Grating development monitoring method and monitoring device based on real-time change of polarization state

Abstract

The present application relates to grating development online monitoring, specifically relates to the grating development monitoring method and monitoring device based on polarization state real-time change, adopt the monochromatic linear polarized light of polarization angle real-time change as monitoring light source, real-time monitoring the diffraction efficiency change situation of the grating to be monitored in development process, the characteristic point of diffraction efficiency curve in the development process under not annihilating single polarized light is monitored, simultaneously, the difference change of diffraction efficiency of different polarization states in different development stages brings multiple additional characteristic points to the diffraction efficiency curve, and based on the multiple characteristic points of diffraction efficiency curve under different polarization states in the development process, the development termination point is comprehensively judged;The technical scheme provided by the present application can effectively overcome the defects of low slot control precision, fuzzy development termination point judgment, complex equipment and high cost in the prior art.

Description

Technical Field

[0001] This invention relates to online monitoring of grating development, specifically to a method and device for monitoring grating development based on real-time changes in polarization state. Background Technology

[0002] As an important precision optical component, the performance of a diffraction grating directly depends on the geometric profile of its groove, such as duty cycle, sidewall angle, and groove depth. The accuracy of these key dimensions has a decisive impact on the final optical performance of the grating (such as diffraction efficiency and polarization-dependent loss). In the manufacturing process of the grating, development is a crucial step in forming the final groove structure, and the quality of its process directly determines the performance and yield of the grating product.

[0003] Currently, the industry generally uses offline detection methods to monitor the results of the developing process. This involves removing the sample from the developing equipment after the developing process is complete and performing sampling and testing using instruments such as scanning electron microscopy (SEM) or atomic force microscopy (AFM). This detection method has significant limitations: it suffers from lag, low efficiency, and the inability to capture dynamic processes. Therefore, online monitoring has become a cutting-edge and hot topic in raster developing monitoring.

[0004] The commonly used method for online monitoring of grating development involves monitoring the diffraction efficiency of the grating in real time under fixed-state laser irradiation and comparing it with a diffraction efficiency curve established based on theoretical models or engineering experience to determine the development termination point. However, this online monitoring method suffers from problems in practical applications, such as low accuracy in grating shape control, ambiguity in determining the development termination point, and susceptibility to misjudgments.

[0005] In patent application CN 111595555 A, a device and method for real-time monitoring of grating mask development using a broad spectral ratio are disclosed. Specifically, the ratio of diffraction efficiency of S-polarized light to P-polarized light at different wavelengths during the development process is used as the basis for determining the development termination point. This method has the following significant drawbacks: First, it uses a supercontinuum laser source combined with an acousto-optic filter as the monitoring light source, resulting in complex equipment and high cost. Second, it requires real-time fitting and comparison of the measured spectral curve with the simulation results during the development process, placing high demands on the processing power of the computing equipment. Third, the accuracy of this method highly depends on the consistency between the simulation model and the actual grating groove shape, and many factors affect the actual grating groove shape, making consistency difficult in practical engineering. In addition, some studies have attempted to introduce machine learning methods for grating development monitoring, but these methods often rely on large amounts of labeled data and complex algorithm training, resulting in significantly more extensive preparatory work and computational burden. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the aforementioned shortcomings of existing technologies, this invention provides a grating development monitoring method and device based on real-time polarization state changes, which can effectively overcome the deficiencies of existing technologies such as low groove control accuracy, ambiguous determination of development termination point, complex equipment, and high cost.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] The grating development monitoring method based on real-time polarization state changes uses monochromatic linearly polarized light with real-time polarization angle changes as the monitoring light source to monitor the diffraction efficiency changes of the grating under monitoring during the development process. While not annihilating the characteristic points of the diffraction efficiency curve during the development process under single polarized light, it uses the difference in diffraction efficiency under different polarization states at different development stages to bring multiple additional characteristic points to the diffraction efficiency curve. Based on the multiple characteristic points of the diffraction efficiency curve under different polarization states during the development process, the development termination point is comprehensively determined.

[0011] Preferably, the characteristic points of the diffraction efficiency curve during the development process under single polarization light include characteristic points at the peak and characteristic points at the valley. The use of the difference in diffraction efficiency under different polarization states at different development stages brings multiple additional characteristic points to the diffraction efficiency curve, including the widest characteristic point and the narrowest characteristic point.

[0012] Preferably, according to rigorous coupled-wave theory simulation calculations, for gratings with different linear densities, different photoresist thicknesses, different film systems, and different groove evolution paths, the diffraction efficiency is different under different polarization states, but the diffraction efficiency curves show the same trend.

[0013] Preferably, the monitoring light source is one of elliptical polarized light with real-time changes in the major or minor axis direction and elliptical polarized light with real-time changes in eccentricity.

[0014] A grating development monitoring device based on real-time polarization state changes includes a laser, a polarizer, a uniformly rotating half-wave plate, an objective lens, a collimating lens, a grating to be monitored placed in a developing tank, a narrow-band filter, a photodetector, and an oscilloscope.

[0015] The laser light generated by the laser is polarized into linearly polarized light after passing through a polarizer. After passing through a uniformly rotating half-wave plate, it becomes monochromatic linearly polarized light with a real-time changing polarization angle, which serves as the monitoring light source. After passing through a beam expander composed of an objective lens and a collimating lens, it forms collimated light with a larger spot size, which illuminates the grating to be monitored placed in the developing tank. The diffracted light is detected by a photodetector after passing through a narrow-band filter, and the diffraction efficiency curve is displayed on an oscilloscope.

[0016] Preferably, the device further includes a motor for driving the 1 / 2 wavelength waveplate to rotate at a constant speed. The lower limit of the rotation frequency of the 1 / 2 wavelength waveplate must ensure that the difference in diffraction efficiency caused by continuous development during half a rotation is negligible. The upper limit of the rotation frequency of the 1 / 2 wavelength waveplate must ensure that the photodetector collects the average diffraction efficiency under a small change in polarization angle in a single operation, rather than the average diffraction efficiency of all polarization states.

[0017] Preferably, the collimated light formed after passing through the beam expander composed of the objective lens and the collimating lens is a wide beam of 10~30mm.

[0018] Preferably, the center wavelength of the narrowband filter is the same as the laser light generated by the laser to improve the signal-to-noise ratio of the system.

[0019] Preferably, the photodetector is a single-point photodetector.

[0020] (III) Beneficial Effects

[0021] Compared with the prior art, the grating development monitoring method and monitoring device based on real-time polarization state changes provided by the present invention have the following beneficial effects:

[0022] 1) While not annihilating the characteristic points of the diffraction efficiency curve during the development process under single polarized light, the difference in diffraction efficiency under different polarization states at different development stages brings multiple additional characteristic points to the diffraction efficiency curve. Based on the multiple characteristic points of the diffraction efficiency curve under different polarization states during the development process, the development termination point is comprehensively judged. By comprehensively comparing multiple characteristic points as the basis for judging the development termination point, the accuracy is very high whether judged manually or by machine, and it can effectively improve the accuracy of the groove control with a low misjudgment rate.

[0023] 2) Simply by inserting a polarizer, a uniformly rotating 1 / 2 wavelength waveplate, and a beam expander into an existing grating development and monitoring device, it can be transformed into the grating development and monitoring device proposed in this invention. The equipment is simple, easy to debug, and has a low cost. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0025] Figure 1 This is a schematic diagram of the device structure of the present invention;

[0026] Figure 2 This is the diffraction efficiency curve of the grating under monitoring light sources with different polarization states in the present invention throughout the entire development process;

[0027] Figure 3 In this invention and Figure 2 Diffraction efficiency curves of the entire development process of gratings with different line densities (1000 lines / mm) under monitoring light sources with different polarization states;

[0028] Figure 4 In this invention and Figure 2 Diffraction efficiency curves of gratings with different photoresist thicknesses (500 nm) under monitoring light sources with different polarization states throughout the development process;

[0029] Figure 5 In this invention and Figure 2 Diffraction efficiency curves of gratings with different film systems under monitoring light sources with different polarization states throughout the development process;

[0030] Figure 6 In this invention and Figure 2 Diffraction efficiency curves of gratings with different groove evolution paths under monitoring light sources with different polarization states throughout the development process;

[0031] Figure 7 This is the diffraction efficiency curve of the grating during the entire development process at a specific 1 / 2 wavelength waveplate rotation frequency in this invention.

[0032] Figure 8 For the present invention Figure 7 The diagram shows the grating groove type corresponding to each feature point in the diffraction efficiency curve. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] The following describes the specific process and technical effects of the grating development and monitoring method based on real-time polarization state changes provided by this invention, using concrete examples. The method specifically includes:

[0035] Using monochromatic linearly polarized light with real-time changes in polarization angle as the monitoring light source, the diffraction efficiency of the grating under test is monitored in real time during the development process. While not annihilating the characteristic points of the diffraction efficiency curve during the development process under single polarized light, the difference in diffraction efficiency under different polarization states at different development stages brings multiple additional characteristic points to the diffraction efficiency curve. Based on the multiple characteristic points of the diffraction efficiency curve under different polarization states during the development process, the development termination point is determined comprehensively.

[0036] Based on rigorous coupled-wave theory simulations, for waves with different linear densities (such as...) Figure 3 As shown), different photoresist thicknesses (e.g.) Figure 4 As shown), different membrane systems (such as...) Figure 5 As shown), different groove evolution paths (such as...) Figure 6 The grating shown has different diffraction efficiencies under different polarization states, but the diffraction efficiency curves show a consistent trend (as shown). Figure 2 (As shown). Therefore, by using monochromatic linearly polarized light with a real-time changing polarization angle as the monitoring light source, the characteristic points of the diffraction efficiency curve during the development process under single polarized light are not annihilated, while the difference in diffraction efficiency at different stages of development under different polarization states is utilized to bring multiple additional characteristic points to the diffraction efficiency curve.

[0037] Figure 7 This is the diffraction efficiency curve of the grating during the entire development process at a specific 1 / 2 wavelength waveplate rotation frequency. In the same development stage, the diffraction efficiency varies depending on the polarization state; the difference between the maximum and minimum values ​​is PV. The characteristic points of the diffraction efficiency curve during development under single polarization include the characteristic points at the peak (…). Figure 7 (points d and f) and feature points at valleys ( Figure 7 The middle point (e) utilizes the difference in diffraction efficiency under different polarization states at different development stages to introduce several additional feature points into the diffraction efficiency curve, including the feature point at the widest point (e). Figure 7 (point a) and the narrowest feature point ( Figure 7 (Points b and c in the middle).

[0038] Figure 8 for Figure 7 The diagram shows the grating groove shape corresponding to each feature point in the diffraction efficiency curve. The dashed box contains multiple additional feature points that the technical solution of this application brings to the diffraction efficiency curve. It can be seen that the technical solution of this application plays an important role in accurately controlling the groove shape and improving the accuracy of determining the development termination point.

[0039] In the technical solution of this application, the monitoring light source adopts one of elliptical polarization with real-time changes in the direction of the major or minor axis, or elliptical polarization with real-time changes in eccentricity.

[0040] The above technical solution, while not annihilating the characteristic points of the diffraction efficiency curve during the development process under single polarized light, utilizes the difference in diffraction efficiency under different polarization states at different development stages to bring multiple additional characteristic points to the diffraction efficiency curve. Based on the multiple characteristic points of the diffraction efficiency curve under different polarization states during the development process, the development termination point is comprehensively determined. By comprehensively comparing multiple characteristic points as the basis for determining the development termination point, the accuracy is very high, whether judged manually or by machine, and it can effectively improve the accuracy of the groove control with a low misjudgment rate.

[0041] Based on the aforementioned grating development monitoring method based on real-time polarization state changes, this application also discloses a grating development monitoring device based on real-time polarization state changes, such as... Figure 1 As shown, it includes:

[0042] Laser 1, polarizer 2, uniformly rotating 1 / 2 wavelength waveplate 3, objective lens 5, collimating lens 6, grating to be monitored placed in developing tank 8 (containing developing solution) 7, narrow band filter 9, photodetector 10 and oscilloscope 11.

[0043] The laser light generated by laser 1 is polarized into linearly polarized light after passing through polarizer 2. After passing through a uniformly rotating half-wavelength waveplate 3, it forms monochromatic linearly polarized light with a real-time changing polarization angle, which serves as the monitoring light source. After passing through a beam expander composed of objective lens 5 and collimating lens 6, it forms collimated light with a larger spot size, which illuminates the grating 7 to be monitored placed in the developing tank 8. The diffracted light is detected by photodetector 10 after passing through narrowband filter 9, and the diffraction efficiency curve is displayed by oscilloscope 11.

[0044] The device also includes a motor 4 for driving the 1 / 2 wavelength waveplate 3 to rotate at a constant speed. The lower limit of the rotation frequency of the 1 / 2 wavelength waveplate 3 must ensure that the difference in diffraction efficiency caused by continuous development during half a rotation is negligible. According to actual engineering experience, the diffraction efficiency difference caused by continuous development within a few minutes and 1 second is small and negligible. That is, the lower limit of the rotation frequency of the 1 / 2 wavelength waveplate 3 is 0.5Hz. In order to ensure monitoring accuracy, the lower limit of the rotation frequency can be set to 5Hz.

[0045] The upper limit of the rotation frequency of the half-wavelength waveplate 3 must ensure that the photodetector 10 collects the average diffraction efficiency under a small change in polarization angle in a single measurement, rather than the average diffraction efficiency of all polarization states. Assume the collection frequency of the photodetector 10 is f. PD Then the upper limit of the rotation frequency of the 1 / 2 wavelength waveplate 3 can be set to f. PD / 10.

[0046] Since the present invention requires that the light intensity detection be highly robust to interference factors such as the placement posture of the grating 7 to be monitored and the shaking of the developer during the development process, the collimated light formed after passing through the beam expander composed of objective lens 5 and collimating lens 6 is a wide beam of 10~30mm, and the photodetector 10 is a single-point photodetector.

[0047] The center wavelength of the narrowband filter 9 is the same as that of the laser generated by the laser 1, so as to improve the signal-to-noise ratio of the system.

[0048] The above technical solution only requires inserting a polarizer, a uniformly rotating 1 / 2 wavelength waveplate, and a beam expander into an existing grating development and monitoring device to transform it into the grating development and monitoring device proposed in this invention. The equipment is simple, easy to debug, and has a low cost.

[0049] In a further embodiment, a 650nm laser 1 is used as the light source.

[0050] In a further embodiment, the refractive index of the developer is 1.33, the refractive index of the photoresist is 1.56, the refractive index of the substrate is 1.46, the line density of the grating is 1740 lines / mm, and the thickness of the photoresist is 300nm.

[0051] In a further embodiment, it is assumed that the groove shape remains rectangular during the development process. In the early stage of the development process, the aspect ratio of 0.8 is kept constant, and the groove depth is gradually increased. In the later stage of the development process, the groove depth of 300nm is kept constant, and the aspect ratio is gradually decreased until the aspect ratio is 0.2.

[0052] In a further embodiment, the simulated diffraction efficiency curves of the grating during the entire development process under monitoring light sources with different polarization states are as follows: Figure 2 As shown.

[0053] In a further embodiment, the rotation frequency of the half-wave plate 3 is 10 Hz, and the acquisition frequency of the photodetector 10 is 360 Hz.

[0054] In a further embodiment, the simulated diffraction efficiency curve of the grating during the entire development process at a specific 1 / 2 wavelength waveplate rotation frequency is shown below. Figure 7 As shown.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for real-time monitoring of grating development based on the real-time change of polarization state, characterized in that: The single-color linearly polarized light with real-time changing polarization angle is used as a monitoring light source to monitor the change of diffraction efficiency of the grating to be monitored in real time during the development process. The characteristic points of the diffraction efficiency curve during the development process under the single polarization light are determined, and the difference of diffraction efficiency under different polarization states in different development stages is used to bring multiple additional characteristic points to the diffraction efficiency curve. The termination point of the development process is determined based on the multiple characteristic points of the diffraction efficiency curve under different polarization states during the development process.

2. The method of claim 1, wherein the polarization state is varied in real time. The characteristic points of the diffraction efficiency curve during the development process under the single polarization light include the characteristic points at the peak and the valley. The multiple additional characteristic points brought to the diffraction efficiency curve by the difference of diffraction efficiency under different polarization states in different development stages include the characteristic points at the widest and the narrowest.

3. The method of claim 1, wherein: According to the simulation calculation based on the rigorous coupled wave theory, the diffraction efficiency under different polarization states is different for gratings with different line densities, different photoresist thicknesses, different film systems and different groove evolution paths, but the change trend of the diffraction efficiency curve is consistent.

4. The method of claim 1, wherein: The monitoring light source adopts one of the elliptical polarized light with real-time changing long axis or short axis and the elliptical polarized light with real-time changing eccentricity.

5. The apparatus for monitoring the development of a grating based on real-time changes in polarization state according to claim 1, characterized in that: The device comprises a laser (1), a polarizer (2), a uniformly rotating 1 / 2 wavelength wave plate (3), an objective lens (5), a collimating lens (6), a grating (7) to be monitored placed in a development tank (8), a narrow-band filter (9), a photodetector (10) and an oscilloscope (11). The laser generated by the laser (1) forms linearly polarized light after the polarizer (2), and then forms single-color linearly polarized light with real-time changing polarization angle as a monitoring light source after the uniformly rotating 1 / 2 wavelength wave plate (3). After passing through the expander composed of the objective lens (5) and the collimating lens (6), the collimated light with a larger spot size is formed, which irradiates the grating (7) to be monitored placed in the development tank (8). The diffracted light is detected by the photodetector (10) after passing through the narrow-band filter (9), and the diffraction efficiency curve is displayed by the oscilloscope (11).

6. The real-time variation of polarization state based grating development monitoring device of claim 5, wherein: The device further comprises a motor (4) for driving the 1 / 2 wavelength wave plate (3) to rotate at a uniform speed. The lower limit of the rotation frequency of the 1 / 2 wavelength wave plate (3) needs to ensure that the difference of diffraction efficiency caused by the continuous development can be ignored during the rotation of half a cycle. The upper limit of the rotation frequency of the 1 / 2 wavelength wave plate (3) needs to ensure that the photodetector (10) collects the average diffraction efficiency under a small polarization angle change amount at a time, rather than the average diffraction efficiency under all polarization states.

7. The real-time variation of polarization state based grating development monitoring device of claim 5, wherein: The collimated light formed after passing through the expander composed of the objective lens (5) and the collimating lens (6) is a wide light beam with a width of 10-30 mm.

8. The real-time variation of polarization state based grating development monitoring device of claim 5, wherein: The center wavelength of the narrow-band filter (9) is the same as the laser generated by the laser (1), so as to improve the signal-to-noise ratio of the system.

9. The real-time variation of polarization state based grating development monitoring device of claim 5, wherein: The photodetector (10) is a single-point photodetector.

Images