Film thickness measuring method and film thickness measuring system

Abstract

The invention relates to a film thickness measuring method and a film thickness measuring system. The method comprises the following steps: measuring a to-be-measured film layer structure based on a white light interference film thickness measuring device to obtain initial measurement data of an interference light signal; establishing a light intensity relationship between the 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 interference peak in the initial measurement data as a first target interference peak of a first interface, and determining a second interference peak as a second target interference peak of a second interface; obtaining theoretical peak light intensity and theoretical positions of pseudo peaks between the non-top-layer interface and the interface above the non-top-layer interface layer by layer from top to bottom, and successively removing the pseudo peaks between the non-top-layer interface and the interface above the non-top-layer interface; and determining the film layer thickness between every two adjacent interfaces in the to-be-measured film layer structure. According to the invention, 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] The present disclosure relates to the field of semiconductor technology, and in particular to a film thickness measurement method and a film thickness measurement system. Background Art

[0002] In the manufacturing process of semiconductor products, most of the device structure layers on the surface of silicon wafers are completed by thin film growth. The performance of the device mainly depends on the material and structure of the thin film, so various parameters need to be precisely controlled during the preparation of the thin film, and one of the key parameters is the film thickness.

[0003] The common methods for measuring film thickness include ellipsometry, probe method, optical method, etc. Among them, the white light interferometry in optical measurement has gradually developed in the field of film thickness measurement due to its measurement advantages. The basic principle of white light interferometry is: the reference light path and the measurement light path are formed by different optical elements. The light emitted by the light source is divided into two beams after passing through the spectroscopic element. One beam is incident on the sample surface through the measurement light path (measurement arm) and is reflected back. The other beam is reflected through the reference light path (reference arm). The two reflected beams finally converge and interfere to generate an interference light signal. The thickness of each film layer in the sample is 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 layer. When the multiple reflection signal is strong enough and its optical path is within the scanning optical path range, an interference peak will be formed in the measurement signal. However, there is no film layer structure matching its optical path in the actual structure of the wafer to be measured. Therefore, the interference peak caused by multiple reflections is a pseudo peak that has no corresponding actual film layer structure, which will lead to errors when inferring the film layer thickness of the wafer to be measured based on the optical path of the interference peak. Summary of the invention

[0005] In order to overcome the problems existing in the related art, the present disclosure provides a film thickness measurement method and a film thickness measurement system.

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

[0007] In some embodiments, the method of acquiring the theoretical peak light intensity and theoretical position of the pseudo-peaks between the non-top interface and the interface above it from top to bottom one by one, and successively removing the pseudo-peaks between the non-top interface and the interface above it to obtain the target measurement data of the interference light signal, includes: determining the theoretical peak light intensity of the first pseudo-peak generated by the multiple reflected light beams between the second interface and the first interface and the theoretical position of the first pseudo-peak 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 multiple interfaces; determining the third interface and the first interface based on the light intensity relationship and the optical path difference relationship. The theoretical peak light intensity of the second pseudo-peak generated by the multiple reflected light beams between the second interfaces and the theoretical position of the second pseudo-peak, the theoretical peak light intensity of the third pseudo-peak generated by the multiple reflected light beams between the third interface and the first interface and the theoretical position of the third pseudo-peak; obtain the theoretical distribution value of the second pseudo-peak and the theoretical distribution value of the third pseudo-peak; subtract the theoretical distribution value of the second pseudo-peak and the theoretical distribution value of the third pseudo-peak from the first intermediate measurement data to obtain the second intermediate measurement data; and so on, based on the second intermediate measurement data, obtain the theoretical peak light intensity, theoretical position and theoretical distribution value of the pseudo-peaks between the remaining non-top interfaces and the interfaces above them one by one, and successively remove the theoretical distribution values ​​of the pseudo-peaks between the remaining non-top interfaces and the interfaces above them to obtain the target measurement data of the interference light signal.

[0008] In some embodiments, determining the theoretical peak light intensity of the first pseudo-peak generated by the multiple reflected light beams between the second interface and the first interface and the theoretical position of the first pseudo-peak 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; 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.

[0009] In some embodiments, obtaining the theoretical distribution value of the first pseudo peak includes: translating the second target interference peak to the theoretical position of the first pseudo peak, and scaling the translated 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 of the corresponding interface is determined by the following formula:

[0011]

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

[0013] In some embodiments, the establishing of 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 by the following formula:

[0014] L xyj =jL xy

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

[0016] In some embodiments, based on the target measurement data, the film thickness between each two adjacent interfaces in the film layer structure to be measured is determined, including: for each two adjacent target interference peaks in the target measurement data, based on the optical path difference between the two adjacent target interference peaks, and the refractive index of the target film layer between two adjacent interfaces corresponding to the adjacent target interference peaks, calculating the film thickness of the target film layer.

[0017] In some embodiments, the white light interference film thickness measurement device includes a low coherence light source, a spectroscope, a scanning mirror and a detector; wherein, based on the white light interference film thickness measurement device, the film layer structure to be measured is measured to obtain initial measurement data of the interference light signal, including: the low coherence light source emits a low coherence light beam; the spectroscope divides the low coherence light beam into a reference beam and a measurement beam, the reference beam is irradiated to the scanning mirror and reflected back to the spectroscope by the scanning mirror, the measurement beam is irradiated to the film layer structure to be measured and reflected back to the spectroscope by each interface in the film layer structure to be measured; the reference beam reflected by the scanning mirror and the measurement beam reflected by each interface in the film layer structure to be measured are combined at the spectroscope to generate an interference light signal; the scanning mirror is moved in a direction away from the spectroscope, and the initial measurement data of the interference light signal is collected through the detector.

[0018] The present disclosure provides a film thickness measurement system, including: a white light interferometric film thickness measurement device, used to measure a film layer structure to be measured to obtain initial measurement data of an interference light signal; wherein the film layer structure to be measured includes multiple interfaces, and the initial measurement data includes a corresponding target interference peak generated by a single reflection light beam of each interface, and a pseudo peak generated by multiple reflection light beams between different interfaces; a processing module, used to establish a light intensity relationship between the pseudo peak and the target interference peak of the corresponding interface, so as to calculate the theoretical peak light intensity of the pseudo peak; establish an optical path difference relationship between the pseudo peak and the target interference peak of the corresponding interface, so as to calculate the theoretical peak light intensity of the pseudo peak; position; 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 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 removing the pseudo peaks 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, determining the film thickness between every two adjacent interfaces in the film layer structure to be measured.

[0019] In some embodiments, the white light interferometric film thickness measuring device includes a low coherence light source, a spectrometer, a scanning reflector and a detector; the low coherence light source is used to emit a low coherence light beam; the spectrometer is used to split the low coherence light beam into a reference beam and a measurement beam, the reference beam is irradiated to the scanning reflector and reflected back to the spectrometer by the scanning reflector, the measurement beam is irradiated to the film layer structure to be measured, and reflected back to the spectrometer by each interface in the film layer structure to be measured; the reference beam reflected by the scanning reflector and the measurement beam reflected by each interface in the film layer structure to be measured are combined at the spectrometer 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 collect the initial measurement data when the scanning mirror is moved in a direction away from the spectrometer; 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 layer structure to be measured, a target interference peak corresponding to the interface is generated.

[0021] The film thickness measurement method provided by the embodiment of the present disclosure measures the film layer structure to be measured based on a white light interference film thickness measurement device to obtain the initial measurement data of the interference light signal; the first interference peak in the initial measurement data is determined as the first target interference peak corresponding to the first interface of the film layer structure to be measured, and the second interference peak in the initial measurement data is determined as the second target interference peak corresponding to the second interface of the film layer structure to be measured; 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 peaks between the non-top interface and the interface above it are successively removed, so that the interference peaks in the target measurement data obtained correspond to each interface of the film layer structure to be measured one by one, and based on the target measurement data, the film thickness of each film layer in the film layer structure to be measured can be accurately determined. On the one hand, this method can eliminate the pseudo peaks existing in the initial measurement data, and avoid the problem of errors in deriving the film thickness due to the existence of pseudo peaks; on the other hand, it can retain the target interference peaks corresponding to each interface in the initial measurement data, so as to accurately obtain the film thickness of each film layer in the film layer structure to be measured.

[0022] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0024] Figure 1is a schematic diagram of a film thickness measurement system for measuring film thickness based on white light interferometry according to an example.

[0025] Figure 2 is an interference light intensity signal diagram shown according to an example.

[0026] Figure 3 The figure is a flow chart of a film thickness measurement method according to an exemplary embodiment.

[0027] Figure 4 It is a schematic diagram of a film layer structure to be tested according to an example.

[0028] Figure 5 Shows Figure 4 The interference light intensity signal diagram corresponding to the film structure to be tested is shown.

[0029] Figure 6 The flowchart of sequentially removing pseudo peaks between a non-top-layer interface and an interface above the top-layer interface is shown according to an exemplary embodiment.

[0030] Figure 7 It is a schematic diagram showing the elimination of pseudo peaks generated by two reflections between a first interface and a second interface according to an example.

[0031] Figure 8 It is a schematic diagram showing the elimination of pseudo peaks generated by two reflections between a first interface and a second interface according to an example.

[0032] Fig. 9 A film thickness measurement system is shown according to an exemplary embodiment. DETAILED DESCRIPTION

[0033] Here, exemplary embodiments will be described in detail, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present disclosure.

[0034] Figure 1 is a schematic diagram of a film thickness measurement system for measuring film thickness based on white light interferometry according to an example.

[0035] refer to Figure 1The film thickness measurement based on the white light reflection method mainly utilizes the absolute optical path matching mechanism of low coherence light interference. The film thickness measurement system may include a low coherence light source 20, a scanning reflector 30, a spectroscope 40 and a detector 50. The low coherence light source 20 emits a light beam, and the spectroscope 40 divides the light beam emitted by the low coherence light source 20 into a reference beam and a measurement beam. Among them, 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 measuring arm 70 is irradiated onto the film structure 10 to be measured and is reflected back to the spectroscope 40 by the interface between different materials in the film structure, wherein the reflected light from different interfaces has different transmission paths, and different transmission paths correspond to different measurement optical paths; the low-coherence light (reference beam) of the reference arm 60 is reflected by the scanning reflector 30 and combined with the reflected light from different interfaces in the film structure at the spectroscope 40 to form a signal beam, wherein the transmission path (i.e., reference optical path) of the reflected light from the reference arm 60 is continuously changed by changing the position of the scanning reflector 30 within a certain range, and when the reference optical path is exactly equal to the measurement optical path of the reflected light from a certain interface (e.g., the first interface 11, the second interface 12, or the third interface 13) of the film structure 10 to be measured, a strong interference peak will be generated. The measurement optical paths of the reflected light from different interfaces are different, and accordingly, interference peaks will be generated with the reference beam at different reference optical path positions. Based on the collected signal of the detector 50, an interference light intensity signal diagram can be obtained, such as Figure 2 shown.

[0036] refer to Figure 2 , the scanning optical path of 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, and the point 0 of the horizontal axis is the moving starting point of the scanning mirror 30 near the end of the beam splitter 40. When 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 light beam of the first interface 11, the second interface 12 and the third interface 13 of the film structure 10 to be measured, and interference peaks are generated at corresponding positions in turn, that is, theoretically, the reference optical path corresponding to the peak value position of each interference peak is respectively equal to the measurement optical path of the reflected light beam of a certain interface.

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

[0038] Based on the transmission path of the light beam, for any film layer, the measured optical path difference L between the first reflected light beam at its upper interface i and the first reflected light beam at its lower interface (i+1) is mi Satisfaction: L mi=2n i h i , where n is the refractive index of the film and h is the thickness of the film. For any interface x and interface y, the optical path difference L between the target interference peak corresponding to interface x and the target interference peak corresponding to interface y xy , satisfying the relationship: y>x≥1. For example, Figure 1 Medium m1 The difference between 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 length difference L m1 ), L m2 is the difference between the measured optical path length of the light reflected from the second interface 12 and the measured optical path length of the light reflected from the third interface 13 (i.e., the measured optical path length difference L m2 ). c1 is the difference in reference optical path length of the reflected light when the scanning reflector 30 is at the same optical path length as the first interface 11 and the second interface 12 (i.e., the reference optical path length difference L c1 ), Lc2 is the difference in reference optical path length of the reflected light when the scanning reflector 30 is at the same optical path length as the second interface 12 and the third interface 13 (i.e., the reference optical path difference L c2 ). Figure 2 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 difference of each section has the following relationship:

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

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

[0041] Among them, 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] Through the relationship between the above optical path differences, L can be extracted from the measurement data. 12 and L 23 Afterwards, 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 interface in the film structure to be measured will produce pseudo 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 signal of the multiple reflections is strong enough and its optical path is within the scanning optical path range, an interference peak will be formed in the measurement signal. However, there is no film structure matching its optical path in the actual structure of the wafer to be measured. Therefore, the interference peak caused by multiple reflections is a pseudo peak that does not correspond to the actual structure, which will lead to errors when inferring the structure and thickness of the film to be measured based on the optical path of the interference peak.

[0044] In view of this, an embodiment of the present disclosure provides a film thickness measurement method. Figure 3 The figure is a flow chart of 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 film layer structure to be measured is measured based on a white light interference film thickness measurement device to obtain initial measurement data of the interference light signal.

[0047] The film structure to be measured includes multiple interfaces, and the initial measurement data includes the corresponding target interference peak generated by the once reflected light beam of each interface, and the pseudo peaks generated by the multiple reflected light beams between different interfaces.

[0048] The target interference peak refers to the interference peak generated by the single reflected light of each interface and the reference light, and the pseudo peak refers to the interference peak generated by the multiple reflected light beams between different interfaces and the reference light beam.

[0049] In the disclosed embodiment, the white light interferometric film thickness measuring device may include a low coherence light source, a spectroscope, a scanning reflector and a detector. The low coherence light source may emit a low coherence light beam; the spectroscope may split the low coherence light beam into a reference light beam and a measuring light beam, the reference light beam is irradiated to the scanning reflector and reflected back to the spectroscope by the scanning reflector, the measuring light beam is irradiated to the film layer structure to be measured and reflected back to the spectroscope by each interface in the film layer structure to be measured; the reference light beam reflected by the scanning reflector and the measuring light beam reflected by each interface in the film layer structure to be measured are combined at the spectroscope to generate an interference light signal; during the measurement process, the scanning reflector may be moved in a direction away from the spectroscope, and the initial measurement data of the interference light signal may be collected by the detector.

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

[0051] In the disclosed embodiment, the initial measurement data of the interference light signal includes a plurality of interference peaks, including target interference peaks generated by a single reflection light beam at each interface in the film structure to be measured and a reference light beam, and pseudo peaks generated by multiple reflection light beams between different interfaces and the reference light beam. The target interference peaks correspond one-to-one to the interfaces in the film structure to be measured. That is to say, among the multiple interference peaks in the initial measurement data of the interference light signal, there are target interference peaks corresponding one-to-one to the interfaces for determining the film thickness, and pseudo peaks that may cause interference, and therefore, the pseudo peaks need to be identified and removed from the initial measurement data.

[0052] Below Figure 4 The film structure to be measured with two film layers is taken as an example to illustrate the generation process of pseudo peaks.

[0053] During the measurement process, when the measuring beam is incident vertically (to facilitate the distinction between the individual beams, Figure 4 When the measuring beam reaches the film structure to be measured, the measuring beam will be reflected at the interfaces of the film structure. Figure 4 In addition to the single reflection of each interface itself, there are also multiple reflected lights reflected from each other between adjacent interfaces. After returning to the beam splitter, these multiple reflected lights will also produce interference peaks with the reference beam when the optical path is matched.

[0054] Figure 4 The diagram shows the first reflected light and the second reflected light between the upper and lower interfaces (the first interface 11 and the second interface 12) of the first film layer in the two-layer film structure. Figure 5 Shows Figure 4 The interference light intensity signal diagram corresponding to the film structure to be tested is shown. Figure 4 and Figure 5 , when the measuring beam i m (Light Intensity I m ) is incident on the film structure to be measured, the measuring beam i m Part of the light is reflected once by the first interface 11 to generate reflected light i 1r1 (Light Intensity I 1r1 ), reflected light i 1r1 The beam returns to the spectroscope and interferes with the reference light returned by the reference arm, generating an interference peak P1. mPart of the light passes through the first interface 11 and then returns to the spectroscope after being reflected once by the second interface 12, where it interferes with the reference light returned by the reference arm, generating an interference peak P2. The returned light is recorded as the first reflected light i of the second interface 12. 2r1 (Light Intensity I 2r1 ); In addition, there is m Part of the light continuously passes through the first interface 11 and the second interface 12, and then returns to the spectroscope after being reflected once by the third interface 13, and interferes with the returning light of the reference arm to generate an interference peak P3. This reflected light is recorded as the first reflected light i of the third interface 13. 3r1 (Light Intensity I 3r1 ). In addition to the first reflected light at each interface, the reflected light returned to the spectroscope also includes multiple reflected light at each interface. Taking the second reflected light at the second interface 12 as an example, when the light beam after the first reflection at the second interface 12 passes through the first interface 11 again, a part of it passes through the first interface 11 and returns to the spectroscope to form the first reflected light at the second interface 12. 2r1 The other part returns to the second interface 12 and is regenerated into transmitted light and reflected light by the second interface 12. The regenerated reflected light passes through the first interface 11 and is again divided into transmitted light and reflected light by the first interface 11. Among them, the part of light reflected by the second interface 12 for the second time and passing through the first interface 11 is recorded as the second reflected light i of the second interface 12. 2r2 (Light Intensity I 2r2 ), reflected light i 2r2 At the beam splitter, interference occurs with the reference beam returned from the reference arm to produce an interference peak P122 (also called a pseudo peak P122).

[0055] The optical path difference between the interference peaks corresponding to the light beams reflected once at different interfaces corresponds to the optical path difference between the corresponding interfaces, that is, to the film structure between the corresponding interfaces. For example, the optical path difference L between the peak points corresponding to the interference peaks P1 and P2 is 12 The optical path difference L between the first interface 11 and the second interface 12 corresponds to m1 , that is, the optical path difference L m1 Corresponding to the first film layer; the optical path difference L between the peak points corresponding to the interference peak P2 and the interference peak P3 23 The optical path difference L between the second interface 12 and the third interface 13 corresponds to m2 , that is, the optical path difference L 23 The pseudo peak P122 is an interference peak formed after two reflections at the second interface 12. The optical path difference between the pseudo 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, errors will occur when the actual film structure of the sample is inferred based on the peak position. Therefore, it is necessary to identify the pseudo peaks in the interference peaks and remove them.

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

[0057] In the disclosed embodiment, 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 of the corresponding interface is determined by the following formula:

[0059]

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

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

[0062] In the disclosed embodiment, 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 relationship between the pseudo peak and the target interference peak of the corresponding interface can be obtained by the following formula:

[0064] L xyj =jL xy (4)

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

[0066] Based on the position of the target interference peak corresponding to the interface x and the optical path difference L xyj , the theoretical position of the pseudo peak xyj can be determined.

[0067] The derivation process of formula (3) is described below.

[0068] When the measuring beam is reflected once between the upper and lower interfaces of the single film structure and interferes with the reference beam, the intensity of the interference light I L It 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 is the incident light intensity of the reference beam at the central wavelength λ0 of the low coherence light source, I m To measure the incident light intensity of the light beam at the central wavelength λ0 of the low coherence light source, α is the light intensity reflectivity of the scanning mirror in the reference arm, β is the light intensity reflectivity of the interface under the film layer, and F λ (OPD) is the interference envelope term, which is determined by the spectral distribution of the low-coherence light source. OPD is the optical path difference of the two light beams (the difference between the reference optical path and the measurement optical path). c is the refractive index of the corresponding medium in the transmission path of the reflected light in the reference arm (usually n c is the refractive index of air), n m is the refractive index of the corresponding medium in the transmission path of the reflected light in the measuring arm, D c is the transmission path length of the light beam in the reference arm, D m is the transmission path length of the light beam in the measurement arm. c ,α,n c are the relevant parameters of the reference beam, and these parameters are the same for the reflected light from different interfaces. m ,β,n m , D m The correlation coefficient of the measured light beam is determined by the film structure. L The first two terms are DC terms, and the third term is the AC phase. When OPD = 0, the third term reaches the maximum value and the light intensity I L Corresponding to the peak light intensity of the interference peak, another relevant parameter D of the reference beam corresponding to OPD = 0 c Then it will follow nm D m changes with the changes of.

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

[0073]

[0074] It can be seen from formula (7) that 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 due to the different measurement optical path, reflectivity and incident light energy of the reflected light beams at different interfaces, the peak values ​​of the interference signals corresponding to the reflected light beam and the reference light beam are different and the positions of the interference signals are different. The measurement optical path of the reflected light from the interface determines the position of the interference peak, and the interface reflectivity and 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 the multiple reflected light, the more times the reflection occurs, the smaller the reflected light energy will be, and the longer the optical path will be. Correspondingly, the peak light intensity of the interference peak with the reference beam will be smaller, and the optical path difference with the interference peak corresponding to the single reflection of the upper interface forming multiple reflections will also increase exponentially. For the sample to be tested, the nominal thickness of each film layer and the reflectivity and transmittance of each interface are all determined. Therefore, according to formula (5) and formula (7), the theoretical position and theoretical peak light intensity of the interference pseudo peak formed by the multiple reflected light beam can be determined.

[0076] For example, the second reflected light (i 2r2 ) compared to the first reflected light (i 2r1 ) has experienced one more reflection at the first interface 11 and the second interface 12, and has also traveled back and forth through the first film layer one more time. According to formula (5), formula (6) and formula (7), the second reflected light (i 2r2 ) corresponding to the interference peak (pseudo peak P122), and the first reflected light (i 2r1 ) can be determined by the relationship between the peak values ​​of the interference peak P2 corresponding to the pseudo peak P122 and the target interference peak P1 generated by the first interface 11. 122 ), and the optical path difference (L ) of the target interference peak P2 generated by the second interface 12 relative to the target interference peak P1 generated by the first interface 11 12 ) can also be determined, that is, L 122 =2L 12 .

[0077] For a multi-layer structure, the light intensity I′ of the target interference peak generated by the first reflected light at interface i (i ≥ 3) i (without DC term) can be expressed as:

[0078]

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

[0080] The light intensity I′ of the interference peak xyj generated by the jth reflected light between the interface x and the interface y xyj (without DC term) can be expressed as:

[0081]

[0082] From formula (8), we can know 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 light 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 jth reflection between interface x and interface y xyj Satisfying formula (10) or formula (11):

[0083]

[0084]

[0085] According to the above formula (10) or (11), formula (3) can be obtained.

[0086] In the above derivation, when the refractive index of each film layer material in the film layer to be measured is determined, the transmittance and reflectance of each interface can also be calculated and determined, and the sum of the transmittance and the reflectance is 1. Therefore, the proportional relationship between the peak light intensities of the interference peaks corresponding to each reflected light is determined, and the optical path difference relationship is also determined. The proportional relationship of the peak light intensities satisfies formula (3), and the optical path difference relationship satisfies formula (4).

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

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

[0089] In the disclosed embodiment, according to the optical path of the reflected light at each interface in the film structure to be measured, when the optical path of the scanning reflector is scanned from small to large, the first interference peak and the second interference peak in the initial measurement data must correspond to the actual film interface in the film structure to be measured, and respectively correspond to the upper and lower interfaces of the first film layer that the measurement light first passes through (i.e., the first interface 11 and the second interface 12), and the interference peak optical path generated by multiple reflections between interfaces must be greater than the interference light optical path generated by the single reflection light of the corresponding interface. Therefore, when identifying and eliminating the pseudo peaks generated by the multiple reflection light beams 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 peaks between the non-top interface and the interface above it are removed successively to obtain the target measurement data of the interference light signal.

[0091] Exemplarily, the top interface refers to the first interface, and the non-top interface refers to the interface other than the first interface. First, the theoretical peak light intensity and theoretical position of the first pseudo-peak between the second interface and the interface above it (i.e., the first interface) are obtained, and the first pseudo-peak between the second interface and the first interface is removed; then the theoretical peak light intensity and theoretical position of the pseudo-peak between the third interface and the interface above it (the second interface, the first interface) are obtained, and the second pseudo-peak between the third interface and the second interface and the third pseudo-peak between the third interface and the first interface are removed, and so on, until all pseudo-peaks are removed.

[0092] Specifically, the theoretical peak light intensity of the first pseudo-peak generated by the multiple reflected light beams 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, and the first pseudo-peak can be removed from the initial measurement data by subtracting 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 the third target interference peak corresponding to the third interface in the actual film layer structure. The theoretical peak light intensity of the second pseudo peak generated by the multiple reflected light beams between the third interface and the second interface is determined based on the light intensity relationship, and the theoretical position of the second pseudo peak is determined based on the optical path difference relationship; the theoretical distribution value of the second pseudo peak can be obtained based on the theoretical peak light intensity and theoretical position of the second pseudo peak, and the second pseudo peak can be removed from the first intermediate measurement data by subtracting the theoretical distribution value of the second pseudo peak from the first intermediate measurement data; similarly, the theoretical peak light intensity of the third pseudo peak generated by the multiple reflected light beams between the third interface and the first interface is determined based on the light intensity relationship, and the theoretical position of the third pseudo peak is determined based on the optical path difference relationship; the theoretical distribution value of the third pseudo peak can be obtained based on the theoretical peak light intensity and theoretical position of the third pseudo peak, and the third pseudo peak can be removed from the first intermediate measurement data by subtracting the theoretical distribution value of the third pseudo peak from the first intermediate measurement data, and so on, until all pseudo peaks in the measurement data are removed to obtain the target measurement data, each interference peak in the target measurement data corresponds to an interface in the actual film layer structure, and the film layer structure to be measured can be inferred based on the target measurement data.

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

[0094] In the embodiment of the present disclosure, after eliminating all pseudo peaks in the initial measurement data, the target measurement data obtained includes target interference peaks corresponding one by one to each interface of the film layer 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 layer thickness between two adjacent interfaces corresponding to these two adjacent target interference peaks can be calculated.

[0095] In an exemplary embodiment, based on the target measurement data, the film thickness between every two adjacent interfaces in the film layer structure to be measured is determined, including: for every two adjacent target interference peaks in the target measurement data, based on the optical path difference between the two adjacent target interference peaks, and the refractive index of the target film layer between two adjacent interfaces corresponding to the adjacent target interference peaks, the film thickness of the target film layer is calculated.

[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 layer, the film thickness of the first film layer can be calculated by 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 layer, the film thickness of the second film layer can be calculated by formula (2), and so on, the film thickness of all film layers can be obtained.

[0097] The film thickness measurement method provided by the embodiment of the present disclosure measures the film layer structure to be measured based on a white light interference film thickness measurement device to obtain the initial measurement data of the interference light signal; the first interference peak in the initial measurement data is determined as the first target interference peak corresponding to the first interface of the film layer structure to be measured, and the second interference peak in the initial measurement data is determined as the second target interference peak corresponding to the second interface of the film layer structure to be measured; 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 peaks between the non-top interface and the interface above it are successively removed, so that the interference peaks in the target measurement data obtained correspond to each interface of the film layer structure to be measured one by one, and based on the target measurement data, the film thickness of each film layer in the film layer structure to be measured can be accurately determined. On the one hand, this method can eliminate the pseudo peaks existing in the initial measurement data, and avoid the problem of errors in deriving the film thickness due to the existence of pseudo peaks; on the other hand, it can retain the target interference peaks corresponding to each interface in the initial measurement data, so as to accurately obtain the film thickness of each film layer in the film layer structure to be measured.

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

[0099] Figure 6 FIG. 1 is a flow chart showing a method for successively removing pseudo peaks between a non-top interface and an interface above the top interface 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 of the first pseudo peak generated by the multi-reflected light beam between the second interface and the first interface and the theoretical position of the first pseudo peak are determined based on the light intensity relationship and the optical path difference relationship.

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

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

[0103] In an exemplary embodiment, 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 reflected light beams between the second interface and the first interface and the theoretical position of the first pseudo-peak are determined, including: 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 and the optical path difference relationship between the first target interference peak and the second target interference peak; 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 Figure 4 The two-layer film structure to be tested is shown as an example. Figure 5 The interference signal shown in FIG. 1 is 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 peak generated by the second reflection between the first interface and the second interface should be L 12 According to the optical path difference relationship, the third interference peak (i.e., interference peak P122) in the interference signal is a pseudo peak generated by two reflections between the first interface and the second interface, that is, the third interference peak is the pseudo peak P122. This is because the optical path difference L between the pseudo peak P122 and the first target interference peak P1 is 122 is the optical path difference L between the first target interference peak P1 and the second target interference peak P2 12 2 times, that is, L 122 =2L 12 . Thus, the position of the pseudo peak P122 generated by the second reflection between the first interface and the second interface is obtained. Similarly, the optical path difference between the pseudo peak 123 (not shown in the figure) generated by the third reflection between the first interface and the second interface 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 the pseudo peak 123 can be derived, and by analogy, the theoretical positions of all first pseudo peaks can be derived.

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

[0106]

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

[0108] Therefore, according to the peak light intensity of the second target interference peak P2, the transmittance of the first interface, and the transmittance of the second interface, the theoretical peak light intensity of the pseudo peak P122 can be calculated based on formula (12). Similarly, according to the light intensity relationship (i.e., formula (3)), the relationship between the peak light intensity of the second target interference peak P2 and the peak light intensity of the pseudo peak 123 can be obtained, so that the theoretical peak light intensity of the pseudo peak 123 can be derived. By analogy, the theoretical peak light 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] Theoretically, all interference peaks can be exactly the same and can overlap after stretching. Therefore, the optical path relationship and light intensity relationship can be used to process and transform (stretch, compress, position shift, etc.) the target interference peak corresponding to the obtained interface x or interface y to obtain the theoretical distribution value of the pseudo peak.

[0111] In the disclosed embodiment, after the theoretical position and theoretical peak light intensity of the first pseudo peak are calculated, 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: translating the second target interference peak to the theoretical position of the first pseudo peak, and scaling the translated 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: performing scaling processing on the second target interference peak based on the theoretical peak light intensity of the first pseudo peak; translating the second target interference peak after scaling processing to the theoretical position of the first pseudo peak to obtain the theoretical distribution value of the first pseudo peak.

[0114] The disclosed embodiment does not limit the order of the above-mentioned translation processing and telescopic processing, that is, the second target interference peak can be translated first and then telescopic processing can be performed on the second target interference peak; or the second target interference peak can be telescopic processing can be performed first and then translation processing can be performed on the second target interference peak.

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

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

[0117] The following description will be made by taking the removal of the pseudo peak P122 generated by the second reflection between the first interface and the second interface as an example.

[0118] Figure 7 It is a schematic diagram showing the elimination of pseudo peaks generated by two reflections between a first interface and a second interface according to an example.

[0119] like Figure 7 As shown in (a) of FIG. 1 , taking the film structure to be measured as a two-layer film structure as an example, the round-trip optical path of the first film layer and the second film layer structure in the film structure is different. When only considering the two reflected lights between the upper and lower interfaces of the first film layer (the first interface 11 and the second interface 12), the film structure is measured using the white light interferometry film thickness measurement technology, and the following is obtained: Figure 7 There are four interference peaks shown in (b), including three target interference peaks corresponding to the first interface 11, the second interface 12, and the third interface 13, and the first pseudo peak generated by the second reflection between the first interface 11 and the second interface 12.

[0120] According to the optical path relationship, the first interference peak P1 and the second interference peak P2 must correspond to the first interface 11 and the second interface 12 in the film structure 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 in 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 by 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 by combining formula (3). t122 , combined with formula (4), the optical path difference L between the pseudo peak P122 and the first target interference peak P1 is calculated 122is the optical path difference L between the first target interference peak P1 and the second target interference peak P2 12 2 times, that is, L 122 =2L 12 , and thus the optical path difference between the pseudo peak P122 and the second target interference peak P2 is calculated to be L 12 , thereby identifying that the position of the third interference peak P122 corresponds to the position of the pseudo peak P122, that is, the third interference peak P122 should be the pseudo peak P122; then, intercept the second target interference peak P2, and calculate the theoretical peak light intensity I of the pseudo peak P122 t122 The second target interference peak P2 is subjected to peak compression processing, and the second target interference peak P2 is subjected to translation processing (i.e., the compressed second target interference peak P2 is translated to the right by L) according to the calculated optical path difference between the pseudo peak P122 and the second target interference peak P2. 12 ), and obtain the theoretical distribution value P of the pseudo peak P122 t 122, such as Figure 7 Then, the theoretical distribution value P is subtracted from the initial measurement data. t 122, such as Figure 7 As shown in (d) in FIG. 1 , the measurement data after eliminating the pseudo peak P122 can be obtained, such as Figure 7 As shown in (e) in .

[0121] Figure 8 It is a schematic diagram showing the elimination of pseudo peaks generated by two reflections between a first interface and a second interface according to an example.

[0122] In actual testing, there may be a situation where multiple reflection pseudo peaks overlap with a single reflection peak of a certain interface in the actual structure in the optical path, for example, the pseudo peak P122 overlaps with the third target interference peak P3 corresponding to the third interface. Using the method proposed in the embodiment of the present disclosure, when the pseudo peak and the target interference peak overlap, the pseudo peak energy of the overlapping part can still be eliminated, and the energy of the target interference peak of the overlapping part can be retained.

[0123] like Figure 8 As shown in (a) of FIG. 1 , the identification and elimination of the two reflected lights between the upper and lower interfaces (the first interface 11 and the second interface 12) of the first film layer in a two-layer film structure is taken as an example to illustrate the identification and elimination process of the pseudo peak when the pseudo peak coincides with the target interference peak. When the film structure is measured using the white light interferometric film thickness measurement technology, the following is 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, and a pseudo peak generated by the second reflection between the first interface 11 and the second interface 12, wherein the pseudo peak generated by the second reflection between the first interface 11 and the second interface 12 coincides with the third target interference peak of the third interface 13.

[0124] According to the optical path relationship, the first interference peak P1 and the second interference peak P2 must correspond to the first interface 11 and the second interface 12 in the film structure 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 in 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 by 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 by combining formula (3). t122 , combined with formula (4), the optical path difference L between the pseudo peak P122 and the first target interference peak P1 is calculated 122 is the optical path difference L between the first target interference peak P1 and the second target interference peak P2 12 2 times, that is, L 122 =2L 12 , and thus the optical path difference between the pseudo peak P122 and the second target interference peak P2 is calculated to be L 12 , thus identifying the position of the third interference peak (formed by the superposition of P3 and P122) corresponding to the position of the pseudo peak P122, since the peak light intensity of the third interference peak is greater than the theoretical peak light intensity I of the pseudo peak P122 t122 Therefore, the third interference peak should be the interference peak after the pseudo peak P122 is superimposed on the third target interference peak P3 of the third interface. Then, the second target interference peak P2 is intercepted, and the theoretical peak light intensity I of the pseudo peak P122 is calculated. t122 The second target interference peak P2 is subjected to peak compression processing, and the second target interference peak P2 is subjected to translation processing (i.e., the compressed second target interference peak P2 is translated to the right by L) according to the calculated optical path difference between the pseudo peak P122 and the second target interference peak P2. 12 ), and obtain the theoretical distribution value P of the pseudo peak P122 t 122, such as Figure 8 As shown in (c) in the figure. t After 122, the theoretical pseudo peak P is subtracted from the initial measurement data. t 122, such as Figure 8 As shown in (d) in FIG. 1 , the measurement data after eliminating the pseudo peak P122 is obtained, as shown in FIG. Figure 8 As shown in (e) in .

[0125] It can be understood that the above is explained by taking the elimination of the pseudo peak P122 generated by the second reflection between the first interface and the second interface as an example. The method of eliminating the pseudo peaks generated by three or more reflections between the first interface and the second interface is similar to the method of eliminating the pseudo peaks generated by two reflections, and the present disclosure will not repeat them here.

[0126] In actual measurement, since the output energy of the sampled low-coherence light source is limited, when measuring a multi-layer film structure, the pseudo peaks that appear in the white light interference measurement signal are basically caused by the second and third reflections of the first film layer. The higher-order reflections of the first film layer, the multiple reflections of other film layers, and the multiple reflections between the interfaces of the film layers are submerged by DC noise because the energy of the reflected light of the corresponding optical path is too small, resulting in very small interference peak signals, and thus it may be impossible to find obvious interference peaks in the initial measurement signal. Therefore, after eliminating the first pseudo peak between the first interface and the second interface, steps S64 to S68 may not be performed, and the thickness of each film layer may be determined directly based on the measurement data after eliminating the first pseudo peak between the first interface and the second interface.

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

[0128] In the disclosed embodiment, the first intermediate measurement data is obtained after eliminating the first pseudo peak from the initial measurement data, and the third interference peak in the first intermediate measurement data is caused 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 of the second pseudo-peak generated by the multiple reflections of the light beam between the third interface and the second interface and the theoretical position of the second pseudo-peak, and the theoretical peak light intensity of the third pseudo-peak generated by the multiple reflections of the light beam between the third interface and the first interface and the theoretical position of the third pseudo-peak are determined.

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

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

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

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

[0134] In the disclosed embodiment, the third target interference peak is translated to the theoretical position of the second pseudo peak, and based on the theoretical peak light intensity of the second pseudo peak, the translated third target interference peak is scaled to obtain the theoretical distribution value of the second pseudo peak.

[0135] In the disclosed embodiment, the third target interference peak is translated to the theoretical position of the third pseudo peak, and based on the theoretical peak light intensity of the third pseudo peak, the translated third target interference peak is scaled to obtain the theoretical distribution value of the third pseudo peak.

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

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

[0138] In the embodiment of the present disclosure, the method of removing the second pseudo peak and the third pseudo peak from the first intermediate measurement data in step S67 is similar to the method of removing the first pseudo peak in step S63, and is not described in detail herein.

[0139] In step S68, and so on, 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 interfaces and the interfaces above them are obtained one by one, and the theoretical distribution values ​​of the pseudo-peaks between the remaining non-top interfaces and the interfaces above them are successively removed to obtain the target measurement data of the interference light signal.

[0140] In the disclosed embodiment, the fourth interference peak in the second intermediate measurement data is determined as the fourth target interference peak corresponding to the fourth interface. Based on the light intensity relationship and the optical path difference relationship, the theoretical peak light intensity of the fourth pseudo peak generated by the multiple reflection light beam between the fourth interface and the third interface and the theoretical position of the fourth pseudo peak, the theoretical peak light intensity of the fifth pseudo peak generated by the multiple reflection light beam between the fourth interface and the second interface and the theoretical position of the fifth pseudo peak, the theoretical peak light intensity of the sixth pseudo peak generated by the multiple reflection light beam between the fourth interface and the first interface and the theoretical position of the sixth pseudo peak 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, and 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 value of the fourth pseudo peak, the theoretical distribution value of the fifth pseudo peak, and the theoretical distribution value of 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, an embodiment of the present disclosure also provides a film thickness measurement system.

[0142] Fig. 9 A film thickness measurement system is shown according to an exemplary embodiment. Fig. 9 The system 900 includes: a white light interferometry film thickness measurement device 901 and a processing module 902.

[0143] The white light interference film thickness measuring device 901 is used to measure the film layer structure to be measured to obtain the initial measurement data of the interference light signal; wherein the film layer structure to be measured includes multiple interfaces, and the initial measurement data includes the corresponding target interference peak generated by the once reflected light beam of each interface, and the pseudo peak generated by the multiple reflected light 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 peaks 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 layer structure to be measured.

[0144] In some embodiments, a white light interferometric film thickness measuring device includes a low coherence light source, a spectrometer, a scanning reflector, and a detector; the low coherence light source is used to emit a low coherence light beam; the spectrometer is used to split the low coherence light beam into a reference beam and a measurement beam, the reference beam is irradiated to the scanning reflector and reflected back to the spectrometer by the scanning reflector, the measurement beam is irradiated to the film layer structure to be measured, and reflected back to the spectrometer by each interface in the film layer structure to be measured; the reference beam reflected by the scanning reflector and the measurement beam reflected by each interface in the film layer structure to be measured are combined at the spectrometer 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 collect initial measurement data when the scanning mirror is moved in a direction away from the spectrometer; 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 to be measured, a target interference peak corresponding to the interface is generated.

[0146] Regarding the system in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0147] Although operations are described in a particular order in the drawings, this should not be understood as requiring that the operations be performed in the particular order shown or in serial order, or that all shown operations be performed to achieve desired results. In certain circumstances, multitasking and parallel processing may be advantageous.

[0148] The methods and apparatus of the present disclosure can be implemented using standard programming techniques, using rule-based logic or other logic to implement various method steps. It should also be noted that the words "apparatus" and "module" 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 steps, operations or procedures 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 including a computer-readable medium containing computer program code, which can be executed by a computer processor to perform any or all of the described steps, operations or procedures.

[0150] The foregoing description of the implementation of the present disclosure has been given for the purpose of illustration and description. The foregoing description is not exhaustive nor is it intended to limit the present disclosure to the exact form disclosed, and various variations and modifications may exist in accordance with the above teachings or may be obtained from the practice of the present disclosure. These embodiments are selected and described in order to illustrate the principles of the present disclosure and its practical application, so that those skilled in the art can utilize the present disclosure in various embodiments and various modifications suitable for the specific purpose contemplated.

[0151] Regarding the device in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0152] It is to be understood that in the present disclosure, "plurality" refers to two or more than two, and other quantifiers are similar. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. The singular forms "a", "the" and "the" are also intended to include plural forms, unless the context clearly indicates other meanings.

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

[0154] It can be further understood that, unless otherwise specified, “connection” includes a direct connection without other components between the two, and also includes an indirect connection with other components between the two.

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

[0156] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any modifications, uses or adaptations of the present disclosure, which follow the general principles of the present disclosure and include common knowledge or customary technical means in the art that are not disclosed in the present disclosure.

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

Claims

1. A film thickness measurement method, characterized in that: The method comprises: The film structure to be measured is measured based on a white light interferometric film thickness measuring device to obtain initial measurement data of the interference light signal; wherein the film structure to be measured includes multiple interfaces, and the initial measurement data includes the corresponding target interference peak generated by the once reflected light beam of each interface, and the pseudo peaks generated by the multiple reflected light beams between different interfaces; Establishing a 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; Establishing an 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 a 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 a second target interference peak corresponding to the second interface among the multiple interfaces; acquire 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 peaks 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, the film thickness between every two adjacent interfaces in the film structure to be measured is determined.

2. The method according to claim 1, characterized in that The method of acquiring theoretical peak light intensities and theoretical positions of pseudo peaks between the non-top interface and the interface above it from top to bottom one by one, and successively removing pseudo peaks between the non-top interface and the interface above it to obtain target measurement data of the interference light signal, includes: Determine the theoretical peak light intensity of a first pseudo peak generated by the multi-reflected light beam between the second interface and the first interface and the theoretical position of the first pseudo peak based on the light intensity relationship and the optical path difference relationship; Obtaining a 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 first intermediate measurement data; determining a third interference peak in the first intermediate measurement data as a third target interference peak corresponding to a third interface among the plurality of interfaces; Based on the light intensity relationship and the optical path difference relationship, determine the theoretical peak light intensity of a second pseudo peak generated by the multiple reflections of the light beam between the third interface and the second interface and the theoretical position of the second pseudo peak, and the theoretical peak light intensity of a third pseudo peak generated by the multiple reflections of the light beam between the third interface and the first interface and the theoretical position of the third pseudo peak; Obtaining a theoretical distribution value of the second pseudo peak and a theoretical distribution value of the third pseudo peak; Subtracting the theoretical distribution value of the second pseudo peak and the theoretical distribution value of the third pseudo peak from the first intermediate measurement data to obtain second intermediate measurement data; 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 interfaces and the interfaces above them are obtained one by one, and the theoretical distribution values ​​of the pseudo-peaks between the remaining non-top interfaces and the interfaces above them are removed successively to obtain the target measurement data of the interference light signal.

3. The method according to claim 2, characterized in that The determining, based on the light intensity relationship and the optical path difference relationship, of a theoretical peak light intensity of a first pseudo peak generated by a multi-reflected light beam between the second interface and the first interface and a theoretical position of the first pseudo peak 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 a theoretical position of the first pseudo peak based on an optical path difference between the first target interference peak and the second target interference peak and the optical path difference relationship; 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 obtaining of the theoretical distribution value of the first pseudo peak includes: The second target interference peak is translated to the theoretical position of the first pseudo peak, and based on the theoretical peak light intensity of the first pseudo peak, the translated second target interference peak is scaled to obtain a theoretical distribution value of the first pseudo peak.

5. The method according to claim 1, characterized in that The intensity relationship between the pseudo peak and the target interference peak of the corresponding interface is determined by the following formula: The subscript xyj represents the pseudo peak generated by the j-th reflected beam between interface x and interface y, I xyj represents the peak light intensity of pseudo peak xyj, I y represents the peak light intensity of the target interference peak corresponding to interface y, t n represents the transmittance of interface n, Indicates t n The jth power, r y represents the reflectivity of the interface y, Represents r y (j-1)th power, r x represents the reflectivity of interface x, Represents r x to the (j-1)th power, y>x≥1, j>1.

6. The method according to claim 1, characterized in that The step of establishing an optical path difference relationship between a pseudo peak and a target interference peak of a corresponding interface to calculate a theoretical position of the pseudo peak comprises: The optical path difference relationship between the pseudo peak and the target interference peak of the corresponding interface is obtained by the following formula: L xyj =jL xy The subscript xyj represents the pseudo peak generated by the j-th reflected beam between interface x and interface y, L xyj represents the optical path difference between the target interference peak and the pseudo peak xyj corresponding to the interface x, L xy represents the optical path difference between the target interference peak corresponding to interface x and the target interference peak corresponding to interface y, y>x≥1, j>1; Based on the optical path difference L xyj Determine the theoretical position of the pseudo-peak xyj.

7. The method according to any one of claims 1 to 6, characterized in that: The step of determining the film thickness between every two adjacent interfaces in the film structure to be measured based on the target measurement data includes: For every two adjacent target interference peaks in the target measurement data, the film thickness of the target film layer is calculated based on the optical path difference between the two adjacent target interference peaks and the refractive index of the target film layer between two adjacent interfaces respectively corresponding to the adjacent target interference peaks.

8. The method according to any one of claims 1 to 6, characterized in that: The white light interference film thickness measuring device comprises a low coherence light source, a spectroscope, a scanning reflector and a detector; Wherein, the film structure to be measured is measured based on the white light interferometric film thickness measuring device to obtain the initial measurement data of the interference light signal, including: The low-coherence light source emits a low-coherence light beam; The spectroscope divides the low-coherence light beam into a reference light beam and a measuring light beam, the reference light beam is irradiated to the scanning reflector and reflected back to the spectroscope by the scanning reflector, and the measuring light beam is irradiated to the film structure to be measured and reflected back to the spectroscope by each interface in the film structure to be measured; the reference light beam reflected by the scanning reflector and the measuring light beam reflected by each interface in the film structure to be measured are combined at the spectroscope to generate an interference light signal; The scanning reflector is moved in a direction away from the beam splitter, and initial measurement data of the interference light signal is collected by the detector.

9. A film thickness measurement system, characterized in that: include: A white light interferometric film thickness measuring device, used to measure a film structure to be measured to obtain initial measurement data of an interference light signal; wherein the film structure to be measured includes multiple interfaces, and the initial measurement data includes a corresponding target interference peak generated by a single reflection light beam at each interface, and pseudo peaks generated by multiple reflection light beams between different interfaces; A processing module is used to establish a light intensity relationship between a pseudo-peak and a target interference peak of a corresponding interface to calculate a theoretical peak light intensity of the pseudo-peak; establish an optical path difference relationship between a pseudo-peak and a target interference peak of a corresponding interface to calculate a theoretical position of the pseudo-peak; determine a first interference peak in the initial measurement data as a first target interference peak corresponding to a first interface among the multiple interfaces, and determine a second interference peak in the initial measurement data as a second target interference peak corresponding to a second interface among the multiple interfaces; obtain the theoretical peak light intensity and theoretical position of the pseudo-peak between a non-top interface and an interface above it layer by layer from top to bottom, and successively remove the pseudo-peaks between the non-top interface and the interface above it to obtain target measurement data of the interference light signal; and determine the film thickness between every two adjacent interfaces in the film layer structure to be measured based on the target measurement data.

10. The system according to claim 9, characterized in that The white light interference film thickness measuring device comprises a low coherence light source, a spectroscope, a scanning reflector and a detector; The low-coherence light source is used to emit a low-coherence light beam; The spectroscope is used to split the low-coherence light beam into a reference light beam and a measuring light beam, wherein the reference light beam is irradiated to the scanning reflector and reflected back to the spectroscope by the scanning reflector, and the measuring light beam is irradiated to the film layer structure to be measured and reflected back to the spectroscope by each interface in the film layer structure to be measured; the reference light beam reflected by the scanning reflector and the measuring light beam reflected by each interface in the film layer structure to be measured are combined at the spectroscope to generate an interference light signal; The detector is used to collect initial measurement data of the interference light signal.

11. The system according to claim 10, characterized in that The detector is used to collect the initial measurement data when the scanning mirror is moved in a direction away from the spectroscope; during the movement of the scanning mirror, when the reference optical path of the reference light beam reflected by the scanning mirror is equal to the measurement optical path of the measurement light beam reflected once by one of the interfaces of the film layer structure to be measured, a target interference peak corresponding to the interface is generated.

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