System error calibration method of plane interferometer based on computer-generated holography

Abstract

The invention discloses a system error calibration method of a plane interferometer based on computer-generated holography, which relates to a pattern-free wafer morphology detection technology, and comprises the following steps of: constructing a system error calibration device of the plane interferometer based on computer-generated holography, and generating a wavefront to be detected by adopting a computer-generated hologram; and four independent wavefronts to be measured are generated by adjusting and calculating holographic poses, and a measurement result is obtained. A computer-generated hologram manufacturing error source is decomposed into manufacturing errors such as substrate surface shape deviation and photoetching pattern deviation, computer-generated hologram manufacturing errors are removed in combination with computer-generated hologram manufacturing error characteristics, and therefore high-precision calibration of interferometer system errors is achieved. The interferometer system error calibration method is simple in structure and ingenious in calibration method design, has the advantage of high-precision error calibration, and has high engineering application value.

Description

Technical Field

[0001] The present invention relates to the technical field of patternless wafer topography detection, and in particular to a system error calibration method of a planar interferometer based on computer-generated holography. Background Art

[0002] Unpatterned wafer topography inspection requires high-precision measurement of key parameters such as warpage. However, optical system aberrations and interferometer reference surface errors can introduce sub-nanometer systematic errors. Especially when measuring ultra-flat wafers, these errors can exceed the actual deformation signal. Therefore, calibrating the interferometer's systematic errors is crucial. Absolute verification methods are required to calibrate both the reference surface errors and the interferometer's optical system errors to improve test accuracy. This error component is referred to as systematic error.

[0003] G. Schulz and J. Schwider first proposed the three-plate mutual inspection method for interferometer system error calibration, but it could only obtain the absolute surface shape distribution in one diameter direction. Hansen et al. added a rotation measurement to this method to obtain the full surface shape distribution. The three-plate mutual inspection method requires the replacement of the reference mirror during the measurement process, which is inconvenient to operate. Subsequently, two-plate absolute inspection methods were developed, mainly including the pseudo-shear method, the rotation-translation method, and the two-plate three-surface mutual inspection method. Keenan proposed the pseudo-shear method, which translates the mirror to be measured to obtain the absolute surface shape deviation and then obtains the absolute surface shape distribution through integration. However, the translation process easily introduces additional tilt, making it impossible to reconstruct the defocus and astigmatism of the measured wavefront. Fujimoto proposed the rotation-translation method, which adds a rotation measurement to the pseudo-shear method. This method reconstructs the astigmatism error but still cannot recover the defocus term. Computational holography has the function of compensating for optical path differences and has received great attention in ultra-high-precision component detection technology. Therefore, it is necessary to provide a simple-to-operate and high-precision system error calibration device and method based on computational holography. Summary of the Invention

[0004] To address the high hardware requirements and complex measurement steps of existing interferometer system error calibration methods, this paper proposes a method for calibrating the system errors of planar interferometers based on computer-generated holography. This method uses only a CGH to generate the measured wavefront. By adjusting the CGH pose, four independent wavefronts are generated and the measurement results are obtained. This method utilizes the manufacturing error characteristics of CGH to eliminate CGH manufacturing errors from the measurement results, achieving high-precision calibration of the interferometer system error.

[0005] The technical solution for achieving the purpose of the present invention is: a method for calibrating the system error of a planar interferometer based on computer-generated holography, comprising the following steps:

[0006] Step 1: Build a planar interferometer system error calibration device based on CGH:

[0007] The planar interferometer system error calibration device comprises an interferometer, a computer-generated hologram and a plane reference mirror sequentially arranged along an optical axis, and a multi-dimensional adjustment frame of the computer-generated hologram for adjustment.

[0008] Turn on the interferometer, use a plane standard mirror to set the side away from the interferometer as the reference surface, and adjust the reference light to the center of the crosshairs through the point camera; fix the computer hologram on the multidimensional adjustment frame to ensure that its optical axis is aligned with the optical axis of the interferometer.

[0009] Step 2: Adjust the pitch angle of the multi-dimensional adjustment frame, and the computational hologram works at the +1 diffraction order to generate the first diffraction wave with a diffraction angle of θ1. Tilt the computational hologram toward the interferometer by an angle of θ1 and record the position as q1. Adjust the computational hologram position to the q1 position. The working wavefront of the computational hologram at the q1 position is used as the first wavefront to be measured. The first measurement result W1 includes the system error W s , the first CGH base surface deviation W pass1 , the first photolithography pattern deviation W pd1 :

[0010] W1=W s +W pass1 +W pd1 ,

[0011] Step 3: Adjust the pitch angle of the multi-dimensional adjustment frame, and the computational hologram works at the +1 diffraction order to generate the second diffraction wave with a diffraction angle of θ2. Tilt the computational hologram toward the interferometer by an angle of θ2, and record the position as q2. Adjust the computational hologram posture to the q2 position. The working wavefront of the computational hologram at the q2 position is used as the second measured wavefront. The second measurement result W2 includes the system error W s , the second CGH base surface deviation W pass2 , the second photolithography pattern deviation W pd2 :

[0012] W2=W s +W pass2 +W pd2 ,

[0013] Step 4: Adjust the pitch angle of the multi-dimensional adjustment frame, and the computational holography works at the -1 diffraction order to generate the third diffraction wave with a diffraction angle of θ1. Tilt the computational holography reverse interferometer direction by θ1 and record the position as q1. Adjust the computational holography position to the q3 position. When in the q3 position, the computational holography working wavefront is used as the third measured wavefront. The third measurement result W3 includes the system error W s , the third calculation of the holographic base surface deviation W pass3 , the third photolithography pattern deviation W pd3 :

[0014] W3=W s +W pass3 +W pd3 ,

[0015] Step 5: Adjust the pitch angle of the multi-dimensional adjustment frame, and the computational holography works at the -1 diffraction order to generate the fourth diffraction wave with a diffraction angle of θ2. Tilt the computational holography reverse interferometer direction by θ2 and record the position as q4. Adjust the computational holography position to the q4 position. The computational holography working wavefront at the q4 position is used as the fourth measured wavefront. The fourth measurement result W4 includes the system error W s , the fourth calculation of the holographic base surface deviation W pass4 , the fourth photolithography pattern deviation W pd4 :

[0016] W4=W s +W pass4 +W pd4 ,

[0017] Step 6: Based on the CGH manufacturing error characteristics, the measurement results W1 to W4 obtained through 4 measurements are eliminated. pass1 ~W pass4 and W pd1 ~W pd4 , and obtain the system error W s .

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) The present invention utilizes the characteristic of computational holography that it can achieve ultra-high detection accuracy at the sub-nanometer level, and replaces the test flat crystal in the two-flat crystal absolute inspection method with the independent diffraction wavefront of the computational holography, thereby avoiding the problem of inaccurate calibration of the interferometer system error due to local defects of the flat crystal and the alignment error of the two flat crystals during the measurement process, and can perform high-precision calibration of the interferometer system error.

[0020] (2) According to the manufacturing error characteristics of CGH and based on the CGH absolute verification technology, the present invention has a calibration device that only requires a multi-dimensional frame and CGH, and has the characteristics of a simple structure. During the measurement process, only a simple posture adjustment of the CGH is required, which greatly optimizes the measurement steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the optical path diagram of the planar interferometer system error calibration device based on computer-generated holography.

[0022] Figure 2 This is a schematic diagram of the computational holographic pose during four measurements in the interferometer system error calibration. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0024] Combine Figure 1 and Figure 2 A method for calibrating the system error of a planar interferometer based on computer-generated holography is proposed. It is applicable to both conventional interferometers and large-aperture interferometers. The specific steps are as follows:

[0025] Step 1: Build a planar interferometer system error calibration device based on CGH:

[0026] The planar interferometer system error calibration device comprises an interferometer S1, a computer-generated hologram S2 and a plane reference mirror S4 which are sequentially arranged along the optical axis, and a multi-dimensional adjustment frame S3 for adjusting the computer-generated hologram S2.

[0027] Turn on interferometer S1. Use a plane standard mirror to set the side away from interferometer S1 as the reference surface. Use a point camera to adjust the reference light to the center of the crosshairs. Secure CGH S2 to the multi-dimensional adjustment frame S3, ensuring that its optical axis is aligned with the interferometer optical axis. CGH S2 can be a phase-type or amplitude-type reflection CGH.

[0028] The CGH S2 is a composite CGH of two linear carrier frequencies. Under the working angles θ1 and θ2 corresponding to the two linear carrier frequencies, the surface deviation of the CGH base in the measured wavefront is calculated as W. pass1 and W pass2 There are the following relationships:

[0029]

[0030] ν1 and ν2 are the spatial frequencies of the CGH S2, and λ is the operating wavelength of the system.

[0031] The computer-generated hologram S2 operates at the plus or minus 1st diffraction order, and its two linear carrier frequencies can generate 4 diffraction wavefronts.

[0032] Specifically, if Figure 1 As shown in the planar interferometer system error calibration device based on CGH, the outgoing light of interferometer S1 after passing through plane reference mirror S4 is generated by CGH S2 to generate four independent wavefronts with different tilt angles along the x-axis. The four independent wavefronts are respectively Figure 2 The operating wavefronts at positions q1, q2, q3, and q4 are shown.

[0033] Step 2: Adjust the pitch angle of the multi-dimensional adjustment frame S3, and the computational hologram S2 works at the +1 diffraction order to generate the first diffraction wave with a diffraction angle of θ1. Tilt the computational hologram S2 toward the interferometer by an angle of θ1 and record the position as q1. Adjust the position of the computational hologram S2 to Figure 2 At the q1 position in the calculation, the working wavefront of the hologram S2 is used as the first wavefront to be measured when it is at the q1 position. The first measurement result W1 includes the system error W s , the first CGH base surface deviation W pass1 , the first photolithography pattern deviation W pd1 :

[0034] W1=W s +W pass1 +W pd1 ,

[0035] Step 3: Adjust the pitch angle of the multi-dimensional adjustment frame S3, and the computational hologram S2 works at the +1 diffraction order to generate the second diffraction wave with a diffraction angle of θ2. Tilt the computational hologram S2 toward the interferometer by an angle of θ2 and record the position as q2. Adjust the position of the computational hologram S2 to Figure 2 At the q2 position in the hologram, the working wavefront of the calculated hologram S2 is used as the second wavefront to be measured when it is at the q2 position. The second measurement result W2 includes the system error W s , the second CGH base surface deviation W pass2 , the second photolithography pattern deviation W pd2 :

[0036] W2=W s +W pass2 +W pd2 ,

[0037] Step 4: Adjust the pitch angle of the multi-dimensional adjustment frame S3, and the computational hologram S2 works at the -1 diffraction order to generate the third diffraction wave with a diffraction angle of θ1. Tilt the computational hologram S2 in the reverse interferometer direction by an angle of θ1 and record the position as q1. Adjust the position of the computational hologram S2 to Figure 2 At the q3 position in the hologram, the working wavefront of the calculated hologram S2 is used as the third wavefront to be measured when it is at the q3 position. The third measurement result W3 includes the systematic error W s , the third calculation of the holographic base surface deviation W pass3 , the third photolithography pattern deviation W pd3 :

[0038] W3=W s +W pass3 +W pd3 ,

[0039] Step 5: Adjust the pitch angle of the multi-dimensional adjustment frame S3, and the computational hologram S2 works at the -1 diffraction order to generate the fourth diffraction wave with a diffraction angle of θ2. Tilt the computational hologram S2 in the reverse interferometer direction by an angle of θ2 and record the position as q4. Adjust the computational hologram S2 posture to Figure 2At the q4 position in the hologram, the working wavefront of the calculated hologram S2 is used as the fourth wavefront to be measured when the hologram S2 is at the q4 position. The fourth measurement result W4 includes the systematic error W s , the fourth calculation of the holographic base surface deviation W pass4 , the fourth photolithography pattern deviation W pd4 :

[0040] W4=W s +W pass4 +W pd4 ,

[0041] Step 6: Based on the CGH manufacturing error characteristics, the measurement results W1 to W4 obtained through 4 measurements are eliminated. pass1 ~W pass4 and W pd1 ~W pd4 , and obtain the system error W s , as follows:

[0042] According to the CGH manufacturing error characteristics: W pass1 =W pass4 , W pass2 =W pass3 , W pass1 =W pass2 / k, where k is a constant; W pd1 =-W pd4 , W pd2 =-W pd3 , W pd1 =gW pd2 , where the coefficient g is a constant.

[0043] System error W s :

[0044] W s =(W1+W2-kW3-kW4) / (2-2k)

[0045] In the above formula, the coefficient k is expressed as:

[0046]

[0047] ν1 and ν2 are both the spatial frequencies of the CGH, and λ is the operating wavelength of the system.

[0048] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any local modification or replacement within the technical scope disclosed by any person familiar with the technology should be included in the scope of the present invention.

Claims

1. A method for calibrating the system error of a planar interferometer based on computer-generated holography, characterized in that: The implementation steps are as follows: Step 1: Build a planar interferometer system error calibration device based on CGH: The planar interferometer system error calibration device comprises an interferometer (S1), a computer-generated hologram (S2), and a plane reference mirror (S4) sequentially arranged along an optical axis, and a multi-dimensional adjustment frame (S3) for adjusting the computer-generated hologram (S2); Turn on the interferometer (S1), use a plane standard mirror to set the side away from the interferometer (S1) as the reference surface, and adjust the reference light to the center of the crosshairs using a point camera; fix the CGH (S2) on the multi-dimensional adjustment frame (S3) to ensure that its optical axis is aligned with the optical axis of the interferometer; Step 2: Adjust the pitch angle of the multi-dimensional adjustment frame (S3), and the computational hologram (S2) works at the +1 diffraction order to generate the first diffraction wave with a diffraction angle of θ1. Tilt the computational hologram (S2) toward the interferometer by an angle of θ1, and record the position as q1. Adjust the position of the computational hologram (S2) to the q1 position. When it is at the q1 position, the working wavefront of the computational hologram (S2) is used as the first wavefront to be measured. The first measurement result W1 includes the system error W s , the first CGH base surface deviation W pass1 , the first photolithography pattern deviation W pd1 : W1=W s +W pass1 +W pd1 , Step 3: Adjust the pitch angle of the multi-dimensional adjustment frame (S3), and the computational hologram (S2) works at the +1 diffraction order to generate the second diffraction wave with a diffraction angle of θ2. Tilt the computational hologram (S2) toward the interferometer by an angle of θ2, and record the position as q2. Adjust the position of the computational hologram (S2) to the q2 position. When it is at the q2 position, the working wavefront of the computational hologram (S2) is used as the second wavefront to be measured. The second measurement result W2 includes the system error W s , the second CGH base surface deviation W pass2 , the second photolithography pattern deviation W pd2 : W2=W s +W pass2 +W pd2 , Step 4: Adjust the pitch angle of the multi-dimensional adjustment frame (S3), and the computational hologram (S2) works at the -1 diffraction order to generate the third diffraction wave with a diffraction angle of θ1. Tilt the computational hologram (S2) in the reverse interferometer direction by an angle of θ1, and record the position as q1. Adjust the position of the computational hologram (S2) to the q3 position. When it is at the q3 position, the working wavefront of the computational hologram (S2) is used as the third wavefront to be measured. The third measurement result W3 includes the system error W s , the third calculation of the holographic base surface deviation W pass3 , the third photolithography pattern deviation W pd3 : W3=W s +W pass3 +W pd3 , Step 5: Adjust the pitch angle of the multi-dimensional adjustment frame (S3), and the computational hologram (S2) works at the -1 diffraction order to generate the fourth diffraction wave with a diffraction angle of θ2. Tilt the computational hologram (S2) in the reverse interferometer direction by an angle of θ2, and record the position as q4. Adjust the computational hologram (S2) to the q4 position. When it is at the q4 position, the working wavefront of the computational hologram (S2) is used as the fourth wavefront to be measured. The fourth measurement result W4 includes the system error W s , the fourth calculation of the holographic base surface deviation W pass4 , the fourth photolithography pattern deviation W pd4 : W4=W s +W pass4 +W pd4 , Step 6: Based on the CGH manufacturing error characteristics, the measurement results W1 to W4 obtained through 4 measurements are eliminated. pass1 ~W pass4 and W pd1 ~W pd4 , and obtain the system error W s .

2. The method for calibrating the system error of a planar interferometer based on computer-generated holography according to claim 1, characterized in that: The computer-generated hologram (S2) is a phase-type or amplitude-type reflection computer-generated hologram.

3. The method for calibrating the system error of a planar interferometer based on computer-generated holography according to claim 2, characterized in that: The CGH (S2) is a composite CGH of two linear carrier frequencies. Under the working angles θ1 and θ2 corresponding to the two linear carrier frequencies, the surface deviation of the CGH base in the measured wavefront is calculated as W. pass1 and W pass2 There are the following relationships: ν1 and ν2 are the spatial frequencies of the CGH (S2), and λ is the system operating wavelength.

4. The method for calibrating the system error of a planar interferometer based on computer-generated holography according to claim 3, characterized in that: Computer-generated holography (S2) operates at plus or minus one diffraction order, and the two linear carrier frequencies it contains can generate four diffraction wavefronts.

5. The method for calibrating the system error of a planar interferometer based on computer-generated holography according to claim 3, characterized in that: In step 6, according to the CGH manufacturing error characteristics, the measurement results W1 to W4 obtained through 4 measurements are eliminated. pass1 ~W pass4 and W pd1 ~W pd4 , and obtain the system error W s : IN s =(W1+W2-kW3-kW4) / (2-2k) In the above formula, the coefficient k is expressed as: ν1 and ν2 are both the spatial frequencies of the CGH, and λ is the operating wavelength of the system.

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