Grating absolute linear density detection system and method

Abstract

The invention discloses a grating absolute linear density detection system and method, and belongs to the technical field of optical detection. By adding an incident light wavelength modulation function and a wavelength monitoring function, different diffraction angles of the same position of the grating are obtained by regulating and controlling the incident light wavelength, so that the absolute linear density of the position is determined. Under the condition that the wavelength of the incident light is not changed, the relative detection precision dN / N of the LTP to the grating linear density is equal to 5 * 10 <-7 >, absolute detection of all positions can be achieved only by changing the wavelength of the incident light once, and the detection efficiency is guaranteed. Through theoretical analysis and actual test, the absolute detection precision of the grating linear density reaches dN / N = 1 * 10 <-6 >.

Description

Technical Field

[0001] The invention belongs to the technical field of optical detection, and relates to a grating absolute line density detection system and method. Background Art

[0002] With the construction of the fourth generation of synchrotron radiation sources and the development of lithography systems, higher requirements are placed on the performance of gratings. Grating line density, as an important indicator for evaluating grating performance, affects its resolution and the reliability of obtaining optical information. In order to improve the monochromaticity of the light beam, better perform coherent diffraction imaging, and meet the high-precision positioning requirements of the motion control platform of the lithography system, more complete means of grating line density detection are also required. Therefore, the development of accurate detection technology for grating line density has important theoretical and application significance.

[0003] At present, there are many methods for detecting line density, such as scanning electron microscopy, interference method, diffraction method and moiré fringe method. Among them, the long-range profilometer (LTP) detection method has the unique advantage of a large detection range. It is the main means of detecting the surface of large-aperture, large-curvature, and aspherical optical components. It also meets the detection requirements of long-range grating rulers. LTP has achieved a very high level of accuracy in detecting line density. Its detection principle is based on the grating equation. First, the incident light is made to be incident vertically, so that the incident light and the diffracted light coincide. The grating base surface shape under the 0th order diffracted light is obtained and the Littrow angle is derived. Then, under the condition of near-Littrow angle, the 1st order diffracted light is used for detection to obtain dual data including the grating line density and the base surface shape. Finally, the line density information of the grating is obtained by deducting the base surface shape.

[0004] However, this detection method can only obtain the relative change of the grating line density by reading the change of the diffraction angle, and cannot detect the absolute line density of the grating. Zero-point calibration of the grating for which only the relative change of the line density is known, whether relying on the data during processing or supplemented by other detection methods, will introduce other errors and reduce the accuracy of positioning. The method of obtaining the absolute line density value while detecting the relative change of line density can avoid the introduction of calibration errors and improve the accuracy of positioning to a certain extent. The detection of absolute line density can also provide a standardized basis for the application of synchrotron radiation light sources, which is conducive to promoting the development and application of related technologies. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a grating absolute line density detection system and method. By adjusting the wavelength of the incident light beam of the long-range profilometer, the relative line density of the grating detected at different wavelengths is obtained, and then the absolute line density of each position of the grating is calculated, and a high detection accuracy is maintained. This invention enables the long-range profilometer system to detect the absolute line density of the grating, and at the same time, on the basis of ensuring the detection accuracy, the detection time is greatly reduced. The relative detection error of the grating line density can be achieved to be dN / N=5×10 -7 , the absolute detection error is dN / N=1×10 -6 The detection accuracy meets the absolute detection requirements of high-precision grating line density. dN / N is the RMS value.

[0006] The invention provides a grating absolute line density detection system, comprising a detector, a Fourier lens, a beam splitter, a laser, a collimator, a beam splitting optical fiber, a wavelength meter, a first plane reflector, a second plane reflector and a grating to be measured; the detector, the Fourier lens, the beam splitter, the beam splitting optical fiber, the collimator and the laser together form an LTP optical probe; when the wavelength is changed to detect the absolute line density of the grating, the laser emits an incident light beam A, which first passes through the beam splitting optical fiber and then enters the wavelength meter to monitor the laser wavelength, and the other path is reflected to the second plane reflector through the collimator and the beam splitter, and then is incident on the surface of the grating to be measured through reflection of the second plane reflector and the first plane reflector, so as to generate a diffracted light beam B, which is then reflected by the first plane reflector and the second plane reflector and transmitted by the beam splitter and the Fourier lens, and finally imaged on the detector, so as to obtain the light spot position information recorded by the detector at this time; then, the wavelength of the incident light beam A is changed by regulating the laser, so as to obtain the position information of the diffracted light beam C imaged on the detector.

[0007] The present invention also proposes a grating absolute line density detection method. When the wavelength of the incident light beam is λ, the grating equation is:

[0008] mNλ=sin(α)+sin(β) (1)

[0009] Where m is the diffraction order; λ is the wavelength of the detection beam; N is the grating line density; α and β are the incident angle and diffraction angle respectively; at the same position, the wavelength of the incident beam increases When , the grating equation is:

[0010] mN(λ+ )=sin(α)+sin(γ) (2)

[0011] γ is the wavelength of the incident beam increased After that, the diffraction angle when the incident angle is α; at the same position, the wavelength of the incident beam increases by 2 When , the grating equation is:

[0012] mN(λ+2 )=sin(α)+sin(δ) (3)

[0013] δ is the wavelength of the incident beam increased by 2 After that, the diffraction angle when the incident angle is α; the accurate values ​​of γ-β and δ-β can be obtained through the LTP optical probe , , that is, γ-β= ,δ-β= , so the three equations (1)(2)(3) can be combined to immediately solve the diffraction angle β:

[0014] β = arctan[(2 sin( )-sin( )) / (cos( )+1-2 cos( ))] (4)

[0015] Substitute it into equation (2)-(1):

[0016] mN =sin(β+ )-sin(β) (5)

[0017] That is, the absolute value N of the grating line density is obtained.

[0018] The present invention has the following beneficial effects:

[0019] The present invention uses the LTP system to detect the absolute linear density of the grating. The incident light wavelength modulation function and wavelength monitoring function are added to the original LTP system. Different diffraction angles at the same position of the grating are obtained by adjusting the wavelength of the incident light, so as to determine the absolute linear density of the position. Without changing the wavelength of the incident light, the relative detection accuracy of the LTP for the grating linear density is dN / N=5×10 -7 The present invention can achieve absolute detection of each position by only changing the wavelength of the incident light twice, thus ensuring detection efficiency. After theoretical analysis and actual testing, the absolute detection accuracy of the grating line density of the present invention reaches dN / N=1×10 -6 . BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The structure and optical path diagram of the LTP variable wavelength detection system;

[0021] Figure 2 is the spot offset variation diagram;

[0022] Figure 3is the relationship diagram between the relative detection error of line density and the line density of the grating to be measured;

[0023] Figure 4 This is a graph showing the relationship between line density detection error and the line density of the grating to be measured.

[0024] In the figure, the reference numerals are: detector 1, Fourier lens 2, beam splitter 3, laser 4, beam splitting optical fiber 5, collimator 6, wavelength meter 7, first plane reflector 8, second plane reflector 9, and grating to be measured 10. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0026] The present invention changes the laser wavelength of the LTP system, that is, changes the wavelength of the incident light, and calculates the absolute line density of the position by monitoring the change of the diffraction angle, such as Figure 1 As shown, a grating absolute line density detection system is proposed, including a detector 1, a Fourier lens 2, a beam splitter 3, a laser 4, a beam splitting optical fiber 5, a collimator 6, a wavelength meter 7, a first plane reflector 8, a second plane reflector 9 and a grating to be measured 10. The detector 1, the Fourier lens 2, the beam splitter 3, the laser 4, the beam splitting optical fiber 5, and the collimator 6 together constitute an LTP optical probe. When the wavelength is changed to detect the absolute line density of the grating, the laser 4 emits an incident light beam A, and a part of it first enters the wavelength meter 7 through the beam splitting optical fiber 5 to obtain the laser wavelength at this time, and the other part is reflected to the second plane reflector 9 through the collimator 6 and the beam splitter 3, and then incident on the surface of the grating to be measured 10 through the reflection of the second plane reflector 9 and the first plane reflector 8, generating a diffracted light beam B, and then through the reflection of the first plane reflector 8 and the second plane reflector 9 and the transmission of the beam splitter 3 and the Fourier lens 2, finally imaged on the detector 1, and the spot position information recorded by the detector at this time is obtained. Then, by adjusting the laser 4, the wavelength of the incident light beam A is changed to obtain the position information of the diffracted light beam C imaged on the detector. The path of the incident light beam does not change. When the wavelength of the incident light beam is λ, the grating equation is:

[0027] mNλ=sin(α)+sin(β) (1)

[0028] Where m is the diffraction order; λ is the wavelength of the detection beam; N is the grating line density; α and β are the incident angle and diffraction angle respectively; at the same position, the wavelength of the incident beam increases When , the grating equation is:

[0029] mN(λ+ )=sin(α)+sin(γ) (2)

[0030] γ is the incident beam increase After that, the diffraction angle when the incident angle is α; at the same position, the wavelength of the incident beam increases by 2 When , the grating equation is:

[0031] mN(λ+2 )=sin(α)+sin(δ) (3)

[0032] δ is the incident beam increased by 2 After that, the diffraction angle when the incident angle is α; the accurate values ​​of γ-β and δ-β can be obtained through the LTP optical probe , , that is, γ-β= ,δ-β= Therefore, the three equations (1), (2) and (3) can be combined to immediately solve the exact diffraction angle β:

[0033] β = arctan[(2 sin( )-sin( )) / (cos( )+1-2 cos( ))] (4)

[0034] Substitute it into equation (2)-(1):

[0035] (5)

[0036] The absolute value N of the grating line density can be obtained.

[0037] The accuracy of using LTP to detect line density is limited by the accuracy of the wavelength meter in monitoring the changing wavelength and the accuracy of LTP in angular resolution.

[0038] The accuracy of LTP on angular resolution mainly affects the relative detection of grating line density. At present, its angular resolution accuracy is better than 50nrad, which is related to the line density detection error E N The relationship is:

[0039] N+E N =(sin(α)+sin(β+E β )) / m λ (6)

[0040] Substituting into formula (1) can be simplified to:

[0041] E N =(sin(β+ E β ) -sin(β)) / m λ;

[0042] Among them, E β is the LTP angle resolution accuracy, E N is the line density detection error. Assuming that the incident angle is the littrow angle and the angle resolution accuracy is 50nrad, the relationship between the line density relative detection error and the line density of the grating to be measured is as follows: Figure 2 As shown in the figure: the horizontal axis represents the grating line density to be measured, and the vertical axis represents the line density detection error. Figure 3 It can be seen that the influence of LTP resolution accuracy on the relative detection error of line density is about 5×10 -7 , which is the RMS value.

[0043] The accuracy of the wavelength meter mainly affects the absolute detection of the grating line density. The accuracy of the wavelength meter used in the verification experiment is E λ = ±0.0002nm, under the condition of near littrow angle, the relationship between line density detection error and wavelength meter accuracy is:

[0044] N+E N =(sin(α)+sin(β)) / m (λ+E λ ) (7)

[0045] N = (sin (α) + sin (β)) / m λ (8)

[0046] From the first two equations, we can get:

[0047] E N = N λ / (λ+ E λ )-N (9)

[0048] From the above formula, it can be seen that the line density detection error is affected by the line density of the grating to be measured and the accuracy of the wavelength meter. When the accuracy of the wavelength meter is ±0.0002nm, the relationship between the line density detection error and the line density of the grating to be measured is as follows: Figure 4 As shown in the figure, the horizontal axis represents the grating line density to be measured, and the vertical axis represents the line density detection error. Therefore, the influence of the wavelength meter accuracy on the line density detection error is about 1×10 -6 , which is the RMS value.

[0049] Since the LTP angle resolution accuracy E β and wavelength meter accuracy E λThey are all RMS values. RMS is the root mean square value, which is used to reflect the error distribution. Therefore, the calculated dN / N is also the RMS value.

[0050] The line density detection error is related to the line density of the grating to be measured. The evaluation index is dN / N. Since the line density detection error in this system is mainly affected by the LTP angle resolution accuracy and the wavelength meter accuracy, after calculation, it can be determined that the relative line density detection error is dN / N=5×10 -7 , the absolute detection error is dN / N=1×10 -6 .

Claims

1. A grating absolute line density detection system, characterized in that: include: The detector, Fourier lens, beam splitter, laser, collimator, beam splitting fiber, wavelength meter, first plane reflector, and second plane reflector are provided. The detector, Fourier lens, beam splitter, laser, beam splitting fiber, and collimator together constitute an LTP optical probe. When the wavelength is changed to detect the absolute linear density of the grating, the laser emits an incident light beam A, a part of which first enters the wavelength meter through the beam splitting fiber to monitor the laser wavelength at this time, and the other part is reflected to the second plane reflector through the collimator and the beam splitter, and then is reflected by the second plane reflector and the first plane reflector, and is incident on the surface of the grating to be measured to generate a diffracted light beam B, which is then reflected by the first plane reflector and the second plane reflector and transmitted by the beam splitter and the Fourier lens, and finally is imaged on the detector, and the light spot position information recorded by the detector at this time is obtained; then, the wavelength of the incident light beam A is changed by adjusting the laser, and the position information of the diffracted light beam C imaged on the detector is obtained.

2. A grating absolute line density detection method using the grating absolute line density detection system according to claim 1, characterized in that: include: When the wavelength of the incident light beam is λ, the grating equation is: mNλ=sin(α)+sin(β) (1) Where m is the diffraction order; λ is the wavelength of the detection beam; N is the grating line density; α and β are the incident angle and diffraction angle respectively; at the same position, the wavelength of the incident beam increases When , the grating equation is: mN(λ+ )=sin(a)+sin(c) (2) γ is the incident beam increase After that, the diffraction angle when the incident angle is α; at the same position, the wavelength of the incident beam increases by 2 When , the grating equation is: mN(λ+2 )=sin(a)+sin(δ) (3) δ is the incident beam increased by 2 After that, the diffraction angle when the incident angle is α; the accurate values ​​of γ-β and δ-β can be obtained through the LTP optical probe , , that is, γ-β= ,δ-β= , so the three equations (1)(2)(3) can be combined to immediately solve the diffraction angle β: β=arctan[(2 without( )-without( )) / (cos( )+1-2 cos( ))] (4) Substitute it into formula (2)-(1): mN =sin(β+ )-sin(β) (5) That is, the absolute value N of the grating line density is obtained.

3. The detection method according to claim 2, characterized in that: The accuracy of the variable wavelength detection line density of the LTP optical probe depends on the accuracy of the wavelength meter in monitoring the changed wavelength and the accuracy of the LTP optical probe in angular resolution.

4. The detection method according to claim 3, characterized in that: Angle resolution accuracy and line density detection error of LTP optical probe E N The relationship is: N+E N =(sin(α)+sin(β+E β )) / m l (6) Substituting into formula (1) and simplifying it into: E N =(sin(β+ E β )-sin(β)) / m l, Among them, E β is the angular resolution accuracy of the LTP optical probe, E N Line density detection error.

5. The detection method according to claim 3, characterized in that: The wavelength meter accuracy is E λ = ±0.0002nm, under the condition of near littrow angle, the relationship between line density detection error and wavelength meter accuracy is: N+E N =(sin(a)+sin(b)) / m (λ+E λ ) (7) N=(sin(α)+sin(β)) / m l (8) E N = N λ / (λ+ E λ )-N (9).

6. The detection method according to claim 3, characterized in that: Without changing the wavelength of the incident light, the relative detection accuracy of the grating line density is dN / N=5×10 -7 , where dN / N is the RMS value.

7. The detection method according to claim 3, characterized in that: The absolute detection accuracy of grating line density reaches dN / N=1×10 -6 , where dN / N is the RMS value.

8. An electronic device, characterized in that: include: one or more processors; A memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 2 to 6.

9. A computer-readable storage medium, characterized in that: Executable instructions are stored thereon, and when the instructions are executed by a processor, the processor implements the method according to any one of claims 2 to 6.

10. An intelligent terminal, comprising a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, the memory is used to store a computer program, the computer program comprises program instructions, and is characterized in that: The processor is configured to call the program instructions to execute the method according to any one of claims 2 to 6.

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