Film thickness measurement method, film thickness measurement system

Abstract

The present disclosure relates to a film thickness measurement method and a film thickness measurement system. The method comprises: measuring a to-be-measured film layer structure based on a white light interference film thickness measurement device to obtain initial measurement data of an interference light signal; establishing a light intensity relationship between a pseudo peak and a target interference peak of a corresponding interface; establishing an optical path difference relationship between the pseudo peak and the target interference peak of the corresponding interface; determining a first target interference peak of a first interface as a first interference peak in the initial measurement data, and determining a second target interference peak of a second interface as a second interference peak; layer by layer from top to bottom, obtaining a theoretical peak light intensity and a theoretical position of a pseudo peak between a non-top interface and an interface above the non-top interface, and successively removing the pseudo peak between the non-top interface and the interface above the non-top interface; and determining a film layer thickness between each two adjacent interfaces in the to-be-measured film layer structure. By the present disclosure, the pseudo peak in the initial measurement data can be eliminated, and the film layer thickness of each film layer in the to-be-measured film layer structure can be accurately obtained.

Description

Technical Field

[0001] This disclosure relates to the field of semiconductor technology, and in particular to a film thickness measurement method and a film thickness measurement system. Background Technology

[0002] In semiconductor manufacturing processes, the vast majority of device structure layers on the surface of silicon wafers are created through thin film growth. The performance of a device depends primarily on the material and structure of the thin film; therefore, precise control of various parameters is required during thin film fabrication, with film thickness being one of the key parameters.

[0003] Common methods for measuring film thickness include elliptic polarization, probe methods, and optical methods. Among these, white light interferometry, a type of optical measurement, has gradually gained popularity in the field of film thickness measurement due to its measurement advantages. The basic principle of white light interferometry is as follows: a reference optical path and a measurement optical path are formed by different optical elements. The light emitted from the light source is split into two beams after passing through a beam splitter. One beam is incident on the sample surface through the measurement optical path (measuring arm) and is reflected back. The other beam is reflected by the reference optical path (reference arm). The two reflected beams eventually converge and interfere to generate an interference light signal. The thickness of each film layer in the sample can be inferred from the position of the interference peak in the interference light signal.

[0004] However, in actual measurements, there are multiple reflections of the light beam between the upper and lower interfaces of the film. When the multiple reflection signals are strong enough and their optical path is within the scanning optical path range, an interference peak will be formed in the measurement signal. However, the actual structure of the wafer under test does not have a film structure that matches its optical path. Therefore, the interference peak caused by multiple reflections is a pseudo-peak without a corresponding actual film structure. This will lead to errors when inferring the film thickness of the wafer under test based on the optical path of the interference peak. Summary of the Invention

[0005] To overcome the problems existing in related technologies, this disclosure provides a film thickness measurement method and a film thickness measurement system.

[0006] This disclosure provides a film thickness measurement method, comprising: measuring a film structure under test using a white light interferometric film thickness measurement device to obtain initial measurement data of the interferometric light signal; wherein the film structure under test includes multiple interfaces, and the initial measurement data includes a corresponding target interference peak generated by a single reflected beam from each interface, and spurious peaks generated by multiple reflected beams between different interfaces; establishing an intensity relationship between the spurious peaks and the target interference peaks of the corresponding interfaces to calculate the theoretical peak intensity of the spurious peaks; establishing an optical path difference relationship between the spurious peaks and the target interference peaks of the corresponding interfaces to calculate the theoretical position of the spurious peaks; determining the first interference peak in the initial measurement data as the first target interference peak corresponding to the first interface among the multiple interfaces, and determining the second interference peak in the initial measurement data as the second target interference peak corresponding to the second interface among the multiple interfaces; acquiring the theoretical peak intensity and theoretical position of the spurious peaks between the non-top interface and the interfaces above it layer by layer from top to bottom, and successively removing the spurious peaks between the non-top interface and the interfaces above it to obtain the target measurement data of the interferometric light signal; and determining the film thickness between every two adjacent interfaces in the film structure under test based on the target measurement data.

[0007] In some embodiments, the step of sequentially acquiring the theoretical peak intensity and theoretical position of the pseudo-peaks between the non-top-level interface and the interfaces above it from top to bottom, and successively removing the pseudo-peaks between the non-top-level interface and the interfaces above it to obtain the target measurement data of the interference light signal includes: determining the theoretical peak intensity and theoretical position of the first pseudo-peak generated by multiple reflections of the light beam between the second interface and the first interface based on the light intensity relationship and the optical path difference relationship; acquiring the theoretical distribution value of the first pseudo-peak; subtracting the theoretical distribution value of the first pseudo-peak from the initial measurement data to obtain the first intermediate measurement data; determining the third interference peak in the first intermediate measurement data as the third target interference peak corresponding to the third interface among the plurality of interfaces; and determining the third interface and the first interface based on the light intensity relationship and the optical path difference relationship. The theoretical peak intensity and theoretical position of the second pseudo-peak generated by multiple reflections of the light beam between the second interface and the third interface, and the theoretical peak intensity and theoretical position of the third pseudo-peak generated by multiple reflections of the light beam between the third interface and the first interface are obtained; the theoretical distribution values ​​of the second pseudo-peak and the third pseudo-peak are obtained; the theoretical distribution values ​​of the second pseudo-peak and the third pseudo-peak are subtracted from the first intermediate measurement data to obtain the second intermediate measurement data; and so on, based on the second intermediate measurement data, the theoretical peak intensity, theoretical position, and theoretical distribution values ​​of the pseudo-peaks between the remaining non-top interface and the interface above it are obtained one by one, and the theoretical distribution values ​​of the pseudo-peaks between the remaining non-top interface and the interface above it are successively removed to obtain the target measurement data of the interference light signal.

[0008] In some embodiments, determining the theoretical peak intensity and theoretical position of the first pseudo-peak generated by multiple reflections of the light beam between the second interface and the first interface based on the light intensity relationship and the optical path difference relationship includes: extracting the peak intensity of the first target interference peak and the peak intensity of the second target interference peak from the initial measurement data, and calculating the optical path difference between the first target interference peak and the second target interference peak; calculating the theoretical position of the first pseudo-peak based on the optical path difference between the first target interference peak and the second target interference peak and the optical path difference relationship; and calculating the theoretical peak intensity of the first pseudo-peak based on the peak intensity of the second target interference peak and the light intensity relationship.

[0009] In some embodiments, obtaining the theoretical distribution value of the first pseudo-peak includes: shifting the second target interference peak to the theoretical position of the first pseudo-peak, and scaling the shifted second target interference peak based on the theoretical peak light intensity of the first pseudo-peak to obtain the theoretical distribution value of the first pseudo-peak.

[0010] In some embodiments, the intensity relationship between the pseudo-peak and the target interference peak at the corresponding interface is determined by the following formula:

[0011]

[0012] Wherein, the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, I xyj I represents the peak intensity of the pseudo-peak xyj. y t represents the peak light intensity of the target interference peak corresponding to interface y. n This represents the transmittance of interface n. Indicates t n power of j, r y This represents the reflectivity of the interface y. Indicates r y r to the power of (j-1) x This represents the reflectivity of interface x. Indicates r x The power of (j-1), y>x≥1, j>1.

[0013] In some embodiments, establishing the optical path difference relationship between the pseudo-peak and the target interference peak of the corresponding interface to calculate the theoretical position of the pseudo-peak includes: obtaining the optical path difference relationship between the pseudo-peak and the target interference peak of the corresponding interface using the following formula:

[0014] L xyj =jL xy

[0015] Where the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, L xyj L represents the optical path difference between the target interference peak and the pseudo-peak xyj corresponding to interface x. xy This represents the optical path difference between the target interference peak corresponding to interface x and the target interference peak corresponding to interface y, where y>x≥1, j>1; based on the optical path difference L xyj Determine the theoretical location of the pseudo-peak xyj.

[0016] In some embodiments, determining the film thickness between every two adjacent interfaces in the film structure under test based on the target measurement data includes: for every two adjacent target interference peaks in the target measurement data, calculating the film thickness of the target film based on the optical path difference between the two adjacent target interference peaks and the refractive index of the target film between the two adjacent interfaces corresponding to the adjacent target interference peaks.

[0017] In some embodiments, the white light interferometric film thickness measurement device includes a low-coherence light source, a beam splitter, a scanning mirror, and a detector. The initial measurement data of the interference light signal based on the measurement of the film structure under test using the white light interferometric film thickness measurement device includes: the low-coherence light source emitting a low-coherence light beam; the beam splitter splitting the low-coherence light beam into a reference beam and a measurement beam; the reference beam illuminating the scanning mirror and being reflected back to the beam splitter by the scanning mirror; the measurement beam illuminating the film structure under test and being reflected back to the beam splitter by each interface of the film structure under test; the reference beam reflected by the scanning mirror and the measurement beam reflected by each interface of the film structure under test combining at the beam splitter to generate an interference light signal; and moving the scanning mirror away from the beam splitter and acquiring the initial measurement data of the interference light signal through the detector.

[0018] This disclosure provides a film thickness measurement system, including: a white light interferometric film thickness measurement device for measuring the film structure under test to obtain initial measurement data of the interference light signal; wherein the film structure under test includes multiple interfaces, and the initial measurement data includes the corresponding target interference peak generated by a single reflected beam from each interface, and pseudo-peaks generated by multiple reflected beams between different interfaces; a processing module for establishing the light intensity relationship between the pseudo-peaks and the target interference peaks of the corresponding interfaces to calculate the theoretical peak light intensity of the pseudo-peaks; and establishing the optical path difference relationship between the pseudo-peaks and the target interference peaks of the corresponding interfaces to calculate the theoretical peak light intensity of the pseudo-peaks. Position; the first interference peak in the initial measurement data is determined as the first target interference peak corresponding to the first interface among the plurality of interfaces, and the second interference peak in the initial measurement data is determined as the second target interference peak corresponding to the second interface among the plurality of interfaces; the theoretical peak light intensity and theoretical position of the pseudo-peaks between the non-top interface and the interface above it are obtained layer by layer from top to bottom, and the pseudo-peaks between the non-top interface and the interface above it are successively removed to obtain the target measurement data of the interference light signal; based on the target measurement data, the film thickness between every two adjacent interfaces in the film structure to be measured is determined.

[0019] In some embodiments, the white light interferometric film thickness measurement device includes a low-coherence light source, a beam splitter, a scanning mirror, and a detector; the low-coherence light source is used to emit a low-coherence light beam; the beam splitter is used to split the low-coherence light beam into a reference beam and a measurement beam, the reference beam illuminates the scanning mirror and is reflected back to the beam splitter by the scanning mirror, the measurement beam illuminates the film structure under test and is reflected back to the beam splitter by each interface in the film structure under test; the reference beam reflected by the scanning mirror and the measurement beam reflected by each interface in the film structure under test are combined at the beam splitter to generate an interference light signal; the detector is used to collect initial measurement data of the interference light signal.

[0020] In some embodiments, the detector is used to acquire the initial measurement data when the scanning mirror is moved along a direction away from the beam splitter; when the reference optical path of the reference beam reflected by the scanning mirror is equal to the measurement optical path of the measurement beam reflected once by one of the interfaces of the film structure under test during the movement of the scanning mirror, a target interference peak corresponding to the interface is generated.

[0021] The film thickness measurement method provided in this disclosure uses a white light interferometric film thickness measurement device to measure the film structure under test and obtain initial measurement data of the interference light signal. The first interference peak in the initial measurement data is identified as the first target interference peak corresponding to the first interface of the film structure under test, and the second interference peak is identified as the second target interference peak corresponding to the second interface of the film structure under test. The theoretical peak intensity and theoretical position of the spurious peaks between the non-top interface and the interfaces above it are obtained layer by layer from top to bottom, and the spurious peaks between the non-top interface and the interfaces above it are successively removed. Thus, the interference peaks in the obtained target measurement data correspond one-to-one with each interface of the film structure under test. Based on the target measurement data, the film thickness of each layer in the film structure under test can be accurately determined. This method, on the one hand, eliminates spurious peaks in the initial measurement data, avoiding errors in deriving film thickness due to the presence of spurious peaks; on the other hand, it retains the target interference peaks corresponding to each interface in the initial measurement data, thereby accurately obtaining the film thickness of each layer in the film structure under test.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0024] Figure 1This is a schematic diagram of a film thickness measurement system based on white light interferometry, as illustrated in an example.

[0025] Figure 2 It is based on an example of an interference light intensity signal diagram.

[0026] Figure 3 This is a flowchart illustrating a film thickness measurement method according to an exemplary embodiment.

[0027] Figure 4 This is a schematic diagram of a test film structure shown in an example.

[0028] Figure 5 It shows Figure 4 The diagram shows the interference light intensity signal corresponding to the film structure under test.

[0029] Figure 6 This is a flowchart illustrating, according to an exemplary embodiment, the successive removal of spurious peaks between a non-top-level interface and interfaces above it.

[0030] Figure 7 This is a schematic diagram illustrating the elimination of spurious peaks generated by two reflections between the first and second interfaces, as shown in an example.

[0031] Figure 8 This is a schematic diagram illustrating the elimination of spurious peaks generated by two reflections between the first and second interfaces, as shown in an example.

[0032] Figure 9 This is a film thickness measurement system illustrated according to an exemplary embodiment. Detailed Implementation

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure.

[0034] Figure 1 This is a schematic diagram of a film thickness measurement system based on white light interferometry, as illustrated in an example.

[0035] refer to Figure 1Film thickness measurement based on white light reflection mainly utilizes the absolute optical path matching mechanism of low-coherence optical interference. The film thickness measurement system may include a low-coherence light source 20, a scanning mirror 30, a beam splitter 40, and a detector 50. The low-coherence light source 20 emits a light beam, and the beam splitter 40 splits the light beam emitted by the low-coherence light source 20 into a reference beam and a measurement beam. The measurement beam enters the measurement arm 70, and the reference beam enters the reference arm 60. The low-coherence light (measurement beam) in the measurement arm 70 illuminates the film structure 10 under test and is reflected back to the beam splitter 40 by the interfaces between different materials in the film structure. The reflected light from different interfaces has different transmission paths, corresponding to different measurement optical paths. The low-coherence light (reference beam) in the reference arm 60 is reflected by the scanning mirror 30 and combined with the reflected light from different interfaces in the film structure at the beam splitter 40 to form a signal beam. By changing the position of the scanning mirror 30 within a certain range, the transmission path (i.e., reference optical path) of the reflected light from the reference arm 60 continuously changes. When the reference optical path is exactly equal to the measurement optical path of the reflected light from a certain interface of the film structure 10 under test (e.g., the first interface 11, the second interface 12, or the third interface 13), a strong interference peak is generated. Since the measurement optical paths of the reflected light from different interfaces are different, interference peaks are generated with the reference beam at different reference optical path positions. Based on the acquisition signal of the detector 50, an interference intensity signal diagram can be obtained, such as... Figure 2 As shown.

[0036] refer to Figure 2 The horizontal axis represents the reference optical path corresponding to the position of the scanning mirror 30 in the reference arm 60 when it moves. The horizontal axis 0 point is the starting point of the movement of the scanning mirror 30 near the beam splitter 40. As the scanning mirror 30 gradually moves away from the beam splitter 40 from the starting point, the reference optical path corresponding to different positions gradually increases, so that the reference optical path is successively equal to the measurement optical path of the reflected beams of the first interface 11, the second interface 12 and the third interface 13 of the film structure 10 under test, and interference peaks are generated at the corresponding positions in sequence. That is, theoretically, the reference optical path corresponding to the peak position of each interference peak is equal to the measurement optical path of the reflected beam of a certain interface.

[0037] The optical path difference between the reflected beams at different interfaces of the film structure under test is related to the refractive index and thickness of the film structure. Therefore, by identifying the optical path difference between the peak points corresponding to different interference peaks, the optical path difference between the reflected beams at the upper and lower interfaces of the corresponding film can be determined, thereby realizing the thickness measurement of the film between different interfaces of the film structure.

[0038] Based on the beam propagation path, for any film layer, the measured optical path difference L between the primary reflected beam at its upper interface i and the primary reflected beam at its lower interface (i+1) is... mi Satisfy: L mi=2n i h i Where n is the refractive index of the film and h is the film thickness. For any interfaces x and y, the optical path difference L between the target interference peaks at interface x and y is... xy Satisfying the relation: y>x≥1. For example, Figure 1 L m1 This represents the difference in the measured optical path length of the light reflected from the first interface 11 and the measured optical path length of the light reflected from the second interface 12 (i.e., the measured optical path difference L). m1 ), L m2 The difference between the measured optical path length of the reflected light from the second interface 12 and the measured optical path length of the reflected light from the third interface 13 (i.e., the measured optical path difference L) m2 L c1 The difference in reference optical path length (i.e., reference optical path difference L) between the reflected light when the scanning mirror 30 is at the same optical path length as the first interface 11 and the second interface 12. c1 Lc2 is the difference in the reference optical path of the reflected light when the scanning mirror 30 is at the same optical path as the second interface 12 and the third interface 13 (i.e., the reference optical path difference L). c2 ). Figure 2 In the diagram, the optical path difference between the target interference peak P1 corresponding to the first interface 11 and the target interference peak P2 corresponding to the second interface 12 is L. 12 The optical path difference between the target interference peak F2 corresponding to the second interface 12 and the target interference peak P3 corresponding to the third interface 13 is L. 23 The optical path differences between the segments have the following relationship:

[0039] L 12 = L m1 =2*n1h1 (1)

[0040] L 23 = L m2 =2*n2h2 (2)

[0041] Wherein, n1 represents the refractive index of the film layer between the first interface 11 and the second interface 12, n2 represents the refractive index of the film layer between the second interface 12 and the third interface 13, h1 represents the thickness of the film layer between the first interface 11 and the second interface 12, and h2 represents the thickness of the film layer between the second interface 12 and the third interface 13.

[0042] Based on the aforementioned relationship between optical path differences, L can be extracted from the measurement data. 12 and L 23 Then, the film thickness h1 between the first interface 11 and the second interface 12, and the film thickness h2 between the second interface 12 and the third interface 13 can be calculated.

[0043] However, multiple reflections at the interfaces of the film structure under test can produce spurious peaks that do not correspond to the actual film structure. In actual measurements, there are situations where the light beam is reflected multiple times between the upper and lower interfaces of the film. When the signals from these multiple reflections are strong enough and their optical path lengths are within the scanning optical path range, interference peaks will form in the measurement signal. However, the actual structure of the wafer under test does not contain a film structure with a matching optical path length. Therefore, the interference peaks caused by multiple reflections are spurious peaks without a corresponding actual structure. This can lead to errors when inferring the structure and thickness of the film under test based on the optical path length of the interference peaks.

[0044] In view of this, embodiments of the present disclosure provide a method for measuring film thickness. Figure 3 This is a flowchart illustrating a film thickness measurement method according to an exemplary embodiment.

[0045] like Figure 3 As shown, the method may include steps S31 to S36.

[0046] In step S31, the structure of the film layer under test is measured using a white light interferometric film thickness measurement device to obtain initial measurement data of the interferometric light signal.

[0047] The film structure under test includes multiple interfaces. The initial measurement data includes the corresponding target interference peak generated by a single reflected beam at each interface, as well as the pseudo peaks generated by multiple reflected beams between different interfaces.

[0048] Among them, the target interference peak refers to the interference peak generated by the first reflected light and the reference light at each interface, while the pseudo peak refers to the interference peak generated by the multiple reflected light beams and the reference light beam between different interfaces.

[0049] In this embodiment, the white light interferometric film thickness measurement device may include a low-coherence light source, a beam splitter, a scanning mirror, and a detector. The low-coherence light source emits a low-coherence light beam; the beam splitter divides the low-coherence light beam into a reference beam and a measurement beam. The reference beam illuminates the scanning mirror and is reflected back to the beam splitter, while the measurement beam illuminates the film structure under test and is reflected back to the beam splitter from each interface of the film structure. The reference beam reflected by the scanning mirror and the measurement beam reflected from each interface of the film structure under test are combined at the beam splitter to generate an interference light signal. During the measurement process, the scanning mirror can be moved away from the beam splitter, and the detector collects initial measurement data of the interference light signal.

[0050] In this embodiment of the disclosure, the film structure to be tested may include multiple film layers and multiple interfaces. Figure 4Taking the test membrane structure shown as an example, it has two membrane layers (which can be referred to as the first membrane layer and the second membrane layer from top to bottom) and three interfaces (which can be referred to as the first interface 11, the second interface 12 and the third interface 13 from top to bottom). It can be understood that the first interface 11 and the second interface 12 are the upper and lower interfaces of the first membrane layer, respectively, and the second interface 12 and the third interface 13 are the upper and lower interfaces of the second membrane layer, respectively.

[0051] In this embodiment, the initial measurement data of the interference optical signal includes multiple interference peaks. These peaks include target interference peaks generated by the primary reflection beam from each interface of the film structure under test and the reference beam, as well as spurious peaks generated by multiple reflection beams between different interfaces and the reference beam. The target interference peaks correspond one-to-one with the interfaces in the film structure under test. In other words, among the multiple interference peaks in the initial measurement data of the interference optical signal, there are target interference peaks that correspond one-to-one with the interfaces for determining the film thickness, and spurious peaks that cause interference. Therefore, it is necessary to identify and remove the spurious peaks from the initial measurement data.

[0052] The following is based on Figure 4 Taking the test film structure with two layers as an example, the process of pseudo-peak generation is explained.

[0053] During the measurement process, when the measurement beam is incident perpendicularly (to facilitate the differentiation of individual beams), Figure 4 When the measurement beam (which has an angle with each interface) strikes the film structure under test, the beam will be reflected at each interface of the film structure. These reflections, in addition to... Figure 4 In addition to the single reflection of each interface itself, there are multiple reflections between adjacent interfaces. These multiple reflections will also produce interference peaks with the reference beam when they return to the beam splitter and are optically matched.

[0054] Figure 4 The diagram illustrates the first and second reflections of light between the upper and lower interfaces (first interface 11 and second interface 12) of the first film layer in a two-layer film structure. Figure 5 It shows Figure 4 The diagram shows the interference light intensity signal corresponding to the film structure under test. (Reference) Figure 4 and Figure 5 When measuring beam i m (Light Intensity I) m When incident on the film structure to be tested, the measurement beam i m Part of the light is reflected once by the first interface 11 to produce reflected light i 1r1 (Light Intensity I) 1r1 ), reflected light i 1r1 The beam returns to the beam splitter and interferes with the reference beam returning from the reference arm, producing an interference peak P1. The measurement beam i... mPart of the light passes through the first interface 11 and then undergoes a first reflection at the second interface 12 before returning to the beam splitter. There, it interferes with the reference light returning from the reference arm, producing an interference peak P2. This returning light is denoted as the first reflection light i from the second interface 12. 2r1 (Light Intensity I) 2r1 In addition, there is i m Part of the light continuously passes through the first interface 11 and the second interface 12, and then, after a first reflection at the third interface 13, returns to the beam splitter and interferes with the returning light from the reference arm to produce an interference peak P3. This reflected light is denoted as the first reflection light i from the third interface 13. 3r1 (Light Intensity I) 3r1 In addition to the primary reflections from each interface, the reflected light returning to the beam splitter also includes multiple reflections from each interface. Taking the secondary reflection from the second interface 12 as an example, when the beam after the first reflection from the second interface 12 passes through the first interface 11 again, a portion of it passes through the first interface 11 and returns to the beam splitter, forming the primary reflection from the second interface 12. 2r1 Another portion returns to the second interface 12 and is regenerated into transmitted and reflected light by the second interface 12. The regenerated reflected light passes through the first interface 11 and is again divided into transmitted and reflected light by the first interface 11. The portion of light that is reflected a second time by the second interface 12 and passes through the first interface 11 is denoted as the second reflected light i of the second interface 12. 2r2 (Light Intensity I) 2r2 ), reflected light i 2r2 Interference occurs at the beam splitter with the reference beam returning from the reference arm, producing an interference peak P122 (also known as a pseudo-peak P122).

[0055] The optical path difference between the interference peaks corresponding to the light beams reflected once from different interfaces corresponds to the optical path difference between the corresponding interfaces, and thus corresponds to the film structure between the corresponding interfaces. For example, the optical path difference L between the peak points corresponding to interference peaks P1 and P2. 12 The optical path difference L between the first interface 11 and the second interface 12 m1 That is, optical path difference L m1 Corresponding to the first film layer; the optical path difference L between the peak points of interference peaks P2 and P3. 23 The optical path difference L between the second interface 12 and the third interface 13 m2 That is, optical path difference L 23 Corresponding to the second film layer, the spurious peak P122 is an interference peak formed after two reflections through the second interface 12. The optical path difference between the spurious peak P122 and other interference peaks does not correspond to the optical path difference between the corresponding interfaces, that is, it does not correspond to the film structure between the corresponding interfaces. Therefore, it will lead to errors if the actual film structure of the sample is inferred from the position of this peak. Therefore, it is necessary to identify and remove the spurious peaks in the interference peaks.

[0056] In step S32, the light intensity relationship between the pseudo-peak and the target interference peak at the corresponding interface is established in order to calculate the theoretical peak light intensity of the pseudo-peak.

[0057] In this embodiment of the disclosure, the light intensity relationship between the pseudo-peak and the target interference peak of the corresponding interface is first established, and then the theoretical peak light intensity of the pseudo-peak of the corresponding interface is calculated based on the established light intensity relationship and the peak light intensity of the target interference peak of the corresponding interface.

[0058] In an exemplary embodiment, the intensity relationship between the pseudo-peak and the target interference peak at the corresponding interface is determined by the following formula:

[0059]

[0060] Wherein, the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, I xyj I represents the peak intensity of the pseudo-peak xyj. y t represents the peak light intensity of the target interference peak corresponding to interface y. n This represents the transmittance of interface n. Indicates t n power of j, r y This represents the reflectivity of the interface y. Indicates r y r to the power of j-1 x This represents the reflectivity of interface x. Indicates r x The power of j-1, y>x≥1, j>1.

[0061] In step S33, the optical path difference relationship between the pseudo-peak and the target interference peak at the corresponding interface is established to calculate the theoretical position of the pseudo-peak.

[0062] In this embodiment of the disclosure, the optical path difference relationship between the pseudo-peak and the target interference peak of the corresponding interface is first established, and then the theoretical position of the pseudo-peak of the corresponding interface is calculated based on the established optical path difference relationship and the optical path difference between the target interference peaks of the corresponding interface.

[0063] In an exemplary embodiment, based on the transmission path of each reflected light, the optical path difference between the pseudo-peak and the target interference peak at the corresponding interface can be obtained using the following formula:

[0064] L xyj =jL xy (4)

[0065] Where the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, L xyj L represents the optical path difference between the target interference peak and the pseudo-peak xyj corresponding to interface x. xyThis represents the optical path difference between the target interference peak corresponding to interface x and the target interference peak corresponding to interface y, where y>x≥1 and j>1.

[0066] Based on the position of the target interference peak corresponding to interface x and the optical path difference L xyj This allows us to determine the theoretical location of the pseudo-peak xyj.

[0067] The derivation process of formula (3) will be explained below.

[0068] When the measurement beam interferes with the reference beam after one reflection between the upper and lower interfaces of the single-layer structure, the intensity I of the interference light is... L This can be expressed by the following formula:

[0069]

[0070] OPD = 2(n c D c -n m D m (6)

[0071] Among them, I c Let I be the incident light intensity of the reference beam at the center wavelength λ0 of the low-coherence source. m To measure the incident light intensity of the beam at the center wavelength λ0 of the low-coherence source, α is the light intensity reflectivity of the scanning mirror in the reference arm, β is the light intensity reflectivity of the lower interface of the film, and F λ (OPD) is the interference envelope term, determined by the spectral distribution of the low-coherence light source. OPD is the optical path difference (the difference between the reference optical path and the measured optical path) of the interference between the two beams. c For the reference arm, the refractive index of the corresponding medium in the reflected light transmission path (typically n) c (refractive index of air), n m To measure the refractive index of the corresponding medium in the transmission path of reflected light in the arm, D c For the reference arm, the propagation path length of the beam, D m To measure the propagation path length of the beam in the arm. I c α, n c The relevant parameters of the reference beam are given, and these parameters are the same for reflected light from different interfaces. m , β, n m D m The correlation coefficient of the light beam is determined by the film structure. Light intensity I L The first two terms are DC terms, and the third term is AC term. When OPD = 0, the third term reaches its maximum value and the light intensity I at this time is... L The other relevant parameter D of the reference beam corresponding to the peak intensity of the interference peak when OPD = 0. c Then it will follow nm D m It changes with the changes.

[0072] Since interferometry is based on the optical path difference between the peak points corresponding to different interference peaks to calculate the thickness of the interfacial film, and the DC term is independent of the optical path difference OPD, the DC term can be ignored. At the same time, with the incident light intensity and reflectivity of the reference beam remaining unchanged, formula (5) can be transformed into the following formula (C is a constant related to the incident light intensity and reflectivity of the reference beam):

[0073]

[0074] As can be seen from formula (7), when the same light source is used, the shapes of the interference peaks of all interfaces are exactly the same and can overlap. The only difference is that the peak values ​​of the interference signals of the reflected beam and the reference beam are different due to the different measurement optical path, reflectivity and incident light energy of the reflected beam at different interfaces. The measurement optical path of the reflected beam at the interface determines the position of the interference peak, and the reflectivity of the interface and the incident light energy determine the peak light intensity of the interference peak.

[0075] Since the reflectivity and transmittance of the interface are both less than 1, for multiple reflections, the more times the light is reflected, the lower the reflected light energy and the longer the optical path. Correspondingly, the peak intensity of the interference peak with the reference beam will be lower, and the optical path difference with the interference peak corresponding to the first reflection of the upper interface that forms multiple reflections will increase exponentially. For the sample to be tested, the nominal thickness of each film layer and the reflectivity and transmittance of each interface are determined. Therefore, according to formulas (5) and (7), the theoretical position and theoretical peak intensity of the interference pseudo-peak formed by the multiple reflection beam can be determined.

[0076] For example, the second reflected light (i) of the second interface 12 2r2 Compared to the first reflected light from the second interface 12 (i) 2r1 The light intensity undergoes one additional reflection each at the first interface 11 and the second interface 12, and the optical path also travels back and forth through the first film layer once more. According to formulas (5), (6), and (7), the light reflected twice from the second interface 12 (i 2r2 The peak value of the interference peak (pseudo-peak P122) corresponding to the second interface 12, and the first reflected light (i) 2r1 The relationship between the peak values ​​of the corresponding interference peak P2 can be determined, and the optical path difference (L) between the pseudo-peak P122 and the target interference peak P1 generated by the first interface 11 can be determined. 122 The optical path difference (L) between the target interference peak P2 generated at the second interface 12 and the target interference peak P1 generated at the first interface 11. 12 The relationship between L and L can also be determined. 122 =2L 12 .

[0077] For a multilayer structure, the light intensity I′ of the target interference peak generated by the first reflected light at interface i (i≥3) is... i (No DC term) can be represented as:

[0078]

[0079] Where n0 represents the air refractive index and D0 represents the distance from the beam splitter to the first interface.

[0080] The light intensity I′ of the interference peak xyj produced by the j-th reflected light between interface x and interface y xyj (No DC term) can be represented as:

[0081]

[0082] From equation (8), we can see that the peak light intensity I of the target interference peak (peak x) corresponding to the first reflection of interface x is... x The peak intensity I of the target interference peak (peak y) corresponding to the first reflection of interface y. y And the peak light intensity I of the interference pseudo-peak xyj corresponding to the j-th reflection between interface x and interface y. xyj Satisfying equation (10) or equation (11):

[0083]

[0084]

[0085] Formula (3) can be obtained from the above formula (10) or (11).

[0086] In the above derivation, once the refractive index of each film material in the film to be tested is determined, the transmittance and reflectance of each interface can also be calculated and determined. The sum of transmittance and reflectance is 1. Therefore, the ratio between the peak light intensity of each reflected light is determined, the optical path difference is also determined, and the ratio of peak light intensity satisfies formula (3), and the optical path difference satisfies formula (4).

[0087] Therefore, after obtaining the target interference peak x corresponding to the first reflection of interface x and the target interference peak y corresponding to the first reflection of interface y, the theoretical position and theoretical peak light intensity of the pseudo-peaks generated by multiple reflections between interface x and interface y can be inferred based on the light intensity relationship and optical path relationship. Based on the theoretical position and theoretical peak light intensity, the pseudo-peaks generated by multiple reflections between interface x and interface y in the measurement data can be identified.

[0088] In step S34, the first interference peak in the initial measurement data is determined as the first target interference peak corresponding to the first interface among multiple interfaces, and the second interference peak in the initial measurement data is determined as the second target interference peak corresponding to the second interface among multiple interfaces.

[0089] In this embodiment of the present disclosure, based on the optical path length of the reflected light from each interface in the film structure under test, when the scanning mirror scans from small to large optical path length, the first and second interference peaks in the initial measurement data must correspond to the actual film interfaces in the film structure under test, and respectively correspond to the upper and lower interfaces of the first film layer (i.e., the first interface 11 and the second interface 12) through which the measurement light first passes. Furthermore, the optical path length of the interference peaks generated by multiple reflections between interfaces is definitely greater than the optical path length of the interference light generated by a single reflection from the corresponding interface. Therefore, when identifying and eliminating spurious peaks generated by multiple reflections between interfaces in the measurement data, the first interference peak in the initial measurement data can be determined as the first target interference peak corresponding to the first interface 11, and the second interference peak in the initial measurement data can be determined as the second target interference peak corresponding to the second interface 12.

[0090] In step S35, the theoretical peak light intensity and theoretical position of the pseudo-peak between the non-top interface and the interface above it are obtained layer by layer from top to bottom, and the pseudo-peak between the non-top interface and the interface above it are removed one by one to obtain the target measurement data of the interference light signal.

[0091] For example, the top-level interface refers to the first interface, and the non-top-level interface refers to any interface other than the first interface. First, obtain the theoretical peak intensity and theoretical position of the first pseudo-peak between the second interface and the interface above it (i.e., the first interface), and remove the first pseudo-peak between the second interface and the first interface; then, obtain the theoretical peak intensity and theoretical position of the pseudo-peak between the third interface and the interface above it (the second interface and the first interface), and remove the second pseudo-peak between the third interface and the second interface, as well as the third pseudo-peak between the third interface and the first interface, and so on, until all pseudo-peaks are removed.

[0092] Specifically, the theoretical peak light intensity of the first pseudo-peak generated by multiple reflections of the light beam between the second interface and the first interface is determined based on the light intensity relationship, and the theoretical position of the first pseudo-peak is determined based on the optical path difference relationship. The theoretical distribution value of the first pseudo-peak can be obtained based on the theoretical peak light intensity and theoretical position of the first pseudo-peak. By subtracting the theoretical distribution value of the first pseudo-peak from the initial measurement data, the first pseudo-peak can be removed from the initial measurement data to obtain the first intermediate measurement data. The third interference peak in the first intermediate measurement data is the third target interference peak corresponding to the third interface in the actual film structure. Based on the light intensity relationship, the theoretical peak light intensity of the second pseudo-peak generated by the multiple reflection beams between the third interface and the second interface is determined, and the theoretical position of the second pseudo-peak is determined based on the optical path difference relationship. Based on the theoretical peak light intensity and theoretical position of the second pseudo-peak, the theoretical distribution value of the second pseudo-peak can be obtained. Subtracting the theoretical distribution value of the second pseudo-peak from the first intermediate measurement data removes the second pseudo-peak from the first intermediate measurement data. Similarly, based on the light intensity relationship, the theoretical peak light intensity of the third pseudo-peak generated by the multiple reflection beams between the third interface and the first interface is determined, and the theoretical position of the third pseudo-peak is determined based on the optical path difference relationship. Based on the theoretical peak light intensity and theoretical position of the third pseudo-peak, the theoretical distribution value of the third pseudo-peak can be obtained. Subtracting the theoretical distribution value of the third pseudo-peak from the first intermediate measurement data removes the third pseudo-peak from the first intermediate measurement data. This process continues until all pseudo-peaks in the measurement data are removed, resulting in the target measurement data. Each interference peak in the target measurement data corresponds to an interface in the actual film structure, and the film structure under test can be deduced from the target measurement data.

[0093] In step S36, the film thickness between every two adjacent interfaces in the film structure to be tested is determined based on the target measurement data.

[0094] In this embodiment of the disclosure, after eliminating all spurious peaks in the initial measurement data, the obtained target measurement data includes target interference peaks that correspond one-to-one with each interface of the film structure to be measured. Therefore, based on the optical path difference between every two adjacent target interference peaks in the target visual measurement data, the film thickness between the two adjacent interfaces corresponding to these two adjacent target interference peaks can be calculated.

[0095] In an exemplary embodiment, determining the film thickness between every two adjacent interfaces in the film structure under test based on target measurement data includes: for every two adjacent target interference peaks in the target measurement data, calculating the film thickness of the target film based on the optical path difference between the two adjacent target interference peaks and the refractive index of the target film between the two adjacent interfaces corresponding to the adjacent target interference peaks.

[0096] For example, based on the optical path difference between the first target interference peak and the second target interference peak, and the refractive index of the first film, the film thickness of the first film can be calculated using formula (1); based on the optical path difference between the second target interference peak and the third target interference peak, and the refractive index of the second film, the film thickness of the second film can be calculated using formula (2), and so on, the film thickness of all films can be obtained.

[0097] The film thickness measurement method provided in this disclosure uses a white light interferometric film thickness measurement device to measure the film structure under test and obtain initial measurement data of the interference light signal. The first interference peak in the initial measurement data is identified as the first target interference peak corresponding to the first interface of the film structure under test, and the second interference peak is identified as the second target interference peak corresponding to the second interface of the film structure under test. The theoretical peak intensity and theoretical position of the spurious peaks between the non-top interface and the interfaces above it are obtained layer by layer from top to bottom, and the spurious peaks between the non-top interface and the interfaces above it are successively removed. Thus, the interference peaks in the obtained target measurement data correspond one-to-one with each interface of the film structure under test. Based on the target measurement data, the film thickness of each layer in the film structure under test can be accurately determined. This method, on the one hand, eliminates spurious peaks in the initial measurement data, avoiding errors in deriving film thickness due to the presence of spurious peaks; on the other hand, it retains the target interference peaks corresponding to each interface in the initial measurement data, thereby accurately obtaining the film thickness of each layer in the film structure under test.

[0098] In this embodiment of the disclosure, the theoretical peak light intensity and theoretical position of the pseudo-peaks between the non-top interface and the interface above it can be obtained one by one from top to bottom, and the pseudo-peaks between the non-top interface and the interface above it can be removed successively to obtain the target measurement data of the interference light signal.

[0099] Figure 6 This is a flowchart illustrating the successive removal of spurious peaks between a non-top-level interface and interfaces above it, according to an exemplary embodiment. Figure 6 As shown, the method may include steps S61 to S68.

[0100] In step S61, the theoretical peak light intensity and theoretical position of the first pseudo-peak generated by the multiple reflections of the light beam between the second interface and the first interface are determined based on the light intensity relationship and the optical path difference relationship.

[0101] Here, the first pseudo-peak refers to all the interference peaks generated by multiple reflections of the light beam between the second interface and the first interface. There can be one or more first pseudo-peaks. For example, the first pseudo-peaks may include pseudo-peak P122 generated by two reflections between the first interface and the second interface, pseudo-peak P123 generated by three reflections between the first interface and the second interface, etc.

[0102] In this embodiment of the disclosure, the theoretical position of the first pseudo-peak can be calculated based on the optical path difference between the first target interference peak and the second target interference peak and the relationship between the optical path difference; the theoretical peak intensity of the first pseudo-peak can be calculated based on the peak intensity of the second target interference peak and the relationship between the peak intensity and the peak intensity.

[0103] In an exemplary embodiment, determining the theoretical peak light intensity and theoretical position of the first pseudo-peak generated by multiple reflections of the light beam between the second interface and the first interface based on the light intensity relationship and the optical path difference relationship includes: extracting the peak light intensity of the first target interference peak and the peak light intensity of the second target interference peak from the initial measurement data, and calculating the optical path difference between the first target interference peak and the second target interference peak; calculating the theoretical position of the first pseudo-peak based on the optical path difference between the first target interference peak and the second target interference peak and the optical path difference relationship; and calculating the theoretical peak light intensity of the first pseudo-peak based on the peak light intensity of the second target interference peak and the light intensity relationship.

[0104] Still with Figure 4 The following explanation uses the two-layer test film structure shown as an example. Figure 5 The interference signals shown are used to determine the first interference peak P1 as the first target interference peak and the second interference peak P2 as the second target interference peak. Figure 5 The optical path difference L1 between the first target interference peak P1 and the second target interference peak P2 can be obtained from the interference signal shown. According to the optical path difference relationship (i.e., formula (4)), the optical path difference between the first target interference peak P1 and the pseudo-peaks generated by the two reflections between the first interface and the second interface should be L. 12 Based on this optical path difference relationship, the third interference peak in the interference signal (i.e., interference peak P122) is a spurious peak generated by two reflections between the first and second interfaces. That is, the third interference peak is a spurious peak P122 because the optical path difference L between the spurious peak P122 and the first target interference peak P1 is twice that of the first target interference peak P1. 122 The optical path difference L between the first target interference peak P1 and the second target interference peak P2 is... 12 Twice that, that is, L 122 =2L 12 Therefore, the position of the pseudo-peak P122 generated by the two reflections between the first and second interfaces was obtained. Similarly, the optical path difference between the pseudo-peak 123 (not shown in the figure) generated by the three reflections between the first and second interfaces and the first target interference peak P1 is three times the optical path difference L1 between the first target interference peak P1 and the second target interference peak P2. Based on this, the theoretical position of pseudo-peak 123 can be derived, and so on, the theoretical positions of all first pseudo-peaks can be derived.

[0105] from Figure 5The peak intensity of the second target interference peak P2 can be obtained from the interference signal shown. According to the intensity relationship (i.e., formula (3)), the peak intensity I2 of the second target interference peak P2 and the peak intensity I of the pseudo-peak P122 can be obtained. 122 The relationship is as follows:

[0106]

[0107] Where r2 represents the transmittance of the second interface and r1 represents the transmittance of the first interface.

[0108] Therefore, based on the peak intensity of the second target interference peak P2, the transmittance of the first interface, and the transmittance of the second interface, the theoretical peak intensity of the pseudo-peak P122 can be calculated using formula (12). Similarly, based on the intensity relationship (i.e., formula (3)), the relationship between the peak intensity of the second target interference peak P2 and the peak intensity of the pseudo-peak P123 can be obtained, thereby deriving the theoretical peak intensity of the pseudo-peak P123. By analogy, the theoretical peak intensity of all first pseudo-peaks can be derived.

[0109] In step S62, the theoretical distribution value of the first pseudo-peak is obtained.

[0110] In theory, all interference peaks can be completely identical and can overlap after stretching. Therefore, the optical path relationship and light intensity relationship can be used to process and transform the target interference peaks corresponding to the obtained interface x or interface y (stretching, compression, position translation, etc.) to obtain the theoretical distribution values ​​of pseudo-peaks.

[0111] In this embodiment of the disclosure, after calculating the theoretical position and theoretical peak light intensity of the first pseudo-peak, the theoretical distribution value of the first pseudo-peak can be obtained based on the theoretical position and theoretical peak light intensity of the first pseudo-peak.

[0112] In an exemplary embodiment, obtaining the theoretical distribution value of the first pseudo-peak includes: shifting the second target interference peak to the theoretical position of the first pseudo-peak, and scaling the shifted second target interference peak based on the theoretical peak light intensity of the first pseudo-peak to obtain the theoretical distribution value of the first pseudo-peak.

[0113] In an exemplary embodiment, obtaining the theoretical distribution value of the first pseudo-peak includes: scaling the second target interference peak based on the theoretical peak light intensity of the first pseudo-peak; and shifting the scaled second target interference peak to the theoretical position of the first pseudo-peak to obtain the theoretical distribution value of the first pseudo-peak.

[0114] The embodiments disclosed herein do not limit the order of the above translation and scaling processes. That is, the second target interference peak can be translated first and then scaled; or the second target interference peak can be scaled first and then translated.

[0115] In step S63, the theoretical distribution value of the first pseudo-peak is subtracted from the initial measurement data to obtain the first intermediate measurement data.

[0116] In this embodiment of the disclosure, after determining the theoretical peak light intensity and theoretical position of the first pseudo-peak, the first pseudo-peak can be removed from the initial measurement data, and the data after removing the first pseudo-peak can be called the first intermediate measurement data.

[0117] The following explanation uses the removal of the pseudo-peak P122 generated by the two reflections between the first and second interfaces as an example.

[0118] Figure 7 This is a schematic diagram illustrating the elimination of spurious peaks generated by two reflections between the first and second interfaces, as shown in an example.

[0119] like Figure 7 As shown in (a), taking a two-layer film structure as an example, the round-trip optical paths of the first and second layers are different. Considering only the two reflected rays between the upper and lower interfaces (first interface 11, second interface 12) of the first layer, the white light interferometry film thickness measurement technique will yield the following results: Figure 7 The four interference peaks shown in (b) include three target interference peaks corresponding to the first interface 11, the second interface 12, and the third interface 13, respectively, as well as the first pseudo-peak generated by the two reflections between the first interface 11 and the second interface 12.

[0120] Based on the optical path relationship, the first interference peak P1 and the second interference peak P2 definitely correspond to the first interface 11 and the second interface 12 in the structure of the film to be measured. That is, the first interference peak P1 is the first target interference peak, and the second interference peak P2 is the second target interference peak. After removing the DC component from the initial measurement data, the peak light intensity I1 of the first target interference peak P1 and the peak light intensity I2 of the second target interference peak P2, as well as the optical path difference L between the first target interference peak P1 and the second target interference peak P2, are obtained. 12 Then, the transmittance and reflectance of each interface are calculated using the refractive index of each material in the film structure, and the theoretical peak light intensity I of the pseudo-peak P122 generated by the second reflection between the first interface 11 and the second interface 12 is calculated using formula (3). t122 The optical path difference L between the pseudo-peak P122 and the first target interference peak P1 is calculated using formula (4). 122The optical path difference L between the first target interference peak P1 and the second target interference peak P2 is... 12 Twice that, that is, L 122 =2L 12 Thus, the optical path difference between the pseudo-peak P122 and the second target interference peak P2 is calculated to be L. 12 This allows us to identify the location of the spurious peak P122 corresponding to the location of the third interference peak P122, meaning the third interference peak P122 should be a spurious peak P122. Then, we extract the second target interference peak P2 and determine its theoretical peak intensity I based on the calculated spurious peak P122. t122 The second target interference peak P2 is subjected to peak compression processing. Based on the calculated optical path difference between the pseudo-peak P122 and the second target interference peak P2, the second target interference peak P2 is shifted (that is, the compressed second target interference peak P2 is shifted to the right by L). 12 The theoretical distribution value P of the pseudo-peak P122 was obtained. t 122, such as Figure 7 As shown in (c) above. Then, the initial measurement data is subtracted from the theoretical distribution value P. t 122, such as Figure 7 As shown in (d) above, the measurement data for eliminating the spurious peak P122 can be obtained, as follows. Figure 7 As shown in (e) in the diagram.

[0121] Figure 8 This is a schematic diagram illustrating the elimination of spurious peaks generated by two reflections between the first and second interfaces, as shown in an example.

[0122] In actual testing, there may be instances where multiple spurious reflection peaks coincide optically with a primary reflection peak at a certain interface in the actual structure. For example, spurious peak P122 may coincide with the third target interference peak P3 corresponding to the third interface. Using the method proposed in this embodiment, even when spurious peaks coincide with the target interference peak, the energy of the spurious peak in the overlapping portion can be eliminated, while the energy of the target interference peak in the overlapping portion can be retained.

[0123] like Figure 8 As shown in (a) of the diagram, taking the identification and elimination of two reflected beams between the upper and lower interfaces (first interface 11 and second interface 12) of the first film layer in a two-layer film structure as an example, this demonstrates the process of identifying and eliminating the spurious peak when it coincides with the target interference peak. When measuring this film structure using white light interferometry, the following results are obtained: Figure 8 The three interference peaks shown in (b) include three target interference peaks corresponding to the first interface 11, the second interface 12, and the third interface 13, respectively, as well as a pseudo-peak generated by two reflections between the first interface 11 and the second interface 12. The pseudo-peak generated by two reflections between the first interface 11 and the second interface 12 coincides with the position of the third target interference peak of the third interface 13.

[0124] Based on the optical path relationship, the first interference peak P1 and the second interference peak P2 definitely correspond to the first interface 11 and the second interface 12 in the structure of the film to be measured. That is, the first interference peak P1 is the first target interference peak, and the second interference peak P2 is the second target interference peak. Therefore, after removing the DC component from the initial measurement data, the peak light intensity I1 of the first target interference peak P1 and the peak light intensity I2 of the second target interference peak P2, as well as the optical path difference L between the first target interference peak P1 and the second target interference peak P2, are obtained. 12 Then, the transmittance and reflectance of each interface are calculated using the refractive index of each material in the film structure, and the theoretical peak light intensity I of the pseudo-peak P122 generated by the second reflection between the first interface 11 and the second interface 12 is calculated using formula (3). t122 The optical path difference L between the pseudo-peak P122 and the first target interference peak P1 is calculated using formula (4). 122 The optical path difference L between the first target interference peak P1 and the second target interference peak P2 is... 12 Twice that, that is, L 122 =2L 12 Thus, the optical path difference between the pseudo-peak P122 and the second target interference peak P2 is calculated to be L. 12 This allows us to identify the location of the spurious peak P122 corresponding to the location of the third interference peak (formed by the superposition of P3 and P122). Since the peak intensity of the third interference peak is greater than the theoretical peak intensity I of the spurious peak P122, t122 Therefore, the third interference peak should be the interference peak resulting from the superposition of the pseudo-peak P122 and the third target interference peak P3 at the third interface. Then, the second target interference peak P2 is extracted, and the theoretical peak intensity I of the calculated pseudo-peak P122 is used as the reference. t122 The second target interference peak P2 is subjected to peak compression processing. Based on the calculated optical path difference between the pseudo-peak P122 and the second target interference peak P2, the second target interference peak P2 is shifted (that is, the compressed second target interference peak P2 is shifted to the right by L). 12 The theoretical distribution value P of the pseudo-peak P122 was obtained. t 122, such as Figure 8 As shown in (c) of the diagram. The theoretical pseudo-peak P is obtained. t After 122, subtract the theoretical pseudo-peak P from the initial measurement data. t 122, such as Figure 8 As shown in (d) above, the measurement data for eliminating the spurious peak P122 were obtained, as follows: Figure 8 As shown in (e) in the diagram.

[0125] It is understood that the above explanation is based on the example of eliminating the false peak P122 generated by the second reflection of the first and second interfaces. The method for eliminating the false peak generated by the third or more reflections of the first and second interfaces is similar to that for eliminating the false peak generated by the second reflection, and will not be repeated here.

[0126] In actual measurements, due to the limited output energy of the sampled low-coherence light source, the spurious peaks appearing in the white light interferometric measurement signal during multilayer film structure measurements are primarily caused by the second and third reflections of the first film layer. Higher-order reflections from the first film layer, multiple reflections from other film layers, and multiple reflections across film interfaces result in very small interference peak signals that are drowned out by DC noise due to the extremely low energy of the reflected light at the corresponding optical path length. Consequently, it may be impossible to find a clear interference peak in the initial measurement signal. Therefore, after eliminating the first spurious peak between the first and second interfaces, steps S64 to S68 can be omitted, and the thickness of each film layer can be determined directly based on the measurement data after eliminating the first spurious peak between the first and second interfaces.

[0127] In step S64, the third interference peak in the first intermediate measurement data is determined as the third target interference peak corresponding to the third interface among multiple interfaces.

[0128] In this embodiment of the disclosure, after eliminating the first spurious peak from the initial measurement data, the first intermediate measurement data is obtained. The third interference peak in the first intermediate measurement data is generated by the first reflection of the third interface, that is, the third interference peak in the first intermediate measurement data is the third target interference peak corresponding to the third interface.

[0129] In step S65, based on the light intensity relationship and the optical path difference relationship, the theoretical peak light intensity and theoretical position of the second pseudo-peak generated by the multiple reflection beams between the third interface and the second interface are determined, as are the theoretical peak light intensity and theoretical position of the third pseudo-peak generated by the multiple reflection beams between the third interface and the first interface.

[0130] The second pseudo-peak refers to all the interference peaks generated by multiple reflections of the light beam between the third interface and the second interface, and there may be one or more second pseudo-peaks; the third pseudo-peak refers to all the interference peaks generated by multiple reflections of the light beam between the third interface and the first interface, and there may be one or more third pseudo-peaks.

[0131] In this embodiment of the disclosure, the theoretical peak intensity of the second pseudo-peak can be determined based on the peak intensity and intensity relationship of the third target interference peak; the theoretical position of the second pseudo-peak can be determined based on the optical path difference and optical path difference relationship between the second target interference peak and the third target interference peak.

[0132] In this embodiment of the disclosure, the theoretical peak intensity of the third pseudo-peak can be determined based on the peak intensity and intensity relationship of the third target interference peak; the theoretical position of the third pseudo-peak can be determined based on the optical path difference and optical path difference relationship between the first target interference peak and the third target interference peak.

[0133] In step S66, the theoretical distribution values ​​of the second pseudo-peak and the third pseudo-peak are obtained.

[0134] In this embodiment, the third target interference peak is shifted to the theoretical position of the second pseudo-peak, and the shifted third target interference peak is stretched based on the theoretical peak light intensity of the second pseudo-peak to obtain the theoretical distribution value of the second pseudo-peak.

[0135] In this embodiment, the third target interference peak is shifted to the theoretical position of the third pseudo-peak, and the shifted third target interference peak is stretched based on the theoretical peak light intensity of the third pseudo-peak to obtain the theoretical distribution value of the third pseudo-peak.

[0136] In step S67, the theoretical distribution values ​​of the second pseudo-peak and the third pseudo-peak are subtracted from the first intermediate measurement data to obtain the second intermediate measurement data.

[0137] In this embodiment of the present disclosure, the second spurious peak and the third spurious peak are successively removed from the first intermediate measurement data to obtain the second intermediate measurement data.

[0138] In this embodiment of the disclosure, the method for removing the second and third spurious peaks from the first intermediate measurement data in step S67 is similar to the method for removing the first spurious peak in step S63, and will not be described again here.

[0139] In step S68, by analogy, based on the second intermediate measurement data, the theoretical peak light intensity, theoretical position and theoretical distribution value of the pseudo-peaks between the remaining non-top interface and the interface above it are obtained one by one, and the theoretical distribution value of the pseudo-peaks between the remaining non-top interface and the interface above it is successively removed to obtain the target measurement data of the interference light signal.

[0140] In this embodiment, the fourth interference peak in the second intermediate measurement data is identified as the fourth target interference peak corresponding to the fourth interface. Based on the light intensity relationship and optical path difference relationship, the theoretical peak light intensity and theoretical position of the fourth pseudo-peak generated by multiple reflections of the light beam between the fourth interface and the third interface are determined; the theoretical peak light intensity and theoretical position of the fifth pseudo-peak generated by multiple reflections of the light beam between the fourth interface and the second interface are determined; the theoretical peak light intensity and theoretical position of the sixth pseudo-peak generated by multiple reflections of the light beam between the fourth interface and the first interface are determined; the theoretical distribution value of the fourth pseudo-peak is obtained based on the theoretical peak light intensity and theoretical position of the fourth pseudo-peak; the theoretical distribution value of the fifth pseudo-peak is obtained based on the theoretical peak light intensity and theoretical position of the fifth pseudo-peak; the theoretical distribution value of the sixth pseudo-peak is obtained based on the theoretical peak light intensity and theoretical position of the sixth pseudo-peak; the theoretical distribution values ​​of the fourth pseudo-peak, the fifth pseudo-peak, and the sixth pseudo-peak are removed from the second intermediate measurement data, and so on, until all pseudo-peaks in the initial measurement data are removed to obtain the target measurement data.

[0141] Based on the same concept, embodiments of this disclosure also provide a film thickness measurement system.

[0142] Figure 9 This is a film thickness measurement system illustrated according to an exemplary embodiment. (Refer to...) Figure 9 The system 900 includes: a white light interferometric film thickness measurement device 901 and a processing module 902.

[0143] The white light interferometric film thickness measurement device 901 is used to measure the film structure under test to obtain initial measurement data of the interference light signal. The film structure under test includes multiple interfaces. The initial measurement data includes the corresponding target interference peak generated by the first reflected beam of each interface, and the pseudo peaks generated by multiple reflected beams between different interfaces. The processing module 902 is used to establish the light intensity relationship between the pseudo peak and the target interference peak of the corresponding interface to calculate the theoretical peak light intensity of the pseudo peak; establish the optical path difference relationship between the pseudo peak and the target interference peak of the corresponding interface to calculate the theoretical position of the pseudo peak; determine the first interference peak in the initial measurement data as the first target interference peak corresponding to the first interface among the multiple interfaces, and determine the second interference peak in the initial measurement data as the second target interference peak corresponding to the second interface among the multiple interfaces; obtain the theoretical peak light intensity and theoretical position of the pseudo peak between the non-top interface and the interface above it layer by layer from top to bottom, and successively remove the pseudo peak between the non-top interface and the interface above it to obtain the target measurement data of the interference light signal; based on the target measurement data, determine the film thickness between every two adjacent interfaces in the film structure under test.

[0144] In some embodiments, the white light interferometric film thickness measurement device includes a low-coherence light source, a beam splitter, a scanning mirror, and a detector; the low-coherence light source is used to emit a low-coherence light beam; the beam splitter is used to split the low-coherence light beam into a reference beam and a measurement beam, the reference beam illuminates the scanning mirror and is reflected back to the beam splitter by the scanning mirror, the measurement beam illuminates the film structure under test and is reflected back to the beam splitter by each interface in the film structure under test; the reference beam reflected by the scanning mirror and the measurement beam reflected by each interface in the film structure under test are combined at the beam splitter to generate an interference light signal; the detector is used to collect initial measurement data of the interference light signal.

[0145] In some embodiments, the detector is used to acquire initial measurement data as the scanning mirror moves in a direction away from the beam splitter; during the movement of the scanning mirror, when the reference optical path of the reference beam reflected by the scanning mirror is equal to the measurement optical path of the measurement beam reflected once by one of the interfaces of the film structure under test, a target interference peak corresponding to the interface is generated.

[0146] Regarding the system in the above embodiments, the specific ways in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated here.

[0147] Although the operations are described in a specific order in the accompanying drawings, this should not be construed as requiring these operations to be performed in the specific order or serial order shown, or requiring all of the operations shown to obtain the desired result. In certain environments, multitasking and parallel processing may be advantageous.

[0148] The methods and apparatus disclosed herein can be implemented using standard programming techniques, utilizing rule-based logic or other logic to implement various method steps. It should also be noted that the terms "apparatus" and "module" as used herein and in the claims are intended to include implementations using one or more lines of software code and / or hardware implementations and / or devices for receiving input.

[0149] Any step, operation, or procedure described herein may be performed or implemented using one or more hardware or software modules, either alone or in combination with other devices. In one embodiment, the software module is implemented using a computer program product comprising a computer-readable medium containing computer program code, which is executable by a computer processor to perform any or all of the described steps, operations, or procedures.

[0150] The foregoing description of embodiments of this disclosure has been provided for purposes of illustration and description. The foregoing description is not exhaustive and is not intended to limit this disclosure to the exact form disclosed; various modifications and variations may be made in accordance with the foregoing teachings, or may be derived from practice of this disclosure. These embodiments were chosen and described to illustrate the principles of this disclosure and its practical application, enabling those skilled in the art to utilize this disclosure in various implementations and modifications suitable for the particular purpose conceived.

[0151] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0152] It is understood that in this disclosure, "multiple" refers to two or more, and other quantifiers are similar. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. The singular forms "a," "the," and "the" are also intended to include the plural forms unless the context clearly indicates otherwise.

[0153] It is further understood that the terms "first," "second," etc., are used to describe various types of information, but this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another, and do not indicate a specific order or degree of importance. In fact, the expressions "first," "second," etc., are completely interchangeable. For example, without departing from the scope of this disclosure, first information can also be referred to as second information, and similarly, second information can also be referred to as first information.

[0154] It can be further understood that, unless otherwise specified, "connection" includes both direct connections where no other components exist between the two parties and indirect connections where other components exist between them.

[0155] It is further understood that although operations are described in a specific order in the accompanying drawings in the embodiments of this disclosure, this should not be construed as requiring these operations to be performed in the specific order or serial order shown, or requiring all of the shown operations to be performed to obtain the desired result. In certain environments, multitasking and parallel processing may be advantageous.

[0156] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein.

[0157] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for measuring film thickness, characterized in that, The method includes: The white light interferometric film thickness measurement device is used to measure the film structure under test and obtain the initial measurement data of the interference light signal. The film structure under test includes multiple interfaces, and the initial measurement data includes the corresponding target interference peak generated by the first reflected beam of each interface, as well as the pseudo peaks generated by the multiple reflected beams between different interfaces. Establish the light intensity relationship between the pseudo-peak and the target interference peak at the corresponding interface in order to calculate the theoretical peak light intensity of the pseudo-peak; Establish the optical path difference relationship between the pseudo-peak and the target interference peak at the corresponding interface in order to calculate the theoretical position of the pseudo-peak; The first interference peak in the initial measurement data is determined as the first target interference peak corresponding to the first interface among the multiple interfaces, and the second interference peak in the initial measurement data is determined as the second target interference peak corresponding to the second interface among the multiple interfaces. The theoretical peak light intensity and theoretical position of the pseudo peaks between the non-top interface and the interface above it are obtained layer by layer from top to bottom, and the pseudo peaks between the non-top interface and the interface above it are successively removed to obtain the target measurement data of the interference light signal. Based on the target measurement data, the film thickness between every two adjacent interfaces in the film structure to be tested is determined; The intensity relationship between the pseudo-peak and the target interference peak at the corresponding interface is determined by the following formula: Wherein, the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, I xyj I represents the peak intensity of the pseudo-peak xyj. y t represents the peak light intensity of the target interference peak corresponding to interface y. n This represents the transmittance of interface n. Indicates t n power of j, r y This represents the reflectivity of the interface y. Indicates r y r to the power of (j-1) x This represents the reflectivity of interface x. Indicates r x (j-1)th power, y>x≥1, j>1; The step of establishing the optical path difference relationship between the pseudo-peak and the target interference peak at the corresponding interface, in order to calculate the theoretical position of the pseudo-peak, includes: The optical path difference relationship between the pseudo-peak and the target interference peak at the corresponding interface can be obtained using the following formula: L xyj =jL xy Where the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, L xyj L represents the optical path difference between the target interference peak and the pseudo-peak xyj corresponding to interface x. xy This represents the optical path difference between the target interference peak corresponding to interface x and the target interference peak corresponding to interface y, where y>x≥1, j>1; Based on optical path difference L xyj Determine the theoretical location of the pseudo-peak xyj.

2. The method according to claim 1, characterized in that, The theoretical peak intensity and theoretical position of the spurious peaks between the non-top-level interface and the interfaces above it are obtained sequentially from top to bottom, and the spurious peaks between the non-top-level interface and the interfaces above it are successively removed to obtain the target measurement data of the interference light signal, including: Based on the light intensity relationship and the optical path difference relationship, the theoretical peak light intensity of the first pseudo-peak generated by the multiple reflections of the light beam between the second interface and the first interface, as well as the theoretical position of the first pseudo-peak, are determined. Obtain the theoretical distribution value of the first pseudo-peak; Subtract the theoretical distribution value of the first pseudo-peak from the initial measurement data to obtain the first intermediate measurement data; The third interference peak in the first intermediate measurement data is determined as the third target interference peak corresponding to the third interface among the plurality of interfaces; Based on the light intensity relationship and the optical path difference relationship, the theoretical peak light intensity and theoretical position of the second pseudo-peak generated by the multiple reflections of the light beam between the third interface and the second interface are determined, as are the theoretical peak light intensity and theoretical position of the third pseudo-peak generated by the multiple reflections of the light beam between the third interface and the first interface. Obtain the theoretical distribution values ​​of the second pseudo-peak and the third pseudo-peak; Subtract the theoretical distribution values ​​of the second pseudo-peak and the third pseudo-peak from the first intermediate measurement data to obtain the second intermediate measurement data; Similarly, based on the second intermediate measurement data, the theoretical peak light intensity, theoretical position, and theoretical distribution value of the pseudo-peaks between the remaining non-top interface and the interface above it are obtained one by one, and the theoretical distribution values ​​of the pseudo-peaks between the remaining non-top interface and the interface above it are successively removed to obtain the target measurement data of the interference light signal.

3. The method according to claim 2, characterized in that, The step of determining the theoretical peak intensity and theoretical position of the first pseudo-peak generated by multiple reflections of the light beam between the second interface and the first interface based on the light intensity relationship and the optical path difference relationship includes: Extract the peak light intensity of the first target interference peak and the peak light intensity of the second target interference peak from the initial measurement data, and calculate the optical path difference between the first target interference peak and the second target interference peak; Based on the optical path difference between the first target interference peak and the second target interference peak and the relationship of the optical path difference, the theoretical position of the first pseudo-peak is calculated; Based on the peak light intensity of the second target interference peak and the light intensity relationship, the theoretical peak light intensity of the first pseudo-peak is calculated.

4. The method according to claim 2, characterized in that, The process of obtaining the theoretical distribution value of the first pseudo-peak includes: The second target interference peak is shifted to the theoretical position of the first pseudo-peak, and the shifted second target interference peak is stretched based on the theoretical peak light intensity of the first pseudo-peak to obtain the theoretical distribution value of the first pseudo-peak.

5. The method according to any one of claims 1 to 4, characterized in that, The step of determining the film thickness between every two adjacent interfaces in the film structure under test based on the target measurement data includes: For each pair of adjacent target interference peaks in the target measurement data, the film thickness of the target film is calculated based on the optical path difference between the two adjacent target interference peaks and the refractive index of the target film between the two adjacent interfaces corresponding to the adjacent target interference peaks.

6. The method according to any one of claims 1 to 4, characterized in that, The white light interferometric film thickness measurement device includes a low coherence light source, a beam splitter, a scanning mirror, and a detector; Among them, the initial measurement data of the interference light signal are obtained by measuring the film structure under test based on the white light interferometry film thickness measurement device, including: The low-coherence light source emits a low-coherence beam; The beam splitter splits the low-coherence beam into a reference beam and a measurement beam. The reference beam illuminates the scanning mirror and is reflected back to the beam splitter. The measurement beam illuminates the film structure under test and is reflected back to the beam splitter from each interface of the film structure under test. The reference beam reflected by the scanning mirror and the measurement beam reflected from each interface of the film structure under test are combined at the beam splitter to generate an interference light signal. The scanning mirror is moved along a direction away from the beam splitter, and initial measurement data of the interference light signal is acquired through the detector.

7. A film thickness measurement system, characterized in that, include: A white light interferometric film thickness measurement device is used to measure the film structure under test to obtain initial measurement data of the interference light signal; wherein, the film structure under test includes multiple interfaces, and the initial measurement data includes the corresponding target interference peak generated by a single reflected beam at each interface, as well as the pseudo peaks generated by multiple reflected beams between different interfaces. The processing module is used to establish the light intensity relationship between the pseudo-peak and the target interference peak of the corresponding interface to calculate the theoretical peak light intensity of the pseudo-peak; establish the optical path difference relationship between the pseudo-peak and the target interference peak of the corresponding interface to calculate the theoretical position of the pseudo-peak; determine the first interference peak in the initial measurement data as the first target interference peak corresponding to the first interface among the multiple interfaces, and determine the second interference peak in the initial measurement data as the second target interference peak corresponding to the second interface among the multiple interfaces; obtain the theoretical peak light intensity and theoretical position of the pseudo-peak between the non-top interface and the interface above it layer by layer from top to bottom, and successively remove the pseudo-peak between the non-top interface and the interface above it to obtain the target measurement data of the interference light signal; and determine the film thickness between every two adjacent interfaces in the film structure to be tested based on the target measurement data. The intensity relationship between the pseudo-peak and the target interference peak at the corresponding interface is determined by the following formula: Wherein, the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, I xyj I represents the peak intensity of the pseudo-peak xyj. y t represents the peak light intensity of the target interference peak corresponding to interface y. n This represents the transmittance of interface n. Indicates t n power of j, r y This represents the reflectivity of the interface y. Indicates r y r to the power of (j-1) x This represents the reflectivity of interface x. Indicates r x (j-1)th power, y>x≥1, j>1; The processing module is also used to obtain the optical path difference relationship between the pseudo-peak and the target interference peak of the corresponding interface using the following formula: L xyj =jL xy Where the subscript xyj represents the pseudo-peak generated by the j-th reflection beam between interface x and interface y, L xyj L represents the optical path difference between the target interference peak and the pseudo-peak xyj corresponding to interface x. xy This represents the optical path difference between the target interference peak corresponding to interface x and the target interference peak corresponding to interface y, where y>x≥1, j>1; The processing module is also used to base the optical path difference L xyj Determine the theoretical location of the pseudo-peak xyj.

8. The system according to claim 7, characterized in that, The white light interferometric film thickness measurement device includes a low coherence light source, a beam splitter, a scanning mirror, and a detector; The low-coherence light source is used to emit low-coherence light beams; The beam splitter is used to split the low-coherence light beam into a reference beam and a measurement beam. The reference beam illuminates the scanning mirror and is reflected back to the beam splitter by the scanning mirror. The measurement beam illuminates the film structure under test and is reflected back to the beam splitter by each interface in the film structure under test. The reference beam reflected by the scanning mirror and the measurement beam reflected by each interface in the film structure under test are combined at the beam splitter to generate an interference light signal. The detector is used to acquire initial measurement data of the interference light signal.

9. The system according to claim 8, characterized in that, The detector is used to acquire the initial measurement data when the scanning mirror is moved in a direction away from the beam splitter; when the reference optical path of the reference beam reflected by the scanning mirror is equal to the measurement optical path of the measurement beam reflected once by one of the interfaces of the film structure under test during the movement of the scanning mirror, a target interference peak corresponding to the interface is generated.

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