CN117331285A - Method for producing patterns with any line width and any space by discrete digital mask photoetching - Google Patents
Method for producing patterns with any line width and any space by discrete digital mask photoetching Download PDFInfo
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70216—Mask projection systems
- G03F7/70283—Mask effects on the imaging process
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- G—PHYSICS
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- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70383—Direct write, i.e. pattern is written directly without the use of a mask by one or multiple beams
- G03F7/70391—Addressable array sources specially adapted to produce patterns, e.g. addressable LED arrays
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- G—PHYSICS
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- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
- G03F7/70491—Information management, e.g. software; Active and passive control, e.g. details of controlling exposure processes or exposure tool monitoring processes
- G03F7/70508—Data handling in all parts of the microlithographic apparatus, e.g. handling pattern data for addressable masks or data transfer to or from different components within the exposure apparatus
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Abstract
The invention discloses a method for producing patterns with any line width and any space by discretized digital mask lithography, which is applied to the field of maskless projection lithography and comprises the following steps: based on a linear relation curve of gray scale and normalized output intensity of the liquid crystal spatial modulator, according to line width and space requirements of a target photoetching pattern, iterative optimization is carried out based on an imaging rule to obtain a corresponding pixelated gray scale mask; the computer controls the liquid crystal space modulator to load a pixelized gray scale mask, discretizes and modulates the incident homogenized light field modulated into a horizontal polarization state by the half-wave plate, and the incident homogenized light field enters the polarization beam splitter prism to be reflected to obtain target light field distribution; and collecting and scaling the target light field distribution to the photoresist layer by the projection objective to obtain a target photoetching pattern meeting the line width and space requirements. The invention solves the problems that the photoetching line width and the line spacing caused by the quantification of discrete pixels of the spatial light modulator can only be reduced by times on the basis of the size of a single pixel, and the high-precision controllable arbitrary value line width and spacing are difficult to realize.
Description
Technical Field
The invention relates to the field of maskless projection lithography, in particular to a method for producing patterns with any line width and any space by discretized digital mask lithography.
Background
The projection lithography technology is still the mainstream lithography technology applied in the semiconductor industry so far, and as a derivative new technology thereof, the maskless digital projection lithography technology based on the spatial light modulator does not depend on an entity mask, so that the production cost of the entity mask, particularly a high-precision mask for realizing high resolution, is greatly saved; meanwhile, the digitalized photomask ensures flexible, controllable and complex mask generation according to requirements, greatly reduces mask replacement caused by different design targets and defects of the solid mask, and ensures the quality of photoetching patterns.
The photolithographic line width and the photolithographic line Zhou Ju are two important indicators that affect the performance of the semiconductor device and reflect the level of integrated circuit technology. For maskless digital projection lithography based on spatial light modulator, the relation between the cured photoresist linewidth of the exposure pattern and the single pixel size of the digital mask is w=n×d/(f) 1 /f 2 ) Wherein N is the number of pixels, d is the single pixel size, f 1 /f 2 And (5) reducing the total system multiple, wherein W is the obtained line width. In theory, any line width can be realized by controlling the exposure dose, the effect of the exposure dose on the line width is more obvious under the condition of a few-pixel exposure structure, so that the fine target line width structure can be realized by selecting a proper exposure dose, using a high-magnification objective lens and combining a nonlinear lithography technology, but the effect caused by the exposure dose presents uneven global property, and therefore, the realization of fine adjustment of the line width only for a specific structure in a micro-nano exposure pattern based on single exposure is challenging. Meanwhile, the line width, especially the line width gradual change precision of high sensitivity and high definition line width change in actual operation is difficult to grasp by controlling the exposure dose. For processing of the photoetching line position high-precision photoetching structure, the photoetching line circumference corresponds to the high linearity of the discrete pixel interval designed by the digital mask, so that a specific high-precision circumference structure is realized theoretically or an expensive high-resolution spatial light modulator is required to be replaced and is combined with an objective lens with different multiplying powers, and the photoetching line position high-precision photoetching structure can be realized by means of a tilting exposure strategy, a swinging photoetching technology, a gray scale photoetching technology and the like with technical innovation. The former is more complex and more costly than the physical high precisionThe mask design and manufacture, the latter can realize sub-pixel resolution by using oblique exposure strategy and swing lithography technology, and reduce pixel quantization error by matching with high-magnification projection objective. The gray scale lithography technology utilizes the image point discreteness of the digital mask pixels to load a two-dimensional gray scale image, so as to realize the distribution of different exposure doses of different gray scale pixels within the same time, and utilizes the property of incomplete development of photoresist under low exposure dose to generate any pattern. Compared with oblique exposure and swing lithography, the gray scale lithography technology has stronger universality and higher flexibility, and is currently used for two-dimensional graph edge optimization and accurate regulation and control of three-dimensional lithography contours.
Although gray scale lithography has great potential to overcome pixel discretization error problem and is applied to the realization of any photolithographic line space, no comprehensive and complete exploration and research for realizing any line width and line space of a digital mask exists at present. Meanwhile, the gray scale digital lithography technology is most widely selected as a Digital Micromirror Device (DMD), and the DMD has high imaging fidelity and better contrast, and is one of the main relying devices of maskless lithography based on a spatial light modulator. However, the gray scale modulation of the DMD is binary, and three gray scale modulations of the DMD, namely spatial gray scale modulation, frame gray scale modulation and pulse width gray scale modulation, are realized by controlling a single micromirror to turn over for multiple times within a period of time by writing an electric signal on the basis of single pixel 'on' and 'off' binary modulation, so that the linearity of gray scale and exposure dose is poor due to light energy loss caused by multiple rapid reflection for high-order gray scale modulation under high modulation frequency.
Therefore, how to provide a method for producing patterns with any line width and any space by using a discretized digital mask lithography which can overcome the defect that the lithography line width and the line space caused by the discrete pixel quantization of a spatial light modulator can only be reduced by multiple on the basis of the single pixel size, and is difficult to realize with high precision and controllable arbitrary value line width and space is a problem to be solved by those skilled in the art.
Disclosure of Invention
In view of this, the present invention proposes a method for producing patterns with arbitrary line width and arbitrary pitch by discretized digital mask lithography. The liquid crystal spatial modulator controlled by a computer is used for carrying out multi-level gray scale modulation on the digital mask, the light field distribution characteristics are changed, the high linearity relation between the high-order gray scale of the liquid crystal spatial modulator and the emergent light intensity ensures the control of the line width with higher precision, and the discrete pixel high-order independent gray scale loads the mask so that the asymmetric deviation of the overlapped light field of mask image points relative to the pixel distribution of the digital mask is realized, and the regulation and control of any line spacing is realized. And the gray value distribution is regulated and controlled through pixelation, so that the light field distribution corresponding to the target graph is obtained, the gap between the digital mask and the entity mask which can be designed and produced at will is reduced, and the potential of the gray-scale-based digital mask is developed.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a method for producing arbitrary linewidth and arbitrary pitch patterns by discretized digital mask lithography, comprising:
step (1): based on a linear relation curve of gray scale and normalized output intensity of the liquid crystal spatial modulator, according to line width and space requirements of a target photoetching pattern, iterative optimization is carried out based on a digital gray scale mask projection imaging rule to obtain a corresponding pixelated gray scale mask;
step (2): the computer controls the liquid crystal space modulator to load a pixelized gray scale mask, discretizes and modulates the incident homogenized light field modulated into a horizontal polarization state by the half-wave plate, and the incident homogenized light field enters the polarization beam splitter prism to be reflected to obtain target light field distribution;
step (3): and collecting and scaling the target light field distribution to the photoresist layer by the projection objective to obtain a target photoetching pattern meeting the line width and space requirements.
Optionally, in step (1), the digital gray mask projection imaging rule specifically includes:
obtaining single line width W, pixel number N and intensity gray value I through downsampling and numerical optimization i The relationship of (2) is as follows:
wherein m is the size of the mask pixel unit projected into the photoresist layer;
the line Pitch is as follows:
Pitch＝N 1 ×m±2×ΔPitch；
wherein N is 1 The number of pixels is the number of the interval pixels; Δpitch is the position offset of the gray scale mask line relative to the binary mask line; n (N) 2 A number of gray scale pixels other than 0 or 255; "+" - "is outside or inside the target pitch depending on the gray pixel distribution, respectively; i i Is the intensity grey value.
Optionally, in step (2), based on the pixelated gray mask, discretizing the incident homogenized light field modulated into the horizontal polarization state by the half-wave plate, specifically:
and carrying out discretization coding treatment on the pixelated gray scale mask, wherein each pixel independently treats the high gray scale polarization state information of the discretized incident homogenized light field.
Optionally, in step (2), the homogenized light field is incident as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j);is the horizontal polarization direction of the linearly polarized light.
Optionally, in step (2), the light field modulated by the lc spatial modulator is as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j); θ is the polarization direction angle of the linearly polarized light.
Optionally, in step (2), the light field reflected by the polarizing beam splitter prism is entered as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j); θ is the polarization direction angle of the linearly polarized light.
Optionally, in step (2), the target light field distribution is as follows:
wherein d is the single pixel size; a's' (m ， n) And assigning values for multiple gray scales.
Compared with the prior art, the invention provides a method for producing patterns with any line width and any space by discretized digital mask photoetching. The corresponding pixelated gray scale mask is obtained through iterative optimization based on the line width and the space requirement of a target photoetching pattern and based on the projection imaging rule of the digital gray scale mask, the pixelated gray scale mask is loaded through a computer control liquid crystal spatial modulator, discretized coding processing is carried out on the pixelated gray scale mask, each pixel independently processes high gray scale polarization state information of discretized incident homogenized light field, discretized modulation is carried out on the incident homogenized light field modulated into a horizontal polarization state through a half-wave plate, the light field distribution characteristic is changed, the high linearity relation between the high-order gray scale of the liquid crystal spatial modulator and the emergent light intensity ensures the control of the line width with higher precision, the discrete pixel high-order independent gray scale loading mask enables the overlapped light field of the mask image point to deviate asymmetrically relative to the pixel distribution of the digital mask, the regulation and control of any line space are realized, the problems that the line width and the line space of the photoetching pattern of the digital mask are limited by the pixel size and the system scaling ratio of the digital mask are overcome, and the potential development of the digital mask instead of the physical mask is greatly promoted.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic flow chart of the method of the present invention.
FIG. 2 is a schematic diagram of a system for improving projection lithography resolution based on phase modulation according to the present invention.
FIG. 3 is a diagram of the light field range of the discretized pixel light field of the present invention distributed within the photoresist layer and exceeding the photoresist threshold intensity.
FIG. 4 is a schematic diagram of the photolithographic line width and the photolithographic line spacing of the present invention.
Fig. 5 is a schematic diagram of the principle of implementing any line width of a specific exposure structure based on gray modulation according to the present invention.
Fig. 6 is a schematic diagram of the gray modulation-based arbitrary line spacing implementation principle of the present invention.
FIG. 7 shows two-pixel single line masks with different gray scales and corresponding two-dimensional light intensity distribution.
Fig. 8 is a schematic diagram of implementing different linewidths for different gray scales according to the present invention.
FIG. 9 is a schematic diagram of a two-pixel single line corresponding mask and two-dimensional light field distribution for loading 176, 180, 184, 186 gray scale according to the present invention.
Fig. 10 (a) is a schematic diagram showing that the two-pixel single line corresponding mask with the loading 176, 180, 184, 186 gray scale of the present invention realizes continuous line width variation under the light intensity of 0.25 threshold.
FIG. 10 (b) is an enlarged schematic view of the intersection of the intensity curves of the mask corresponding to the two-pixel single lines of the loading 176, 180, 184, 186 gray scale of the present invention and the 0.25 threshold.
FIG. 11 is a schematic diagram showing the distribution of light fields with two lines with different degrees of separation obtained by gray scale modulation according to the present invention.
Fig. 12 is a schematic diagram of two-line light field distribution obtained by gray scale modulation according to the present invention.
Fig. 13 is a schematic diagram of a mask and a two-dimensional light intensity distribution corresponding to a 3-pixel-width 3-pixel-space line array and a 4-pixel-width 4-pixel-space line array according to the present invention.
Fig. 14 is a schematic diagram of a light field distribution curve corresponding to a 3-pixel-width 3-pixel-interval line array and a 4-pixel-width 4-pixel-interval line array mask according to the present invention.
FIG. 15 is a graph showing the distribution of the light intensity in the 564nm line circumference corresponding mask and the two dimensions according to the present invention.
FIG. 16 is a diagram showing the distribution of light fields corresponding to 564nm line pitch masks according to the present invention.
The reference symbols in the drawings: 101-incident homogenized light field, 102-half wave plate, 103-liquid crystal spatial modulator, 104-polarization beam splitter prism, 105-projection objective, 106-photoresist layer, 107-photoresist threshold intensity, 108-discretized pixel image split field, 109-lithography linewidth and lithography line Zhou Ju, 201-binary amplitude modulation, 202-gray scale amplitude modulation, 203-specific photoresist exposure threshold, 301 and 304-light field distribution obtained from a plurality of pixels with normalized light intensity of 1, 302, 303-light field distribution with peak offset from mask line center, 305-pixels with normalized light intensity of 1, 306-discrete gray scale pixels.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1:
the embodiment 1 of the invention discloses a method for producing patterns with any line width and any space by discretization digital mask photoetching, which comprises the following steps of obtaining different targets with any line width under one exposure condition by exploring exposure process parameters of pixel photoetching, and obtaining a line array with any space by customizing a structural light field by using a gray mask, as shown in fig. 1:
step (1): based on the linear relation curve of gray scale and normalized output intensity of the liquid crystal spatial modulator 103, according to the line width and space requirements of a target photoetching pattern, a pixelated gray scale mask corresponding to a specific photoetching condition (comprising photoetching light source wavelength, photoresist exposure threshold, system scaling multiple, single pixel size of the spatial liquid crystal modulator and the like) is obtained based on iterative optimization of a digital gray scale mask projection imaging rule.
The liquid crystal spatial light modulator 103 is used as another important tool of maskless digital lithography, and based on the liquid crystal twisted nematic effect, 256-order intensity modulation of the emergent light is realized by changing the polarization direction of the polarized light of the emergent line, so that the method is more dominant in the aspect of obtaining a target pattern by quickly, efficiently and flexibly realizing one-time exposure.
The digital gray mask projection imaging rule specifically comprises the following steps:
obtaining single line width W, pixel number N and intensity gray value I through downsampling and numerical optimization i The relationship of (2) is as follows:
wherein m is the size of the mask pixel unit projected into the photoresist layer;
the line Pitch is as follows:
Pitch＝N 1 ×m±2×ΔPitch；
wherein N is 1 The number of pixels is the number of the interval pixels; Δpitch is the position offset of the gray scale mask line relative to the binary mask line; n (N) 2 A number of gray scale pixels other than 0 or 255; "The "+" - "is outside or inside the target pitch depending on the gray scale pixel distribution, respectively; i i For the intensity grey value, [0,255 ]]If the two-dimensional light field is distributed, the digital mask I i Writable I i,j ；
Due to the complexity of light intensity superposition, the obtained initial target digital gray mask is different from the target light field, and the minimum difference between the light field generated by designing the digital gray mask and the target light field is realized based on the digital gray mask projection imaging rule for repeated iterative optimization.
Step (2): as shown in fig. 2, the computer controls the liquid crystal spatial modulator 103 to load a pixelized gray scale mask, discretized modulation is performed on the incident homogenized light field 101 modulated into a horizontal polarization state by the half-wave plate 102, and the incident homogenized light field enters the polarization beam splitter prism 104 to be reflected to obtain target light field distribution.
Step (3): the target light field distribution is collected by the projection objective 105 and scaled to the photoresist layer 106 to obtain a target photoetching pattern meeting the line width and space requirements, and fine pattern transfer of the target line width and space is realized. As shown in fig. 3, the discretized pixel light field 108 is distributed within the photoresist layer 106, and the light field range exceeding the photoresist threshold intensity 107 determines the resulting photolithographic line width 109, and the periodic bright field interval determines the photolithographic line spacing 109, as shown in fig. 4.
The line width is always proportional to the number of pixels used in the binary digital mask under the condition of specific exposure dose. The limitation of controlling the line width through the exposure dose is that under the efficient single projection exposure condition, the change of the incident exposure dose can cause the change of the global line width of the complex exposure pattern, and the high-precision adjustment of the light field smaller than the single pixel exposure cannot be realized for the specific line width. Meanwhile, the gray level exposure improves the line width variation precision in single exposure and enriches the variation range of the line width. As shown in fig. 5, under certain exposure conditions (incident power and exposure time), characterized by a specific photoresist exposure threshold 203, the gray-scale amplitude modulation 202 achieves a change in line width from d2 to d3 without changing the exposure dose to affect other line widths d1, as opposed to the binary amplitude modulation 201 that would necessarily affect other line widths by changing the incident exposure dose.
As shown in fig. 6, unlike the 0 and 1 modulations of binary masks, gray scale masks can achieve values between normalized intensities of 0 and 1, unlike the light field distributions 301, 304 obtained from a plurality of pixels 305 having normalized intensities of 1, the overlapping of non-uniform light at discrete gray scale pixels 306 imposes light field distributions 302, 303 that have peaks that are offset from the center of the mask line. By adjusting the gray scale of the line digital mask, the lines are left or right, so that the two line circumferences (Pitch 2) are subjected to position fine change at the pixel level, and are not limited by the line Pitch (Pitch 1) of the pixel size.
Based on the pixelated gray scale mask, discretized modulation is performed on the incident homogenized light field 101 modulated into a horizontal polarization state by the half-wave plate 102, specifically:
the pure amplitude liquid crystal spatial modulator 103 loads a pixelated gray scale mask through a computer, performs discretization coding processing on the pixelated gray scale mask, and independently processes high gray scale polarization state information of the discretized incident homogenized light field 101 by each pixel, and can be regarded as directly regulating and controlling the amplitude information by combining the use of the incident horizontal linear polarization and the polarizing prism 104, namely performing m×n matrix discrete coding on the parallel incident light field.
The incident homogenized light field 101 incident on pixel point (i, j) is as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j);is the horizontal polarization direction of the linearly polarized light.
The light field of the pixel point (i, j) modulated by the pure amplitude liquid crystal spatial modulator 103 is as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j); θ is the polarization direction angle of the linearly polarized light.
The light field reflected by the entrance polarizing prism 104 is as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j); θ is the polarization direction angle of the linearly polarized light; because the incident light is normally incident to the pure amplitude liquid crystal spatial modulator, the P values of different pixels are the same, the pixels are loaded with different gray scales, and the theta values are different, so that different A 'is obtained' (i，j) 。
For an m×n pixel array, which is the target surface of pure amplitude liquid crystal spatial modulation, the target light field distribution of the obtained pixel (m, n) is as follows:
wherein d is the single pixel size; a's' (m，n) Assigning values for multiple gray scales; the pixel array profile is shown in table 1.
TABLE 1 Pixel array Profile of the target surface of pure amplitude liquid Crystal spatial modulation, i.e., m n
| 1 | 2 | … | m-1 | m | |
| 1 | A′ (1，1) | A′ (2，1) | A′ (...，1) | A′ (m-1，1) | A′ (m，1) |
| 2 | A′ (1，2) | A′ (2，2) | A′ (...，2) | A′ (m-1，2) | A′ (m，2) |
| … | A′ (1，...) | A′ (2，...) | A′ (...，...) | A′ (m-1，...) | A′ (m，...) |
| n-1 | A′ (1，n-1) | A′ (2，n-1) | A′ (...，n-1) | A′ (m-1，n-1) | A′ (m，n-1) |
| n | A′ (1，n) | A′ (2，n) | A′ (...，n) | A′ (m-1，n) | A′ (m，n) |
The line spacing obtained by digital mask projection lithography is relatively strictly adhered to the scaling relationship with the mask design line spacing, and the manufacture of any line Zhou Ju of the discrete digital mask is a key point for replacing a physical mask in the future.
In summary, according to the pattern design of the target line width and the target space (the line width and the space requirements, namely, the generation of any line width and space patterns), the layout required to be loaded by the liquid crystal spatial modulator is obtained through iterative optimization based on the digital gray mask projection imaging rule, namely, the layout comprises pixel gray information, gray pixel arrangement conditions and the like, and finally, the exposure pattern closest to the line width and the space of the target pattern can be obtained.
Example 2:
the embodiment 2 of the invention discloses a method for producing patterns with any line width and any space by discretized digital mask photoetching, which comprises the following steps:
in the embodiment 2 of the invention, the exposure light source is femtosecond laser with the wavelength of 517nm, the amplitude type liquid crystal space modulator array is 1080 multiplied by 1920, the single pixel size of the liquid crystal space modulator is 8 mu m, and a reflection light field with the range of about 8 mu m can be generated. Each pixel is controlled by an independent electrode to change the polarization of liquid crystal molecules, and the polarization beam splitter prism is matched to realize the multi-order emergence rate between the digital masks 0 and 1, A' (m，n) Positive to gray valueCorrelation, i.e. gray modulation. 256-level gray scale modulation of 0-255, transmitting light beams with corresponding emergent rate according to the loaded gray scale, projecting a discrete image light field to the photoresist through a scaling system, and realizing construction of various line widths and existence positions of structures by combining different gray scale pixels under the condition of keeping incident light parameters unchanged.
The projection zoom ratio of the projection objective system in embodiment 2 of the present invention is: 1/100×, objective na=1.45. The aim is to obtain a dense high-resolution micro-nano structure as much as possible under the condition of keeping the pixel width of the liquid crystal space modulator fixed.
The gray scale digital mask generated in the embodiment 2 of the present invention is a single line, two pixels loaded with non-0 gray scale are located in the middle, and other pixels are loaded with 0 gray scale values. The pixel array profile is shown in table 2 with the middle two columns of pixels, 960 and 961, defined as column numbers i and i+1, and the middle rows 540 and 541 defined as column numbers j and j+1.
TABLE 2 Pixel array Profile in example 2 of the present invention
In the embodiment 2 of the invention, gray values 255, 180, 80 and 20 are taken for value, and the measured mask normalized transmittance values 1, 0.8, 0.6 and 0.4 respectively correspond to each other. The theoretical exposure linewidth of the two-pixel single line mask is 160nm, different grayscales are loaded on the two-pixel single line mask, as shown in fig. 7, the light intensity and the light intensity concentration range are different, and when the exposure threshold value and the intensity ratio are 0.25, the linewidths of 224.4nm, 209.3nm, 186.6nm and 135.2nm are respectively realized by 255, 180, 80 and 20 gray scale values. Namely, under the condition that the exposure threshold and the intensity ratio are 0.25, two pixels are loaded with different gray scales under the parameters of a 100X and 1.45NA oil immersion objective photoetching system, and the line width modulation range with the variation range of 89.2nm can be realized. Meanwhile, as shown in fig. 8, the line width varies with the gray scale at different incident light doses, i.e., different exposure threshold to intensity ratios.
Example 3:
the embodiment 3 of the invention discloses a method for producing patterns with any line width and any space by discretized digital mask photoetching, which comprises the following steps:
in example 3 of the present invention, the laser light source was a 517nm femtosecond laser, the pixels of the amplitude type liquid crystal spatial light modulator were arranged to be 1080×1920, and the single pixel size was 8 μm, and a reflected light field in the range of about 8 μm could be generated.
In embodiment 3 of the present invention, the projection zoom ratio of the projection objective system is: 1/100×, objective na=1.45. The aim is to obtain a dense high-resolution micro-nano structure as much as possible under the condition of keeping the pixel width of the liquid crystal space modulator fixed.
In embodiment 3 of the present invention, the amplitude type liquid crystal spatial light modulator loads the center two-pixel single line gray scale map of embodiment 2 of the present invention, and gray scales are respectively loaded 176, 180, 184, 186, and the two-pixel single line corresponds to the mask and the two-dimensional light field distribution, as shown in fig. 9. As shown in fig. 10 (a) and 10 (b), when the exposure threshold and intensity ratio were 0.25, the photolithographic line widths were 209.1nm, 209.3nm, 209.5nm, and 209.7nm, respectively. High precision continuous linewidth variation can be achieved by gray scale modulation, which is difficult to do completely by varying the incident optical power or controlling the exposure time.
Example 4:
the embodiment 4 of the invention discloses a method for producing patterns with any line width and any space by discretized digital mask photoetching, which comprises the following steps:
in example 4 of the present invention, the laser light source was a 517nm femtosecond laser, the pixels of the amplitude type liquid crystal spatial light modulator were arranged to be 1080×1920, and the single pixel size was 8 μm, and a reflected light field in the range of about 8 μm could be generated.
In embodiment 4 of the present invention, the projection zoom ratio of the projection objective system is: 1/100×, objective na=1.45. The aim is to obtain a dense high-resolution micro-nano structure as much as possible under the condition of keeping the pixel width of the liquid crystal space modulator fixed.
In embodiment 4 of the present invention, the digital mask generated by the lc spatial modulator is a two-pixel line mask pattern with a pitch of 3 pixels, the middle two columns of pixels, i.e., columns 960 and 961, are defined as column numbers i and i+1, the middle rows 540 and 541 are defined as column numbers j and j+1, and the digital gray scale mask is distributed as shown in table 3.
TABLE 3 digital gray scale mask distribution in example 4 of the present invention
| i-3 | i-2 | i-1 | i | i+1 | i+2 | i+3 | |
| j-3 | value1 | value2 | 0 | 0 | 0 | value2 | value1 |
| j-2 | value1 | value2 | 0 | 0 | 0 | value2 | value1 |
| j-1 | value1 | value2 | 0 | 0 | 0 | value2 | value1 |
| j | value1 | value2 | 0 | 0 | 0 | value2 | value1 |
| j+1 | value1 | value2 | 0 | 0 | 0 | value2 | value1 |
| j+2 | value1 | value2 | 0 | 0 | 0 | value2 | value1 |
| j+3 | value1 | value2 | 0 | 0 | 0 | value2 | value1 |
In embodiment 4 of the invention, pixels in the middle 3 columns i-1, i and i+1 of the mask are loaded with 0 gray scale, the gray scales of the two pixel lines close to the inner columns i-2 and i+2 are the same, the gray scale is loaded with value2, and the gray scales of the outer columns i-3 and i+3 are loaded with value1. For different pixels forming the same line, the line position can shift to the position where the gray value is high, because the light field intensity of the high gray pixel is larger, and the light field superposition of the high gray pixel and the low gray pixel can lead the peak value of the total light field to deviate to the position corresponding to the high gray pixel.
In embodiment 4 of the present invention, when value1 is 255, value2 is 255, 180, 100, 60, 30, and 20 respectively, so that the two lines are separated to different extents, as shown in fig. 11, and when value2 is 255, value1 is 255, 180, 100, 60, 30, and 20 respectively, so that the two lines are close to each other to different extents, as shown in fig. 12.
In fig. 11, (1), (2), (3), (4), (5), (6) correspond to value2 values, respectively: 255. 180, 100, 60, 30, 20. The peak-to-peak distance is used to characterize the pitch, which is respectively: 385nm, 395nm, 405nm, 415nm, 425nm, 435nm. The fixed garyscale1 is unchanged, a certain gray value is taken for value2, the continuous change of the distance between two lines with the precision of 10 is realized, the 50nm change range of which the change range is 385nm to 435nm is realized, the half of single pixels with the size of more than 8 mu m are imaged at 100X, the different approaching states of the lines are realized by matching with gray modulation, and the line distance modulation of the single pixel imaging level is realized.
In fig. 12, (1), (2), (3), (4), (5) when value2 is 255, value1 corresponds to 255, 180, 60, 30, 20, respectively. The peak-to-peak distance is used to characterize the pitch, which is respectively: 385nm, 375nm, 365nm, 355nm, 345nm. The fixed garyscale2 is unchanged, a certain change gray value is taken for value1, the continuous change of the distance between two lines with the precision of 10 is realized, the 40nm change range of 385nm to 345nm can be realized, the half of the single pixel with the change range of 8 mu m in 100X imaging is equal, and the line distance modulation range of more than 80nm is realized by combining with the gray level regulation line separation state.
Example 5:
the embodiment 5 of the invention discloses a method for producing patterns with any line width and any space by discretized digital mask photoetching, which comprises the following steps:
in example 5 of the present invention, the laser light source was a 517nm femtosecond laser, the pixels of the amplitude type liquid crystal spatial light modulator were arranged to be 1080×1920, and the single pixel size was 8 μm, and a reflected light field in the range of about 8 μm could be generated.
In embodiment 5 of the present invention, the projection zoom ratio of the projection objective system is: 1/100×, objective na=1.45. The aim is to obtain a dense high-resolution micro-nano structure as much as possible under the condition of keeping the pixel width of the liquid crystal space modulator fixed.
The invention can also be implemented for any pitch of the multi-line pattern. For a plurality of line patterns with 3 pixel widths and 3 intervals, 255 gray scales are loaded on the line pixels, and 0 gray scales are loaded on the other line pixels. Similarly, a line pattern with 4 pixel width and 4 pixel interval may be loaded, where the 3 pixel width and 3 pixel interval line array corresponds to a mask and a two-dimensional light intensity distribution (1) and the 4 pixel width and 4 pixel interval line array corresponds to a mask and a two-dimensional light intensity distribution (2), as shown in fig. 13, and the theoretical pitches are 480nm and 640nm, respectively, as shown in fig. 14. The average peak distance of the simulated light field is 478nm and 645nm, which is in accordance with the theoretical distance, so that for a binary amplitude modulation line array, only line circle distances in proportional relation with pixel size and scaling multiple can be realized.
In embodiment 5 of the present invention, the gray scale digital mask is generated as a plurality of lines. By specific loading of the constituent gray levels of the multiple lines, specific spacing of the multiple lines can be achieved. The middle two columns of pixels, columns 960 and 961, are defined as column numbers i and i+1, and the middle rows 540 and 541 are defined as column numbers j and j+1, distributed as shown in table 4.
TABLE 4 digital gray scale mask distribution in example 5 of the present invention
The single line graph consists of 5 non-zero pixels, and the single pixel is independently loaded with gray scale to realize high-precision regulation and control of the line imaging position. The 564nm line circumference corresponds to the mask and the two-dimensional light intensity distribution, as shown in fig. 15, the light field distribution curve, as shown in fig. 16, represents the line interval by the peak value of the light intensity waveform distribution, and the gray scale mask realizes the 564nm line circumference, which indicates that under the condition that the single pixel size is fixed with the system scaling multiple and the bright light field of the line mask has mutual superposition influence, under the condition of designing a proper gray scale layout, any uniform line interval which is not limited by the single pixel size can be realized.
The embodiment of the invention discloses a method for producing patterns with any line width and any space by discretized digital mask photoetching. The corresponding pixelated gray scale mask is obtained through iterative optimization based on the line width and the space requirement of a target photoetching pattern and based on the projection imaging rule of the digital gray scale mask, the pixelated gray scale mask is loaded through a computer control liquid crystal spatial modulator, discretized coding processing is carried out on the pixelated gray scale mask, each pixel independently processes high gray scale polarization state information of discretized incident homogenized light field, discretized modulation is carried out on the incident homogenized light field modulated into a horizontal polarization state through a half-wave plate, the light field distribution characteristic is changed, the high linearity relation between the high-order gray scale of the liquid crystal spatial modulator and the emergent light intensity ensures the control of the line width with higher precision, the discrete pixel high-order independent gray scale loading mask enables the overlapped light field of the mask image point to deviate asymmetrically relative to the pixel distribution of the digital mask, the regulation and control of any line space are realized, the problems that the line width and the line space of the photoetching pattern of the digital mask are limited by the pixel size and the system scaling ratio of the digital mask are overcome, and the potential development of the digital mask instead of the physical mask is greatly promoted.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (7)
1. A method for producing patterns with any line width and any space by discretized digital mask lithography, comprising:
step (1): based on a linear relation curve of gray scale and normalized output intensity of the liquid crystal spatial modulator, according to line width and space requirements of a target photoetching pattern, iterative optimization is carried out based on a digital gray scale mask projection imaging rule to obtain a corresponding pixelated gray scale mask;
step (2): the liquid crystal spatial modulator is controlled by a computer to load the pixelated gray scale mask, discretized modulation is carried out on an incident homogenized light field modulated into a horizontal polarization state through a half-wave plate, and the incident homogenized light field enters a polarization beam splitter prism to be reflected so as to obtain target light field distribution;
step (3): and collecting and scaling the target light field distribution to a photoresist layer by a projection objective to obtain a target photoetching pattern meeting the line width and space requirements.
2. The method for producing patterns with any line width and any pitch by using discretized digital mask lithography according to claim 1, wherein in the step (1), the digital gray scale mask projection imaging rule is specifically:
obtaining single line width W, pixel number N and intensity gray value I through downsampling and numerical optimization i The relationship of (2) is as follows:
wherein m is the size of the mask pixel unit projected into the photoresist layer;
the line Pitch is as follows:
Pitch＝N 1 ×m±2×ΔPitch；
wherein N is 1 The number of pixels is the number of the interval pixels; Δpitch is the position offset of the gray scale mask line relative to the binary mask line; n (N) 2 A number of gray scale pixels other than 0 or 255; "+" - "is outside or inside the target pitch depending on the gray pixel distribution, respectively; i i Is the intensity grey value.
3. The method for producing patterns with arbitrary line width and arbitrary pitch by using discretized digital mask lithography according to claim 1, wherein in the step (2), based on the pixelated gray scale mask, discretized modulation is performed on an incident homogenized light field modulated into a horizontal polarization state by a half-wave plate, specifically:
and performing discretization coding processing on the pixelated gray scale mask, wherein each pixel independently processes the high gray scale polarization state information of the discretized incident homogenized light field.
4. The method of producing arbitrary line width and arbitrary pitch patterns by discretized digital mask lithography according to claim 1, wherein in step (2), the incident homogenized light field is as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j);is the horizontal polarization direction of the linearly polarized light.
5. The method of producing arbitrary line width and arbitrary pitch patterns by discretized digital mask lithography according to claim 1, wherein in step (2), the optical field modulated by the liquid crystal spatial modulator is as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j); θ is the polarization direction angle of the linearly polarized light.
6. The method of producing arbitrary line width and arbitrary pitch patterns by discretized digital mask lithography according to claim 1, wherein in step (2), the light field reflected by the polarization splitting prism is entered as follows:
wherein A is (i，j) Light field amplitude for pixel point (i, j); p (P) (i，j) Light field phase for pixel point (i, j); θ is the polarization direction angle of the linearly polarized light.
7. The method of producing arbitrary line width and arbitrary pitch patterns by discretized digital mask lithography according to claim 1, wherein in step (2), the target light field distribution is as follows:
wherein d is the single pixel size; a's' (m ， n) And assigning values for multiple gray scales.
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