Motion tracking measurement method for spectroscopic ellipsometry
By setting up a motor testing fixture in a spectroscopic ellipsometry, screening and recording motor characteristic data, establishing a database, and using trapezoidal acceleration and deceleration curves to drive the motor, the problem of synchronization between stepper motor movement and signal reception was solved, thus improving testing accuracy and stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DEPT INSTR (SHANGHAI) CO LTD
- Filing Date
- 2023-09-11
- Publication Date
- 2026-07-21
AI Technical Summary
Existing spectroscopic ellipsometers have errors in the synchronization between stepper motor movement and signal reception, resulting in low measurement accuracy and unstable data, especially when the type of film being tested changes.
By constructing a spectral ellipsometry motor testing fixture, screening and recording motor characteristic data, establishing a motor database, integrating test application algorithms, achieving synchronization matching between motor movement and signal reception, using trapezoidal acceleration and deceleration curves to drive the motor, calculating time differences and recording corresponding relationships, and forming a standard database for testing.
The test accuracy of the spectroscopic ellipsometer has been improved, with film thickness test accuracy reaching 0.1 nm and refractive index test accuracy reaching 0.01. The influence of motor delay on measurement accuracy has been eliminated, and the additional test time is less than 0.5 seconds.
Smart Images
Figure CN117169126B_ABST
Abstract
Description
Technical Field
[0001] This invention pertains to spectral ellipsometers, specifically relating to a motion tracking measurement method for spectral ellipsometers. Background Technology
[0002] A spectroscopic ellipsometer is an optical measurement device used to detect thin film thickness, optical constants, and microstructural properties of materials. Measurable samples include bulk materials, thin films, and multilayer structures grown or deposited on planar substrates. The properties of multilayer solids, liquids, liquids adjacent to solids, and gas-phase plasmas in contact with solids can all be detected using this technique. Because it is non-contact, non-destructive to the sample, and does not require a vacuum, ellipsometers are a highly attractive detection device.
[0003] A spectroscopic ellipsometer typically uses a broadband light source as the output light. This light passes through a polarizer, waveplate, and various lenses before illuminating the surface under test. The light then passes through a lens, analyzer, and filter before finally being received by a broadband spectrometer. The optical path contains numerous rotating mechanisms driven by stepper motors, enabling precise adjustment of the optical signal. Due to the high testing accuracy of spectrometers (down to 0.1 nm for film thickness and 0.01 nm for refractive index), the requirements for stepper motor motion positioning and signal reception synchronization are extremely high. A sophisticated motion tracking algorithm is needed to ensure the synchronization between the stepper motor movement and the detection signal. Because of the limitations of the optical path and lens mounting space in a spectroscopic ellipsometer, servo motors are not suitable as motion motors; therefore, stepper motors are generally used as the moving parts.
[0004] Some existing spectral ellipsometers do not consider the issue of synchronization, and the rotation of the driving stepper motor is completely independent of the signal reception, resulting in large measurement errors. Others simply use a fixed delay time, that is, after the driving stepper motor sends a signal, there is a certain delay before the signal is acquired. This method also has errors, and the data is unstable and will change with the motion parameters and the type of test film. Summary of the Invention
[0005] In view of the above-mentioned problems, the present invention provides a motion tracking measurement method for a spectral ellipsometer.
[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A motion tracking measurement method for a spectroscopic ellipsometer includes the following steps: S10, Build a test fixture for the motor of a spectrometer ellipsometry; S20, perform motor screening and characteristic data recording, record the correspondence between time difference and motor speed, and establish a motor database; S30 completes the testing and data recording of the motor required for a spectroradiometer, installs the motor on the spectroradiometer, and copies the motor data to the specified location in the software for later use; S40 integrates the test application algorithm into the installed spectro ellipsometry application to complete the test and application.
[0007] In one possible implementation, S20 specifically includes: Start testing; A motor n is installed on the test fixture, and a test waveplate is installed on the shaft of motor n. The light source is kept stable, and motor n is driven to rotate 1 revolution. The time Td is recorded. Read the light intensity curve of a certain wavelength from the spectrometer; obtain the start and end times of the light intensity change, and calculate the time difference Tq between them. Calculate the absolute value of the difference between Tq and Td, and determine if it is less than 5ms. If it is not less than 5ms, the current motor is considered unqualified and the motor is replaced. If it is less than 5ms, the current motor is considered qualified, and the motor acceleration / deceleration curve and spectral intensity curve are normalized. The theoretical spectral intensity curve is derived from the motor acceleration and deceleration curve. The theoretical intensity curve is compared with the actual spectral intensity curve, and the time difference at the same amplitude is calculated. Record the correspondence between the acceleration / deceleration position of the motor and the time difference, and store it in the database; Test complete.
[0008] In one possible implementation, the drive motor n rotates with a trapezoidal acceleration and deceleration curve.
[0009] In one possible implementation, the trapezoidal acceleration / deceleration curve represents a uniform acceleration phase with an initial velocity V0 = 0 r / m and an acceleration of a, lasting t0 seconds. The maximum speed is Vm = a * t0. The uniform acceleration phase lasts t1 seconds. The deceleration phase has an acceleration of -a and a time of t2 = t0 seconds. Therefore, the motor motion curve is: (1) Where t represents the specific time.
[0010] In one possible implementation, the criterion for determining the starting point of the light intensity change is the light intensity value at the next moment minus the previous moment. If five consecutive differences are positive (or negative), the first point is determined as the starting point.
[0011] In one possible implementation, the criterion for determining the end point is the light intensity value of the next moment minus the previous moment. If five consecutive differences show positive or negative changes or are 0, and the absolute value of the difference is less than 4, the light intensity is strongest at 65535, and the first point is determined as the end point.
[0012] In one possible implementation, the spectral intensity curve is as follows: (2) Where t is the specific time; b is the phase delay parameter; and y is the actual light intensity value.
[0013] In one possible implementation, the spectral intensity curve is normalized as follows: (3) Where y1 is the normalized light intensity value, with a maximum of 1; t is the specific time; and c is the normalized phase delay parameter. The standard sine curve is then obtained as follows: (4) The phase delay c is taken to be the same as the phase delay of the spectral intensity curve after normalization.
[0014] In one possible implementation, formula (1) is multiplied by formula (4) to calculate the theoretical light intensity-time curve. The actual normalized spectral intensity curve formula (3) is compared with the curve. For each identical amplitude, the time difference is calculated. The correspondence between the time difference and the motor speed is recorded to establish the motor database.
[0015] In one possible implementation, S40 specifically includes: Test begins; The auxiliary motor rotates and takes position; Look up the delay time of the corresponding motor in the database; Maximum delay time; The core motor is driven to rotate, and the measurement and synchronous acquisition of spectral data begins. After the core motor completes its rotation, the spectral data acquisition stops after a maximum delay time. Based on the core motor database, the delay time at different speeds is extracted and correlated with the speed and time of the core motor during the test. The data of "spectral recording time + delay time" is extracted as the actual test data. Data is collected and analyzed to obtain test results, and the test ends.
[0016] The present invention has the following beneficial effects: (1) It achieves good motor motion tracking and eliminates the influence of motor signal and mechanical delays on measurement accuracy.
[0017] (2) Improved the testing accuracy of the spectroscopic ellipsometer, making the film thickness test accuracy reach 0.1 nm and the refractive index test accuracy reach 0.01.
[0018] (3) A selection mechanism for stepper motors suitable for use in spectral ellipsometers has been developed.
[0019] (4) Using this motion tracking measurement method, the additional test time is less than 0.5 seconds and does not affect the normal use of the equipment. Attached Figure Description
[0020] Figure 1 This is a flowchart of the motion tracking measurement method for a spectroscopic ellipsometer according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the motor selection and feature data recording process in this invention. Figure 3 This is a flowchart of the test application algorithm in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the spectral ellipsometry motor testing fixture in one embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of a spectroscopic ellipsometry in one embodiment of the present invention. Detailed Implementation
[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] Reference Figure 1 The diagram shows a flowchart of a motion tracking measurement method for a spectroscopic ellipsometer according to an embodiment of the present invention, including the following steps: S10, Set up the testing fixture for the spectral ellipsometry motor. When testing different motors, the fixture must match the actual application scenario, and the remaining motor positions must be left empty. The polarizer and fixing mechanism, serving as the load, must have the same moment of inertia and mass as the corresponding motor's actual load characteristics. This consistency requires the test load to be identical to the actual load in terms of total mass, moment of inertia, dimensions, and installation method. An actual load can be used as the test load; for accuracy, a single set of actual loads is generally used to ensure consistent characteristics.
[0023] S20, perform motor screening and characteristic data recording, record the correspondence between time difference and motor speed, and establish a motor database; S30 completes the testing and data recording of the motor required for a spectroradiometer, installs the motor on the spectroradiometer, and copies the motor data to the specified location in the software for later use; S40 integrates the test application algorithm into the installed spectro ellipsometry application to complete the test and application.
[0024] In one embodiment of the present invention, see Figure 4 This is a schematic diagram of the motor testing fixture for the spectrometer ellipsometry in S10. All parts are mounted on the fixed bracket 101, from left to right: fiber optic interface 102, adjustment bracket 103, motor test position 104, load mounting position 105, fixture lens 106, and projection plate 107. The fiber optic interface 102 connects to the light source via optical fiber. The adjustment bracket 103 is used to adjust the direction of the light, ensuring that the light is perpendicular and passes through each lens at the center. The motor test position 104 mounts the motor to be tested, the load mounting position 105 mounts the corresponding load for the motor, and the fixture lens 106 is used for focusing and collimation, forming an easily identifiable pattern on the projection plate 107. Different motors are tested on the fixture, and the acquired data is saved for later use.
[0025] In one embodiment of the present invention, see Figure 5 The diagram above shows the structure of the spectroscopic ellipsometer in the S40. It mainly consists of a support wall plate 210, a receiving lens 209, an output lens 214, a stage support 216, a stage 215, and four motors: a first auxiliary motor 211, a second auxiliary motor 212, a core motor 213, and a third auxiliary motor 208. The support wall plate 210 supports and fixes all components of the spectroscopic ellipsometer. Light is emitted from the output lens 214, reaches the sample to be tested on the stage, and is reflected back to the receiving lens 209. The stage 215 is fixed on the stage support 216, and the sample to be tested is placed on the stage 215 for measurement. The first auxiliary motor 211, the second auxiliary motor 212, and the third auxiliary motor 208 need to be rotated to a fixed position before measurement but do not rotate during measurement. The core motor 213 rotates during measurement to adjust the beam state. The positioning accuracy, positioning speed, and time delay with the acquisition system of each motor directly affect the accuracy of the test results. By using the motion tracking measurement method of the spectral ellipsometer of the present invention, the time delay between the rotation of each motor and the acquisition of measurement data by the acquisition system can be effectively matched, thereby improving the measurement accuracy.
[0026] In one embodiment of the present invention, see Figure 2 In order to select stepper motors that meet the accuracy requirements of the equipment, S20 specifically includes: Start testing; A motor n is installed on the test fixture, and a test waveplate is installed on the shaft of motor n. The light source is kept stable, and motor n is driven to rotate 1 revolution. The time Td is recorded. Reading a spectrometer One Light intensity curves for wavelengths (wavelength range can be 350-1000nm light sources, or other wavelengths; select wavelengths with high stability, such as 600nm, based on the characteristics of the light source); obtain the start and end times of light intensity changes, and calculate the time difference Tq between them; Calculate the absolute value of the difference between Tq and Td, and determine if it is less than 5ms. If it is not less than 5ms, the current motor is considered unqualified and the motor is replaced. If it is less than 5ms, the current motor is considered qualified, and the motor acceleration / deceleration curve and spectral intensity curve are normalized. The theoretical spectral intensity curve is derived from the motor acceleration and deceleration curve. The theoretical intensity curve is compared with the actual spectral intensity curve, and the time difference at the same amplitude is calculated. Record the correspondence between the acceleration / deceleration position of the motor and the time difference, and store it in the database; Test complete.
[0027] In one embodiment of the present invention, the drive motor n rotates using a trapezoidal acceleration / deceleration curve. The trapezoidal acceleration / deceleration curve represents the acceleration phase as a uniform acceleration process, with an initial speed V0 = 0 r / m and an acceleration of a, the acceleration time being t0, and the maximum speed Vm = a * t0. The uniform speed process takes t1, the deceleration process has an acceleration of -a, and the deceleration time is t2 = t0. Therefore, the motor motion curve is as follows: (1) Where t represents the specific time.
[0028] In one embodiment of the present invention, the criterion for determining the starting point of the light intensity change is the light intensity value at the next moment minus the previous moment. If five consecutive differences are positive (or negative), the first point is determined as the starting point.
[0029] In one embodiment of the present invention, the criterion for determining the end point is that the light intensity value of the next moment minus the previous moment, and five consecutive differences show positive or negative changes or are 0, and the absolute value of the difference is less than 4, with the strongest light intensity being 65535, the first point is determined as the end point.
[0030] In one embodiment of the present invention, the spectral intensity curve is as follows: (2) Where t is the specific time; b is the phase delay parameter; and y is the actual light intensity value.
[0031] In one embodiment of the present invention, the spectral intensity curve is normalized as follows: (3) Where y1 is the normalized light intensity value, with a maximum of 1; t is the specific time; and c is the normalized phase delay parameter. The standard sine curve is then obtained as follows: (4) The phase delay c is taken to be the same as the phase delay of the spectral intensity curve after normalization.
[0032] Multiply formula (1) and formula (4) to calculate the theoretical light intensity-time curve. Compare it with the actual normalized spectral intensity curve formula (3). For each identical amplitude, calculate the time difference. Record the correspondence between the time difference and the motor speed to establish the motor database.
[0033] In one embodiment of the present invention, see Figure 3 S40 specifically includes the following steps: After the test begins, the auxiliary motors are first rotated into position. The maximum delay time for each auxiliary motor is retrieved from the motor database. After the maximum delay time is reached, the core motor is driven to rotate, and spectral data is collected simultaneously. After the core motor has rotated, the maximum delay time for the core motor is delayed, and then spectral data collection stops. Based on the core motor database, the delay times at different speeds are extracted and correlated with the speed and time of the core motor during the test. The data of "spectral recording time + delay time" is extracted as the actual test data. The data is analyzed and calculated to obtain the final test result, and the test ends.
[0034] Test begins; The auxiliary motor rotates and takes position; Find the maximum delay time for the corresponding motor in the motor database; Maximum delay time; The core motor is driven to rotate, and the measurement and synchronous acquisition of spectral data begins. After the core motor completes its rotation, the spectral data acquisition stops after a maximum delay time. Based on the core motor database, the delay time at different speeds is extracted and correlated with the speed and time of the core motor during the test. The data of "spectral recording time + delay time" is extracted as the actual test data. Data is collected and analyzed to obtain test results, and the test ends.
[0035] The data processing and analysis specifically involves converting the test data tables into a database storage format for the main program to access. Characteristic data, such as the motor's maximum delay time, installation location, starting speed, acceleration / deceleration, and maximum speed, are stored in specific locations within the database so that the main program can distinguish the motor and retrieve its basic parameters. The test results primarily determine whether the motor is qualified, whether it can be used as a core motor, and its actual application. After obtaining the test results, they are stored in the database for the main program to access.
[0036] The motion tracking measurement method, stepper motor selection and feature data recording method, and test application algorithm described above for the spectral ellipsometer are used in combination. The stepper motor selection and feature data recording algorithm generates speed-delay data for each qualified motor, forming a standard database for use by the test application algorithm. Each spectral ellipsometer uses five motors, and the database for each device only needs to include the data information of the motors in that device, distinguished by motor number. In actual testing, only one core motor is used, and only the delay of the core motor needs to be considered. This achieves good motion tracking of the stepper motor, eliminating the impact of motor signal and mechanical delays on measurement accuracy, and thus improving test precision and accuracy.
[0037] It should be understood that the exemplary embodiments described herein are illustrative and not restrictive. Although one or more embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art will understand that various changes in form and detail may be made without departing from the spirit and scope of the invention as defined by the appended claims.
Claims
1. A motion tracking measurement method for a spectroscopic ellipsometer, characterized in that, Includes the following steps: S10, Build a test fixture for the motor of the spectrometer ellipsometry; S20, perform motor screening and characteristic data recording, record the correspondence between time difference and motor speed, and establish a motor database; S30 completes the testing and data recording of the motor required for a spectroradiometer, installs the motor on the spectroradiometer, and copies the motor data to the specified location in the software for later use; S40 integrates the test application algorithm into the installed spectroradiometer application to complete the test and application; S20 specifically includes: Start testing; A motor n is installed on the test fixture, and a test waveplate is installed on the shaft of motor n. The light source is kept stable, and motor n is driven to rotate 1 revolution. The time Td is recorded. Reading a spectrometer one Light intensity curve at wavelength; obtain the start and end times of light intensity change, and calculate the time difference Tq between them; Calculate the absolute value of the difference between Tq and Td, and determine if it is less than 5ms. If it is not less than 5ms, the current motor is considered unqualified and the motor is replaced. If it is less than 5ms, the current motor is considered qualified, and the motor acceleration / deceleration curve and spectral intensity curve are normalized. The theoretical spectral intensity curve is derived from the motor acceleration and deceleration curve. The theoretical intensity curve is compared with the actual spectral intensity curve, and the time difference at the same amplitude is calculated. Record the correspondence between the acceleration / deceleration position of the motor and the time difference, and store it in the database; Test complete.
2. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 1, characterized in that, When the drive motor n rotates, it is driven to rotate in a trapezoidal acceleration and deceleration curve.
3. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 1, characterized in that, The trapezoidal acceleration / deceleration curve represents a uniform acceleration phase with an initial velocity V0 = 0 r / m and an acceleration of a. The acceleration time is t0, and the maximum speed is Vm = a * t0. The uniform acceleration phase takes t1, and the deceleration phase has an acceleration of -a. The deceleration time is t2 = t0. Therefore, the motor motion curve is: （1） Where t represents the specific time.
4. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 1, characterized in that, The criterion for determining the starting point of light intensity change is the difference between the light intensity value at the next moment and the light intensity value at the previous moment. If the difference is positive or negative for five consecutive moments, the first point is determined as the starting point.
5. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 2, characterized in that, The criterion for determining the end point is the light intensity value of the next moment minus the previous moment. If five consecutive differences show positive or negative changes or are 0, and the absolute value of the difference is less than 4, the light intensity is the strongest at 65535, and the first point is determined as the end point.
6. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 1, characterized in that, The spectral intensity curve is as follows: （2） Where t is the specific time; b is the phase delay parameter; and y is the actual light intensity value.
7. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 6, characterized in that, The spectral intensity curve is normalized as follows: （3） Where y1 is the normalized light intensity value, with a maximum of 1; t is the specific time; and c is the normalized phase delay parameter. The standard sine curve is then obtained as follows: （4） The phase delay c is taken to be the same as the phase delay of the spectral intensity curve after normalization.
8. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 7, characterized in that, Multiply formula (1) and formula (4) to calculate the theoretical light intensity-time curve. Compare it with the actual normalized spectral intensity curve formula (3). For each identical amplitude, calculate the time difference. Record the correspondence between the time difference and the motor speed to establish the motor database.
9. The motion tracking measurement method for a spectroscopic ellipsometer as described in claim 1, characterized in that, S40 specifically includes: Test begins; The auxiliary motor rotates and takes position; Look up the delay time of the corresponding motor in the database; Maximum delay time; The core motor is driven to rotate, and the measurement and synchronous acquisition of spectral data begins. After the core motor completes its rotation, the spectral data acquisition stops after a maximum delay time. Based on the core motor database, the delay time at different speeds is extracted and correlated with the speed and time of the core motor during the test. The data of "spectral recording time + delay time" is extracted as the actual test data. Data is collected and analyzed to obtain test results, and the test ends.