CN113835294A - Method and apparatus for forming three-dimensional microstructures - Google Patents
Method and apparatus for forming three-dimensional microstructures 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
- G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
- G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
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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
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- G03F7/70—Microphotolithographic exposure; Apparatus therefor
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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
- G03F7/70216—Mask projection systems
- G03F7/70358—Scanning exposure, i.e. relative movement of patterned beam and workpiece during imaging
Abstract
The present invention provides methods and apparatus for forming three-dimensional microstructures, such as light guide plates or integrated circuits. The invention allows relative movement between a mask array having one or more special-profile masks and a substrate covered by a photoresist layer, and allows each light projected through the mask array to be individually and dynamically adjusted, thereby exposing the photoresist layer into a patterned photoresist layer having different portions corresponding to different three-dimensional microstructures. In particular, the relative motion direction between the mask array and the substrate is mutually crossed with the column direction and the row direction of the mask array. By adjusting the relative movement direction, it is able to at least adjust how the photoresist layer is patterned and the profile and distribution of each three-dimensional microstructure correspondingly formed on the substrate.
Description
Technical Field
The present invention claims priority from U.S. provisional application No. 63/042,608, filed on 23/6/2020, the entire contents of which are hereby incorporated by reference.
The present invention relates to a method and apparatus for forming three-dimensional microstructures, and more particularly, to a method and apparatus for forming three-dimensional microstructures by using a mask array (mask array) to scan a substrate covered by a photoresist and elastically transferring the mask array pattern to the photoresist.
Background
In modern electronic products and modern electronic product manufacturing processes, three-dimensional microstructures (three-dimensional microstructures) are also increasing in importance. For example, in a flat panel display, it is often necessary to form a plurality of three-dimensional microstructures on a light guide plate (light guide plate), and the uniformity and light extraction efficiency of the entire light guide plate are changed by changing the propagation direction and the propagation intensity of light passing through any one of the three-dimensional microstructures. For example, in integrated circuits, with the increasing popularity of non-planar devices such as Fin-shaped transistors (finfets), it is often unavoidable to use three-dimensional microstructures in semiconductor manufacturing processes to form non-planar transistors or the like or even to directly form three-dimensional microstructures as part of non-planar devices. Accordingly, there is a strong need for developing new methods and apparatus to form the desired three-dimensional microstructures.
Disclosure of Invention
The invention provides a method for processing a three-dimensional microstructure by using a light spot array oblique scanning technology of a high-precision photomask-free exposure machine and matching a polygonal micro photomask array through dragging motion of the photomask array. The new exposure processing principle is that the ultraviolet light spot array is obliquely scanned, a Digital Micromirror Device (DMD) and an ultraviolet light source module are used for regulating and controlling Digital images, a micro lens array is used, and an arbitrary polygonal photomask array is matched to be used as a spatial filter and ultraviolet light beam shaping (UV beam shaping), so that a three-dimensional microstructure (3D micro-structure) with the highest precision and the minimum line width can be obtained; the most important invention of this patent is to adopt a processing method of ultraviolet light beam shaping (UV beam shaping), cooperate with the above-mentioned ultraviolet light mask array to scan obliquely, this micro-structure processing method is applied to the die making of the Display backlight module, have advantages such as high productivity, large area, design elasticity, etc., can be used for replacing the cutter that the tradition uses the mechanical ultra-precision processing machine to meet is apt to damage, the die makes the cycle overlength, design process end integrate difficult scheduling problem, apply to the industry of Liquid Crystal Display backlight module (Liquid Crystal Display, LCD backlight module).
Some embodiments of the invention use a plurality of digital micro-reflectors and an arbitrary polygonal mask array to perform beam shaping, not only directly exposing the photoresist, but also adjusting the exposure dose and the exposure position. Based on the characteristic that the exposure dose can be adjusted and controlled at will, the embodiments can flexibly adjust the exposure result of the photoresist, thereby forming the required three-dimensional microstructure on the substrate covered by the photoresist. Depending on the actual requirements, such as three-dimensional microstructures with different sizes to be exposed, one digital micro-mirror can be corresponding to one polygonal photomask array, or any number of digital micro-mirrors can be corresponding to one polygonal photomask array, so that the optimal combination of the digital micro-mirror and the polygonal photomask can be selected according to the size and the shape of the three-dimensional microstructures to be formed.
Some embodiments of the invention use the digital micro-reflector array as the basis, and match the polygonal photomask array, and achieve the processing goal of the three-dimensional microstructure by the oblique scanning motion of the photomask array. In the embodiments, a Digital Micromirror Device (DMD) and a light source module are used for regulation and control, and a light beam shaping (light beam shaping) is realized by matching any polygonal photomask arranged in an array, so that a three-dimensional microstructure with high precision and small line width is obtained on a substrate covered by a photoresist. Implementation of these embodiments is not technically difficult, since micromirror devices and microlenses, etc., are already commercially available products, such as those disclosed by Texas instruments web pages https:// www.mouser.com/new/texas-instruments/ti-dlp470 tp-dmd.
In the present invention, the main feature of the mask array is a mask having a special profile, where the special profile may be a profile equal to the profile of the three-dimensional microstructure to be formed, or a profile similar to the profile of the three-dimensional microstructure calculated based on the properties of the photoresist, etc. In the present invention, the relative motion path between the mask array and the substrate covered by the photoresist, that is, the scan line, is intersected with the arrangement direction of the masks on the mask array, that is, when the masks are respectively arranged along the row direction and the column direction to form a two-dimensional array, or the scan line is simultaneously intersected with the row direction and the column direction, or the mask array rotates by an angle relative to the scan line, that is, the mask array and the substrate are obliquely scanned. The digital micro-mirror array (or light spot array) formed by combining the digital micro-mirror device and the light source module is mainly characterized in that different parts of the digital micro-mirror array (or light spot array) can be opened or closed or adjusted respectively, so that light projected to a photoresist on a substrate can come from different parts of the photoresist at different times, and even the light intensity and/or direction from different parts at different times can be different.
In the invention, the projection position and the projection profile of each photomask in the photomask array on the photoresist can be adjusted by changing the included angle between the scanning line and the row direction and the column direction of the photomask array, or by adjusting the rotation angle of the photomask array relative to the scanning line. In the invention, during the relative movement of the mask array and the substrate covered by the photoresist, the light projected through the mask array at different times to reach different parts of the photoresist layer can be either the same light or different lights. Therefore, the invention can flexibly adjust the profile of the exposed photoresist, thereby adjusting the three-dimensional microstructure formed on the substrate covered by the exposed photoresist in the subsequent process.
It must be emphasized that the invention does not need to be limited to specific details. For example, ultraviolet light may be used, but other wavelengths of light may be used, a Digital Micromirror Device (DMD) may be used in combination with the mask array, but other hardware may be used in combination with the mask array to transfer different mask patterns to the photoresist layer at different times. For example, each mask of the mask array typically has the same profile (size/shape) and the same alignment direction, but may be varied if desired. For example, the angle of the oblique scan, or the angle between the mask array and the scan line, usually depends on how many masks are on the mask array along the scan line direction when the angle between the mask array and the scan line is zero, that is, the number of masks on the mask array or the number of mask projections in the direction perpendicular to the scan line during the oblique scan, but may also depend on other factors, such as the distribution density, shape, planar size, and three-dimensional depth of each three-dimensional structure to be formed on the substrate.
Briefly, the present invention provides a method and apparatus for forming a three-dimensional microstructure. The method firstly makes the light shield array and the substrate covered by the light resistance layer scan obliquely, that is, makes the scanning lines between the light shield array and the light shield array cross each other in the arrangement direction, and secondly elastically projects light rays according to needs during the oblique scanning process to reach the light resistance layer on the substrate to form the patterned light resistance layer corresponding to the needed three-dimensional microstructure, so that the subsequent process can use the patterned light resistance layer to form the needed three-dimensional microstructure on the substrate. The device at least has a light spot array (such as digital micro-reflector array) capable of elastically providing light, a mask array with a special outline mask, and a driving assembly capable of driving the mask array and a substrate covered by the photoresist layer to perform oblique scanning, so as to expose the photoresist layer into a patterned photoresist layer corresponding to a required three-dimensional microstructure under the control of a computer or a microprocessor.
Drawings
FIG. 1 is a schematic diagram of a conventional photoresist patterning process.
Fig. 2 shows in summary a slant scan used by the present invention.
Fig. 3 is a method of forming a three-dimensional microstructure according to the present invention.
Fig. 4 is an apparatus for forming a three-dimensional microstructure according to the present invention.
FIG. 5 shows how a single mask of different shapes may be patterned on a photoresist layer after relative motion and exposure.
Fig. 6 shows some embodiments of the apparatus for forming a three-dimensional microstructure according to the present invention.
Fig. 7A to 7H show an exposure embodiment of the digital micromirror device according to the present invention.
FIGS. 8A-8B are graphs showing the exponential profile of a conventional photoresist material and the relationship between the exposure dose and the depth of the structure corrected by the present invention, respectively.
Fig. 9 qualitatively illustrates the basic mathematical properties of some equations used to calculate the actual profile of exposure dose versus development depth for a photoresist.
Fig. 10 is a Surface Fitting (Surface Fitting) and the optical power distribution per unit area is calculated assuming the energy distribution.
Fig. 11A shows a graph of structure depth versus exposure dose for a single-sided slope structure and a designed d-scale mask pattern calculated according to the above.
FIGS. 11B-11C show cross-sections of two target structures and the reticle patterns of the designs calculated as described above, respectively.
Fig. 12 shows the target of three-dimensional microstructure processing, and the corresponding three-dimensional exposure dose distribution and the developed three-dimensional structure depth are calculated.
Detailed Description
The present invention improves the existing photoresist patterning process. As shown in the abstract of FIG. 1, the substrate 110 is covered by the photoresist layer 120, the mask 130 and the light source 140 are sequentially arranged and separated from each other along the Z-axis, and also separated from the photoresist layer 110. The substrate 110 and the photoresist layer 120 can move along the X-axis and the mask 130 (or even the light source 140) can move along the Y-axis. By controlling the respective movements, the photoresist layer 120 can be converted into a patterned photoresist layer having a specific pattern 150, so that the specific pattern 150 can be transferred to the substrate 110 in a subsequent etching process to form a desired three-dimensional microstructure.
The present invention has at least the following improvements over the existing photoresist patterning process. First, oblique scanning is used, that is, when a plurality of masks are arranged into a two-dimensional mask array, the mask array is rotated at an angle relative to a scanning line between the mask array and a substrate, or the scanning line intersects with both the row direction and the column direction of the two-dimensional mask array when the mask array is located on a two-dimensional plane. By adjusting the angle between the two masks, the profile (size, dimension and direction) of each mask projection and the distribution (density and position) of all the mask projections along the direction perpendicular to the scan line can be adjusted, so as to change the special pattern of the patterned photoresist layer and adjust the three-dimensional microstructure formed on the substrate 110. Second, the light projected onto the photoresist layer can be dynamically and flexibly adjusted to project or not project light onto different portions of the mask array at different times during the relative motion between the mask array and the substrate to transfer different mask patterns, or even project light with different intensities onto the same or different portions of the mask array at different times to fully or partially transfer the same or different portions of the mask array, so as to form a desired specific pattern on different portions of the photoresist layer 120, or even to form different desired specific patterns respectively.
The oblique scanning used in the present invention can be summarized as shown in fig. 2, in which a plurality of masks having the same profile are arranged into a mask array 201 having M rows and N columns, each mask itself corresponds to M and N light spots in the row direction and the column direction, the scanning direction 202 between the substrate (not shown) and the mask array 201 intersects with the column direction of the mask array 201 at an angle θ, the light direction of the light from the light source (not shown) also intersects with the scanning direction, so that each mask has a mask projection 203 in the scanning direction, and the distance between the adjacent mask projections 203 in the scanning direction 202 is smaller than the distance between the adjacent masks in the row direction or the column direction of the mask array 201. As shown in FIG. 2, the distance between adjacent mask projections 202 is different from the distance between adjacent masks depending on the angle between the scanning direction and the row direction (or column direction) of the two-dimensional array.
Briefly, the present invention provides a method of forming a three-dimensional microstructure, as shown in FIG. 3. First, as shown in block 301, a mask array and a substrate covered by a photoresist layer are moved relative to each other along a scan line, where the mask array has at least one mask with a special profile arranged as an array, and the scan line intersects with the arrangement direction of the mask array. Next, as shown in block 302, during the relative motion between the mask array and the substrate, the light is projected through the mask array to the photoresist layer, thereby forming a patterned photoresist layer having a profile corresponding to the three-dimensional microstructure to be formed. Of course, although not shown in fig. 3, the method may also perform an etching process after the relative motion is completed and the patterned photoresist layer is formed, so as to form a three-dimensional microstructure on the substrate.
Briefly, the present invention provides an apparatus for forming three-dimensional microstructures, as shown in FIG. 4, having a mask array 401, a light spot array (such as a digital micromirror array) 402, and a driving assembly 403. Here, mask array 401 is configured to have at least one mask with a special profile arranged as an array, light spot array 402 is configured to have at least one light spot (such as a digital micromirror array consisting of at least one digital micromirror which is individually operable and arranged as an array) which is individually operable and arranged as an array, and drive assembly 403 is configured to move mask array 401 and substrate 4042 covered by photoresist layer 4041 relative to each other along scan line 405. Here, scan lines 405 are crossed with the direction of alignment of mask array 401, and light spot array 402 (such as a digital micromirror array) provides light during the relative motion between mask array 401 and substrate 4042, thereby forming a patterned photoresist layer having a profile corresponding to the three-dimensional microstructure to be formed. Although not shown in FIG. 4, the apparatus may further comprise an etching assembly configured to perform an etching process to form a three-dimensional microstructure on the substrate 4042 after the relative motion is completed and the photoresist layer is patterned.
It must be emphasized that the present invention does not require much limiting hardware detail and flow detail. For example, as long as the oblique scanning can be achieved, it is sufficient to rotate the mask array and adjust the rotation angle, after all, the key point is to rotate the mask array to an angle relative to the scanning line so as to correspondingly adjust how the photoresist layer is patterned. For example, it is only necessary to move the mask array, the substrate, or both the mask array and the substrate at the same time, and it is sufficient if the mask array and the substrate perform relative motion along the scan line (or the relative motion direction) at a constant speed. For example, it is feasible how the light spot array (such as the digital micromirror array), the mask array and the substrate are moved relative to each other as long as the light spot array can transmit light to the photoresist layer through the mask array to form a desired specific pattern. For example, ultraviolet light, deep ultraviolet light, yellow light, or light having other wavelengths may be used depending on the profile of the particular pattern to be formed (or depending on the three-dimensional microstructure to be formed). For example, in order to dynamically transfer the pattern of different portions of the mask array to different portions of the photoresist layer, different digital micromirrors (i.e., different light spots) can be individually turned on or off, and the intensity of the generated light can be individually adjusted, and the light from a first light spot group (such as a first digital micromirror group) and a second light spot group (such as a second digital micromirror group) can be respectively passed through the mask array to reach the photoresist layer at a first time and a second time that are different during the relative motion of the mask array and the substrate, wherein the one or more light spots (or the one or more digital micromirrors) included in the first light spot group are different from the one or more light spots (or the one or more digital micromirrors) included in the second light spot group. The light spot array may be a combination of a large light source and a plurality of digital micro-mirrors (i.e., a digital micro-mirror array) to dynamically provide light through different portions of the mask array by dynamically adjusting whether each digital micro-mirror reflects light from the large light source to the mask array, or may be a plurality of micro-light sources arranged in a two-dimensional array to dynamically provide light through different portions of the mask by dynamically adjusting on or off of each micro-light source. For example, each mask in the mask array typically has the same shape, the same size, and the same arrangement direction, but at least two masks may have different shapes, different sizes, and/or different arrangement directions as required.
It should be emphasized that the present invention does not require any limitation as to the three-dimensional microstructure formed, i.e., the present invention can be applied to many modern electronic products and modern electronic product processes. For example, the invention can be applied to the production and manufacture of the light guide plate in the backlight module used in a liquid crystal display, and the like, and can be used for freely regulating and controlling the exposure dose, so that the invention has higher elasticity in design and manufacture, and can also improve the production efficiency of the whole light guide plate mold, thereby improving the defects of low processing speed, low yield, difficult control of microstructure morphology, difficult large-area production and the like in the conventional light guide plate manufacture process in the aspects of chemical etching, ultra-precise machining, photolithography, internal diffusion and the like. For example, the present invention may be applied to the fabrication of memory and/or integrated circuits, as is well known in the art, and may further optimize the conventional photolithography process by using a diagonal scan between the mask and the substrate and a light source that outputs light with different spatial distributions at different times, thereby more efficiently and flexibly fabricating the desired three-dimensional microstructure without significantly improving the hardware used.
Further, when the slant scan is used in the present invention, basically, it is common to make the projection of each mask on the mask array in the direction perpendicular to the scan line be uniformly distributed, and/or make the projection of at least M masks on the mask array in the direction perpendicular to the scan line be overlapped with each other, where M is a positive integer greater than 1. In particular, one common option is to rotate the mask array at an angle relative to the scan line
And the number of the light covers along the scanning line direction when the N is zero. When a certain light of the mask arrayWhen the mask is illuminated by light from a portion of an array of light spots (e.g., an array of digital micromirrors) having m and n light spots in each row and each column, and having a length and width dimension of □, the mask pattern forms an energy distribution in the exposed portion of the photoresist layer, and further accumulates along the scan lines as a three-dimensional energy distribution along with relative motion between the mask array and the substrate. Here, if the scan line is parallel to the y-axis, then there will be different mask opening sizes at different x-coordinates in the direction perpendicular to the scan line
Wherein k is a constant undetermined coefficient, and the size of the opening of the mask determines the accumulation of exposure dose along the scan line after the relative motion and the exposure of the photoresist layer. Obviously, as long as the value of m and/or □ is increased, a three-dimensional photoresist structure with high spatial resolution can be exposed in a large area range, so that a three-dimensional microstructure with high spatial resolution can be formed on the substrate after the subsequent etching process. For example, in one embodiment, 64 micromirrors with a length and width of 13.68 μm are used as the sub-cells of the dmd array, and 8 rows and 8 columns of the dmd array are used, and a mask array with a number of rows and columns between 128 and 1024 and 96 and 768 is used, respectively, where the constant undetermined coefficient k ranges from 0.1 to 5, and the included angle θ ranges from 0.010416 to 0.001302 (rad/radian). By way of example, fig. 5 shows how a single mask (left side of fig. 5) of different shapes may be patterned on a photoresist layer (right side of fig. 5) after relative motion and exposure (middle of fig. 5), wherein the black portion represents light being blocked, the white portion represents light being completely transmitted, and the gray portion represents a ramp band where the dose is gradually accumulated. Obviously, when the three-dimensional microstructures to be formed have different profiles, the patterns to be formed on the photoresist layer are different, and thus a single mask with different shapes is required. That is, the pattern of each mask in the mask array is designed according to the profile of the three-dimensional microstructure to be formed. ImageThe openings of the mask 130 of fig. 1 through which light passes are diamond-shaped, which is specifically designed for the particular pattern 150 that needs to be transferred to the photoresist layer 120.
Some embodiments of the apparatus for forming three-dimensional microstructures according to the present invention can be summarized as shown in fig. 6. Here, the Digital Micromirror array 601 is used as a Light spot array, and includes an UltraViolet Light Emitting Diode Light Source (UltraViolet Light-Emitting Diode Light Source)6011 capable of providing UltraViolet Light, a Reflection Mirror (Reflection Mirror)6012 capable of changing the direction of the UltraViolet Light, an inversion Total Internal Reflection Mirror (inversion Total Internal Reflection)6013 having opposite surfaces capable of respectively refracting and reflecting the UltraViolet Light, a Digital Micromirror Device (Digital Micromirror Device)6014 having one or more Digital micromirrors capable of reflecting the UltraViolet Light and changing the Reflection direction, and a first and a second imaging Lens group (Projection Lens)6015/6016 capable of adjusting the uniformity of the passing UltraViolet Light beams. Here, mask Array 602 includes a spatial filter Array (Microlens vertical Array)6021 disposed between two imaging lens assemblies 6015/6016, and drive assembly 603 includes motion stage 6031 and is capable of moving substrate 605 covered by photoresist layer 604. Obviously, in this embodiment, only the substrate 605 moves but both the micromirror array 601 and the mask array 602 are fixed, and the number of micromirrors of the micromirror device 6014 can be adjusted. By the program control of the computer 6061 and the motion controller 6062, it is possible to designate that at different times during the relative motion between the mask array 602 and the substrate 605, each of the digital micromirrors of the dmd 6014 is turned on to reflect the uv light from the mirror 6012 via the tir mirror 6013 back, that is, the uv light from the dmd 6014 via the tir mirror 6013 is controlled to pass through portions of the mask array 602 (or illuminate the masks of the mask array 602), that is, the beam shaping effect is generated after the uv light passes through the mask array 602 (or the profile of the uv light beam reaching the photoresist layer 604 is changed). Therefore, it can be arbitrarily controlled how the pattern of the mask array 602 is transferred to the photoresist layer 604 at different times, such as transferring the entire pattern of the mask array 602 at a specific time or transferring only a specific portion of the pattern of the mask array 602 at a specific time, i.e. transferring different patterns to the photoresist layer 604 at different portions of the scan line. That is, since the relative motion between the two-dimensional mask array 602 and the substrate 605 can generate a three-dimensional energy accumulation distribution on the photoresist layer 604 along the scanning lines, and can control the digital micromirror device 6014 to be turned on or off at specific positions, these embodiments can be used to fabricate the patterned photoresist layer 604 with any position distribution, variable length, and special pattern of three-dimensional topography corresponding to the three-dimensional microstructure to be formed on the substrate 605.
The present invention provides two exposure modes of the digital micromirror device, the first is that one digital micromirror projection corresponds to one polygonal photomask array, as shown in fig. 7A and 7B, and the second is that any plurality of (8 x8 ═ 64) digital micromirror projections correspond to one polygonal photomask array, as shown in fig. 7C and 7D, the difference between the two architectures is that three-dimensional microstructures with different sizes can be exposed, so that a user can select the optimal digital micromirror/pinhole photomask combination according to the size and the shape of the microstructures.
An arbitrary polygonal photomask array manufactured by a semiconductor photolithography process, such as fig. 7E, and a Digital Micromirror Device (DMD) produced by Texas Instruments (TI), in which reflected uv light is projected and imaged by a first imaging lens group, such as fig. 7F, each uv light reflecting unit is projected and imaged on the surface of the photomask array, and lights up the corresponding photomask array individually, such as fig. 7G, the DMD and the first imaging lens group provide a uniform uv light source for illuminating the photomask array, the light source generates a "beam shaping" effect after passing through the photomask array, and the pattern of the polygonal photomask is projected on an exposure processing imaging surface after being imaged by a second imaging lens group, and the direction of the arrow head of the motion platform is the scanning direction, such that the energy of the two-dimensional polygonal photomask array generates a three-dimensional energy accumulation distribution along the scanning line direction, at the moment, if the digital micro-mirror device is controlled to be switched on or switched off at a specific position, a three-dimensional microstructure with any spatial distribution can be manufactured on the processing surface.
In addition, in practical applications, different photoresist materials often have different exposure dose and development depth characteristics, and the commonly used photoresist materials have an exponential profile. As shown in fig. 8A, the normalized exposure dose reaches a dose threshold of 22% or more, which is sufficient to enable the photoresist to be developed and then to undergo a sufficient chemical reaction to strip (positive photoresist) or leave (negative photoresist) and form the structure. If the photoresist is to be stripped or left completely, the exposure dose needs to be raised again to exponentially increase or decrease the depth of the structure after development. Thus, the present invention may reconsider the exposure dose and structure depth profiles and use the modified exponential distribution as shown in FIG. 8B to calculate the relationship between exposure dose and structure depth
Wherein h (x, y) represents the depth h, h of the structure after the exposure intensity of the cumulative dose I (x, y) on the Karl coordinates (x, y) obtained by developing the photoresistmaxThickness of the photoresist layer before exposure, I0Is the cumulative exposure dose threshold, and A and B are the coefficients to be determined. In certain embodiments, h and hmaxIn the range of 1 to 50 μm, I0In the range of 1 to 100mJ/cm2 (millijoules per square centimeter), which is a property of typical photoresists, and both a and B in the range of 0 to 50. In the case of negative resists, when the cumulative exposure dose I (x, y) is sufficiently large, the post-development feature depth approaches the thickness of the resist coating, i.e., the thickness of the resist coating
By taking the photoresist characteristic curve processed by the correction index analysis as a starting point, the relation among the photomask array graph, the exposure dose, the three-dimensional micro-dose morphology and the like can be calculated. If FIG. 9 is Surface Fitting and the energy distribution is assumed to be Two-Dimensional Gaussian distribution function (Two-Dimensional)Gaussian Function) to calculate the optical power distribution per unit area
Is composed of
C and sigmax,σyIs the undetermined coefficient. In some embodiments, the pending coefficient C is greater than 0 but less than 1000, and each of the other two pending coefficients is greater than 0.01 but less than 100. Next, consider the Two-Dimensional Image Convolution (Two-Dimensional Image conversion), the scan speed, and the exposure start point (x)1,y1) And end point of exposure (x)2,y2) A three-dimensional cumulative energy distribution can be obtained
Wherein, I (x, y) is the accumulated energy and its unit is mJ, N is the step number of the moving platform for pushing the substrate covered by the photoresist layer during exposure scanning, and
δ(x+(x1-kΔx),y+(y1-k Δ y)) is the amount of offset in space (x)1+kΔx,y1The Dirac function of + k Δ Y), Δ X and Δ Y are small steps along the scan direction on the X-Y plane, Δ t is the dose integration time factor representing the time it takes for the start of exposure to the end of exposure, and can also be expressed as
Therefore, the calculation can be known from the two-dimensional image convolution
Where xi, eta are Dummy variables (Dummy variables) in the range- ∞ < xi, eta < ∞, for preventing variable collision when two-dimensional convolution and variable transformation are mathematically calculated. Finally, substituting the result into the exposure dose and structure depth equation
A complete modified version of the equation can be obtained:
according to this equation, the exposure dose to structure depth relation is measured and calculated as coefficients A, B, and the scanning exposure path (x) is determined1,y1)→(x2,y2) The step (Deltax, Deltay) and speed v, and the three-dimensional energy distribution equation e (x, y) of the opening of the mask array can be calculated to obtain the three-dimensional structural morphology equation after exposure and development. In addition, when the optical power distribution is axisymmetric and the exposure scan is along the + x direction, e (x, y) can be simplified to
And will be δ (x + (x)1-kΔx),y+(y1-k Δ y)) to δ (x + (x))1-k Δ x)), the cumulative energy distribution I (x, y) can be reduced to I (x), i.e. I (x) is reduced to
In this regard, FIG. 10 qualitatively illustrates the basic mathematical properties of some of the above equations used to calculate the actual exposure dose versus development depth profile of a photoresist. In addition, fig. 11A shows a graph of structure depth versus exposure dose for a single-sided slope structure and a designed mask pattern according to the above calculation, and fig. 11B and 11C show two target structure cross sections and a designed mask pattern according to the above calculation, respectively.
The invention provides a light spot array slant scanning technology of a high-precision maskless exposure machine, which is matched with a polygonal micro-mask array, achieves the processing target of a three-dimensional microstructure by means of dragging motion of the mask array, and calculates to obtain corresponding three-dimensional exposure dose distribution and the developed three-dimensional structure depth, as shown in figure 12.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention; it is intended that all such equivalent changes and modifications be included within the scope of the present invention without departing from the spirit thereof.
Claims (11)
1. A method of forming a three-dimensional microstructure, comprising:
making a photomask array and a substrate covered by a photoresist layer move relatively along a scanning line, wherein the photomask array is provided with at least one photomask with a special outline which is arranged into an array, and the scanning line is mutually crossed with the arrangement direction of the photomask array; and
during the relative motion between the mask array and the substrate, the projected light passes through the mask array to reach the photoresist layer to form a patterned photoresist layer with a profile corresponding to the three-dimensional microstructure to be formed; and
after the relative movement is finished and the patterned photoresist layer is formed, an etching procedure is carried out to form a three-dimensional microstructure on the substrate.
2. The method of claim 1, further comprising at least one of:
making the mask array and the substrate move relatively along the scanning line at a fixed speed;
moving the mask array along the scan line; and
only the substrate is moved along the scan line.
3. The method of claim 1, further comprising at least one of:
the projection of each photomask on the photomask array in the direction vertical to the scanning line is uniformly distributed;
enabling the projection of at least M photomasks on the photomask array in the direction vertical to the scanning line to be overlapped with each other, wherein M is a positive integer larger than 1; and
rotating the mask array by an angle relative to the scan line
When N is zero, the number of the masks in the direction of the scan line is the number of the masks in the mask array.
4. The method of claim 1, further comprising passing light from a first spot group and a second spot group of a spot array through the mask array to the photoresist layer at a first time and a second time different from each other during the relative motion of the mask array and the substrate, respectively, wherein the first spot group comprises one or more spots different from the one or more spots comprised by the second spot group, wherein the operation of the spot array comprises at least one of:
the different spots can be individually switched on or off;
the different light spots can be individually adjusted in intensity of the generated light; and
a digital micromirror array having at least one digital micromirror is used as the light spot array, where the different digital micromirrors can be individually turned on, turned off, and/or adjusted in intensity of the generated light.
5. The method of claim 1, further comprising setting a profile of each mask in the mask array based on at least the profile of the three-dimensional microstructure to be formed and the photoresist material, and using the following three-dimensional topography equation to extrapolate how to form the desired patterned photoresist layer based on the profile of the desired three-dimensional microstructure:
where h (x, y) is the structural depth of the developed photoresist after exposure intensity of cumulative dose I (x, y) at Karschner coordinates (x, y), hmax is the thickness of the photoresist layer, I0For tirednessThe product exposure dose threshold, A, B and k, is three coefficients, (x)1，y1) And (x)2，y2) The Karschner coordinates of the start point and the end point of the scan line are respectively (Δ x, Δ y) the minute steps along the scan line, and v is the relative movement speed of the mask array and the substrate along the scan line.
6. An apparatus for forming a three-dimensional microstructure, comprising:
a mask array configured to have at least one mask with a special profile arranged as an array;
a driving assembly configured to make the mask array and a substrate covered by a photoresist layer move relatively along a scanning line, wherein the scanning line is crossed with the arrangement direction of the mask array;
an array of light spots arranged to have at least one light spot that can be individually operated and arranged in an array;
the light spot array provides light during the relative movement of the mask array and the substrate, so as to form a patterned photoresist layer with the profile corresponding to the three-dimensional microstructure to be formed; and
an etching assembly is configured to perform an etching process after the relative movement is finished and the patterned photoresist layer is formed, so as to form a three-dimensional microstructure on the substrate.
7. The apparatus of claim 6, further comprising at least one of:
the driving assembly makes the mask array and the substrate move relatively along the scanning line at a fixed speed;
the driving assembly only moves the mask array along the scanning line;
the driving assembly only enables the substrate to move along the scanning line; and
each of the mask arrays has the same shape, the same size and the same arrangement direction.
8. The apparatus of claim 6, further comprising at least one of:
the driving assembly enables the projection of each photomask on the photomask array in the direction vertical to the scanning line to be uniformly distributed;
the driving assembly enables the projection of at least M photomasks on the photomask array in the direction vertical to the scanning line to be mutually overlapped, wherein M is a positive integer larger than 1; and
the drive assembly rotates the mask array at an angle relative to the scan line
When N is zero, the number of the masks in the direction of the scan line is the number of the masks in the mask array.
9. The apparatus of claim 6, further comprising a light spot array for passing light from the first light spot group and the second light spot group through the mask array to the photoresist layer at a first time and a second time different from each other during the relative motion of the mask array and the substrate, respectively, wherein the first light spot group comprises one or more light spots different from the one or more light spots comprised by the second light spot group.
10. The apparatus of claim 6, wherein the operation of the array of light spots comprises at least one of:
the different spots can be individually switched on or off;
the different light spots can be individually adjusted in intensity of the generated light; and
when a digital micromirror array having at least one digital micromirror is used as the light spot array, different digital micromirrors can be individually turned on, turned off, and/or adjusted in intensity of the generated light.
11. The apparatus of claim 6, further comprising a control assembly configured to perform at least one of:
controlling the operation of the light spot array, the photomask array and the driving assembly; and
setting the profile of each photomask in the photomask array according to at least the profile of the three-dimensional microstructure to be formed and the material of the photoresist, wherein the control assembly uses the following three-dimensional structure profile equation to reversely deduce how to form the required patterned photoresist layer according to the profile of the required three-dimensional microstructure:
where h (x, y) is the structural depth of the developed photoresist after exposure intensity of cumulative dose I (x, y) at Karschner coordinates (x, y), hmax is the thickness of the photoresist layer, I0For cumulative exposure dose threshold, A, B and k are three coefficients, (x)1，y1) And (x)2，y2) The Karschner coordinates of the start point and the end point of the scan line are respectively (Δ x, Δ y) the minute steps along the scan line, and v is the relative movement speed of the mask array and the substrate along the scan line.
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