Optimization Method of Grating Structure for Reducing Position Measurement Error

Abstract

The present invention provides an optimization method for a grating structure to reduce position measurement errors, including: establishing an evaluation method for a phase grating structure according to the intensities of signals of different diffraction orders to describe the quality of the structure; then selecting one or more grating structures with better results as the initial grating structure according to this evaluation method; generating corresponding deformed grating structures according to the deformations that may be introduced during the manufacturing process; then comparing the above initial grating structure and the deformed grating structure to give multiple groups of grating arrangement combinations for comparison, and making plates for them to process a marked measurement plate for experiments; then establishing a corresponding relationship between the deformation of the grating structure and the introduced position error based on the comparison measurement results; and finally optimizing the initial grating structure according to this corresponding relationship to obtain an optimized grating structure. The optimized grating structure can offset or alleviate the influence of the deformation introduced during the manufacturing process on the position measurement accuracy and reduce the position measurement error.

Description

Technical Field

[0001] The present invention relates to the field of optical precision position detection, and particularly to a method for optimizing a grating structure for accurately measuring position errors in a phase grating position measurement system. Background Art

[0002] A phase grating position measurement system irradiates a periodic grating structure with an incident light beam and extracts relevant information from the reflected light beam to obtain accurate position information. It has the advantages of fast measurement speed, high measurement accuracy, and little influence by the environment, so it is widely used in the steps that require high-precision position measurement in the integrated circuit process.

[0003] As the technology nodes in the field of integrated circuits continue to shrink, the requirements for the measurement accuracy of the phase grating measurement system are becoming more and more stringent. However, the grating structure will undergo a certain degree of deformation during the manufacturing process, which not only weakens the intensity of the signal light but also introduces additional phase information, resulting in measurement errors and reducing the position measurement accuracy.

[0004] Regarding the structural design of the phase grating mark, in a detection system using single-wavelength illumination, the influence of deformation on the position accuracy can be reduced by selecting a laser with a wavelength adaptable to the grating structure as the light source. However, since the grating also changes during the process, the signal intensity of the measurement light beam still cannot meet the signal-to-noise ratio requirement under the condition of the adaptable wavelength. Based on this, by increasing the wavelength range and optimizing the position measurement results at different wavelengths, the measurement accuracy is improved. However, the multi-wavelength scheme will not only increase the design complexity of the optical system but may also require additional operation steps during the measurement process, increasing the measurement cost and reducing the measurement efficiency. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a method for optimizing a grating structure to reduce position measurement errors, including:

[0006] Step S1, establishing an evaluation function of the phase grating structure according to the intensities of signals of different diffraction orders;

[0007] Step S2, selecting an initial grating structure according to the evaluation function;

[0008] Step S3, substituting the initial grating structure into the deformation model caused by the manufacturing process to generate a deformed grating structure;

[0009] Step S4, comparing the initial grating structure and the deformed grating structure to give multiple groups of grating arrangement combinations for comparison;

[0010] Step S5: According to the preset board manufacturing process, fabricate boards for multiple groups of the grating arrangement combinations to produce a marked measurement board for experiments.

[0011] Step S6: Measure each group of the grating arrangement combinations on the marked measurement board, analyze the measurement results, and establish a corresponding relationship between the grating structure deformation and the introduced position error.

[0012] Step S7: According to the preset error control requirements and in combination with the corresponding relationship, optimize the design of the initial grating structure to obtain an optimized grating structure.

[0013] Preferably, the evaluation function is:

[0014]

[0015] where W is the evaluation function, w m is the weight of the m-th diffraction order, η m is the diffraction efficiency of the m-th diffraction order, and is the possible maximum diffraction efficiency of the m-th diffraction order.

[0016] Preferably, the weight w m is configured according to the following principle:

[0017] For odd diffraction orders, the higher the diffraction order, the higher the configured weight; for even diffraction orders and the zero diffraction order, negative weights are assigned.

[0018] Preferably, substitute the above diffraction efficiency into the evaluation function, and select one or more structures with better results as the initial grating structure. Among them, for any known-phase grating structure, the diffraction efficiency can be calculated using the rigorous coupled-wave theory.

[0019] Furthermore, the above deformation model simultaneously includes deformation parameters that describe the deformation type and the deformation degree.

[0020] Furthermore, for each group of corresponding initial grating structures and deformed grating structures, according to the number of gratings in the group and the deformation parameters, multiple groups of grating arrangement combinations for comparison are given.

[0021] Furthermore, the grating arrangement combinations can be used to compare the initial grating structures and the deformed grating structures with the same deformation type but different deformation degrees; compare the initial grating structures and the deformed grating structures with the same deformation degree but different deformation types; and compare the initial grating structures with different structures.

[0022] Furthermore, the board manufacturing process includes a mask manufacturing process or a basic silicon wafer manufacturing process.

[0023] Furthermore, applying the above method to optimize the initial grating structure with a certain degree of deformation can achieve high-precision position measurement of the phase grating position measurement system within the range of error control requirements.

[0024] Compared with the prior art, the grating structure optimization method for reducing position measurement error provided by the present invention has at least the following beneficial effects:

[0025] (1) Through the grating structure optimization method for reducing position measurement error provided by the present invention, an optimized grating structure is obtained, which can at least partially alleviate the influence of deformation introduced during the manufacturing process on the position measurement accuracy, reduce the position measurement error, and ensure the position measurement accuracy.

[0026] (2) Compared with the multi-wavelength scheme, not only will it increase the design complexity of the optical system, but it may also require additional operation steps during the measurement process. Through the

[0027] grating structure optimization method for reducing position measurement error provided by the present invention, an optimized grating structure is obtained, and it is used in the phase grating position measurement system to achieve the purpose of reducing the measurement position error and ensuring the position measurement accuracy. The problems of increased measurement cost and reduced measurement efficiency are avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the flowchart of the implementation of the embodiment of the present invention;

[0029] Figure 2 is the schematic cross-sectional view of the periodic phase grating structure;

[0030] Figure 3 is the schematic cross-sectional view of an initial grating structure;

[0031] Figure 4 is the schematic cross-sectional view of an initial grating structure and a deformed grating structure;

[0032] Figure 5 is the schematic layout diagram of an initial grating structure and a series of deformed grating structures with the same deformation type but different deformation degrees;

[0033] Figure 6 is the schematic layout diagram of an initial grating structure and a series of deformed grating structures with the same deformation degree but different deformation types;

[0034] Figure 7 is the schematic layout diagram of a series of initial grating structures with different structures;

[0035] Figure 8 is the schematic diagram of the measurement mark plate making. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings.

[0037] The present invention provides a method for optimizing a grating structure to reduce position measurement errors. By optimizing the grating structure, simulating structural deformation, and conducting information comparison, etc., before actual measurement, a correspondence relationship between grating structure deformation and measurement errors is established. In the original measurement system, through the optimized design of a specific structure, the deformation errors caused by process steps can be alleviated. The lithography process is the most complex and crucial step in the semiconductor chip production process. In this step, by adopting the method proposed in this patent, while improving the alignment accuracy, the measurement time and cost can also be saved.

[0038] To obtain a grating structure with reduced position measurement errors, first, according to the intensities of signals of different diffraction orders, an evaluation method for a phase grating structure is established to describe the advantages and disadvantages of structural parameter design. Then, one or more grating structures with better results are selected as the initial grating structure according to this evaluation method. Next, one or more deformed grating structures are generated based on the possible deformations during the manufacturing process. Then, multiple sets of grating arrangement combinations for comparison are given by comparing the above initial grating structure and the deformed grating structures, and experimental marker measurement plates are processed by making plates for the above multiple sets of grating arrangement combinations. Immediately afterwards, a correspondence relationship between grating structure deformation and the introduced position errors is established based on the comparison measurement results. Finally, the initial grating structure is optimized according to the above correspondence relationship to obtain the optimized grating structure.

[0039] Figure 1 The flowchart of an embodiment of a method for optimizing a grating structure to reduce position measurement errors according to an embodiment of the present invention is schematically shown.

[0040] As Figure 1 shown, a method for optimizing a grating structure to reduce position measurement errors according to this embodiment may include the following steps:

[0041] Step S1, establish an evaluation function for the phase grating structure according to the intensities of signals of different diffraction orders.

[0042] As Figure 2As shown, in the phase grating position measurement system, the position information is contained in the odd-order diffracted light signals of the phase grating, while the zero-order and even-order diffracted lights are stray lights introducing noise. Among the odd-order diffracted lights, the diffracted lights of orders ±1, ±3, ±5, ±7, and ±9 are usually used as measurement signals. Among them, the 1st and 3rd diffraction orders are usually used to expand the measurement range, while the 5th, 7th, and 9th diffraction orders are used to improve the measurement accuracy. Therefore, by assigning different weights to the intensities of signals of different diffraction orders, an evaluation function of the phase grating structure can be given.

[0043] Preferably, the evaluation function is:

[0044]

[0045] where W is the evaluation function, w m is the weight of the mth diffraction order, η m is the diffraction efficiency of the mth diffraction order, is the maximum possible diffraction efficiency of the mth diffraction order.

[0046] Among them, for the weight w m of the mth diffraction order, the configuration needs to follow the following principles:

[0047] To improve the measurement accuracy, higher weights need to be assigned to higher odd diffraction orders; and since the intensities of the zero diffraction order light and even diffraction order lights are negatively correlated with the measurement accuracy, negative weights need to be assigned to the zero diffraction order and even diffraction orders.

[0048] Preferably, the weights can be configured as:

[0049] {w m} = {-0.6, -0.1, -0.1, -0.1, -0.1} where m = 0, 2, 4, 6, 8;

[0050] {w m} = {0.25, 0.3, 0.45, 0.5, 0.5} where m = 1, 3, 5, 7, 9.

[0051] Step S2, select an initial grating structure according to the evaluation function.

[0052] Specifically, for any phase grating with a known structure, the diffraction efficiency of each diffraction order of the phase grating can be calculated using the rigorous coupled-wave theory. Therefore, the diffraction efficiencies of each diffraction order of each phase grating can be substituted into the above evaluation function respectively, and one or more structures with better results can be selected as the initial grating structure. A schematic cross-sectional view of one of the initial grating structures is as Figure 3 shown.

[0053] Step S3: Substitute the initial grating structure into the deformation model caused by the manufacturing process to generate the deformed grating structure.

[0054] Specifically, substitute the initial grating structure selected in step S2 into the deformation model caused by the manufacturing process. Depending on the different deformation models, multiple deformed grating structures can be obtained.

[0055] Among them, the deformation model contains deformation parameters that describe both the deformation type and the degree of deformation.

[0056] As Figure 4 shown, it is a schematic cross-sectional view of an initial grating structure and the deformed grating structure obtained after the above step S3.

[0057] Step S4: Compare the initial grating structure and the deformed grating structure, and give multiple groups of grating arrangement combinations for comparison.

[0058] Specifically, compare and measure one or more initial grating structures and deformed grating structures obtained in step S2 and step S3. Depending on the number of gratings and the deformation parameters in each group, multiple grating arrangement combinations for comparison can be given respectively.

[0059] One group of arrangement combinations can be as Figure 5 shown. This arrangement can be used to compare the deformed grating structure with the same deformation type but different degrees of deformation with the initial grating structure. Among them, SM0 represents the initial grating structure in the reference position; DM1, DM2, and DM3 represent a series of deformed grating structures with the same deformation type but different degrees of deformation.

[0060] Another arrangement combination can be as Figure 6 shown. This arrangement can be used to compare the deformed grating structure with the same degree of deformation but different deformation types with the initial grating structure. Among them, 1, 2, 3, and 4 represent the initial grating structures; 5, 6, 7, and 8 represent the deformed grating structures. (U), (D), (L), and (R) represent different deformation types.

[0061] Another arrangement combination can be as Figure 7 shown. This arrangement can be used to compare the initial grating structures with different structures. The figures in the four quadrants of the diagram can respectively correspond to the initial grating structures with different structural parameters.

[0062] Step S5: Plate multiple groups of the grating arrangement combinations according to the preset plate-making process to process the marker measurement plate for experiments.

[0063] Specifically, according to the preset board manufacturing process, the processing drawings of the measurement templates used in the experiment are given, and then an appropriate board manufacturing process is selected to process the marked measurement board for the experiment.

[0064] Among them, the board manufacturing process includes, but is not limited to, the mask manufacturing process or the basic silicon wafer manufacturing process.

[0065] One of the plate-making styles can be as Figure 8 shown. The area within the dotted line frame in the figure is the distribution area of the grating structure design, which may include one or more grating arrangement combinations for comparison in step S4.

[0066] Step S6: Measure each group of the grating arrangement combinations on the marked measurement board, analyze the measurement results, and establish the corresponding relationship between the grating structure deformation and the introduced position error.

[0067] Specifically, according to the measurement scheme, measure each group of the grating arrangement combinations for comparison on the measurement template. By analyzing the measurement results of each group, the corresponding relationship between the grating structure deformation and the introduced position error can be given.

[0068] Step S7: According to the preset error control requirements, combined with the corresponding relationship, optimize the design of the initial grating structure to obtain the optimized grating structure.

[0069] Specifically, according to the error control requirements of the actual position measurement system applied, combined with the corresponding relationship between the deformation and the position error obtained in step S6, perform corresponding optimization design on the initial grating structure, and an optimized phase grating structure that can still meet the measurement accuracy requirements even after a certain degree of deformation can be given.

[0070] In summary, through the grating structure optimization method for reducing position measurement error provided by the present invention, an optimized grating structure is obtained, which can be used in a phase grating position measurement system, at least partially alleviate the influence of the deformation introduced in the manufacturing process on the position measurement accuracy, achieve the purpose of reducing the position measurement error and ensuring the position measurement accuracy, and will not increase the design complexity of the optical system. While achieving the above purpose, the measurement efficiency is ensured.

[0071] The specific embodiments described above have further elaborated on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An optimization method for a grating structure to reduce position measurement error, characterized in that Including: Step S1: Establish an evaluation function for the phase grating structure according to the intensities of signals of different diffraction orders. Step S2: Select an initial grating structure according to the evaluation function. Step S3: Substitute the initial grating structure into the deformation model caused by the manufacturing process to generate a deformed grating structure. Step S4: Compare the initial grating structure and the deformed grating structure, and give multiple sets of grating arrangement combinations for comparison. Step S5: Perform plate making on multiple sets of the grating arrangement combinations according to the preset plate making process to process a marked measurement plate for experiments. Step S6: Measure each set of the grating arrangement combinations on the marked measurement plate, analyze the measurement results, and establish a corresponding relationship between the deformation of the grating structure and the introduced position error. Step S7: According to the preset error control requirements and in combination with the corresponding relationship, optimize the design of the initial grating structure to obtain an optimized grating structure.

2. The method for optimizing a grating structure to reduce position measurement error according to claim 1, characterized in that, In the said Step S1, the evaluation function is: Among them, is the evaluation function, is the weight of the m-th diffraction order, is the diffraction efficiency of the m-th diffraction order, is the maximum diffraction efficiency of the m-th diffraction order.

3. The method for optimizing a grating structure to reduce position measurement error according to claim 2, characterized in that The weights are configured according to the following principles: For odd diffraction orders, the higher the diffraction order, the higher the configured weight; for even diffraction orders and the zero diffraction order, negative weights are assigned.

4. The method for optimizing a grating structure to reduce position measurement error according to claim 1, characterized in that, The said Step S2 includes: Substitute the diffraction efficiencies of each diffraction order of a phase grating with any known structure into the evaluation function, and select one or more phase gratings with better results as the initial grating structure. Among them, for a phase grating with any known structure, the diffraction efficiencies of each diffraction order are calculated by the rigorous coupled-wave theory.

5. The method for optimizing a grating structure to reduce position measurement error according to claim 1, wherein The deformation model simultaneously includes deformation parameters describing the deformation type and the deformation degree.

6. The method for optimizing a grating structure to reduce position measurement error according to claim 5, characterized in that The said Step S4 includes: For each set of the corresponding initial grating structure and the deformed grating structure, according to the number of gratings in each set and the deformation parameters, give multiple sets of grating arrangement combinations for comparison.

7. The optimized method for grating structure to reduce position measurement error according to claim 5, characterized in that The grating arrangement combinations are used for comparison in at least one of the following ways: The initial grating structure and the deformed grating structure with the same deformation type but different deformation degrees; The initial grating structure and the deformed grating structure with the same deformation degree but different deformation types; Initial grating structures with different structures.

8. The method for optimizing a grating structure to reduce position measurement error according to claim 1, characterized in that In the said Step S5, the plate making process includes a mask plate manufacturing process or a basic silicon wafer manufacturing process.

9. The method for optimizing a grating structure to reduce position measurement error according to claim 1, characterized in that, Apply the method to optimize the initial grating structure that generates deformation and reduce the position measurement error.

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