Optical measurement system and method

Abstract

A measurement system and method are provided for use in optical measurement. The measurement system is configured to communicate with a measurement data provider to receive and process raw measurement data representing a spectral interferometer signal measured on a sample in response to an illumination electromagnetic field incident on the upper part of the sample, and includes a control system comprising at least one spectral range that is not substantially absorbed by the sample. The processing extracts a portion of the spectral interferometer signal from the raw measurement data that describes a change in signal intensity due to a change in the optical path difference OPD during the interferometer measurement, wherein the extracted portion of the spectral interferometer signal is independent of the interferometer signal returned from the lower part of the sample in response to the illumination electromagnetic field, and from the extracted portion of the interferometer signal, both the spectral amplitude and phase of the electromagnetic field reflected from the upper part of the sample are directly determined, thereby enabling the determination of a measured spectral signature that characterizes the upper part of the sample.

Description

Technology Field

[0001] The present invention relates to the field of optical measurement for patterned structures such as semiconductor wafers, and in particular to the field of optical measurement useful for metrology.

[0002] Optical measurement methods widely used in semiconductor metrology and process control traditionally rely on spectroreflectometers and / or spectral ellipsometers. However, spectral interferometers are used because the electromagnetic fields scattered from structures contain spectral phase information that is not possible at optical frequencies and can be very useful for extracting more accurate information from measurements.

[0003] Some spectral interferometer technologies are described, for example, in U.S. Patents 10,739,277 and 10,161,885 assigned to the assignee of the present invention application. Background Technology

[0004] A new technique is required to implement infrared (IR)-based spectral interferometric measurements within patterned structures that enables the separation of contributions from the rear of the structure based on the limited temporal consistency of the interferometer.

[0005] Extending the wavelength range of scattering measurements to the IR range offers several advantages, including the ability to transmit light through opaque materials, particularly in the Vis-UV range, inherent sensitivity (e.g., material properties), and simulation simplicity. Specifically, when measuring on structures that are partially or completely transparent for part or all of the optical system's operating wavelength (e.g., structures fabricated on (standard) Si wafers), incident light is not absorbed within the structure but rather continues to propagate within it, partially reflecting backward from the bottom (back) and providing parasitic signals that must be separated from top surface reflections when outputting through the top of the structure. For wavelengths exceeding ~1.1 μm, the Si substrate becomes transparent, and severe contamination can occur due to reflections from the back of the wafer. Bottom reflections from the wafer are unstable due to low repeatability / wafer chucking surfaces.

[0006] In general, it is desirable to use normal incidence measurements, which offer several advantages over oblique incidence operations. Examples of these advantages include hardware simplicity (illumination and collection optics are common for a significant portion of the optical path), miniaturization of device size, the ability to integrate solutions into small footprints (such as integrated metrology), and the simplicity of simulating light-matter interactions.

[0007] However, the vertical incidence mode using IR illumination inevitably collects reflections from both the upper part of the structure (desired data) and the lower part (contamination). As is common in today's metrology requirements, where high spectral quality is necessary, this contamination can hinder the correct interpretation of the measured data. Therefore, it is desirable to prevent or accurately eliminate this contamination while maintaining other system parameters, such as spot size and throughput.

[0008] Several approaches can be used to mitigate this problem. For example, wafer back-side reflections can be eliminated through a common-focus optical layout (implementing a common-focus layout can significantly reduce out-of-focus contributions). However, the common-focus mode presents a problem for scattering measurements in that it introduces strong sensitivity to small focus errors. Following the algorithmic elimination of wafer back-side reflections, the contribution of the signal originating from the back-side reflections is estimated and subtracted from the measured signal by the algorithm. However, back-side reflections vary between different locations on the wafer (depending on the roughness or characteristics of the base stage holding the wafer), and the measured structures (created on the wafer surface) affect the signal reflected from the back. This is because variations in such structures affect the overall light transmission, and back-side reflections cannot be considered a 'constant' contribution. The expected spectral error associated with back-side reflections is on the order of a few percent (or fractions of a percent for some optical layouts), which sometimes allows for a quantitative interpretation as a reasonable error. However, for advanced scatterometry dealing with high-end applications, such errors are completely unacceptable, so simply ignoring backside contributions cannot be used. Consequently, IR scatterometry for semiconductor measurement is generally based on oblique incidence measurements. The problem to be solved

[0009] The technology of the present invention is based on a novel approach for the analysis of raw measurement data using an operating wavelength that represents the spectral interferometer signal measured at a sample with respect to different optical path differences between the sample and the reference arms of the interferometer, and includes wavelength(s) that the sample does not absorb significantly. The present invention can directly extract both the upper portion spectral reflection and the phase of the sample, regardless of whether the raw measurement data includes reflections from the sample interface other than the upper portion (e.g., lower portion reflection).

[0010] The above is achieved in the present invention by extracting a portion of the interferometric signal describing the change in signal intensity due to a change in the optical path difference (OPD) between the sample and the reference arm from the raw measurement data over several (at least four) values ​​of the OPD. Since such a portion of the measured spectral interferometric signal is independent of the interferometric signal returned from one or more internal interfaces of the sample, the spectral amplitude and phase of the signal returned from the upper portion of the sample can be determined directly from said portion. In the description provided below, the portion of the signal describing such change in intensity (amplitude) is sometimes referred to as the "AC portion of the signal" measured over a change in the optical path difference.

[0011] As described below, the inventors have discovered that the so-called "DC portion" of the measured signal—that is, the portion independent of the OPD—is ​​the only portion of the signal associated with the back surface (or other internal interface) of the sample, and that only the AC portion of the signal is associated with the upper portion reflection. These conditions are maintained under the assumption that optical field reflections from the interference mirror (typically an optical path difference induction device), as well as optical field reflections from the lower surface (typically the internal interface of the sample) and the upper portion, do not change across the pixel spectral bandwidth, because the spectral bandwidth of a single pixel is generally very narrow (typically ~1-several nm).

[0012] Although the present invention is particularly useful for optical measurements of silicon structures (semiconductor wafers) requiring vertical incidence measurements using the IR spectral range, the principles of the present invention are not limited to the type of sample or the spectral range of the operating wavelength. The present invention is advantageously useful for spectral interferometric measurements of a type of sample where the top response (amplitude and phase) of the sample to an illumination applied from above must be determined, provided that the illumination includes wavelengths that are not substantially absorbed by the sample material. means of solving the problem

[0013] Accordingly, according to one major aspect of the present invention, a measurement system for use in optical measurement is provided, wherein the measurement system comprises a control system comprising a computer system including a data input utility, memory and a data processor, and is configured to communicate with a measurement data provider to receive raw measurement data representing a measured spectral interferometer signal returned from a sample in response to an illumination electromagnetic field incident on the upper part of the sample, and includes at least one spectral range that is not substantially absorbed by the sample, and comprises an analyzer utility configured and operable for the data processor to perform the following:

[0014] A portion of the spectral interferometer signal describing the change in signal intensity due to the change in the optical path difference OPD during interference measurement is extracted from the raw measurement data, and said spectral interferometer signal portion is the interferometer signal returned from the sample sub-part responding to the illumination electromagnetic field and Independent and; and

[0015] From the extracted portion of the spectral interferometer signal, both the spectral amplitude and phase of the illumination electromagnetic field reflected from the upper portion of the sample are directly determined, thereby enabling the determination of the measured spectral signature characterizing the upper portion of the sample.

[0016] The control system may further include a fitting utility configured to apply model-based processing to the measured spectrum signature to determine one or more parameters of the sample being measured, and operable.

[0017] The technology of the present invention is essentially useful for monitoring measurements of samples / structures made of silicon materials using an IR spectrum or a combination of the visible light spectrum and the IR spectrum.

[0018] In some embodiments, raw measurement data includes data representing spectral interferometer signals returned from the upper and lower parts of a sample made of silicon material in response to an illumination electromagnetic field containing an IR spectrum (possibly returned from one or more internal interfaces of the sample).

[0019] In some embodiments, the measurement system comprises a measurement unit configured as a measurement data provider for generating and providing the raw measurement data, and the measurement unit is configured and operable to perform a spectral interferometric measurement of a sample using an operating wavelength comprising at least one spectral range that the sample does not substantially absorb.

[0020] For example, a spectrum interferometer measurement signal has a signal intensity profile determined as follows.

[0021]

[0022] Here: is the spectral amplitude of the electromagnetic field reflection from the upper part, and is the spectral amplitude of the electromagnetic field reflection from the lower part of the sample; is the electromagnetic field reflection from the interferometer mirror. is the operating wavelength, and z is at a position on the interferometer mirror; and is the spectral phase of the measured spectral interferometer signal.

[0023] The signal portion to be extracted is as follows:

[0024]

[0025] This explains the change in signal intensity with respect to changes in the position z of the interferometer mirror and is independent of the interferometer signal returned from the lower part of the sample. Through this, the spectral amplitude and phase of the electromagnetic field reflection in the upper part can be directly determined.

[0026] According to another major feature of the present invention, a method for use in optical metrology is provided, said method:

[0027] Provides raw measurement data representing a measured spectral interferometer signal returned from a sample in response to an illumination electromagnetic field incident on the upper part of the sample, and includes at least one spectral range that the sample does not substantially absorb,

[0028] As a step of processing the above raw measurement data, the processing step is:

[0029] A step of extracting a portion of a spectral interferometer signal from raw measurement data that describes the change in signal intensity according to the change in optical path difference OPD during interferometer measurement—said that the portion of the spectral interferometer signal is independent of the interferometer signal returned from the lower part of the sample in response to the illumination electromagnetic field—, and

[0030] It includes the step of determining a measured spectral signature characterizing the upper part of a sample by directly determining the spectral amplitude and phase of the illumination electromagnetic field reflection from the upper part of the sample from an extracted portion of the spectral interferometer signal.

[0031] According to another feature of the present invention, a measurement system comprising the following is provided:

[0032] A measurement unit configured and operable to perform normal incidence spectral interferometric measurements on a sample and to generate raw measurement data representing spectral interferometric signals measured on the sample for a plurality of different optical path differences (OPDs) between the sample and a reference arm, using an operating wavelength that includes at least one spectral range that the sample does not substantially absorb; and

[0033] A control system configured and operable to perform the following: extracting a portion of a spectral interferometer signal from raw measurement data that describes a change in signal intensity according to a change in the optical path difference OPD during interference measurement, wherein the portion of the spectral interferometer signal is independent of the interferometer signal returned from the lower portion of the sample responding to the illumination electromagnetic field; and, from the extracted portion of the spectral interferometer signal, directly determining both the spectral amplitude and phase reflecting the illumination electromagnetic field in the upper portion of the sample, thereby enabling the determination of a measured spectral signature characterized by the upper portion of the sample. Brief explanation of the drawing

[0034] To better understand the invention disclosed in this specification and to illustrate how it can be actually carried out, embodiments of the invention will be described as non-limiting examples with reference to the accompanying drawings. FIG. 1 is a block diagram of the control system of the present invention related to a spectrum interferometer measurement unit. FIG. 2 is a flowchart of the method of the present invention for use in data analysis of spectral interferometer data for direct extraction of the amplitude and phase of the sample response to illumination. FIGS. 3 and 4 are drawings illustrating the principles that form the basis of the present invention. FIG. 5 is a diagram illustrating a specific example of the measurement system of the present invention. Specific details for implementing the invention

[0035] Referring to FIG. 1, a measurement system (10) of the present invention is illustrated in a block diagram. This system includes a measurement unit (12) and a control system (14).

[0036] The measurement unit (12) is configured as an operable spectral interferometer system capable of determining one or more parameters of a structure (e.g., pattern parameters) by measuring the spectral phase of a light beam returned (reflected and / or scattered) from a structure / sample S (e.g., a semiconductor wafer). The measurement unit (12) may be based on a general spectral reflectometer configuration in which the sample reflectance is accurately measured and modified for spectral interferometer measurements.

[0037] For the purposes of the present invention, the spectral signature of the upper portion of the sample must be measured using a vertical incidence measurement applied to the upper portion of the sample, and the operating wavelength includes at least one spectral range that the sample does not substantially absorb. Accordingly, the raw measurement data inevitably includes "parasitic" signal components related to reflection / scattering of the internal interface of the sample (e.g., the lower portion of the sample) in addition to the effective signal (reflection / scattering of the upper portion of the sample).

[0038] Accordingly, the measurement unit (12) includes a vertical incidence interferometer assembly comprising a light source system (16) that provides a broadband input light beam Lin (e.g., including an IR spectral range), a detection system (18) (including a spectrometer), and a beam-directing optical device (20). The beam-directing optical device (20) includes a beam splitter / coupler (22, 24), an objective lens unit (26) (one or more lenses), and an optical path difference induction unit (28) (e.g., an interferometer mirror).

[0039] The beam splitter / coupler (22) is located within the optical path of the input light beam (Lin) and directs (reflects) the input light beam (Lin) so that it propagates toward the objective lens unit (26) which focuses the input light beam (Lin) on the measurement plane (MP) where the structure S is located, and directs (transmits) the light beam Lcom so that it is reflected from the measurement plane to propagate to the detection system (18).

[0040] The beam splitter (24) is positioned between the objective lens unit (26) and the measurement plane (MP), and the sample and reference light components ( ) propagate the input light (Lin) along different optical paths toward the measurement plane (sample plane) and the optical path difference induction unit (28), respectively. L sam and L ref )eww Divided into, and the reflection of the sample and mirror (28) combined beam ( L com) The beam is combined and directed toward an objective lens unit (26) that images the beam onto a detection plane where an interference pattern is generated.

[0041] The control system (14) is composed of a computer system including, in particular, a data input / output utility (14A), a memory (14B), and a data processor (14C). Additionally, the control system is provided with a controller (14D) associated with the mirror (28) to control the change in the mirror position and thus the optical path difference between the sample and the reference arms. Wavelength range of interest ( E m (l i )) The reflectivity of the mirror (28) can be measured once and stored in memory (14B).

[0042] A data processor (14C) is configured and operable to analyze raw measurement data generated by a detection system (18) that includes data representing a measured spectral interferometer signal. According to the present invention, the data processor (14C) includes an analyzer (30) comprising a signal portion extractor utility (15) that extracts a portion of a spectral interferometer signal describing a change in signal intensity (amplitude) having a change in several (at least four) different OPD values ​​from the raw measurement data, and an upper portion characterization utility (17). The latter utilizes a predetermined (once measured) reflectance of the mirror (28) and the spectral reflection of the upper portion of the sample from the extracted portion of the interferometer signal. and phase It is configured and operable to directly decide both.

[0043] The upper part characterization utility (17) is further configured to utilize the spectral reflection and phase of the upper part and to generate a spectral signature that characterizes the upper part of the sample.

[0044] Additionally, the control system (14) is provided with a fitting utility (32). The fitting utility is configured and operable to apply model-based processing to the spectral signature of the upper part of the sample and to determine one or more parameters of the sample.

[0045] The control system (14) may or may not be integrated with the measurement unit (12). Generally, the control system (14) may be a standalone system configured for data communication with a measured data provider, which may be the measurement unit (12) itself or a storage device in which such measurement data can be stored.

[0046] According to the present invention, regardless of whether the raw measurement data contains any contamination component related to the reflection of the intermediate layer / interface within the sample, the upper spectral reflection and phase of the sample can be directly determined (extracted) from the raw measured spectral interferometer signal.

[0047] An optical path difference inducing element (e.g., an interferometer mirror) does not suffer from problems related to reflection from the back side. This can be avoided by making a mirror (28) made of one material opaque in the measured spectral range (e.g., using a metal or metal-coated mirror, particularly in the IR range) or by using a mirror thick enough to ensure the loss of temporal coherence between the back side and other reflections of the system. More specifically, the mirror must be made of a material composition different from the composition of the material of the measured sample (in the case of a semiconductor wafer—typically Si) and have a different thickness to eliminate or at least significantly reduce the interferometer contribution of coherent reflections from the sample and to mirror the bottom surface with the measured signal.

[0048] The following is an explanation of the principles of the present invention. In the description below, the upper part is sometimes referred to as the "upper surface."

[0049] Considering the case of an interferometric reflectometer where only the upper surface reflection of the sample is detected (as in the case of visible wavelengths), the single-wavelength l interferometer equation is as follows:

[0050] (1)

[0051] Here This is the electromagnetic field reflectance of the mirror (28). The structure S can be measured when it is outside the field of view of the objective lens unit (26);

[0052] is the electromagnetic field reflectance of sample S( The mirror (28) can be measured when it is in a tilted position where the light reflected from the mirror propagates along an axis that does not intersect the objective lens unit;

[0053]

[0054] z is the optical path difference between the mirror (28) plane and the sample plane.

[0055] MP ;

[0056] is the interferometer phase.

[0057] Now, let us consider an interferometric reflectometer for spectroscopic resolution. Each pixel of the spectrometer observes a finite spectral width. For simplification, each pixel is It is considered to be the average of the range. The interferometer equation is as follows:

[0058] (2)

[0059] Optical Path Difference (OPD) condition In this case, the interferometer equation is as follows:

[0060] (3)

[0061] and , obtain the following:

[0062]

[0063] Therefore, in the case of interference reflection measurements where generally only the reflection from the upper surface of the sample is detected (as in the case of visible wavelengths), the electromagnetic field reflection from the sample The reference or “DC” of the measured intensity of the interferometer signal can be extracted, and the phase data can be extracted from the variable or “AC” component of the measured data. To this end, a “reference” measurement of the sample reflection is performed without mirror contribution, and then several interference (e.g., four) measurements are performed while changing the optical path difference (e.g., moving the mirror (28)).

[0064] The inventors of the present invention have shown that when operating with a broadband interferometer, the "desired" component of the sample reflection (i.e., the top surface reflection) can be extracted from the changing component, which is a profile of the measured amplitude that varies according to optical path differences in several interferometer measurements (e.g., at least four interferometer measurements). Such a technique can be used in a visible channel spectrum interferometer. However, the advantage of this technique is much more significant when using an IR spectrum, in which case using this technique allows for the separation of contributions from the back-side of the sample based on the limited temporal coherence of the interferometer.

[0065] A description of the technology of the present invention for an IR spectrum interferometer is provided below. For the sake of simplicity, several assumptions regarding the reflection characteristics of the sample and the interferometer mirror are made herein. However, it should be understood that the principles of the present invention do not rely on these assumptions but are used to simplify the explanation.

[0066] The temporal consistency of a spectrometer is determined by spectral resolution. To this end We examine a specific pixel of the spectrometer that measures the spectral range of. Here is the center wavelength read by this pixel, and δ determines the spectral bandwidth.

[0067] l i The intensity measured at a pixel for is given as follows:

[0068]

[0069] The measured interferometer intensity is the interferometer mirror and samples It is defined by interference between reflected fields.

[0070] The material composition of the interferometric mirror is selected so that there are no abrupt spectral changes in reflectance. Since the spectral bandwidth of a single pixel is generally very narrow (typically ~1 to several nm), it can be assumed that the mirror reflectance in this range is constant:

[0071] .

[0072] The sample reflectance in this spectral range is similarly nearly constant (typical samples also show little significant spectral variation within such a narrow spectral range), provided that it consists of the following two contributions:

[0073]

[0074] First term is related to reflection from the top of the sample. Under the simplified assumption that reflectance does not change (approximately) across the pixel spectral bandwidth, the following conditions can be used:

[0075] .

[0076] Second term is related to reflection from the bottom of the sample and bottom reflectance and added phase moving through the sample, It includes, and is related to the phase difference between this second term and the upper surface reflection, and is related to the optical path z of the light beam as it passes through the inside of the sample.

[0077] Here 2h is twice the total sample thickness, which is the path where the light ray goes down to the bottom of the sample and then back up. In reality, the light ray can pass through multiple reflections between the sides of the two samples, but for simplicity, these terms are ignored in the analysis of the present invention.

[0078] Similarly, the following assumption can be made: However, the oscillating term It should be noted that it cannot be assumed to be constant across the pixel's spectral range. This is a factor For example, Si, n~4 and h~700mm This is because, in the case of certain types of samples such as, they can be very large.

[0079] The measured intensity is determined by the interference of the electromagnetic field reflected from the sample and the mirror. The mirror (28) position z is scanned controllably through multiple values ​​to provide multiple interference spectra in which both the reflected phase and amplitude can be induced.

[0080] For a specific mirror position z, the intensity for a specific wavelength l is given by the following equation (4):

[0081]

[0082] l i The intensity measured at a pixel for is given as follows:

[0083]

[0084] Under the above assumption, this strength is provided by the following equation:

[0085] (5)

[0086] Now define the following:

[0087] · (6)

[0088] Independent of mirror position z and sample back It represents the signal contribution related to reflection from.

[0089] Therefore, unlike measurements using the UV-VIS spectrum, the DC portion of the signal measured when operating with the IR spectrum, cannot be used, It cannot be used to extract upper surface reflections because it is connected to.

[0090] · (7)

[0091] It relates to the interference between the light ray reflected from the mirror and the light ray reflected from the top of the sample, which is the actual structure under interference measurement (i.e., the desired component).

[0092] The above equation (7) can be written differently:

[0093] (8)

[0094] Here, is the spectral phase between the electromagnetic field reflections from the mirror and the top of the sample. The characteristics measured by a spectral interferometer are and Includes

[0095] · (9)

[0096] It is related to interference between the bottom surface of the sample and reflections from the mirror.

[0097] The mirror position (z) is typically on the order of the measured wavelength because it is used to measure the effect of the phase change between the sample and the mirror. Therefore, this is a typical value of several hundred nanometers or at most a few microns, and in any case, the optical path length indicated by the reflection from the back of the sample, i.e. It is much smaller than.

[0098] The term can be extracted from the integral. Of course,

[0099] .

[0100] If you rearrange it, Depending on the integral of the value, Since the value of is almost unchanged, it means that it can be extracted from the above integral.

[0101] The integral term is related to temporal decoherence and reflects the fact that interference from the back of the sample generates a high oscillation signal that averages on the pixel.

[0102] Specifically, n~4 , h~700mm and for the typical spectral response of the spectrometer pixel (e.g., spectral bandwidth of δ to 1 nm) and the measured wavelength of ~2000 nm, such a term is approximately <10 -10 It exhibits attenuation and effectively and completely eliminates this contribution from the measurement.

[0103] Therefore, the spectral interferometer measurement signal can be expressed as follows:

[0104] (10)

[0105] Here The term includes some influence from reflections from the back of the sample, but is independent of the interferometer mirror position z. and is the reflected field amplitude and phase, which are characteristics measurable by a spectrum interferometer unit, and is the mirror reflectance, and z is the mirror position.

[0106] Therefore, z-independent term , is affected by reflection from the back of the sample, but the z-dependent term There is no such effect on it. Therefore, according to the present invention, the required upper surface reflection It is extracted from the z-dependent (OPD-dependent) measured intensity profile.

[0107] FIGS. 2, 3, and 4 illustrate a measurement method according to the present invention. As shown in the flowchart (100) of the method of the present invention in FIG. 2, the mirror reflectance once measured E m (l i ) , and taken at various mirror positions Measured data including several measurements of is provided.

[0108] Fig. 3 shows the measured intensity according to the change in mirror position z. I(l i ) It shows the change of. This graph shows the AC component, I AC , that is, illustrates the intensity change profile during the z-scan. Figure 4 shows similar spectral measurements for two wavelengths l1 and l2 (e.g., IR spectrum).

[0109] According to the technology of the present invention, such a part of the raw measurement data (i.e., the interferometric signal part describing the intensity / amplitude change according to the change in OPD value) is extracted and used to directly determine the spectral reflection and phase of the upper part of the sample. To this end, four or more measurements may be performed with different optical path difference values ​​(z values).

[0110] As explained above (Equation (10) above), only a portion of the spectral interferometer measurement signal related to the lower reflection of the sample is a z-independent term. Therefore, the upper reflectance of the sample and topology All can be extracted solely from the amplitude change signal portion, that is, the intensity profile of the signal measured for z-change. Ignoring the intensity average in the interpretation of the measured data completely eliminates all contributions related to back reflections of the (incoherent) sample.

[0111] Equation (10) can be expressed as follows:

[0112] (11)

[0113] Here, A is a z-independent constant (i.e., a term that includes some influence from reflections from the back of the sample but is independent of the interferometer mirror position z). ) and parameter B (i.e., ) and parameter C(i.e., ) can be used to interpret the measured data and completely ignores the constant A.

[0114] For example, the spectrum amplitude and phase can be determined as follows:

[0115]

[0116] Returning to FIG. 1, the control system (14) receives raw measurement data representing a spectral interferometer measurement signal measured for at least four different values, for example, different z positions of the mirror (28), an optical path difference between the sample and the reference arm, from, for example, a spectral interferometer measurement unit (12). The data processor (14C) (corresponding analyzer (30)) operates to extract a portion of the interferometer signal with an amplitude varying over various z values ​​from the raw measurement data, and from this portion of the signal, an upper surface reflection and phase I decide everything myself.

[0117] It should be understood that while the present invention is suitable for use with any spectral interferometer to directly filter reflection components from the sample interface other than the upper portion in data analysis, it is particularly useful for the interpretation of IR measurements. Otherwise, the IR measurements would not allow for the direct extraction of the upper portion response.

[0118] Refer to FIG. 5, which schematically illustrates a specific but non-limiting example of a measurement system (200) utilizing the present invention. The system (200) is generally configured similarly to the system (10) described above in FIG. 1, namely, it includes a spectrum interferometer measurement unit (12) and a control system (14). The same reference numerals are used to denote system components common to both examples.

[0119] The system (200) comprises: a light source system (216) that provides a broadband input light beam in both the visual and IR spectra in this example; a detection system (218) that includes a spectrometer (spectrophotometer) (18) for generating spectral data of a light beam incident on the system in this example, and also includes an imaging detector (19) for navigating to a measurement site on the structure and / or collecting an interferometric pattern; and an optical system (220) configured as a light directing device for directing a light beam from the light source (216) toward a sample / structure (S) under measurement located on a support of the sample and toward an optical path difference induction mechanism (28) (e.g., a planar reference mirror in this non-limiting example) and directing the returned light beam toward the detection system (216). The output of the detection unit (216) is transmitted to a control system (14) (via wired or wireless signal communication).

[0120] The optical system (20) sends an input beam (from a light source (216) toward a measurement plane MP (structure plane) L in A lighting channel for propagating ) and a light ray to be measured ( LcomIt is configured to define a detection channel for propagating the input beam () to the detection system (218). L in ) is directed (reflected) toward an objective lens unit (26) that directs such light rays toward a beam splitter / coupler (24) by a beam splitter / coupler (22), and the beam splitter / coupler (24) directs the input light ray (Lin) toward a sample and reference beam ( L sam and L ref Divide into ).

[0121] These beams of light ( L sam and L ref ) interacts with each of the sample S and the optical path difference induction unit (28), and each reflection (scattering) (L' sam and L' ref ) is combined by a splitter / combiner (24) into a beam of light ( L com ) is combined. The latter is directed toward the detection units (18, 19) of the detection system (218) by the lens unit (26) and the beam splitter / combiner (22). To this end, the optical system (20) also directs the returned light beam to a light beam portion ((L com )1 and (L com It includes a beam splitter / coupler (29) that splits into )2), and the steel wire portions are directed to an imaging detector (19) and a spectrum sensor (spectrometer) (18), respectively.

[0122] In a non-limiting embodiment of the present invention, the light-directing device (20) also optionally propagates an input beam (22) from a light source (216) toward a beam splitter / coupler (22). L in It includes a collimation lens (21) of an illumination channel within the optical path of the ) and a tube lens (23) in a detection channel within the optical path of a measured light beam propagating to a detection unit (18).

[0123] Additionally, in such a non-limiting embodiment, the optical system (20) includes polarizers (32, 34) positioned respectively within the illumination and detection channels. More specifically, an input light beam ( L in The input light beam passes through a polarizer (32) and is specially polarized (e.g., linearly polarized) by means of a beam splitter / coupler (22) and is directed toward an objective lens (26), which directs the input light beam toward a beam splitter / coupler (24). The latter directs the polarized input light beam toward a sample and reference polarized beam (L sam and L ref ) is divided into and sent to structure S and reference mirror (28), respectively. The reflections from the structure and mirror are combined into a beam having the specific polarization by a beam splitter / combiner (24). L com The wires are combined by ), and the combined wires pass through the objective lens (26) and the beam splitter / coupler (24) to the polarizer (34), allowing only the light of the specific polarization to propagate to the detection system. The polarized beam thus combined is directed by the beam splitter (29) to the imaging detector (19) and the spectrometer (18), respectively, into a portion of the light ((L com )1 and (L com It is divided into )2). The spectrometer (18) separates and measures the intensity of all wavelengths, and the measured data generated by the spectrometer corresponds to a spectral interferometer pattern (which may also be detected by an image detector (19)).

[0124] The system (200) also includes a driving unit (33) associated with one or both of the mirror (28) and the support of the sample along the optical axis, i.e., the z-axis, thereby inducing an optical path difference that causes a time variation of the spectral interference pattern. It should be noted that although not specifically illustrated in FIG. 1, the measurement unit (12) of FIG. 1 may also include a similar driving unit.

[0125] It should be understood that using the polarizers (32, 34) that are received and oriented as described above actually provides a cross-polarization mode resulting in a dark-field measurement mode. It should be understood that when the mirror (28) is not used (i.e., moved out of the optical path of the incident light or disabled using an appropriate shutter), the measurement unit (12) can operate as a spectroscopic reflectometer. Thus, the same measurement unit (12) can be switched between two different modes of operation as a spectral interferometer and a spectral reflectometer.

[0126] The control system (14) is a computer system configured and operable as described above with reference to FIGS. 1 and FIGS. 2.

[0127] Referring to FIGS. 1 and 5, it can be seen that while a refractive optical system is described in these embodiments, a partially or fully reflective optical system (mirror-based) may be used. For a wide range of IR, a reflective optical system may be preferred.

Claims

Claim 1 A measurement system (10) for use in optical measurement, wherein the measurement system (10) comprises a control system (14) composed of a computer system including a data input utility (14A), a memory (14B), and a data processor (14C), and is configured to communicate with a measurement data provider to receive raw measurement data representing a measured spectral interferometer signal returned from a sample (S) in response to an illumination electromagnetic field (Lin) incident on the upper part of a sample (S), and the spectral range in which the illumination electromagnetic field (Lin) is reflected from the upper part of the sample (S) and the spectral range in which the sample (S) passes through and is transmitted without substantial absorption, and the data processor (14C) extracts a portion of the spectral interferometer signal from the raw measurement data that describes a change in signal intensity according to a change in optical path difference (OPD) during the interference measurement, wherein the portion of the spectral interferometer signal is independent of the interferometer signal returned from the lower part of the sample (S) in response to the illumination electromagnetic field (Lin); and from the extracted portion of the spectral interferometer signal, A measurement system (10) for use in optical measurement, comprising an analyzer (30) configured and operable to directly determine both the spectral amplitude and phase of a reflection of an illuminating electromagnetic field (Lin) reflected from the upper part of a sample (S), thereby determining a measured spectral signature that characterizes the upper part of the sample (S), and further comprising a measurement unit (12) configured as a measurement data provider for generating and providing the raw measurement data, wherein the measurement unit (12) is configured and operable to perform a spectral interferometer measurement on the sample (S), and is configured and operable to perform a spectral interferometer measurement on the sample (S) using a light source (16) that emits light at an operating wavelength including a spectral range reflected from the upper part of the sample (S) and a spectral range transmitted through the sample (S) without substantially absorbing. Claim 2 A measurement system for use in optical measurement, wherein the raw measurement data comprises data representing spectral interferometer signals returned from the upper and lower parts of a sample made of silicon material in response to an illumination electromagnetic field including an IR spectrum. Claim 3 A measurement system for use in optical measurement, wherein the raw measurement data comprises data representing a spectral interferometer signal returned from one or more internal interfaces and from the upper and lower portions of a sample in response to an illumination electromagnetic field including an IR spectrum. Claim 4 delete Claim 5 A measurement system for use in optical measurement, wherein the operating wavelength of claim 1 includes an IR spectrum. Claim 6 A measurement system for use in optical measurement, wherein, in claim 1, the control system is configured to apply model-based processing to a measured spectrum signature to determine one or more parameters of a sample being measured and further comprises an operable fitting utility. Claim 7 A measurement system for use in optical measurement, wherein, in claim 1, the control system is configured to apply model-based processing to a measured spectrum signature to determine one or more parameters of a sample being measured and further comprises an operable fitting utility. Claim 8 A measurement system for use in optical measurement, wherein, in claim 1, the control system is configured to apply model-based processing to a measured spectrum signature to determine one or more parameters of a sample being measured and further comprises an operable fitting utility. Claim 9 In claim 1, the raw measurement data comprises a spectral interferometer measurement signal having a signal intensity profile determined as follows: Here: is the spectral amplitude of the electromagnetic field reflection from the upper part, and is the spectral amplitude of the electromagnetic field reflection from the lower part of the sample; is the electromagnetic field reflection from the interferometer mirror. is the operating wavelength, and z is at a position on the interferometer mirror; and is the spectral phase of the measured spectral interferometer signal, and the analyzer is configured and operable to extract the portion of the interferometer signal, A measurement system for use in optical measurement, wherein the above z-dependent term describes the change in signal intensity according to the change in position z of the interferometer mirror, is independent of the interferometer signal returned from the lower part of the sample, and thereby enables the direct determination of the spectral amplitude and phase of the electromagnetic field reflection of the upper part. Claim 10 A method for use in optical measurement, wherein the method comprises: providing raw measurement data representing a measured spectral interferometer signal returned from a sample (S) in response to an illumination electromagnetic field (Lin) incident on the upper part of a sample (S), wherein the raw measurement data includes a spectral range in which the illumination electromagnetic field (Lin) is reflected from the upper part of the sample (S) and a spectral range in which the illumination electromagnetic field (Lin) is transmitted through the sample (S) without substantially absorbing it; and a step of processing the raw measurement data, wherein the processing step comprises: extracting a portion of the spectral interferometer signal from the raw measurement data that describes a change in signal intensity due to a change in optical path difference (OPD) during the interferometer measurement, wherein the portion of the spectral interferometer signal is independent of the interferometer signal returned from the lower part of the sample (S) in response to the illumination electromagnetic field (Lin); and determining a measured spectral signature characterizing the upper part of the sample (S) by directly determining the spectral amplitude and phase of the reflection of the illumination electromagnetic field (Lin) from the upper part of the sample (S) from the extracted portion of the spectral interferometer signal. A method for use in optical measurement, comprising the step of performing a spectral interferometer measurement on a sample (S) using a light source (16) that emits light at an operating wavelength including a spectral range reflected from the upper part of the sample (S) and a spectral range transmitted through the sample (S) without substantially absorbing. Claim 11 A method for use in optical measurement, wherein the raw measurement data comprises data representing spectral interferometer signals returned from the upper and lower parts of a sample made of silicon material in response to an illumination electromagnetic field including an IR spectrum. Claim 12 A method for use in optical measurement, wherein the raw measurement data comprises data representing a spectral interferometer signal returned from one or more internal interfaces and from the upper and lower parts of a sample in response to an illumination electromagnetic field including an IR spectrum. Claim 13 A method for use in optical measurement, wherein, in claim 10, the above processing further comprises applying model-based fitting to a measured spectral signature to determine one or more parameters of a sample being measured. Claim 14 delete Claim 15 A method for use in optical measurement, wherein the above-mentioned operating wavelength includes an IR spectrum, in paragraph 10. Claim 16 A method for use in optical measurement, wherein the sample is a silicon structure in paragraph 10. Claim 17 In paragraph 10, the above raw measurement data comprises a spectral interferometer measurement signal having a signal intensity profile determined as follows: Here: is the spectral amplitude of the electromagnetic field reflection from the upper part, and is the spectral amplitude of the electromagnetic field reflection from the lower part of the sample; is the electromagnetic field reflection from the interferometer mirror. is the operating wavelength, and z is at a position on the interferometer mirror; and is the spectral phase of the measured spectral interferometer signal, and the signal portion to be extracted is as follows; A method for use in optical measurement, wherein the above z-dependent term describes the change in signal intensity according to the change in position z of the interferometer mirror, is independent of the interferometer signal returned from the lower part of the sample, and thereby can directly determine the spectral amplitude and phase of the electromagnetic field reflection of the upper part.

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