same components.

[0050] In operation 709, a reading (e.g., a signal from reflected light, refracted light, or scattered light) is received from the substrate. As described above, the substrate can include one or more films formed thereon. In other embodiments, the substrate may not include any films (or films of negligible thickness, such as a native oxide formed on a silicon wafer). The reading from operation 709 is converted to a digital signal in operation 711 from a detector (e.g., an analog signal), for example, through ADC107 of FIG. 1. In an embodiment, operations 701 to 711 can be repeated multiple times to collect a spectrum of measurement values at different wavelengths.

[0051] In operation 713, a Fourier transform of the digital signal of operation 709 is prepared. In various embodiments, operations 701 to 711 can be repeated with either a wavelength change or a polarization state change such that a plurality of data points are obtained prior to operation 713. In operation 715, one or more peak amplitudes of the Fourier transform are determined. The thickness of the substrate and the one or more films is calculated in operation 717 from the peak amplitudes determined in operation 715.

[0052] As used herein, the term "or" can be interpreted in an inclusive or exclusive sense. Further, other embodiments will be understood by those skilled in the art based on reading and understanding the provided disclosure. Further, those skilled in the art will readily understand that all various combinations of the techniques and examples provided herein can be applied in various combinations.

[0053] Throughout this specification, multiple instances may implement components, operations, or structures described as a single instance. Although individual operations are illustrated and described as separate operations, one or more of the individual operations may be executed simultaneously, and unless otherwise stated, it is not necessary for the operations to be executed in the order illustrated. Structures and functions presented as separate components in an exemplary configuration may be implemented as a combined structure or component. Similarly, structures and functions presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements fall within the scope of the subject matter described in this specification.

[0054] Furthermore, although not explicitly shown and understandable to those skilled in the art, each of the various arrangements, amounts, and numbers of elements can be changed (e.g., the number and type of light sources and optical elements). Additionally, each of the examples illustrated and described in this specification merely represents one possible configuration and should not be considered as limiting the scope of the present disclosure.

[0055] Although various embodiments are considered separately, these separate embodiments are not intended to be regarded as independent technologies or designs. As shown above, each of the various parts may be related to each other and each may be used separately or in combination with other embodiments considered in this specification. For example, various embodiments of operations, systems, and processes have been described, but these methods, operations, systems, and processes may be used separately or in various combinations.

[0056] As a result, many modifications and variations will be apparent to those skilled in the art upon reading and understanding the disclosure provided herein. In addition to those listed herein, functionally equivalent methods and devices within the scope of the present disclosure will be apparent to those skilled in the art from the foregoing description. Portions and features of some embodiments may be included in or substituted for portions and features of other embodiments. Such modifications and variations are intended to fall within the scope of the appended claims. Accordingly, the present disclosure should be limited only by the appended claims, along with the full scope of equivalents to which such claims are entitled. It should also be understood that the terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting.

[0057] The abstract is provided to enable the reader to quickly ascertain the nature of the technical disclosure. The abstract is submitted with the understanding that it will not be used to interpret or limit the claims. In addition, in the detailed description of the invention, it can be seen that various features may be grouped together in a single embodiment for the purpose of simplifying the disclosure. This method of disclosure should not be construed as limiting the claims. Accordingly, the following claims are incorporated into the detailed description of the invention, and each claim stands on its own as a separate embodiment.

[0058] The description provided herein includes exemplary embodiments, devices, and apparatuses that embody various aspects of the subject matter described in this document. In the description, numerous specific details are set forth for the purpose of providing an understanding of various embodiments of the subject matter being considered. However, it will be apparent to those skilled in the art that the various embodiments of the disclosed subject matter may be practiced without these specific details. Further, well-known structures, materials, and techniques have not been shown in detail so as not to obscure the various exemplary embodiments. As used herein, the terms "about," "approximately," and "substantially" may refer to a value that is within, for example, + 10% of a given value or range of values. The following numbered examples are specific embodiments of the disclosed subject matter

[0059] Example 1: A measuring device for measuring the thickness of a substrate. The measuring device includes an illumination source oriented substantially perpendicular to the upper surface of the substrate, and a polarizer coupled between the illumination source and the substrate. The substrate is for receiving light after the light from the illumination source passes through the polarizer in a predetermined polarization state. The optical detector is for receiving the light returned from the substrate, and the optical detector is disposed substantially perpendicular to the upper surface of the substrate and between the illumination source and the substrate. The analyzer is coupled between the substrate and the optical detector. The analyzer is configured to determine an angle within the rotated polarization plane of the light received from the substrate due to at least one optical property of the substrate and the film formed on the substrate.

[0060] Example 2. The measuring device according to Example 1, further comprising a compensator plate coupled between the substrate and the optical detector.

[0061] Example 3. The measuring device according to any one of Example 1 or Example 2, wherein the illumination source comprises at least one laser.

[0062] Example 4. The measuring device according to any one of Examples 1 to 3, wherein the illumination source comprises at least one laser having a plurality of selectable wavelengths.

[0063] Example 5. The measuring device according to any one of Examples 1 to 4, further comprising at least one optical compensator plate for determining an optical path difference between the illumination source and the received light returned from the substrate.

[0064] Example 6. The measuring device according to any one of Examples 1 to 5, wherein the illumination source is configured to be modified in a polarization state to match the eigenmode of the substrate.

[0065] Example 7. The measuring device according to any one of Examples 1 to 6, wherein the substrate includes optical anisotropy.

[0066] Example 8. The measuring device according to Example 7, wherein the optical anisotropy includes chiral properties.

[0067] Example 9. The measuring device according to any one of Examples 1 to 8, wherein each of the polarizer and the analyzer is located in a common optical path.

[0068] Example 10. A method for measuring the thickness of a substrate. The method includes setting the polarization state of a light source, selecting at least one wavelength from the light source, setting the components of an analyzer based on the return light signal from the substrate, causing a light beam from the light source to impinge substantially perpendicularly on the substrate, and calculating the thickness of the substrate based on the return light signal from the substrate.

[0069] Example 11. The method according to Example 10, further including calculating the thickness of a film formed on the substrate based on the return light signal from the substrate and the film.

[0070] Example 12. The method according to any one of Example 10 or Example 11, further including receiving a read value from the substrate, the read value being based on a signal from a light beam impinging on the substrate that has been reflected, refracted, or scattered from the substrate.

[0071] Example 13. The method according to any one of Examples 10 to 12, further including converting the received read value into a digital signal.

[0072] Example 14. The method according to Example 13, further including preparing a Fourier transform of the digital signal and determining the peak amplitude of the Fourier transform.

[0073] Example 15. The method according to any one of Examples 10 to 14, further including receiving a return light signal from the substrate in a common optical path through which the light beam is transmitted to the substrate.

[0074] Example 16. The method according to any one of Examples 10 to 15, further comprising setting a polarization state to match the natural mode of the substrate.

[0075] Example 17. A measuring device for measuring the thickness of a substrate having chiral properties. The measuring device includes an illumination source directed substantially perpendicular to the upper surface of the substrate, and a polarizer coupled between the illumination source and the substrate. The substrate is for receiving light after the light from the illumination source has passed through the polarizer within a predetermined polarization plane. The optical detector is for receiving the light returned from the substrate, and the optical detector is disposed substantially perpendicular to the upper surface of the substrate. The analyzer is coupled between the substrate and the optical detector. The analyzer is for determining the angle within the rotated polarization plane of the light received from the substrate due to the chiral properties of the substrate, and each of the polarizer and the analyzer is located in a common optical path. At least one optical compensator is for determining the optical path difference between the illumination source and the received light returned from the substrate.

[0076] Example 18. The measuring device according to Example 17, wherein the optical detector includes a photodetector.

[0077] Example 19. The measuring device according to either Example 17 or Example 18, wherein the optical detector includes a spectrometer.

[0078] Example 20. The measuring device according to any one of Examples 17 to 19, wherein the illumination source is configured to be rotated to a polarization state to match the natural mode of silicon.

[0079] Example 21. The measuring device according to any one of Examples 17 to 20, further comprising a collimator for converting the divergent light emitted by the illumination source into parallel light rays directed substantially perpendicular to the upper surface of the substrate, and an objective lens for collecting the received light returned from the substrate.

Claims

1. A measuring apparatus for measuring the thickness of a substrate, the measuring apparatus comprising: an illumination source directed substantially perpendicular to the upper surface of the substrate; a polarizer coupled between the illumination source and the substrate, wherein light from the illumination source passes through the polarizer in a predetermined polarization state and then the substrate receives the light; an optical detector for receiving the light returned from the substrate, the optical detector being disposed substantially perpendicular to the upper surface of the substrate and between the illumination source and the substrate; an analyzer coupled between the substrate and the optical detector, the analyzer determining an angle within the plane of polarization in which the light received from the substrate has been rotated due to at least one optical property of the substrate and a film formed on the substrate.

2. The measuring apparatus according to claim 1, further comprising a compensator plate coupled between the substrate and the optical detector.

3. The measuring apparatus according to claim 1, wherein the illumination source comprises at least one laser.

4. The measuring apparatus according to claim 1, wherein the illumination source comprises at least one laser having a plurality of selectable wavelengths.

5. The measuring apparatus according to claim 1, further comprising at least one optical compensator plate for determining an optical path difference between the illumination source and the received light returned from the substrate.

6. The measuring apparatus according to claim 1, wherein the illumination source is configured to be modified in a polarization state to match a specific mode of the substrate.

7. The measuring apparatus according to claim 1, wherein the substrate includes optical anisotropy.

8. The measuring apparatus according to claim 7, wherein the optical anisotropy includes chiral properties.

9. The measuring apparatus according to claim 1, wherein each of the polarizer and the analyzer is located in a common optical path.

10. A method for measuring the thickness of a substrate, the method comprising: setting a polarization state of a light source; selecting at least one wavelength from the light source; setting components of an analyzer based on a return light signal from the substrate; causing a light beam from the light source to impinge substantially perpendicular to the substrate; calculating the thickness of the substrate based on the return light signal from the substrate.

11. The method according to claim 10, further comprising calculating a thickness of a film formed on the substrate based on the return optical signal from the substrate and the film.

12. The method according to claim 10, further comprising receiving a read value from the substrate, the read value being based on a signal from the light beam that has impinged on the substrate and has been reflected, refracted, or scattered from the substrate.

13. The method according to claim 12, further comprising converting the received read value into a digital signal.

14. preparing a Fourier transform of the digital signal; The method according to claim 13, further comprising determining a peak amplitude of the Fourier transform.

15. The method according to claim 10, further comprising receiving the return optical signal from the substrate in a common optical path through which the light beam is transmitted to the substrate.

16. The method according to claim 10, further comprising setting the polarization state to match a specific mode of the substrate.

17. A measuring device for measuring the thickness of a substrate having chiral properties, the device comprising: an illumination source oriented substantially perpendicular to an upper surface of the substrate; a polarizer coupled between the illumination source and the substrate, the light from the illumination source passing through the polarizer in a predetermined plane of polarization before the substrate receives the light; an optical detector for receiving the light returned from the substrate, the optical detector being disposed substantially perpendicular to the upper surface of the substrate; an analyzer coupled between the substrate and the optical detector, the analyzer determining an angle in the plane of polarization by which the light received from the substrate has been rotated due to the chiral properties of the substrate, and each of the polarizer and the analyzer being located in a common optical path; at least one optical compensator for determining an optical path difference between the illumination source and the received light returned from the substrate.

18. The measuring device according to claim 17, wherein the optical detector comprises a photodetector.

19. The measuring device according to claim 17, wherein the optical detector comprises a spectrometer.

20. The measuring device according to claim 17, wherein the illumination source is configured to be rotated to a polarization state to match a specific mode of silicon.

21. A collimator for converting the divergent light emitted by the illumination source into parallel light rays directed substantially perpendicular to the upper surface of the substrate, and An objective lens for collecting the received light returned from the substrate, The measuring apparatus according to claim 17, further comprising.

Images