Moire fringe-based photoetching alignment system and method

Abstract

The invention belongs to the technical field of photoetching for manufacturing micro-nano devices, and particularly relates to a photoetching alignment system and method based on Morie fringes. The system comprises a template and a substrate, wherein the surfaces of the template and the substrate are respectively provided with coarse alignment marks distributed at four corners and Moire fringe marks distributed at four sides; the illumination imaging unit comprises a camera, a telecentric lens group and a coaxial light source; the displacement mechanism drives the template or the substrate to move. The method comprises the following steps of: coarsely aligning to precision through geometric imaging of a cross mark, overlapping a Morie fringe mark to form a fringe with an amplified displacement effect, calculating deviation through phase analysis, and returning to zero. According to the invention, the optical diffraction limit is broken through, the alignment precision of 10-100 nm is realized, and the complexity and high cost of a traditional interference system are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of photolithography for manufacturing micro-nano devices, and in particular relates to a photolithography alignment system and method based on moiré fringes, which is applicable to projection or contact photolithography equipment. Background Art

[0002] As the cornerstone of micro- and nanofabrication, photolithography technology's alignment accuracy directly determines the quality of microstructures such as integrated circuits and MEMS devices. In projection or contact photolithography processes, the overlay accuracy of multiple layers between the template and substrate must be controlled to submicron or even nanometer levels, placing stringent demands on position metrology. Currently, mainstream photolithography alignment solutions fall into two categories: geometric imaging alignment and interferometric alignment.

[0003] Geometric imaging alignment relies on a high-resolution optical system (usually equipped with a 20x or greater magnification lens) to directly observe the alignment marks (such as a cross or square pattern) on the template and substrate, and to determine the positional deviation based on the overlap of the marks. Although this method is intuitive and cost-effective, due to the physical constraints of the optical diffraction limit, its theoretical upper limit of accuracy is approximately one-third of the wavelength of the illumination light source. In practical applications, the typical alignment accuracy can only reach about 300 nanometers. For example, in deep ultraviolet lithography systems, even with expensive apochromatic lenses, it is still difficult to break through the 150-nanometer accuracy barrier, which obviously cannot meet the overlay error control requirements of processes below 7 nanometers.

[0004] Interferometric alignment technology offers another path to improving accuracy. This approach typically uses a multi-wavelength laser light source, which transmits a beam through a template and then reflects off the coated substrate surface. Lateral displacement is calculated by analyzing the phase shift of the interference fringes of the reflected beam. While such systems can theoretically achieve nanometer-level measurement accuracy, their implementation is technically expensive:

[0005] First, the system requires high-coherence lasers and precision interferometers, which more than double the number of optical components compared to geometric imaging systems. This poses a significant challenge to optical path stability. Environmental vibrations or temperature fluctuations can easily cause optical path difference drift, necessitating the addition of a real-time compensation module.

[0006] Secondly, the interferometric optical path has strict requirements on spatial layout. To avoid stray light interference, a large amount of isolation space must be reserved for optical components, which significantly increases the size of the equipment and limits its applicability in compact lithography machines.

[0007] Finally, the energy consumption and maintenance costs of the laser subsystem and its supporting temperature control device account for approximately 35% of the total equipment cost, significantly weakening the economic feasibility of the solution.

[0008] In summary, both of these technologies have inherent flaws that are difficult to overcome. Geometric imaging is limited by optical resolution and completely fails in subwavelength-scale alignment scenarios. While interferometry has the potential for high precision, its system complexity, environmental sensitivity, and implementation cost constitute a triple barrier to application. Especially with the development of emerging technologies such as three-dimensional integrated circuits and heterogeneous integration, multi-layer stacked structures require lithographic alignment with both high precision and strong robustness in the 10-100 nanometer range. Existing technology systems have shown significant inadaptability.

[0009] Therefore, the industry urgently needs to develop a new alignment solution that can break through physical limits and avoid complex architectures. This solution does not rely on expensive optical amplification components or laser interferometer modules, but can achieve nanometer-level positioning through innovative measurement principles while maintaining a simple optical path and cost competitiveness. This technological gap has become a key bottleneck restricting the evolution of micro-nano manufacturing to smaller nodes. Summary of the Invention

[0010] 1. Technical Issues

[0011] 1. Break through the optical diffraction limit and achieve sub-wavelength (10-100nm) alignment accuracy;

[0012] 2. Avoid the complex optical path and high cost of interference alignment;

[0013] 3. Solve the periodic blurring problem of moiré fringes (it cannot be distinguished when the displacement is super-periodic).

[0014] 2. Technical Solution

[0015] In order to solve the above problems, the present invention provides a lithography alignment system based on moiré fringe, comprising:

[0016] The template has a surface provided with:

[0017] Multiple sets of template coarse alignment marks, distributed at the four corners of the template;

[0018] Multiple sets of template moiré fringe marks are distributed on the four sides of the template;

[0019] The substrate is arranged parallel to the template and has the following surface:

[0020] multiple groups of substrate coarse alignment marks, the positions of which correspond to the template coarse alignment marks;

[0021] Multiple groups of substrate moiré fringe marks, positions of which correspond to the template moiré fringe marks;

[0022] Illumination and imaging unit, comprising:

[0023] A coaxial illumination light source is located above the template, with the optical axis illuminating the overlapping area of ​​the template and the substrate vertically downward;

[0024] The telecentric lens group is located on one side of the coaxial illumination light source, and the optical axis is coaxial with the coaxial illumination light source and perpendicular to the template plane;

[0025] A camera, with an optical path connected to the telecentric lens group, receives an image of the overlapping area of ​​the template and the substrate;

[0026] The displacement mechanism is mechanically connected to the template or substrate and drives it to move in the X / Y direction parallel to the template plane;

[0027] The calculation control unit, which connects the camera and the displacement mechanism with signals, is configured as follows:

[0028] Receive image signals transmitted by the camera; perform fast Fourier transform and position deviation calculation; output displacement control instructions to the displacement mechanism.

[0029] Preferably, the line width a1 of the template coarse alignment mark is 30 μm-150 μm, and the outer frame size a2 is 200 μm-1000 μm;

[0030] The line width a3 of the substrate coarse alignment mark satisfies a3≤(a2-a1).

[0031] Preferably, the period of the template moiré fringe mark is p1, the period of the substrate moiré fringe mark is p2, and the period of the template moiré fringe mark is p1, and ... substrate moiré fringe mark is p2, and the period of the substrate moir

[0032]

[0033] Preferably, the line width b2 of the template moiré fringe mark is the period p1.

[0034] The line width b4 of the substrate moiré fringe mark is the period p2

[0035] On the other hand, the present invention further provides a moiré fringe lithography alignment method, which uses the moiré fringe lithography alignment system described in the first aspect, comprising:

[0036] S1. Overlap the template and substrate and place them within the observation range of the telecentric lens group;

[0037] S2. Illuminate the overlapping area with a coaxial illumination source, and image it to the camera through a telecentric lens assembly;

[0038] S3. Perform geometric imaging coarse alignment based on the template coarse alignment mark and the substrate coarse alignment mark, with an accuracy of

[0039] S4. Overlapping the template moiré mark and the substrate moiré mark to form moiré fringes;

[0040] S5. Capture the moiré fringe image with a camera and extract the phase signal And calculate the position deviation

[0041] S6. Control the displacement mechanism to move the template or substrate to return the deviation x to zero.

[0042] Preferably, in step S5, the phase signal Extracted via Fast Fourier Transform.

[0043] Preferably, in step S6, the deviations x of at least 8 independent measurement points are reset to zero respectively.

[0044] Preferably, the method is used in a projection lithography apparatus or a contact lithography apparatus.

[0045] 3. Beneficial Effects

[0046] The present invention significantly improves lithography alignment performance through an innovative two-level alignment architecture. Its beneficial effects are mainly reflected in three closely related aspects:

[0047] In terms of technical performance, it is the first to combine geometric imaging coarse alignment with moiré fringe fine alignment, use complementary cross marks to achieve initial positioning, constrain the deviation to one-half of the template moiré fringe period, and effectively avoid the ambiguity caused by displacement super-period in traditional moiré measurement; then, through the overlapping of grating marks with a period difference of 0.5% to 5%, a displacement amplification effect is generated, so that tiny displacements are amplified 100-200 times, and combined with Fourier phase analysis, the measurement accuracy is improved to 10-100 nanometers, thus breaking through the diffraction limit of the geometric imaging method.

[0048] At the system simplification level, telecentric lenses and coaxial lighting are used to replace complex interference optical paths, which not only eliminates the dependence on lasers and precision mirrors, but also significantly reduces the number of optical components, thereby bringing dual benefits: on the one hand, it significantly reduces the difficulty of optical assembly and adjustment and improves the system's ability to resist vibration interference; on the other hand, it reduces the size of the equipment and is more suitable for compact lithography machine layouts.

[0049] In terms of economy, the optimization of hardware costs and the reduction of maintenance costs have jointly led to a significant reduction in overall implementation costs. At the same time, the algorithm processes displacement signals in real time, improving alignment efficiency and providing a complete solution for micro-nano manufacturing that combines ultra-high precision, strong robustness and excellent cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 1 is a schematic diagram of the optical path of a photolithography alignment system according to a first embodiment of the present invention;

[0051] Figure 2 Schematic diagram showing the correspondence between the positions of the four coarse alignment marks and the eight moiré fringe alignment marks on the template;

[0052] Figure 3 Schematic diagram showing the correspondence between the positions of four coarse alignment marks and eight moiré alignment marks on the substrate;

[0053] Figure 4 is a schematic diagram of a template with a coarse alignment mark as a cross;

[0054] Figure 5 for Figure 2 The moiré fringe on the middle template is marked as an enlarged image of a periodic fringe;

[0055] Figure 6 for Figure 3 an enlarged view of the coarse alignment mark on the substrate;

[0056] Figure 7 for Figure 3 The moiré pattern on the substrate in the middle is marked as an enlarged image of a periodic fringe;

[0057] Figure 8 A schematic diagram of the overlapping effect formed by the moiré fringes on the template and the moiré fringes on the substrate;

[0058] In the figure: camera 1, telecentric lens group 2, coaxial illumination light source 3, template 4, substrate 5, displacement device 6, template mark arrangement position 7, substrate mark arrangement position 8, template coarse alignment mark 9, template moiré mark 10, substrate coarse alignment mark 11, substrate moiré mark 12. DETAILED DESCRIPTION

[0059] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0060] Example 1:

[0061] See also Figure 1The present embodiment provides a photolithography alignment system based on moiré fringe, comprising: a template 4, on the surface of which are provided: a plurality of groups of template coarse alignment marks 9, distributed at the four corners of the template 4; a plurality of groups of template moiré fringe marks 10, distributed at the four sides of the template 4; a substrate 5, arranged parallel to and opposite to the template 4, on the surface of which are provided: a plurality of groups of substrate coarse alignment marks 11, the positions of which correspond to the template coarse alignment marks 9; a plurality of groups of substrate moiré fringe marks 12, the positions of which correspond to the template moiré fringe marks 10; an illumination imaging unit, comprising: a coaxial illumination light source 3, located above the template 4, with an optical axis vertically downwardly irradiating the template 4 and the substrate 5. The overlapping area of ​​the template 4 and the substrate 5 is formed by the telecentric lens group 2, and the optical axis is coaxial with the optical axis of the coaxial illumination light source 3 and perpendicular to the plane of the template 4; the camera 1 is optically connected to the telecentric lens group 2 and receives the image of the overlapping area between the template 4 and the substrate 5; the displacement mechanism 6 is mechanically connected to the template 4 or the substrate 5 and drives it to move in the X / Y direction parallel to the plane of the template 4; the computing control unit is signal-connected to the camera 1 and the displacement mechanism 6 and is configured to: receive the image signal transmitted by the camera 1; perform fast Fourier transform and position deviation calculation; and output displacement control instructions to the displacement mechanism 6.

[0062] Specifically, the lighting imaging unit includes a coaxial lighting light source 3, a telecentric lens group 2 and a camera 1; the telecentric lens group 2 has its own reflector and a light-transmitting hole is opened on the side wall corresponding to the reflector. The coaxial lighting light source 3 is arranged vertically on one side of the telecentric lens group 2 through a bracket (not shown in the figure) to horizontally project the lighting light beam through the light-transmitting hole onto the reflector. The reflector refracts the light beam so that its optical axis coincides with the optical axis of the telecentric lens group 3, and is perpendicular to the plane of the template 4, covering the overlapping area between the template 4 and the substrate 5.

[0063] The camera 1 is connected to the rear optical path of the telecentric lens group 2 through a mechanical interface, and is used to receive the transmitted or reflected image of the overlapping area of ​​the template 4 and the substrate 5. The displacement mechanism 6 adopts a precision piezoelectric platform, which is connected to the edge of the template 4 or the substrate 5 through a mechanical clamp, and drives it to perform nanometer-level displacement in the X / Y direction parallel to the plane of the template 4. The computing control unit adopts an embedded industrial computer, which is respectively connected to the image output interface of the camera 1 and the drive controller of the displacement mechanism 6 through a data cable. Among them, the piezoelectric platform is a common positioning device in the prior art, such as the XLS series of Hongjian Optoelectronics. In view of this, its positioning adjustment principle and structure will not be repeated in this embodiment.

[0064] like Figure 2 and Figure 3 As shown, the template 4 is provided with two sets of marks on its surface: four sets of template alignment marks 9 are distributed in the four corner areas of its outer contour, and four sets of template moiré marks 10 are distributed in the four edge areas. Figure 4The center-symmetrical cross structure shown in FIG. 1 has a line width a1 of 80 μm and an outer frame size a2 of 300 μm. The template moiré mark 10 can be as follows: Figure 5 The periodic stripes shown in the figure have a period p1 of 0.5 μm and a line width b2 of the period p1. That is about 0.17μm.

[0065] The substrate 5 is arranged parallel to the template 4, and its surface is provided with substrate alignment marks 11 and substrate moiré marks 12. The position of the substrate alignment mark 11 strictly corresponds to the template alignment mark 9, and its line width a3 must satisfy a3 ≤ (a2 - a1). Optionally, a3 is set to 100μm to form a complementary nested structure with the template alignment mark 9. This complementary nested structure creates a mechanical vernier caliper effect through the dimensional difference between the template mark outer frame a2 = 300μm and the substrate mark line width a3 = 100μm. The sharp intensity step at the nested edge breaks through the optical diffraction limit, compressing the coarse alignment accuracy to within the range of a single-cycle moiré fringe displacement, completely eliminating the periodic ambiguity during the fine alignment stage. At the same time, the nesting gap formed by this dimensional difference gives the system process tolerance, ensuring that micron-level machining errors do not affect nanometer-level positioning results. This effectively bridges the scale gap between macroassembly and nanometrology, becoming the core cornerstone of the two-level alignment architecture.

[0066] Furthermore, the period p2 of the substrate moiré fringe mark 12 can be 0.495 μm, and its line width b4 is 1 / 4 of the period p2. That is about 0.165μm, and the difference from p1 is

[0067] During operation, the collimated light beam emitted by the coaxial illumination light source 3 is refracted by the reflector and vertically illuminates the overlapping mark area of ​​the template 4 and the substrate 5. The light signal passing through the mark is collected by the telecentric lens group 2 and imaged onto the photosensitive surface of the camera 1. The calculation control unit executes the image processing algorithm: first, it identifies the geometric center deviation between the template relative alignment mark 9 and the substrate relative alignment mark 11, generates a coarse adjustment command to drive the displacement mechanism 6 to move to the coarse alignment accuracy. That is, within the range of 0.25μm; then extract the moiré fringe image formed by the overlap of the template moiré fringe mark 10 and the substrate moiré fringe mark 12, and calculate the phase signal by fast Fourier transform And according to the formula The position deviation x is calculated and the displacement mechanism 6 is finally controlled to return the deviation x to zero, thus achieving sub-micron alignment.

[0068] This embodiment achieves coarse alignment through complementary cross marks, breaking through the optical diffraction limit and constraining the displacement within a single period of the Moiré fringe. Utilizing a grating with a period difference of 0.5% to 5%, it produces Moiré fringe with a magnification of 100-200 times. This can convert an 80nm displacement into a measurable fringe movement of 8-16μm, ensuring alignment accuracy.

[0069] Example 2:

[0070] This embodiment provides a lithography alignment method based on moiré fringes. The method adopts the system described in Example 1 and specifically includes six steps:

[0071] In step S1 , the template 4 and the substrate 5 are placed on the carrier platform of the displacement mechanism 6 , and their relative positions are adjusted so that the overlapping area of ​​their marks falls into the field of view of the telecentric lens group 2 .

[0072] Step S2 , starting the coaxial illumination light source 3 , the light beam vertically penetrates the template 4 and the marking layer of the substrate 5 , and the telecentric lens group 2 transmits the overlapping area image to the camera 1 .

[0073] Step S3, perform geometric imaging coarse alignment: the calculation control unit identifies the cross outer frame of the template relative alignment mark 9 and the center of the embedded pattern of the substrate relative alignment mark 11, and when the deviation between the two exceeds That is, when the deviation is 0.25 μm, the displacement mechanism 6 is driven to move until the deviation is ≤ 0.25 μm.

[0074] Step S4: The template moiré fringe mark 10 and the substrate moiré fringe mark 12 are overlapped to form a low-frequency moiré fringe with a period of For example, when p1 = 0.5 μm and p2 = 0.495 μm, p is 49.5 μm.

[0075] Step S5: Capture the moiré fringe image through camera 1, and calculate the control unit to perform fast Fourier transform to extract the phase Substitute into the formula Solve for the position deviation x.

[0076] Step S6 , generating compensation instructions for the deviation values ​​of the eight independent measurement points on the four sides of the template 4 , and controlling the displacement mechanism 6 to move the template 4 or substrate 5 step by step until the deviations x of all measurement points return to zero.

[0077] Optionally, the line width a1 in the coarse alignment stage is selected to be 80 μm, a2 is 300 μm, and a3 is 100 μm; the period difference in the fine alignment stage is Set to 1%, the line width ratio Preferred Phase extraction uses fast Fourier transform rather than geometric analysis to avoid errors introduced by image noise.

[0078] This embodiment uses micron-level marks to achieve 0.25μm accuracy in the coarse alignment stage, and improves the measurement sensitivity to within 100nm in the fine alignment stage through the moiré fringe amplification effect; the fast Fourier transform is used to process the phase signal, which reduces the complexity of the optical system by 40% compared with the traditional interferometry method; the coordinated control of multiple marking points enables the overall alignment accuracy to reach ±50nm, which is suitable for mask-wafer alignment of projection lithography machines or nanoimprinting of contact lithography.

[0079] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A lithography alignment system based on moiré fringe, characterized in that: include: The template (4) has a surface provided with: Multiple sets of template coarse alignment marks (9), distributed at the four corners of the template (4); Multiple sets of template moiré fringe marks (10) are distributed on the four sides of the template (4); The substrate (5) is arranged parallel to the template (4) and has the following surface: Multiple groups of substrate coarse alignment marks (11), the positions of which correspond to the template coarse alignment marks (9); Multiple groups of substrate moiré fringe marks (12), positions of which correspond to the template moiré fringe marks (10); Illumination and imaging unit, comprising: A coaxial illumination light source (3) is located above the template (4), with the optical axis irradiating the overlapping area of ​​the template (4) and the substrate (5) vertically downward; A telecentric lens group (2) is located on one side of the coaxial illumination light source (3), with an optical axis coaxial with the optical axis of the coaxial illumination light source (3) and perpendicular to the plane of the template (4); A camera (1) is optically connected to a telecentric lens assembly (2) to receive an image of an overlapping area between the template (4) and the substrate (5); a displacement mechanism (6) mechanically connected to the template (4) or substrate (5) to drive it to move in an X / Y direction parallel to the plane of the template (4); The calculation control unit, signal-connecting the camera (1) and the displacement mechanism (6), is configured to: receiving an image signal transmitted by a camera (1); Perform fast Fourier transform and position deviation calculation; Outputting a displacement control instruction to the displacement mechanism (6).

2. The lithography alignment system based on moiré fringe according to claim 1, characterized in that: The template coarse alignment mark (9) has a line width a1=30μm-150μm and an outer frame size a2=200μm-1000μm; The line width a3 of the substrate coarse alignment mark (11) satisfies a3≤(a2-a1).

3. The lithography alignment system based on moiré fringe according to claim 1, characterized in that: The period of the template moiré fringe mark (11) is p1, the period of the substrate moiré fringe mark (12) is p2, and the period satisfies 4. The lithography alignment system based on moiré fringe according to claim 1, characterized in that: The line width b2 of the template moiré fringe mark (10) is the period p1. The line width b4 of the substrate moiré mark (12) is the period p2.

5. A moiré lithography alignment method, using the moiré lithography alignment system according to any one of claims 1 to 4, characterized in that: include: S1. The template (4) and the substrate (5) are overlapped and placed within the observation range of the telecentric lens group (2); S2. The overlapping area is illuminated by a coaxial illumination light source (3) and imaged to the camera (1) via a telecentric lens group (2); S3. Perform geometric imaging coarse alignment based on the template coarse alignment mark (9) and the substrate coarse alignment mark (11), with an accuracy of S4. Overlapping the template moiré fringe mark (10) and the substrate moiré fringe mark (12) to form moiré fringes; S5. Capture the moiré fringe image through the camera (1) and extract the phase signal And calculate the position deviation S6. Control the displacement mechanism (6) to move the template (4) or substrate (5) to return the deviation x to zero.

6. The lithography alignment method based on moiré fringe according to claim 5, characterized in that: In step S5, the phase signal Extracted via Fast Fourier Transform.

7. The lithography alignment method based on moiré fringe according to claim 5, characterized in that: In step S6 , the deviations x of at least 8 independent measurement points are reset to zero respectively.

8. The lithography alignment method based on moiré fringe according to claim 5, characterized in that: The method is used in a projection lithography apparatus or a contact lithography apparatus.

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