A method for fabricating a continuous surface profile spiral phase plate using a digital mask

Abstract

This invention discloses a method for fabricating a continuous surface spiral phase plate using a digital mask. The method divides the target continuous surface into multiple sector substructures along the rotation azimuth direction. Based on the exposure dose corresponding to the sector substructures, the method involves constructing binary discrete graphics, combining digital mask sub-images, and transforming coordinates to form digital mask frame images. A computer-controlled SLM then sequentially projects multiple digital mask frame images onto the same position on a substrate according to a pre-set exposure time, thereby obtaining a continuous surface spiral phase plate on the photoresist. The method described in this invention is simple, has low manufacturing cost, high manufacturing efficiency, and strong technical versatility.

Description

Technical Field

[0001] This invention relates to the field of microfabrication technology, and in particular to a method for fabricating a continuous surface spiral phase plate using a digital mask. Background Technology

[0002] A spiral phase plate is a pure phase diffraction optical element whose optical thickness is proportional to its rotation azimuth angle. It possesses superior properties such as small size, rapid loading of vortex beams, simple operation, and no power requirements, and has been widely applied in cutting-edge research fields such as optical micromanipulation, quantum information processing, super-resolution imaging, and stimulated emission loss super-resolution microscopy in recent years. Currently, conventional processing techniques for spiral phase plates mainly include molding, laser direct writing, and electron beam lithography. Molding technology produces spiral phase plates with smooth surfaces and high quality, but the phase plates are still in the millimeter range, and the manufacturing accuracy largely depends on the accuracy of the mold. Laser direct writing technology offers high processing accuracy, but its single-point scanning mode limits processing efficiency. Electron beam lithography technology has extremely high resolution, but its complex processing steps and point-by-point processing result in long processing cycles, expensive equipment, and high processing costs. Conventional processing techniques suffer from problems such as low processing accuracy, low processing efficiency, and high processing costs. Therefore, there is an urgent need for high-precision, short-cycle, and low-cost spiral phase plate processing technology. To address the aforementioned urgent needs, this invention proposes a method for fabricating a continuous surface spiral phase plate using a digital mask. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problems existing in the prior art and to provide a method for fabricating a continuous surface spiral phase plate using a digital mask.

[0004] To achieve the above objectives, the technical solution provided by this invention is: a method for fabricating a continuous surface spiral phase plate using a digital mask, the method comprising the following steps:

[0005] (1) A continuous surface spiral phase plate can be represented as F(r,θ) in polar coordinates. If the resolution of the SLM in the digital mask fabrication system is M×N, F(r,θ) is divided into N sector substructures along the rotation azimuth direction of the spiral phase plate.

[0006] (2) Extract the cross-sectional contours of the sector-shaped substructures in sequence to form N contour lines;

[0007] (3) Combine the response curve of photoresist to exposure dose, and convert each contour line into an exposure dose line;

[0008] (4) Based on the discretized exposure dose line, construct an L-row, M-column binary discrete graph to form N binary discrete graphs;

[0009] (5) Extract the i-th row of N binary discrete graphics in sequence, i = 1, 2, 3, ..., L, and combine them to form the i-th digital mask sub-image, which can form L digital mask sub-images;

[0010] (6) Convert the digital mask sub-image described in step (5) into a digital mask frame image in polar coordinates to form L digital mask frame images;

[0011] (7) The computer controls the SLM to project L digital mask frames sequentially at the same position on the substrate according to the preset exposure time;

[0012] (8) After development, fixing and post-baking processes, a continuous spiral phase plate can be formed on the photoresist.

[0013] Preferably, the azimuth direction of rotation along the spiral phase plate in step (1) includes either a clockwise or counterclockwise azimuth direction.

[0014] Preferably, the SLM in step (1) includes spatial light modulators such as digital micromirror devices (DMD), liquid crystal (LCD), and liquid crystal on silicon (LCOS).

[0015] Preferably, in step (4), constructing an L-row M-column binary discrete graphic based on the discretized exposure dose line means discretizing the exposure dose line into M points along the r direction and into L points along the dose height E direction. Then, the L-row M-column graphic that is completely "black" is filled with "white". The filling rule is to fill each column one by one. The number of "white" micro-elements in the j-th column of the binary graphic is determined by the discrete dose height of the j-th point of the exposure dose line.

[0016] Preferably, "black" means a grayscale value of 0, and "white" means a grayscale value of 255.

[0017] Preferably, in step (5), the i-th digital mask sub-image is formed by extracting the i-th row of the first binary discrete image as the first row of the i-th digital mask sub-image, extracting the i-th row of the second binary discrete image as the second row of the i-th digital mask sub-image, and so on, extracting the i-th row of the N-th binary discrete image as the N-th row of the i-th digital mask sub-image.

[0018] Preferably, the exposure time of each digital mask frame in step (7) is determined by the discrete order L of the exposure dose line.

[0019] Preferably, the photoresist in step (8) includes positive or negative photoresist for photolithography.

[0020] Beneficial effects of this invention:

[0021] 1. This invention allows for flexible adjustment of the quantization order of the exposure dose line and the exposure time of each digital mask frame to meet the high requirements for the continuity of the spiral phase plate surface shape in practical applications.

[0022] 2. This invention completes the fabrication of a spiral phase plate by computer-controlled exposure of SLM continuous projection digital mask frames. The process is simple, requires no physical mask, has low manufacturing cost, and uses surface exposure, resulting in high manufacturing efficiency.

[0023] 3. This invention can also be further extended to the fabrication of other microstructures with rotational symmetry or local rotational symmetry, and the technology has strong versatility. Attached Figure Description

[0024] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0025] Figure 1 This is a schematic diagram of the method for fabricating a continuous surface spiral phase plate using a digital mask according to the present invention. Detailed Implementation

[0026] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0027] Digital mask lithography technology can flexibly load mask information and adopts a face-by-face lithography method, which greatly improves the operating efficiency of the lithography system and therefore has a wide range of applications in many fields.

[0028] Reference Figure 1 A preferred embodiment of the present invention provides a method for fabricating a continuous surface spiral phase plate using a digital mask, the method comprising the following steps:

[0029] (1) A continuous spiral phase plate can be represented as F(r,θ) in polar coordinates. If the resolution of the SLM in the digital mask fabrication system is M×N, F(r,θ) is divided into N sector substructures in a clockwise direction along the azimuth angle of the spiral phase plate. These are sector substructure 1, ..., sector substructure k-1, sector substructure k, sector substructure k+1, ..., sector substructure N.

[0030] (2) Extract the cross-sectional contours of the sector substructures in sequence. Specifically, extract the cross-sectional contour of sector substructure 1 to form the first contour line; ...; extract the cross-sectional contour of sector substructure k-1 to form the (k-1)th contour line; extract the cross-sectional contour of sector substructure k to form the kth contour line; extract the cross-sectional contour of sector substructure k+1 to form the k+1th contour line; ...; extract the cross-sectional contour of sector substructure N to form the Nth contour line.

[0031] (3) Combining the response curve of photoresist to exposure dose, each contour line is converted into an exposure dose line. Specifically, the first contour line is converted into the first exposure dose line; ...; the (k-1)th contour line is converted into the (k-1)th exposure dose line; the kth contour line is converted into the kth exposure dose line; the (k+1)th contour line is converted into the (k+1)th exposure dose line; ...; the Nth contour line is converted into the Nth exposure dose line.

[0032] (4) Based on the discretized exposure dose lines, construct an L-row, M-column binary discrete graphic. Specifically, the 1st, ..., k-1st, kth, k+1st, ..., Nth contour lines are discretized into M points along the r direction and into L points along the dose height E direction. Then, the L-row, M-column graphic, which is completely "black" (grayscale value set to 0), is filled with "white" (grayscale value set to 255). The filling rule is to fill each column sequentially. The number of "white" micro-elements in the j-th column of the binary graphic is determined by the discrete dose height of the j-th point of the corresponding exposure dose line. N exposure dose lines can be used to construct N binary discrete graphics.

[0033] (5) Sequentially extract the i-th row (i = 1, 2, 3, ..., L) of N binary discrete graphics simultaneously and combine them to form the i-th digital mask sub-image. Specifically, extract the i-th row of the 1st binary discrete graphic as the 1st row of the i-th digital mask sub-image; ...; extract the i-th row of the (k-1)th binary discrete graphic as the (k-1)th row of the i-th digital mask sub-image; extract the i-th row of the k-th binary discrete graphic as the k-th row of the i-th digital mask sub-image; extract the i-th row of the (k+1)th binary discrete graphic as the (k+1)th row of the i-th digital mask sub-image; ...; extract the i-th row of the Nth binary discrete graphic as the Nth row of the i-th digital mask sub-image. This process continues until L digital mask sub-images are formed.

[0034] (6) Convert the digital mask sub-image described in step (5) into a digital mask frame image in polar coordinates to form L digital mask frame images.

[0035] (7) The computer controls the SLM to project L digital mask frames sequentially at the same position on the substrate according to the preset exposure time. The exposure time of each digital mask frame is determined by the discrete order L of the exposure dose line.

[0036] (8) After development, fixing and post-baking processes, a continuous spiral phase plate can be formed on the photoresist.

[0037] This invention allows for flexible adjustment of the quantization order of the exposure dose line and the exposure time of each digital mask frame to meet the high requirements for the continuity of the spiral phase plate surface shape in practical applications. This invention completes the fabrication of the spiral phase plate through computer-controlled SLM continuous projection digital mask frame exposure. The process is simple, requires no physical mask fabrication, has low manufacturing costs, and employs surface exposure, resulting in high fabrication efficiency. This invention can also be further extended to the fabrication of other microstructures with rotational symmetry or locally rotational symmetry surface shapes, demonstrating strong technical versatility.

[0038] Without causing conflict, those skilled in the art can freely combine and use the above-mentioned additional technical features.

[0039] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by essentially the same means is within the protection scope of the present invention.

Claims

1. A method of fabricating a continuous surface profile spiral phase plate using a digital mask, the method comprising: The method includes the following steps: ​ (1) The continuous surface spiral phase plate is represented as F(r,θ) in the polar coordinate system. If the SLM resolution in the digital mask fabrication system is M×N, F(r,θ) is divided into N sector substructures along the rotation azimuth direction of the spiral phase plate, namely sector substructure 1, ..., sector substructure k-1, sector substructure k, sector substructure k+1, ..., sector substructure N; (2) Extract the cross-sectional contours of the fan-shaped substructures in sequence. Extract the cross-sectional contour of fan-shaped substructure 1 to form the first contour line; ...; Extract the cross-sectional contour of fan-shaped substructure k-1 to form the (k-1)th contour line; Extract the cross-sectional contour of fan-shaped substructure k to form the kth contour line; Extract the cross-sectional contour of fan-shaped substructure k+1 to form the k+1th contour line; ...; Extract the cross-sectional contour of fan-shaped substructure N to form N contour lines; (3) Combine the response curve of photoresist to exposure dose, and convert each contour line into an exposure dose line; (4) Based on the discretized exposure dose lines, construct an L-row M-column binary discrete graphic. Discretize the 1st, ..., k-1st, kth, k+1st, ..., Nth contour lines into M points along the r direction and into L points along the dose height E direction. Then fill the L-row M-column graphic that is completely "black" with "white". The filling rule is to fill each column one by one. The number of "white" micro-elements in the j-th column of the binary graphic is determined by the discrete dose height of the j-th point of the corresponding exposure dose line. N exposure dose lines are used to construct N binary discrete graphics. Among them, "black" means that the gray value is set to 0 and "white" means that the gray value is set to 255. (5) Simultaneously extract the i-th row of N binary discrete graphics, i = 1, 2, 3, ..., L, and combine them to form the i-th digital mask sub-image. Extract the i-th row of the 1st binary discrete graphics as the 1st row of the i-th digital mask sub-image; ...; extract the i-th row of the (k-1)th binary discrete graphics as the (k-1)th row of the i-th digital mask sub-image; extract the i-th row of the kth binary discrete graphics as the kth row of the i-th digital mask sub-image; extract the i-th row of the (k+1)th binary discrete graphics as the (k+1)th row of the i-th digital mask sub-image; ...; extract the i-th row of the Nth binary discrete graphics as the Nth row of the i-th digital mask sub-image; and so on, to form L digital mask sub-images. (6) Convert the digital mask sub-image described in step (5) into a digital mask frame image in polar coordinates to form L digital mask frame images; (7) The computer controls the SLM to project L digital mask frames sequentially at the same position on the substrate according to the preset exposure time; (8) After development, fixing and post-baking processes, a continuous spiral phase plate is finally formed on the photoresist.

2. The method of claim 1, wherein: The azimuth direction of rotation along the spiral phase plate in step (1) includes either clockwise or counterclockwise rotation along the spiral phase plate.

3. The method of claim 1, wherein: In step (7), the exposure time of each digital mask frame is determined by the discrete order L of the exposure dose line.

4. The method of claim 1, wherein: The photoresist in step (8) includes positive or negative photoresist used for photolithography.

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