A stepped calibration plate for grating profile characterization and a preparation method thereof

Abstract

The present application relates to the technical field of semiconductor optoelectronic devices, and discloses a stepped debugging sheet for grating topography characterization and a preparation method thereof.The stepped debugging sheet comprises a first diagnostic unit distributed in a central region of a substrate, a second test unit distributed in a middle region of the substrate, and a third diagnostic unit distributed in an edge region of the substrate, the second test unit is provided with a stepped observation substructure, and the first diagnostic unit and the third diagnostic unit are both provided with a topography correlation substructure and a multi-parameter substructure; the topography correlation substructure comprises a contrast grating group, and the contrast grating group comprises a non-etched photoresist grating and an etched material grating arranged side by side.The stepped debugging sheet for grating topography characterization and the preparation method thereof can not only make test data truly reflect the performance of the process on the whole substrate, but also simplify the layout complexity of a single test unit and improve the feasibility of preparation.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device technology, and in particular to a stepped debugging chip for grating morphology characterization and its preparation method. Background Technology

[0002] In the fabrication of devices such as DFB lasers and silicon photonics chips, the optical performance of the devices is highly dependent on the morphology of the grating. In traditional processes, to evaluate the etching depth, duty cycle, and sidewall angle of the grating, it is usually necessary to cleave the chip sample, including the target grating, in a direction perpendicular to the grating, and then observe the cross-section using a scanning electron microscope. The width of the target grating region is typically only 10 to 20 micrometers, and the success rate of precise cleaving in such a narrow area is very low, hindering the efficiency of process development and monitoring.

[0003] To address the aforementioned observation challenges, Chinese patent CN111562723B proposes arranging multiple grating units in a stepped, staggered pattern along the direction perpendicular to the grating on a test wafer. This ensures that when performing lateral cleaving at any location, the cross-section will likely capture at least one complete grating section, thereby improving the observation success rate. However, this patented technology only improves the success rate of single-point observations and does not consider the morphological inhomogeneity issues caused by the inherent center-edge effect of the etching process on large-area wafers (e.g., 8-inch or 12-inch wafers). An isolated observation point cannot reflect the uniformity of the entire wafer or process cavity, potentially leading to biased process debugging conclusions. Summary of the Invention

[0004] Therefore, the purpose of this invention is to overcome the problem of morphological inhomogeneity caused by the inherent center-edge effect in the etching process in the prior art. This invention provides a stepped test piece for grating morphology characterization and its preparation method, which can enable the test data to truly reflect the performance of the process on the entire substrate (wafer), realize a comprehensive process diagnosis of the uniformity of the entire substrate or process cavity, and simplify the layout complexity of a single test unit, thereby improving the feasibility of preparation.

[0005] To address the aforementioned technical problems, the present invention provides a stepped debugging sheet for grating morphology characterization, comprising a test array distributed on a substrate. The test array includes a first diagnostic unit, a second test unit, and a third diagnostic unit. The first diagnostic unit is distributed in the central region of the substrate, the second test unit is distributed in the middle region of the substrate, and the third diagnostic unit is distributed in the edge region of the substrate.

[0006] The second test unit is provided with a stepped observation substructure, which includes a plurality of first grating strips, the first grating strips being arranged in a stepped, staggered manner along a direction perpendicular to the length of their internal grating lines;

[0007] Both the first diagnostic unit and the third diagnostic unit are provided with a morphology correlation substructure and a multi-parameter substructure in parallel; the morphology correlation substructure includes a contrast grating group, which includes unetched photoresist gratings and etched material gratings arranged in parallel; the multi-parameter substructure includes a grating array, which includes multiple sets of grating units with different duty cycles.

[0008] On the other hand, the present invention provides a method for preparing a stepped adjustment piece for grating morphology characterization, comprising the following steps:

[0009] A photoresist layer is formed on the substrate;

[0010] The composite pattern is transferred to the photoresist layer, and the exposure dose is set for different pattern areas to obtain the exposed photoresist layer.

[0011] The exposed photoresist layer is developed to form a developed pattern, so that a photoresist residue layer is formed on the substrate area corresponding to the photoresist grating pattern, and the thickness of the photoresist residue layer is 5 nanometers to 15 nanometers.

[0012] Using the developed pattern as a mask, the substrate is etched once to form a stepped observation substructure, a morphology-related substructure, and a multi-parameter substructure.

[0013] Remove the residue from the substrate surface to obtain the stepped adjustment piece used for grating morphology characterization.

[0014] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0015] The stepped calibration wafer for grating morphology characterization described in this invention integrates test units with different functions in the central, intermediate, and edge regions of the substrate (wafer). The intermediate region is responsible for macroscopic uniformity observation (corresponding to the stepped observation substructure), while the central and edge regions are responsible for microscopic process analysis (corresponding to morphology-related substructures and multi-parameter substructures). This ensures that the test data accurately reflects the process performance on the entire substrate. Furthermore, the partitioning of observation and analysis functions avoids interference between complex functional structures (i.e., stepped observation substructures, corresponding morphology-related substructures, and multi-parameter substructures) in the same region. While maintaining diagnostic dimensionality, this simplifies the layout complexity of individual regions (i.e., test units) and improves fabrication feasibility.

[0016] The method for fabricating a stepped test piece for grating morphology characterization, as described in this invention, involves setting the exposure dose for different patterned regions. After development, a residual photoresist layer is formed on the substrate region corresponding to the photoresist grating pattern, enabling the formation of a stepped test piece for grating morphology characterization through a single etching process. Since all functional structures are fabricated in the same etching process, the test data obtained from different regions (central region, intermediate region, and edge region) exhibit spatiotemporal correlation, providing a technological and structural basis for subsequent problem localization and cause analysis. Attached Figure Description

[0017] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0018] Figure 1 This is a schematic diagram of a stepped debugging piece used for grating morphology characterization in an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of a stepped observation substructure in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of a structure of the first grating strip in an embodiment of the present invention.

[0021] Figure 4 This is a schematic diagram of a test unit in an embodiment of the present invention.

[0022] Figure 5 This is a partial schematic diagram of the composite layout graphic in an embodiment of the present invention.

[0023] Figure 6 This is a schematic flowchart illustrating a method for preparing a stepped adjustment piece for grating morphology characterization in an embodiment of the present invention.

[0024] Explanation of reference numerals in the accompanying drawings: 11. Central region; 12. Middle region; 13. Edge region; 14. Invalid region; 21. First diagnostic unit; 22. Second test unit; 23. Third diagnostic unit; 3. Stepped observation substructure; 31. First grating strip; 411. Photoresist grating; 412. Material grating; 511. Grating unit; 6. Transition pattern; 71. First strip pattern; 72. Second strip pattern. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0026] To achieve comprehensive etching process diagnostics, three functional structures—a stepped observation substructure, a morphology-related substructure, and a multi-parameter substructure—can be integrated within the same test unit. While this test unit offers comprehensive functionality, its implementation is challenging. Traditional techniques for obtaining such a test unit require unconventional step-by-step etching processes. These processes are difficult to control, have poor repeatability, and can easily affect the stability of the equipment cavity. In particular, the morphology-related substructure requires the inclusion of an unetched photoresist grating 411. During the complex step-by-step etching process, the photoresist grating 411 is easily damaged or contaminated, leading to morphological distortion of the photoresist grating 411 as a pre-etching reference, thus rendering comparative analysis ineffective.

[0027] To avoid using complex processes such as step-by-step etching, and to eliminate mutual interference caused by the integration of multifunctional structures, thereby reducing the fabrication difficulty and process risk of the debug sheet itself, this invention provides a stepped debug sheet for grating morphology characterization and its fabrication method.

[0028] The stepped debugging wafer obtained in this application includes a test array with a first diagnostic unit, a second test unit, and a third diagnostic unit, obtained through a single etching process. The first diagnostic unit is distributed in the central region of the substrate, the second test unit is distributed in the middle region of the substrate (wafer), and the third diagnostic unit is distributed in the edge region of the substrate. Furthermore, the second test unit has a stepped observation substructure, which includes multiple first grating strips. Both the first and third diagnostic units have parallel morphology correlation substructures and multi-parameter substructures. The morphology correlation substructure includes a set of parallel-arranged comparison gratings of unetched photoresist gratings and etched material gratings, and the multi-parameter substructure includes multiple sets of grating units with different duty cycles.

[0029] When using this stepped test wafer for grating morphology characterization for etching process diagnostics, a transverse cleavage is performed along the radial direction of the wafer to obtain a cross-section that runs through the central region, intermediate region, and edge region. When observing the cross-section using a scanning electron microscope, the following can be simultaneously observed: the cross-section of the first grating strip in the intermediate region, the cross-section of the morphology-related substructure in the central and edge regions, and the cross-section of the multi-parameter substructure.

[0030] Based on the cross-section of the first grating strip, the morphological parameters (e.g., etching depth, sidewall angle, linewidth) of the first grating strip at different radial positions (corresponding to different positions on the wafer) are measured. The morphological parameters of the first grating strip are correlated with the positional information to plot a positional morphological parameter curve of the first grating strip, reflecting the uniformity trend of the etching process on the wafer. For example, if the etching depth in the edge region is significantly less than the etching depth in the center region, it indicates the presence of a center-edge effect.

[0031] By directly comparing the unetched photoresist grating (reference) with the etched material grating (result) using cross-sections of morphology-related substructures, the overall offset or error of the etching process can be evaluated. Specifically, this includes:

[0032] Since the unetched photoresist grating area is a flat surface with a straight cross-section, representing the reference surface before etching, while the etched material grating cross-section exhibits a periodic convex and concave structure, by measuring the etching depth of the material grating and comparing it with the reference surface, the actual removal amount of the etching process can be directly obtained. Therefore, the systematic deviation of the etching depth can be evaluated based on the actual removal amount and the target removal amount.

[0033] By comparing the flat surface of the photoresist grating with the periodic structure of the material grating, it is possible to intuitively determine whether problems such as structural deformation, sidewall tilting, and increased bottom roughness have occurred during the etching process, and thus evaluate the morphological transfer fidelity of the pattern from the photoresist to the substrate material.

[0034] If the morphology-related substructures set in the central and edge regions show significant differences, for example, the etching depth of the material grating in the edge region is lower than that in the central region, then the spatial distribution characteristics of process fluctuations can be further confirmed by combining the uniformity trend of the first grating strip.

[0035] Based on the cross-section of the multi-parameter substructure, the morphological parameters of grating units with different duty cycles are measured, and the relationship curves between duty cycle and actual morphological parameters are plotted to reflect the sensitivity of the etching process to different design parameters, thereby determining the optimal process window (e.g., duty cycle). Furthermore, by comparing the morphological differences of grating units in different regions (central and edge regions) under the same duty cycle, the impact of etching process uniformity on different process windows can be evaluated, providing a basis for the sensitivity of design parameters to subsequent etching process optimization.

[0036] Since all functional structures are formed synchronously in the same exposure and etching process, the test data (e.g., morphology parameters) obtained from the central, intermediate, and edge regions are spatially and temporally correlated. Therefore, by combining and analyzing the test data from these three regions, a comprehensive process diagnostic of the uniformity of the entire substrate (wafer) or process cavity can be achieved.

[0037] For example, by spatially superimposing the uniformity trend of the first grating strip with the local deviation data of the morphology-related substructure, a distribution map of key parameters such as etching depth and sidewall angles across the entire wafer can be drawn to identify systematic non-uniformity patterns within the process cavity, such as radial gradient deviation and symmetry deviation.

[0038] For example, by combining the relationship curves between duty cycle and morphology parameters in multi-parameter substructures, the consistency of the process window in different regions can be analyzed. If a certain duty cycle performs well in the central region but shows morphology deterioration in the edge region, it indicates that the etching process is location-sensitive and further optimization of etching conditions is needed.

[0039] Example 1: This example discloses a stepped adjustment chip for grating morphology characterization.

[0040] To ensure that the test data accurately reflects the etching process across the entire substrate while simplifying the layout complexity of individual test units and improving fabrication feasibility, the stepped test wafer used for grating morphology characterization in this embodiment integrates test units with different functions in the central region 11, middle region 12, and edge region 13 of the substrate (wafer). This partitions the observation and analysis functions, preventing interference between the stepped observation substructure 3, corresponding morphology-related substructures, and multi-parameter substructures within the same test unit.

[0041] The substrate of the stepped debugging chip in this embodiment can be a wafer.

[0042] In applications, the wafer can be a circular semiconductor wafer, such as a circular silicon wafer. Furthermore, the wafer diameter can be 6 inches, 8 inches, or 12 inches.

[0043] In practical applications, the substrate includes an effective region and an ineffective region 14 surrounding the effective region. (See reference) Figure 1 The effective area consists of a central area 11, a middle area 12, and an edge area 13, arranged sequentially from the center to the outer edge. The edge area 13 connects to the ineffective area 14.

[0044] In actual implementation, the ratio of the radial width of the central region 11, the radial width of the middle region 12, and the radial width of the edge region 13 is 1:(1~2):(1~1.5). Preferably, the ratio of the radial width of the central region 11, the radial width of the middle region 12, and the radial width of the edge region 13 is 1:1.5:1.

[0045] The stepped debug chip in this embodiment includes a test array distributed on a substrate, and the test array includes multiple test units.

[0046] In application, the test unit includes a first diagnostic unit 21, a second test unit 22, and a third diagnostic unit 23. Furthermore, the first diagnostic unit 21, the second test unit 22, and the third diagnostic unit 23 can be obtained through a single etching process. Even further, multiple test units can be arranged in a periodic rectangular grid.

[0047] In practical applications, the first diagnostic unit 21 is located in the central region 11 of the substrate, the second test unit 22 is located in the middle region 12 of the substrate, and the third diagnostic unit 23 is located in the edge region 13 of the substrate. Further, the first diagnostic unit 21 is disposed within the central region 11, or on the boundary line between the central region 11 and the middle region 12. The second test unit 22 is disposed within the middle region 12, or on the boundary line between the middle region 12 and the edge region 13. The third diagnostic unit 23 is disposed within the edge region 13.

[0048] To achieve functional integration through system integration, the second test unit 22 in this embodiment is provided with a stepped observation substructure 3. Both the first diagnostic unit 21 and the third diagnostic unit 23 are provided with a morphology-related substructure and a multi-parameter substructure side-by-side. Furthermore, the morphology-related substructure and the multi-parameter substructure are arranged side-by-side along the substrate radial direction, with an isolation gap between them. The substrate radial direction is the wafer radial direction. Even further, the width of the isolation gap is 50 micrometers to 200 micrometers. Preferably, it is 150 micrometers.

[0049] refer to Figure 2 The stepped observation substructure 3 in this embodiment includes multiple first grating strips 31.

[0050] When applying, refer to Figure 2 and Figure 3 The first grating strips 31 are arranged in a stepped, staggered pattern along a direction perpendicular to the length of their internal grating lines to ensure that multiple strip cross-sections can be captured by any lateral cleaving. Specifically, the grating lines within the first grating strips 31 are oriented radially perpendicular to the substrate; the first grating strips 31 are arranged radially along the substrate within the test unit. Furthermore, each of the first grating strips 31 includes at least two steps. Even further, the length of each step is between 5 micrometers and 30 micrometers.

[0051] In practical applications, all first grating strips 31 have the same period and duty cycle (e.g., a period of 310 nanometers and a duty cycle of 50%). The spacing between any two adjacent first grating strips 31 is greater than or equal to the width of the first grating strip 31.

[0052] The topography correlation substructure in this embodiment includes a contrast grating group. (Reference) Figure 4 The comparison grating group includes an unetched photoresist grating 411 and an etched material grating 412 arranged side-by-side. Furthermore, the photoresist grating and the material grating are arranged side-by-side radially along the substrate. During evaluation, directly comparing the test data of the photoresist grating 411 and the material grating 412 can reveal errors in the transfer process from the composite pattern to the target device structure.

[0053] In application, the photoresist grating 411 is a flat silicon surface, specifically a flat substrate region, serving as a morphological reference before the etching process. The material grating 412 is a periodic nanograting structure etched on the substrate.

[0054] The multi-parameter substructure of this embodiment includes a grating array, wherein the grating array, photoresist grating, and material grating are arranged in parallel along the radial direction of the substrate. (Reference) Figure 4 The grating array includes multiple sets of grating units 511, each set of grating units 511 having a different duty cycle.

[0055] In application, the grating array is a rectangular array, with each row of grating units 511 having the same duty cycle, and the duty cycles of each row of grating units 511 are set in a gradient (e.g., a duty cycle gradient from 30%, 40%, 50% to 60%).

[0056] It is worth noting that the direction of the grating lines inside the material grating 412 and each grating unit 511 is parallel to the direction of the grating lines inside the first grating strip 31, and the grating structures inside the material grating 412, the first grating strip 31 and the grating units 511 have the same period.

[0057] Example 2: This example discloses a method for preparing a stepped adjustment sheet for grating morphology characterization, which can obtain the stepped adjustment sheet for grating morphology characterization described in Example 1.

[0058] Topography correlation testing requires preserving the unetched photoresist baseline pattern, while uniformity testing requires etching the material. It is difficult to achieve both in the same etching process step, and usually requires complex multi-step etching or additional mask protection processes, which increases cost, complexity and error.

[0059] To fabricate the stepped observation substructure 3, the morphology-related substructure, and the multi-parameter substructure simultaneously on the same substrate (wafer), this embodiment improves the design of the composite pattern and the type and ratio of etching gases. The three major functional modules of the morphology-related substructure, the multi-parameter substructure, and the stepped observation substructure 3 are integrated into the same wafer and fabricated simultaneously in one step. This solves the process contradiction between etching and protection, and eliminates the need for additional masks or step-by-step etching processes, thereby improving the information dimension and efficiency of etching process debugging.

[0060] For details, please refer to Figure 6 The method for preparing the stepped debugging piece in this embodiment includes steps S1 to S5.

[0061] Step S1 forms a photoresist layer on the substrate.

[0062] In applications, the substrate is a wafer, and more specifically, the wafer is a circular semiconductor wafer, such as a circular silicon wafer.

[0063] In practical applications, the target thickness of the photoresist layer is determined based on the graphic feature dimensions, etching depth, and photoresist type of the composite pattern. For example, the target thickness may be 300 nanometers or 500 nanometers, preferably 300 nanometers. Further, liquid photoresist is uniformly coated onto the surface using a spin-coating process, followed by pre-baking curing to form the photoresist layer.

[0064] The composite layout pattern includes the corresponding test array. Further, the pattern corresponding to the second test unit 22 (i.e., the second test unit pattern) in the composite layout pattern includes the pattern corresponding to the stepped observation substructure 3, i.e., the stepped observation substructure pattern. The patterns corresponding to the first diagnostic unit 21 and the third diagnostic unit 23 (i.e., the first diagnostic unit pattern and the third diagnostic unit pattern) in the composite layout pattern include the patterns corresponding to the topography-related substructure and the multi-parameter substructure, i.e., the topography-related substructure pattern and the multi-parameter substructure pattern.

[0065] The composite pattern corresponding to the stepped observation substructure 3 includes patterns corresponding to multiple sets of first grating strips 31, i.e., first grating strip patterns. The composite pattern corresponding to the multi-parameter substructure includes patterns corresponding to multiple sets of grating units 511 with different duty cycles, i.e., grating unit patterns. The composite pattern corresponding to the morphology-related substructure includes patterns corresponding to photoresist gratings 411 and material gratings 412, i.e., photoresist grating patterns and material grating patterns.

[0066] The feature dimensions of the composite pattern are the duty cycle and period of the grating lines within the pattern corresponding to the first grating strip 31, grating unit 511, and material grating 412. Further, the duty cycle and period of the grating lines are determined based on the optical performance of the target device (e.g., emission wavelength, mode coupling coefficient). The etching depth of the composite pattern is determined based on the optical coupling strength or electrical performance of the target device.

[0067] In practical implementation, the photoresist type can be determined based on the graphic feature size and etching depth of the composite pattern. The resolution of the photoresist should meet the minimum graphic feature size, i.e., be able to create grating lines with steep sidewalls and smooth edges. Furthermore, the target thickness of the photoresist layer is determined based on the etching depth of the composite pattern and the etching selectivity of the photoresist.

[0068] Step S2: Transfer the composite pattern to the photoresist layer, and set the exposure dose for different pattern areas to obtain the exposed photoresist layer.

[0069] In application, the composite pattern is written into the photoresist layer, and the exposure dose of the pattern area corresponding to the photoresist grating 411 in the composite pattern is modulated to obtain the exposed photoresist layer.

[0070] In practical applications, step S2 includes steps S21 to S22.

[0071] Step S21: Using electron beam direct writing exposure technology, transfer the composite pattern to the photoresist layer.

[0072] In application, an electron beam direct writing exposure system is used to control the electron beam to scan and irradiate the device (a wafer with a photoresist layer) point by point, thereby transforming the geometric patterns in the composite pattern into specific chemical property change regions inside the photoresist layer.

[0073] In practical applications, refer to Figure 5 In the composite pattern, a transition pattern 6 is provided around the photoresist grating pattern.

[0074] Furthermore, the transition pattern 6 is a dot array surrounding the photoresist grating pattern, with the distance between the dot array and the boundary of the photoresist grating pattern ranging from 0.5 micrometers to 2 micrometers. The diameter of each dot in the dot array is 50 nanometers to 150 nanometers, and the spacing between dots is 100 nanometers to 300 nanometers. For example, a dot diameter of 100 nanometers and a dot spacing of 200 nanometers.

[0075] Step S22: Set the exposure dose for each zone of the composite pattern.

[0076] In application, the exposure dose of the patterned area corresponding to the photoresist grating pattern in the composite pattern is the first dose; the exposure dose of the patterned area of ​​the transition pattern 6 set around the morphology-related substructure pattern in the composite pattern is the second dose; and the exposure dose of the patterned areas of other patterns in the composite pattern is the third dose. These other patterns include the second test unit pattern, the multi-parameter substructure pattern, and the material grating pattern in the composite pattern. Furthermore, the first dose is less than the third dose, and the second dose is greater than the third dose.

[0077] In practical applications, based on the electron beam proximity effect, by setting the first dose and the second dose, and arranging the transition pattern 6, the total energy deposition of the patterned area of ​​the photoresist grating 411 is lower than the critical dose for complete development, so that the patterned area of ​​the corresponding photoresist grating 411 retains a photoresist residue layer after development.

[0078] Furthermore, the total energy deposition received by the patterned region of the photoresist grating 411 is slightly below the critical dose for complete development. The total energy deposition received by the patterned region of the photoresist grating 411 is adjusted to 90% to 99% of the complete development threshold to facilitate the subsequent formation of a photoresist residue layer with a thickness of 5 to 15 nanometers.

[0079] The critical dose for complete development is the minimum exposure dose required to completely dissolve the photoresist layer after development (i.e., develop to the substrate surface) without leaving any residue (photoresist). The total energy received by the patterned area of ​​the photoresist grating 411 refers to the total electron energy absorbed by each point within the patterned area of ​​the photoresist grating 411 during electron beam exposure, including direct incident energy and scattering contribution energy. Direct incident energy is the energy of the electron beam directly irradiating the patterned area of ​​the photoresist grating 411. Scattering contribution energy is the additional energy from electrons scattered from other exposed areas (e.g., the patterned area of ​​transition pattern 6) to the patterned area of ​​the photoresist grating 411.

[0080] In some embodiments, the first dose is determined based on an experimental calibration curve between the photoresist residual layer thickness and the exposure dose. Further, the first dose is 0.5 to 0.8 times the critical dose for complete development. Even further, the exposure dose corresponding to a photoresist residual layer thickness of 5 nanometers to 15 nanometers is selected as the first dose from the experimental calibration curve between the photoresist residual layer thickness and the exposure dose.

[0081] It is worth noting that the method for preparing the experimental calibration curve between the thickness of the photoresist residual layer and the exposure dose includes steps S2211 to S2215.

[0082] Step S2211: Form a first test photoresist layer on the first test substrate.

[0083] In application, the first test substrate is identical in material, shape, and size to the first test substrate. The thickness of the first test photoresist layer is also identical to that of the first test substrate.

[0084] Step S2212: Set the first test pattern; write the first test pattern into the first test photoresist layer on the first test substrate.

[0085] In application, the first test pattern includes multiple identical first test patterns. Furthermore, the first test pattern can be a photoresist grating pattern.

[0086] Step S2213: Using an electron beam exposure system, apply different values ​​of first test exposure dose to the pattern areas corresponding to different first test patterns on the first test photoresist layer to obtain the first test device after exposure.

[0087] In applications, exposure dose refers to the amount of charge received by a unit area of ​​photoresist during electron beam exposure.

[0088] In practical applications, the different values ​​of the first test exposure dose cover a range from far below the estimated critical dose for complete development to slightly above the estimated critical dose for complete development. For example, different values ​​of the first test exposure dose include 80 μC / cm². 2 90μC / cm 2 100μC / cm 2 110μC / cm 2 120μC / cm 2 130μC / cm 2 140μC / cm 2 150μC / cm 2 160μC / cm 2 170μC / cm 2 .

[0089] Step S2214: Place the first test device after exposure into the developing solution for development.

[0090] In application, the entire first test device after exposure is placed under uniform development conditions (e.g., the developer formula, temperature, time and stirring method are all the same) for development, and then cleaned and dried.

[0091] Step S2215: Measure the actual residual photoresist layer thickness of the first test photoresist layer after development, corresponding to the pattern area of ​​each first test pattern. Fit the first test exposure dose and the actual residual photoresist layer thickness to form an experimental calibration curve between the residual photoresist layer thickness and the exposure dose. In application, an atomic force microscope is used to measure the actual residual photoresist layer thickness of the first test photoresist layer after development, corresponding to the pattern area of ​​each first test pattern; the test exposure dose and the actual residual photoresist layer thickness are fitted to form an experimental calibration curve between the residual photoresist layer thickness and the exposure dose.

[0092] In practical applications, the first test exposure dose is used as the independent variable (X-axis), and the corresponding actual photoresist residue thickness is used as the dependent variable (Y-axis). Data fitting is performed to obtain the experimental calibration curve between the photoresist residue thickness and the exposure dose.

[0093] In some embodiments, the third dose is greater than or equal to the critical dose for complete development that enables the photoresist to fully develop. Preferably, the third dose is slightly greater than the critical dose for complete development, for example, the third dose is 1.1 times the critical dose for complete development. Further, the critical dose for complete development can be determined based on an experimental calibration curve between the photoresist residual layer thickness and the exposure dose, that is, the exposure dose corresponding to a photoresist residual layer thickness of 0 is selected as the critical dose for complete development from the experimental calibration curve between the photoresist residual layer thickness and the exposure dose.

[0094] In some embodiments, the second dose is determined to ensure that the transition pattern 6 itself can be fully developed and generate a strong scattering field; simultaneously, the second dose, in conjunction with the first dose, ensures that the total energy received by the target region (the patterned region of the photoresist grating 411) is deposited at 90% to 99% of the total energy required for full development, so as to facilitate the subsequent formation of a photoresist residue layer with a thickness of 5 nm to 15 nm in the corresponding substrate region. Further, the second dose is 2 to 4 times the critical dose for full development. Even further, the second dose can be further determined based on iterative optimization experiments.

[0095] It is worth noting that the iterative optimization experiments included:

[0096] Step S2221: Form a second test photoresist layer on the second test substrate.

[0097] In application, the second test substrate is identical in material, shape, and size to the original substrate. The thickness of the second test photoresist layer is the same as the thickness of the photoresist layer.

[0098] Step S2222: Set the second test pattern; write the second test pattern into the second test photoresist layer on the second test substrate.

[0099] In application, the second test pattern includes multiple identical second test patterns, with a first pattern surrounding each second test pattern. Further, the second test pattern can be a photoresist grating pattern, and the first pattern can be a transition pattern 6. Even further, the distance between the second test pattern and the first pattern is the same as the distance between the photoresist grating pattern and the transition pattern 6.

[0100] Step S2223: Using an electron beam exposure system, apply a first exposure dose to the area of ​​the second test photoresist layer corresponding to the second test pattern, and apply a second test exposure dose of different values ​​to the pattern areas of the second test photoresist layer corresponding to different first patterns, to obtain the second test device after exposure.

[0101] In application, the second test exposure dose of different values ​​is higher than the estimated critical dose for complete development. Specifically, the second test exposure dose of different values ​​is 1 to 5 times the critical dose for complete development, with a gradient of 0.5 times the critical dose for complete development.

[0102] Step S2224: Place the exposed second test device in the developer solution for development.

[0103] In application, the entire second test device after exposure is placed under uniform development conditions for development, and then cleaned and dried.

[0104] Step S2225: Using the developed pattern as a mask, etch the second device sample; take the second test exposure dose corresponding to the second device sample whose substrate is not etched, corresponding to the pattern area of ​​the etched photoresist grating 411 as the second dose.

[0105] When there are multiple unetched second device samples, the second test exposure dose with the lowest corresponding dose is used as the second dose.

[0106] Step S3: Develop the exposed photoresist layer to form a developed pattern.

[0107] In application, the entire exposed device is placed under uniform development conditions for development, and then cleaned and dried.

[0108] In practical applications, the substrate surface corresponding to the patterned area of ​​the photoresist grating 411 has a photoresist residue layer, and the thickness of the photoresist residue layer is 5 nanometers to 15 nanometers; the substrate surface corresponding to the patterned areas of other patterns (i.e., the second test unit 22, the multi-parameter substructure, and the material grating 412) does not have a photoresist residue layer.

[0109] Step S4: Using the developed pattern as a mask, the substrate is etched once to form a stepped observation substructure 3, a morphology-related substructure, and a multi-parameter substructure.

[0110] In application, the developed pattern is used as a mask, and a dry etching process is used to perform a uniform etching on the device, simultaneously forming the stepped observation substructure 3 in the second test unit 22, the morphology correlation substructure in the first diagnostic unit 21 and the third diagnostic unit 23, and the multi-parameter substructure.

[0111] In practical applications, the substrate surface with a residual photoresist layer is not etched. Specifically, the residual photoresist layer protects the underlying substrate from etching during the etching process.

[0112] Step S5: Remove the residue on the substrate surface to obtain a stepped debugging piece for grating morphology characterization.

[0113] During application, the residual photoresist layer on the substrate surface is removed, and the surface of the photoresist grating 411 is flat and smooth, without raised grating lines or recessed grooves. The first grating strip 31, the grating unit 511 of the multi-parameter substructure, and the material grating 412 of the second test unit 22 all have raised grating lines.

[0114] Example 3: Based on Example 1 and / or Example 2, this example discloses a method for preparing a stepped adjustment piece for grating morphology characterization.

[0115] In this embodiment, the thickness of the photoresist residue layer is 5 to 15 nanometers. Instantaneous fluctuations or inhomogeneities in the dry etching process can easily lead to premature breakdown of the photoresist residue layer in localized areas. Microscopic inhomogeneities in plasma density and ion energy within the etching chamber are inherent phenomena, which may cause the photoresist residue layer (especially in the wafer edge region 13 or downstream of the chamber gas flow) to be completely consumed before the etching process ends. Once the photoresist residue layer is damaged or fails, the substrate beneath it will be etched, resulting in the destruction of the reference morphology of the photoresist grating 411, and consequently, the complete loss of function of the entire morphology-related substructure.

[0116] Therefore, in this embodiment, the method for preparing the stepped adjustment wafer for grating morphology characterization involves adding a fluorocarbon gas to the etching gas during dry etching to form a fluorocarbon-containing polymer film on the etched surface, thereby protecting the residual photoresist layer. The fluorocarbon gas can be CHF3 or C4F8.

[0117] The main differences between this embodiment and Embodiment 2 are in the composite pattern, the modulation of the exposure dose, the pattern after development, and the etching gas in the dry etching process in step S4.

[0118] Based on Example 2, and referring to Figure 5 In this embodiment, a protective strip pattern is provided between the transition pattern 6 and the photoresist grating pattern in the composite layout pattern.

[0119] In application, the protective strip pattern is parallel to the direction of the grating lines of the material grating 412. Furthermore, the distance between the protective strip pattern and the photoresist grating pattern is 100 nanometers to 300 nanometers.

[0120] In practical applications, refer to Figure 5 The protective strip pattern includes a first strip pattern 71 and a second strip pattern 72, which are respectively disposed on both sides of the photoresist grating pattern.

[0121] In actual implementation, the width of both the first strip pattern 71 and the second strip pattern 72 is 50 nanometers to 100 nanometers, and the length of both the first strip pattern 71 and the second strip pattern is greater than the length of the photoresist grating pattern. Furthermore, the length of both the first strip pattern 71 and the second strip pattern is slightly longer than the length of the photoresist grating 411.

[0122] Based on Example 2, in this example, the exposure dose of the pattern area of ​​the photoresist grating pattern is the first dose; the exposure dose of the pattern area of ​​the transition pattern 6 is the second dose; the exposure dose of the pattern areas of other patterns is the third dose; and the exposure dose of the pattern area of ​​the protective strip pattern is the fourth dose.

[0123] In application, the fourth dose is greater than the second dose. Furthermore, the fourth dose is 3 to 5 times the critical dose for complete development, so that the image area of ​​the protective strip forms a raised structure after development and serves as a carbon source for the photoresist residue layer in the etching process.

[0124] In practical applications, the photoresist of the guard strip with a higher exposure dose (fourth dose) will experience severe electron scattering (i.e., proximity effect), causing the photoresist in the surrounding area (such as the photoresist residue layer) to receive additional energy injection, which causes the photoresist residue layer to cross-link or even partially carbonize. As a result, after development, not only is a photoresist residue layer left, but the photoresist residue layer itself also has a higher carbon content and density, thus having stronger etching resistance, such as a higher etching selectivity.

[0125] Based on Example 2, in this example, the patterned area of ​​the protective strip after development has a high exposure dose, resulting in complete cross-linking of the photoresist and the formation of a raised structure.

[0126] In application, the raised structure is a solid, elongated strip with steep sidewalls and a flat top. The height of the raised structure is equal to the thickness of the photoresist layer, and the width of the raised structure is equal to the width of the protective strip. The ratio of the height to the width of the raised structure is (3~6):1.

[0127] In subsequent plasma etching, the high aspect ratio (i.e., a large height-to-width ratio) of the protrusions causes their tops and edges to become points of localized electric field concentration. Positive ions in the plasma (e.g., Ar) + The material is strongly attracted and vertically bombarded at the tip, causing the material in the protective strip area (the protruding structure formed by highly cross-linked photoresist) to be preferentially and rapidly removed by physical sputtering, thereby removing the protruding structure.

[0128] In the unified etching process of step S4 in this embodiment, during the etching process, positive ions in the plasma (e.g., Ar) +The bombardment of the protrusion structure imparts enormous energy to its surface, making the carbon-carbon and carbon-hydrogen bonds within it more prone to breakage. Because the protrusion structure is adjacent to the protected area (i.e., the photoresist residue layer) (with a spacing of 100 to 300 nanometers), the carbon source material sputtered and dissociated is adsorbed onto the surface of the adjacent photoresist residue layer before it is completely carried away by the main gas flow (e.g., etching gas).

[0129] Based on Example 2, the etching gas in this example further includes a fluorocarbon gas, such as C4F8. In practical applications, this example uses an etching gas specifically designed for silicon wafers, namely a mixture of C4F8, HBr, Cl2, and O2. The flow rate of HBr is 50 to 100 sccm; the flow rate of Cl2 is 10 to 30 sccm; and the flow rate of O2 is 5 to 15 sccm. The flow rate of the fluorocarbon gas is 5 to 20 sccm. Further, the flow rate of C4F8 is 5 to 20 sccm (the etching gas in Example 2 is a mixture of HBr, Cl2, and O2).

[0130] In application, C4F8 dissociates in plasma to produce CF2. + CF2•, F•, to form polymer precursors (e.g., CF2•, F•) for generating protective fluorocarbon polymer films. + , CF2•) and etchants (e.g. F•).

[0131] On the vertical sidewalls and exposed silicon surfaces (i.e., the exposed wafer surfaces) that need to be etched, the main reaction is the reaction of high-energy F• and Cl• with Si (generating volatile SiF4 and SiCl4), making it difficult for polymer precursors to be stably adsorbed on the exposed wafer surfaces.

[0132] However, the situation differs on the horizontal surface of the photoresist residue layer compared to the exposed wafer surface. The horizontal surface of the photoresist residue layer has been pre-covered and modified with hydrocarbon fragments provided by the raised structure. Compared to the exposed wafer surface, the horizontal surface of the photoresist residue layer pre-covered and modified with hydrocarbon fragments exhibits a higher chemical affinity for the polymer precursor. Through the reaction of the carbon source from the raised structure with the polymer precursor in plasma on the horizontal surface of the photoresist residue layer, a Teflon-like structure (C0.05) is cross-linked to form a Teflon-like structure. x F y A fluorocarbon polymer protective film.

[0133] In practical applications, the flow rate ratio of fluorocarbon gas to O2 is 1:(2~5). For example, the flow rate ratio of C4F8 to O2 is 1:(2~5). O2 can selectively remove polymer precursors on vertical sidewalls and other areas (exposed wafer surfaces) to maintain clean etching, while allowing the polymer precursors to form a stable film on the horizontal surface of the photoresist residue layer. By adjusting the flow rate ratio of C4F8 to O2, a fluorocarbon polymer protective film can be generated on the surface of the photoresist residue layer in conjunction with the carbon source provided by the protrusion structure, while avoiding unnecessary polymer deposition (e.g., polymer precursors) on the vertical sidewall areas to be etched (exposed wafer surfaces). Furthermore, the thickness of the fluorocarbon polymer protective film is 5 nm to 20 nm; the etching selectivity ratio of the fluorocarbon polymer protective film to the substrate material is (10~50):1.

[0134] If the flow ratio of C4F8 to O2 is too high (e.g., greater than 1:2), it may result in an excessively thick fluorocarbon polymer protective film and may easily lead to polymer precursor deposition on the exposed wafer surface, resulting in deterioration of the sidewall morphology and requiring frequent cleaning of the cavity.

[0135] If the flow ratio of C4F8 to O2 is too low (e.g., less than 1:5), the polymer precursor will not be generated sufficiently, and the carbon source provided by the protrusion structure will be oxidized into CO and CO2 and consumed. This will result in the fluorocarbon polymer protective film being too thin or discontinuous, making the photoresist residue layer still at risk of being broken down.

[0136] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A stepped adjustment plate for grating morphology characterization, characterized in that, The test array includes a test array distributed on a substrate, the test array including a first diagnostic unit, a second diagnostic unit and a third diagnostic unit, the first diagnostic unit being distributed in the central region of the substrate, the second diagnostic unit being distributed in the middle region of the substrate, and the third diagnostic unit being distributed in the edge region of the substrate; The second test unit is provided with a stepped observation substructure, which includes a plurality of first grating strips, the first grating strips being arranged in a stepped, staggered manner along a direction perpendicular to the length of their internal grating lines; Both the first diagnostic unit and the third diagnostic unit are provided with a morphology correlation substructure and a multi-parameter substructure in parallel; the morphology correlation substructure includes a contrast grating group, which includes unetched photoresist gratings and etched material gratings arranged in parallel; the multi-parameter substructure includes a grating array, which includes multiple sets of grating units with different duty cycles.

2. The stepped adjustment piece for grating morphology characterization according to claim 1, characterized in that, All first grating strips have the same period and duty cycle; The photoresist grating, material grating, and grating array are arranged in parallel along the radial direction of the substrate.

3. The stepped adjustment piece for grating morphology characterization according to claim 1, characterized in that, The direction of the material grating and the grating lines inside the grating unit are parallel to the direction of the grating lines inside the first grating strip; The direction of the grating lines within the first grating strip is perpendicular to the radial direction of the substrate. The first grating strips are arranged along the radial direction of the substrate within the test unit, and the spacing between any two adjacent first grating strips is greater than or equal to the width of the first grating strip. The substrate is a wafer; The ratio of the radial width of the central region, the radial width of the middle region, and the radial width of the edge region is 1:(1~2):(1~1.5).

4. A method for preparing a stepped adjustment piece for grating morphology characterization as described in claim 1, characterized in that, Includes the following steps: A photoresist layer is formed on the substrate; The composite pattern is transferred to the photoresist layer, and the exposure dose is set for different pattern areas to obtain the exposed photoresist layer. The exposed photoresist layer is developed to form a developed pattern, so that a photoresist residue layer is formed on the substrate area corresponding to the photoresist grating pattern, and the thickness of the photoresist residue layer is 5 nanometers to 15 nanometers. Using the developed pattern as a mask, the substrate is etched once to form a stepped observation substructure, a morphology-related substructure, and a multi-parameter substructure. Remove the residue from the substrate surface to obtain the stepped adjustment piece used for grating morphology characterization.

5. The method for preparing a stepped adjustment piece for grating morphology characterization according to claim 4, characterized in that, The composite layout graphic includes: The pattern of multiple sets of first grating strips in the stepped observation substructure; The diagram of multiple grating units with different duty cycles in a multi-parameter substructure; The patterns of the photoresist grating and the material grating in the corresponding morphology-related substructure; A transition pattern set around the photoresist grating pattern; A protective strip pattern is set between the photoresist grating pattern and the transition pattern.

6. The method for preparing a stepped adjustment piece for grating morphology characterization according to claim 5, characterized in that, The transition pattern includes a dot array arranged around the photoresist grating pattern, and the distance between the dot array and the boundary of the photoresist grating pattern is 0.5 micrometers to 2 micrometers. The protective strip pattern includes a first strip pattern and a second strip pattern, which are respectively disposed on both sides of the photoresist grating pattern; The protective strip pattern is parallel to the direction of the grating lines of the material grating; The distance between the protective strip pattern and the photoresist grating pattern is 100 nanometers to 300 nanometers.

7. The method for preparing a stepped adjustment piece for grating morphology characterization according to claim 5, characterized in that, The step of setting the exposure dose for different graphic regions includes: The exposure dose of the pattern area of ​​the photoresist grating pattern in the composite pattern is the first dose; The exposure dose of the graphic area of ​​the transition graphic in the composite graphic is the second dose; In the composite pattern, the exposure dose of the pattern areas of the second test unit pattern, the multi-parameter substructure pattern, and the material grating pattern are all the third dose; The exposure dose of the graphic area of ​​the protective strip pattern in the composite pattern is the fourth dose; Among them, the first dose is less than the third dose, the second dose is greater than the third dose, and the fourth dose is greater than the second dose.

8. The method for preparing a stepped adjustment piece for grating morphology characterization according to claim 5, characterized in that, When the substrate is etched once using the developed pattern as a mask, the etching gases include: HBr, Cl2, O2, and fluorocarbon gases; The flow rates of HBr are 50 sccm to 100 sccm; the flow rates of Cl2 are 10 sccm to 30 sccm; the flow rates of O2 are 5 sccm to 15 sccm; and the flow rates of fluorocarbons are 5 sccm to 20 sccm.

9. The method for preparing a stepped adjustment piece for grating morphology characterization according to claim 8, characterized in that, The flow rate ratio of the fluorocarbon gas to O2 is 1:(2~5). The fluorocarbon gas is CHF3 or C4F8.

10. The method for preparing a stepped adjustment piece for grating morphology characterization according to claim 9, characterized in that, During a single etching process on the substrate, a fluorocarbon polymer protective film is formed on the photoresist residue layer; The thickness of the fluorocarbon polymer protective film is 5 nanometers to 20 nanometers; the etching selectivity ratio of the fluorocarbon polymer protective film to the substrate material is (10~50):1.

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