Calibration method for installation error of grating interferometer

Abstract

The invention provides an installation error calibration method for a grating interferometer, and the method comprises the steps: selecting a point which can reflect the mutual influence between a grating and a reading head as a reference point, measuring the reference point through the grating interferometer to obtain the number of fringes, obtaining the displacement of the reading head through calculation, and calibrating the installation error of the grating interferometer. Performing least square fitting according to the function relationship between the displacement setting points of the reading head to obtain parameters reflecting geometric errors; and after the parameters are updated, the position of the workpiece table is recalculated, and calibration of the geometric error of the grating interferometer is completed. The method can be used for calibrating the installation error of the grating interferometer and optimizing the algorithm of a nanoscale grating interference displacement measurement system.

Description

(1) Technical Field

[0001] The present invention relates to a calibration method for installation errors of a grating interferometer, which can be used for the optimization and calibration of a nano-level grating interference displacement measurement system, and belongs to the field of precision measurement. (2) Background Art

[0002] Due to its shorter air path, the grating interferometer has better environmental stability than the laser interferometer and has currently become the mainstream choice for displacement measurement sensors in immersion lithography scanning systems.

[0003] Based on principles such as grating diffraction principle, geometric optics theory, Doppler frequency shift, etc., and the analytical relationship between the number of grating interference fringes and the ideal displacement, a grating interference displacement measurement model is established.

[0004] In the actual positioning of the grating interference system, due to errors in the processing and installation of devices such as gratings and reading heads, it is difficult for the system positioning accuracy to meet the actual requirements.

[0005] Considering the errors between individual degrees of freedom caused by installation errors and the coupling errors that affect each other between degrees of freedom, a grating interference displacement measurement model considering installation errors is derived. (3) Summary of the Invention

[0006] The present invention provides a calibration method for installation errors of a grating interference displacement measurement model, which is used to solve the problem that there is a large gap between the calculated position and the actual position of the model in the grating interference displacement measurement system due to the processing and installation errors of the grating and the reading head, and improve the measurement accuracy of the grating interference displacement measurement system.

[0007] The present invention discloses a calibration method for installation errors of a grating interference displacement measurement system, which specifically includes the following contents:

[0008] In the method: 1 According to the influence of the installation error coefficient on the degrees of freedom in the model, reference points that can separately stimulate the action of each parameter are planned as follows:

[0009] In the method: 2 The number of fringes of the reading head is converted into the displacement of the reading head, and the formula is as follows: Where Sx and Sz are the displacements of the reading head, Hx and Hz are the number of fringes measured by the reading head, R is the electronic subdivision number, P is the grating pitch, and λ is the laser wavelength.

[0010] In the method: 3 A mathematical model of the reading head displacement with the fulcrum is established, and the pose of the reference point and the reading head displacement of the reference point are brought in to solve the installation error parameters. The formula is as follows:

[0011] In the said method: 4. Substitute the updated installation error parameters into the grating interference displacement measurement model, calculate the six-degree-of-freedom displacement under the new trajectory, and compare it with the set point to observe the effect. Complete the geometric error calibration of the grating interference displacement measurement system. (IV) Description of the Drawings

[0012] Figure 1 It is a schematic diagram of the hardware structure of a controllable negative high-voltage APD drive circuit based on a dual-frequency laser interferometer. (V) Specific Embodiments

[0013] The present invention will be further elaborated below in conjunction with specific examples.

[0014] Please refer to Figure 1 . The present invention discloses a calibration method for the installation error of a grating interference displacement measurement model, which can be specifically divided into the following 4 steps.

[0015] Step 1: Based on the grating interference measurement model containing geometric error terms, analyze the relationship between the six-degree-of-freedom position error and the error terms, and select a reference point that can independently activate the action of a certain error term according to this relationship. The specific selection is shown in Table 1

[0016] Step 2: According to the reference point selected in Step 1, use the uncalibrated grating interference displacement measurement system to measure and obtain the reading head stripe of the reference point. Convert the number of stripes into the reading head displacement through Formulas 1 and 2 for use in the calculation of the installation error parameters in Step 3.

[0017] Step 3: According to the mathematical relationship between the reading head displacement and the reference point, substitute the reference point pose in Step 1 and the reading head displacement in Step 2, and calculate the installation error parameters by the method of least squares fitting. The upper and lower limits of the accuracy of the installation parameters are limited to the maximum installation error tolerable during manual installation. The system tolerance is set as the system accuracy requirement. Finally, obtain the most suitable installation error parameters.

[0018] Step 4: After completing the calculation of the installation error parameters in Step 3, update the obtained parameters into the grating interference measurement system considering the installation error, and use the test data to verify the correctness and accuracy of the calculated parameters. Table 1

Claims

1. A method for calibrating an installation error of a grating interferometer, the method comprising: The reference point 1 is determined based on the influence coefficient of the installation error in the grating interferometry model. The number of fringes generated by the reading head measuring the reference point is converted and calculated to obtain the reading head displacement 2. The installation error parameter 3 is calculated based on the mathematical relationship between the reference point pose and the reading head displacement. The updated installation error parameters are brought into the six-degree-of-freedom model to calculate the six-degree-of-freedom position 4 of the workpiece table.

2. The reference point selection method 1 used in the method for calibrating the installation error of a grating interferometer according to claim 1 is characterized by: In the grating interferometry displacement measurement model with installation errors, points that can activate these coefficients are selected as reference points according to the installation error coefficients that affect the six-degree-of-freedom positioning.

3. The installation error parameter calculation method 3 used in the installation error calibration method for a grating interferometer according to claim 1 is characterized in that: The number of reference point fringes measured by the grating interferometer readhead is converted into readhead displacement, and the installation error parameters are calculated by fitting based on the relationship between the reference point posture and the readhead displacement.

4. The installation error calibration method 4 used in the method for calibrating the installation error of a grating interferometer according to claim 1 is characterized in that: The calculated installation error parameters are brought into the grating interferometry displacement measurement model, and the six degrees of freedom of the positioning point are obtained through updating and iterative methods.

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