Self-coherent optical fiber interference device and method for simultaneously measuring morphology and thickness

Abstract

The invention relates to a self-coherence optical fiber interference device and method for simultaneously measuring morphology and thickness. The device comprises a light source module (1), a measurement light path (2), a compensation light path (3), a spectrograph (4), a mechanical motion module (6) and a data processing module (5), the measuring light path (2) comprises an optical fiber circulator (21), an optical fiber retroreflector (22) and an optical probe (23) and is used for realizing focusing measurement and enabling reflected light of the end face of the optical fiber retroreflector (22) and reflected light of a transparent object to be measured to return; reflected light of the end face of the optical fiber retroreflector (2) and reflected light of the transparent object to be measured form a measuring light beam, and the measuring light beam enters the compensation light path (3); the compensation light path (3) comprises an optical fiber splitter (31), an optical fiber delay line (32) and an optical fiber coupler (33), the measuring light beam is subjected to optical path compensation to generate a compensation light beam, and the compensation light beam and the measuring light beam are combined and input into the spectrograph (4) together.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement, and particularly relates to a self-coherent fiber optic interferometer and method for simultaneously measuring morphology and thickness. Background Technology

[0002] Thickness and warpage are critical parameters in wafer fabrication processes, and their quality directly affects the overall production and the smooth progress of subsequent processes. Therefore, precise detection of wafer thickness and warpage is necessary during wafer manufacturing.

[0003] Currently, there are various optical methods for simultaneously measuring morphology and thickness, most of which are based on low-coherence Michelson interferometry (CN105044035B). This technique calculates the morphology and thickness of a wafer by detecting the change in optical path between the measuring arm and the reference arm. However, Michelson interferometry is very sensitive to the environment, and different errors may be introduced between the measuring arm and the reference arm, thus affecting the accuracy of the optical path difference measurement. In addition, the setup of a Michelson interferometer requires two probes, which makes the measurement device cumbersome and prone to introducing subjective errors from the operator during installation. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a self-coherent fiber optic interferometer device and method capable of simultaneously measuring the morphology and thickness of transparent objects such as wafers. It utilizes interference generated by light reflected from the fiber end face and light reflected from the wafer surface, thus solving the technical problem of requiring two arms in Michelson interferometers. Furthermore, this device requires only one probe, offering advantages such as simple measurement equipment and ease of integration into semiconductor equipment environments. The technical solution of this invention is as follows:

[0005] A self-coherent fiber optic interferometer for simultaneously measuring morphology and thickness includes a light source module 1, a measurement optical path 2, a compensation optical path 3, a spectrometer 4, a mechanical motion module 6, and a data processing module 5.

[0006] Light source module 1 is used to generate and output measurement light with a predetermined wavelength width;

[0007] The measurement optical path 2 includes an optical fiber circulator 21, an optical fiber retroreflector 22, and an optical probe 23. It is used to converge the output light of the light source module 1 and incident it onto the transparent object to be measured in order to achieve focused measurement, and to make the reflected light from the end face of the optical fiber retroreflector 2 and the reflected light from the transparent object to be measured return. The reflected light from the end face of the optical fiber retroreflector 2 and the reflected light from the transparent object to be measured form a measurement beam, and the measurement beam enters the compensation optical path 3.

[0008] The compensation optical path 3 includes: fiber optic splitter 31, fiber optic delay line 32 and fiber optic coupler 33, which are used to generate a compensation beam. The measurement beam is generated after optical path compensation. The compensation beam and the measurement beam are combined and input together to the spectrometer 4.

[0009] The data processing module 5 is used by the spectrometer 4 to perform calculations and analysis on the collected spectral data and generate a Fourier spectrum of the spectral signal. The peaks in the Fourier spectrum correspond to the thickness of the transparent object to be tested and the geometric distance between the upper surface of the transparent object to be tested and the optical probe 23, respectively.

[0010] Mechanical motion module 6 is used to carry the transparent object under test and move it under the optical probe to realize thickness measurement and geometric distance measurement at different positions.

[0011] Furthermore, the light source module 1 is a superluminescent diode (SLD) used to output unbiased single-mode near-infrared broadband light signals.

[0012] Furthermore, the first port of the fiber optic circulator 21 of the measurement optical path 2 is connected to the light source module 1, and the second port is connected to the fiber optic retroreflector 22; the coated port of the fiber optic retroreflector 22 is connected to the optical probe 23; and the third port of the fiber optic circulator 21 is connected to the fiber optic splitter 31 of the compensation optical path 3.

[0013] Furthermore, the optical probe 23 includes two lenses: the first lens is used to collimate the measurement light, and the second lens is used to focus the measurement light.

[0014] Furthermore, the fiber lengths of the output end of the fiber splitter 31 and the input end of the fiber coupler 33 in the compensation optical path should be relatively matched; the third port of the fiber circulator 21 in the measurement optical path 1 is connected to the first port of the fiber splitter 31; the second port of the fiber splitter 31 is connected to the second port of the fiber coupler via the fiber delay line 32; the third port of the fiber splitter 31 is directly connected to the third port of the fiber coupler; and the first port of the fiber coupler is connected to the spectrometer 4.

[0015] Furthermore, the fiber delay line 32 is used to compensate for the optical path between the reflected light from the end face of the fiber retroreflector 22 and the reflected light from the transparent object under test. The length of the fiber delay line 32 is calculated as follows:

[0016]

[0017] In the formula, L d n is the length of the fiber delay line 32. dT1 is the internal refractive index of the optical fiber, n1 is the thickness at the center of the first lens, n2 is the refractive index of the first lens, T2 is the thickness at the center of the second lens, n2 is the refractive index of the second lens, and L represents the distance between the end face of the optical fiber connected to the optical probe 23 and the upper surface of the transparent object to be measured in the working state.

[0018] The present invention also provides a method for simultaneously measuring morphology and thickness using the aforementioned device, characterized by comprising the following steps:

[0019] Step A: Turn on the light source module 1 and the spectrometer 4, set the appropriate light source intensity and the integration time of the spectrometer 4, and place the transparent object to be tested below the optical probe 23;

[0020] Step B: The mechanical motion module 6 carries the transparent object to be measured and moves along the set route under the optical probe 23, so that the measurement points of the optical probe 23 are distributed throughout the entire surface of the transparent object to be measured, thereby ensuring that the measurement spectrum covers the entire object being measured.

[0021] Step C: The data processing module 5 calculates the reflection spectrum of each measurement point to obtain the thickness of the object at each location and the geometric distance between the upper surface of the transparent object to be measured and the optical probe 23.

[0022] Step D: Organize and plot the thickness distribution calculated in Step C to obtain the overall thickness distribution of the measured object; organize and plot the absolute position of the measured object from the optical probe 23 in Step C to obtain the morphological data of the measured object.

[0023] Furthermore, step C specifically includes the following sub-steps:

[0024] Sub-step C1: By performing Fourier transform on the detected spectral signal, two sets of optical path difference signals are obtained:

[0025] The first group of optical path differences opd1 = 2·ΔL

[0026] The second group of optical path differences opd2 = 2·n s • THK represents the optical path difference caused by the internal thickness of the transparent object being measured.

[0027] In the formula, ΔL is the geometric distance between the upper surface of the transparent object to be measured and the optical probe 23, and n s is the refractive index of the transparent object to be measured, and THK is the geometric thickness of the transparent object to be measured;

[0028] Sub-step C2: Perform mathematical operations on the optical path difference calculated in sub-step C1 according to the above formula to calculate the geometric distance between the upper surface of the transparent object to be tested and the optical probe 23, as well as the geometric thickness of the transparent object to be tested, thereby realizing the synchronous acquisition of the spatial position information and thickness information of the transparent object to be tested.

[0029] As can be seen from the above technical solutions, the self-coherent fiber interferometer device and method for simultaneously measuring morphology and thickness of the present invention have at least one or a part of the following beneficial effects:

[0030] (1) By using self-coherent technology, the interference of the environment on the optical path difference of the two arms can be effectively reduced;

[0031] (2) It can simultaneously measure the morphology and thickness of the wafer;

[0032] (3) The optical path is simple, the scalability is good, and it is easy to integrate into the semiconductor production line. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a self-coherent fiber interferometry device for simultaneously measuring morphology and thickness according to an embodiment of the present invention; Figure 2 This is a flowchart of a self-coherent fiber interferometry method for simultaneously measuring morphology and thickness according to an embodiment of the present invention;

[0034] Figure 3 This is a variant of a schematic diagram of a self-coherent fiber interferometry apparatus for simultaneously measuring morphology and thickness according to an embodiment of the present invention;

[0035] The above appendix Figure 1 In the attached figures, the meanings of the labels are as follows:

[0036] 1-Light source module; 2-Measurement optical path

[0037] 3-Compensation optical path 4-Spectrometer

[0038] 5-Data Processing Module 6-Mechanical Motion Module

[0039] in:

[0040] 21-Fiber Circulator 22-Fiber Optic Retroreflector 23-Optical Probe

[0041] 31-Fiber optic splitter; 32-Fiber optic delay line; 33-Fiber optic combiner

[0042] The above appendix Figure 3 In the attached figures, the meanings of the labels are as follows:

[0043] 1-Light source module; 2-Measurement optical path

[0044] 3-Compensation optical path 4-Spectrometer

[0045] 5-Data Processing Module 6-Mechanical Motion Module

[0046] in:

[0047] 21-Fiber Circulator 22-Fiber Optic Retroreflector 23-Optical Probe

[0048] 31-Fiber optic splitter; 32-Fiber optic delay line; 33-Fiber optic combiner Detailed Implementation

[0049] This invention provides a self-coherent fiber optic interferometer device and method for simultaneously measuring morphology and thickness. By utilizing the interference of light reflected from the fiber end face and the wafer surface, this system simplifies the traditional Michelson interferometer measurement device, giving it significant advantages such as simple structure and easy integration into semiconductor equipment.

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0051] The self-coherent fiber optic interferometer of the present invention for measuring morphology and thickness, such as Figure 1 As shown, it includes a light source module 1, a measurement optical path 2, a compensation optical path 3, a spectrometer 4, a mechanical motion module 6, and a data processing module 5.

[0052] Light source module 1 is used to generate and output measurement light with a predetermined wavelength width; light source module 1 is a superluminescent light-emitting diode (SLD) used to output an unbiased single-mode near-infrared broadband light signal. Light source module 1 can be an SLD with a center wavelength of 1310nm and a bandwidth of 70nm, but is not limited to this.

[0053] Measurement optical path 2 is used to converge the output light of the light source module 1 and incident it onto the object being measured to form a small light spot for focused measurement. It also allows the reflected light from the end face of the fiber optic retroreflector 2 and the reflected light from the sample to return, forming a measurement beam. This measurement beam further enters the compensation optical path 3. Measurement optical path 2 includes a fiber optic circulator 21, a fiber optic retroreflector 22, and an optical probe 23. The first port of the fiber optic circulator 21 is connected to the light source module 1, and the second port is connected to the fiber optic retroreflector 22. The coated port of the fiber optic retroreflector 22 is connected to the optical probe 23, and the third port of the fiber optic circulator 21 is connected to the fiber optic splitter 31.

[0054] The fiber optic retroreflector 22 can be configured with a 50:50 reflection and transmission output ratio; the optical probe 23 consists of two convex lenses, the first lens is used to collimate the measurement light, and the second lens is used to focus the measurement light, and can be composed of aspherical lenses with focal lengths of 4.59mm and 15.3mm respectively.

[0055] The compensation optical path 3 is used to generate a compensation beam. After optical path compensation, the measurement beam is used to generate the compensation beam. The compensation beam and the measurement beam are combined and input together to the spectrometer 4. The compensation optical path 3 includes: an optical fiber splitter 31, an optical fiber delay line 32, and an optical fiber coupler 33. The fiber lengths at the output end of the optical fiber splitter 31 and the input end of the optical fiber coupler 33 should be matched. The third port of the optical fiber circulator 21 of the measurement optical path 1 is connected to the first port of the optical fiber splitter 31; the second port of the optical fiber splitter 31 is connected to the second port of the optical fiber coupler via the optical fiber delay line 32; the third port of the optical fiber splitter 31 is directly connected to the third port of the optical fiber coupler; and the first port of the optical fiber coupler is connected to the spectrometer 4.

[0056] Spectrometer 4 is used to detect light signals within a specific wavelength range, perform spectral processing, and measure the light intensity corresponding to each wavelength to obtain complete spectral data. A low-noise, research-grade spectrometer that matches the light source parameters should be selected.

[0057] The data processing module 5 is used to perform calculations and analysis on the acquired spectral data to generate a Fourier spectrum of the spectral signal. The peaks in the Fourier spectrum correspond to the thickness of the wafer under test and the distance between the upper surface of the sample and the optical probe 23, respectively.

[0058] Mechanical motion module 6 is used to carry the wafer under test and move it precisely under the optical probe to realize thickness measurement and geometric distance measurement at different positions. A high-precision motion control console can be selected to carry the wafer under test and move it precisely under the optical probe.

[0059] The spectral measurement range of this invention is 1240–1380 nm, the spot size of the optical probe after focusing is 30 μm, and the working distance is 12 mm.

[0060] The broadband light emitted by the light source module 1 first enters the first port of the fiber optic circulator 21, and then enters the fiber optic retroreflector 22 via the second port. Part of the light is reflected at the retroreflector end face and returns to the second port of the circulator, while the other part passes through the end face and is focused onto the surface of the wafer under test by the optical probe 23. After reflection at the upper and lower surfaces of the sample, the beam returns along its original path to the second port of the circulator, and then enters the first port of the fiber optic splitter 31 via the third port. Here, the beam is split into two paths at a fixed splitting ratio: one path serves as a compensation beam, undergoing optical path compensation via the fiber optic delay line 32; the other path serves as the measurement beam, transmitted directly without compensation. The two beams are then combined by the fiber optic combiner and enter the spectrometer 4.

[0061] During this process, the measurement beams reflected from the upper and lower surfaces of the sample interfere, forming an interference signal containing information about the sample thickness. Simultaneously, the reflected light from the upper surface of the sample in the compensation beam interferes with the uncompensated reflected light from the retroreflector end face in the measurement beam, forming an interference signal containing information about the distance between the retroreflector end face and the upper surface of the sample. After being detected by the spectrometer 4, the two sets of interference signals are transmitted to the computer (data processing module 5) and processed by Fourier transform, allowing the simultaneous acquisition of the thickness and geometric distance information of the wafer under test.

[0062] The optical path difference between the reflected light from the sample's upper surface in the measurement beam and the reflected light from the fiber retroreflector 22 end face in the compensation beam is equal to twice the optical distance between the retroreflector end face and the sample's upper surface, minus the optical compensation distance introduced by the fiber delay line 32. When this condition is met, the optical path difference will not exceed the coherence length of the light source, thus enabling the direct generation and observation of interference signals in the spectrometer 4.

[0063] The fiber delay line 32 is used to compensate for the optical path between the reflected light from the end face of the fiber retroreflector 22 and the reflected light from the wafer under test. The length of the fiber delay line 32 is calculated as follows:

[0064]

[0065] In the formula, L d n is the length of the fiber delay line 32. d T1 is the internal refractive index of the optical fiber, n1 is the thickness at the center of the first lens, n2 is the refractive index of the first lens, T2 is the thickness at the center of the second lens, n2 is the refractive index of the second lens, and L represents the distance between the optical fiber end face connected to the optical probe 23 and the upper surface of the wafer under test in the working state.

[0066] The method for measuring morphology and thickness includes the following steps:

[0067] Step A: Turn on the light source and spectrometer 4, and set the appropriate light source intensity and the integration time of the spectrometer 4. Place the wafer to be tested below the optical probe 23, and adjust the orientation and working distance of the optical probe 23 to ensure that the spectrum acquired by the spectrometer 4 is in a state with low noise.

[0068] Step B: The mechanical motion module 6 carries the wafer under test and moves along the set route under the optical probe 23, so that the measurement points of the optical probe 23 are distributed throughout the entire surface of the wafer under test, thereby ensuring that the measurement spectrum covers the entire measurement object.

[0069] Step C: The data processing module 5 calculates the reflection spectrum of each measurement point to obtain the thickness of each position of the measured object and the absolute position of the upper surface of the wafer to be measured from the optical probe 23.

[0070] Step C specifically includes the following sub-steps:

[0071] Sub-step C1: By performing Fourier transform on the detected spectral signal, two sets of optical path difference signals are obtained:

[0072] The first group of optical path differences opd1 = 2·ΔL

[0073] The second group of optical path differences opd2 = 2·n s • THK, corresponding to the optical path difference caused by the internal thickness of the wafer under test.

[0074] In the formula, ΔL is the geometric distance between the upper surface of the wafer under test and the optical probe 23, and n s is the refractive index of the wafer to be tested, and THK is the geometric thickness of the wafer to be tested.

[0075] Sub-step C2: Perform mathematical operations on the optical path difference calculated in sub-step C1 according to the above formula to calculate the geometric distance between the upper surface of the wafer under test and the optical probe 23, as well as the geometric thickness of the sample, thereby realizing the synchronous acquisition of the spatial position information and thickness information of the wafer under test.

[0076] Step D: Organize and plot the thickness distribution calculated in Step C to obtain the overall thickness distribution of the measured object; organize and plot the absolute position of the measured object from the optical probe 23 in Step C to obtain the morphological data of the measured object.

[0077] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. It should be noted that implementations not illustrated or described in the drawings or the main text of the specification are forms known to those skilled in the art and are not described in detail. Furthermore, the definitions of the above elements and methods are not limited to the various specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can easily substitute or replace them.

[0078] In summary, this invention enables simultaneous measurement of sample morphology and thickness. The self-coherent fiber optic interferometry setup in this invention effectively reduces the impact of environmental disturbances on the measurement. Furthermore, it simplifies the measurement setup, facilitating integration into online measurement applications.

Claims

1. A self-coherent fiber optic interferometer for simultaneously measuring morphology and thickness, comprising a light source module (1), a measurement optical path (2), a compensation optical path (3), a spectrometer (4), a mechanical motion module (6), and a data processing module (5), wherein, A light source module (1) is used to generate and output measurement light with a predetermined wavelength width; The measurement optical path (2) includes an optical fiber circulator (21), an optical fiber retroreflector (22), and an optical probe (23), which is used to converge the output light of the light source module (1) and incident it onto the transparent object to be measured in order to achieve focused measurement, and to make the reflected light from the end face of the optical fiber retroreflector (2) and the reflected light from the transparent object to be measured return; the reflected light from the end face of the optical fiber retroreflector (2) and the reflected light from the transparent object to be measured form a measurement beam, and the measurement beam enters the compensation optical path (3); The compensation optical path (3) includes: fiber splitter (31), fiber delay line (32) and fiber coupler (33), which are used to generate compensation beam. The measurement beam is generated after optical path compensation. The compensation beam and the measurement beam are combined and input together to the spectrometer (4). The data processing module (5) is used by the spectrometer (4) to perform calculation and analysis on the collected spectral data and generate a Fourier spectrum of the spectral signal. The peaks in the Fourier spectrum correspond to the thickness of the transparent object to be tested and the geometric distance between the upper surface of the transparent object to be tested and the optical probe (23). The mechanical motion module (6) is used to carry the transparent object to be measured and move it under the optical probe to realize thickness measurement and geometric distance measurement at different positions.

2. The self-coherent fiber interferometer apparatus for simultaneously measuring morphology and thickness according to claim 1, characterized in that, The light source module (1) is a superluminescent diode (SLD) used to output unbiased single-mode near-infrared broadband light signals.

3. The self-coherent fiber optic interferometer for simultaneously measuring morphology and thickness according to claim 1, characterized in that, The first port of the fiber optic circulator (21) of the measurement optical path (2) is connected to the light source module (1), and the second port is connected to the fiber optic retroreflector (22); the coated port of the fiber optic retroreflector (22) is connected to the optical probe (23); and the third port of the fiber optic circulator (21) is connected to the fiber optic splitter (31) of the compensation optical path (3).

4. The self-coherent fiber optic interferometer for simultaneously measuring morphology and thickness according to claim 3, characterized in that, The optical probe (23) includes two lenses: the first lens is used to collimate the measurement light, and the second lens is used to focus the measurement light.

5. The self-coherent fiber optic interferometer for simultaneously measuring morphology and thickness according to claim 4, characterized in that, The fiber lengths of the output end of the fiber splitter (31) of the compensation optical path and the input end of the fiber coupler (33) should be relatively matched; the third port of the fiber circulator (21) of the measurement optical path (1) is connected to the first port of the fiber splitter (31); the second port of the fiber splitter (31) is connected to the second port of the fiber coupler through the fiber delay line (32); the third port of the fiber splitter (31) is directly connected to the third port of the fiber coupler; the first port of the fiber coupler is connected to the spectrometer (4).

6. The self-coherent fiber optic interferometer for simultaneously measuring morphology and thickness according to claim 4, characterized in that, The fiber delay line (32) is used to compensate for the optical path between the reflected light from the end face of the fiber retroreflector (22) and the reflected light from the transparent object under test. The length of the fiber delay line (32) is calculated as follows: In the formula, L d n is the length of the fiber delay line (32). d T1 is the internal refractive index of the optical fiber, T2 is the thickness at the center of the first lens, n1 is the refractive index of the first lens, T2 is the thickness at the center of the second lens, n2 is the refractive index of the second lens, and L represents the distance between the optical fiber end face connected to the optical probe (23) and the upper surface of the transparent object to be measured in the working state.

7. A method for simultaneously measuring morphology and thickness using the apparatus according to any one of claims 1-6, characterized in that, Includes the following steps: Step A: Turn on the light source module (1) and the spectrometer (4), set the appropriate light source intensity and the integration time of the spectrometer (4), and place the transparent object to be tested below the optical probe (23); Step B: The mechanical motion module (6) carries the transparent object to be measured and moves along the set route under the optical probe (23), so that the measurement points of the optical probe (23) are covered throughout the entire surface of the transparent object to be measured, thereby ensuring that the measurement spectrum covers the entire measurement object; Step C: The data processing module (5) calculates the reflection spectrum of each measurement point to obtain the thickness of each position of the measured object and the geometric distance between the upper surface of the transparent object to be measured and the optical probe (23). Step D: Organize and plot the thickness distribution calculated in step C to obtain the overall thickness distribution of the measured object; organize and plot the absolute position of the measured object from the optical probe (23) in step C to obtain the morphological data of the measured object.

8. The method for simultaneously measuring morphology and thickness according to claim 7, characterized in that, Step C specifically includes the following sub-steps: Sub-step C1: By performing Fourier transform on the detected spectral signal, two sets of optical path difference signals are obtained: The first group of optical path differences opd1 = 2·ΔL The second group of optical path differences opd2 = 2·n s • THK represents the optical path difference caused by the internal thickness of the transparent object being measured. In the formula, ΔL is the geometric distance between the upper surface of the transparent object to be measured and the optical probe, and n s is the refractive index of the transparent object to be measured, and THK is the geometric thickness of the transparent object to be measured; Sub-step C2: Perform mathematical operations on the optical path difference calculated in sub-step C1 according to the above formula to calculate the geometric distance between the upper surface of the transparent object to be tested and the optical probe, as well as the geometric thickness of the transparent object to be tested, thereby realizing the synchronous acquisition of the spatial position information and thickness information of the transparent object to be tested.

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