A grating mark for photolithography alignment and alignment method thereof

Abstract

The present application relates to a grating mark for photolithography alignment and an alignment method thereof, wherein the mark includes: a wafer alignment mark and a mask alignment mark. The method includes: etching a wafer alignment mark and a mask alignment mark on a wafer and a mask respectively; illuminating the wafer mark and the mask mark simultaneously with an alignment light source, and causing the diffracted light to interfere to generate a square moiré fringe pattern; using a computer to pre-process the outer contour of the moiré fringe pattern to achieve coarse alignment; extracting the phase information of the moiré fringe through 2D-FFT, and using an intensity equation unwrapping algorithm to calculate the absolute phase; calculating the actual misalignment between the wafer and the mask based on the phase difference of the moiré fringe; inputting the misalignment into a translation stage to implement feedback adjustment until high-precision alignment is achieved. The present invention can achieve precise alignment of multiple degrees of freedom in photolithography alignment through a single set of centrally symmetrical marks and its alignment method, greatly reducing the occupation of the effective area of ​​the wafer, and significantly improving photolithography efficiency and alignment accuracy.

Description

Technical Field

[0001] The present application relates to the field of photolithography technology, and in particular to a grating mark for photolithography alignment and an alignment method thereof. Background Art

[0002] The effective application of nanolithography technology has played a vital role in the development of higher-process integrated circuits. The manufacture of integrated circuits usually involves a variety of different overlay processes, each of which requires the precise exposure of the lithography alignment pattern onto the wafer. Before the circuit diagram on the mask is accurately transferred to the wafer, it is necessary to ensure that the pattern to be etched is aligned with the existing pattern on the wafer with high precision and multiple degrees of freedom. At present, the alignment between the wafer and the mask is usually achieved by detecting alignment marks. However, the existing alignment marks cannot achieve multi-degree-of-freedom alignment independently and occupy a large effective area of ​​the wafer. In addition, the imaging-based mark detection method is gradually unable to meet the requirements of the next generation of lithography manufacturing in terms of accuracy.

[0003] Currently, the technology of forming moiré fringes by overlapping gratings has been widely studied due to its advantages of high precision and high sensitivity. Among them, the circular moiré fringes formed by the superposition of circular gratings can realize detection in orthogonal directions due to their symmetry, non-periodicity and isotropy, but their detection accuracy is low, and they can only realize misalignment detection at the level of tens of nanometers. They are usually used as coarse alignment marks. The linear moiré fringes formed by the superposition of line gratings are usually used for fine alignment due to their inherent high precision and high sensitivity. However, this method can only detect misalignment in a single direction, so in practical applications, multiple groups of alignment marks are required to realize misalignment detection in different directions. At present, no effective solution has been proposed to the problem that existing alignment marks cannot independently realize multi-degree-of-freedom alignment during the fine alignment process. Summary of the Invention

[0004] The present invention provides a grating mark for photolithography alignment and an alignment method thereof, so as to solve the problem that the existing alignment mark cannot independently achieve multi-degree-of-freedom alignment during the fine alignment process.

[0005] In a first aspect, the present invention provides a grating mark for lithography alignment, comprising:

[0006] A wafer alignment mark for etching on a wafer, which is divided into four quadrants according to the quadrants, each quadrant of the wafer alignment mark includes a plurality of L-shaped light-shielding lines at equal intervals, two sides of each L-shaped light-shielding line are equal in length and are respectively perpendicular to two quadrant boundaries, the spacing between the L-shaped light-shielding lines in the first and third quadrants of the wafer alignment mark is a first spacing, and the spacing between the L-shaped light-shielding lines in the second and fourth quadrants is a second spacing;

[0007] A mask alignment mark for etching on a mask, which is divided into four quadrants according to the quadrants, each quadrant of the wafer alignment mark includes a plurality of L-shaped light-shielding lines at equal intervals, two sides of each L-shaped light-shielding line are equal in length and perpendicular to two quadrant boundaries, the grating pitch of the first and third quadrants of the mask alignment mark is the second pitch, and the grating pitch of the second and fourth quadrants of the mask alignment mark is the first pitch;

[0008] The first spacing is greater than the second spacing, and a duty cycle of the multiple L-shaped light-shielding lines in each quadrant of the wafer alignment mark and the mask alignment mark is 1 / 2.

[0009] In some embodiments, the first spacing is 1.1 times the second spacing.

[0010] In a second aspect, the present invention provides a lithography alignment method based on grating marks, comprising:

[0011] Etching a wafer alignment mark at the center of the wafer and etching a mask alignment mark on the mask, wherein the wafer alignment mark and the mask alignment mark are the grating marks for photolithography alignment as described in the first aspect;

[0012] The wafer and the mask are superimposed on each other so that the wafer alignment mark and the mask alignment mark overlap, and the wafer alignment mark and the mask alignment mark are illuminated simultaneously by an alignment light source to generate a square moiré fringe pattern;

[0013] Coarse alignment is performed by adjusting the position of the wafer and mask according to the square moiré fringe pattern;

[0014] The square moiré fringe pattern is divided into four isosceles triangle regions by diagonal lines. The four regions are upper region, lower region, left region and right region. Each region is divided into two parts by its own perpendicular median.

[0015] Extract the moiré fringe phases of the two parts of each region respectively, and calculate the absolute phase difference between the two parts of each region respectively;

[0016] The actual misalignment Δx and Δy between the wafer and the mask along the X and Y directions, respectively, are calculated using the misalignment calculation formula. The misalignment calculation formula includes:

[0017]

[0018] Wherein, P1 is the first spacing, P2 is the second spacing, Δx1 and Δx2 represent the first candidate misalignment amount and the second candidate misalignment amount between the wafer and the mask along the X direction, respectively, Δy3 and Δy4 represent the third candidate misalignment amount and the fourth candidate misalignment amount between the wafer and the mask along the Y direction, respectively. and Represents the absolute phase difference between two parts of the left area, right area, upper area and lower area respectively, Δx takes Δx1 or Δx2, Δy takes Δy3 or Δy4;

[0019] The actual misalignment values ​​Δx and Δy between the wafer and the mask along the X and Y directions, respectively, are input into the translation stage of the lithography machine for feedback, and the translation stage is used to precisely align the positions of the wafer and the mask.

[0020] In some embodiments, adjusting the positions of the wafer and the mask according to the square moiré fringe pattern to perform coarse alignment includes:

[0021] The outer contour of the square Moiré fringe pattern is extracted through a computer image processing algorithm for pre-processing, the misalignment between the wafer and the mask is determined and preliminary adjustments are made to bring the misalignment into the precise alignment range.

[0022] In some embodiments, etching of the wafer alignment mark and the mask alignment mark is achieved by electron beam direct writing.

[0023] In some of the embodiments, the image processing method used when extracting the moiré fringe phases of the two parts of each region is 2D-FFT.

[0024] In some embodiments, the absolute phase difference between the two parts of each region is expressed as follows:

[0025]

[0026] in, are the absolute phase differences of the two parts of the left area, right area, upper area and lower area respectively, and are the moiré fringe phases of the upper and lower parts of the left region, and are the moiré fringe phases of the upper and lower parts of the right region, and are the moiré fringe phases of the left and right parts of the upper region, and The moiré fringe phases of the left and right parts of the lower area, respectively.

[0027] In some of the embodiments, the calculation formulas for the misalignment amounts of the two parts of the upper region, the lower region, the left region and the right region are obtained by unpacking the Moire fringe intensity equations of the two parts of the upper region, the lower region, the left region and the right region, respectively.

[0028] In some embodiments, when the wafer and the mask are misaligned in the X direction, the moiré fringe intensity of the two portions in the left region can be expressed as:

[0029]

[0030] Among them, (x,y) represents the pixel coordinates, and Represent the Moire fringe intensity of the upper and lower parts of the left area, a(x, y) and b(x, y) represent the background light intensity and amplitude modulation of the fringe pattern, respectively. m =(P2P1) / (P2-P1), Δx is the misalignment between the wafer and the mask along the X direction;

[0031] When the wafer and mask are misaligned in the X direction, the fringes in the right region move in opposite directions to the fringes in the corresponding positions in the left region. The intensity of the moiré fringes in the two parts of the right region can be expressed as:

[0032]

[0033] in, and The moiré fringe intensities of the upper and lower parts of the right region, respectively;

[0034] When the wafer and mask are misaligned in the Y direction, the moiré fringe intensity of the two parts of the upper area can be expressed as:

[0035]

[0036] in, and They represent the moiré fringe intensities of the left and right parts of the upper region, respectively, and Δy is the misalignment between the wafer and the mask along the Y direction;

[0037] When the wafer and mask are misaligned in the Y direction, the fringes in the lower region move in opposite directions to the fringes at the corresponding positions in the upper region. The Moire fringe intensity of the two parts of the lower region can be expressed as:

[0038]

[0039] in, and Represents the fringe intensity of the left and right parts of the lower area, respectively.

[0040] In a third aspect, the present invention provides a lithography machine, which uses the grating mark-based lithography alignment method described in the second aspect when implementing lithography alignment.

[0041] Compared with the related art, the present invention has the following beneficial effects:

[0042] 1. The present invention proposes a set of grating alignment marks with a symmetrical structure that generates a square moiré fringe pattern when illuminated by a light source. The offsets of the light-shielding lines between the first and second quadrants and between the third and fourth quadrants are used for misalignment detection in the X direction, while the offsets of the light-shielding lines between the first and fourth quadrants and between the second and third quadrants are used for misalignment detection in the Y direction. Therefore, only one set of grating alignment marks is required to simultaneously detect misalignment in multiple directions, eliminating the need for multiple sets of alignment marks. This solves the problem that existing alignment marks cannot independently achieve multi-degree-of-freedom alignment during fine alignment, significantly reduces the effective wafer area occupied, and improves the efficiency of photolithography alignment.

[0043] 2. The present invention performs coarse alignment using the outer contour of the square Moiré fringe pattern, calculates the misalignment between the wafer and the mask in both the X and Y directions by dividing the area and detecting the fringe intensity and phase information. Finally, the data is fed back to the translation stage of the lithography machine and the positions of the wafer and mask are adjusted to achieve fine alignment. By measuring the phase change of the Moiré fringes, the relative displacement between the wafer and the mask can be accurately calculated, achieving sub-nanometer alignment accuracy and improving the accuracy of lithography alignment.

[0044] 3. The present invention utilizes the high sensitivity of moiré fringes and combines it with a two-dimensional fast Fourier transform (2D-FFT) and an intensity equation unwrapping algorithm to further optimize and improve the alignment accuracy between the wafer and the mask and the calculation efficiency of the misalignment amount.

[0045] The details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a structural diagram of the wafer alignment mark;

[0047] Figure 2 A structural diagram of a mask alignment mark;

[0048] Figure 3 This is the moiré fringe pattern when there is an X-direction misalignment between the wafer and the mask;

[0049] Figure 4 This is the moiré fringe pattern when there is Y-direction misalignment between the wafer and the mask;

[0050] Figure 5 This is the moiré fringe pattern when the wafer and mask are perfectly aligned;

[0051] Figure 6 This is the principle diagram of moiré fringe misalignment detection;

[0052] Figure 7 Direction diagram for detection of moiré fringe misalignment of grating marks;

[0053] Figure 8 The figure is a flowchart of the specific steps of the lithography alignment method based on grating marks. DETAILED DESCRIPTION

[0054] In order to more clearly understand the purpose, technical solutions and advantages of the present application, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments.

[0055] In this embodiment, a grating mark for photolithography alignment is provided, including: a wafer alignment mark for etching on a wafer and a mask alignment mark for etching on a mask.

[0056] Reference Figure 1 As shown, the wafer alignment mark is divided into four quadrant parts according to the quadrants. Each quadrant part of the wafer alignment mark includes a plurality of L-shaped shading lines with equal spacing. The two sides of each L-shaped line are equal in length and are perpendicular to the two quadrant boundaries respectively. The grating spacing of the first quadrant part and the third quadrant part of the wafer alignment mark is a first spacing, and the grating spacing of the second quadrant part and the fourth quadrant part of the wafer alignment mark is a second spacing. The first spacing is greater than the second spacing. The total area of ​​the multiple L-shaped shading lines in each quadrant part of the wafer alignment mark accounts for half of the total area of ​​the quadrant part.

[0057] Reference Figure 2 As shown, the mask alignment mark is divided into four quadrant parts according to the quadrants. Each quadrant part of the wafer alignment mark includes multiple L-shaped shading lines with equal intervals. The two sides of each L-shaped line are equal in length and are respectively perpendicular to the two quadrant boundaries. The grating spacing of the first quadrant part and the third quadrant part of the mask alignment mark is the second spacing, and the grating spacing of the second quadrant part and the fourth quadrant part of the mask alignment mark is the first spacing.

[0058] The first spacing is greater than the second spacing, and the total area of ​​the multiple L-shaped light-shielding lines in each quadrant of the wafer alignment mark and the mask alignment mark accounts for half of the total area of ​​the quadrant.

[0059] In this embodiment, the grating duty cycle of the two grating marks is set to 1 / 2, which can maximize the light intensity contrast of the moiré fringes, improve the detection signal-to-noise ratio, and thus enhance the recognizability of the moiré fringes. The wafer alignment mark and the mask alignment mark are both designed with this symmetrical structure, which not only facilitates the implementation of the grating etching process, but also helps to generate a symmetrical diffraction light field, ensuring the generation of a high-quality moiré fringe interference image, and then more accurately adjust the alignment level of the wafer alignment mark and the mask alignment mark, thereby more accurately achieving lithography alignment.

[0060] In this embodiment, the first pitch is 1.1 times the second pitch. The first pitch is P2, the second pitch is P1, that is, P2 = 1.1P1. Since the moiré fringe period P m =(P2P1) / (P2-P1). When the grating period satisfies P2=1.1P1, the denominator (P2-P1) is reduced, which can significantly enhance the displacement amplification effect of the Moire fringe and improve the measurement accuracy when aligning the wafer and the mask. At the same time, because the period P of the Moire fringe is m Significantly larger than a single grating period, this allows even tiny relative displacements to cause noticeable fringe displacements, thereby improving measurement resolution. Furthermore, this period ratio design reduces fringe artifacts, lowers high-order harmonic interference, improves fringe contrast and signal-to-noise ratio, enhances the system's tolerance to manufacturing errors, and improves the stability and robustness of wafer-mask alignment.

[0061] Reference Figure 6 As shown, to detect misalignment in a certain direction, the grating lines need to be perpendicular to the detection direction. The grating lines cannot sense movement in the same direction. Therefore, when using traditional differential line gratings for misalignment detection, multiple sets of marks need to be placed to simultaneously detect misalignment in the X and Y directions. In this embodiment, a set of grating alignment marks is proposed, which adopts a symmetrical structure design and can generate a square moiré pattern under the illumination of a light source. Figure 7 As shown, the offset of the light-shielding lines between the first and second quadrants and the offset of the light-shielding lines between the third and fourth quadrants are used for misalignment detection in the X direction, and the offset of the light-shielding lines between the first and fourth quadrants and the offset of the light-shielding lines between the second and third quadrants are used for misalignment detection in the Y direction. Therefore, only one set of grating alignment marks is needed to simultaneously realize multi-directional misalignment detection, and no longer relies on the combination of multiple sets of alignment marks. This solves the problem that existing alignment marks cannot independently realize multi-degree-of-freedom alignment during the fine alignment process, significantly reduces the occupation of the effective area of ​​the wafer, and improves the efficiency of lithography alignment.

[0062] This embodiment also provides a lithography alignment method based on grating marks, referring to Figure 8 As shown, the method comprises step S1, step S2, step S3, step S4, step S5 and step S6.

[0063] Step S1, etching a wafer alignment mark at the center of the wafer and etching a mask alignment mark on the mask.

[0064] Furthermore, to achieve high-precision mark etching, both wafer and mask alignment marks are etched using electron beam direct writing. Because the electron beam direct writing system can precisely control the electron beam's scanning path and exposure dose, it helps ensure the precise placement of alignment marks on the wafer and mask, improving overlay accuracy during the photolithography process.

[0065] Step S2 , superimposing the wafer and the mask so that the wafer alignment mark and the mask alignment mark overlap, and irradiating the wafer alignment mark and the mask alignment mark simultaneously with an alignment light source to generate a square moiré fringe pattern.

[0066] For example, in a photolithography alignment system, when there is a slight relative displacement between the periodic gratings on the mask alignment mark and the wafer alignment mark, their superposition will produce moiré fringes, and the interference of diffracted light from the two symmetrical marks will generate a square moiré fringe pattern.

[0067] Step S3 , adjusting the positions of the wafer and the mask according to the square moiré fringe pattern to perform coarse alignment.

[0068] For example, since the moiré fringes are periodic, when the relative displacement of the moiré fringes exceeds P1P2 / (P1+P2), the pattern of the moiré fringes will repeat, resulting in ambiguity in its phase measurement, making the alignment result invalid. Therefore, in the photolithography alignment process, it is necessary to first control the initial misalignment of the wafer and the mask within the fine alignment range through coarse alignment to avoid the influence of the periodicity of the moiré fringes. Generally speaking, coarse alignment does not require absolute precision, but it is necessary to ensure that the misalignment is small enough to ensure the effectiveness of the subsequent fine alignment. Coarse alignment is usually performed using a frame structure (the outer contour of the square fringe pattern in this embodiment can be regarded as a square frame structure). For example, in this embodiment, the square moiré fringe pattern is used to adjust the position of the wafer and the mask for coarse alignment, including extracting the outer contour of the square moiré fringe pattern through a computer image processing algorithm for preprocessing, determining the misalignment of the wafer and the mask and performing preliminary adjustments so that the misalignment falls within the fine alignment range.

[0069] Step S4: Divide the square moiré fringe pattern by diagonal lines to obtain four isosceles triangle regions, namely, an upper region, a lower region, a left region, and a right region. Each region is divided into two parts by its own perpendicular midline as a dividing line.

[0070] For example, in this embodiment, the symmetrical diffraction light interference generation period of the two marks is P m =P2P1) / (P2-P1), where P1 is the first spacing and P2 is the second spacing. When the wafer and the mask are misaligned in the X direction, refer to Figure 3As shown, according to the displacement amplification effect of the moiré fringe, the amplification factor of the micro displacement of the moiré fringe is ΔX = Δx (P2 + P1) / (P2 - P1), where Δx is the actual misalignment between the wafer and the mask, and ΔX is the amplified displacement of the moiré fringe between the wafer alignment mark and the mask alignment mark. The same is true for the Y direction. Figure 4 The displacement amplification effect of moiré fringes can significantly amplify tiny displacement changes between the wafer and the mask, and is reflected in the relative displacement of the fringes in the square moiré fringe pattern. This is because the period of the moiré fringes is much longer than the period of a single grating, and such long-period fringes are extremely sensitive to tiny displacement changes. Even nanometer-scale displacements can cause a significant shift in the moiré fringe position, thereby improving detection resolution and achieving sub-nanometer alignment accuracy.

[0071] Step S5 , extracting the moiré fringe phases of the two parts of each region respectively, and calculating the absolute phase difference between the two parts of each region respectively.

[0072] Furthermore, in this embodiment, the image processing method used to extract the moiré fringe phases of the two parts of each region is 2D-FFT. (2D-FFT, also known as two-dimensional fast Fourier transform, is an efficient algorithm used to convert two-dimensional discrete signals from the spatial domain to the frequency domain. Through 2D-FFT, the moiré fringe pattern can be converted to the frequency domain, and its phase information can be extracted.) Furthermore, the absolute phase difference formula between the two parts of each region is:

[0073]

[0074] in, are the absolute phase differences of the two parts of the left area, right area, upper area and lower area respectively, and are the moiré fringe phases of the upper and lower parts of the left region, and are the moiré fringe phases of the upper and lower parts of the right region, and are the moiré fringe phases of the left and right parts of the upper region, and The moiré fringe phases of the left and right parts of the lower area, respectively.

[0075] The actual misalignment Δx and Δy between the wafer and the mask along the X and Y directions, respectively, are calculated using the misalignment calculation formula. The misalignment calculation formula includes:

[0076]

[0077] Wherein, P1 is the first spacing, P2 is the second spacing, Δx1 and Δx2 represent the first candidate misalignment amount and the second candidate misalignment amount between the wafer and the mask along the X direction, respectively, Δy3 and Δy4 represent the third candidate misalignment amount and the fourth candidate misalignment amount between the wafer and the mask along the Y direction, respectively. and represents the absolute phase difference between the two parts of the left region, right region, upper region, and lower region, respectively. Δx is Δx1 or Δx2, and Δy is Δy3 or Δy4. Furthermore, the formulas for calculating the misalignment between the two parts of the upper region, lower region, left region, and right region are obtained by unwrapping the moiré fringe intensity equations for the two parts of the upper region, lower region, left region, and right region, respectively.

[0078] Furthermore, when the wafer and the mask are misaligned in the X direction, the moiré fringe intensity of the two parts in the left region can be expressed as:

[0079]

[0080] Among them, (x,y) represents the pixel coordinates, and Represent the Moire fringe intensity of the upper and lower parts of the left area, a(x, y) and b(x, y) represent the background light intensity and amplitude modulation of the fringe pattern, respectively. m =(P2P1) / (P2-P1), Δx is the misalignment between the wafer and the mask along the X direction.

[0081] When the wafer and mask are misaligned in the X direction, the fringes in the right region move in opposite directions to the fringes in the corresponding positions in the left region. The intensity of the moiré fringes in the two parts of the right region can be expressed as:

[0082]

[0083] in, and Represents the moiré fringe intensities of the upper and lower parts of the right area, respectively.

[0084] When the wafer and mask are misaligned in the Y direction, the moiré fringe intensity of the two parts of the upper area can be expressed as:

[0085]

[0086] in, and They represent the moiré fringe intensities of the left and right parts of the upper area, respectively, and Δy is the misalignment between the wafer and the mask along the Y direction.

[0087] When the wafer and mask are misaligned in the Y direction, the fringes in the lower region move in opposite directions to the fringes at the corresponding positions in the upper region. The Moire fringe intensity of the two parts of the lower region can be expressed as:

[0088]

[0089] in, and Denotes the fringe intensity of the left and right parts of the lower region respectively. By unwrapping the Moire fringe intensity equation of each region and substituting it into the absolute phase difference formula, we can obtain:

[0090]

[0091] in, are the absolute phase differences of the two parts of the left area, right area, upper area and lower area respectively, and are the moiré fringe phases of the upper and lower parts of the left region, and are the moiré fringe phases of the upper and lower parts of the right region, and are the moiré fringe phases of the left and right parts of the upper region, and The moiré fringe phases of the left and right parts of the lower area, respectively.

[0092] Thus, the calculation formula of the misalignment is further obtained:

[0093]

[0094]

[0095] Wherein, P1 is the first spacing, P2 is the second spacing, Δx1 and Δx2 represent the first candidate misalignment amount and the second candidate misalignment amount between the wafer and the mask along the X direction, respectively, Δy3 and Δy4 represent the third candidate misalignment amount and the fourth candidate misalignment amount between the wafer and the mask along the Y direction, respectively. and The absolute phase difference between two parts represents the left area, right area, upper area and lower area respectively.

[0096] In step S6 , the actual misalignment values ​​Δx and Δy between the wafer and the mask along the X and Y directions, respectively, are input into the translation stage of the lithography machine for feedback, and the translation stage is used to precisely align the positions of the wafer and the mask.

[0097] By measuring the phase change of the moiré fringes, the relative displacement between the wafer and the mask can be accurately calculated to achieve sub-nanometer alignment accuracy. Figure 5 As shown, the image at this time is the moiré fringe pattern after perfect alignment between the wafer and the mask.

[0098] This embodiment also proposes a photolithography machine, which uses the above-mentioned photolithography alignment method based on grating marks when implementing photolithography alignment.

[0099] This embodiment proposes a set of grating alignment marks, which adopt a symmetrical structural design and can generate a square moiré fringe pattern under illumination by a light source. The offset of the light-shielding lines between the first and second quadrants and the offset of the light-shielding lines between the third and fourth quadrants are used for misalignment detection in the X direction, and the offset of the light-shielding lines between the first and fourth quadrants and the offset of the light-shielding lines between the second and third quadrants are used for misalignment detection in the Y direction. Therefore, only one set of grating alignment marks is required to simultaneously perform multi-directional misalignment detection, eliminating the need for multiple sets of alignment marks. This solves the problem that existing alignment marks cannot independently achieve multi-degree-of-freedom alignment during the fine alignment process, significantly reduces the effective area occupied by the wafer, and improves the efficiency of lithography alignment.

[0100] Furthermore, in this embodiment, wafer alignment marks are etched on the wafer and mask alignment marks are etched on the mask, and then the wafer and mask are superimposed on each other, and the wafer alignment marks and the mask alignment marks are simultaneously illuminated by an alignment light source to generate a square moiré fringe pattern. The positions of the wafer and the mask are then roughly aligned based on the square moiré fringe pattern. The square moiré fringe pattern is then divided by diagonal lines to obtain four isosceles triangle regions, namely the upper region, the lower region, the left region, and the right region. Each region is divided into two parts with its own perpendicular midline as the dividing line, and the moiré fringe phases of the two parts of each region are extracted, and the absolute phase difference between the two parts of each region is calculated. The actual misalignment Δx and Δy between the crystal and the mask along the X and Y directions, respectively, are calculated. Finally, Δx and Δy are input into the translation stage of the lithography machine for feedback, and the translation stage is used to finely align the positions of the wafer and the mask. By measuring the phase change of the Moiré fringes, the relative displacement between the wafer and the mask can be accurately calculated, achieving sub-nanometer alignment accuracy and improving the accuracy of lithography alignment.

[0101] Furthermore, this embodiment utilizes the high sensitivity characteristics of the Moiré fringes and combines them with the two-dimensional fast Fourier transform (2D-FFT) and intensity equation unwrapping algorithm to further optimize and improve the alignment accuracy between the wafer and the mask and the calculation efficiency of the misalignment amount.

[0102] It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit it. Based on the embodiments provided in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0103] Obviously, the accompanying drawings are merely examples or embodiments of the present application. A person skilled in the art can also apply the present application to other similar situations based on these drawings without inventive effort. Furthermore, it is understandable that, although the work involved in this development process may be complex and lengthy, certain design, manufacturing, or production changes based on the technical content disclosed in this application are merely routine technical means for a person skilled in the art and should not be considered to constitute a deficiency in the disclosure of the present application.

Claims

1. A lithography alignment method based on grating marks, characterized in that: include: Etching a wafer alignment mark at the center of the wafer and etching a mask alignment mark on the mask, wherein the wafer alignment mark and the mask alignment mark are grating marks used for photolithography alignment; The grating mark includes: a wafer alignment mark for etching on a wafer, which is divided into four quadrants according to the quadrants, each quadrant of the wafer alignment mark includes a plurality of L-shaped light-shielding lines with equal spacing, the two sides of each L-shaped light-shielding line are equal in length and are respectively perpendicular to the boundaries of the two quadrants, the spacing between the L-shaped light-shielding lines in the first quadrant and the third quadrant of the wafer alignment mark is a first spacing, and the spacing between the L-shaped light-shielding lines in the second quadrant and the fourth quadrant is a second spacing; a mask alignment mark for etching on a mask, which is divided into four quadrants according to the quadrants, each quadrant of the wafer alignment mark includes a plurality of L-shaped light-shielding lines with equal spacing, the two sides of each L-shaped light-shielding line are equal in length and are respectively perpendicular to the boundaries of the two quadrants, the spacing between the L-shaped light-shielding lines in the first quadrant and the third quadrant of the wafer alignment mark is a first spacing, and the spacing between the L-shaped light-shielding lines in the second quadrant and the fourth quadrant is a second spacing; The mask alignment mark is divided into four quadrants, each quadrant of the wafer alignment mark includes a plurality of L-shaped light-shielding lines at equal intervals, two sides of each L-shaped light-shielding line are equal in length and perpendicular to two quadrant boundaries respectively, the grating pitch of the first quadrant and the third quadrant of the mask alignment mark is the second pitch, and the grating pitch of the second quadrant and the fourth quadrant of the mask alignment mark is the first pitch; wherein the first pitch is greater than the second pitch, and a duty ratio of the plurality of L-shaped light-shielding lines in each quadrant of the wafer alignment mark and the mask alignment mark is 1 / 2; The wafer and the mask are superimposed on each other so that the wafer alignment mark and the mask alignment mark overlap, and the wafer alignment mark and the mask alignment mark are illuminated simultaneously by an alignment light source to generate a square moiré fringe pattern; Coarse alignment is performed by adjusting the position of the wafer and mask according to the square moiré fringe pattern; The square moiré fringe pattern is divided into four isosceles triangle regions by diagonal lines. The four regions are upper region, lower region, left region and right region. Each region is divided into two parts by its own perpendicular median. Extract the moiré fringe phases of the two parts of each region respectively, and calculate the absolute phase difference between the two parts of each region respectively; The actual misalignment Δx and Δy between the wafer and the mask along the X and Y directions are calculated using the misalignment calculation formula. The misalignment calculation formula includes: Wherein, P1 is the first spacing, P2 is the second spacing, Δx1 and Δx2 represent the first candidate misalignment amount and the second candidate misalignment amount between the wafer and the mask along the X direction, respectively, Δy3 and Δy4 represent the third candidate misalignment amount and the fourth candidate misalignment amount between the wafer and the mask along the Y direction, respectively. and Represents the absolute phase difference between two parts of the left area, right area, upper area and lower area respectively, Δx takes Δx1 or Δx2, Δy takes Δy3 or Δy4; The actual misalignment values ​​Δx and Δy between the wafer and the mask along the X and Y directions, respectively, are input into the translation stage of the lithography machine for feedback, and the translation stage is used to precisely align the positions of the wafer and the mask.

2. The grating mark-based photolithography alignment method according to claim 1, wherein: The first spacing is 1.1 times the second spacing.

3. The lithography alignment method based on grating marks according to claim 1, characterized in that: Coarse alignment of the wafer and mask based on a square moiré pattern involves: The outer contour of the square Moiré fringe pattern is extracted through a computer image processing algorithm for pre-processing, the misalignment between the wafer and the mask is determined and preliminary adjustments are made to bring the misalignment into the precise alignment range.

4. The lithography alignment method based on grating marks according to claim 1, characterized in that: The etching of wafer alignment marks and mask alignment marks is achieved by electron beam direct writing.

5. The grating mark-based photolithography alignment method according to claim 1, wherein: The image processing method used to extract the moiré fringe phases of the two parts of each area is 2D-FFT.

6. The grating mark-based photolithography alignment method according to claim 1, wherein: The absolute phase difference between the two parts of each region is given by: in, are the absolute phase differences of the two parts of the left area, right area, upper area and lower area respectively, and are the moiré fringe phases of the upper and lower parts of the left region, and are the moiré fringe phases of the upper and lower parts of the right region, and are the moiré fringe phases of the left and right parts of the upper region, and The moiré fringe phases of the left and right parts of the lower area, respectively.

7. The lithography alignment method based on grating marks according to claim 1, characterized in that: The calculation formulas for the misalignment amounts of the two parts of the upper region, the lower region, the left region, and the right region are obtained by unwrapping the Moire fringe intensity equations of the two parts of the upper region, the lower region, the left region, and the right region, respectively.

8. The grating mark-based photolithography alignment method according to claim 7, wherein: When the wafer and mask are misaligned in the X direction, the moiré fringe intensity of the two parts in the left area can be expressed as: Among them, (x,y) represents the pixel coordinates, and Represent the Moire fringe intensity of the upper and lower parts of the left area, a(x, y) and b(x, y) represent the background light intensity and amplitude modulation of the fringe pattern, respectively. m =(P2P1) / (P2-P1), Δx is the misalignment between the wafer and the mask along the X direction; When the wafer and mask are misaligned in the X direction, the fringes in the right region move in opposite directions to the fringes in the corresponding positions in the left region. The intensity of the moiré fringes in the two parts of the right region can be expressed as: in, and The moiré fringe intensities of the upper and lower parts of the right region, respectively; When the wafer and mask are misaligned in the Y direction, the moiré fringe intensity of the two parts of the upper area can be expressed as: in, and They represent the moiré fringe intensities of the left and right parts of the upper region, respectively, and Δy is the misalignment between the wafer and the mask along the Y direction; When the wafer and mask are misaligned in the Y direction, the fringes in the lower region move in opposite directions to the fringes at the corresponding positions in the upper region. The Moire fringe intensity of the two parts of the lower region can be expressed as: in, and Represents the fringe intensity of the left and right parts of the lower area, respectively.

9. A photolithography machine, characterized in that: The lithography machine performs the grating mark-based lithography alignment method according to any one of claims 1 to 8 when implementing lithography alignment.

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