A maskless photolithography optical system based on periodically stacked rectangular superlenses and phase-shifting DMD

Abstract

This invention discloses a maskless lithography optical system based on periodically stacked rectangular superlenses and a phase-shifting DMD, comprising the following steps: a laser emits a laser beam, which is focused using an ultraviolet objective. Then, a pinhole filter is used to eliminate high-frequency noise generated when the beam passes through the objective and other optical components. A collimating lens is used to convert the spherical wave into a plane wave, making the light parallel. The parallel light is combined with the phase-shifting DMD to generate a specific spatial intensity distribution for the shaping process. The laser reflected from the phase-shifting DMD is imaged onto the target using a 4f imaging system and the periodically stacked rectangular superlenses. A single exposure is divided into multiple shorter exposures to increase the number of measurements. Between each exposure, a digital holographic feedback system uses a hologram captured by a camera to measure the optical phase map of the sample at each step and calculates the phase difference between each point and the target. The input image for grayscale lithography is then adjusted based on the phase difference, and the required correction is applied by changing the pattern projected onto the phase-shifting DMD to achieve near real-time lithography. The advantages are that this invention is a new method for shrinking imaging lithography based on periodically stacked rectangular superlenses and phase-shifting DMDs. Within the error range, the imaging size can break through the diffraction limit to reach one-sixth of the wavelength, ensuring that the input and output surfaces of the light are parallel planes, optimizing the edges of the lithographic pattern, and eliminating the need for pre-calibration of the photoresist. It also provides high stability under external vibration conditions.

Description

Technical Field

[0001] This invention relates to the field of photolithography technology, and in particular to a maskless photolithography optical system and its working method. Background Technology

[0002] The high operating costs and lack of flexibility of traditional mask lithography have spurred the development of non-traditional manufacturing methods. Maskless lithography, a potential solution to overcome the high costs caused by rising mask prices, offers advantages such as low cost, high flexibility, and short production cycles, attracting significant attention. Maskless lithography based on digital micromirror devices (DMDs) has shown potential for fabricating large-scale microstructures with high throughput due to its rapid, flexible, and efficient dynamic pattern generation capabilities for spatial light modulation. However, traditional DMD-based maskless lithography can only meet the lithography needs of industries with relatively low precision requirements, and its low efficiency makes it unsuitable for applications requiring high pattern transfer accuracy and high production efficiency. Summary of the Invention

[0003] The purpose of this invention is to solve the problems in the prior art. It proposes a new photolithography method based on periodically stacked rectangular superlenses, and realizes that the input and output surfaces of the superlenses are parallel planes. It also uses phase-shifting DMD to optimize the edges of the photolithographic pattern to achieve a micro-patterning effect, which meets the requirements for high pattern transfer accuracy. Furthermore, it is equipped with a more compact and stable digital holographic feedback system based on a Sagnac interferometer, which greatly reduces the error in the photolithography process and improves production efficiency.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a maskless photolithography optical system based on periodically stacked rectangular superlenses and phase-shifting DMDs, comprising periodically stacked rectangular superlenses and phase-shifting DMD imaging modules, a computer system, and a holographic digital feedback system based on a Sagnac interferometer, comprising the following steps:

[0005] Step 1: To emit a laser beam, first focus the light using an ultraviolet objective. Then, use a pinhole filter to eliminate high-frequency noise generated when the beam passes through the objective and other optical components, and use a collimating lens to convert the spherical wave into a plane wave, making the light parallel.

[0006] Step 2: Combine parallel light with phase-shifted DMD to generate a specific spatial intensity distribution for the shaping process;

[0007] Step 3: The laser reflected by the phase-shifted DMD is imaged onto the target by a 4f imaging system and periodically stacked rectangular superlenses;

[0008] Step 4: Divide a single exposure into multiple shorter exposures to increase the number of measurements. Between each exposure, the accompanying digital holographic feedback system uses the hologram captured by the camera to measure the optical phase map of the sample at each step, and calculates the difference in phase between each point and the target. The required correction is then applied by changing the pattern projected on the phase-shifting DMD.

[0009] Compared with the prior art, the advantages of the present invention are as follows:

[0010] 1) By controlling the projected image, we can control the total light dose projected onto a point, thereby controlling the phase delay at that point. This allows us to accurately create any desired phase plate without prior calibration of the photoresist;

[0011] 2) The compact cyclic Sagnac interferometer and residual decollimated beams are used for illumination. The two counter-propagating beams in the interferometer travel through almost similar optical paths, thus providing high stability even under external vibration conditions.

[0012] 3) A new method of shrinking imaging lithography based on periodically stacked rectangular superlenses is used to ensure that the input and output surfaces of the superlenses are parallel planes and to break the diffraction limit.

[0013] 4) The image edge is optimized by introducing optical phase shift at the pattern edge through phase-shifting DMD. Attached Figure Description

[0014] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0015] Figure 1 This is a schematic diagram of the photolithography system structure of the present invention;

[0016] Figure 2 This is a schematic diagram of the periodically stacked rectangular superlens of the present invention;

[0017] Figure 3 This is an iterative flowchart for determining the phase in this invention;

[0018] Figure 4 This is a schematic diagram of the phase-shifting DMD of the present invention;

[0019] In the diagram, 1-365nm laser, 2-shutter, 3-attenuator, 4-ultraviolet objective, 5-pinhole filter, 6-collimating lens, 7-aperture stop, 8-mirror, 9-phase-shifting DMD, 10-tube lens, 11-spatial filter, 12-lens, 13-periodicly stacked rectangular superlens, 14-mirror, 15-target sample, 16-600nm laser, 17-spatial filter, 18-lens, 19-half-wave plate, 20-beam splitter, 21-mirror, 22-lens, 23-lens, 24-electronic coupling component CCD, 25-beam splitter. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments listed below are not intended to limit the scope of the present invention.

[0021] Step 1: First, focus the laser emitted by laser 1 with a center wavelength of 365nm using ultraviolet objective lens 4 (UOBJ, 10×, NA0.25);

[0022] Step 2: Use pinhole filter 5 (pinhole filter size is 5μm) to eliminate high-frequency noise generated when the light beam passes through the objective lens and other optical components;

[0023] Step 3: Use collimating lens 7 to convert the spherical wave into a plane wave, making the light parallel;

[0024] Step 4: Project parallel light onto the phase-shifted DMD9;

[0025] Here, the phase-shifting DMD9 chip consists of a 1024*1024 micromirror array, each mirror measuring 13.68μm*13.68μm. Different types of micromirrors are distributed around each micromirror, some coated and some uncoated. The coating or uncoated nature of the micromirrors introduces light, creating a 180° phase difference. All micromirrors are individually controlled by a controller. Figure 4 As shown. During projection, the image is roughly projected using the same type of micromirrors. Another type of micromirror is added around the outer edge of the image to introduce light rays with a phase difference of 180° at the image edge, thereby clarifying the edge of the pattern.

[0026] Step 5: The projected laser image is first reduced by passing through lens 10 and 200x objective lens 12 (CF Plan Apo 200, Nikon; NA=0.9);

[0027] Here, the phase-shifting DMD9, the barrel lens 10, the 200x objective lens 12, and the target sample 15 constitute a classic 4f imaging system, wherein the focal length of the barrel lens 10 is 190mm, the focal length of the 200x objective lens 12 is 1mm, and the projection laser is first reduced to 1 / 190.

[0028] Step 6: The laser emitted from the 200x objective lens 12 further reduces the image by passing through the periodically stacked rectangular superlenses 13, and exposes the photoresist on the target surface to perform photolithography;

[0029] Here, the periodically stacked rectangular superlens structure is a multi-layer rectangular superlens unit. Each rectangular superlens unit consists of two consecutive double layers of Ag and Al₂O₃, with dielectric constants of 3.217 and -2.4012 +0.24i for Ag and Al₂O₃, and fill ratios C₁ and C₂ of 0.57 and 0.43, respectively. The first layer has a left-side double-layer height T₁ of 150 nm and a right-side double-layer height Tr of 30 nm. The second layer also has a left-side double-layer height T₁ of 30 nm and a right-side double-layer height Tr of 150 nm. The periodically stacked rectangular superlens used comprises a total of 10 consecutive double layers. When a parallel-plane laser passes through the periodically stacked rectangular superlens, the wave propagates almost perpendicular to the layers. The curvature of the first consecutive double layer is greater to the right, and the curvature of the second consecutive double layer is greater to the left. Figure 2 As shown by the black arrow in the image, the convergence region of the wave at the output port is smaller than that at the initial beam region of the input port, thus achieving image reduction.

[0030] Step 7: Use a laser with a center wavelength of 600nm to perform holographic imaging of the target surface through a cyclic Sagnac interferometer;

[0031] Step 8: Use the hologram captured by the charge-coupled device CCD24 to measure the optical phase map of the sample at each step;

[0032] Step 9: Fourier filtering is applied to the hologram to find the quantitative phase, and then the least squares phase estimation method is used to find the total final phase;

[0033] Step 10: Divide a single exposure into multiple shorter exposures to increase the number of measurements. Between each exposure, measure the current phase of the sample and calculate the difference between each point and the target phase.

[0034] Step 11: Adjust the input image of grayscale lithography according to the phase difference, and apply the required correction by changing the pattern projected on the charge-coupled device CCD24.

[0035] Here, since the phase delay is not proportional to the dose, and there is a threshold for the phase delay to begin, the desired phase plate is placed on the background value. For the open-circuit condition of the feedback loop, the average difference between the current phase and the target phase is calculated. If the average value is below a certain threshold, the loop will terminate, such as... Figure 3 As shown.

[0036] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention, and these modifications are all within the protection scope of the present invention.

Claims

1. A maskless photolithography optical system based on periodically stacked rectangular superlenses and a phase-shifting DMD, characterized in that, It includes a periodically stacked rectangular superlens-phase-shifting DMD imaging module, a computer system, and a holographic digital feedback system based on a Sagnac interferometer; The periodically stacked rectangular superlens-phase-shifting DMD imaging module uses a phase-shifting DMD to complete image projection and introduces the phase difference of light rays Π. The 4f imaging system and the periodically stacked rectangular superlens reduce the reflected light rays of the phase-shifting DMD to break the diffraction limit and achieve the target photolithography process. The holographic digital feedback system is used to acquire holograms of the target sample; The computer system is connected to the periodically stacked rectangular superlens-phase-shifting DMD imaging module and the holographic digital feedback system, respectively, and is used to perform digital reconstruction of the hologram and control the operation of the imaging module. The phase-shifting DMD chip in the periodically stacked rectangular superlens-phase-shifting DMD imaging module has a square structure. Different types of micromirrors are distributed around each micromirror. The micromirrors are divided into two types: coated and uncoated. Each micromirror can be independently controlled by a controller. The periodically stacked rectangular superlens is a multi-layer rectangular superlens unit periodically stacked structure. The rectangular superlens unit adopts a continuous double-layer structure composed of two layers of metal and dielectric. The thickness of the left and right sides of each continuous double-layer structure is less than one-quarter of the working wavelength, and the thickness dimensions of the left and right sides of the double-layer structure are different from each other. This optical system integrates maskless lithography and digital holography, enabling near real-time, in-situ, non-destructive measurement of sample quantitative phase and establishing a feedback mechanism through digital holography. The system breaks down a single complete exposure into multiple short exposures, effectively increasing the measurement frequency. After each near-ultraviolet exposure, the holographic digital feedback system acquires and measures the phase retardation map of the photosensitive polymer. The computer system accurately calculates the difference between the actual phase and the target phase at each point, adjusts the grayscale lithography input image in real time based on the phase deviation, and achieves precise compensation for lithography phase deviation by correcting the projection pattern of the phase-shifted DMD.

2. The maskless photolithography optical system based on periodically stacked rectangular superlenses and phase-shifting DMD according to claim 1, characterized in that, The periodically stacked rectangular superlens-phase-shifting DMD imaging module includes a laser (1), a shutter (2), an attenuator (3), an ultraviolet objective (4), a pinhole filter (5), a collimating lens (6), an aperture stop (7), a mirror (8), a phase-shifting DMD (9), a barrel lens (10), a spatial filter (11), an objective (12), a periodically stacked rectangular superlens (13), a mirror (14), and a target sample (15).

3. The maskless photolithography optical system based on periodically stacked rectangular superlenses and phase-shifting DMD according to claim 1, characterized in that, The holographic digital feedback system includes a reflector (14), a target sample (15), a laser (16), a spatial filter (17), a lens (18), a half-wave plate (19), a beam splitter (20), a reflector (21), a reflector (22), a reflector (23), a CCD (24), and a beam splitter (25).

4. The maskless photolithography optical system based on periodically stacked rectangular superlenses and phase-shifting DMD according to claim 1, characterized in that, The holographic digital feedback system has a built-in cyclic Sagnac interferometer component, which consists of a reflector (21), a reflector (22), and a beam splitter (25).

5. The maskless photolithography optical system based on periodically stacked rectangular superlenses and phase-shifting DMD according to claim 1, characterized in that: By combining maskless lithography with digital holography, digital holography can be used to measure the quantitative phase of the sample in near real-time and in situ non-destructive measurement. The single exposure is divided into multiple shorter exposures to increase the number of measurements. After each near-ultraviolet exposure, the phase delay map of the exposed photosensitive polymer is measured by the digital holographic part of the system, and the difference between each point and the target phase is calculated accordingly. Then, the input image of grayscale lithography is adjusted according to the phase difference. Any deviation from the target phase can be corrected by changing the pattern projected on the phase-shifting DMD (9).

Images