Optical model optimization method and optical proximity correction method

Abstract

An optical model optimization method and an optical proximity correction method, the optical model optimization method comprising: providing a photomask substrate and an initial optical model; determining the position and size of defects in the photomask substrate; obtaining the light intensity ratio at any defect position and a normal position, which is used as a light intensity correction factor, and the light intensity correction factor is related to the position and size of the corresponding defect; adding the light intensity correction factor to the initial optical model to obtain the optical model. The light intensity correction factor of the present invention can characterize the change of actual light intensity caused by the existence of defects, so that the accuracy of the optical model is higher, and the optical model is used to establish an optical proximity correction model, so that a better optical proximity correction model can be established according to the actual light intensity to compensate for the influence of the defects of the photomask substrate, thereby improving the accuracy of the optical proximity correction.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of semiconductor manufacturing, and in particular to an optical model optimization method and an optical proximity correction method. Background Art

[0002] Photolithography is a crucial technology in semiconductor manufacturing. Photolithography can transfer patterns from masks to silicon wafers to form semiconductor products that meet design requirements. With the rapid development of semiconductor technology, the critical dimension (CD) to be exposed by photolithography is getting smaller and smaller, and the resolution of photolithography is required to be higher and higher. The resolution of photolithography is mainly reflected in the feature size. The reduction of feature size can be achieved in three ways: reducing the exposure wavelength, increasing the numerical aperture or reducing the photolithography factor.

[0003] In order to obtain graphics with smaller feature sizes by reducing the exposure wavelength, extreme ultraviolet (EUV) lithography has been gradually applied to the lithography process as a more advanced lithography technology. Correspondingly, the EUV lithography process has higher requirements on the quality of the mask.

[0004] In addition, in order to improve the optical proximity effect (OPE) caused by the continuous reduction of feature size, optical proximity correction (OPC) was created. When establishing an OPC model, it is usually necessary to first establish an optical model, and then obtain the actual resist model based on the optical model. Summary of the invention

[0005] The problem solved by the embodiments of the present invention is to provide an optical model optimization method and an optical proximity correction method to improve the accuracy of optical proximity correction.

[0006] To solve the above problems, an embodiment of the present invention provides an optimization method for an optical model, comprising: providing a photomask substrate and an initial optical model; determining the position and size of defects in the photomask substrate; obtaining the light intensity ratio at any defect position and a normal position, which is used as a light intensity correction factor, and the light intensity correction factor is related to the corresponding position and size of the defect; adding the light intensity correction factor to the initial optical model to obtain an optical model.

[0007] Optionally, after determining the position and size of the defect in the photomask substrate and before obtaining the light intensity ratio at any of the defect positions and at a normal position, the optimization method of the optical model further includes: obtaining the ratio of the light wave at any of the defect positions to the light wave at a normal position, which is used as a light intensity interference term, and the light intensity interference term is related to the corresponding position and size of the defect; in the step of obtaining the light intensity ratio at any of the defect positions and at a normal position, the light intensity ratio is obtained through the light intensity interference term.

[0008] Optionally, in the step of providing a photomask substrate, the photomask substrate has a three-dimensional spatial coordinate system, and the three-dimensional spatial coordinate system includes a Z-axis perpendicular to the surface of the photomask substrate; and in the step of obtaining a ratio of the light wave at any defect position to the light wave at a normal position, for use as a light intensity interference term, the light intensity interference term is related to a focusing plane of the corresponding defect on the Z-axis, and the focusing plane is related to the position and size of the corresponding defect.

[0009] Optionally, in the step of providing a photomask substrate, the photomask substrate has a three-dimensional spatial coordinate system, and the three-dimensional spatial coordinate system includes a Z-axis perpendicular to the surface of the photomask substrate, and also includes an X-axis and a Y-axis perpendicular to each other, and the X-axis and the Y-axis are both perpendicular to the Z-axis; the step of determining the position and size of a defect in the photomask substrate includes: obtaining the coordinates of the defect on the X-axis and the Y-axis, and the height and half-height full width of the defect, the coordinates of the defect on the X-axis and the Y-axis are used to characterize the position of the defect, and the height and half-height full width of the defect are used to characterize the size of the defect.

[0010] Optionally, the light intensity interference term is related to the difference between the light wave at any of the defect positions and the light wave at a normal position in the focusing plane of the Z axis.

[0011] Optionally, the spherical equivalent volume diameter of any of the defects is used to determine the focal plane of the light wave at the corresponding defect position on the Z axis, and the spherical equivalent volume diameter is used to characterize the size of the defect.

[0012] Optionally, the three-dimensional space coordinate system further includes an X-axis and a Y-axis which are perpendicular to each other, and the X-axis and the Y-axis are both perpendicular to the Z-axis; the light intensity interference term is characterized by formula (I) and formula (II),

[0013]

[0014]

[0015] Wherein, R represents the light intensity interference term, A represents the amplitude of the light wave at any position of the photomask substrate, and A0 represents the amplitude of the light wave at the normal position, represents the phase of the light wave at any position of the photomask substrate, Represents the phase of the light wave at the normal position, OP (x,y) represents the focal plane of the light wave at any position of the photomask substrate on the Z axis, x represents the X-axis coordinate at any position of the photomask substrate, y represents the Y-axis coordinate at any position of the photomask substrate, and Z 0 Represents the focal plane of the light wave at the normal position on the Z axis.

[0016] Optionally, the spherical equivalent volume diameter is characterized by formula (III),

[0017]

[0018] Wherein, SEVD represents the spherical equivalent volume diameter, h 0 represents the height of the defect, and FWHM represents the full width at half maximum of the defect.

[0019] Optionally, the three-dimensional space coordinate system further includes an X-axis and a Y-axis which are perpendicular to each other, and the X-axis and the Y-axis are both perpendicular to the Z-axis; formula (V) and formula (VI) are used to characterize the focusing plane of the light wave at any position of the photomask substrate on the Z-axis,

[0020]

[0021]

[0022] Among them, OP (x,y) The light wave at any position of the photomask substrate is in the focal plane of the Z axis, Z 0 represents the focal plane of the light wave at the normal position on the Z axis, M represents the reduction factor of the optical system, (SEVD) i represents the spherical equivalent volume diameter of the i-th defect, x represents the X-axis coordinate at any position of the photomask substrate, and x i represents the X-axis coordinate of the i-th defect position, y represents the Y-axis coordinate of any position on the photomask substrate, and y i represents the Y-axis coordinate of the i-th defect position, σ xi Represents the standard deviation of the Gaussian distribution in the X-axis direction, σ yi Represents the standard deviation of the Gaussian distribution in the Y-axis direction.

[0023] Optionally, the product of the light intensity interference term and the conjugate function of the light intensity interference term is used as the light intensity correction factor.

[0024] Optionally, after providing a photomask substrate and an initial optical model, the optical model optimization method further includes: performing defect detection on the photomask substrate; and during the defect detection on the photomask substrate, determining the position and size of the defect in the photomask substrate.

[0025] Optionally, the initial optical model is a lithography system model based on the Hopkins formula.

[0026] Optionally, the step of adding the light intensity correction factor to the initial optical model includes: multiplying the light intensity correction factor by each parameter in the initial optical model.

[0027] Optionally, the photomask substrate is used to form a mask plate, and the mask plate is a reflective mask plate.

[0028] Optionally, the photomask substrate is used to form a mask, and the mask is an extreme ultraviolet mask.

[0029] Optionally, the photomask substrate is an optically transparent substrate; and the defect is located on the surface of the optically transparent substrate.

[0030] Correspondingly, an embodiment of the present invention also provides an optical proximity correction method, comprising: obtaining an optical model using the aforementioned optical model optimization method; establishing an optical proximity correction model using the optical model; providing a wafer layout pattern; and performing optical proximity correction on the wafer layout pattern using the optical proximity correction model.

[0031] Compared with the prior art, the technical solution of the embodiment of the present invention has the following advantages:

[0032] After determining the defects in the photomask substrate, the embodiment of the present invention determines the position and size of the defects in the photomask substrate, and then obtains the light intensity ratio (ratio of intensity) at any defect position and a normal position, which is used as a light intensity correction factor. The light intensity correction factor is related to the corresponding position and size of the defect. The light intensity correction factor can characterize the change in actual light intensity caused by the defect, so that after adding the light intensity correction factor to the initial optical model to obtain the optical model, the accuracy of the optical model is higher. The optical model is used to establish an optical proximity correction model. Therefore, a better optical proximity correction model can be established according to the actual light intensity to compensate for the impact of the defects of the mask substrate, thereby improving the accuracy of the optical proximity correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of a wavefront at any defect position of a photomask substrate;

[0034] Figure 2 is a flow chart of an embodiment of an optimization method of an optical model of the present invention;

[0035] Figure 3 yes Figure 2 A schematic diagram of a photomask substrate in accordance with an embodiment is shown. DETAILED DESCRIPTION

[0036] Defects in the masks used in extreme ultraviolet lithography systems seriously affect the yield of chip production, and it is currently impossible to process and manufacture defect-free masks.

[0037] Multilayer film defects are unique defects in EUV masks. They can be divided into amplitude defects and phase defects according to their different effects on the reflectivity of the mask. Phase defects are located at the bottom of the multilayer film (multiple layer, ML), causing deformation of the multilayer film.

[0038] Figure 1 Schematic diagram of a wavefront at any defect position of a photomask substrate. As an example, the photomask substrate includes an optically transparent substrate 10 and a multilayer film 11 covering the optically transparent substrate 10.

[0039] The photomask substrate is used to form an extreme ultraviolet mask plate. Therefore, the photomask substrate is a reflective mask substrate. The incident light 20 is reflected by the multilayer film 11 to form reflected light 30 .

[0040] However, if Figure 1 As shown, when the surface of the optically transparent substrate 10 has a defect 15, under the influence of the defect 15, the multilayer film 11 is deformed at the position of the defect 15. Therefore, under the interference of the defect 15, the reflected wavefront 31 is also deformed compared with the incident wavefront 21, resulting in a phase shift and reduced intensity of the reflected wavefront 31. Accordingly, when a mask having the defect 15 is used for photolithography and the mask pattern on the mask is transferred to a wafer, the pattern on the wafer may be distorted or the line width may be changed.

[0041] In order to reduce the impact caused by the defect 15 , one method is to perform optical proximity correction using a rule-based optical proximity correction model after determining the position of the defect 15 on the photomask substrate. However, the correction accuracy of the rule-based optical proximity correction model is low.

[0042] Another method is to stagger the formation position of the shielding layer and the position of the defect 15 when forming a patterned shielding layer (e.g., a chromium layer) on the photomask substrate during the process of manufacturing the mask, thereby avoiding the defect 15. However, as the feature size continues to shrink, the pattern complexity and pattern density of the shielding layer become higher accordingly, so it is difficult to completely avoid the randomly distributed defects 15.

[0043] In addition, the defect 15 cannot be removed without destroying the structure of the multilayer film 11. The cost of removing the defect 15 is high, and reworking the mask will increase the time cost, thereby reducing the manufacturing efficiency of chip manufacturing.

[0044] Due to the limitations of the above factors, there is an urgent need to provide an optimization method for an optical model, which can reduce or eliminate the optical impact caused by defects in the photomask substrate.

[0045] In order to solve the technical problem, an embodiment of the present invention provides an optical model optimization method, including: providing a photomask substrate and an initial optical model; determining the position and size of defects in the photomask substrate; obtaining the light intensity ratio at any defect position and a normal position, which is used as a light intensity correction factor, and the light intensity correction factor is related to the corresponding position and size of the defect; adding the light intensity correction factor to the initial optical model to obtain an optical model.

[0046] After determining the defects in the photomask substrate, the embodiment of the present invention determines the position and size of the defects in the photomask substrate, and then obtains the light intensity ratio at any defect position and the normal position for use as a light intensity correction factor. The light intensity correction factor is related to the corresponding position and size of the defect. The light intensity correction factor can characterize the change in actual light intensity caused by the defect, so that after adding the light intensity correction factor to the initial optical model to obtain the optical model, the accuracy of the optical model is higher. The optical model is used to establish an optical proximity correction model. Therefore, a better optical proximity correction model can be established according to the actual light intensity to compensate for the impact of the defects of the mask substrate, thereby improving the accuracy of the optical proximity correction.

[0047] refer to Figure 2 , shows a flow chart of an embodiment of an optical model optimization method of the present invention. The optical model optimization method of this embodiment includes the following basic steps:

[0048] Step S1: providing a photomask substrate and an initial optical model;

[0049] Step S2: Determine the location and size of the defect in the photomask substrate

[0050] Step S3: Obtaining a light intensity ratio at any defect position and a normal position, which is used as a light intensity correction factor, wherein the light intensity correction factor is related to the position and size of the corresponding defect;

[0051] Step S4: adding the light intensity correction factor to the initial optical model to obtain an optical model.

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0053] Combined with reference Figure 3 , Figure 3 is a schematic diagram of a photomask substrate of this embodiment. Step S1 is performed to provide a photomask substrate 100 and an initial optical model.

[0054] The photomask substrate 100 is used to prepare for forming a mask.

[0055] In this embodiment, the mask is a reflective mask, which means that when the mask is used to expose the photosensitive material on the wafer, the exposure light is irradiated to the side of the mask with the pattern, and the exposure light reflected by the pattern of the mask is irradiated to the wafer coated with the photosensitive material for exposure.

[0056] Specifically, the mask is an extreme ultraviolet (EUV) mask, that is, the mask is used in an EUV lithography system. EUV lithography is a lithography technology with higher resolution, and the wavelength of EUV light is approximately in the range of 10nm to 20nm, and can even be in the range of 13.4nm to 13.5nm. The wavelength of EUV light is short and is easily absorbed by the material in the transmissive mask. Therefore, EUV lithography uses a reflective mask instead of a transmissive mask.

[0057] like Figure 3 As shown, in this embodiment, the photomask substrate 100 is an optically transparent substrate. Specifically, the optically transparent substrate may be titanium silicate glass.

[0058] During the manufacturing process of the mask, a multilayer film (ML) is subsequently formed on the optically transparent substrate, wherein the multilayer film includes a multilayer film with alternating refractive indices, for example, a multilayer film includes alternating stacked molybdenum (Mo) layers and silicon (Si) layers.

[0059] In this embodiment, the photomask substrate 100 has a three-dimensional space coordinate system, which includes a Z axis perpendicular to the surface of the photomask substrate 100, and also includes an X axis and a Y axis perpendicular to each other, and both the X axis and the Y axis are perpendicular to the Z axis.

[0060] It should be noted that it is currently impossible to manufacture defect-free masks, and therefore, defects 150 are easily formed in the photomask substrate 100 .

[0061] As an example, the defect 150 is a particle. In other embodiments, the defect may also be a depression. Specifically, the defect 150 is located on the surface of the optically transparent substrate.

[0062] The defect 150 is a phase defect, which is located on the surface of the optically transparent substrate, thereby causing deformation of the subsequent multilayer film.

[0063] The mask is a reflective mask. During the photolithography process, the presence of the defect 150 will cause deformation of the reflected wavefront, resulting in a phase shift and reduced intensity of the reflected wavefront, which in turn causes problems such as pattern distortion or change in pattern line width.

[0064] Subsequently, the initial optical model is optimized to obtain an optical model, and the optical model is enabled to characterize the actual light intensity under the influence of the defect 150. The initial optical model is established based on various parameters of the optical lens system, such as numerical aperture, exposure wavelength, and type, thickness, refractive index, extinction coefficient, etc. of the photoresist stack.

[0065] In this embodiment, the initial optical model is a photolithography system model based on the Hopkins formula.

[0066] Specifically, the initial optical model is characterized by formula (VII):

[0067]

[0068] Where I(x,y) represents the light intensity on the wafer, J(x 1 -x 2 ,y 1 -y 2 ) represents the description of the light intensity of the light source, H(x 1 -x 2 ,y 1 -y 2 )×H * (x 1 -x 2 ,y 1 -y 2) represents the description of the pupil, O(x 1 ,y 1 )×O * (x 2 ,y 2 ) represents the description of the mask information.

[0069] Continue to refer Figure 2 In this embodiment, after providing the photomask substrate 100 , the method further includes: executing step S11 to perform defect inspection on the photomask substrate 100 .

[0070] By performing defect detection on the photomask substrate 100 , it is determined whether the photomask substrate 100 has a defect 150 .

[0071] It should be noted that when a multilayer film is formed on the photomask substrate 100, it becomes more difficult to detect the morphology of the bottom of the multilayer film. Therefore, in this embodiment, before forming the multilayer film, the photomask substrate 100 is subjected to defect detection to reduce the difficulty and accuracy of defect detection.

[0072] In this embodiment, defect detection is performed using a defect detection device. For example, an atomic force microscope is used for defect detection. Specifically, in the step of using the defect detection device to perform defect detection, an optical system is used for defect detection, and optical information is collected and extracted to obtain relevant information of the defect 150.

[0073] Continue to refer Figure 3 , executing step S2 to determine the position and size of the defect 150 in the photomask substrate 100 .

[0074] By confirming the position and size of the defect 150 , the influence of the defects 150 at different positions on the light intensity under the influence of corresponding sizes can be confirmed.

[0075] In this embodiment, during the defect detection process, the coordinates of the defect 150 on the X-axis and Y-axis, as well as the height and full width at half maximum (FWHM) of the defect 150 are obtained. The defect detection device uses an optical system to perform defect detection, so the defect detection device has the function of obtaining the above information.

[0076] The coordinates of the defect 150 on the X-axis and the Y-axis are used to characterize the position of the defect 150 .

[0077] The height and half-height full width of the defect 150 are used to characterize the size of the defect 150. The height and half-height full width of the defect 150 will affect the deformation degree of the multilayer film, thereby affecting the deformation degree of the reflected wavefront, and further affecting the phase shift and intensity reduction degree of the reflected wavefront. Among them, the height of the defect 150 is its size along the Z axis; the half-height full width is an optical parameter and can be used to characterize the size of the defect 150.

[0078] Specifically, the spherical equivalent volume diameter (SEVD) of the defect 150 is used to characterize the size of the defect 150 .

[0079] The spherical equivalent volume diameter is used to convert the size of a particle into the diameter of a sphere of the same volume as the particle. The spherical equivalent volume diameter of the defect 150 is related to the height and full width at half maximum of the defect 150, thereby more accurately reflecting the effect of the morphology and size of the defect 150 on the intensity of light.

[0080] In this embodiment, the spherical equivalent volume diameter of the defect 150 is represented by formula (III):

[0081]

[0082] Wherein, SEVD represents the spherical equivalent volume diameter, h 0 represents the height of the defect 150 , and FWHM represents the full width at half maximum of the defect 150 .

[0083] Continue to refer Figure 2 In this embodiment, when determining the photomask substrate 100 (such as Figure 3 Defect 150 (as shown) Figure 3 After determining the position and size of the defect 150, the method further includes: executing step S22 to obtain the ratio of the light wave at the position of any defect 150 to the light wave at the normal position, which is used as a light intensity interference item, and the light intensity interference item is related to the corresponding position and size of the defect 150.

[0084] The normal position refers to a position in the photomask substrate 100 that has no defects.

[0085] Under the interference of the defect 150, the reflected wavefront will be deformed compared with the incident wavefront. Therefore, the interference of the defect 150 on the light wave can be characterized by the ratio of the light wave at any position of the defect 150 to the light wave at a normal position.

[0086] In this embodiment, the light intensity interference term is related to the focus plane of the corresponding defect 150 on the Z axis, and the focus plane is related to the position and size of the corresponding defect. The focus plane is an optical surface.

[0087] In the field of optical proximity correction, the spatial light intensity distribution curve should be the spatial light intensity distribution of the best focusing plane. The surface of the photosensitive material is located in the best focusing plane to obtain the best critical size and is conducive to forming a better quality pattern in the photosensitive material.

[0088] Therefore, when a mask is used to expose the photosensitive material on the wafer, at the normal position of the photomask substrate 100, the focusing plane should be located in the plane formed by the X-axis and the Y-axis, that is, the focusing plane should be located on the surface of the photosensitive material, so that the desired pattern can be obtained in the photosensitive material.

[0089] However, it is difficult to obtain the optimal focusing plane at the location of the defect 150, and the actual focusing plane is located above the photosensitive material rather than on the surface of the photosensitive material. Accordingly, after the photosensitive material is exposed, a missing or distorted pattern will appear at the location corresponding to the defect 150 in the photosensitive material.

[0090] Therefore, by making the light intensity interference term correlated with the focal plane of the defect 150 on the Z axis, the influence of the defect 150 on the light intensity variation is reflected.

[0091] Specifically, the light intensity interference term is the ratio of the light wave at any of the defect 150 positions to the light wave at the normal position, and according to the expression of the light wave, the ratio is related to the phase difference between the two light waves. Therefore, in this embodiment, the light intensity interference term is related to the difference between the light wave at any of the defect 150 positions and the light wave at the normal position in the focal plane of the Z axis.

[0092] In this embodiment, the light intensity interference term is characterized by formula (I) and formula (II),

[0093]

[0094]

[0095] Wherein, R represents the light intensity interference term, A represents the amplitude of the light wave at any position of the photomask substrate 100, and A 0 represents the amplitude of the light wave at the normal position, represents the phase of the light wave at any position of the photomask substrate 100, Represents the phase of the light wave at the normal position, OP (x,y)represents the focal plane of the light wave at any position of the photomask substrate 100 on the Z axis, x represents the X-axis coordinate at any position of the photomask substrate 100, y represents the Y-axis coordinate at any position of the photomask substrate 100, and Z 0 Represents the focal plane of the light wave at the normal position on the Z axis.

[0096] Correspondingly, Z 0 This is the plane where light is best focused.

[0097] Therefore, when it is determined that the photomask substrate 100 has a defect 150 and the coordinates of any defect 150 on the X-axis and Y-axis are determined, the light wave at the position of the defect 150 is used as the numerator of the light intensity interference term, and the light wave at the normal position is used as the denominator of the light intensity interference term, thereby obtaining the ratio of the light wave at the position of the defect 150 to the light wave at the normal position.

[0098] In this embodiment, the spherical equivalent volume diameter (SEVD) of any defect 150 is used to determine the focal plane of the light wave at the corresponding position of the defect 150 on the Z axis, and the spherical equivalent volume diameter is used to characterize the size of the defect 150.

[0099] In this embodiment, a Gaussian function is used to characterize the focal plane of the defect 150 on the Z axis. Gaussian defect parameters can characterize the morphology of phase defects.

[0100] Therefore, formula (V) and formula (VI) are used to characterize the focusing plane of the light wave at any position of the photomask substrate 100 on the Z axis.

[0101]

[0102]

[0103] Among them, OP (x,y) represents the focusing plane of the light wave at any position of the photomask substrate 100 on the Z axis, Z 0 represents the focal plane of the light wave at the normal position on the Z axis, M represents the reduction factor of the optical system, (SEVD) i represents the spherical equivalent volume diameter of the i-th defect 150, x represents the X-axis coordinate at any position of the photomask substrate 100, and x i represents the X-axis coordinate of the position of the i-th defect 150, y represents the Y-axis coordinate of any position of the photomask substrate 100, and y i represents the Y-axis coordinate of the i-th defect 150, σ xi Represents the standard deviation of the Gaussian distribution in the X-axis direction, σ yiRepresents the standard deviation of the Gaussian distribution in the Y-axis direction.

[0104] The preset interval range of the horizontal axis and the vertical axis is used to characterize the influence range of the defect 150 , so as to determine whether any selected position is the position of any defect 150 .

[0105] At any position of the photomask substrate 100, when both the horizontal coordinate and the vertical coordinate of the position are within the preset interval, it means that the position falls within the influence range of the defect 150, that is, the position is a position with the defect 150, and therefore formula (V) is used to represent the focusing plane of the light wave at the position on the Z axis; when both the horizontal coordinate and the vertical coordinate of the position are not within the preset interval, it means that the position is a normal position, and therefore formula (VI) is used to characterize the focusing plane of the light wave at the position on the Z axis.

[0106] Continue to refer Figure 2 , execute step S3 to obtain the light intensity ratio at any of the defect 150 positions and the normal position, which is used as a light intensity correction factor. The light intensity correction factor is proportional to the corresponding defect 150 (such as Figure 3 The position and size of the components are related.

[0107] Specifically, the light intensity ratio at the position of the defect 150 and at the normal position is obtained through the light intensity interference term, which is used as a light intensity correction factor.

[0108] The light intensity interference term is related to the position and size of the corresponding defect 150. Therefore, the light intensity ratio at the position of the defect 150 and the normal position is obtained through the light intensity interference term. After being used as a light intensity correction factor, the light intensity correction factor can characterize the change in actual light intensity caused by the defect 150.

[0109] In this embodiment, the product of the light intensity interference term and the conjugate function of the light intensity interference term is used as the light intensity correction factor. The expression of light intensity can be obtained by multiplying the expression of light wave with its conjugate function.

[0110] Therefore, in this embodiment, formula (VIII) is used to characterize the light intensity correction factor:

[0111] R I =R×R * (VIII)

[0112] Among them, R I represents the light intensity correction factor, R represents the light intensity interference term, and R* represents the conjugate function of the light intensity interference term.

[0113] Continue to refer Figure 2, execute step S4, add the light intensity correction factor to the initial optical model to obtain an optical model.

[0114] The light intensity correction factor can characterize the change of the actual light intensity caused by the defect 150. After the light intensity correction factor is added to the initial optical model to obtain the optical model, the optical model can characterize the actual light intensity, that is, the optical model has higher accuracy. The optical model is used to establish an optical proximity correction model. Therefore, a better optical proximity correction model can be established according to the actual light intensity to compensate for the mask substrate 100 (such as Figure 3 The influence of the defect 150 as shown in FIG. 1 is reduced, thereby improving the accuracy of the optical proximity correction.

[0115] In this embodiment, the initial optical model includes multiple parameters. Therefore, the step of adding the light intensity correction factor to the initial optical model includes: multiplying the light intensity correction factor with each parameter in the initial optical model to characterize the change in actual light intensity caused by the defect 150, thereby enabling the optical model to characterize the actual light intensity.

[0116] In this embodiment, the optical model is characterized by formula (IX):

[0117]

[0118] Where I'(x,y) represents the light intensity on the wafer.

[0119] Correspondingly, the present invention also provides an optical proximity correction method.

[0120] The optical proximity correction method described in this embodiment includes: obtaining an optical model using the aforementioned optical model optimization method; establishing an optical proximity correction model using the optical model; providing a wafer layout pattern; and performing optical proximity correction on the wafer layout pattern using the optical proximity correction model.

[0121] The optical proximity correction model includes an optical model (Initial Optical Model) and a photoresist model (CTRModel), and the optical model described in this embodiment has high accuracy. The optical model can characterize the actual light intensity. Therefore, when the optical proximity correction model is established using the optical model, a better optical proximity correction model can be established according to the actual light intensity to compensate for the impact of defects in the mask substrate, thereby improving the accuracy of the optical proximity correction.

[0122] For the specific description of the optical model, reference may be made to the corresponding description in the aforementioned embodiment, which will not be repeated here.

[0123] The photoresist model includes a photoresist exposure reference threshold, and the photoresist model is established based on parameters such as the photoresist exposure reference threshold (ie, the minimum energy required for photoresist exposure).

[0124] In this embodiment, when the photoresist material is known and the photoresist exposure reference threshold is fixed, the minimum energy required for photoresist exposure can be known.

[0125] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. An optimization method for an optical model, It is characterized in that include: Providing a photomask substrate and an initial optical model, wherein the photomask substrate is an optically transparent substrate, the photomask substrate is used to form a reflective mask, and the photomask substrate has a three-dimensional spatial coordinate system, wherein the three-dimensional spatial coordinate system includes a Z axis perpendicular to the surface of the photomask substrate; Determining the position and size of a defect in the photomask substrate, wherein the defect is a phase defect; Obtaining a light intensity interference term, wherein the light intensity interference term is related to a difference between a light wave at any defect position and a light wave at a normal position on a focal plane of the Z axis, and the light wave at the defect position is related to a position and size of the corresponding defect on the focal plane of the Z axis; Obtaining the light intensity ratio at any defect position and a normal position through the light intensity interference term, which is used as a light intensity correction factor, wherein the light intensity correction factor is related to the position and size of the corresponding defect; The light intensity correction factor is added to the initial optical model to obtain an optical model.

2. The method for optimizing the optical model according to claim 1, It is characterized in that Acquiring the light intensity interference term includes: acquiring a ratio of the light wave at any of the defect positions to the light wave at a normal position, which is used as the light intensity interference term.

3. The method for optimizing the optical model according to claim 1, It is characterized in that In the step of providing a photomask substrate, the three-dimensional space coordinate system further includes an X-axis and a Y-axis which are perpendicular to each other, and the X-axis and the Y-axis are both perpendicular to the Z-axis; The step of determining the position and size of the defect in the photomask substrate includes: obtaining the coordinates of the defect on the X-axis and Y-axis, and the height and half-height full width of the defect, wherein the coordinates of the defect on the X-axis and Y-axis are used to characterize the position of the defect, and the height and half-height full width of the defect are used to characterize the size of the defect.

4. The method for optimizing the optical model according to claim 1, It is characterized in that The spherical equivalent volume diameter of any of the defects is used to determine the focal plane of the light wave at the corresponding defect position on the Z axis, and the spherical equivalent volume diameter is used to characterize the size of the defect.

5. The method for optimizing the optical model according to claim 2, It is characterized in that The three-dimensional space coordinate system also includes an X-axis and a Y-axis which are perpendicular to each other, and the X-axis and the Y-axis are both perpendicular to the Z-axis; the light intensity interference term is characterized by formula (I) and formula (II), Wherein, R represents the light intensity interference term, A represents the amplitude of the light wave at any position of the photomask substrate, and A 0 represents the amplitude of the light wave at the normal position, represents the phase of the light wave at any position of the photomask substrate, Represents the phase of the light wave at the normal position, OP (x,y) represents the focal plane of the light wave at any position of the photomask substrate on the Z axis, x represents the X-axis coordinate at any position of the photomask substrate, y represents the Y-axis coordinate at any position of the photomask substrate, and Z 0 Represents the focal plane of the light wave at the normal position on the Z axis.

6. The method for optimizing an optical model according to claim 4, It is characterized in that Formula (III) is used to characterize the spherical equivalent volume diameter: Wherein, SEVD represents the spherical equivalent volume diameter, h 0 represents the height of the defect, and FWHM represents the full width at half maximum of the defect.

7. The method for optimizing an optical model according to claim 1, It is characterized in that The three-dimensional space coordinate system also includes an X-axis and a Y-axis which are perpendicular to each other, and the X-axis and the Y-axis are both perpendicular to the Z-axis; Formula (V) and formula (VI) are used to characterize the focusing plane of the light wave at any position of the photomask substrate on the Z axis. Among them, OP (x,y) The light wave at any position of the photomask substrate is in the focal plane of the Z axis, Z 0 represents the focal plane of the light wave at the normal position on the Z axis, M represents the reduction factor of the optical system, (SEVD) i represents the spherical equivalent volume diameter of the i-th defect, x represents the X-axis coordinate at any position of the photomask substrate, and x i represents the X-axis coordinate of the i-th defect position, y represents the Y-axis coordinate of any position on the photomask substrate, and y i represents the Y-axis coordinate of the i-th defect position, σ xi Represents the standard deviation of the Gaussian distribution in the X-axis direction, σ yi Represents the standard deviation of the Gaussian distribution in the Y-axis direction.

8. The method for optimizing the optical model according to claim 1 or 5, It is characterized in that The product of the light intensity interference term and the conjugate function of the light intensity interference term is used as the light intensity correction factor.

9. The method for optimizing an optical model according to claim 1, It is characterized in that After providing the photomask substrate and the initial optical model, the optical model optimization method further includes: performing defect detection on the photomask substrate; During defect detection of the photomask substrate, the location and size of defects in the photomask substrate are determined.

10. The method for optimizing an optical model according to claim 1, It is characterized in that The initial optical model is a lithography system model based on the Hopkins formula.

11. The method for optimizing an optical model according to claim 1 or 10, It is characterized in that The step of adding the light intensity correction factor to the initial optical model includes: multiplying the light intensity correction factor by each parameter in the initial optical model.

12. The method for optimizing an optical model according to claim 1, It is characterized in that The mask is an extreme ultraviolet mask.

13. The method for optimizing an optical model according to claim 1, It is characterized in that The defects are located on the surface of the optically transparent substrate.

14. An optical proximity correction method, It is characterized in that include: Obtaining an optical model using the optical model optimization method of any one of claims 1 to 13; establishing an optical proximity correction model using the optical model; Provide wafer layout graphics; The optical proximity correction model is used to perform optical proximity correction on the wafer layout pattern.

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