A method and system for focal plane leveling based on multi-point detection

Abstract

The application provides a focus plane leveling method based on multi-point detection, which comprises the following steps: dividing a sample exposure area into a grid by using a computer; recording the x and y axis coordinates of each grid point; collecting a focus image of a detection beam focused on each grid point; recording the z axis height of the grid point as the z axis coordinate of the grid point when the difference between the focus image of the grid point and the standard image data is within the accuracy control range by using the computer to control the z axis height of the moving table; and establishing a grid point coordinate (x, y, z) database; calculating the z axis coordinate of any point (x, y) in the region surrounded by four adjacent grid points according to the coordinates of the four adjacent grid points; and moving the exposure beam to the exposure area by using the computer to control the moving table, and exposing the exposure area after the z axis displacement compensation of the focus plane. The focus plane leveling method provided by the application can compensate the change of the focus plane height in real time during the photolithography exposure process, and realize the consistency control of the imaging or exposure focus plane height.

Description

Technical Field

[0001] This invention relates to the field of photolithography, and more specifically, to a focal plane leveling method and system based on multi-point detection. Background Technology

[0002] With the explosive growth of smart device research and development, the socio-economic landscape has placed demands on the integration and multifunctionality of the manufacturing of functional nanostructure units and devices. Maskless lithography, with its low cost, high precision, high efficiency, and personalized processing capabilities, is a revolutionary lithography technology that adapts to the progress of social science and technology.

[0003] Photon beam maskless lithography, represented by femtosecond laser two-photon direct writing and digital micromirror device (DMD) surface projection exposure technology, is a low-cost lithography technology for complex structures. As resolution continues to break through from micrometers to submicrometers and even tens of nanometers, high numerical aperture oil immersion lenses are used as lithography projection focusing lenses. Traditional off-axis focusing techniques are suitable for focusing clean air layer interfaces, but not for multi-layer dielectric interfaces closely attached to the oil immersion lens. Due to the introduction of the oil layer in the objective lens, a transparent sheet (cover glass) needs to be added between the photoresist material and the oil layer to prevent contamination of the photoresist material. Therefore, the actual exposure area is a multi-layer dielectric structure, containing multiple interfaces with abrupt changes in refractive index from the objective surface to the photoresist substrate surface, such as the oil layer and the upper surface of the cover glass, the lower surface of the cover glass and the upper surface of the photoresist material, the lower surface of the photoresist material and the upper surface of the substrate material, and the multi-layer dielectric surface of the substrate material itself. Each interface has a different reflectivity to the focusing light source, and the superposition of reflected light from multiple interfaces will result in different spot images and intensities at different interfaces.

[0004] Existing coaxial focusing methods can only determine the focal plane position and approach it in real time, provided that the reflected light signal from the substrate surface has sufficient intensity. However, when the signal from the substrate surface is weak, or when it is interfered with by strong signals from other interfaces, these focusing methods may suffer from inaccurate focal plane determination and long focusing times. Moreover, there is currently no rapid focusing method suitable for multi-layered medium interfaces in oil immersion lenses. Summary of the Invention

[0005] One of the objectives of this invention is to provide a focal plane leveling method based on multi-point detection for controlling the high uniformity of substrate surface in the field of photolithography systems.

[0006] To address the aforementioned problems, the first aspect of this invention provides a focal plane leveling method based on multi-point detection, comprising the following steps:

[0007] The area of ​​the sample to be exposed is divided into grids using a computer.

[0008] The computer-controlled moving stage is used to position the focus of the detection beam at each grid point, and the x and y coordinates of each grid point are recorded.

[0009] For each grid point, a focused image of the detection beam focused on that grid point is acquired. The z-axis height of the moving stage is controlled by a computer. The z-axis height when the difference between the focused image of the grid point and the standard image data is within the accuracy control range is recorded as the z-axis coordinate of the grid point, and a grid point coordinate (x, y, z) database is established.

[0010] Calculate the z-axis coordinate of any point (x, y) within the area enclosed by the four adjacent grid points, based on the coordinates of each of the four adjacent grid points.

[0011] The exposure beam is moved to the exposure area using a computer-controlled moving stage, and the exposure area is then compensated for by the focal plane z-axis displacement before exposure.

[0012] Preferably, the spacing between adjacent grid points in the exposure area is 100nm-100μm.

[0013] Preferably, the image of the detection beam focused at the grid point is a spot image of the focused detection beam, an interference image formed by the superposition of the incident light and the interface reflected light, or an image of the diffracted incident light after passing through the objective lens.

[0014] Preferably, the method for calculating the z-axis coordinate of any point (x, y) within the region enclosed by the four grid points is as follows:

[0015]

[0016] Wherein, the coordinates of the four adjacent grid points are respectively (x i y j , z i,j ), (x i+1 y j , z i+1,j ), (x i y j+1 , z i,j+1 ) and (x i+1 y j+1 , z i+1,j+1 ).

[0017] Preferably, the detection beam is focused using an oil immersion objective.

[0018] A second aspect of the present invention provides a focal plane leveling system based on multi-point detection, the system comprising:

[0019] Light source, used to provide the detection beam and exposure beam;

[0020] Beam focusing unit;

[0021] An imaging detector is used to acquire a focused image of the detection beam;

[0022] 3D moving stage;

[0023] The computer control unit is used to divide the area to be exposed into grids, control the three-dimensional moving stage to move along the three dimensions, record the z-axis height of the grid point when the difference between the focused image and the standard image data is within the accuracy control range as the z-axis coordinate of the grid point, establish a grid point coordinate library, and perform focal plane z-axis displacement compensation on the exposed area.

[0024] Preferably, the laser source is a continuous laser source or a pulsed laser source, with a wavelength adjustment range of 157nm-1064nm, and the polarization state is linear polarization, circular polarization, or elliptical polarization.

[0025] Preferably, the focusing unit includes an oil immersion objective.

[0026] A third aspect of the present invention provides a photon beam maskless lithography system, the lithography system including a focal plane leveling system based on multi-point detection.

[0027] Preferably, the sample to be lithographically lithographically processed in the lithography system has a multilayer dielectric interface.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. The present invention provides a focal plane leveling method based on multi-point detection, which pre-detects the surface height of the sample to be exposed area on the moving stage and establishes a sample height database in the photolithography system, thereby achieving rapid focal plane height compensation during the sample stage movement process of photolithography exposure.

[0030] 2. The focal plane leveling method based on multi-point detection provided by this invention is particularly suitable for focal plane leveling of samples to be lithographically processed using high numerical aperture oil immersion lenses in photon beam maskless lithography systems.

[0031] 3. The focal plane leveling method based on multi-point detection provided by this invention can be applied to leveling different interfaces with multilayer dielectric films. Attached Figure Description

[0032] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0033] Figure 1 This diagram illustrates the implementation steps of a focal plane leveling method based on multi-point detection provided by the present invention.

[0034] Figure 2 The simulation diagram shows the focal plane coordinates after the 5×5 grid is divided according to the present invention.

[0035] Figure 3This is a schematic diagram of a focal plane leveling system based on multi-point detection provided by the present invention.

[0036] Figure 4 The diagram shows a batch-consistent exposure structure obtained by using a 5×5 grid to achieve focal plane leveling in the DMD surface projection lithography system provided by this invention.

[0037] Figure 5 This is a batch structure diagram of the DMD surface projection lithography system for exposure without using a focal plane leveling method, as provided in this invention.

[0038] Figure 6 The diagram shows the large-area exposure stability structure obtained by using a 100×100 grid to achieve focal plane leveling in the cross-scale lithography system provided by this invention.

[0039] Figure 7 This invention provides a batch structure exposed by a cross-scale lithography system that does not utilize focal plane leveling methods for focal plane leveling. Detailed Implementation

[0040] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0041] A preferred embodiment of the present invention provides a focal plane leveling method based on multi-point detection. This method includes: dividing the sample's exposure area into grids using a computer; using a computer-controlled moving stage to position the focus of the detection beam at each grid point, recording the x and y coordinates of each grid point; for each grid point, acquiring a focused image of the detection beam focused at that grid point, and using the computer-controlled moving stage to record the z-axis height of the grid point when the difference between the focused image and the standard image data is within a precision control range, thus establishing a grid point coordinate (x, y, z) database; calculating the z-axis coordinate of any point (x, y) within the area enclosed by four adjacent grid points based on the coordinates of every four adjacent grid points; and using the computer-controlled moving stage to move the exposure beam to the exposure area, performing focal plane z-axis displacement compensation on the exposure area before exposure. The standard image data refers to the image data acquired at the focal plane of the objective lens on the surface of the substrate to be exposed. The difference between the grid focused image and the standard image data within the accuracy control range means that the detection laser beam is moved to a position where the difference between the laser beam and the standard image data in terms of spot shape and intensity is within an acceptable range. The focal plane z-axis displacement compensation of the exposure area means that the sample area to be exposed is located at the focal plane of the exposure beam by controlling the z-axis movement of the stage, thereby achieving consistent control of the imaging or exposure focal plane height.

[0042] In this invention, the spacing between adjacent grid points in the exposure area is preferably 100nm-100μm, and the image of the detection beam focused on the grid point is the spot image of the detection beam, the interference image formed by the superposition of the incident light and the interface reflected light, or the image of the diffracted object of the incident light after passing through the objective lens.

[0043] The present invention further provides a focal plane leveling system based on multi-point detection for implementing the above method. The system includes a light source for providing a detection beam and an exposure beam; a beam focusing unit; an imaging detector for acquiring a focused image of the detection beam; a three-dimensional moving stage; and a computer control unit for dividing the area to be exposed into a grid, controlling the three-dimensional moving stage to move along three dimensions, recording the z-axis height of the grid point when the difference between the focused image of the grid point and the standard image data is within the accuracy control range as the z-axis coordinate of the grid point, establishing a grid point coordinate library, and performing focal plane z-axis displacement compensation on the exposure area.

[0044] According to a preferred embodiment of the present invention, the light source can be a single light source capable of providing both a detection beam and an exposure beam, or it can include multiple light sources providing both detection and exposure beams respectively. In a preferred embodiment, the light source is a laser light source, such as a continuous laser light source or a pulsed laser light source, with a wavelength adjustment range of 157 nm to 1064 nm, and a polarization state of linear polarization, circular polarization, or elliptical polarization. The focusing objective is a high numerical aperture oil immersion objective. The multi-point detection focal plane leveling system provided by the present invention is preferably applicable to photon beam maskless lithography techniques, such as femtosecond laser two-photon direct writing technology and digital micromirror device (DMD) surface projection exposure technology, and is also preferably applicable to samples to be lithographicated with multi-layer dielectric interfaces, for achieving precise lithography of complex structures.

[0045] Figure 1 The diagram illustrates the implementation steps of a focal plane leveling method based on multi-point detection according to the present invention. In a specific implementation example, the exposure area of ​​the sample is set using a computer, and the area to be exposed is divided into grids to obtain the x and y coordinates of each grid point. The computer controls the moving stage to position the laser focus at each grid point, and the image of the laser focused at that grid point is acquired. The computer controls the z-axis height of the moving stage until the difference between the image of that grid point and the standard image data is within the accuracy control range. The z-axis coordinate of that grid point is recorded, and a grid point coordinate (x, y, z) database is established.

[0046] Figure 2This diagram illustrates a database simulation of the focal plane coordinates obtained using a 5×5 grid. Based on the (x, y, z) coordinates of every four adjacent grid points, the z-axis coordinate of any point (x, y) within the area enclosed by the four grid points is calculated. The camera is then moved to any point within the exposure area using computer-controlled movement, and exposure is performed after focal plane z-axis displacement compensation. The specific calculation method for the z-axis coordinates of any point (x, y) within the area enclosed by the four grid points is as follows:

[0047]

[0048] The coordinates of the four adjacent grid points are (x, y, y) i y j , z i，j ), (x i+1 y j , z i+1，j ), (x i y j+1 , z i，j+1 ) and (x i+1 y j+1 , z i+1，j+1 ).

[0049] Figure 3 The diagram illustrates the focal plane leveling system based on multi-point detection of the present invention, including a laser source 1, a beam expander 2, a beam splitter 3, an objective lens 4, a three-dimensional moving stage 5, a lens 6, an imaging detector 7, and a computing control unit 8. Parallel light emitted from the laser source 1 is expanded by the beam expander 2, then passes through the beam splitter 3 and is focused onto the exposure area by the objective lens 4. The computer control unit 8 divides the exposure area into a grid and controls the three-dimensional moving stage 5 to position the laser focus at each grid point. The reflected light image from each grid point passes through the objective lens 4, the beam splitter 3, and then through the lens 6 to reach the imaging detector 7.

[0050] Preferably, the laser source 1 is a continuous laser source or a pulsed laser source; more preferably, the wavelength adjustment range is 157nm-1064nm; more preferably, the polarization state of the source is linear polarization, circular polarization or elliptical polarization; more preferably, the frequency of the pulsed laser source is 1Hz-100MHz.

[0051] Preferably, the beam expander 2 can be implemented by a lens combination, such as a combination of two convex lenses or a combination of a concave lens and a group of convex lenses; the beam expansion factor of the beam expander 2 can be in the range of 0.1-100.

[0052] Preferably, the objective lens 4 is a dry objective lens, a water immersion objective lens, or an oil immersion objective lens; more preferably, the numerical aperture is 0.01-1.8 and the magnification is 1-200.

[0053] Preferably, the three-dimensional moving stage 5 is selected from the following: a three-dimensional moving stage composed of three discrete linear motion moving stages; a three-dimensional moving stage composed of a two-dimensional parallel moving stage and a discrete moving stage; a three-dimensional parallel moving stage; wherein the moving range is preferably 1nm-10000mm, more preferably 0.1μm-1m.

[0054] Preferably, the imaging detector 7 is a charged coupled device (CCD) or a position sensor (PSD).

[0055] The present invention will be explained in detail below with specific examples, and the purpose and effects of the present invention will become more apparent.

[0056] Example 1

[0057] Figure 4 This embodiment illustrates multiple identical optical microscope images fabricated using DMD surface projection lithography within a 3mm × 2mm area on a 1.5cm × 1.4cm silicon substrate after focal plane leveling via a 5×5 grid. An 800nm ​​femtosecond laser source was used as the focal plane image detection source, with a pulse width of 100fs and a pulse repetition frequency of 82MHz. The laser beam was expanded into a 10mm diameter parallel beam by a beam expander lens group and focused onto the semiconductor silicon substrate material through an oil immersion objective with a numerical aperture of 1.45 and a magnification of 100x. The exposure range was set to 3mm × 2mm, and a 5×5 grid was created. After obtaining the coordinates of each grid point, a computer-controlled 3D stage moved to each grid point, controlling its up-and-down movement. A CCD acquired Newton's rings images generated by the interference of reflected light from the lower surface of the glass and the upper surface of the substrate. A database was established by finding the z-axis coordinates of each grid point that corresponded to the standard Newton's rings image. Then, based on the database information, the z-axis coordinates of each point within this region are calculated, and z-axis offset compensation is automatically performed as the stage moves. Subsequently, 400 structures (using ARN4340 photoresist) are fabricated within this region using the DMD surface projection exposure method, with a nanowire linewidth of 171.6 nm and a linewidth deviation within 7.5%. Figure 4 As can be seen, the consistency of the pattern is good when any area is selected for observation.

[0058] Figure 5 This diagram shows a batch structure exposed by a DMD surface projection lithography system without focal plane leveling. Multiple optical micrographs of the same structure fabricated by the DMD surface projection lithography method within a small area on a silicon substrate reveal that, upon selective observation of a small region, the gaps between the cube structures are inconsistent in size. This inconsistency is caused by uneven focal plane.

[0059] Example 2

[0060] Figure 6 This embodiment illustrates the structure prepared by a femtosecond laser direct writing and DMD surface projection co-exposure method within a 10.2cm × 10.3cm area on a 6-inch silicon substrate, after focal plane leveling using a 100 × 100 grid. An 800nm ​​femtosecond laser source is used as the focal plane image detection source, with a pulse width of 100fs and a pulse repetition frequency of 82MHz. The laser source is expanded into a parallel beam with a diameter of 10mm by a beam expander lens group, and then focused onto the semiconductor silicon substrate material through an air objective lens with a numerical aperture of 0.9 and a magnification of 100x. The exposure range is set to 110mm × 110mm, and a 100 × 100 grid is created. After obtaining the coordinates of each grid point, a computer-controlled 3D stage moves to each grid point and controls its up-and-down movement. The CCD acquires the circular spot pattern of the center point of the reflected light spot on the silicon substrate surface. A database is established by finding the z-axis coordinates of each grid point that have the same diameter and intensity as the standard spot center point image. Then, based on the database information, the z-axis coordinate of each point in the region is calculated, and z-axis offset compensation is automatically performed when the moving stage moves. Subsequently, 3600 structures are fabricated in this region using femtosecond laser direct writing and DMD surface projection exposure methods. The block structures on both sides are obtained by DMD surface projection exposure, while the line structure in the center of the block structures is obtained by femtosecond laser direct writing; both methods are exposed simultaneously. Figure 6 Figures (b), (c), (d), and (e) are all... Figure 6 (a) A 100x optical microscope image of a randomly selected sample. Figure 6 As can be seen, when the focal plane is leveled, the nanowire structure at the center of any structure is clearly visible, and the linewidth consistency is good.

[0061] Figure 7 This image shows batch structures exposed using a multi-scale lithography system without focal plane leveling. The structures are fabricated on a silicon substrate using a small-scale femtosecond laser direct writing and DMD surface projection co-exposure method. The block structures on both sides are obtained by DMD surface projection exposure, while the line structures in the center of the block structures are obtained by femtosecond laser direct writing. The two methods are used in synergistic exposure. It can be observed that the nanowire structures in the center of the structure are of uneven thickness, and some are even absent; this inconsistency is due to focal plane unevenness.

[0062] The focal plane leveling method based on multi-point detection provided by this invention pre-detects and establishes a database of sample substrate height in the photolithography system. This database is used to compensate for focal plane height changes in real time during sample stage movement, achieving focal plane consistency control. The substrate height data is obtained by dividing the substrate coordinates within the exposure range into a two-dimensional grid and obtaining the x, y, and z coordinates of each grid point. The x and y coordinates of each grid point are determined during grid division and reached by moving the stage along their x and y axes. The z-axis coordinate of each grid point is obtained by acquiring a laser focal plane image and moving the stage to a position with the same spot shape and intensity, thus establishing a database of the three-dimensional coordinates of each grid point. The slope is calculated based on the coordinates of four adjacent grid points, obtaining the z-axis data for all x and y coordinates within the exposure range. This allows for real-time compensation of focal plane height changes during photolithography exposure, achieving consistent control of the imaging or exposure focal plane height. The focal plane leveling method of this invention features a simple optical structure, convenient operation, and high efficiency, making it suitable for focal plane leveling in various photolithography systems.

[0063] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A focal plane leveling method based on multi-point detection, characterized in that, Includes the following steps: The area of ​​the sample to be exposed is divided into grids using a computer. The computer-controlled moving stage is used to position the focus of the detection beam at each grid point, and the x and y coordinates of each grid point are recorded. For each grid point, a focused image of the detection beam focused on that grid point is acquired. The z-axis height of the moving stage is controlled by a computer. The z-axis height when the difference between the focused image of the grid point and the standard image data is within the accuracy control range is recorded as the z-axis coordinate of the grid point, and a grid point coordinate (x, y, z) database is established. Calculate the z-axis coordinate of any point (x, y) within the area enclosed by the four adjacent grid points, based on the coordinates of each of the four adjacent grid points. The exposure beam is moved to the exposure area using a computer-controlled moving stage, and the exposure area is then compensated for by the focal plane z-axis displacement before exposure. The sample has a multilayered media interface; The detection beam is focused using an oil immersion objective.

2. The focal plane leveling method based on multi-point detection according to claim 1, characterized in that, The spacing between adjacent grid points in the exposure area is 100nm-100μm.

3. The focal plane leveling method based on multi-point detection according to claim 1, characterized in that, The image of the detection beam focused on the grid point is either the focused spot image of the detection beam, the interference image formed by the superposition of the incident light and the reflected light from the interface, or the image of the diffracted object of the incident light after passing through the objective lens.

4. The focal plane leveling method based on multi-point detection according to claim 1, characterized in that, The method for calculating the z-axis coordinate of any point (x, y) within the region enclosed by four grid points is as follows: Wherein, the coordinates of the four adjacent grid points are respectively (x i y j , z i,j ), (x i+1 y j , z i+1,j ), (x i y j+1 , z i,j+1 ) and (x i+1 y j+1 , z i+1,j+1 ).

5. A focal plane leveling system based on multi-point detection using the method described in any one of claims 1 to 4, characterized in that, The system includes Light source, used to provide the detection beam and exposure beam; Beam focusing unit; An imaging detector is used to acquire a focused image of the detection beam; 3D moving stage; The computer control unit is used to divide the area to be exposed into grids, control the three-dimensional moving stage to move along the three dimensions, record the z-axis height of the grid point when the difference between the focused image and the standard image data is within the accuracy control range as the z-axis coordinate of the grid point, establish a grid point coordinate library, and perform focal plane z-axis displacement compensation on the exposed area.

6. A focal plane leveling system based on multi-point detection according to claim 5, characterized in that, The light source is a continuous laser source or a pulsed laser source, with a wavelength adjustment range of 157nm-1064nm, and the polarization state is linear polarization, circular polarization, or elliptical polarization.

7. A focal plane leveling system based on multi-point detection according to claim 5, characterized in that, The focusing unit includes an oil immersion objective.

8. A photon beam maskless lithography system, characterized in that, The lithography system includes the focal plane leveling system based on multi-point detection as described in claim 5.

9. The photon beam maskless lithography system according to claim 8, characterized in that, The sample to be photolithographically lithographically processed has multiple dielectric interfaces.

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