A projection lithography Moiré alignment device and method

Abstract

The present invention discloses a projection lithography moiré alignment device, wherein the device includes: an illumination system, a mask mark, a lithography projection objective lens, an alignment mark, a DMD spatial modulator, a CCD camera, and a sensor motion stage; the illumination system emits light, which passes through the mask mark and then forms an aerial image through the lithography projection objective lens; the position of the aerial image is found by controlling the movement of the sensor motion stage, so that the light passing through the alignment mark is diffracted to form moiré fringes; the moiré fringes reach the DMD spatial modulator and are encoded; the encoded moiré fringes reach the CCD camera, and the moiré fringes are reconstructed based on the collected light intensity information; the position deviation between the ideal image and the actual image is obtained based on the reconstructed moiré fringes, and the position deviation is fed back to the sensor motion stage for correction to achieve alignment. The present invention does not require a spatial filter, simplifies the optical system, reduces hardware costs, and can be widely applied in the field of optical precision detection technology.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement and optical precision detection of photolithography systems, and in particular to a projection photolithography moiré alignment device and method. Background Art

[0002] In the semiconductor manufacturing sector, photolithography machines are one of the core technologies driving the industry's development. As one of the three core systems of a photolithography machine, the lithography projection objective lens's imaging quality determines the clarity of the exposed lines and whether overlay errors meet tolerances. Therefore, the actual imaging position must be detected and corrected to achieve a position close to the ideal imaging position. Common photolithography alignment methods include brightfield and darkfield alignment, grating diffraction alignment, aerial image sensors, and moiré fringe alignment.

[0003] Brightfield and darkfield alignment are photometric alignment methods. The brightfield image comes from the reflected and scattered light from the alignment marks on the silicon wafer, while the darkfield image comes from the scattered and diffracted light at the edges of the alignment marks, and blocks the directly reflected light. The signal intensity of brightfield alignment is stronger than that of darkfield, but the accuracy is not as good as darkfield alignment.

[0004] Grating diffraction usually uses alignment light to diffract the alignment mark, adds a spatial filter in the middle to filter out unnecessary orders, and interferes with the mark on the mask through the imaging system. The sensor records the signal and demodulates it to obtain the position offset.

[0005] The spatial image sensor uses a mask mark and alignment mark of the same design shape to scan across the imaging field of view through the workpiece stage. This convolution creates a spatial image formed by the alignment mark on the workpiece stage and the mask mark, converting the light intensity signal into an electrical signal. The maximum value of the signal represents the alignment position, and the imaging offset is obtained through analog-to-digital conversion. While spatial image sensor alignment offers high precision and the ability to scan 3D spatial images, it requires the design of corresponding TIS marks, resulting in lengthy detection times and limited accuracy by the workpiece stage.

[0006] Traditional moiré fringe alignment methods use a laser beam to illuminate an alignment mark on a silicon wafer. The reflected light then passes through a spatial filter and projection objective lens before illuminating a reference mark on a mask. Diffraction produces moiré fringes, and a photodetector receives the light signal to measure the positional offset between the actual image and the ideal image. This method is simple in principle and does not require expensive equipment, but it does require an additional laser light path and a spatial filter to intercept the ±1st order diffracted light. Summary of the Invention

[0007] In order to at least solve one of the technical problems existing in the prior art to a certain extent, an object of the present invention is to provide a projection lithography moiré alignment device and method.

[0008] The technical solution adopted in the present invention is:

[0009] A projection lithography moiré alignment device comprises: an illumination system, a mask mark, a lithography projection objective lens, an alignment mark, a DMD spatial modulator, a CCD camera and a sensor motion stage; the alignment mark, the DMD spatial modulator and the CCD camera are arranged on the sensor motion stage;

[0010] The illumination system emits light, which passes through the mask marks and then through the lithography projection objective to form an aerial image. The position of the aerial image is determined by controlling the movement of the sensor motion stage, causing it to diffract against the alignment marks, forming moiré fringes. The moiré fringes reach the DMD spatial modulator for encoding. The encoded moiré fringes reach the CCD camera, which reconstructs the moiré fringes based on the acquired light intensity information. The positional deviation between the ideal image and the actual image is determined based on the reconstructed moiré fringes, and this deviation is fed back to the sensor motion stage for correction, achieving alignment. This ideal image can be calculated in advance through simulation.

[0011] Furthermore, the intensity distribution of the mask mark is:

[0012]

[0013] The intensity distribution of the alignment mark is:

[0014]

[0015] Where f1 represents the frequency of the mask mark, f2 represents the frequency of the alignment mark; t xy1 are the x and y coordinates of the mask mark, t xy2 are the x and y coordinates of the alignment mark.

[0016] Furthermore, the aerial image is a superposition of intensity distributions of a group of mutually incoherent point light sources on the image plane.

[0017] Furthermore, the aerial image I is represented as follows:

[0018]

[0019] Where I is the spatial image, is the diffracted light amplitude, P is the pupil function, S is the effective light source, and FT is the two-dimensional Fourier transform;

[0020] Converted into discrete form as follows:

[0021]

[0022]

[0023]

[0024]

[0025] Where, wave number k = 2π / λ, λ is the wavelength of the monochromatic light source; W aberration (f, g) is the wavefront aberration, where n is the Zernike order, Zn is the coefficient of the nth order Zernike polynomial, and R n (ρ,θ) is the nth-order Zernike polynomial of pupil plane regularization; f, g are pupil spectrum coordinates, and f', g' are light source spectrum coordinates.

[0026] Furthermore, the expression of the moiré fringe is:

[0027]

[0028] Where, I y1 (x,y) represents the light intensity distribution of the mask mark, I y2 (x,y) represents the light intensity distribution of the alignment mark.

[0029] Furthermore, reconstructing the moiré fringes based on the collected light intensity information includes:

[0030] The compressed sensing algorithm is used to reconstruct the moiré fringes at a lower sampling rate, wherein the wavelet transform is used in the reconstruction process to improve the sparsity of the moiré fringe signal.

[0031] Furthermore, the expression of the reconstructed moiré fringes is:

[0032] I more =Φx=ΦΨs=As

[0033] Where Φ represents the M×N dimensional random measurement matrix, Ψ represents the N×N dimensional wavelet transform orthogonal basis, s is the N×1 dimensional sparse signal after the original signal is transformed by wavelet, A represents the M×N dimensional observation matrix composed of the measurement matrix and the wavelet orthogonal basis; M represents the number of random matrix encoding measurements, and N represents the length of the measurement signal.

[0034] Furthermore, obtaining the position deviation between the ideal imaging and the actual imaging based on the reconstructed moiré fringes includes:

[0035] By detecting the centroid coordinate offset of the moiré fringe, the position deviation between the ideal imaging and the actual imaging is obtained;

[0036] The expression of the position deviation is:

[0037]

[0038]

[0039] Among them, X and Y are the coordinates of the center of mass under ideal imaging. is the coordinate of the centroid of the moiré fringe in the misaligned state.

[0040] Furthermore, the projection lithography moiré alignment device further includes a mask stage, a first convex lens and a second convex lens;

[0041] The mask stage is used to place mask marks;

[0042] The first convex lens is arranged between the alignment mark and the DMD spatial modulator, and the light passing through the alignment mark enters the DMD spatial modulator through the first convex lens;

[0043] The second convex lens is arranged between the DMD spatial modulator and the CCD camera, and the encoded light passes through the second convex lens to reach the CCD camera.

[0044] Another technical solution adopted in the present invention is:

[0045] A projection lithography moiré alignment method, applied to the projection lithography moiré alignment device described above, comprises the following steps:

[0046] The illumination system emits light, which passes through the mask mark and forms an aerial image through the lithography projection lens;

[0047] The position of the spatial image is found by controlling the movement of the sensor motion stage so that the light passing through the alignment mark is diffracted to form moiré fringes;

[0048] The moiré fringes reach the DMD spatial modulator for encoding;

[0049] The encoded moiré fringes reach the CCD camera, which reconstructs the moiré fringes based on the collected light intensity information;

[0050] The position deviation between the ideal imaging and the actual imaging is obtained based on the reconstructed Moiré fringes, and the position deviation is fed back to the sensor motion stage for correction to achieve alignment.

[0051] The beneficial effects of the present invention are: the present invention does not require a spatial filter, the optical system is simpler, and the hardware cost is reduced; in addition, the storage space required for CCD array sampling is reduced through encoding and reconstruction. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following introduction is made to the drawings of the embodiments of the present invention or the related technical solutions in the prior art. It should be understood that the drawings introduced below are only for the convenience of clearly describing some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative work.

[0053] Figure 1 1 is a schematic structural diagram of a projection lithography moiré alignment device according to an embodiment of the present invention;

[0054] Figure 2 is a schematic diagram of a mask mark and an alignment mark in an embodiment of the present invention;

[0055] Figure 3 is a schematic diagram of ideal imaging in an embodiment of the present invention;

[0056] Figure 4 2 is a schematic diagram of alignment position deviation detection according to an embodiment of the present invention;

[0057] Figure 5 This is a flowchart of the steps of a projection lithography moiré alignment method in an embodiment of the present invention.

[0058] Figure 1 Figure numerals: 1. Illumination system; 2. Mask mark; 3. Mask stage; 4. Lithography projection objective lens; 5. Alignment mark; 6. First convex lens; 7. DMD spatial modulator; 8. Second convex lens; 9. CCD camera; 10. Sensor motion stage. DETAILED DESCRIPTION

[0059] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and are not to be construed as limiting the present invention. The step numbers in the following embodiments are provided for ease of explanation only and do not limit the order of the steps. The order of execution of the steps in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0060] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0061] In the description of the present invention, "several" means one or more, "many" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" in the description is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0062] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0063] Explanation of terms:

[0064] Mask mark: refers to the mask grating pattern; in the present invention, light passes through it, and the pattern is transmitted on the imaging surface and diffracted by the alignment mark to form moiré fringes.

[0065] To address the challenges of existing technologies, the present invention proposes a moiré lithography alignment method based on compressed sensing. Under illumination from a light source, the mask's grating pattern, after passing through the projection objective, diffracts against alignment marks of varying frequencies on the workpiece stage, forming moiré fringes. These fringes are then captured by a CCD after passing through a lens and a DMD-encoded measurement matrix. Finally, an algorithm is used to detect the positional offset between the actual image and the ideal image. Compared to traditional methods, this method eliminates the need for spatial filters, resulting in a simpler optical system. This method not only reduces costs but also reduces the storage space required for CCD array sampling.

[0066] like Figure 1 As shown, a projection lithography moiré alignment device comprises an illumination system 1, a mask mark 2, a mask stage 3, a lithography projection objective lens 4, an alignment mark 5, a first convex lens 6, a DMD spatial modulator 7, a second convex lens 8, a CCD camera 9, and a sensor motion stage 10. The alignment mark 5, the first convex lens 6, the DMD spatial modulator 7, the second convex lens 8, and the CCD camera 9 are disposed on the sensor motion stage 10 and move in response to the movement of the sensor motion stage 10.

[0067] The working principle of the above device is as follows: the illumination system emits light to illuminate the mask mark, which forms a spatial image through the projection objective lens. The sensor motion stage carries the alignment mark to scan and find the position of the mask mark spatial image, which forms moiré fringes through diffraction. The moiré fringes are incident on the DM spatial modulator surface through the lens and encoded and then collected by the CCD. The collected light intensity information is accurately reconstructed into the moiré fringes at a lower sampling rate through the compressed sensing algorithm. The position deviation between the ideal image and the actual image is obtained by detecting the offset of the center of mass coordinate of the moiré fringes. The position deviation is fed back to the sensor motion stage for correction to achieve alignment.

[0068] As an optional embodiment, the movement of the sensor stage can be manually controlled to find the spatial image position. As another optional embodiment, the movement of the sensor stage can be automatically controlled, with a preset movement path and step length. Each step is captured by a CCD and a determination is made as to whether moiré fringes appear. When moiré fringes are detected, the movement step is stopped. It should be noted that in addition to the two methods described above, other control methods can also be used to achieve this, and all other control methods should fall within the scope of protection of the present invention.

[0069] As a further optional embodiment, the projection lithography moiré alignment device also includes a host computer, which is connected to the DMD spatial modulator, CCD camera and sensor motion stage to control the working status of the DMD spatial modulator, CCD camera and sensor motion stage.

[0070] Figure 2 Schematic diagram of mask marks and alignment marks, their distribution is as follows:

[0071]

[0072] Where: y1 is the intensity distribution of the mask mark, y2 is the intensity distribution of the alignment mark, f1 and f2 represent the frequency of the mask mark and alignment mark, that is, the inverse of the period T. In this embodiment, the mask mark period is 8um, and the alignment mark period is 2um. Figure 2 (a) is a schematic diagram of the mask marking, Figure 2 (b) is a schematic diagram of the alignment mark.

[0073] Figure 3 As a schematic diagram of ideal imaging, the imaging process in optical lithography is modeled as a pupil function with a partially coherent light source, that is, a partially coherent system. The system is considered to be a set of mutually incoherent point light sources, and the intensity distribution on the entire image plane is the superposition of the intensities formed by all point light sources. In Abbe theory, the aerial image is directly calculated from the sum of all point sources, and each point source requires a Fourier transform (FT). The analytical representation of Abbe's method can be written as:

[0074]

[0075] Where I is the spatial image, is the diffracted light amplitude, P is the pupil function, S is the effective light source, and FT is the two-dimensional Fourier transform. We can rewrite the spatial image intensity I into a discrete form:

[0076]

[0077] The pupil function characterizes the entire projection objective, including the wave aberrations in the projection objective:

[0078]

[0079] The wave number k = 2π / λ, λ is the wavelength of the monochromatic light source, Waberrati The on(f,g) wave aberration can be characterized by the orthogonal Zernike polynomial expansion form:

[0080]

[0081] Where n is the Zernike order, Zn is the coefficient of the nth order Zernike polynomial, R n (ρ,θ) is the nth-order Zernike polynomial of the pupil plane regularization. Ideally, the wavefront aberration is zero.

[0082] Figure 4 A schematic diagram of moiré fringe detection is given when the imaging position deviates from the ideal position. In this case, the pupil function is not zero and contains offset errors in the x and y directions, which can be represented by the Z2 and Z3 terms in the Zernike polynomials. The generated moiré fringes can be represented as follows:

[0083]

[0084] The compressed sensing algorithm uses random encoding to construct a measurement matrix using a DMD spatial modulator. The wavelet transform is used as an orthogonal basis to increase the sparsity of the original signal. With a sampling rate as low as 0.2, we can accurately reconstruct the moiré fringes:

[0085] I more =Φx=ΦΨs=As (7)

[0086] Φ represents the M×N dimensional random measurement matrix, Ψ represents the N×N dimensional wavelet transform orthogonal basis, s represents the N×1 dimensional sparse signal after the wavelet transform of the original signal, and A represents the M×N dimensional observation matrix composed of the measurement matrix and the wavelet orthogonal basis. M represents the number of random matrix encoding measurements, and N represents the length of the measurement signal.

[0087] Finally, by reconstructing the centroid offset of the moiré fringes, we can get the alignment offset:

[0088]

[0089] Among them, X and Y are the coordinates of the center of mass under ideal imaging. is the coordinate of the center of mass of the moiré fringe in the misaligned state. The offset is fed back to the sensor motion stage for correction to achieve photolithography alignment.

[0090] See also Figure 5 Based on the above device, this embodiment further provides a projection lithography moiré alignment method, comprising the following steps:

[0091] S1. The illumination system emits light, which passes through the mask mark and forms a spatial image through the lithography projection lens.

[0092] The illumination system emits light to illuminate the mask mark, which forms an aerial image through the magnification zoom of the projection objective lens and the Abbe imaging principle.

[0093] S2. The position of the spatial image is found by controlling the movement of the sensor motion stage so that the light passing through the alignment mark is diffracted to form moiré fringes.

[0094] The sensor motion stage carries the alignment mark to scan and find the position of the mask mark space image and diffracts with the mask mark space image to form moiré fringes.

[0095] S3. The moiré fringes reach the DMD spatial modulator for encoding.

[0096] The moiré fringes are incident on the surface of the DMD spatial modulator through the lens. The DMD will randomly generate an array of '0' and '1', where '0' represents no reflection and '1' represents reflection. The encoded moiré fringes are collected by the CCD.

[0097] S4: The encoded moiré fringes arrive at the CCD camera, and the moiré fringes are reconstructed based on the collected light intensity information.

[0098] The light intensity information collected by the CCD camera is transformed by wavelet to increase the sparsity of the signal, thereby improving the accuracy of compressed sensing reconstruction. The compressed sensing algorithm accurately reconstructs the moiré fringes at a lower sampling rate and performs interpolation fitting, which greatly saves computing and storage space.

[0099] S5. Obtain the position deviation between the ideal imaging and the actual imaging based on the reconstructed moiré fringes, and feed the position deviation back to the sensor motion stage for correction to achieve alignment.

[0100] The position deviation between the ideal imaging and the actual imaging is obtained by detecting the coordinate offset of the center of mass of the Moiré fringe reconstructed by interpolation fitting. The position deviation is fed back to the sensor motion stage for correction to achieve alignment.

[0101] Compared with the traditional method, the method of this embodiment does not require a spatial filter and has a simpler optical system. This method not only reduces costs but also reduces the storage space required for CCD array sampling.

[0102] In the above description of this specification, reference to the terms "one embodiment / example," "another embodiment / example," or "certain embodiments / examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0103] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

[0104] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A projection lithography moiré alignment device, characterized in that: include: An illumination system, a mask mark, a lithography projection objective lens, an alignment mark, a DMD spatial modulator, a CCD camera, and a sensor motion stage; the alignment mark, the DMD spatial modulator, and the CCD camera are arranged on the sensor motion stage; The illumination system emits light, which passes through the mask mark and then forms an aerial image through the lithography projection objective. The position of the aerial image is found by controlling the movement of the sensor motion stage, so that the aerial image diffracts with the alignment mark to form moiré fringes. The moiré fringes reach the DMD spatial modulator and are encoded. The encoded moiré fringes reach the CCD camera and are reconstructed based on the collected information. The position deviation between the ideal image and the actual image is obtained based on the reconstructed moiré fringes, and the position deviation is fed back to the sensor motion stage for correction to achieve alignment.

2. The projection lithography moiré alignment device according to claim 1, characterized in that: The intensity distribution of the mask mark is: The intensity distribution of the alignment mark is: Where f1 represents the frequency of the mask mark, f2 represents the frequency of the alignment mark; t xy1 are the x and y coordinates of the mask mark, t xy2 are the x and y coordinates of the alignment mark.

3. The projection lithography moiré alignment device according to claim 1, characterized in that: The spatial image is a superposition of the intensity distributions of a group of mutually incoherent point light sources on the image plane.

4. The projection lithography moiré alignment device according to claim 3, characterized in that: The aerial image I is represented as follows: Where I is the spatial image, is the diffracted light amplitude, P is the pupil function, S is the effective light source, and FT is the two-dimensional Fourier transform; Converted into discrete form as follows: Where, wave number k = 2π / λ, λ is the wavelength of the monochromatic light source; W aberration (f, g) is the wavefront aberration, where n is the Zernike order, Zn is the coefficient of the nth order Zernike polynomial, and R n (ρ,θ) is the nth-order Zernike polynomial of pupil plane regularization; f, g are pupil spectrum coordinates, and f', g' are light source spectrum coordinates.

5. The projection lithography moiré alignment device according to claim 4, characterized in that: The expression of the moiré fringe is: Where, I y1 (x,y) represents the light intensity distribution of the mask mark, I y2 (x,y) represents the light intensity distribution of the alignment mark.

6. The projection lithography moiré alignment device according to claim 1, characterized in that: The reconstructing of moiré fringes according to the collected light intensity information includes: The compressed sensing algorithm is used to reconstruct the moiré fringes at a lower sampling rate; wherein, the wavelet transform is used in the reconstruction process to improve the sparsity of the moiré fringe signal.

7. The projection lithography moiré alignment device according to claim 6, characterized in that: The expression of the reconstructed moiré fringes is: I more =Φx=ΦΨs=As Where Φ represents the M×N dimensional random measurement matrix, Ψ represents the N×N dimensional wavelet transform orthogonal basis, s is the N×1 dimensional sparse signal after the original signal is transformed by wavelet, and A represents the M×N dimensional observation matrix composed of the measurement matrix and the wavelet orthogonal basis; M represents the number of random matrix coding measurements, and N represents the measurement signal length.

8. The projection lithography moiré alignment device according to claim 1, characterized in that: The step of obtaining the position deviation between the ideal imaging and the actual imaging based on the reconstructed moiré fringes includes: By detecting the centroid coordinate offset of the moiré fringe, the position deviation between the ideal imaging and the actual imaging is obtained; The expression of the position deviation is: Among them, X and Y are the coordinates of the center of mass under ideal imaging. is the coordinate of the centroid of the moiré fringe in the misaligned state.

9. The projection lithography moiré alignment device according to claim 1, characterized in that: The projection lithography moiré alignment device further includes a mask stage, a first convex lens and a second convex lens; The mask stage is used to place mask marks; The first convex lens is arranged between the alignment mark and the DMD spatial modulator, and the light passing through the alignment mark enters the DMD spatial modulator through the first convex lens; The second convex lens is arranged between the DMD spatial modulator and the CCD camera, and the encoded light passes through the second convex lens to reach the CCD camera.

10. A projection lithography moiré alignment method, applied to a projection lithography moiré alignment device according to any one of claims 1 to 9, characterized in that: The following steps are involved: The illumination system emits light, which passes through the mask mark and forms an aerial image through the lithography projection lens; The position of the spatial image is found by controlling the movement of the sensor motion stage so that the light passing through the alignment mark is diffracted to form moiré fringes; The moiré fringes reach the DMD spatial modulator for encoding; The encoded moiré fringes reach the CCD camera, which reconstructs the moiré fringes based on the acquired information; The position deviation between the ideal imaging and the actual imaging is obtained based on the reconstructed Moiré fringes, and the position deviation is fed back to the sensor motion stage for correction to achieve alignment.

Images