Wafer exposure system and compensation method thereof

Abstract

The application discloses a wafer exposure system and a compensation method thereof. The compensation method comprises the following steps: performing exposure preprocessing by using the wafer exposure system; obtaining a first compensation value of a lens in the exposure preprocessing process; obtaining a mask error value in the exposure preprocessing process; obtaining a second compensation value of the lens according to the mask error value; and generating a third compensation value according to the first compensation value and the second compensation value. The wafer exposure system and the compensation method thereof provided by the application can convert the mask error value caused by the thermal effect of the mask into the second compensation value of the lens, so that the wafer exposure system can compensate according to the third compensation value obtained according to the first compensation value and the second compensation value, thereby improving the overlay accuracy in the exposure process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor integrated circuit, in particular to a wafer exposure system and a compensation method thereof. BACKGROUND

[0002] Photolithography is one of the core technologies in the semiconductor industry. The essence of photolithography is to transfer the pattern on a mask to a substrate using photochemical principles. In this process, components or materials such as light sources, masks, projection lenses, wafer chips, and photoresists are involved. The radiation from the light source is projected through the projection lens to the mask (photomask), and the pattern on the mask is given to the radiation, which then irradiates the photoresist on the surface of the wafer chip with the pattern information of the mask, so that the pattern information of the mask is transferred to the photoresist on the surface of the wafer chip, and the wafer chip is etched through the photoresist to obtain the corresponding pattern.

[0003] However, when exposing the wafer, due to the large exposure energy or high mask transmittance, thermal effects will occur in the lens and the mask. The light absorbed by the lens and the mask is converted into heat, causing the local temperature of the lens and the mask to rise, which will result in two consequences: (1) the lens and the mask material expands, changing the local geometry of the lens and the mask; (2) the refractive index and other optical parameters of the lens change. The aberration caused by the thermal effect of the lens and the mask will further reduce the imaging contrast and alignment accuracy during exposure, resulting in a loss of the photolithography process window, and the thermal effect will accumulate, causing changes in process parameters, resulting in a large difference in line width between the first wafer and the nth wafer, causing major problems for industrial production. SUMMARY

[0004] In view of the above problems, the present application provides a wafer exposure system and a compensation method thereof. By converting the mask error value caused by the thermal effect of the mask into a second compensation value of the lens, the wafer exposure system is compensated according to a third compensation value obtained from the first compensation value and the second compensation value, thereby improving the overlay accuracy during exposure.

[0005] According to a first aspect of the present application, a compensation method for a wafer exposure system is provided, which comprises: performing exposure preprocessing using a wafer exposure system; obtaining a first compensation value of the lens during the exposure preprocessing; obtaining a mask error value during the exposure preprocessing; obtaining a second compensation value of the lens according to the mask error value; and generating a third compensation value according to the first compensation value and the second compensation value,

[0006] Optionally, in the step of performing exposure preprocessing using a wafer exposure system, a wafer exposure system with lens compensation function is used to perform exposure processing on a batch of wafers.

[0007] Optionally, the lens and the mask in the wafer exposure system reach thermal stability after exposure pre-treatment.

[0008] Optionally, in the step of obtaining the second compensation value of the lens according to the mask error value, the step comprises: obtaining a plurality of parameters in the mask error value; converting the plurality of parameters into distortion modulation parameters; and obtaining the second compensation value of the lens according to the distortion modulation parameters.

[0009] Optionally, the plurality of parameters comprise coma, spherical aberration, defocus, astigmatism, low-order aberration and high-order aberration.

[0010] Optionally, in the step of obtaining the second compensation value of the lens according to the distortion modulation parameters, the distortion modulation parameters are converted into Zernike polynomials to obtain the second compensation value of the lens.

[0011] Optionally, in the step of obtaining the first compensation value of the lens in the exposure pre-treatment process, the first compensation value is obtained according to Zernike polynomials.

[0012] Optionally, in the step of obtaining the first compensation value of the lens in the exposure pre-treatment process, the first compensation value is obtained by consulting records of the wafer exposure system.

[0013] Optionally, after the step of generating the third compensation value according to the first compensation value and the second compensation value, the method further comprises: compensating the lens of the wafer exposure system according to the third compensation value and exposing the wafer.

[0014] According to another aspect of the present application, a wafer exposure system is provided for performing the above-mentioned compensation method, wherein the wafer exposure system comprises: a radiation source for generating a radiation beam for exposure; an illumination system located behind the radiation source for shaping and adjusting the radiation beam generated by the radiation source; a mask located behind the illumination system and comprising a pattern to be transferred to a wafer; an objective system located behind the mask and comprising a plurality of lenses for reducing and adjusting the radiation light source passing through the mask; and a resist layer located behind the objective and forming a pattern before wafer etching.

[0015] The present application has the following unexpected technical effects:

[0016] According to the wafer exposure system and the compensation method thereof, the first compensation value of the lens and the mask error value of the mask plate are obtained in the exposure pretreatment of the machine table with the lens compensation function being turned on, the second compensation value of the lens is obtained according to the mask error value, the third compensation value is generated according to the first compensation value and the second compensation value of the lens, and the lens of the machine table is compensated and the wafer is exposed according to the third compensation value. The third compensation value is obtained according to the first compensation value of the initial machine table and the second compensation value converted from the error value of the subsequent mask plate, so that the exposure of the machine table according to the third compensation value can greatly reduce the error of the lens and the mask plate caused by the thermal effect, thereby improving the overlay accuracy in the exposure process.

[0017] Further, the wafer exposure system and the compensation method thereof convert the influence of the thermal effect on the mask plate into the second compensation value of the lens, so that the machine table only needs to compensate the lens to reduce the overlay error caused by the influence of the thermal effect on the lens and the mask plate in the wafer exposure, thereby reducing the complexity of the machine table. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 A structure diagram of a wafer exposure system according to an embodiment of the present application is shown;

[0020] Figure 2 A flowchart of a compensation method of a wafer exposure system according to an embodiment of the present application is shown;

[0021] Figure 3 A diagram of the idea of a compensation method of a wafer exposure system according to an embodiment of the present application is shown;

[0022] Figure 4 A Zernike diagram in a compensation method of a wafer exposure system according to an embodiment of the present application is shown;

[0023] Figure 5 A fitting surface distribution diagram in a compensation method of a wafer exposure system according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0024] The present application will be described in more detail by referring to the attached drawings. In each of the drawings, the same elements are denoted by like reference numerals for the sake of clarity. Each portion in the drawings is not drawn to scale. In addition, some well-known portions can not be shown. The present application can be presented in various forms, and some examples thereof will be described below.

[0025] The present application can be presented in various forms, some examples of which will be described below.

[0026] Figure 1 A schematic diagram of a wafer exposure system according to an embodiment of the present application is shown, the wafer exposure system 100 is used to image the pattern of a mask 121 in a resist layer PR 122. As shown, the wafer exposure system 100 includes, in order along the path of the light rays, a radiation source 101, an illumination system 102, the mask 121, an objective system 103, and the resist layer PR 122. Figure 1

[0027] The radiation source 101 is the core component of the wafer exposure system 100, which is responsible for generating the radiation beam used for exposure. This radiation can be deep ultraviolet (DUV), extreme ultraviolet (EUV) or other suitable electromagnetic radiation for photolithography process. The radiation source 101 can include a laser, a mercury lamp or other types of light source that can provide the required wavelength and power to achieve high-precision photolithography.

[0028] The illumination system 102, also known as the illumination system or illuminator, receives the light beam from the radiation source 101 and shapes and adjusts it to form a specific light intensity distribution. This system can include beam shapers, beam homogenizers and beam controllers, etc. The illumination system 102 ensures that the light beam has a uniform or predetermined intensity distribution before it is illuminated onto the mask 121, which is crucial for controlling the pattern transfer in the photolithography process.

[0029] The mask 121 is a key component in the photolithography process, which is located in the light path of the illumination system 102 and contains the pattern to be transferred to the wafer 120. The mask 121 can be transmissive or reflective, depending on the photolithography technology used. The mask 121 includes exposure patterns and alignment marks, and in transmissive photolithography, the mask 121 allows the radiation beam to pass through its transparent areas. The exposure pattern on the mask 121 determines the exposure area of the resist layer PR 122 on the wafer 120.

[0030] The objective system 103, also known as the projection lens, is located on the side of the mask 121 away from the illumination system 102, and the objective system 103 is a component in the wafer exposure system 100 used to reduce and accurately project the radiation beam that passes through the mask 121 and carries the pattern on the mask 121 onto the resist layer PR 122 on the wafer 120 surface. The objective system 103 is usually composed of a combination of multiple high-quality lenses specially designed and precisely manufactured, which work together to correct various optical distortions and ensure accurate pattern transfer. The design and adjustment of the objective system 103 are crucial for achieving high-resolution and high-contrast photolithography patterns.

[0031] ​A photoresist layer PR 122 is coated on the surface of the wafer 120. The photoresist layer PR 122 is a photosensitive material that changes its chemical properties when exposed to light of a specific wavelength. In the photolithography step, the objective lens system 103 projects the pattern on the mask 121 onto the photoresist layer PR 122 through the light beam adjusted by the illumination system 102, thereby forming an image corresponding to the pattern on the mask 121 in the photoresist layer PR 122 as the pattern before etching of the wafer.

[0032] In one exposure process, the radiation beam generated by the radiation source 101 is incident on the mask 121 after being shaped and adjusted by the illumination system 102, and penetrates according to the area of the exposure pattern in the mask 121 when the radiation beam passes through the mask 121, so that the radiation beam carries the shape information of the exposure pattern after passing through the mask 121. Further, the radiation beam carrying the shape information of the exposure pattern is illuminated on the photoresist layer PR 122 after being reduced by the objective lens system 103. After exposure and development, the photoresist layer PR 122 obtains the same pattern as the exposure pattern in the mask 121.

[0033] Figure 2 A flowchart of a compensation method of a wafer exposure system according to an embodiment of the present application is shown; Figure 3 A schematic diagram of a compensation method of a wafer exposure system according to an embodiment of the present application is shown; Figure 4 A Zernike chart in a compensation method of a wafer exposure system according to an embodiment of the present application is shown; Figure 5 A fitting surface distribution chart in a compensation method of a wafer exposure system according to an embodiment of the present application is shown.

[0034] Specifically, the wafer exposure system 100 is a system with lens compensation function. The lens compensation function refers to the function of correcting and compensating for imaging defects caused by the lens due to its own characteristics and external factors in an optical system (such as the wafer exposure system 100), so as to improve the imaging quality and precision of the optical system.

[0035] In the present application, as shown in Figure 3 The compensation method of the wafer exposure system 100 includes the following steps.

[0036] Step S210: Pre-exposure treatment is performed using a wafer exposure system with lens compensation function.

[0037] In this step, the exposure pre-treatment refers to starting up the wafer exposure system, and then patterning the resist layer PR122 of a batch of wafers by the wafer exposure system 100. During the exposure pre-treatment, the mask 121 and the lenses in the objective lens system 103 will be deformed due to the thermal energy of the radiation beam generated by the radiation source 101, and the thermal effects of the lenses and the mask 121 will tend to be stable after the exposure of the nth wafer.

[0038] Therefore, the exposure pre-treatment in this step makes the thermal effects of the lenses and the mask 121 in the wafer exposure system 100 tend to be stable, or in other words, the exposure pre-treatment makes the temperature of the lenses and the mask 121 reach a saturation temperature.

[0039] In the existing wafer exposure system 100, a lens compensation function is usually provided to compensate for the errors of the lenses caused by thermal effects during exposure. Therefore, the exposure pre-treatment in this step also has the initial lens compensation function of the machine, and the compensation method of the wafer exposure system of the present application is based on this.

[0040] Step S220: obtaining a first compensation value of the lenses during the exposure pre-treatment.

[0041] In this step, the lenses in the objective lens system 103 will generate errors due to the distortion caused by the thermal effects of the radiation beam during the exposure pre-treatment, but the wafer exposure system 100 has a lens compensation function. Therefore, in this step, the first compensation value of the lenses by the wafer exposure system 100 during the exposure pre-treatment is obtained.

[0042] Specifically, during the process of the lenses reaching thermal stability, the temperature distribution graph and the Zernike map of the lenses under the exposure condition are obtained. The Zernike map is a graphical representation formed by using Zernike polynomials to describe the wavefront aberration distribution of the lenses in the optical system.

[0043] The temperature distribution graph during the process of the lenses reaching thermal stability can also be obtained, and the first compensation value of the lenses is obtained by performing thermal-optical effect calculation and Zernike polynomial calculation based on the temperature distribution graph and the Zernike map of the lenses. In this embodiment, when calculating the first compensation value of the lenses, multiple parameters such as the thermal-optical coefficient and the refractive index of the lens material are involved. By establishing a relationship model between the temperature distribution of the lenses and the wavefront distortion, and then according to the optical propagation theory, the phase change in the light propagation process is calculated by using the refractive index change, and the first compensation value of the lenses is calculated by using the photolithography process, so as to reduce the deviation between the exposure patterns before and after the lenses. The first compensation value in the present application is an array containing multiple lens parameters.

[0044] In the present application, for the wafer exposure system 100 containing the initial lens compensation function, the first compensation value of the lens in the exposure pre-processing process can also be directly queried from the record in the wafer exposure system.

[0045] Step S230: Obtain the mask error value in the exposure pre-processing process.

[0046] In the exposure pre-processing process, the mask 121 will also generate errors due to the thermal effect of the radiation beam, but since the initial compensation mechanism of the wafer exposure system 100 is for the compensation of the lens, the influence of the thermal effect generated by the mask 121 has not been compensated or the compensation effect is poor.

[0047] In this step, the mask error value in the exposure pre-processing process is obtained, for example, the temperature distribution diagram of the mask 121 in the exposure process is obtained, or the offset between the standard exposure pattern (before exposure) on the mask 121 and the exposure pattern after the mask 121 and before the lens.

[0048] Specifically, in this embodiment, the mask error value is, for example, the temperature distribution, so that the temperature distribution diagram of the mask 121 under the exposure condition is obtained in this step. For example, an infrared temperature sensor is used to collect the temperature distribution of the mask 121.

[0049] In other embodiments, when the mask error value is the offset, the offset is, for example, the change of the local length, thickness, etc. of the mask 121 caused by the radiation thermal energy, which causes the pattern in the mask 121 to change slightly, and then the pattern transferred to the resist layer PR 122 through the radiation beam and the lens also has errors. That is, the offset of the actual exposure pattern on the resist layer PR 122 comes from the mask 121 and the lens, and since the materials of the mask 121 and the lens are different, the change rule of the offset is different.

[0050] Step S240: Obtain the second compensation value of the lens according to the mask error value.

[0051] In this step, the mask error value of the mask 121 is converted into a parameter related to the lens, and the second compensation value of the lens is calculated according to the converted parameter.

[0052] In this embodiment, for example, Zernike map and Zernike polynomial are used to convert the mask error value and the lens compensation value.

[0053] Zernike polynomials can be used to fit the surface profile of optical elements, mainly by using the fixed relationship between the two kinds of aberrations in the rotation angle to change the lens surface profile and rotate the lens. Zernike polynomials are a complete set of polynomials with two variables R and θ, where R represents the radius and θ represents the phase angle. Table 1 below lists a part of Zernike polynomials. In order to facilitate the representation, Z1 represents the first row of formulas, Z2 represents the second row of formulas, and so on. Since Zernike polynomials are common knowledge in the field of optics, the meaning of each formula in Zernike polynomials will not be described here. Since Zernike polynomials are infinite in number, it is impossible to list them all here. Table 1 only lists 16 polynomials as an example. Those skilled in the art can understand that other unlisted parts are also within the protection scope of the present application. It should also be noted that the arrangement order of Zernike polynomials listed in the present application is the commonly used arrangement order, but other arrangement orders are not excluded. Those skilled in the art can understand that other arrangement orders of Zernike polynomials are also within the protection scope of the present application.

[0054] Table 1: Partial Zernike polynomials

[0055] Z1 1 Z2 R cos θ Z3 R sin θ Z4 2R 2 -1]]> Z5 [R 2 cos(2θ) Z6 R 2 sin(2θ) Z7 [(3R 3 -2R) cos theta]] Z8 <![CDATA[(3R 3 -2R)sinθ]]> Z9 6R 4 -6R 2 +1]]> Z10 [R 3 cos(3θ) Z11 R 3 sin(3θ) Z12 4 -3R 2 ) cos (2θ) ​ Z13 4 -3R 2 )sin(2θ) ​ Z14 5 -12R 3 +3R)cosθ]]> ​ Z15 5 -12R 3 +3R)sinθ]]> ​ Z16 20R 6 -30R 4 +12R 2 -1]]>

[0056] Specifically, the wavefront of the lens itself changes with the extension of the exposure time, and the Zernike polynomials presented are different, as shown in Figure 4 , and the corresponding distortion modulation according to the Zernike polynomials is also different, as shown in Figure 5 .

[0057] After obtaining the mask error value of the mask 121, a plurality of parameters K7, K8, K9, K10, K11, etc. are split according to the temperature distribution map of the mask 121 in the exposure process, and then these parameters are converted into corresponding distortion modulation parameters, and finally converted into Zernike map and Zernike polynomials, thereby realizing the conversion between the error value of the mask 121 and the compensation value of the lens.

[0058] Among the plurality of parameters split from the temperature distribution map of the mask 121, K7, for example, refers to coma and y-axis tilt. In Zernike polynomials, if K is regarded as similar to Z (Zernike polynomial coefficient represents commonly used Z), then K7 may correspond to the correlation coefficient term of coma and y-axis tilt aberration. Coma will cause the imaging light beam to focus at different positions, resulting in a comet-like blur in the image; y-axis tilt indicates that the optical system has a tilt in the y direction, causing the direction of light propagation to change in the y direction.

[0059] K8 refers to, for example, the correlation coefficient of astigmatism, spherical aberration, and defocus. Astigmatism refers to the phenomenon that different directions of light rays cannot form a clear point image but form two mutually perpendicular focal lines in front and back when the light rays pass through an aspherical or defective optical element (such as a lens, a mirror, etc.). Spherical aberration refers to a kind of aberration caused by different aperture focusing positions of light rays due to the spherical lens and other elements of an optical system; defocus refers to the phenomenon that the imaging plane does not coincide with the ideal focusing plane, so that the whole image becomes blurred.

[0060] K9 and the parameters thereafter refer to, for example, low-order aberration, high-order aberration, or other more complex composite aberration. For example, K9 is a combination of a certain third-order aberration and other aberrations, and K10 and K11 involve more complex aberration interactions or aberration performances related to other parameters of an optical system.

[0061] Zernike map compensation is to correct or compensate for these aberrations according to the wavefront aberration shown in the Zernike map, so as to optimize the performance of the optical system. The principle is based on the fact that Zernike polynomials can decompose complex wavefront aberration into a series of basic aberration modes with specific physical meanings, such as astigmatism, coma, spherical aberration, etc. By calculating and analyzing the coefficients and distribution of each aberration mode in the Zernike map, the compensation amount and compensation method to be applied are determined to eliminate or reduce the influence of aberration on optical imaging or light propagation.

[0062] In this embodiment, the second compensation value is the compensation value of the lens, but the function of the second compensation value is to reduce the error caused by the thermal effect of the mask 121.

[0063] Step S250: generating a third compensation value according to the first compensation value and the second compensation value.

[0064] In this step, the second compensation value and the third compensation value are combined and calculated to obtain the third compensation value.

[0065] Step S260: compensating the lens of the wafer exposure system according to the third compensation value and exposing the wafer.

[0066] In this step, the first compensation value of the wafer exposure system 100 is modified to the third compensation value, and the subsequent wafer is exposed according to the third compensation value.

[0067] According to the wafer exposure system and the compensation method thereof, the first compensation value of the lens and the mask error value of the mask plate are obtained in the exposure pre-processing of the machine table with the lens compensation function being turned on, the second compensation value of the lens is obtained according to the mask error value, the third compensation value is generated according to the first compensation value and the second compensation value of the lens, and the lens of the machine table is compensated and the wafer is exposed according to the third compensation value. The third compensation value is obtained according to the first compensation value of the initial machine table and the second compensation value converted from the error value of the subsequent mask plate, so that the exposure of the machine table according to the third compensation value can greatly reduce the error of the lens and the mask plate caused by the thermal effect, thereby improving the overlay accuracy in the exposure process.

[0068] Further, the wafer exposure system and the compensation method thereof convert the influence of the thermal effect on the mask plate into the second compensation value of the lens, so that the machine table only needs to compensate the lens to reduce the overlay error caused by the influence of the thermal effect on the lens and the mask plate in the wafer exposure, thereby reducing the complexity of the machine table.

[0069] According to the embodiments of the present application as described above, these embodiments do not describe all the details, nor limit the present application to only the specific embodiments described. Obviously, many modifications and variations can be made according to the above description. The present description selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well utilize the present application and make modifications and uses on the basis of the present application. The present application is limited only by the claims and their full scope and equivalents.

Claims

1. A compensation method for a wafer exposure system, wherein, include: Exposure preprocessing is performed using a wafer exposure system; Obtain the first compensation value of the lens during the exposure preprocessing; Obtain the mask error value during the exposure preprocessing process; The second compensation value of the lens is obtained based on the mask error value; A third compensation value is generated based on the first and second compensation values. The step of obtaining the second compensation value of the lens based on the mask error value includes: obtaining multiple parameters in the mask error value; converting the multiple parameters into distortion modulation parameters; and obtaining the second compensation value of the lens based on the distortion modulation parameters.

2. The compensation method according to claim 1, wherein, The step of exposure preprocessing using a wafer exposure system includes: exposing a batch of wafers using a wafer exposure system with lens compensation function.

3. The compensation method according to claim 1, wherein, The lenses and photomasks in the wafer exposure system achieve thermal stability after exposure pretreatment.

4. The compensation method according to claim 1, wherein, The parameters include: coma, spherical aberration, defocus, astigmatism, lower-order aberrations, higher-order aberrations, and compound aberrations.

5. The compensation method according to claim 4, wherein, In the step of obtaining the second compensation value of the lens based on the distortion modulation parameters, the distortion modulation parameters are converted into Zernike polynomials to obtain the second compensation value of the lens.

6. The compensation method according to claim 1, wherein, In the step of obtaining the first compensation value of the lens during the exposure preprocessing, the first compensation value is obtained according to the Zernike polynomial.

7. The compensation method according to claim 1, wherein, In the step of obtaining the first compensation value of the lens during the exposure preprocessing, the first compensation value is obtained by consulting the records of the wafer exposure system.

8. The compensation method according to claim 1, wherein, After the step of generating the third compensation value based on the first and second compensation values, the method further includes: The lens of the wafer exposure system is compensated according to the third compensation value, and the wafer is exposed.

9. A wafer exposure system for performing the compensation method as described in any one of claims 1-8, wherein, The wafer exposure system includes: A radiation source that produces a beam of radiation used for exposure; An illumination system, located after the radiation source, shapes and adjusts the radiation beam generated by the radiation source; A photomask, located after the illumination system, includes a pattern to be transferred onto the wafer; The objective lens system, located behind the mask, includes multiple lenses to reduce and adjust the radiation source passing through the mask; A resist layer, located behind the objective lens, forms the pattern before wafer etching.

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