A method and system for confocal measurement of film thickness

Abstract

The present application belongs to the technical field of color confocal sensor measurement, and discloses a film thickness confocal measurement method and system. The present application uses a light source in a laser generating unit to emit a multi-wavelength light beam as incident light. The incident light is transmitted to a fiber coupler through a first optical fiber and is emitted through a third optical fiber. After being emitted, the incident light is scanned and focused on a sample to be measured through a scanning unit. The sample to be measured is transversely scanned by the scanning unit, and longitudinally scanned by a sample stage. After being refracted by the sample to be measured, the incident light is focused on a mirror. The reflected light formed after the mirror passes through the sample to be measured and the scanning unit in turn, and reaches the fiber coupler through the third optical fiber. Then, the reflected light is transmitted to a spectrometer through a second optical fiber. The corresponding measurement information of the sample to be measured is obtained by the spectrometer. The new scanning mode and the new film measurement light path provided by the present application can effectively improve the range, precision and efficiency of film thickness measurement.

Description

Technical Field

[0001] This invention belongs to the field of color confocal sensor measurement technology, and more specifically, relates to a confocal measurement method and system for thin film thickness. Background Technology

[0002] In the semiconductor manufacturing industry, thin film thickness significantly impacts product performance. Therefore, real-time monitoring and measurement of thin film thickness is crucial in semiconductor manufacturing processes. Currently, the mainstream method for measuring thin film thickness involves planar movement of the thin film sample for mechanical scanning. A color confocal sensor outputs a colored beam of light to the film, with different wavelengths of monochromatic light focused onto the upper and lower surfaces, respectively, and then received by a spectrometer through reflection. By utilizing the pre-calibrated wavelength-focal-length correspondence, the focal length difference between the two focused monochromatic lights is determined, thus calculating the film thickness at that point. Finally, planar movement of the film surface yields the overall film thickness. However, this measurement method has several significant drawbacks, including: a relatively small measurement range (i.e., a small range per unit time or per single measurement during planar movement); low scanning accuracy and slow speed, making real-time online precision measurement difficult. Summary of the Invention

[0003] This invention provides a confocal method and system for measuring thin film thickness, which solves the problems of small measurement range, low scanning accuracy, and slow speed in the prior art.

[0004] This invention provides a confocal film thickness measurement system, comprising: a laser generating unit, an optical fiber coupler, a scanning unit, a reflector, a stage, and a spectrometer;

[0005] The laser generating unit includes a light source, which is used to emit multi-wavelength beams as incident light;

[0006] The first port of the fiber optic coupler is connected to a first optical fiber, the second port of the fiber optic coupler is connected to a second optical fiber, and the third port of the fiber optic coupler is connected to a third optical fiber. The incident light is transmitted to the fiber optic coupler via the first optical fiber and exited via the third optical fiber. The exited incident light is then scanned and focused onto the sample to be tested by the scanning unit, which is used to perform a lateral scan on the sample to be tested.

[0007] The stage is used to hold the sample to be tested, and the reflector is disposed between the sample to be tested and the stage; the stage is equipped with a moving component, and the longitudinal scanning of the sample to be tested is achieved by using the stage.

[0008] The incident light is refracted by the sample under test and focused onto the reflector. The reflected light formed after passing through the reflector passes sequentially through the sample under test and the scanning unit, then through the third optical fiber to the optical fiber coupler, and then through the second optical fiber to the spectrometer. The spectrometer obtains the measurement information corresponding to the sample under test.

[0009] Preferably, the laser generating unit further includes a collimating lens and a first lens; the collimating lens and the first lens are both disposed in the optical path between the light source and the fiber coupler; the collimating lens is used to collimate the light beam emitted by the light source; the first lens is used to converge the collimated light beam into the first optical fiber.

[0010] Preferably, the light source is an LED light source.

[0011] Preferably, the scanning unit includes a dispersive probe and a galvanometer scanner; the dispersive probe has different focal lengths for light of different wavelengths, and the galvanometer scanner is used to perform lateral scanning of the sample to be tested; the incident light is scanned and focused onto the sample to be tested after passing through the dispersive probe and the galvanometer scanner in sequence.

[0012] Preferably, the scanning unit further includes: a second lens; the second lens is located in the optical path between the fiber coupler and the dispersive probe; the incident light is converted into parallel light after passing through the second lens and irradiates the dispersive probe; the reflected light is transmitted to the fiber coupler after passing through the galvanometer scanner, the dispersive probe, and the second lens in sequence.

[0013] Preferably, the moving component is a stepper motor.

[0014] Preferably, the confocal film thickness measurement system further includes: a data processing unit; the data processing unit stores pre-calibration information, and the data processing unit is used to receive measurement information from the spectrometer and combine it with the pre-calibration information to obtain film thickness information.

[0015] Preferably, the pre-calibration information includes the relationship between wavelength and focal length, and the thin film refractive index information of the sample to be tested.

[0016] On the other hand, the present invention provides a confocal method for measuring thin film thickness, which is implemented using the above-mentioned confocal measurement system for thin film thickness. The confocal method for measuring thin film thickness includes the following steps:

[0017] A multi-wavelength beam of light is emitted from a light source in a laser generating unit as incident light. The incident light is transmitted through a first optical fiber to an optical fiber coupler and then exits through a third optical fiber. After exiting, the incident light is scanned and focused onto the sample to be tested by a scanning unit. The scanning unit performs a lateral scan of the sample to be tested, and a stage is used to perform a longitudinal scan of the sample to be tested. The incident light is refracted by the sample to be tested and focused onto a reflector. The reflected light formed after passing through the reflector passes sequentially through the sample to be tested and the scanning unit, then through the third optical fiber to the optical fiber coupler, and then through a second optical fiber to a spectrometer. The spectrometer is used to obtain the measurement information corresponding to the sample to be tested.

[0018] Preferably, a collimating lens disposed between the light source and the fiber optic coupler is used to collimate the light beam emitted by the light source, and a first lens is used to converge the collimated light beam into the first fiber optic cable; a second lens disposed between the fiber optic coupler and the dispersive probe is used to convert the incident light into parallel light that illuminates the dispersive probe in the scanning unit.

[0019] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0020] This invention utilizes a laser generator unit to emit multi-wavelength beams as incident light. The incident light is transmitted through a first optical fiber to an optical fiber coupler and then exits through a third optical fiber. The exited incident light is scanned and focused onto the sample to be tested by a scanning unit. The scanning unit performs a lateral scan on the sample to be tested, and the stage performs a longitudinal scan on the sample to be tested. The incident light is refracted by the sample to be tested and focused onto a reflector. The reflected light formed after passing through the reflector passes sequentially through the sample to be tested and the scanning unit, then reaches the optical fiber coupler through the third optical fiber, and is then transmitted to a spectrometer through a second optical fiber. The spectrometer is used to obtain the measurement information corresponding to the sample to be tested. This invention utilizes a confocal color sensor to scan the sample laterally via a galvanometer scanner, while longitudinal scanning is achieved by moving the thin film sample longitudinally. This improves scanning accuracy and speed. Furthermore, by placing a reflector below the thin film, a new optical path for thin film thickness scanning is created, reducing the requirements for film placement. This can also be understood as reducing the precision requirements for the stage, as traditional scanning methods rely on mechanical movement of the stage in both the lateral and longitudinal directions. In this invention, the galvanometer scanner allows for high-precision mechanical movement of the stage in only one direction, eliminating the need for precision in the other direction. Additionally, traditional scanning methods rely on mechanical movement of the stage in both directions, and planar movement introduces transmission errors, resulting in a smaller measurement range per unit time or per measurement. Moreover, common moving thin film platforms introduce vibration noise, leading to a low signal-to-noise ratio. Compared to traditional measurement methods, this invention provides a novel scanning method and a new optical path for thin film measurement, effectively improving the range, accuracy, and efficiency of thin film thickness measurement. This enables efficient and high-precision online monitoring and measurement in most thin film fabrication processes. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a thin film thickness confocal measurement system provided in an embodiment of the present invention.

[0022] Among them, 1-light source, 2-collimating lens, 3-first lens, 4-first optical fiber, 5-second optical fiber, 6-spectrometer, 7-fiber coupler, 8-third optical fiber, 9-second lens, 10-dispersion probe, 11-galvanometer scanner, 12-sample to be tested, 13-reflector, 14-stage. Detailed Implementation

[0023] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0024] Example 1:

[0025] Example 1 provides a confocal film thickness measurement system, see [link to example]. Figure 1 The system includes: a laser generating unit, an optical fiber coupler 7, a scanning unit, a reflector 13, a stage 14, and a spectrometer 6. The laser generating unit includes a light source 1, which emits multi-wavelength beams as incident light. The first port of the optical fiber coupler 7 is connected to a first optical fiber 4, the second port of the optical fiber coupler 7 is connected to a second optical fiber 5, and the third port of the optical fiber coupler 7 is connected to a third optical fiber 8. The incident light is transmitted through the first optical fiber 4 to the optical fiber coupler 7 and exits through the third optical fiber 8. The exited incident light is then scanned and focused onto the sample 12 to be tested by the scanning unit, which performs a lateral scan of the sample 12. The stage 14 is used to carry the sample 12 to be tested, and the reflector 13 is disposed between the sample 12 to be tested and the stage 14. The stage 14 is equipped with a moving component, and the stage 14 can realize the longitudinal movement of the sample 12 to be tested. The longitudinal scanning of the sample 12 to be tested can be realized by using the stage 14. The incident light is refracted by the sample 12 to be tested and focused onto the reflector 13. The reflected light formed after passing through the reflector 13 passes through the sample 12 to be tested and the scanning unit in sequence, and then reaches the fiber coupler 7 through the third fiber 8. Then it is transmitted to the spectrometer 6 through the second fiber 5. The spectrometer 6 obtains the measurement information corresponding to the sample 12 to be tested.

[0026] The light source 1 can be an LED light source, that is, an LED light source as a multi-wavelength light source.

[0027] The laser generating unit may further include: a collimating mirror 2 and a first lens 3; the collimating mirror 2 and the first lens 3 are both disposed in the optical path between the light source 1 and the fiber coupler 7; the collimating mirror 2 is used to collimate the light beam emitted by the light source 1; the first lens 3 is used to converge the collimated light beam into the first optical fiber 4.

[0028] Specifically, the scanning unit includes a second lens 9, a dispersive probe 10, and a galvanometer scanner 11. The second lens 9 is located in the optical path between the fiber coupler 7 and the dispersive probe 10. The dispersive probe 10 has different focal lengths for different wavelengths of light. The galvanometer scanner 11 is used to perform a lateral scan of the sample 12 to be tested. The incident light is converted into parallel light after passing through the second lens 9 and irradiates the dispersive probe 10. Then, it passes through the dispersive probe 10 and the galvanometer scanner 11 in sequence before being scanned and focused onto the sample 12 to be tested. The reflected light passes through the galvanometer scanner 11, the dispersive probe 10, and the second lens 9 in sequence before being transmitted to the fiber coupler 7.

[0029] The moving component can be a stepper motor, that is, the stage 14 is equipped with a stepper motor, which can realize the longitudinal movement of the sample 12 to be tested.

[0030] Furthermore, the confocal film thickness measurement system may also include: a data processing unit; the data processing unit stores pre-calibration information, and is used to receive measurement information from the spectrometer 6 and combine it with the pre-calibration information to obtain film thickness information. The pre-calibration information includes wavelength-focal length relationship information and film refractive index information corresponding to the sample to be measured.

[0031] The measurement optical path involved in Example 1 will be described in its entirety below.

[0032] (1) Incident light path.

[0033] First, the light source 1 emits multi-wavelength beams, which are then collimated into parallel light by the collimating lens 2. The collimated beams are then converged into the first optical fiber 4 by the first lens 3. Subsequently, the incident light passes through the fiber coupler 7, which acts as a beam splitter, separating the incident and reflected light. The incident light exiting the third optical fiber 8 is then collimated into parallel light by the second lens 9 and illuminates the dispersive probe 10, which has different focal lengths for different wavelengths of light. Afterward, the incident light is reflected by the galvanometer scanner 11 into the sample 12 under test. The galvanometer scanner 11 can be mechanically rotated to achieve a lateral scan of the sample 12. The incident light is refracted by the sample 12 and focused onto the reflecting mirror 13. The thickness and refractive index of the sample 12 affect the wavelength of the focused light; the refractive index of the sample 12 needs to be measured and calibrated beforehand. The stage 14 is equipped with a moving component, enabling a longitudinal scan of the sample 12.

[0034] (2) Reflected light path.

[0035] According to the principle of optical path reversibility, the reflected light formed after passing through the reflector 13 passes sequentially through the sample to be tested 12, the galvanometer scanner 11, the dispersive probe 10, the second lens 9 and the third optical fiber 8 to the optical fiber coupler 7, and finally passes through the second optical fiber 5 to be received by the spectrometer 6.

[0036] The spectrometer 6 can transmit the received data to a data processing unit (e.g., a PC). The data processing unit first extracts the wavelength with the highest light intensity from the spectrum, then calculates the film thickness at that point corresponding to that wavelength based on the pre-calibrated wavelength-focal-length correspondence and the film refractive index, and finally integrates the data of each scanned point to obtain complete film thickness data.

[0037] In summary, Example 1 provides a novel confocal color sensor scanning method and optical path for thin film thickness measurement. The light input from the confocal color sensor is scanned laterally on the test sample using a galvanometer scanner, and a reflector is placed below the thin film to form a new optical path for thin film thickness measurement. Example 1 improves scanning efficiency, enables online monitoring and measurement of thin film samples, reduces the requirements for thin film placement, and improves the measurement range and accuracy. Furthermore, the measurement system provided in Example 1 uses common optical instruments, making it easy to implement. Using the measurement system provided in Example 1, thin film thickness can be measured quickly and accurately during semiconductor manufacturing processes, providing a feasible and efficient solution for online monitoring and measurement of thin film thickness.

[0038] Example 2:

[0039] Example 2 provides a confocal method for measuring thin film thickness, implemented using the confocal thin film thickness measurement system described in Example 1. Example 2 includes the following steps: a multi-wavelength beam of light is emitted from a light source in a laser generating unit as incident light; the incident light is transmitted through a first optical fiber to an optical fiber coupler and then exited through a third optical fiber; the exited incident light is scanned and focused onto the sample to be tested by a scanning unit; the scanning unit performs a transverse scan of the sample to be tested, and a stage is used to perform a longitudinal scan of the sample to be tested; the incident light is refracted by the sample to be tested and focused onto a reflector; the reflected light formed after passing through the reflector passes sequentially through the sample to be tested and the scanning unit, then through the third optical fiber to the optical fiber coupler, and then through a second optical fiber to a spectrometer; the spectrometer is used to obtain the measurement information corresponding to the sample to be tested.

[0040] Furthermore, corresponding to Embodiment 1, Embodiment 2 can also use a collimating lens disposed between the light source and the fiber coupler to collimate the light beam emitted by the light source, use a first lens to focus the collimated light beam into the first fiber, and use a second lens disposed between the fiber coupler and the dispersion probe to convert the incident light into parallel light to illuminate the dispersion probe in the scanning unit.

[0041] Corresponding to Example 1, Example 2 can also transmit the measurement information of the spectrometer to the data processing unit, and use the data processing unit to obtain the film thickness information based on the measurement information and pre-calibration information.

[0042] Since the method provided in Embodiment 2 is implemented using the system provided in Embodiment 1, the method steps in Embodiment 2 can be understood by referring to the functional descriptions of each device in Embodiment 1, and will not be repeated here.

[0043] In summary, this invention proposes a new scanning method and a new optical path for thin film measurement, which can improve scanning efficiency while increasing the range and accuracy of thin film thickness measurement.

[0044] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A confocal film thickness measurement system, characterized in that, include: Laser generating unit, fiber optic coupler, scanning unit, reflector, stage and spectrometer; The laser generating unit includes a light source, which is used to emit multi-wavelength beams as incident light; The first port of the fiber optic coupler is connected to a first optical fiber, the second port of the fiber optic coupler is connected to a second optical fiber, and the third port of the fiber optic coupler is connected to a third optical fiber. The incident light is transmitted to the fiber optic coupler via the first optical fiber and exited via the third optical fiber. The exited incident light is then scanned and focused onto the sample to be tested by the scanning unit, which is used to perform a lateral scan on the sample to be tested. The stage is used to hold the sample to be tested, and the reflector is disposed between the sample to be tested and the stage; the stage is equipped with a moving component, and the longitudinal scanning of the sample to be tested is achieved by using the stage. The incident light is refracted by the sample under test and focused onto the reflector. The reflected light formed after passing through the reflector passes sequentially through the sample under test and the scanning unit, then through the third optical fiber to the optical fiber coupler, and then through the second optical fiber to the spectrometer. The spectrometer obtains the measurement information corresponding to the sample under test.

2. The thin film thickness confocal measurement system according to claim 1, characterized in that, The laser generating unit further includes a collimating lens and a first lens; both the collimating lens and the first lens are disposed in the optical path between the light source and the fiber coupler; the collimating lens is used to collimate the light beam emitted by the light source; the first lens is used to converge the collimated light beam into the first optical fiber.

3. The thin film thickness confocal measurement system according to claim 1, characterized in that, The light source is an LED light source.

4. The thin film thickness confocal measurement system according to claim 1, characterized in that, The scanning unit includes a dispersive probe and a galvanometer scanner; the dispersive probe has different focal lengths for light of different wavelengths, and the galvanometer scanner is used to perform lateral scanning of the sample to be tested; the incident light is scanned and focused onto the sample to be tested after passing through the dispersive probe and the galvanometer scanner in sequence.

5. The thin film thickness confocal measurement system according to claim 4, characterized in that, The scanning unit further includes a second lens; the second lens is located in the optical path between the fiber coupler and the dispersive probe; the incident light becomes parallel light after passing through the second lens and illuminates the dispersive probe; the reflected light is transmitted to the fiber coupler after passing through the galvanometer scanner, the dispersive probe, and the second lens in sequence.

6. The thin film thickness confocal measurement system according to claim 1, characterized in that, The moving component uses a stepper motor.

7. The thin film thickness confocal measurement system according to claim 1, characterized in that, Also includes: A data processing unit; the data processing unit stores pre-calibration information, and the data processing unit is used to receive measurement information from the spectrometer and combine it with the pre-calibration information to obtain film thickness information.

8. The thin film thickness confocal measurement system according to claim 7, characterized in that, The pre-calibration information includes the relationship between wavelength and focal length, as well as the thin film refractive index information of the sample to be tested.

9. A confocal method for measuring thin film thickness, characterized in that, The thin film thickness confocal measurement system as described in any one of claims 1-8 is used, and the thin film thickness confocal measurement method includes the following steps: A multi-wavelength beam of light is emitted from a light source in a laser generating unit as incident light. The incident light is transmitted through a first optical fiber to an optical fiber coupler and then exits through a third optical fiber. After exiting, the incident light is scanned and focused onto the sample to be tested by a scanning unit. The scanning unit performs a lateral scan of the sample to be tested, and a stage is used to perform a longitudinal scan of the sample to be tested. The incident light is refracted by the sample to be tested and focused onto a reflector. The reflected light formed after passing through the reflector passes sequentially through the sample to be tested and the scanning unit, then through the third optical fiber to the optical fiber coupler, and then through a second optical fiber to a spectrometer. The spectrometer is used to obtain the measurement information corresponding to the sample to be tested.

10. The confocal method for measuring thin film thickness according to claim 9, characterized in that, The light beam emitted by the light source is collimated by a collimating lens disposed between the light source and the fiber coupler, and the collimated light beam is focused into the first fiber by a first lens; the incident light is converted into parallel light and irradiated onto the dispersive probe by a second lens disposed between the fiber coupler and the dispersive probe in the scanning unit.

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