CN117968539A - Film thickness confocal measurement method and system - Google Patents

Abstract

The invention belongs to the technical field of measurement of color confocal sensors, and discloses a film thickness confocal measurement method and a film thickness confocal measurement system. The invention uses the light source in the laser generation unit to emit multi-wavelength light beam as incident light, the incident light is transmitted to the optical fiber coupler through the first optical fiber and is emitted through the third optical fiber, the emitted incident light is scanned and focused on the sample to be detected through the scanning unit, the scanning unit is used for carrying out transverse scanning on the sample to be detected, and the objective table is used for realizing longitudinal scanning of the sample to be detected; the incident light is focused on the reflecting mirror after being refracted by the sample to be detected, and the reflected light formed after passing through the reflecting mirror sequentially passes through the sample to be detected and the scanning unit, then reaches the optical fiber coupler through the third optical fiber, and then is transmitted to the spectrometer through the second optical fiber, so that the measurement information corresponding to the sample to be detected is obtained by the spectrometer. The novel scanning mode and the novel film measuring light path provided by the invention can effectively improve the range, the precision and the efficiency of film thickness measurement.

Description

A confocal measurement method and system for thin film thickness

Technical Field

The present invention belongs to the technical field of color confocal sensor measurement, and more specifically, relates to a film thickness confocal measurement method and system.

Background technique

In the semiconductor manufacturing industry, the thickness of the film will have a great impact on the performance indicators of the product. Therefore, in the semiconductor manufacturing process, it is very important to monitor and measure the thickness of the film in real time. At present, the mainstream method for measuring the thickness of the film is to move the film sample in a plane for mechanical scanning. The color confocal sensor outputs a color beam to the film, and the monochromatic light of different wavelengths is focused on the upper and lower surfaces of the film respectively, and then received by the spectrometer through reflection. With the help of the correspondence between the wavelength and the focal length calibrated before the measurement, the focal length difference of the monochromatic light focused twice is obtained, so as to obtain the film thickness at this point, and finally the film surface is moved in a plane to obtain the overall thickness of the film. However, the above measurement method has some significant disadvantages, including: the range of film thickness measurement is small, that is, the range per unit time or a single measurement is small when the plane moves; the scanning accuracy is low and the speed is slow, and it is difficult to achieve real-time online accurate measurement.

Summary of the invention

The present invention provides a film thickness confocal measurement method and system to solve the problems of small film thickness measurement range, low scanning accuracy and slow speed in the prior art.

The present invention provides a film thickness confocal measurement system, comprising: a laser generating unit, a fiber coupler, a scanning unit, a reflector, a stage and a spectrometer;

The laser generating unit comprises a light source, and the light source is used to emit a multi-wavelength light beam as incident light;

The first port of the fiber coupler is connected to a first optical fiber, the second port of the fiber coupler is connected to a second optical fiber, and the third port of the fiber coupler is connected to a third optical fiber; the incident light is transmitted to the fiber coupler through the first optical fiber and emitted through the third optical fiber, and the incident light after emission is scanned and focused on the sample to be tested by the scanning unit, and the scanning unit is used to perform a transverse scan on the sample to be tested;

The stage is used to carry the sample to be tested, and the reflector is arranged between the sample to be tested and the stage; the stage is equipped with a moving component, and the stage is used to realize the longitudinal scanning of the sample to be tested;

The incident light is refracted by the sample to be tested and focused on the reflector. The reflected light formed after passing through the reflector passes through the sample to be tested and the scanning unit in sequence, reaches the fiber coupler through the third optical fiber, and is then transmitted to the spectrometer through the second optical fiber. The spectrometer obtains measurement information corresponding to the sample to be tested.

Preferably, the laser generating unit further includes: a collimating mirror and a first lens; the collimating mirror and the first lens are both arranged on the optical path between the light source and the optical fiber coupler; the collimating mirror is used to collimate the light beam emitted by the light source; and the first lens is used to converge the collimated light beam into the first optical fiber.

Preferably, the light source is an LED light source.

Preferably, the scanning unit includes: a dispersion probe and a galvanometer scanner; the dispersion probe has different focal lengths for light of different wavelengths, and the galvanometer scanner is used to perform a transverse scan on the sample to be tested; the incident light is scanned and focused on the sample to be tested after passing through the dispersion probe and the galvanometer scanner in sequence.

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

Preferably, the moving component adopts a stepping motor.

Preferably, the film thickness confocal measurement system further comprises: a data processing unit; pre-calibration information is stored in the data processing unit, and the data processing unit is used to receive measurement information from the spectrometer and obtain film thickness information in combination with the pre-calibration information.

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

On the other hand, the present invention provides a thin film thickness confocal measurement method, which is implemented by using the above-mentioned thin film thickness confocal measurement system, and the thin film thickness confocal measurement method comprises the following steps:

A light source in a laser generating unit is used to emit a multi-wavelength light beam as incident light; the incident light is transmitted to a fiber coupler via a first optical fiber and emitted via a third optical fiber; the incident light after emission is scanned and focused on a sample to be tested by a scanning unit; the scanning unit is used to perform a transverse scan on the sample to be tested, and a stage is used to perform a longitudinal scan on the sample to be tested; the incident light is refracted by the sample to be tested and focused on a reflector; the reflected light formed after the reflector passes through the sample to be tested and the scanning unit in sequence, reaches the fiber coupler via the third optical fiber, and is then transmitted to a spectrometer via a second optical fiber; and the spectrometer is used to obtain measurement information corresponding to the sample to be tested.

Preferably, a collimator lens arranged between the light source and the optical fiber 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 optical fiber; a second lens arranged between the optical fiber coupler and the dispersion probe is used to convert the incident light into parallel light to irradiate the dispersion probe in the scanning unit.

One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

The present invention utilizes 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 via a first optical fiber, and is emitted via a third optical fiber, the emitted incident light is scanned and focused on a sample to be tested by a scanning unit, the sample to be tested is horizontally scanned by the scanning unit, and the sample to be tested is longitudinally scanned by a stage; the incident light is refracted by the sample to be tested and focused on a reflector, the reflected light formed by the reflector passes through the sample to be tested and the scanning unit in sequence, reaches the fiber coupler via the third optical fiber, and is then transmitted to a spectrometer via a second optical fiber, and the spectrometer is used to obtain measurement information corresponding to the sample to be tested. That is, the present invention uses a galvanometer scanner to perform a horizontal scan on the sample to be tested by the light input by the confocal color sensor, and the vertical scan is achieved by moving the film sample longitudinally, thereby improving the scanning accuracy and speed. At the same time, the present invention places a reflector under the film to form a new film thickness scanning optical path, which reduces the film position placement requirements, and can also be understood as reducing the accuracy requirements for the stage, because the traditional scanning method is achieved by mechanical movement of the stage in both the horizontal and vertical directions. In the present invention, since the film is mechanically scanned by a galvanometer scanner, the stage only needs to perform high-precision mechanical movement of the film in one direction, and there is no requirement for the movement accuracy in the other direction; in addition, the traditional scanning method is achieved by mechanical movement of the stage in both the horizontal and vertical directions, and there will be transmission errors in the plane movement, which will result in a smaller range per unit time or a single measurement during the plane movement, and the common mobile film platform will bring vibration noise resulting in a low signal-to-noise ratio. Compared with the above-mentioned traditional measurement method, the new scanning method and the new film measurement optical path provided by the present invention can effectively improve the range, accuracy and efficiency of film thickness measurement, and can realize efficient and high-precision online monitoring and measurement in most film preparation processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a film thickness confocal measurement system provided by an embodiment of the present invention.

Among them, 1-light source, 2-collimating mirror, 3-first lens, 4-first optical fiber, 5-second optical fiber, 6-spectrometer, 7-optical 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 ways

In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

Embodiment 1:

Embodiment 1 provides a thin film thickness confocal measurement system, see FIG1, comprising: a laser generating unit, a fiber coupler 7, a scanning unit, a reflector 13, a stage 14 and a spectrometer 6; the laser generating unit comprises a light source 1, the light source 1 is used to emit a multi-wavelength light beam as incident light; the first port of the fiber coupler 7 is connected to a first optical fiber 4, the second port of the fiber coupler 7 is connected to a second optical fiber 5, and the third port of the fiber coupler 7 is connected to a third optical fiber 8; the incident light is transmitted to the fiber coupler 7 through the first optical fiber 4, and is emitted through the third optical fiber 8, and the incident light after being emitted is scanned and focused on the sample to be measured 12 by the scanning unit, and the scanning unit is used to The sample 12 is scanned transversely; the stage 14 is used to carry the sample 12 to be tested, and the reflector 13 is arranged 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, and 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 on the reflector 13, and 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 optical fiber coupler 7 through the third optical fiber 8, and then is transmitted to the spectrometer 6 through the second optical fiber 5, and the spectrometer 6 obtains the measurement information corresponding to the sample 12 to be tested.

The light source 1 may be an LED light source, that is, the LED light source may be used as a multi-wavelength light source.

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 arranged on the optical path between the light source 1 and the optical 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.

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

The moving component may be a stepping motor, that is, the stage 14 is equipped with a stepping motor to achieve longitudinal movement of the sample 12 to be tested.

In addition, the film thickness confocal measurement system may further include: 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 6, and obtain film thickness information in combination with the pre-calibration information. The pre-calibration information includes the relationship information between the wavelength and the focal length, and the film refractive index information corresponding to the sample to be measured.

The measurement optical path involved in Example 1 is generally described below.

(1) Optical path of incident light.

First, the light source 1 emits a multi-wavelength light beam, which then passes through the collimator 2 and becomes parallel light. The collimated light beam passes through the first lens 3 and converges into the first optical fiber 4. Subsequently, the incident light passes through the optical fiber coupler 7, which acts as a spectrometer to separate the incident light and the reflected light. The incident light emitted from the third optical fiber 8 passes through the second lens 9 and becomes parallel light to irradiate the dispersion probe 10. The dispersion probe 10 has different focal lengths for light of different wavelengths. Afterwards, the incident light is reflected by the galvanometer scanner 11 into the sample to be tested 12, and the galvanometer scanner 11 can be mechanically rotated to achieve lateral scanning of the sample to be tested 12. The incident light is refracted by the sample to be tested 12 and focused on the reflector 13. The thickness and refractive index of the sample to be tested 12 will affect the wavelength of the focused light, and the refractive index of the sample to be tested 12 needs to be measured and calibrated in advance. The stage 14 is equipped with a moving component, so that the longitudinal scanning of the sample to be tested 12 can be achieved.

(2) Reflected light path.

According to the reversible principle of optical path, the reflected light formed after passing through the reflector 13 passes through the sample to be tested 12, the galvanometer scanner 11, the dispersion probe 10, the second lens 9 and the third optical fiber 8 in sequence to reach the optical fiber coupler 7, and is finally received by the spectrometer 6 through the second optical fiber 5.

The spectrometer 6 can transmit the received data to a data processing unit (such as a PC), which first extracts the wavelength with the maximum light intensity from the spectrum, and then calculates the film thickness at the point corresponding to the 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.

In summary, Example 1 provides a new type of confocal color sensor scanning method and film thickness measurement optical path, in which the light input by the confocal color sensor is scanned laterally on the test sample through a galvanometer scanner, and a reflector is placed under the film to form a new film thickness measurement optical path. Example 1 not only improves the scanning efficiency and realizes the online monitoring and measurement of thin film samples, but also reduces the requirements for the placement of the film position and improves the film thickness measurement range and accuracy. In addition, the measurement system provided in Example 1 uses commonly used optical instruments, which is easy to implement. Using the measurement system provided in Example 1, the film thickness can be measured quickly and accurately during the semiconductor manufacturing process, providing a feasible and efficient solution for the online monitoring and measurement of film thickness.

Embodiment 2:

Embodiment 2 provides a thin film thickness confocal measurement method, which is implemented using the thin film thickness confocal measurement system as described in Embodiment 1. Embodiment 2 includes the following steps: using the light source in the laser generating unit to emit a multi-wavelength light beam as incident light; the incident light is transmitted to the fiber coupler via the first optical fiber and emitted via the third optical fiber, and the incident light after emission is scanned and focused on the sample to be measured by the scanning unit, the scanning unit is used to perform a transverse scan on the sample to be measured, and the stage is used to perform a longitudinal scan of the sample to be measured; the incident light is refracted by the sample to be measured and focused on the reflector, and the reflected light formed after the reflector passes through the sample to be measured and the scanning unit in turn, and reaches the fiber coupler through the third optical fiber, and then is transmitted to the spectrometer via the second optical fiber, and the measurement information corresponding to the sample to be measured is obtained by the spectrometer.

In addition, corresponding to Example 1, Example 2 can also utilize a collimator lens disposed between the light source and the optical fiber coupler to collimate the light beam emitted by the light source, and utilize a first lens to converge the collimated light beam into the first optical fiber; utilize a second lens disposed between the optical fiber coupler and the dispersion probe to convert the incident light into parallel light to irradiate the dispersion probe in the scanning unit.

Corresponding to Example 1, Example 2 can also transmit the measurement information of the spectrometer to a data processing unit, and use the data processing unit to obtain the film thickness information according to the measurement information and pre-calibration information.

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

In summary, the present invention proposes a new scanning method and a new thin film measurement optical path, which can improve the scanning efficiency and increase the measurement range and accuracy of the thin film thickness.

Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims (10)

1. A confocal measurement system for thin film thickness, characterized in that it comprises: a laser generating unit, a fiber coupler, a scanning unit, a reflector, a stage and a spectrometer; The laser generating unit comprises a light source, and the light source is used to emit a multi-wavelength light beam as incident light; The first port of the fiber coupler is connected to a first optical fiber, the second port of the fiber coupler is connected to a second optical fiber, and the third port of the fiber coupler is connected to a third optical fiber; the incident light is transmitted to the fiber coupler through the first optical fiber and emitted through the third optical fiber, and the incident light after emission is scanned and focused on the sample to be tested by the scanning unit, and the scanning unit is used to perform a transverse scan on the sample to be tested; The stage is used to carry the sample to be tested, and the reflector is arranged between the sample to be tested and the stage; the stage is equipped with a moving component, and the stage is used to realize the longitudinal scanning of the sample to be tested; The incident light is refracted by the sample to be tested and focused on the reflector. The reflected light formed after passing through the reflector passes through the sample to be tested and the scanning unit in sequence, reaches the fiber coupler through the third optical fiber, and is then transmitted to the spectrometer through the second optical fiber. The spectrometer obtains measurement information corresponding to the sample to be tested. 2. The thin film thickness confocal measurement system according to claim 1 is characterized in that the laser generating unit further comprises: a collimator and a first lens; the collimator and the first lens are both arranged on the optical path between the light source and the optical fiber coupler; the collimator is used to collimate the light beam emitted by the light source; and 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 , wherein the light source is an LED light source. 4. The thin film thickness confocal measurement system according to claim 1 is characterized in that the scanning unit comprises: a dispersion probe and a galvanometer scanner; the dispersion probe has different focal lengths for light of different wavelengths, and the galvanometer scanner is used to perform a transverse scan on the sample to be measured; the incident light is scanned and focused on the sample to be measured after passing through the dispersion probe and the galvanometer scanner in sequence. 5. The thin film thickness confocal measurement system according to claim 4 is characterized in that the scanning unit further comprises: a second lens; the second lens is located on the optical path between the fiber coupler and the dispersion probe; the incident light is converted into parallel light after passing through the second lens and irradiates the dispersion probe; the reflected light is transmitted to the fiber coupler after passing through the galvanometer scanner, the dispersion probe and the second lens in sequence. 6 . The thin film thickness confocal measurement system according to claim 1 , wherein the moving component adopts a stepping motor. 7. The thin film thickness confocal measurement system according to claim 1 is characterized in that it 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 obtain thin film thickness information in combination with the pre-calibration information. 8. The thin film thickness confocal measurement system according to claim 7, characterized in that the pre-calibration information includes relationship information between wavelength and focal length, and thin film refractive index information corresponding to the sample to be measured. 9. A film thickness confocal measurement method, characterized in that it is implemented by using the film thickness confocal measurement system according to any one of claims 1 to 8, and the film thickness confocal measurement method comprises the following steps: A light source in a laser generating unit is used to emit a multi-wavelength light beam as incident light; the incident light is transmitted to a fiber coupler via a first optical fiber and emitted via a third optical fiber; the incident light after emission is scanned and focused on a sample to be tested by a scanning unit; the scanning unit is used to perform a transverse scan on the sample to be tested, and a stage is used to perform a longitudinal scan on the sample to be tested; the incident light is refracted by the sample to be tested and focused on a reflector; the reflected light formed after the reflector passes through the sample to be tested and the scanning unit in sequence, reaches the fiber coupler via the third optical fiber, and is then transmitted to a spectrometer via a second optical fiber; and the spectrometer is used to obtain measurement information corresponding to the sample to be tested. 10. The thin film thickness confocal measurement method according to claim 9 is characterized in that a collimator lens arranged between the light source and the fiber 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 optical fiber; a second lens arranged between the fiber coupler and the dispersion probe is used to convert the incident light into parallel light to irradiate the dispersion probe in the scanning unit.