Lighting compensation methods

Abstract

The illumination compensation method disclosed herein includes the steps of: obtaining a working distance between an imaging film layer (2) and a mask (1) in an exposure imaging system; calculating the imaging light intensity of a photoresist layer (22) on the imaging film layer (2) corresponding to different working distances; establishing a relationship between the change in line width of an imaged pattern on the photoresist layer (22) on the imaging film layer (2) and the change in working distance based on the imaging light intensity; calculating compensation parameters for the illumination light according to the relationship between the change in line width of the imaged pattern and the change in working distance; and performing illumination compensation on the exposure imaging system according to the compensation parameters. This method can calculate the compensation parameters for the illumination light corresponding to different working distances. Then, pixelated adjustment of parameters such as the light intensity, polarization, and phase of the incident light at different positions according to the compensation parameters can be performed to match the imaging light fields on the photoresist layer (22) at different working distances, thereby improving the line width uniformity of large-area imaging patterns and meeting the requirement for exposure line width uniformity.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to the field of exposure resolution enhancement in integrated circuit manufacturing, and more particularly to illumination compensation methods. [Background technology]

[0002] During the exposure process, incident light from an illumination source passes through an illumination system and penetrates a mask blank at normal or oblique incidence to reach the mask, where it interacts with the mask. The evanescent waves, carrying the subwavelength information of the mask pattern, undergo a photochemical reaction with a photoresist layer spin-coated on a substrate. When the photoresist layer is developed, an image of the mask pattern is formed. The gap between the mask and the imaging film layer structure, including the photoresist layer, is called the working distance, and the light intensity in the photoresist layer is sensitive to changes in the working distance. As the working distance changes, the light intensity in the photoresist layer changes, and so does the linewidth of the imaged pattern. In an ideal case, when the pattern on the mask is uniformly distributed with the same linewidth, the light intensity in the photoresist layer and the imaged pattern are also uniformly distributed with the same dimensions.

[0003] However, in an actual exposure process, the working distance varies at each position, and the light intensity distribution within the photoresist layer is not uniform but varies according to the undulations, resulting in a non-uniform linewidth distribution of the imaged pattern. The difference in working distance can be caused by various factors, such as undulations on the substrate surface of the imaging film layer, non-uniform processing thickness of the imaging film layer, or non-uniform height of the mask pattern. For example, the substrate surface of the imaging film layer is not absolutely flat but has certain undulations. Because the imaging film layer is very thin, applying an imaging film layer cannot improve the undulations on the substrate surface of the imaging film layer. Such undulations cause the working distance to shrink or expand, resulting in a non-uniform light intensity distribution within the photoresist layer that varies according to the undulations. Ultimately, the imaging pattern also has a non-uniform distribution, which has a significant impact on the exposure results and may even lead to exposure failure. Summary of the Invention [Means for solving the problem]

[0004] Regarding the above technical problem, the present disclosure provides an illumination compensation method for at least partially solving the technical problem in the prior art that non-uniformity of the imaging pattern due to differences in working distance has a significant impact on the exposure result.

[0005] Based on the above, the present disclosure provides an illumination compensation method, which includes the steps of obtaining a working distance between an imaging film layer and a mask in an exposure imaging system; calculating the intensity of imaging light of the photoresist layer in the imaging film layer corresponding to different working distances; and establishing a relationship between the change in line width of the imaging pattern of the photoresist layer in the imaging film layer and the change in working distance based on the intensity of the imaging light; calculating compensation parameters required for the illumination light according to the relationship between the change in line width of the imaging pattern and the change in working distance; and performing illumination compensation on the exposure imaging system according to the compensation parameters.

[0006] According to an embodiment of the present disclosure, the step of obtaining the working distance between the imaging film layer and the mask in the exposure imaging system includes the steps of measuring the surface relief information of the imaging film layer and determining the working distance between the imaging film layer and the mask according to the relief information.

[0007] According to an embodiment of the present disclosure, the step of calculating the intensity of imaging light of the photoresist layer in the imaging film layer corresponding to different working distances includes the steps of constructing an optical simulation model from the illumination light to the imaging light field in the photoresist layer, and calculating the intensity of imaging light of the photoresist layer corresponding to different working distances for a predetermined mask pattern and illumination light distribution based on the optical simulation model, wherein the optical simulation model includes a lens group optical simulation model from the illumination light to the light incident on the top surface of the mask, and an imaging film layer optical simulation model from the light incident on the top surface of the mask to the imaging light field in the photoresist.

[0008] According to an embodiment of the present disclosure, the optical simulation model comprises:

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[0009] I Pr (x, y) is the intensity distribution of the imaging light in the photoresist layer, and I ill (x,y) is the parameter distribution corresponding to the illumination light, and PSF lens and PSF near-filed are the optical point spread functions of the lens group optical simulation model and the imaging film layer optical simulation model, respectively, and Mask(x, y) is the pattern distribution of the mask.

[0010] According to an embodiment of the present disclosure, an optical simulation model is constructed using the finite-difference time-domain method, rigorous coupled-wave analysis, or finite element method.

[0011] According to an embodiment of the present disclosure, the step of constructing a relationship between changes in line width of the imaging pattern of the photoresist layer in the imaging film layer and changes in working distance based on the intensity of the imaging light includes a step of performing threshold processing on the intensity of the imaging light of the photoresist layer corresponding to each working distance to obtain the line width of the imaging pattern of the photoresist layer corresponding to the working distance, and a step of constructing a relationship between changes in line width of the imaging pattern of the photoresist layer and changes in working distance based on each working distance and the line width of the imaging pattern corresponding to the working distance.

[0012] According to an embodiment of the present disclosure, the step of calculating compensation parameters required for illumination light according to the relationship of change in line width of the imaging pattern with respect to change in working distance includes the steps of calculating the line width of the imaging pattern of the photoresist layer that requires compensation for different working distances based on the relationship of change in line width of the original imaging pattern with respect to change in working distance and the relationship of change in line width of the desired imaging pattern with respect to change in working distance, and converting the line width of the imaging pattern of the photoresist layer that requires compensation into the intensity of the imaging light, substituting it into an optical simulation model, and calculating compensation parameters including light intensity, polarization, and phase.

[0013] According to an embodiment of the present disclosure, the step of performing illumination compensation on the exposure imaging system according to the compensation parameters includes the steps of: constructing an illumination compensation system by a light field modulation technique according to the compensation parameters; and pixelating and adjusting the incident light field of the exposure imaging system by the illumination compensation system.

[0014] According to an embodiment of the present disclosure, the illumination compensation method further includes the steps of: calculating evaluation indexes of line width uniformity of the imaged pattern of the photoresist layer before and after performing illumination compensation, respectively; determining whether the line width uniformity index of the imaged pattern of the photoresist layer after compensation is better than the line width uniformity index of the imaged pattern of the photoresist layer before compensation; and if so, determining the illumination compensation as effective compensation.

[0015] According to an embodiment of the present disclosure, the step of calculating the line width uniformity evaluation index of the imaged pattern of the photoresist layer includes the steps of determining a central working distance and setting the value of the line width uniformity of the imaged pattern of the photoresist layer when the working distance changes around the central working distance as the uniformity evaluation index.

[0016] The illumination compensation method according to the embodiment of the present disclosure has at least the following beneficial effects.

[0017] Based on the distribution of working distances, the imaging light intensities corresponding to different working distances are calculated, and the relationship between the change in line width of the imaging pattern and the change in working distance is determined based on the imaging light intensities, so that the compensation parameters required for the illumination light can be calculated. Then, the light intensity, polarization, phase, and other parameters of the incident light at different positions are pixelated and adjusted according to the compensation parameters to match the imaging light fields of the photoresist layer for different working distances, thereby improving the line width uniformity of the large-area imaging pattern and meeting the requirement of exposure line width uniformity (CDU).

[0018] Furthermore, by constructing an optical simulation model, compensation parameters for the light intensity, polarization, and phase of incident light at different positions can be accurately calculated, improving the accuracy of illumination compensation and ensuring the line width uniformity of the imaged pattern.

[0019] Furthermore, the illumination compensation system is constructed by light field modulation technology according to the compensation parameters, and the incident light field is pixelated and adjusted, so that the illumination compensation method can be easily realized by the modulator, which improves the convenience of illumination compensation.

[0020] Furthermore, since the line width of the imaged pattern changes according to the changes in the light intensity, polarization state, and phase of the incident light, this illumination compensation method is applicable to exposures with different working distances, and not only improves the uniformity of the imaged line width and the image quality of the mask pattern, but also enables the illumination compensation technology to clearly image mask patterns with different line widths. [Brief explanation of the drawings]

[0021] [Figure 1] 1 illustrates a schematic flow chart of an illumination compensation method according to an embodiment of the present disclosure. [Figure 2] 1A and 1B show schematic diagrams of optical imaging systems according to embodiments of the present disclosure; [Figure 3] 10 illustrates a schematic flow chart of a method for calculating the intensity of imaging light in step S102 according to an embodiment of the present disclosure. [Figure 4] 10 is a schematic diagram illustrating a flowchart of a method for establishing a relationship between a change in line width of an imaging pattern and a change in working distance in step S102 according to an embodiment of the present disclosure. [Figure 5] 10 illustrates a schematic flow chart of a method for calculating compensation parameters required for illumination light in step S103 according to an embodiment of the present disclosure. [Figure 6] 1 is a schematic diagram of an illumination compensation system according to an embodiment of the present disclosure; [Figure 7] 10 schematically illustrates a flowchart of an illumination compensation method according to another embodiment of the present disclosure. [Figure 8] 3 is a schematic diagram showing a distribution curve of the intensity of imaging light in a photoresist layer before illumination compensation at normal incidence according to the first embodiment; FIG. [Figure 9]10 is a schematic diagram showing a curve of change in the maximum intensity of imaging light before illumination compensation at normal incidence with respect to a change in working distance according to the first embodiment. FIG. [Figure 10] 10A and 10B are schematic diagrams showing curves of changes in line width of an original image pattern and a desired image pattern at normal incidence with respect to changes in working distance according to the first embodiment. [Figure 11] 10A and 10B are schematic diagrams showing curves of the line width of the imaged pattern that need to be compensated for different working distances at normal incidence according to the first embodiment. [Figure 12] 10 is a schematic diagram showing a curve diagram of the change in the maximum intensity of imaging light before and after compensation for illumination at normal incidence with respect to a change in working distance according to the first embodiment. FIG. [Figure 13] 3 is a schematic diagram showing a distribution curve of the intensity of imaging light in a photoresist layer after illumination compensation at normal incidence according to the first embodiment; FIG. [Figure 14] FIG. 10 is a schematic diagram showing a curve of change in line width of an imaged pattern after illumination compensation at normal incidence with respect to a change in working distance according to the first embodiment. [Figure 15] 10 is a schematic diagram showing a distribution curve of the intensity of imaging light in a photoresist layer before illumination compensation at an oblique incidence according to the second embodiment. FIG. [Figure 16] FIG. 10 is a schematic diagram showing a curve of change in maximum intensity of imaging light before illumination compensation at oblique incidence with respect to change in working distance according to the second embodiment. [Figure 17] 10A and 10B are schematic diagrams showing curves of changes in line width of an original image pattern and a desired image pattern at oblique incidence with respect to changes in working distance according to the second embodiment. [Figure 18] 10A and 10B are schematic diagrams showing curves of the line width of the imaging pattern that require compensation for different working distances at oblique incidence according to the second embodiment. [Figure 19] 10 is a schematic diagram showing a curve diagram of the change in the maximum intensity of imaging light before and after compensation for illumination at oblique incidence with respect to a change in working distance according to the second embodiment. FIG. [Figure 20]10 is a schematic diagram showing a distribution curve of the intensity of imaging light in a photoresist layer after illumination compensation at oblique incidence according to the second embodiment; FIG. [Figure 21] 10 is a schematic diagram showing a curve of change in line width of an imaged pattern after illumination compensation at oblique incidence with respect to a change in working distance according to an embodiment of the present disclosure; DETAILED DESCRIPTION OF THE INVENTION

[0022] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure with reference to the drawings.

[0023] In order to make the objectives, technical solutions and advantages of the present disclosure clearer, the present disclosure will be described in more detail below with reference to specific embodiments and drawings. Of course, the described embodiments are only some of the embodiments of the present disclosure, and do not represent all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without using their inventive abilities fall within the scope of protection of the present disclosure.

[0024] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present disclosure. As used herein, the terms "comprises" and "including" refer to the presence of stated features, steps, operations, and / or components, but do not imply the exclusion of the presence or addition of one or more other features, steps, operations, or components.

[0025] In this disclosure, unless otherwise clearly defined or limited, terms such as "attached," "linked," "connected," and "fixed" should be understood in a broad sense. For example, they may refer to a fixed connection, a detachable connection, or an integral connection. They may also refer to a mechanical connection, an electrical connection, or a communication connection. They may also refer to a direct connection, an indirect connection via an intermediate, or two elements may communicate with each other or interact with each other. Those skilled in the art will be able to understand the specific meanings of the above terms in this disclosure depending on the specific circumstances.

[0026] In describing the present disclosure, directions or positional relationships expressed using terms such as "longitudinal," "length," "circumferential," "front," "rear," "left," "right," "top," "bottom," "inner," "outer," etc. are based on the drawings and are merely for the purpose of conveniently and simply describing the present disclosure, and should not be understood as limiting the present disclosure, as they do not expressly or imply that the subsystems or elements in question necessarily have a particular orientation or are configured or operated in a particular direction.

[0027] In all drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations are omitted if they may cause confusion in understanding the present disclosure. Furthermore, the shape, dimensions, and positional relationship of each part in the drawings do not reflect the actual size, scale, or actual positional relationship. Furthermore, in the claims, the reference numerals between parentheses do not limit the scope of the claims.

[0028] Similarly, in the above description of exemplary embodiments of the present disclosure, each feature of the present disclosure may be assigned to a single embodiment, figure, or description thereof to simplify the disclosure and facilitate understanding of one or more aspects of the disclosure. The use of terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "several examples" means that the specific features, structures, materials, and characteristics described in connection with the embodiment or examples are included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the described specific features, structures, materials, and characteristics may be combined in any suitable manner in any one or more of the embodiments or examples.

[0029] It should be understood that terms such as "first," "second," etc. are for descriptive purposes only and do not express or imply relative importance or the number of technical features. Thus, features qualified by "first" and "second" may expressly or imply the inclusion of one or more of the features. In the description of this disclosure, unless specifically limited otherwise, "plurality" means two or more, e.g., two, three, etc.

[0030] The present disclosure aims to provide an illumination compensation method. This method adjusts the distribution of the imaging light field in a photoresist layer at different positions in a plane by changing parameters such as the light intensity, polarization, and phase of incident light at different positions in a plane, thereby improving exposure linewidth uniformity (CDU) and enhancing large-area exposure uniformity. The illumination compensation method will be described in detail below with reference to the drawings and specific examples.

[0031] FIG. 1 schematically shows a flow chart of an illumination compensation method according to one embodiment of the present disclosure. As shown in FIG. 1, the illumination compensation method may include, for example, steps S101 to S104.

[0032] In step S101, the working distance between the imaging film layer and the mask in the exposure imaging system is obtained.

[0033] In step S102, the intensity of the imaging light of the photoresist layer in the imaging film layer corresponding to different working distances is calculated, and based on the intensity of the imaging light, a relationship between the change in line width of the imaging pattern of the photoresist layer in the imaging film layer and the change in working distance is established.

[0034] In step S103, compensation parameters required for the illumination light are calculated according to the relationship between the change in the line width of the imaged pattern and the change in the working distance. In step S104, illumination compensation is performed on the exposure imaging system according to the compensation parameters.

[0035] According to an illumination compensation method according to an embodiment of the present disclosure, the intensity distribution of imaging light in a photoresist layer corresponding to different working distances and the line width of the pattern are calculated by measuring the working distance, and the distribution of compensation parameters (e.g., light intensity, polarization, phase, etc.) required for the incident light is calculated using an inverse optimization method to improve the line width uniformity of the exposed photoresist pattern, and the incident light field is pixelated and adjusted to improve the line width uniformity of the imaged photoresist pattern.

[0036] FIG. 2 is a schematic diagram illustrating a structure of an optical imaging system according to an embodiment of the present disclosure.

[0037] 2, the optical imaging system includes a mask 1 and an imaging film layer 2. The mask 1 includes a mask blank 11 and a mask pattern layer 12, and the imaging film layer 2 includes a metal transmission layer 21, a photoresist layer 22, a metal reflective layer 23, and an imaging film layer substrate 24. The mask blank 11 is, for example, a silicon substrate or a silica substrate, the material of the mask pattern layer 12 is, for example, Cr, the material of the metal transmission layer 21 and the metal reflective layer 23 is, for example, Ag, Au, Cu, etc., the material of the photoresist layer 22 is, for example, Pr, etc., and the imaging film layer substrate 24 can be a substrate structure such as a silicon substrate, a silica substrate, a silicon substrate with an anti-reflection layer, or a silica substrate with an anti-reflection layer.

[0038] The illumination system transmits light at normal or oblique incidence through the mask blank 11 to reach the mask pattern layer 12 and interacts with the mask pattern layer 12. The evanescent waves carrying the sub-wavelength information of the mask pattern undergo a photochemical reaction with the photoresist layer 22, and when the photoresist layer 22 is developed, an image of the mask pattern is formed.

[0039] In an embodiment of the present disclosure, an interferometer or other device can be used to measure the surface relief information of the imaging film layer 2 in the exposure imaging system, and the working distance between the mask 1 and the imaging film layer 2 can be obtained from the relief information. Furthermore, if the surface relief information of the mask 1 and the imaging film layer 2 has a small effect on the working distance, an interferometer or other device can be used to measure the surface relief information of the imaging film layer substrate 24, calculate the working distance from the relief information, and then prepare other layers of the exposure imaging system on the imaging film layer substrate by spin coating, sputtering, or other methods. Furthermore, a certain working distance value can be used as a reference working distance value. Other working distance values ​​vary above and below this reference working distance value.

[0040] FIG. 3 schematically shows a flowchart of a method for calculating the intensity of imaging light in step S102 according to an embodiment of the present disclosure. As shown in FIG. 3, the method for calculating the intensity of imaging light may include, for example, steps S301 and S302.

[0041] In step S301, an optical simulation model from illumination light to an imaging light field in a photoresist layer is constructed.

[0042] In step S302, the imaging light intensity of the photoresist layer corresponding to different working distances for a given mask pattern and illumination light distribution is calculated based on the optical simulation model.

[0043] In an embodiment of the present disclosure, the optical simulation model includes a lens group optical simulation model from illumination light to light incident on the upper surface of the mask, and an imaging film layer optical simulation model from light incident on the upper surface of the mask to the imaging light field in the photoresist. Factors such as the illumination mode, lens group, mask, working distance, imaging film layer structure, and substrate are all taken into consideration. The optical simulation model can be constructed using the Finite-Difference Time-Domain (FDTD), Rigorous Coupled Wave Analysis (RCWA), or Finite Element Method (FEM), etc.

[0044] Furthermore, the optical simulation model

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[0045] I Pr (x, y) is the intensity distribution of the imaging light in the photoresist layer, and I ill (x,y) is the distribution of parameters corresponding to the illumination light, such as light intensity, and PSF lens and PSF near-filed are the optical point spread functions of the lens group optical simulation model and the imaging film layer optical simulation model, respectively, and Mask(x, y) is the distribution of the mask pattern.

[0046] For a given mask pattern and illumination distribution, Mask(x,y) and I ill (x, y) are known, and based on the constructed optical simulation model, the optical point spread function PSF is calculated. lens and PSF near-filed is also known, the intensity of the imaging light on the photoresist layer corresponding to different working distances can be calculated.

[0047] Based on this optical simulation model, it is also possible to simulate the illumination distribution required for the imaging light field distribution of a particular photoresist.

[0048] The illumination mode used to construct the optical simulation model is the illumination mode used in the actual exposure, the mask blank used in the simulation model is the mask blank used in the actual exposure, the mask used in the simulation model is the mask used in the actual exposure, and the thickness distribution of the working distance layer used in the simulation model is the working distance value measured during the actual exposure.

[0049] Once the intensity distribution of the imaging light in the photoresist layer is obtained, a relationship can be constructed between the change in line width of the imaged pattern and the change in working distance.

[0050] FIG. 4 is a schematic flowchart illustrating a method for establishing a relationship between a change in line width of an imaged pattern and a change in working distance in step S102 according to an embodiment of the present disclosure.

[0051] As shown in FIG. 4, the construction method may include, for example, step S401 and step S402.

[0052] In step S401, threshold processing is performed on the intensity of the imaging light of the photoresist layer corresponding to each working distance, and the line width of the imaging pattern of the photoresist layer corresponding to the working distance is obtained.

[0053] In step S402, a relationship between the change in the line width of the imaged pattern of the photoresist layer and the change in the working distance is established based on each working distance and the line width of the imaged pattern corresponding to the working distance.

[0054] For example, the line width of the photoresist pattern can be obtained by thresholding the intensity of the imaging light on the photoresist layer.

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[0055] Once the relationship between the change in the line width of the imaged pattern and the change in the working distance has been established, the distribution of compensation parameters required for the incident light can be calculated using the established optical simulation model.

[0056] FIG. 5 schematically shows a flowchart of a method for calculating compensation parameters required for illumination light in step S103 according to an embodiment of the present disclosure. As shown in FIG. 5, the calculation method may include, for example, step S501 and step S502.

[0057] In step S501, the line width of the imaged pattern in the photoresist layer that needs to be compensated for different working distances is calculated based on the relationship between the change in line width of the original imaged pattern and the change in line width of the desired imaged pattern and the change in working distance.

[0058] In step S502, the line width of the imaged pattern of the photoresist layer that needs compensation is converted into the intensity of the imaging light, and substituted into the optical simulation model to calculate compensation parameters including the light intensity, polarization, and phase.

[0059] As explained above, the line width of the imaged pattern in the photoresist layer can be obtained by performing threshold processing on the intensity of the imaging light. Conversely, however, the line width of the imaged pattern in the photoresist layer that requires compensation can be converted into the intensity of the imaging light and then substituted into the optical simulation model to calculate compensation parameters that may include light intensity, polarization, and phase.

[0060] Once the compensation parameters are calculated, illumination compensation can be performed.

[0061] In an embodiment of the present disclosure, the step of performing illumination compensation on the exposure imaging system according to the compensation parameters specifically includes: constructing an illumination compensation system by light field modulation technology according to the compensation parameters; and pixelating and adjusting the incident light field of the exposure imaging system by the illumination compensation system.

[0062] FIG. 6 schematically illustrates a structural diagram of an illumination compensation system according to an embodiment of the present disclosure.

[0063] The constructed illumination compensation system may include, for example, an optical field modulator 3 and a coupling lens group 4. The optical field modulator 3 adjusts the distribution of compensation parameters of the incident light according to the calculated compensation parameters, and directs the modulated light to a specified position on the mask via the coupling lens group 4 to perform illumination compensation. This makes it possible to achieve the optical modulation depth, modulation range, and modulation accuracy required for the illumination compensation information. This makes it possible to achieve linewidth uniformity in large-area exposure patterns through illumination compensation when unevenness exists on the photoresist substrate.

[0064] The light field modulator includes, for example, a modulator such as a Digital Micromirror Device (DMD) or a Spatial Light Modulator (SLM).

[0065] After completing the illumination compensation by constructing the illumination compensation system, the effect of the illumination compensation can also be evaluated.

[0066] FIG. 7 schematically shows a flowchart of an illumination compensation method according to another embodiment of the present disclosure. As shown in FIG. 7, after step S104, the illumination compensation method further includes steps S105 and S106.

[0067] In step S105, the line width uniformity evaluation indexes of the imaged pattern on the photoresist layer before and after illumination compensation are calculated respectively.

[0068] In step S106, to determine the compensation effect, it is determined whether the line width uniformity index of the imaged pattern of the photoresist layer after compensation is better than the line width uniformity index of the imaged pattern of the photoresist layer before compensation.

[0069] For example, the central working distance can be determined first, and the linewidth uniformity (CDU) value of the imaged pattern of the photoresist layer as the working distance changes around the central working distance can be used as a uniformity evaluation index. The CDU value is calculated by dividing the difference between the linewidth of the imaged pattern when the working distance deviates from the central working distance and the linewidth of the imaged pattern at the central working distance by the linewidth of the imaged pattern at the central working distance, and is expressed as a percentage. When multiple deviated working distances exist, the CDU value is the average of the CDU values ​​at these working distances. The smaller the CDU value, the better the uniformity of the imaged pattern. The better the uniformity, the less the effect of the working distance deviation from the central working distance, i.e., the larger the exposure process window. The linewidth of the imaged pattern is determined according to the distribution of the intensity of the imaging light. Once the central working distance is selected, the magnitude of the deviation of the working distance from the central working distance can be determined from the exposure system and can typically be 10% to 25% of the central working distance. The present disclosure is also applicable when other parameters are used as evaluation indices.

[0070] Before illumination compensation, a curve of the change in line width of the imaged pattern on the photoresist layer with respect to the change in working distance is calculated based on the distribution curve of the intensity of the imaging light at different working distances, and the CDU value before illumination compensation is calculated based on the curve of the change.

[0071] After illumination compensation, a curve of the line width of the photoresist pattern versus the working distance is calculated, and a CDU value after illumination compensation is determined based on the curve of the change. The CDU value before illumination compensation in step S105 is compared with the CDU value after illumination compensation in this step. If the CDU value after illumination compensation is smaller than the CDU value before illumination compensation, it is considered that illumination compensation has the effect of improving the uniformity of the imaged line width.

[0072] In addition, light sources applicable to the illumination compensation method according to the embodiments of the present disclosure may include ultraviolet illumination sources and light sources of other wavelength bands. Applicable illumination forms may include conventional illumination, annular illumination, quadrupole illumination, or other types of off-axis illumination. Applicable mask patterns may include other complex patterns, such as dense or sparse lines with a single line width. For other mask patterns, the exposure light source may be a linear superposition of two incoherent polarizations of TM (transverse magnetic) polarization and TE (transverse electric) polarization, and the intensity of the imaging light in the photoresist layer may be the sum of the intensities of the imaging light of the two polarizations. The optical simulation model constructed by the illumination compensation method may be a two-dimensional exposure imaging model or a three-dimensional exposure imaging model. The two-dimensional exposure imaging model is considered to be a special case of the three-dimensional exposure imaging model.

[0073] To verify the advantages of the illumination compensation method according to the embodiments of the present disclosure, some specific examples and experimental data are provided below for explanation.

[0074] First Example In this example, the illumination uses a conventional illumination mode. In the exposure imaging system, the mask 1 has a thickness of 40 nm, a working distance of 20 nm, a metal transparent layer 21 has a thickness of 22 nm, a metal reflective layer 23 has a thickness of 40 nm, and a photoresist layer 22 has a thickness of 18 nm. The wavelength of the incident light is 365 nm, and the TM wave is normal incidence.

[0075] FIG. 8 is a diagram showing a distribution curve of the intensity of imaging light in a photoresist layer before illumination compensation at normal incidence according to the first embodiment.

[0076] Figure 8 shows the distribution curves of the imaging light intensity corresponding to working distances of 15 nm, 20 nm, and 30 nm, where the x-axis coordinate represents the position in the plane of the optical imaging system in Figure 2 in the direction perpendicular to the dense line, and the y-axis coordinate represents the value of the imaging light intensity in the photoresist.

[0077] FIG. 9 is a schematic diagram showing a curve of change in the maximum intensity of imaging light before illumination compensation at normal incidence with respect to a change in working distance according to the first embodiment.

[0078] As shown in Figure 9, the maximum intensity of the imaging light before illumination compensation is the peak value of the curve in Figure 8. The maximum intensity of the imaging light varies with different working distances (hGap), and is larger as the working distance is smaller.

[0079] FIG. 10 is a schematic diagram showing curves of changes in line width of the original image pattern and the desired image pattern at normal incidence with respect to changes in working distance according to the first embodiment.

[0080] As shown in Figure 10, the dashed line is a curve plot of the change in the line width (CD) of the desired imaged pattern with respect to the working distance. Since it is parallel to the x-axis, it represents the desired uniform line width of the imaged pattern. The solid line is a curve plot of the change in the line width of the original imaged pattern with respect to the working distance. Within a 6 nm range around the working distance where the central working distance is 20 nm, that is, within a working distance range of 17 nm to 23 nm, the line width of the imaged pattern varies from 47.2 nm to 42.7 nm, with a CDU value of ±5.1%.

[0081] FIG. 11 is a schematic diagram showing the curve of the line width of the imaged pattern that needs to be compensated for different working distances at normal incidence according to the first embodiment.

[0082] As can be seen by comparing Figures 11 and 10, the curve of the change in line width of the imaging pattern that requires compensation is complementary to the curve of the change in line width of the original imaging pattern with respect to the change in working distance, so that the line width of the imaging pattern after compensation matches the desired line width of the imaging pattern.

[0083] FIG. 12 is a schematic diagram showing a curve of change in maximum intensity of imaging light before and after compensation for illumination at normal incidence with respect to a change in working distance according to the first embodiment.

[0084] As shown in Figure 12, after illumination compensation, the maximum intensity of the imaging light corresponding to a small working distance (15 nm) decreases, while the maximum intensity of the imaging light corresponding to a middle working distance (20 nm to 25 nm) increases slightly. The trend in the curve indicates that the change in the maximum intensity of the imaging light after illumination compensation with respect to the change in working distance becomes gentler. When obtaining compensation information, the undulations of the substrate surface correspond to changes in working distance, with convex portions on the surface corresponding to working distances smaller than the middle working distance and concave portions on the surface corresponding to working distances larger than the middle working distance.

[0085] FIG. 13 is a diagram showing a distribution curve of the intensity of imaging light in a photoresist layer after illumination compensation at normal incidence according to the first embodiment. Similar to FIG. 8, FIG. 13 shows distribution curves of the intensity of imaging light corresponding to working distances of 15 nm, 20 nm, and 30 nm.

[0086] FIG. 14 is a schematic diagram showing a curve of change in line width of an imaged pattern after illumination compensation at normal incidence with respect to a change in working distance according to the first embodiment.

[0087] As shown in Figure 14, within a 6 nm range around the central working distance, the linewidth of the imaged pattern changes from 44.5 nm to 45 nm, with a CDU value of ±0.6%. Compared to Figure 10, the curve changes more gradually near the central working distance. Comparing the CDU values ​​before and after compensation shows that illumination compensation can significantly reduce the CDU value. The CDU value after illumination compensation is only 11.76% of the CDU value before illumination compensation, demonstrating the excellent effect of illumination compensation.

[0088] Second Example In this example, the illumination uses an off-axis illumination mode. In the exposure imaging system, the thickness of the mask 1 is 40 nm, the working distance is 40 nm, the thickness of the metal transparent layer 21 is 16 nm, the thickness of the metal reflective layer 23 is 28 nm, the thickness of the photoresist layer 22 is 50 nm, the wavelength of the incident light is 365 nm, and the TM wave is obliquely incident at angles of 72.4 degrees and -72.4 degrees from both sides, respectively.

[0089] FIG. 15 is a diagram showing a distribution curve of the intensity of imaging light in a photoresist layer before illumination compensation at an oblique incidence according to the second embodiment.

[0090] 15 shows the distribution curves of the imaging light intensity corresponding to working distances of 30 nm, 40 nm, and 50 nm. Similarly, the x-axis coordinate represents the position in the plane of the optical imaging system in FIG. 2 in the direction perpendicular to the dense line, and the y-axis coordinate represents the value of the imaging light intensity in the photoresist.

[0091] FIG. 16 is a schematic diagram showing a curve of change in the maximum intensity of imaging light before illumination compensation at oblique incidence with respect to change in working distance according to the second embodiment.

[0092] As shown in Fig. 16, the maximum intensity of the imaging light before illumination compensation is the peak value of the curve in Fig. 15. The maximum intensity of the imaging light varies with different working distances (hGap), and is larger as the working distance is smaller.

[0093] FIG. 17 is a schematic diagram showing curves of changes in line width of the original image pattern and the desired image pattern at oblique incidence with respect to changes in working distance according to the second embodiment.

[0094] As shown in Figure 17, the dashed line is a curve plot of the change in the line width (CD) of the desired imaged pattern with respect to the change in working distance. Since it is parallel to the x-axis, it represents the desired line width of the uniformed imaged pattern. The solid line is a curve plot of the change in the line width of the original imaged pattern with respect to the change in working distance. Within a 20 nm range around the working distance where the central working distance is 40 nm, that is, within the working distance range of 30 nm to 50 nm, the line width of the imaged pattern varies from 51.5 nm to 21.8 nm, with a CDU value of ±33.3%.

[0095] FIG. 18 is a schematic diagram showing a curve of the line width of the imaged pattern that needs to be compensated for different working distances at oblique incidence according to the second embodiment.

[0096] As can be seen by comparing Figures 18 and 17, the curve of the change in line width of the imaging pattern that requires compensation is complementary to the curve of the change in line width of the original imaging pattern with respect to the change in working distance, so that the line width of the imaging pattern after compensation matches the line width of the desired imaging pattern.

[0097] FIG. 19 is a schematic diagram showing a curve of change in maximum intensity of imaging light before and after compensation for illumination at oblique incidence with respect to a change in working distance according to the second embodiment.

[0098] As shown in Figure 19, after illumination compensation, the maximum intensity of the imaging light corresponding to a small working distance (30 nm to 40 nm) decreases, while the maximum intensity of the imaging light corresponding to a middle working distance (40 nm to 50 nm) increases slightly. The trend in the curve indicates that the change in the maximum intensity of the imaging light after illumination compensation with respect to the change in working distance becomes gentler. When obtaining compensation information, the undulations on the substrate surface correspond to changes in working distance, with convex portions on the surface corresponding to working distances smaller than the central working distance and concave portions on the surface corresponding to working distances larger than the central working distance.

[0099] FIG. 20 is a diagram showing a distribution curve of the intensity of imaging light in a photoresist layer after illumination compensation at oblique incidence according to the second embodiment. Similar to FIG. 15, FIG. 20 shows distribution curves of the intensity of imaging light corresponding to working distances of 30 nm, 40 nm, and 50 nm.

[0100] FIG. 21 is a schematic diagram showing a curve of change in line width of an imaged pattern after illumination compensation at oblique incidence with respect to a change in working distance according to an embodiment of the present disclosure.

[0101] As shown in Figure 21, within a 20 nm range around the central working distance, the linewidth of the imaged pattern changes from 42.5 nm to 47.2 nm, with a CDU value of ±6.3%. Compared to Figure 17, the curve changes more gradually near the central working distance. Comparing the CDU values ​​before and after compensation shows that illumination compensation can significantly reduce the CDU value. The CDU value after illumination compensation is only 18.92% of the CDU value before illumination compensation, demonstrating the excellent effect of illumination compensation.

[0102] As described above, the illumination compensation method according to the embodiment of the present disclosure can compensate for the line width non-uniformity of an imaged pattern caused by differences in working distance, i.e., the line width non-uniformity. By measuring the working distance distribution and performing illumination compensation, the line width non-uniformity of a photoresist exposure pattern caused by differences in working distance can be reduced or eliminated. Therefore, the line width uniformity requirement for large-area exposure of a single line width pattern or the line width requirement for a cross-scale pattern can be met, and the pattern exposure requirements can be satisfied.

[0103] The above-described specific examples further illustrate the objectives, technical solutions, and beneficial effects of the present disclosure. Furthermore, the above descriptions are merely specific examples of the present disclosure and are not intended to limit the present disclosure. As long as they do not deviate from the essence and spirit of the present disclosure, all modifications, equivalent replacements, improvements, etc., fall within the scope of protection of the present disclosure. [Explanation of symbols]

[0104] 1: mask, 11: mask blank, 12: mask pattern layer, 2: imaging film layer, 21: metal transmission layer, 22: photoresist layer, 23: metal reflective layer, 24: imaging film layer substrate, 3: optical field modulator, 4: coupling lens group

Claims

1. obtaining a working distance between an imaging film layer and a mask in an exposure imaging system; calculating the intensity of the imaging light of the photoresist layer in the imaging film layer corresponding to different working distances, and establishing a relationship between the change in line width of the imaging pattern of the photoresist layer in the imaging film layer and the change in the working distance based on the intensity of the imaging light; calculating a compensation parameter required for illumination light according to a relationship between the change in the line width of the imaged pattern and the change in the working distance; performing illumination compensation on the exposure imaging system according to the compensation parameters.

10. A method for illumination compensation comprising:

2. The step of obtaining a working distance between an imaging film layer and a mask in an exposure imaging system includes: measuring surface relief information of the imaging film layer; determining a working distance between the imaging film layer and a mask according to the relief information.

2. The illumination compensation method of claim 1.

3. The step of calculating the intensities of the imaging light of the photoresist layer in the imaging film layer corresponding to different working distances includes: constructing an optical simulation model from the illumination light to an imaging light field in the photoresist layer; and calculating the intensities of the imaging light on the photoresist layer corresponding to different working distances for a given mask pattern and illumination light distribution based on the optical simulation model; The optical simulation model includes a lens group optical simulation model from the illumination light to the light incident on the upper surface of the mask, and an imaging film layer optical simulation model from the light incident on the upper surface of the mask to the imaging light field in the photoresist.

2. The illumination compensation method of claim 1.

4. The optical simulation model is [Equation 1] And I Ｐｒ (x, y) is the intensity distribution of the imaging light in the photoresist, and I ｉｌｌ (x, y) is the distribution of parameters corresponding to the illumination light, and PSF ｌｅｎｓ and PSF ｎｅａｒ－ｆｉｌｅｄ are the optical point spread functions of the lens group optical simulation model and the imaging film layer optical simulation model, respectively, and Mask(x, y) is the pattern distribution of the mask.

4. The illumination compensation method according to claim 3.

5. Construct the optical simulation model using the finite-difference time-domain method, rigorous coupled-wave analysis, or finite element method.

5. The illumination compensation method according to claim 3 or 4.

6. The step of establishing a relationship between a change in line width of an imaged pattern of a photoresist layer on an imaging film layer and a change in the working distance based on the intensity of the imaging light includes: performing threshold processing on the intensity of the imaging light of the photoresist layer corresponding to each working distance to obtain the line width of the imaging pattern of the photoresist layer corresponding to the working distance; and establishing a relationship between a change in the line width of the imaged pattern of the photoresist layer and a change in the working distance based on each working distance and the line width of the imaged pattern corresponding to the working distance.

5. The illumination compensation method according to claim 3 or 4.

7. The step of calculating a compensation parameter required for illumination light according to a relationship between a change in the line width of the imaged pattern and a change in the working distance includes: calculating a line width of the imaged pattern of the photoresist layer that needs to be compensated for different working distances based on a relationship between a change in line width of the original imaged pattern and a change in line width of the desired imaged pattern and a change in working distance; converting the line width of the imaged pattern of the photoresist layer that needs compensation into the intensity of the imaging light, and substituting the converted line width into the optical simulation model to calculate the compensation parameters including the light intensity, polarization, and phase.

5. The illumination compensation method according to claim 3 or 4.

8. performing illumination compensation on the exposure imaging system according to the compensation parameters, constructing an illumination compensation system by light field modulation technology according to the compensation parameters; and pixelating and adjusting the incident light field of the exposure imaging system with the illumination compensation system.

2. The illumination compensation method of claim 1.

9. The illumination compensation method includes: calculating line width uniformity evaluation indexes of the imaged pattern of the photoresist layer before and after illumination compensation; determining whether a linewidth uniformity index of the imaged pattern of the photoresist layer after compensation is better than a linewidth uniformity index of the imaged pattern of the photoresist layer before compensation; If so, determining the illumination compensation as a valid compensation.

2. The illumination compensation method of claim 1.

10. The step of calculating a line width uniformity evaluation index of an imaged pattern of the photoresist layer includes: determining a central working distance; and setting the value of the line width uniformity of the imaged pattern of the photoresist layer when the working distance changes around the central working distance as the uniformity evaluation index.

10. The illumination compensation method of claim 9.

Images