Grating mark for photoetching alignment and alignment method thereof

Abstract

The invention relates to a grating mark for photoetching alignment and an alignment method thereof, and the mark comprises a wafer alignment mark and a mask alignment mark. The method comprises the following steps: etching a wafer alignment mark and a mask alignment mark on a wafer and a mask respectively; irradiating the wafer mark and the mask mark at the same time through an alignment light source, and generating a square Moire fringe pattern through diffraction light interference; preprocessing the outer contour of the moire fringe pattern by using a computer to realize coarse alignment; phase information of the moire fringes is extracted through 2D-FFT, and an absolute phase is calculated through an intensity equation unwrapping algorithm; calculating the actual dislocation amount between the wafer and the mask according to the phase difference of the moire fringes; and inputting the dislocation quantity into a displacement table to realize feedback adjustment until high-precision alignment is realized. According to the invention, multi-degree-of-freedom fine alignment in photoetching alignment can be realized through the single group of centrosymmetric marks and the alignment method thereof, the occupation of the effective area of the wafer is greatly reduced, and the photoetching efficiency and the alignment precision are remarkably improved.

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 lithography alignment pattern to be accurately exposed to 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 needs 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, and 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. There is currently no effective solution 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 to solve the problem that the existing alignment mark cannot independently achieve multi-degree-of-freedom alignment during the precise 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 quadrant parts according to quadrants, each quadrant part of the wafer alignment mark includes a plurality of L-shaped light shielding lines with equal spacing, 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 quadrant part and the third quadrant part of the wafer alignment mark is a first spacing, and the spacing between the L-shaped light shielding lines in the second quadrant part and the fourth quadrant part is a second spacing;

[0007] A mask alignment mark for etching on a mask, which is divided into four quadrant parts according to quadrants, each quadrant part of the wafer alignment mark includes a plurality of L-shaped light shielding lines with equal spacing, two sides of each L-shaped light shielding line are equal in length and are respectively perpendicular to 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;

[0008] The first spacing is greater than the second spacing, and the duty cycle 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.

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

[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 simultaneously illuminated 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 the mask according to the square moiré fringe pattern;

[0014] The square moiré fringe pattern is 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 by its own perpendicular midline.

[0015] 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;

[0016] The actual misalignment Δx and Δy between the wafer and the mask along the X direction and the Y direction respectively are calculated by 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 Respectively represent the absolute phase difference between two parts of the left area, the right area, the upper area and the lower area, Δx takes Δx1 or Δx2, Δy takes Δy3 or Δy4;

[0019] The actual misalignment Δx and Δy between the wafer and the mask along the X direction and the Y direction 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 preprocessing, 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 of the embodiments, etching of the wafer alignment mark and the mask alignment mark are both achieved by electron beam direct writing.

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

[0024] In some of the embodiments, the absolute phase difference between the two parts of each region is given by:

[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 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.

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

[0029]

[0030] Among them, (x, y) represents the pixel coordinates, and represents the moiré fringe intensity of the upper and lower parts of the left region, 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 the mask are misaligned in the X direction, the fringes in the right area move in the opposite direction to the fringes in the corresponding position in the left area. The intensity of the moiré fringes in the two parts of the right area 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 the 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 intensity 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;

[0037] When the wafer and the mask are misaligned in the Y direction, the fringes in the lower area move in the opposite direction to the fringes at the corresponding positions in the upper area. The intensity of the moiré fringes in the two parts of the lower area 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 group of grating alignment marks, which adopt a symmetrical structure design and can generate a square moiré fringe pattern under the illumination of a light source. The offset of the shading line between the first quadrant and the second quadrant and the offset of the shading line between the third quadrant and the fourth quadrant are used for misalignment detection in the X direction, and the offset of the shading line between the first quadrant and the fourth quadrant and the offset of the shading line between the second quadrant and the third quadrant are used for misalignment detection in the Y direction. Therefore, only one group of grating alignment marks is needed to realize multi-directional misalignment detection at the same time, and no longer rely on the combination of multiple groups of alignment marks. The problem that the existing alignment marks cannot independently realize multi-degree-of-freedom alignment in the precise alignment process is solved, the occupation of the effective area of ​​the wafer is significantly reduced, and the efficiency of lithography alignment is improved.

[0043] 2. The present invention completes the rough alignment through the outer contour of the square Moiré fringe pattern, uses area division and detects the fringe intensity and phase information to calculate the misalignment of the wafer and the mask in the X and Y directions, and finally feeds the data back to the translation stage of the lithography machine and adjusts the position of the wafer and the mask to achieve fine alignment. By measuring the phase change of the Moiré fringe, the relative displacement of 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 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.

[0045] 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 A structural diagram of wafer alignment marks;

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

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

[0049] Figure 4 This is the moiré fringe pattern when there is a 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, and each quadrant part of the wafer alignment mark includes a plurality of L-shaped shading lines with equal intervals, and 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 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, and the total area of ​​the plurality of 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 a plurality of L-shaped shading lines with equal spacing, 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 and improve the detection signal-to-noise ratio, thereby enhancing the recognizability of the moiré fringes. The wafer alignment mark and the mask alignment mark are both designed with such a 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, and the second pitch is P1, that is, P2 = 1.1P1. Due to 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 moiré fringes and improve the measurement accuracy when aligning the wafer and the mask. At the same time, because the period of the moiré fringes P m Significantly larger than a single grating period, a tiny relative displacement can cause a noticeable fringe displacement, thereby improving the measurement resolution. In addition, this period ratio design can reduce fringe artifacts, reduce high-order harmonic interference, improve fringe contrast and signal-to-noise ratio, enhance the tolerance of the system to manufacturing errors, and improve the stability and robustness of wafer and mask alignment.

[0061] Reference Figure 6 As shown in FIG. 1 , to detect misalignment in a certain direction, the line direction of the grating needs to be perpendicular to the detection direction. The grating lines cannot sense the movement in the same direction. Therefore, when using the traditional differential line grating 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 fringe pattern under the illumination of a light source. Figure 7 As shown, the offset of the shading line between the first quadrant and the second quadrant and the offset of the shading line between the third quadrant and the fourth quadrant are used for misalignment detection in the X direction, and the offset of the shading line between the first quadrant and the fourth quadrant and the offset of the shading line between the second quadrant and the third quadrant 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 rely on the combination of multiple sets of alignment marks. This solves the problem that the existing alignment marks cannot independently realize multi-degree-of-freedom alignment during the precise 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, in order to achieve high positioning accuracy mark etching, the etching of wafer alignment marks and mask alignment marks are both achieved by electron beam direct writing. Since the electron beam direct writing system can accurately control the scanning path and exposure dose of the electron beam, it helps to ensure that the alignment marks are accurately positioned on the wafer and mask, thereby improving the registration 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] Exemplarily, since the moiré fringes are periodic, when the relative displacement of the moiré fringes exceeds P1P2 / (P1+P2), the moiré fringes pattern will be repeated, 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 subsequent fine alignment. Coarse alignment is usually performed using a frame (frame) structure (the outer contour of the square fringe pattern in this embodiment can be regarded as a square frame structure). Exemplarily, 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 making preliminary adjustments so that the misalignment enters the fine alignment range.

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

[0070] Exemplarily, 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 the moiré fringe can significantly amplify the change of the tiny displacement between the wafer and the mask, and is reflected in the relative displacement of the fringes in the square moiré fringe diagram. Because the period of the moiré fringe is much larger than the period of a single grating, and this long-period fringe is extremely sensitive to tiny displacement changes, even nanometer-level displacements will cause a significant shift in the position of the moiré fringe, thereby improving the detection resolution and achieving sub-nanometer-level alignment accuracy.

[0071] Step S5, extracting the moire 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 phase of the two parts of each region is 2D-FFT. (2D-FFT, also known as two-dimensional fast Fourier transform, is an efficient algorithm for converting a two-dimensional discrete signal from a spatial domain to a frequency domain. Through 2D-FFT, the moiré fringe pattern can be converted to the frequency domain, and then 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 direction and the Y direction respectively are calculated by 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 Respectively represent the absolute phase difference between the two parts of the left region, the right region, the upper region and the lower region, Δx takes Δx1 or Δx2, and Δy takes Δy3 or Δy4. Further, the calculation formulas for the misalignment of the two parts of the upper region, the lower region, the left region and the right region are obtained by unwrapping the moiré fringe intensity equations of the two parts of the upper region, the lower region, the left region and the 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 area can be expressed as:

[0079]

[0080] Among them, (x, y) represents the pixel coordinates, and represents the moiré fringe intensity of the upper and lower parts of the left region, 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 the mask are misaligned in the X direction, the fringes in the right area move in the opposite direction to the fringes in the corresponding position in the left area. The intensity of the moiré fringes in the two parts of the right area can be expressed as:

[0082]

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

[0084] When the wafer and the 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 the mask are misaligned in the Y direction, the fringes in the lower area move in the opposite direction to the fringes at the corresponding positions in the upper area. The intensity of the moiré fringes in the two parts of the lower area can be expressed as:

[0088]

[0089] in, and Represent the fringe intensity of the left and right parts of the lower area respectively. By unwrapping the moiré fringe intensity equation of each area and substituting it into the absolute phase difference formula, we can get:

[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] Step S6, inputting the actual misalignment amounts Δx and Δy between the wafer and the mask along the X direction and the Y direction respectively into the translation stage of the lithography machine for feedback, and the translation stage performs precise alignment on 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 lithography machine, which uses the above-mentioned grating mark-based lithography alignment method when implementing lithography alignment.

[0099] In the present embodiment, a group of grating alignment marks are proposed, which adopt a symmetrical structure design and can generate a square moiré fringe pattern under the illumination of a light source. The offset of the shading lines between the first quadrant and the second quadrant and the offset of the shading lines between the third quadrant and the fourth quadrant are used for misalignment detection in the X direction, and the offset of the shading lines between the first quadrant and the fourth quadrant and the offset of the shading lines between the second quadrant and the third quadrant are used for misalignment detection in the Y direction. Therefore, only one group of grating alignment marks is needed to realize multi-directional misalignment detection at the same time, and no longer rely on the combination of multiple groups of alignment marks. This solves the problem that the existing alignment marks cannot independently realize multi-degree-of-freedom alignment in the precise alignment process, significantly reduces the occupation of the effective area of ​​the wafer, and improves the efficiency of lithography alignment.

[0100] Furthermore, in this embodiment, a wafer alignment mark is etched on the wafer and a mask alignment mark is etched on the mask, and then the wafer and the mask are superimposed on each other, and the wafer alignment mark and the mask alignment mark are simultaneously irradiated with an alignment light source to generate a square moiré fringe pattern, and then the positions of the wafer and the mask are roughly aligned according to the square moiré fringe pattern, and then the square moiré fringe pattern is divided by diagonal lines to obtain four isosceles triangle regions, which are an upper region, a lower region, a left region and a right region, and each region is divided into two parts with its own perpendicular midline as a 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, and then the actual misalignment Δx and Δy between the crystal and the mask along the X direction and the Y direction respectively are calculated, and finally Δx and Δy are input into the displacement stage of the lithography machine for feedback, and the displacement stage is used to precisely 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, the present embodiment utilizes the high sensitivity characteristics of the moiré fringes and combines the two-dimensional fast Fourier transform (2D-FFT) and the 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 the application, rather than 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 protection scope of this application.

[0103] Obviously, the drawings are only some examples or embodiments of the present application. For ordinary technicians in the field, the present application can also be applied to other similar situations based on these drawings without creative work. In addition, it is understandable that although the work done in this development process may be complicated and lengthy, for ordinary technicians in the field, certain changes in design, manufacturing or production based on the technical content disclosed in this application are only conventional technical means and should not be regarded as insufficient content disclosed in this application.

Claims

1. A grating mark for photolithography alignment, characterized in that: include: A wafer alignment mark for etching on a wafer, which is divided into four quadrant parts according to quadrants, each quadrant part of the wafer alignment mark includes a plurality of L-shaped light shielding lines with equal spacing, 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 quadrant part and the third quadrant part of the wafer alignment mark is a first spacing, and the spacing between the L-shaped light shielding lines in the second quadrant part and the fourth quadrant part is a second spacing; A mask alignment mark for etching on a mask, which is divided into four quadrant parts according to quadrants, each quadrant part of the wafer alignment mark includes a plurality of L-shaped light shielding lines with equal spacing, two sides of each L-shaped light shielding line are equal in length and are respectively perpendicular to 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; The first spacing is greater than the second spacing, and the duty cycle 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.

2. The grating mark for lithography alignment according to claim 1, characterized in that: The first spacing is 1.1 times the second spacing.

3. 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 for photolithography alignment in claim 1; 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 simultaneously illuminated by an alignment light source to generate a square moiré fringe pattern; Coarse alignment is performed by adjusting the position of the wafer and the mask according to the square moiré fringe pattern; The square moiré fringe pattern is 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 by its own perpendicular midline. 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; The actual misalignment Δχ and Δy between the wafer and the mask along the X direction and the Y direction are calculated by the misalignment calculation formula. include: 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 Respectively represent the absolute phase difference between two parts of the left area, the right area, the upper area and the lower area, Δx takes Δx1 or Δx2, Δy takes Δy3 or Δy4; The actual misalignment Δx and Δy between the wafer and the mask along the X direction and the Y direction 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.

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

5. The grating mark-based photolithography alignment method according to claim 3, characterized in that: The etching of wafer alignment marks and mask alignment marks are both achieved by electron beam direct writing.

6. The grating mark-based photolithography alignment method according to claim 3, characterized in that: The image processing method used to extract the moiré fringe phases of the two parts of each area is 2D-FFT.

7. The grating mark-based photolithography alignment method according to claim 3, characterized in that: The formula for the absolute phase difference between the two parts of each region is: 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.

8. The grating mark-based photolithography alignment method according to claim 3, 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.

9. The grating mark-based photolithography alignment method according to claim 8, characterized in that: When the wafer and the 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 represents the moiré fringe intensity of the upper and lower parts of the left region, 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 the mask are misaligned in the X direction, the fringes in the right area move in the opposite direction to the fringes in the corresponding position in the left area. The intensity of the moiré fringes in the two parts of the right area 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 the 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 intensity 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; When the wafer and the mask are misaligned in the Y direction, the fringes in the lower area move in the opposite direction to the fringes at the corresponding positions in the upper area. The intensity of the moiré fringes in the two parts of the lower area can be expressed as: in, and Represents the fringe intensity of the left and right parts of the lower area, respectively.

10. A photolithography machine, characterized in that: The lithography machine executes the grating mark-based lithography alignment method as described in any one of claims 3 to 9 when implementing lithography alignment.

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