Film thickness measurement method and equipment based on spectral confocal

Abstract

The present invention provides a film thickness measurement method and device based on spectral confocal. It is applied to the field of high-precision measurement technology. The method comprises: obtaining the outgoing light modulation coefficient of the spectral confocal system in advance; using a spectrometer to collect the reflected light spectrum focused on the upper and lower surfaces of a flat piece, and obtaining a real-time characteristic spectrum carrying position information under incident light and a real-time incident light modulated light source spectrum; calculating a light source reference spectrum according to the outgoing light modulation coefficient and the incident light modulated light source spectrum; demodulating the characteristic spectrum using the light source reference spectrum to obtain a standard reflected light spectrum; and calculating the thickness of the flat piece according to the standard reflected light spectrum.

Description

Technical Field

[0001] The present invention relates to the technical field of high-precision measurement, and in particular to a film thickness measurement method and device based on spectral confocalization. Background Art

[0002] Displacement measurement plays an important role in modern industry and scientific research. Spectral confocal technology is widely used because it can generate continuous focus on the optical axis through a broadband light source. According to the principle of chromatic aberration, the axial position of the sample surface is related to the focus peak of the continuous focus in the reflection spectrum. Therefore, the spectral confocal technology can obtain a characteristic spectrum with sample position information from the reflection spectrum and extract the focus peak wavelength from it to quickly obtain the axial position of the sample surface.

[0003] However, it is a challenge to extract the accurate focus peak wavelength from the characteristic spectrum. Although there are a variety of fitting algorithms (such as parabola fitting, Gaussian fitting, centroid algorithm, etc.) for extracting the focus peak wavelength, these algorithms will be affected by various interference factors in the spectral confocal measurement system during calculation, thus affecting the extraction result of the focus peak wavelength. In the spectral confocal system, the characteristic spectrum with the position information of the sample to be measured received by the detector is mainly affected by the light source, the sample surface and passive units (such as fiber couplers, probes and spectrometers). Among them, the changes in the light source itself and the modulation of the characteristic spectrum carrying the position information by the passive unit are the main factors affecting whether the accurate focus peak wavelength can be obtained.

[0004] In complex measurement environments, such as real-time in-situ non-contact detection of workpiece thickness changes due to thinning, the light source is unstable and aging due to temperature during continuous operation, and the light source is attenuated by passive units. The characteristic spectrum carrying position information will be modulated, and different wavelengths will have different modulation ratios, resulting in an offset in the focused peak wavelength and inaccurate measurement of the axial position, which in turn leads to inaccurate sample thickness measurement. How to demodulate the characteristic spectrum in real time is the key to improving the accuracy of thickness measurement. Summary of the invention

[0005] In view of this, the present invention provides a film thickness measurement method based on spectral confocal imaging, comprising:

[0006] Pre-obtain the output light modulation coefficient of the spectral confocal system ;

[0007] The spectrometer is used to collect the reflected light spectrum focused on the upper and lower surfaces of the flat piece to obtain a real-time characteristic spectrum carrying position information under the incident light. and real-time incident light modulation light source spectrum ;

[0008] According to the output light modulation coefficient and the incident light modulated light source spectrum Calculate the reference spectrum of the light source ;

[0009] Using the light source reference spectrum The characteristic spectrum Demodulate and obtain the standard reflected light spectrum ;

[0010] According to the standard reflected light spectrum Calculates the thickness of flat parts.

[0011] Optionally, the output light modulation coefficient of the spectral confocal system is obtained in advance ,include:

[0012] The light emitted by the light source of the spectral confocal system simulates the reflected light on the surface of the flat piece, and obtains the spectrum collected by the spectrometer through the reflected light path. ;

[0013] According to the spectrum and light source spectrum Calculate the outgoing light modulation coefficient .

[0014] Optionally, the output light modulation coefficient is calculated as follows: :

[0015] .

[0016] Optionally, a spectrometer is used to collect a spectrum of reflected light focused on the upper and lower surfaces of the flat member, including:

[0017] Two spectrometers are used to collect the reflected light spectra focused on the upper and lower surfaces of the flat piece to obtain the characteristic spectrum. and the incident light modulates the light source spectrum .

[0018] Optionally, a spectrometer is used to collect a spectrum of reflected light focused on the upper and lower surfaces of the flat member, including:

[0019] The two channels of the spectrometer are used to collect the reflected light spectra focused on the upper and lower surfaces of the flat piece to obtain the characteristic spectrum. and the incident light modulates the light source spectrum .

[0020] Optionally, the light source reference spectrum is calculated using the following formula: :

[0021] .

[0022] Optionally, according to the standard reflected light spectrum Calculate the thickness of flat parts, including:

[0023] The standard reflected light spectrum Extract the upper and lower surface focusing peak wavelengths to obtain the upper surface focusing peak wavelength and the lower surface focusing peak wavelength;

[0024] Calculate the upper surface position of the flat piece and the lower surface position of the flat piece according to the upper surface focusing peak wavelength, the lower surface focusing peak wavelength and the pre-constructed spectrum peak center corresponding parameter-displacement model;

[0025] The thickness of the flat member is calculated according to the position of the upper surface of the flat member and the position of the lower surface of the flat member.

[0026] Optionally, the light source reference spectrum is used The characteristic spectrum Demodulate and obtain the standard reflected light spectrum ,include:

[0027] .

[0028] Optionally, the light source reference spectrum is used The characteristic spectrum Demodulate and obtain the standard reflected light spectrum Before, it also includes:

[0029] Get the background noise spectrum ;

[0030] According to the background noise spectrum The characteristic spectrum Perform noise removal.

[0031] Optionally, the characteristic spectrum is analyzed using the following formula: Perform demodulation and normalization to obtain the standard reflected light spectrum :

[0032] .

[0033] A second aspect of the present invention provides a film thickness measurement device based on spectral confocal microscopy, the device comprising: a processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor performs the above-mentioned film thickness measurement method based on spectral confocal microscopy.

[0034] The film thickness measurement method and device based on spectral confocalization provided by the present invention calculate the light source reference spectrum by using the outgoing light modulation coefficient and the incident light source spectrum measured in real time, and modulate the real-time characteristic spectrum carrying position information according to the real-time change of the light source and the attenuation of the transmission light path. The calculated light source reference spectrum is used for demodulation, and the obtained standard reflected light spectrum can accurately reflect the position information of the flat surface, thereby improving the accuracy of the film thickness measurement of the flat part. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 is the original optical path diagram for film thickness measurement in an embodiment of the present invention;

[0037] Figure 2 It is a flow chart of a film thickness measurement method based on spectral confocal in an embodiment of the present invention;

[0038] Figure 3 A dual optical path diagram of film thickness measurement in an embodiment of the present invention;

[0039] Figure 4 is another dual optical path diagram for film thickness measurement in an embodiment of the present invention;

[0040] Figure 5 A light path diagram for obtaining the modulation coefficient of the outgoing light in an embodiment of the present invention;

[0041] Figure 6 is a graph of original spectrum data collected by the spectrometer in an embodiment of the present invention at a certain moment;

[0042] Figure 7 is the reference spectrum of the light source in the embodiment of the present invention;

[0043] Figure 8 This is a reflection spectrum data diagram obtained after demodulation in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0046] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] Figure 1 In order to measure the original optical path diagram of the film thickness of the flat piece, the white light source 1 emits incident light to the surface 4 of the flat piece through the optical fiber 2 and the dispersion objective lens 3, and the reflection spectrum reflected by the flat piece is collected by the spectrometer 5.

[0049] like Figure 2 As shown, an embodiment of the present invention provides a film thickness measurement method based on spectral confocal, which is executed by an electronic device such as a computer or a server, and specifically includes:

[0050] S1, pre-acquire the output light modulation coefficient of the spectral confocal system . Output light modulation coefficient It indicates the loss of light in the process of entering the spectrometer through the transmission path, and its value can be measured and calculated in an experimental environment. represents the wavelength, It is not a constant coefficient, but a function of wavelength, that is, the loss is different at different wavelengths.

[0051] S2, using a spectrometer to collect the reflected light spectrum focused on the upper and lower surfaces of the flat piece, to obtain a real-time characteristic spectrum carrying position information under incident light and real-time incident light modulation light source spectrum The wavelength It can be the full wavelength of the incident light or a partial wavelength. The flat piece can be a wafer thin film, such as a silicon oxide layer, a silicon carbide layer, and the like.

[0052] S3, according to the outgoing light modulation coefficient and the incident light modulates the light source spectrum Calculate the reference spectrum of the light source .

[0053] S4, using light source reference spectrum For characteristic spectrum Demodulate and obtain the standard reflected light spectrum .

[0054] S5, according to the standard reflected light spectrum Calculates the thickness of flat parts.

[0055] The film thickness measurement method and device based on spectral confocal provided in the embodiment of the present invention calculate the light source reference spectrum by using the outgoing light modulation coefficient and the incident light source spectrum measured in real time. The real-time characteristic spectrum carrying position information is modulated according to the real-time change of the light source and the attenuation of the transmission light path. The calculated light source reference spectrum is used for demodulation. The obtained standard reflected light spectrum can accurately reflect the position information of the flat surface, thereby improving the accuracy of the film thickness measurement of the flat part.

[0056] In one embodiment, in step S1, a spectrometer is used to collect the reflected light spectrum focused on the upper and lower surfaces of the flat member, which specifically includes:

[0057] Two spectrometers are used to collect the reflected light spectra focused on the upper and lower surfaces of the flat piece to obtain the characteristic spectrum. and the incident light modulates the light source spectrum .

[0058] like Figure 3 As shown, in this embodiment Figure 1 The exit of the optical fiber 2 in the optical path diagram leads to another split light path, and the two split light paths are connected to a spectrometer respectively. The optical fiber is a 2×2 type optical fiber. Since a large amount of light intensity at the exit is used for displacement measurement, the split ratio at the exit is set to 5:5. A spectrometer 51 (SM1) is used to collect the reflected light spectrum focused on the upper and lower surfaces of the flat piece carrying characteristic information, that is, the characteristic spectrum Passive optical components such as optical fibers inevitably introduce reflection and transmission losses in the optical path, and the instability of the light source itself will lead to characteristic spectra. Inaccurate, therefore, for accurate characteristic spectra , it is necessary to consider the effect of these optical elements on the characteristic spectrum The spectrum of the incident light modulated light source for thickness measurement after passing through passive units such as optical fiber is collected in real time by another spectrometer 52 (SM2). By collecting spectral data through the optical fiber under actual usage conditions, we can better understand and quantify the impact of these components on the spectrum, so that appropriate corrections can be made during data processing to ensure the accuracy of the measurement results.

[0059] In another embodiment, the spectrometer is used to collect the reflected light spectrum focused on the upper and lower surfaces of the flat member in step S1, which can also be:

[0060] The two channels of the spectrometer are used to collect the reflected light spectra focused on the upper and lower surfaces of the flat piece to obtain the characteristic spectrum. and the incident light modulates the light source spectrum .

[0061] like Figure 4 As shown, the characteristic spectrum can be collected using two channels of a spectrometer 5 and the incident light modulates the light source spectrum Utilizing two channels of one spectrometer for spectrum acquisition provides high synchronization, system stability and cost-effectiveness, and can also simplify demodulation and maintenance work.

[0062] In one embodiment, the following can be used in advance: Figure 5 The experimental system shown measures and calculates the modulation coefficient of the output light Specifically, the light emitted by the light source 1 of the spectral confocal system simulates the reflected light on the surface of the flat piece, and obtains the spectrum collected by the spectrometer 5 through the reflected light path. The reflected light path refers to the path that the light reflected from the flat surface is transmitted to the spectrometer. Figure 5 For example, the reflected light path of the experimental system is the path of light emitted by light source 1 transmitted to spectrometer 5 through optical fiber 2 and other devices (such as probes and fiber couplers, etc.). Since the light source 1 in this system simulates the light emitted from the surface of a flat part, its transmission path is called the reflected light path.

[0063] The splitting ratio used in the reflected light path should be consistent with the splitting ratio used in the measurement system, such as Figure 5 One branch of the light splitting path at the outlet end of the optical fiber 2 is connected to the spectrometer 5, and the other branch may not be connected to other components. Figure 3 or Figure 4 System settings shown Figure 5 The system shown has a split ratio of 5:5.

[0064] According to the spectrum and light source spectrum Calculate the outgoing light modulation coefficient , where the light source spectrum can be measured directly. Further, .

[0065] The incident light path refers to the path that the light emitted by the light source takes when it enters the surface of the flat piece. The spectrometer collects the incident light modulating the light source spectrum There are also losses. Figure 3 or Figure 4 The measurement system shown captures The path and Figure 5 Collect spectrum The transmission direction of light in the path is opposite. Although the incident light and the reflected light pass through almost the same components, due to the asymmetry of the optical path loss, the quality of the connection part and the end face, and the layout problems such as light bending, the attenuation ratio of the incident light path and the reflected light path is different. Therefore, the incident light modulation coefficient from the incident light modulating light source to the spectrometer is recorded as , ;

[0066] Combination Figure 3-5 , the reference spectrum of the light source in this scheme for

[0067] ,

[0068] because , , it can be calculated as follows:

[0069] .

[0070] In the process of measuring thickness, only the incident light modulated light source spectrum needs to be collected The reference spectrum of the light source can be calculated .

[0071] In one embodiment, in step S5, according to the standard reflected light spectrum Calculate the thickness of flat parts, including:

[0072] S51, standard reflected light spectrum The upper and lower surface focusing peak wavelengths are extracted to obtain the upper surface focusing peak wavelength and the lower surface focusing peak wavelength.

[0073] S52, calculating the upper surface position and the lower surface position of the flat piece according to the upper surface focusing peak wavelength, the lower surface focusing peak wavelength and a pre-constructed spectral peak center corresponding parameter-displacement model.

[0074] The parameter-displacement model corresponding to the spectral peak center is calibrated by the measured data, specifically:

[0075] ,

[0076] in Indicates the parameter corresponding to the center of the spectrum peak location, It is a parameter determined by the corresponding parameters of the spectral peak center and the distance. Through the above step measurement process, the corresponding parameters of the spectral peak center at each step position and the reliable distance value at each step position can be collected, and a large amount of data can be used to calculate The value of is taken to complete the model construction.

[0077] S53, calculating the thickness of the flat part according to the upper surface position of the flat part and the lower surface position of the flat part.

[0078] This embodiment calculates the actual positions of the upper and lower surfaces of the flat part by substituting the extracted peak wavelength into the pre-built displacement model. Finally, the thickness of the flat part is calculated based on these positions, which improves the accuracy of the film thickness measurement of the flat part and eliminates the influence of actual working conditions such as the unstable light source and the reflectivity change of the sample flat part.

[0079] In one embodiment, step S3 uses a light source reference spectrum For characteristic spectrum Demodulate and obtain the standard reflected light spectrum Before, it also includes:

[0080] Get the background noise spectrum The background noise spectrum refers to the noise spectrum of the optical signal received by the spectrometer when there is no measurement object. This background noise mainly comes from various light sources in the environment, which may include sunlight, indoor lighting, scattered light, and the noise of the optical fiber system itself. The background noise can be obtained in real time or as a fixed value measured in advance.

[0081] According to the background noise spectrum For characteristic spectrum Noise removal can be performed by .

[0082] In this embodiment, a background noise spectrum is obtained and applied. For characteristic spectrum Noise removal can improve the signal-to-noise ratio (SNR) of the characteristic spectrum, thereby enhancing the clarity and readability of the signal, which helps to improve data accuracy and thickness measurement precision.

[0083] In one embodiment, the characteristic spectrum is calculated using the following formula: Perform demodulation and normalization to obtain the standard reflected light spectrum :

[0084] .

[0085] The spectrum is normalized, that is, the data is scaled to a specific range, which reduces the model's need for input data scale changes and improves processing capabilities. At the same time, the characteristic spectrum carrying displacement information is demodulated according to the above formula to restore the weight of each defocused wavelength in the reflection spectrum to achieve the purpose of peak center drift correction.

[0086] For example, when the wafer is thinned by a wafer thinner, the characteristic spectral data collected by the spectrometer at a certain moment is as follows: Figure 6 shown.

[0087] No characteristic spectrum During demodulation, the peak wavelength is extracted as 569.4997 nm through the peak extraction algorithm, and the upper surface focusing position is calculated to be 0.55028 mm using the wavelength-displacement model.

[0088] The incident light modulated light source spectrum is collected through the spectrometer in real time , and calculate the reference spectrum of the light source ,like Figure 7 As shown. According to the formula The standard reflected light spectrum obtained after demodulation by normalizing the spectral characteristics is as follows: Figure 8 shown.

[0089] Using the peak extraction algorithm Figure 8 The peak wavelength is extracted from the spectrum in the image, and the extracted peak wavelength is 569.5458nm. The upper surface focusing position is calculated to be 0.55068mm with the wavelength-displacement model. The peak center position changes by 0.0461nm, and the displacement correction is 0.4um.

[0090] In one embodiment, step S3 uses a light source reference spectrum For characteristic spectrum Demodulate and obtain the standard reflected light spectrum ,include:

[0091] .

[0092] The peak wavelength extracted according to the calculation method of this embodiment is 569.5331 nm, and the upper surface focusing position is calculated to be 0.55059 mm using the wavelength-displacement model. Compared with the result without demodulation processing, the final displacement correction amount is 0.31 um.

[0093] It can be seen from the above embodiments that by performing demodulation processing according to the solution provided in the embodiments of the present invention, the position calculation of the flat surface can be corrected to a certain extent, and the correction amount can be referenced in real time during actual measurement, thereby improving measurement accuracy.

[0094] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0095] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0096] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0097] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0098] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A film thickness measurement method based on spectral confocal, characterized in that: include: The light emitted by the light source of the spectral confocal system simulates the reflected light on the surface of the flat piece, and obtains the spectrum collected by the spectrometer through the reflected light path. ; According to the spectrum and light source spectrum Calculate the outgoing light modulation coefficient ; The spectrometer is used to collect the reflected light spectrum focused on the upper and lower surfaces of the flat piece to obtain a real-time characteristic spectrum carrying position information under the incident light. and real-time incident light modulation light source spectrum ; According to the output light modulation coefficient and the incident light modulated light source spectrum Calculate the reference spectrum of the light source ; Using the light source reference spectrum The characteristic spectrum Demodulate and obtain the standard reflected light spectrum ; According to the standard reflected light spectrum Calculates the thickness of flat parts.

2. The method according to claim 1, characterized in that The spectrometer is used to collect the reflected light spectrum focused on the upper and lower surfaces of the flat piece, including: Two spectrometers are used to collect the reflected light spectra focused on the upper and lower surfaces of the flat piece to obtain the characteristic spectrum. and the incident light modulates the light source spectrum .

3. The method according to claim 1, characterized in that The spectrometer is used to collect the reflected light spectrum focused on the upper and lower surfaces of the flat piece, including: The two channels of the spectrometer are used to collect the reflected light spectra focused on the upper and lower surfaces of the flat piece to obtain the characteristic spectrum. and the incident light modulates the light source spectrum .

4. The method according to claim 1, characterized in that: Use the following formula to calculate the reference spectrum of the light source : 。 5. The method according to claim 1, characterized in that: According to the standard reflected light spectrum Calculate the thickness of flat parts, including: The standard reflected light spectrum Extract the upper and lower surface focusing peak wavelengths to obtain the upper surface focusing peak wavelength and the lower surface focusing peak wavelength; Calculate the upper surface position of the flat piece and the lower surface position of the flat piece according to the upper surface focusing peak wavelength, the lower surface focusing peak wavelength and the pre-constructed spectrum peak center corresponding parameter-displacement model; The thickness of the flat member is calculated according to the position of the upper surface of the flat member and the position of the lower surface of the flat member.

6. The method according to claim 1, characterized in that Using the light source reference spectrum The characteristic spectrum Demodulate and obtain the standard reflected light spectrum ,include: 。 7. The method according to claim 1, characterized in that Using the light source reference spectrum The characteristic spectrum Demodulate and obtain the standard reflected light spectrum Before, it also includes: Get the background noise spectrum ; According to the background noise spectrum The characteristic spectrum Perform noise removal.

8. The method according to claim 7, characterized in that The characteristic spectrum is analyzed using the following formula Perform demodulation and normalization to obtain the standard reflected light spectrum : 。 9. A film thickness measurement device based on spectral confocal, characterized in that: include: A processor and a memory connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor executes the film thickness measurement method based on spectral confocal as described in any one of claims 1 to 8.

Images