Apparatus for characterizing substrates and films

Abstract

Various examples include an apparatus for characterizing a substrate thickness and a film thickness of a substrate and a film formed thereon. The apparatus detects the substrate using one or more wavelengths of light from a light source (e.g., a scanning laser). The light is directed substantially perpendicularly to an 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 a beam propagation path from the light source to the substrate. An optical detector is arranged substantially perpendicular to the upper surface of the substrate. The optical detector receives light returning from the substrate. The device 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 characteristics or stress inducing films. Other apparatus and methods are also disclosed.

Description

[0001] Claiming priority

[0002] This patent application claims priority to U.S. utility patent application serial number 17 / 871,384, filed on July 22, 2022, entitled “APPARATUS TO CHARACTERIZESUBSTRATES AND FILMS”; the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The disclosed subject matter generally relates to the field of metrology tools used in semiconductor and related industries (e.g., flat panel display and solar cell production facilities). More specifically, in various embodiments, the disclosed subject matter relates to the measurement of substrates (e.g., such as silicon wafers) and films formed on substrates. Background Art

[0004] One aspect of semiconductor manufacturing is the measurement of substrate thickness. Current technologies for measuring substrate thickness include, for example: capacitive sensors, which measure the capacitance of the substrate; height sensor technology, which utilizes two sensors, one sensor above the substrate and one sensor below the substrate; and reflectometers. The use of capacitive sensors generally requires a deep understanding of the materials that make up the substrate. In addition, capacitive sensors generally only work correctly with a single substrate material, and not 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, capacitive sensors have a lower thickness limit of approximately 200 microns and are limited to small samples of the material.

[0005] Height sensor technology is similarly limited to reflectometer-based technology. For example, height sensor technology generally works on thinner samples and can accommodate multi-layer wafer stacks made of almost any material because the technology detects the physical surface of the wafer. However, height sensor technology does require precise alignment in all three axes and requires calibration so that the sensor knows how far apart each axis is in space. This calibration requirement is a lower limit on the accuracy of the measurements made.

[0006] Current reflectometers do not adjust for the polarization state of an incident light source (e.g., a laser) on a substrate. In addition, current reflectometers do not analyze the light returning from the substrate. Therefore, current reflectometers cannot be used to accurately measure substrates with optical anisotropy such as chiral properties or stress-inducing films.

[0007] In addition, substrates with multiple layers or substrates with chiral properties can currently only be measured by methods such as ellipsometry. However, ellipsometry techniques require specialized training and can be expensive and time consuming. Therefore, a device is needed to accurately and precisely measure the thickness of substrates and films formed thereon. Ideally, the use of such a device should be relatively easy, cheap, and fast. Summary of the invention

[0008] This document describes, among other things, a device for characterizing substrate thickness and film thickness and other metrics of a substrate and a film formed thereon. The device uses light of one or more wavelengths from a light source (e.g., a scanning laser) to detect the substrate. The light is directed substantially vertically to the upper surface of the substrate. Both a polarizer and an analyzer element are coupled between the light source and the substrate. In various embodiments, the polarizer and the analyzer may comprise a single element. Therefore, both the polarizer and the analyzer are located in a beam propagation path from the light source to the substrate. An optical detector is arranged substantially perpendicular to the upper surface of the substrate. The optical detector receives light returned from the substrate. The device is capable of determining the thickness of the substrate and one or more films contained thereon, regardless of whether the substrate has chiral properties or a stress-inducing film.

[0009] In various embodiments, the disclosed subject matter is a metrology device for measuring the thickness of a substrate. The metrology device includes an illumination source directed substantially perpendicularly to the upper surface of the substrate and a polarizer coupled between the illumination source and the substrate. The substrate is used to receive the light from the illumination source after it passes through the polarizer in a predetermined polarization state. An optical detector is used to receive light returned from the substrate, the optical detector being arranged 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 the angle to which the light received from the substrate has been rotated in the polarization plane due to the optical properties of at least one of the substrate and the film formed on the substrate.

[0010] In various embodiments, the disclosed subject matter is 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 an analyzer component based on an optical signal returned from the substrate; irradiating a light beam from the light source substantially perpendicularly onto the substrate; and calculating the thickness of the substrate based on the optical signal returned from the substrate.

[0011] In various embodiments, the disclosed subject matter is a metrology device for measuring the thickness of a substrate having a chiral property. The metrology device includes an illumination source directed substantially perpendicularly to the upper surface of the substrate and a polarizer coupled between the illumination source and the substrate. The substrate is used to receive the light from the illumination source after it passes through the polarizer in a predetermined polarization plane. An optical detector is used to receive light returned from the substrate, wherein the optical detector is arranged substantially perpendicular to the upper surface of the substrate. An analyzer is coupled between the substrate and the optical detector. The analyzer is used to determine the angle to which the light received from the substrate has been rotated in the polarization plane due to the chiral property of the substrate, each of the polarizer and the analyzer being located in a common optical path. At least one optical compensator is used to determine the optical path difference between the illumination source and the light received returning from the substrate.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The figures in the drawings depict only example implementations of the present disclosure and should not be considered limiting of its scope.

[0014] Figure 1 shows a high-level example of a system for characterizing substrate thickness and film thickness, as well as other metrics, of substrates and films formed thereon, in accordance with various embodiments of the disclosed subject matter;

[0015] Figure 2 Showing various embodiments according to the disclosed subject matter Figure 1 Additional exemplary details of a portion of a system of;

[0016] Figure 3 An example graph showing a signal received from a silicon wafer having a nominal thickness of 780 μm as a function of the frequency of the probe laser;

[0017] FIG. 4A to FIG. 4D An example of a graph showing the signal received from a silicon wafer having a nominal thickness of about 780 μm as a function of the frequency of the probe laser in various polarization states;

[0018] Figure 5A and Figure 5B Show FIG. 4A to FIG. 4D Example of a plot of Fourier transformed amplitude of the received signal versus thickness,

[0019] Fig. 6A shows an example graph of a signal received from a silicon wafer having a nominal thickness of approximately 70 μm as a function of the frequency of a probe laser;

[0020] Figure 6B Show Fig. 6A An example graph of Fourier transformed amplitude of the received signal versus thickness; and

[0021] Figure 7 A generalized example of a method for measuring the thickness of substrates and films using the system of the disclosed subject matter is shown according to various embodiments. DETAILED DESCRIPTION

[0022] The disclosed subject matter relates to polarization control sensors capable of characterizing the layer thickness of one or more materials having optical anisotropy, such as chiral objects and films, at least a portion of which may be stress-induced. In normal incidence reflectometers, there is currently no adjustment of the polarization state of the incident light source (e.g., a laser used as a light source). In addition, there is no analysis of the light returned from the object being probed (measured), such as a substrate or a substrate having a film formed thereon.

[0023] Optical anisotropy, such as chirality, causes standard metrology tools, such as standard reflectometers, to misread the actual thickness of various materials. Linearly polarized light will rotate to the left (counterclockwise) or right (clockwise) when passing through a sample with optically anisotropic properties. The amount by which the light is rotated is called the angle of rotation. The direction (clockwise or counterclockwise) and magnitude of the rotation reveal information about the optically anisotropic properties of the sample, such as, for example, the relative concentrations of the enantiomers present in the sample in the case of chirality.

[0024] Generally, a type of optical anisotropy (chirality) is an optical structure or property, such as the configuration of a molecule or the spin of a particle, which makes the structure or property distinguishable from its mirror image or symmetrical opposite. If a molecule or ion cannot be superimposed on its mirror image by any combination of rotation, translation and some conformational changes, the molecule or ion is considered to be chiral. Chiral molecules or ions exist in two stereoisomers, which are mirror images of each other, called enantiomers. Enantiomers are often distinguished as "right-handed" or "left-handed" by their absolute configuration or some other standard. The two enantiomers have the same physical properties, but they often have opposite optical properties. Therefore, substrates with chiral properties often cannot be easily or accurately measured by optical-based metrology tools.

[0025] In various embodiments, the disclosed subject matter is a metrology tool that uses a light source having an incident angle set to about 0 degrees relative to the upper surface of the substrate (i.e., substantially perpendicular to the substrate). Polarization control is provided in the detection beam path and between the sensor device and the substrate. In addition, an analyzer component is provided in the return beam path and between the substrate and the sensor device. In various embodiments, polarization control can also be used for the purpose of the analyzer. In an embodiment, the light source is set to a polarization state that matches the eigenmode of the substrate (e.g., if the substrate includes a silicon wafer, the eigenmode of silicon). In an embodiment, specific information about one or more film layers can be input to the sensor device to determine the refractive index and thickness of the layer. Regardless of the optical anisotropy of the material, the refractive index and thickness of the layer can be determined. 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 within the substrate introduced by the thinning process.

[0026] Typically, a standard reflectometer measures the thickness of a transparent layer of a wafer by measuring the wavelength dependence of the Fabry-Perot interference that occurs in reflected or transmitted light. When the layer is illuminated with a spatially coherent beam, both the upper and lower surfaces of the substrate and / or film result in reflections. These reflections interfere with each other, and depending on whether the interference is constructive or destructive, the reflected light amplitude can be large or small. The interference depends on the layer thickness, its refractive index, and the wavelength of the light. A layer is defined as any uniform medium with approximately parallel upper and lower surfaces. Examples are films deposited on a substrate and the substrate itself, such as a silicon wafer. These interference patterns are discussed in more detail below.

[0027] For example, the reflection intensity of a single layer is:

[0028]

[0029] where r1 is the reflection coefficient at the first surface, r2 is the reflection coefficient at the second surface, n is the refractive index, l is the thickness, and λ is the wavelength. Due to the complex index, the reflected intensity is is periodic. Proportional to the optical frequency (c / λ), the reflected intensity is periodic in 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.

[0030] As described below, the advanced metrology tool of the disclosed subject matter is combined with a light source that consists of a single wavelength light source, multiple wavelengths, or a light source that sweeps through multiple wavelengths over time. The dependence of the reflected light on wavelength is then analyzed. If the refractive index is also known, the thickness of the substrate and / or layer can be determined by determining the period of the reflected intensity as a function of the optical frequency (the optical frequency is inversely proportional to the wavelength). If other factors are known, the reflectometer can be used to measure the thickness or refractive index of a transparent layer. If the light source uses an infrared wavelength, specifically, a wavelength longer than, for example, 1.4 μm, the reflectometer can be used to measure the thickness of, for example, a silicon substrate. As also described below, the advanced reflectometer of the disclosed subject matter can also be used to measure structures having optically anisotropic or stress-induced substrates and / or film layers.

[0031] When the object to be measured consists of multiple layers, the formula for the reflected intensity contains terms for various combinations of combined thicknesses. As described above, the resulting reflectance spectrum contains several periods, such as periods corresponding to the optical thickness of each individual layer and periods corresponding to the total optical thickness.

[0032] In order to generate sufficient interference signals to be observed by the fringe visibility of the reflected signal, the reflections from the upper and lower surfaces of the substrate include similar beam divergence. For example, if the beam on the substrate is collimated, the reflected beams from the front and lower surfaces will be collimated, and the interference will be strong and the fringe visibility will be high.

[0033] When the substrate is composed of multiple layers, Fabry-Perot interference results in a reflected signal composed of multiple cycles in the optical frequency. The reflected signal can be analyzed to recover the thickness of the substrate and the thickness of other layers on the substrate. However, as mentioned above, standard reflectometers cannot accurately measure chiral substrates or films with induced stress.

[0034] Reference now Figure 1 , shows a high-level example of a metrology system 100 for characterizing substrate thickness and film thickness and other metrics of substrates and films formed thereon, according to various embodiments of the disclosed subject matter. The metrology system 100 is shown to include a hardware-based processor 101 coupled to a firmware and / or software component 103 for controlling and analyzing signals received from the metrology system 100. The hardware-based processor 101 and the firmware / software component 103 are electrically coupled to supply signals to and receive signals from an analog-to-digital converter (ADC) 107 via a bidirectional communication path 105. The analog signal converted by the ADC 107 is received from an analyzer-type reflectometer 113 via a communication path 109. The ADC 107 also supplies signals via a communication path 111 to control the analyzer-type reflectometer 113.

[0035] The analyzer reflectometer 113 provides a probe light source 115 substantially perpendicular to the surface of a substrate 119. The substrate 119 may be, for example, a bare silicon wafer with or without one or more films formed thereon. Signals 117 in the form of reflected, refracted, and scattered light are received by the analyzer reflectometer 113 from the substrate 119. The signals received from and supplied to the analyzer reflectometer 113 are described in more detail below. For example, a hardware-based processor 101 coupled to a firmware and / or software component 103 may be used to control and analyze the signals received from the analyzer reflectometer 113. In an embodiment, the firmware and / or software component 103 may also be at least partially hardware-based, including, for example, a dedicated processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), which is programmed in software, firmware, or as a hardware implementation to perform one or more aspects related to the disclosed subject matter described herein.

[0036] In various embodiments, the hardware-based processor 101 and the firmware and / or software components 103 may be used to determine the thickness of the substrate and the film formed thereon by performing Fourier analysis on the signal 117 initially received from the substrate 119 by the analyzer-type reflectometer 113. For example, the hardware-based processor 101 and the firmware and / or software components 103, after receiving the digital signal from the ADC 107 via the bidirectional communication path 105, may perform operations including: (1) 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.

[0037] The substrate 119 may include, for example, various types of substrates, such as wafers including elemental semiconductors (e.g., silicon or germanium), wafers including compound semiconductors (e.g., gallium arsenide (GaAs) or gallium nitride (GaN)), or various other substrate types known in the art (including conductive substrates, semiconductive substrates, and non-conductive substrates). Thus, the substrate 119 may include, for example, 400 mm, 300 mm, 200 mm, 150 mm, 125 mm, and 100 mm circular substrates (e.g., wafers), or any one or more of other shapes and / or sizes, including opaque (e.g., at visible wavelengths), light-transmitting, and bonded substrates.

[0038] Figure 2 Showing various embodiments according to the disclosed subject matter Figure 1 Additional exemplary details of portion 200 of metering system 100 . Figure 2 The optical circuit component 203 is shown to include a light source 201, an optical circuit component 203, an optical element 205, and a substrate 211. The combination of the light source 201, the photonic circuit component 203, and the optical element 205 can be used with Figure 11. The analyzer-type reflectometer 113 of the metrology system 100 is the same or similar. In addition, although the portion 200 of the metrology system 100 is shown as including three discrete components (light source 201, photonic circuit component 203, and optical component 205), these three components are shown only to help those of ordinary skill in the art recognize and understand the relevant parts of the disclosed subject matter. For example, some or all of the discrete components may be combined into a single component.

[0039] In various embodiments, light source 201 is an illumination source that may include a scanning laser. A scanning laser is a laser in which the output wavelength of the laser can be adjusted over a wide range of wavelengths. The selected wavelength and the rate at which the wavelength changes can be set by its own controller, a remote controller, or by Figure 1 The combination of the hardware-based processor 101 and the firmware / software component 103 supplies an appropriate signal to the analyzer reflectometer 113 via the ADC 107. In other embodiments, the light source 201 may include a broadband light source, such as a broadband incoherent infrared or ultraviolet light source or a broadband incoherent visible light source.

[0040] The photon circuit component 203 may include a plurality of different photon devices. For example, the photon device may include components for generating, manipulating and / or detecting light. These components may include laser diodes, light emitting diodes, optical amplifiers, and other components for generating, detecting, or manipulating (e.g., splitting, recombining, and / or transmitting) light. In various embodiments, the photon circuit component 203 may also include an optical detector to receive light returned from the substrate. The optical detector is arranged so that it receives light substantially vertically from the upper surface of the substrate 211. The optical detector may include, for example, a photodetector or a spectrometer. The selection of using a photodetector or a spectrometer may be determined based at least in part on the configuration of the light source 201.

[0041] In various embodiments, the optical element 205 may include a collimator and an objective lens. The collimator may be used to convert divergent light or other radiation emitted by the light source 201 into a parallel beam that is substantially perpendicular to the upper surface of the substrate 211. In various embodiments, the objective lens may be used to focus the beam onto the substrate 211. The objective lens is also used to collect light returning from the substrate 211. The optical element 205 may also include an optical detector, such as a photodetector or a spectrometer, as described above. Therefore, in various embodiments, the photodetector or the spectrometer may be included in the photonic circuit component 203.

[0042] The photonic circuit component 203 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. The substrate 211 receives the light from the light source 201 after it passes through the polarizer in a predetermined polarization plane. For example, the light from the light source 201 may be rotated to a polarization state so that the light incident on the sample matches the eigenmode of the sample.

[0043] The analyzer is used to determine the angle to which light received from the substrate 211 has been rotated in the polarization plane due to the optical properties of the substrate 211 and the film. For example, the optical properties of the substrate may include rotation of light in the polarization plane due to the chiral properties of the substrate.

[0044] At least one optical compensator may be used to determine the optical path difference between the light source 201 and the light received back from the substrate 211. The optical path difference may be used to determine the phase of the light, which may determine interference and diffraction of the light as it propagates, as described in more detail below.

[0045] The substrate 211 may be, for example, a bare silicon wafer with or without one or more films formed thereon. Figure 1 The substrate 119 is the same or similar.

[0046] Figure 3 An example graph 300 shows 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 probe laser. The signal 301 forms an envelope of the fringe pattern received from the substrate. The ordinate axis (y-axis or vertical axis) is Figure 1 and Figure 2 Any detector voltage 303 received by the system.

[0047] FIG. 4A to FIG. 4D Examples of graphs 400 , 410 , 420 , 430 are shown of signals received from a silicon wafer having a nominal thickness of approximately 780 μm as a function of the wavelength of the probe laser at various polarization states.

[0048] Figure 4A An exemplary graph 400 is shown with a signal 401 received from a silicon wafer approximately 780 μm thick. The signal 401 forms an envelope of a fringe pattern received from the substrate. The probe 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 ordinate axis is Figure 1 and Figure 2 Any detector voltage 403 received by the system.

[0049] Figure 4BAn exemplary graph 410 is shown with a signal 411 received from a silicon wafer approximately 780 μm thick. The signal 411 forms an envelope of the fringe pattern received from the substrate. The probe 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 ordinate axis is Figure 1 and Figure 2 Any detector voltage 413 received by the system.

[0050] Figure 4C An exemplary graph 420 is shown with 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 probe 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 ordinate axis is Figure 1 and Figure 2 Any detector voltage 423 received by the system.

[0051] Figure 4D An exemplary graph 430 is shown with 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 probe 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 ordinate axis is Figure 1 and Figure 2 Any detector voltage 433 received by the system.

[0052] Figure 5A and Figure 5B Show FIG. 4A to FIG. 4D 1 and 2. Examples of graphs of Fourier transform amplitude of the received signal versus thickness in micrometers (μm). Each graph indicates the polarization state of the probe beam at approximately 0 degrees 501, at approximately 45 degrees 503, at approximately 90 degrees 505, and at approximately 135 degrees 507.

[0053] Figure 5AAn exemplary graph 500 is shown indicating arbitrary units on the ordinate axis 509 (e.g., the square of the Fourier components) and micrometer units on the abscissa 511 (x-axis or horizontal axis). Graph 500 indicates two distinct peaks; one peak centered at approximately 5 μm and the other peak centered at approximately 25 μm. These two peaks are caused by reflection and / or scattering of the laser from the surface of the metal carrier holding the silicon wafer. A vacuum is applied to hold the wafer down during the measurement process. There is typically a small air gap between the wafer and the metal carrier. These two features are a result of the gaps and are caused by the underlying roughness of the metal surface. The air gap thickness is approximately 3.5 times the value shown in the graph. In other words, the measurement of the sample includes metal, air, and silicon, not just silicon. However, the presence of these gaps does not change the measured silicon thickness, but rather introduces side peaks near the main peak (as shown below Figure 5B shown).

[0054] Figure 5B An exemplary graph 520 is shown indicating arbitrary units on an ordinate axis 521 and micrometer units on an abscissa 523. Graph 520 indicates a distinct peak centered at approximately 780 μm. FIG. 4A to FIG. 4D The silicon wafer tested in the experiment is about 780 μm thick. Therefore, the thickness of the silicon wafer can be determined using the above Figure 1 and Figure 2 is determined by the apparatus shown and described in .

[0055] Fig. 6A An example graph 600 showing a signal 601 received from a thinned silicon wafer having a nominal thickness of approximately 70 μm as a function of the wavelength of a probe laser. In this example, no polarization is applied to the probe beam. The received signal 601 is shown as a function of the wavelength of the probe laser. The ordinate axis is Figure 1 and Figure 2 Any detector voltage 603 received by the system.

[0056] Figure 6B Show Fig. 6A 620. Each transformed signal indicates the polarization state of the probe beam at no polarization 621, at about 0 degrees 623, at about 45 degrees 625, and at about 135 degrees 627. Graph 620 indicates a distinct peak centered at slightly less than about 70 μm. Fig. 6A The silicon wafer tested in the experiment was about 70 μm thick. Therefore, the thickness of the thinned silicon wafer can be determined using the above Figure 1 and Figure 2 is determined by the apparatus shown and described in .

[0057] Figure 7A generalized example of a method 700 for measuring the thickness of a substrate and a film (if present) using a system of the disclosed subject matter according to various embodiments is shown. However, not all of the steps shown may be required for a given operation. Exemplary steps may include at least some of the following steps discussed below. In addition, the following steps may be performed in accordance with Figure 7 The exemplary steps may be performed in a different order than the order shown in method 700. Therefore, method 700 is provided as an example of how the exemplary steps may be performed using Figure 1 and Figure 2 Examples of apparatus for determining the thickness of a substrate (including a substrate having a film formed thereon) are provided. For example, if the substrate is known not to have chiral properties, or if one or more of the films are known not to have induced stresses that potentially change their optical properties, then the steps of setting the polarization state of the light source of the apparatus or setting the analyzer component may not be required.

[0058] In various embodiments, at operation 701, a light source (e.g., Figure 2 At operation 703, at least one wavelength of the light source is set. In the case of, for example, using a scanning laser as the light source, multiple wavelengths may be used and set to sequentially detect the substrate.

[0059] At operation 705, an analyzer component may be set as needed to determine the state of a signal received from the substrate. One of ordinary skill in the art will recognize that the setting of the analyzer component may be performed later in method 700. Then, at operation 707, a light source is irradiated substantially vertically onto the substrate under test. In an embodiment, if the polarizer and the analyzer include the same component, the operation of setting the polarization state of the light source at operation 701 and the operation of setting the analyzer component at operation 705 may consist of the same operation.

[0060] At operation 709, a reading (e.g., a signal from reflected, refracted, or scattered light) is received from the substrate. As described above, the substrate may include one or more films formed thereon. In other embodiments, the substrate may not include any films (or include films with negligible thickness, such as native oxides formed on silicon wafers). At operation 711, the reading from operation 709 is obtained by, for example, Figure 1 The ADC 107 converts the signal from the detector (eg, analog signal) into a digital signal. In an embodiment, operations 701 to 711 may be repeated multiple times to collect measurement spectra at different wavelengths.

[0061] At operation 713, a Fourier transform of the digital signal of operation 709 is prepared. In various embodiments, operations 701 to 711 may be repeated with the wavelength changed or the polarization state changed so that multiple data points are obtained before operation 713. At operation 715, one or more peak amplitudes of the Fourier transform are determined. At operation 717, the thickness of the substrate and one or more films are calculated based on the peak amplitudes determined at operation 715.

[0062] As used herein, the term "or" may be interpreted as inclusive or exclusive. In addition, based on reading and understanding the disclosure provided, one of ordinary skill in the art will understand other embodiments. In addition, one of ordinary skill in the art will readily appreciate that various combinations of the techniques and examples provided herein may all be applied in various combinations.

[0063] Throughout the specification, multiple instances can be implemented as parts, operations or structures described as single instances. Although each operation is shown and described as a separate operation, one or more of each operation can be performed simultaneously, and unless otherwise specified, it is not required that these operations must be performed in the order of illustration. The structure and function presented as a separate component in the example configuration can be implemented as a combined structure or component. Similarly, the structure and function presented as a single component can be implemented as a separate component. These and other variations, modifications, additions and improvements all fall within the scope of the subject matter described herein.

[0064] In addition, although not explicitly shown, it will be appreciated by those skilled in the art that each of the various arrangements, quantities, and numbers of elements may be different (e.g., the number and type of light sources and optical elements). In addition, each example shown and described herein represents only one possible configuration and should not be considered to limit the scope of the present invention.

[0065] Although various embodiments are discussed separately, these separate embodiments are not intended to be considered independent techniques or designs. As indicated above, each of the various parts can be interrelated, and each can be used alone or in combination with other embodiments discussed herein. For example, although various embodiments of operations, systems, and processes have been described, these methods, operations, systems, and processes can be used alone or in various combinations.

[0066] Therefore, as will be apparent to those of ordinary skill in the art when reading and understanding the disclosure provided herein, many modifications and variations can be made. According to the foregoing description, in addition to those methods and devices listed herein, functionally equivalent methods and devices within the scope of the present disclosure will be apparent to those skilled in the art. Portions and features of some embodiments may be included in portions and features of other embodiments, or replace portions and features of other embodiments. Such modifications and variations are intended to fall within the scope of the appended claims. Therefore, the present disclosure is limited only by the terms of the appended claims and the full scope of equivalents to which these claims are entitled. It should also be understood that the terms used herein are only for the purpose of describing specific embodiments and are not intended to be limiting.

[0067] The abstract of the specification is provided to allow the reader to quickly determine the essence of the present 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 foregoing detailed description, it can be seen that various features can be combined together in a single embodiment for the purpose of simplifying the present disclosure. This method of disclosure should not be interpreted as limiting the claims. Therefore, the following claims are hereby incorporated into the detailed description, with each claim acting as a separate embodiment by itself.

[0068] The description provided herein includes illustrative examples, devices, and apparatuses that embody various aspects of the subject matter described in the present invention document. In this description, for the purpose of explanation, numerous specific details are set forth in order to provide an understanding of the various embodiments of the subject matter discussed. However, it is apparent to one of ordinary skill in the art that the various embodiments of the disclosed subject matter can be practiced without these specific details. In addition, well-known structures, materials, and techniques are not shown in detail in order to avoid obscuring the various exemplified embodiments. As used herein, the terms "about," "approximately," and "substantially" may refer to, for example, within a given value or range of values. + Value within 10%.

[0069] The following numbered examples are specific embodiments of the disclosed subject matter.

[0070] Embodiment 1: A metrology device for measuring the thickness of a substrate. The metrology device includes an illumination source directed substantially perpendicularly to an upper surface of the substrate and a polarizer coupled between the illumination source and the substrate. The substrate is used to receive light from the illumination source after the light passes through the polarizer in a predetermined polarization state. An optical detector is used to receive light returned from the substrate, the optical detector being arranged substantially perpendicularly 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 to which the light received from the substrate has been rotated in a polarization plane due to optical properties of at least one of the substrate and a film formed on the substrate.

[0071] Embodiment 2. The metrology apparatus of Embodiment 1, further comprising a compensator coupled between the substrate and the optical detector.

[0072] Embodiment 3. The metrology device of Embodiment 1 or Embodiment 2, wherein the illumination source comprises at least one laser.

[0073] Embodiment 4. The metrology device of any preceding embodiment, wherein the illumination source comprises at least one laser having a plurality of selectable wavelengths.

[0074] Embodiment 5. The metrology apparatus according to any of the preceding embodiments, further comprising at least one optical compensator for determining an optical path difference between the illumination source and the light received back from the substrate.

[0075] Embodiment 6. The metrology apparatus of any preceding embodiment, wherein the illumination source is configured to be modified in polarization state to match an eigenmode of the substrate.

[0076] Embodiment 7 The metrology device of any preceding embodiment, wherein the substrate has optical anisotropy.

[0077] Embodiment 8. The metrology device of embodiment 7, wherein the optical anisotropy comprises a chiral property.

[0078] Embodiment 9 The metrology device of any preceding embodiment, wherein each of the polarizer and the analyzer is located in a common optical path.

[0079] Embodiment 10. A method for measuring the thickness of a substrate. The method comprises setting a polarization state of a light source; selecting at least one wavelength from the light source; setting an analyzer component based on an optical signal returned from the substrate; irradiating a light beam from the light source substantially vertically onto the substrate; and calculating the thickness of the substrate based on the optical signal returned from the substrate.

[0080] Embodiment 11. The method according to embodiment 10, further comprising calculating the thickness of the film based on optical signals returned from the substrate and the film formed on the substrate.

[0081] Embodiment 12. The method of Embodiment 10 or Embodiment 11, further comprising receiving a reading from the substrate, the reading being based on a signal from a light beam impinging on the substrate that is reflected, refracted, or scattered from the substrate.

[0082] Embodiment 13. The method according to any one of embodiments 10 to 12 further includes converting the received reading into a digital signal.

[0083] Embodiment 14. The method of embodiment 13 further comprising preparing a Fourier transform of the digital signal; and determining a peak amplitude of the Fourier transform.

[0084] Embodiment 15. The method according to any one of Embodiments 10 to 14, further comprising receiving the optical signal returned from the substrate in a common optical path along which the optical beam is transmitted to the substrate.

[0085] Embodiment 16. The method according to any one of embodiments 10 to 15 further includes setting the polarization state to match an eigenmode of the substrate.

[0086] Embodiment 17. A metrology device for measuring the thickness of a substrate having a chiral property. The metrology device includes an illumination source directed substantially perpendicularly to an upper surface of the substrate and a polarizer coupled between the illumination source and the substrate. The substrate is used to receive light from the illumination source after the light passes through the polarizer in a predetermined polarization plane. An optical detector is used to receive light returned from the substrate, wherein the optical detector is arranged substantially perpendicular to the upper surface of the substrate. An analyzer is coupled between the substrate and the optical detector. The analyzer is used to determine an angle to which the light received from the substrate has been rotated in the polarization plane due to the chiral property of the substrate, each of the polarizer and the analyzer being located in a common optical path. At least one optical compensator is used to determine an optical path difference between the illumination source and the light received returned from the substrate.

[0087] Embodiment 18. The metering device of Embodiment 17, wherein the optical detector comprises a photodetector.

[0088] Embodiment 19. The metrology device of Embodiment 17 or Embodiment 18, wherein the optical detector comprises a spectrometer.

[0089] Embodiment 20 The metrology apparatus of any one of Embodiments 17 to 19, wherein the illumination source is configured to be rotated to a polarization state to match an eigenmode of silicon.

[0090] Embodiment 21. The metrology device according to any one of Embodiments 17 to 20, further comprising: a collimator for converting divergent light emitted by the illumination source into a parallel light beam directed substantially perpendicularly to the upper surface of the substrate; and an objective lens for collecting the received light returned from the substrate.

Claims

1. A metrology device for measuring the thickness of a substrate, the metrology device comprising: an illumination source directed substantially perpendicularly toward the upper surface of the substrate; a polarizer coupled between the illumination source and the substrate, the substrate being configured to receive light from the illumination source after the light passes through the polarizer in a predetermined polarization state; an optical detector for receiving light returned from the substrate, the optical detector being arranged substantially perpendicular to the upper surface of the substrate and between the illumination source and the substrate; and An analyzer is coupled between the substrate and the optical detector, the analyzer being used to determine an angle to which the light received from the substrate has been rotated in a polarization plane due to optical properties of at least one of the substrate and a film formed on the substrate. 2 . The metrology device of claim 1 , further comprising a compensator coupled between the substrate and the optical detector.

3. The metrology device of claim 1, wherein the illumination source comprises at least one laser.

4. The metrology device of claim 1, wherein the illumination source comprises at least one laser having a plurality of selectable wavelengths.

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

6. The metrology apparatus of claim 1, wherein the illumination source is configured to be modified in polarization state to match an eigenmode of the substrate.

7. The metrology device according to claim 1, wherein the substrate has optical anisotropy.

8. The metrology device of claim 7, wherein the optical anisotropy comprises a chiral property.

9. The metrology device of claim 1, wherein each of the polarizer and the analyzer are located in a common optical path.

10. A method for measuring the thickness of a substrate, the method comprising: Set the polarization state of the light source; selecting at least one wavelength from said light source; providing an analyzer component based on an optical signal returned from the substrate; irradiating a light beam from the light source substantially vertically onto the substrate; as well as The thickness of the substrate is calculated based on the optical signal returned from the substrate. 11 . The method of claim 10 , further comprising calculating a thickness of the film based on the optical signal returned from the substrate and the film formed on the substrate.

12. The method of claim 10, further comprising receiving a reading from the substrate based on a signal from a light beam impinging on the substrate that is reflected, refracted, or scattered from the substrate.

13. The method of claim 12, further comprising converting the received readings into digital signals.

14. The method according to claim 13, further comprising: preparing a Fourier transform of the digital signal; as well as The peak amplitude of the Fourier transform is determined.

15. The method of claim 10, further comprising receiving the optical signal returned from the substrate in a common optical path along which the optical beam is transmitted to the substrate.

16. The method of claim 10, further comprising setting the polarization state to match an eigenmode of the substrate.

17. A metrology device for measuring the thickness of a substrate having chiral properties, the metrology device comprising: an illumination source directed substantially perpendicularly toward the upper surface of the substrate; a polarizer coupled between the illumination source and the substrate, the substrate being adapted to receive light from the illumination source after the light passes through the polarizer in a predetermined polarization plane; an optical detector for receiving light returned from the substrate, the optical detector being arranged substantially perpendicular to the upper surface of the substrate; an analyzer coupled between the substrate and the optical detector, the analyzer for determining an angle to which the light received from the substrate has been rotated in the polarization plane due to the chiral property of the substrate, each of the polarizer and the analyzer being located in a common optical path; and At least one optical compensator for determining an optical path difference between the illumination source and received light returned from the substrate.

18. The metering device of claim 17, wherein the optical detector comprises a photodetector.

19. The metrology device of claim 17, wherein the optical detector comprises a spectrometer.

20. The metrology apparatus of claim 17, wherein the illumination source is configured to be rotated to a polarization state to match an eigenmode of silicon.

21. The metering device according to claim 17, further comprising: a collimator for converting divergent light emitted by the illumination source into a parallel light beam directed substantially perpendicularly toward the upper surface of the substrate; and An objective lens is used to collect the received light returned from the substrate.

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