Method and apparatus for producing a multi-tooth grating

Abstract

This application discloses a method and apparatus for fabricating a multi-tooth grating. First, a laser beam is modulated into a parallel beam within a preset plane. This parallel beam is then incident on a phase mask with preset parameters. Since the phase mask has multiple grating lines extending along a first direction and periodically spaced along a second direction on its surface away from the parallel beam, and the first and second directions are perpendicular, and the preset plane is perpendicular to the first direction, the parallel beam is modulated into at least three diffracted beams using the phase mask. These at least three diffracted beams are also located within the preset plane. Through coplanar pairwise interference of these at least three diffracted beams, interference fringes with a multi-tooth grating pattern are formed. Then, the interference fringes are used to expose a sample coated with photoresist at a preset distance from the phase mask. After development, a multi-tooth grating is formed. This fabrication method belongs to near-field holographic lithography, has a compact structure, lower cost, and higher efficiency.

Description

Technical Field

[0001] This application relates to the field of micro-nano fabrication technology of diffractive optical elements, and in particular to a method and apparatus for fabricating a multi-tooth grating. Background Technology

[0002] Multi-tooth diffraction gratings (i.e., multi-tooth gratings) are a type of subwavelength optical device, characterized by wide operating wavelengths, high diffraction efficiency, and a large operating angle range. For example, bitooth gratings, as a metasurface structure with periodic bitooth teeth, have shown great application potential in fields such as displays due to their broadband filtering and achromatic functions.

[0003] Currently, multi-tooth gratings are mainly fabricated using electron beam lithography. Although electron beam lithography can produce patterns with small feature sizes, it suffers from high processing costs and low efficiency. Therefore, there is an urgent need to provide a low-cost, high-efficiency method for fabricating multi-tooth gratings. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a method and apparatus for fabricating multi-tooth gratings, enabling the fabrication of multi-tooth gratings at low cost and high efficiency.

[0005] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0006] A method for fabricating a multi-tooth grating includes:

[0007] The laser beam is modulated into a parallel beam within a preset plane, and the parallel beam is incident on a phase mask with preset parameters. The phase mask has a plurality of grating lines extending along a first direction and periodically spaced along a second direction on its surface away from the parallel beam. The first direction and the second direction are perpendicular, and the preset plane is perpendicular to the first direction.

[0008] The parallel beam is modulated into at least three diffracted beams using the phase mask. The at least three diffracted beams are located in the preset plane, and the at least three diffracted beams interfere with each other to form interference fringes with a multi-tooth grating pattern.

[0009] The sample coated with photoresist at a preset distance from the phase mask is exposed for a preset time using the interference fringes, and then developed to form a multi-tooth grating on the sample.

[0010] Optionally, the multi-tooth grating is a double-tooth grating, and the phase mask is used to modulate the parallel beam into at least three diffracted beams, including:

[0011] The parallel beam is modulated into three diffractive beams using the phase mask.

[0012] Optionally, modulating the parallel beam into three diffracted beams using the phase mask includes:

[0013] The parallel beam is modulated into a zero-order diffraction beam, a positive first-order diffraction beam, and a negative first-order diffraction beam using the phase mask.

[0014] Optionally, the preset parameters include the ratio of the zero-order to the first-order diffraction efficiency of the phase mask. The factors affecting the ratio of the zero-order to the first-order diffraction efficiency of the phase mask include the period of the phase mask, the grating aspect ratio, and the depth of the grating lines. The period of the phase mask is the sum of the width of the grating lines and the interval between two adjacent grating lines. The grating aspect ratio is the ratio of the width of the grating lines to the period of the phase mask.

[0015] Optionally, the preset distance includes multiple target distances arranged periodically. Under the same conditions, the same bidental grating structure is obtained on the samples at each of the target distances from the phase mask, and the interval between two adjacent target distances is 2d. 2 / λ, where λ is the wavelength of the laser beam, d is the period of the phase mask, and the period of the phase mask is the sum of the width of the grating lines and the interval between two adjacent grating lines.

[0016] Optionally, the multi-tooth grating is a symmetrical bitooth grating, which modulates the laser beam into a parallel beam within a preset plane, causing the parallel beam to be incident on a phase mask with preset parameters, including:

[0017] The laser beam is modulated into a parallel beam within a preset plane, and the parallel beam is incident perpendicularly onto a phase mask with preset parameters.

[0018] Optionally, the multi-tooth grating is an asymmetric double-tooth grating, which modulates the laser beam into a parallel beam within a preset plane, causing the parallel beam to be incident on a phase mask with preset parameters, including:

[0019] The laser beam is modulated into a parallel beam within a preset plane, and the parallel beam is incident on a phase mask with preset parameters at a preset angle. The preset angle is the angle between the transmission direction of the parallel beam and the normal direction of the phase mask, and the preset angle is not equal to 0°. The normal direction of the phase mask is perpendicular to both the first direction and the second direction.

[0020] Optionally, the multi-tooth grating is a bi-tooth grating, and the bi-tooth grating includes a plurality of bi-tooth structures arranged at periodic intervals, the total height of the bi-tooth structures is H, the height of the part between the bi-tooths in the bi-tooth structure is h, and 0≤h / H≤1 / 2.

[0021] A fabrication apparatus for a multi-tooth grating includes a laser, a modulation optical path, a phase mask, and a sample coated with photoresist arranged sequentially along the optical path transmission direction.

[0022] The laser is used to generate a laser beam;

[0023] The modulation optical path is used to modulate the laser beam into a parallel beam in a preset plane, so that the parallel beam is incident on the phase mask with preset parameters. The phase mask has a plurality of grating lines extending along a first direction and periodically spaced along a second direction on the surface opposite to the parallel beam. The first direction and the second direction are perpendicular, and the preset plane is perpendicular to the first direction.

[0024] The phase mask is used to modulate the parallel beam into at least three diffracted beams, which are located in the preset plane and interfere with each other to form interference fringes with a multi-tooth grating pattern. The interference fringes are used to expose a photoresist-coated sample at a preset distance from the phase mask for a preset time, and then after development, a multi-tooth grating is formed on the sample.

[0025] Optionally, the fabrication apparatus for the multi-tooth grating further includes a displacement stage, on which both the phase mask and the sample are located. The displacement stage is used to adjust the position of the phase mask, the position of the sample, and the distance between the phase mask and the sample.

[0026] Compared with existing technologies, the above technical solution has the following advantages:

[0027] The method and apparatus for fabricating a multi-tooth grating provided in this application first modulate a laser beam into a parallel beam within a preset plane, and then incident the parallel beam onto a phase mask with preset parameters. Since the surface of the phase mask opposite to the parallel beam is provided with multiple grating lines extending along a first direction and periodically spaced along a second direction, and the first and second directions are perpendicular, and the preset plane is perpendicular to the first direction, the parallel beam can be modulated into at least three diffracted beams using the phase mask. These at least three diffracted beams are also located within the preset plane. Through the coplanar pairwise interference of these at least three diffracted beams, interference fringes with a multi-tooth grating pattern are formed. Then, the formed interference fringes are used to expose a sample coated with photoresist at a preset distance from the phase mask for a preset time. After development, a multi-tooth grating is formed on the sample. Compared with existing electron beam lithography methods, the method for fabricating a multi-tooth grating provided in this application belongs to near-field holographic lithography, which has a compact structure, lower cost, and higher efficiency. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the fabrication apparatus for the multi-tooth grating provided in the embodiments of this application;

[0030] Figure 2 A top view schematic diagram of the second surface of the phase mask in the fabrication apparatus for the multi-tooth grating provided in the embodiments of this application;

[0031] Figure 3 A schematic cross-sectional view of the optical path transmission of a parallel beam of light incident on a phase mask in the fabrication apparatus for a multi-tooth grating provided in this application embodiment;

[0032] Figure 4 A schematic diagram of the light intensity of the interference fringes formed by two beams;

[0033] Figure 5 A schematic diagram of the light intensity of the interference fringes formed by three beams;

[0034] Figure 6 A schematic diagram of the light intensity of the interference fringes formed by five beams;

[0035] Figure 7 This is a schematic flowchart of the fabrication method of the multi-tooth grating provided in the embodiments of this application;

[0036] Figure 8 This is a schematic diagram of a symmetrical double-toothed grating.

[0037] Figure 9 The measurement results of a set of bitooth grating profiles obtained by using the fabrication method of the multitooth grating provided in the embodiments of this application;

[0038] Figure 10 for Figure 9 The curves showing how the various structural parameters of the bidental grating change with the zero-order diffraction efficiency of the phase mask and the corresponding ratio of the zero-order to the first-order diffraction efficiency.

[0039] Figure 11 This is a measurement result of another set of bidental grating profiles obtained using the fabrication method of the multidental grating provided in the embodiments of this application;

[0040] Figure 12 This is another set of measurement results for the profile of a double-toothed grating obtained using the fabrication method of the multi-toothed grating provided in the embodiments of this application;

[0041] Figure 13 The simulation results of several asymmetric bitooth grating profiles obtained by using the fabrication method of the multitooth grating provided in the embodiments of this application are shown.

[0042] Figure 14a This is a scanning electron microscope result of the profile of another asymmetric double-toothed grating obtained by using the multi-toothed grating fabrication method provided in the embodiments of this application;

[0043] Figure 14b for Figure 14a The simulation results. Detailed Implementation

[0044] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0046] To facilitate understanding of this application, the fabrication apparatus and method for the multi-tooth grating provided in the embodiments of this application will be described below in conjunction with the following description.

[0047] Figure 1 A schematic diagram of the fabrication apparatus for the multi-tooth grating provided in the embodiments of this application is shown, as follows: Figure 1 As shown, the fabrication apparatus for a multi-tooth grating provided in this application embodiment includes a laser 10, a modulation optical path 20, a phase mask 30, and a sample 40 coated with photoresist arranged sequentially along the optical path transmission direction. The laser 10 generates a laser beam; the modulation optical path 20 modulates the laser beam generated by the laser 10 into a parallel beam within a preset plane, causing the parallel beam to be incident on the phase mask 30 with preset parameters; the phase mask 30 modulates the parallel beam into at least three diffracted beams, which are also located within the preset plane, and these at least three diffracted beams interfere in pairs to form interference fringes with a multi-tooth grating pattern. These interference fringes are then used to expose the photoresist-coated sample 40 at a preset distance from the phase mask 30 for a preset time, followed by development to form a double-tooth grating on the sample 40.

[0048] like Figure 1As shown, the phase mask 30 has a first surface 301 and a second surface 302 that are disposed opposite to each other. Specifically, Figure 2 A top view schematic diagram of the second surface 302 of the phase mask 30 is shown, as follows: Figure 2 As shown, the second surface 302 of the phase mask 30 is provided with a plurality of grating lines 31 extending along the first direction Z and periodically spaced along the second direction X. The first surface 301 of the phase mask 30 is a flat surface, and the first direction Z and the second direction X are perpendicular to each other.

[0049] Figure 3 A cross-sectional schematic diagram of the optical path transmission of a parallel beam incident on a phase mask 30 with a preset plane is further shown. It can be seen that the first surface 301 of the phase mask 30 faces the parallel beam, while the second surface 302 of the phase mask 30 faces away from the parallel beam. Since the second surface 302 of the phase mask 30 facing away from the parallel beam is provided with periodically spaced grating lines 31, diffraction will occur after the parallel beam is incident on the phase mask 30, forming diffracted light of various orders. From... Figure 3 You can also see that Figure 3 The cross-section shown is the preset plane, which is perpendicular to the first direction Z. The parallel beam is located within the preset plane, and the parallel beam, after being modulated by the phase mask 30, forms at least three diffracted beams (such as...). Figure 3 The zero-order diffracted beam (marked as 0), the positive first-order diffracted beam (marked as +1), and the negative first-order diffracted beam (marked as -1) are also located in the preset plane. That is to say, the parallel beam and at least three diffracted beams modulated by the phase mask 30 are coplanar. Figure 3 As shown, in practical applications, photoresist 41 is coated on substrate 42 to form a sample 40 coated with photoresist.

[0050] It should be noted that the formation mechanism of the toothed grating is mainly based on multi-beam interference. Specifically, Figure 4 The diagram illustrates the intensity of interference fringes formed by two beams. It shows that the interference fringes formed by the superposition of two conventional beams in space correspond to a sinusoidal intensity distribution with a spatial period of p = λ / 2sin(θ), where λ is the exposure wavelength (i.e., the beam wavelength) and θ is half the angle between the two coherent beams. Near-field holographic lithography uses a phase mask as a beam splitter in the holographic optical path, recording the pattern onto the photoresist by utilizing the interference between the diffracted beams generated by the incident light passing through the phase mask. Conventional near-field holographic lithography uses the interference between the two diffracted beams of the phase mask to generate grating patterns with equal or variable spacing.

[0051] It is understandable that as the number of interfering beams increases, different beams interfere with each other to form interference fringes (i.e. interference fields) with different spatial periods and amplitudes. The superposition of each set of interference fields can form a toothed grating. Figure 5A schematic diagram of the light intensity of the interference fringes formed by the three beams is shown. Figure 6 A schematic diagram of the light intensity of the interference fringes formed by five beams is shown.

[0052] Therefore, to fabricate a multi-tooth grating using holographic lithography, interference between at least three diffracted beams is required. However, conventional near-field holographic lithography can only generate grating patterns with equal or variable spacing by utilizing the interference between two diffracted beams of a phase mask. Furthermore, conventional multi-beam interference is usually non-coplanar multi-beam interference to fabricate three-dimensional structures. To fabricate a multi-tooth grating using conventional multi-beam interference optical paths, multiple beam splitters are required to adjust the incident angles of three or more non-coplanar beams to ensure that the multiple non-coplanar beams ultimately interfere within a single plane. This results in a complex optical path and significant difficulty in adjusting it.

[0053] In this embodiment, the laser beam is modulated into a parallel beam within a preset plane using the modulation optical path 20. The parallel beam is then incident on a phase mask 30 with preset parameters. The phase mask 30 modulates the parallel beam into at least three diffracted beams, which are also located within the preset plane. Since the parallel beam incident on the phase mask 30 and the at least three diffracted beams modulated by the phase mask 30 are both located within the preset plane, and the preset plane is parallel to the arrangement direction (i.e., the second direction X) of the grating lines 31 of the phase mask 30 and perpendicular to the extension direction (the first direction Z) of the grating lines 31 of the phase mask 30, the at least three diffracted beams modulated by the phase mask 30 interfere with each other to form interference fringes with a multi-tooth grating pattern. The interference fringes with the multi-tooth grating pattern are then used to expose a photoresist-coated sample 40 at a preset distance from the phase mask 30 for a preset time. After development, a multi-tooth grating is formed on the sample 40.

[0054] In summary, the fabrication apparatus for the multi-tooth grating provided in this application embodiment is a near-field holographic exposure system. By designing the parameters of the phase mask 40, the phase mask 40 can modulate a parallel beam (approximately a plane wave light field) incident in a preset plane into at least three diffracted beams. By designing that the parallel beam incident on the phase mask 40 and the at least three diffracted beams modulated by the phase mask 40 are all located in a preset plane (i.e., coplanar), and that the preset plane is parallel to the arrangement direction (second direction X) of the grating lines 31 of the phase mask 30 and perpendicular to the extension direction (first direction Z) of the grating lines 31 of the phase mask 30, the near-field light field pattern of the at least three diffracted beams modulated by the phase mask 30 is controlled, and interference fringes with a multi-tooth grating pattern are superimposed to form the fabrication of a multi-tooth photoresist grating.

[0055] Optionally, the laser 10 can be a coherent light source in the ultraviolet band.

[0056] Optional, such as Figure 1 As shown, the modulation optical path 20 may include a reflector 21, a pinhole filter 22, a beam expander objective lens 23, an aperture stop 24 and a collimating lens 25 arranged sequentially along the optical path transmission direction. However, this application does not limit the modulation optical path 20, as long as the modulation optical path 20 can modulate the laser beam into a parallel beam in a preset plane.

[0057] Optionally, phase mask 30 is a fused silica phase mask.

[0058] In practical applications, such as Figure 1 As shown, the phase mask 30 and the photoresist-coated sample 40 are located on the displacement stage 50. The displacement stage 50 can adjust the position of the phase mask 30, the position of the photoresist-coated sample 40, and the relative position between the phase mask 30 and the sample 40.

[0059] like Figure 7 As shown, and in combination Figures 1-3 As shown in the figure, this application provides a method for fabricating a multi-tooth grating, the method comprising:

[0060] S100: Modulate the laser beam into a parallel beam in a preset plane, so that the parallel beam is incident on a phase mask 30 with preset parameters. The phase mask 30 is provided with a plurality of grating lines 31 extending along the first direction Z and periodically spaced along the second direction X on the surface (second surface 302) away from the parallel beam. The first direction Z and the second direction X are perpendicular, and the preset plane is perpendicular to the first direction Z.

[0061] S200: The parallel beam is modulated into at least three diffracted beams using a phase mask 30. The at least three diffracted beams are located in a preset plane and interfere with each other to form interference fringes with a multi-tooth grating pattern.

[0062] S300: The sample 40 coated with photoresist at a preset distance from the phase mask 30 is exposed for a preset time using interference fringes, and then developed to form a multi-tooth grating on the sample 40.

[0063] The method for fabricating multi-tooth gratings provided in this application belongs to the near-field holographic lithography method based on phase masks. It has the characteristics of low cost and high processing efficiency. It solves the limitations of electron beam lithography in fabricating toothed gratings, which is time-consuming and labor-intensive, as well as the problem of the extremely complex optical path of non-coplanar multi-beam interference lithography in fabricating toothed gratings. It can expand the flexibility and operability of near-field holographic lithography in fabricating submicron grating patterns, and will have practical value in the field of micro-nano fabrication, such as the fabrication of periodic submicron structures related to multi-tooth gratings like bitooth gratings.

[0064] Optionally, considering that the dobby tooth grating is a widely used multi-tooth grating, when the multi-tooth grating to be prepared is a dobby tooth grating, in step S200, the parallel beam is modulated into at least three diffraction beams using the phase mask 30, including:

[0065] S210: The parallel beam is modulated into three diffracted beams using phase mask 30.

[0066] Further optional, such as Figure 3 As shown, the parallel beam is modulated into three diffracted beams using phase mask 30, including:

[0067] S211: Using phase mask 30, the parallel beam is modulated into a zero-order diffraction beam (corresponding to...). Figure 3 The beam region between the arrows marked 0), the positive first-order diffraction beam (corresponding to...) Figure 3 The beam region between the arrows marked with +1) and the negative first-order diffraction beam (corresponding to...) Figure 3 (The beam area between the arrows marked -1).

[0068] Specifically, such as Figure 3 As shown, let the normal direction of the phase mask 30 be the third direction Y. The third direction Y is perpendicular to the first direction Z and the second direction X. Then the preset plane is the XY plane. When the parallel beam in the preset plane is perpendicularly incident on the first surface 301 of the phase mask 30 with preset parameters, the zero-order diffracted beam, the positive first-order diffracted beam, and the negative first-order diffracted beam are diffracted from the second surface 302 of the phase mask 30 (which has periodically spaced grating lines 31). At this time, the parallel beam in the preset plane is perpendicularly incident on the phase mask 30, that is, the transmission direction of the parallel beam is the third direction Y. Thus, the transmission direction of the zero-order diffracted beam is parallel to the third direction Y, the clockwise angle between the transmission direction of the positive first-order diffracted beam and the third direction Y is θ1, and the counterclockwise angle between the transmission direction of the negative first-order diffracted beam and the third direction Y is θ. -1 Furthermore, since the parallel beam within the preset plane is incident perpendicularly onto the phase mask 30, the positive first-order diffraction beam and the negative first-order diffraction beam are symmetrically distributed along the third direction Y, i.e., θ1 = θ -1 Furthermore, the overlapping region of these three diffracted beams is as follows: Figure 3 As shown in the triangular region, the three diffraction beams interfere in the overlapping region to form interference fringes with a double-toothed grating pattern. Then, by placing the sample 40 in the overlapping region and exposing and developing it, the double-toothed grating pattern can be recorded, thus forming a double-toothed grating on the sample 40.

[0069] According to the diffraction principle of phase masks, when a parallel beam in a preset plane is incident perpendicularly on the phase mask 30, the propagation direction of the positive first-order diffracted beam makes an angle θ1 with the clockwise direction Y of the third direction, satisfying the following:

[0070] θ1=arcsin(λ / d) (1)

[0071] The propagation direction of the negative first-order diffracted beam makes an angle θ with the clockwise direction of the third direction Y. -1 satisfy:

[0072] θ -1 =arcsin(-λ / d) (2)

[0073] Where λ is the wavelength of the laser beam, and d is the period of the phase mask 30, as shown below. Figure 3 As shown, the period d of the phase mask 30 is the sum of the width c of the grating line 31 and the interval g between two adjacent grating lines 31.

[0074] It should be noted that, Figure 3 The example demonstrates how a parallel beam within a preset plane is perpendicularly incident on a phase mask 30, which modulates the beam into three diffracted beams: a zero-order diffracted beam, a positive first-order diffracted beam, and a negative first-order diffracted beam, forming a double-toothed grating. In other embodiments of this application, by changing the period d of the phase mask 30, specifically changing the width c of the grating lines 31 and / or the spacing g between adjacent grating lines 31, more diffracted beams of different orders can be obtained. In other words, the phase mask 30 can be used to modulate a parallel beam into more than three diffracted beams. For example, when a parallel beam within a preset plane is perpendicularly incident on the phase mask 30, at least three orders of diffracted beams (0th, + / -1st, + / -2nd) can be obtained. A multi-toothed grating structure can then be generated through interference between these at least three orders of diffracted beams. The efficiency distribution of each order of diffracted beam participating in the interference can be adjusted using the structural parameters of the phase mask.

[0075] It should also be noted that to form a bidental grating, the three diffraction beams—the zeroth-order diffraction beam, the positive first-order diffraction beam, and the negative first-order diffraction beam—are preferentially utilized. For example, as... Figure 3 As shown, by setting the period d of the phase mask 30, the phase mask 30 modulates the parallel beam into three diffracted beams: a zero-order diffracted beam, a positive first-order diffracted beam, and a negative first-order diffracted beam. For example, even if the incident parallel beam forms multiple diffracted beams of at least three orders after passing through the phase mask 30, such as 0th order, + / -1st order, + / -2nd order, + / -3rd order, and other higher orders, in order to form a bidental grating, the + / -2nd order, + / -3rd order, and other higher orders diffracted beams can be suppressed, while the interference between the 0th order, + / -1st order, and other diffracted beams continues to form the bidental grating structure.

[0076] However, this application does not limit whether the three diffracted beams forming the double-toothed grating structure must be the zero-order diffracted beam, the positive first-order diffracted beam, and the negative first-order diffracted beam. That is, when the parallel beam is modulated into three diffracted beams using the phase mask 30 to form the double-toothed grating structure, these three diffracted beams are not limited to the zero-order diffracted beam, the positive first-order diffracted beam, and the negative first-order diffracted beam; they can also be other combinations of three diffracted beams. For example, after the incident parallel beam passes through the phase mask 30, it forms multiple diffracted beams of no less than three orders, such as 0th order, + / -1st order, + / -2nd order, + / -3rd order, and other higher orders. In this case, selecting the 0th order and + / -2nd order diffracted beams and suppressing other diffracted beams can form a double-toothed grating structure with a smaller period. In principle, diffracted beams that do not need to be interfered with can be suppressed by optimizing the structural parameters of the phase mask 30.

[0077] The following explanation continues with an example of a parallel beam of light incident perpendicularly onto a phase mask 30 within a preset plane. The phase mask 30 modulates the parallel beam into three diffracted beams: a zero-order diffracted beam, a positive first-order diffracted beam, and a negative first-order diffracted beam, forming a bidental grating. The interference of other combinations of three or more diffracted beams after passing through the phase mask 30 can be deduced by analogy, depending on the specific circumstances.

[0078] Figure 8 A schematic diagram of a symmetrical bidental grating is shown. It can be seen that the two teeth of the symmetrical bidental grating are arranged symmetrically. The remaining height h between the two teeth is greater than 0, meaning that there is residual photoresist between the teeth after the photolithography process; when h is 0, there is no residual photoresist between the teeth after the photolithography process. Figure 8 As shown, the symmetrical double-tooth grating structure also has parameters such as the total grating height H, the tooth spacing w1, and the tooth width w2. Among them, the total grating height H of the symmetrical double-tooth grating structure is the total longitudinal height of the symmetrical double-tooth grating structure, the tooth spacing w1 of the symmetrical double-tooth grating structure is the distance between the transverse center lines of the two teeth of the symmetrical double-tooth grating structure, and the tooth width w2 of the symmetrical double-tooth grating structure is the width of any one of the two teeth of the symmetrical double-tooth grating structure.

[0079] Based on this, the inventors discovered that by adjusting the structural parameters of the phase mask 30, specifically the period of the phase mask 30, the grating aspect ratio, and the depth of the grating lines 31, the zero-order diffraction efficiency and the first-order diffraction efficiency (including the diffraction efficiency of the positive first-order diffracted beam and the negative first-order diffracted beam) of the phase mask 30 can be controlled. Furthermore, the ratio of the zero-order diffraction efficiency to the first-order diffraction efficiency of the phase mask 30 (referred to as the ratio of zero-order to first-order diffraction efficiency) can be controlled. In other words, if... Figure 3As shown, the factors influencing the ratio of the zero-order to the first-order diffraction efficiency of the phase mask 30 include the period d of the phase mask, the grating fill factor c / d, and the depth s of the grating lines. The period d of the phase mask 30 is the sum of the width c of the grating lines 31 and the interval g between two adjacent grating lines 31, i.e., d = c + g. The grating fill factor is the ratio of the width c of the grating lines 31 to the period d of the phase mask 30, i.e., c / d. When the period d of the phase mask 30 is determined, the ratio of the zero-order to the first-order diffraction efficiency of the phase mask 30 is mainly determined by the grating fill factor c / d and the depth s of the grating lines.

[0080] Furthermore, by using phase masks 30 with different ratios of zero-order to first-order diffraction efficiencies, different slot profiles of bidental gratings can be obtained. In other words, the slot profile of the bidental grating can be controlled by adjusting the ratio of the zero-order to first-order diffraction efficiencies of the phase mask 30.

[0081] Specifically, taking phase mask 30 as a fused silica phase mask, with a parallel beam incident perpendicularly onto phase mask 30 as an example, and under the same exposure-development conditions for sample 40 (specifically, exposure time of 55s and development time of 70s), and with a distance G of 5mm between phase mask 30 and sample 40, the groove profile of the obtained double-toothed grating for phase mask 30 with a period d of 666.7nm but a different ratio of zero-order to first-order diffraction efficiency is as follows: Figure 9 As shown, in Figure 9 In the diagram, from top to bottom, the ratios of the zero-order to first-order diffraction efficiencies of the phase mask are 2, 10 / 8, 1 / 2, 10 / 27, 10 / 36, 10 / 76, 10 / 98, and 10 / 125. It can be seen that the groove profiles of the corresponding bidental gratings are different. Figure 10 Correspondingly shown Figure 9 The curves showing how the various structural parameters of the bidental grating change with the ratio of the zeroth-order to the first-order diffraction efficiency of the phase mask, combined with... Figure 9 and Figure 10 It can be seen that the ratio of the zero-order to the first-order diffraction efficiency of phase mask 30 is different. The main difference is the remaining photoresist height h and the tooth spacing w1 between the teeth of the bidental grating. The total grating height H and tooth width w2 of each bidental grating are similar.

[0082] More specifically, from Figure 9 and Figure 10As can be seen, for a fused silica phase mask with a period d of 666.7 nm, an exposure time of 55 s for the photoresist, a development time of 70 s, and a distance G of 5 mm between the phase mask 30 and the sample 40, the remaining height h of the photoresist between the teeth of the double-tooth grating gradually decreases as the ratio of the zero-order to the first-order diffraction efficiency of the phase mask decreases. Specifically, when the ratio of the zero-order to the first-order diffraction efficiency of the phase mask is 10 / 76, 10 / 98, and 10 / 125, respectively, the remaining height h of the photoresist between the teeth is 0.

[0083] As can be seen from the above analysis, in step S100, when the parallel beam in the preset plane is incident on the phase mask 30 with preset parameters, and in step S200, when the parallel beam is modulated into a zero-order diffraction beam, a positive first-order diffraction beam, and a negative first-order diffraction beam using the phase mask 30 with preset parameters, the preset parameters of the phase mask 30 include the ratio of the zero-order to the first-order diffraction efficiency. By adjusting the ratio of the zero-order to the first-order diffraction efficiency of the phase mask 30, different double-tooth grating structures can be obtained, and the remaining height h between the double teeth can be made to satisfy: 0≤h≤H / 2. Furthermore, the influencing factors of the ratio of the zero-order to the first-order diffraction efficiency of the phase mask 30 include the period d of the phase mask 30, the grating coverage ratio c / d, and the depth s of the grating lines 31.

[0084] In summary, when the ratio of the zero-order to the first-order diffraction efficiency of the phase mask is in the range of 1 / 2 to 1 / 4 (including the endpoint value), the remaining height h of the photoresist between the two teeth of the bitooth grating can be adjusted; when the ratio of the zero-order to the first-order diffraction efficiency of the phase mask is less than or equal to 1 / 8, the remaining height h of the photoresist between the two teeth of the bitooth grating is 0, and the spacing w1 between the two teeth can be further adjusted.

[0085] The inventors also discovered that, based on Figure 3 As shown, when a parallel beam is incident perpendicularly onto a phase mask 30 with preset parameters, the incident parallel beam, after passing through the phase mask 30, exhibits a periodic optical field along the third direction Y. Specifically, when the distance G between the phase mask 30 and the sample 40 is 2d... 2 When the interval / λ changes periodically, the groove profile of the obtained double-tooth grating exhibits periodic changes, where λ is the exposure wavelength, i.e., the wavelength of the laser beam, parallel beam, and diffraction beam; d is the period of the phase mask 30, which is the sum of the width c of the grating line 31 and the interval g between two adjacent grating lines 31, i.e., the distance between the starting position of one grating line 31 of the phase mask 30 and the starting position of the adjacent grating line 31.

[0086] In practical applications, such as Figure 1As shown in the embodiment of this application, the fabrication apparatus for the bidental grating further includes a displacement stage 50. The phase mask 30 and the sample 40 are both located on the displacement stage 50. The displacement stage 50 is used to adjust the position of the phase mask 30, the position of the sample 40, and the distance between the phase mask 30 and the sample 40. Thus, by moving at least one of the phase mask 30 and the sample 40 via the displacement stage 50, the distance G between the phase mask 30 and the sample 40 can be changed. Each time the distance G between the phase mask 30 and the sample 40 is changed, the sample 40 is exposed and developed under the same conditions to obtain a bidental grating photoresist pattern. By repeating the translation of the relative positions of the phase mask 30 and the sample 40 and the same exposure and development conditions, a set of different bidental grating photoresist patterns can be obtained. In other words, by changing the distance G between the phase mask 30 and the sample 40, the groove profile of the bidental grating can be controlled.

[0087] Specifically, taking phase mask 30 as a fused silica phase mask, with a parallel beam incident perpendicularly onto phase mask 30 as an example, and with a period of 666.7 nm for phase mask 30, a zero-order to first-order diffraction efficiency ratio of 10 / 98, and exposure and development times of the diffracted beam after phase mask 30 on sample 40 of 55 s and 70 s respectively, i.e., under certain parameters of phase mask 30 and certain exposure and development times on sample 40, by changing the distance G between phase mask 30 and sample 40 (i.e., the relative position of phase mask 30 and photoresist 41), the contour of the double-toothed grating on sample 40 is obtained as follows. Figure 11 As shown in the figure, the outline of the double-tooth grating presented in the second to last figures from the top is approximately a periodic shape. When the distance G between the phase mask 30 and the sample 40 is at different positions within a periodic shape, it mainly affects the tooth spacing w1 and the remaining height h of the photoresist between the teeth. Furthermore, by adjusting the distance G between the phase mask 30 and the sample 40, the remaining height h between the teeth can be made to satisfy: 0 ≤ h ≤ H / 2.

[0088] It should be noted that the above explanation uses the example of a parallel beam incident perpendicularly onto the phase mask 30. However, the inventors have discovered that when the parallel beam is not incident perpendicularly onto the phase mask 30, the same condition is met: when the distance G between the phase mask 30 and the sample 40 is 2d... 2 When / λ is a periodic variation, the groove profile of the obtained bidental grating exhibits a periodic variation.

[0089] As can be seen from the above analysis, in step S300, when the photoresist-coated sample 40 at a preset distance from the phase mask 30 is exposed for a preset time using interference fringes and then developed to form a double-toothed grating on the sample 40, the preset distance between the phase mask 30 and the sample 40 can include multiple periodically arranged target distances. Under the same conditions, the same double-toothed grating structure can be obtained on the sample 40 at each target distance from the phase mask 30, and the interval between two adjacent target distances is 2d. 2 / λ, where λ is the exposure wavelength, i.e. the wavelength of the laser beam, parallel beam, and diffraction beam; d is the period of the phase mask 30, which is the sum of the linewidth of the grating line 31 and the interval between two adjacent grating lines 31, i.e. the distance between the starting position of one grating line 31 of the phase mask 30 and the starting position of the adjacent grating line 31.

[0090] The inventors also discovered that the groove profile of the bidental grating can be controlled by adjusting the exposure time of the interference fringes of the photoresist 40 after passing through the phase mask 30.

[0091] Specifically, taking phase mask 30 as a fused silica phase mask, with a parallel beam incident perpendicularly onto phase mask 30 as an example, under the following conditions: the period d of phase mask 30 is 666.7 nm, the grating aspect ratio c / d is between 0.40 and 0.45, the depth s of grating line 31 is 470 nm, the corresponding zero-order diffraction efficiency is 4.4%, the first-order diffraction efficiency is 43%, the ratio of zero-order to first-order diffraction efficiency is 10 / 98, and the distance G between phase mask 30 and photoresist 40 is 5 mm, the sample 40 is exposed using the interference fringes of the zero-order diffracted beam, the negative first-order diffracted beam, and the positive first-order diffracted beam after passing through phase mask 30. By changing different exposure-development conditions, specifically changing the exposure time, the contour of the bitooth grating on the sample 40 is obtained as shown in the figure. Figure 12 As shown, the measured optical power of the parallel beam reaching the first surface 301 (incident surface) of the phase mask 30 is approximately 850 nW-900 nW. Figure 12 The exposure times from top to bottom are 25s, 30s, 35s, 40s, 45s, 50s, 55s, and 60s, meaning that a set of bidental gratings is obtained every 5s between 25s and 60s, and the development time is 70s for each set. Figure 12As can be seen, within a certain exposure time range (25s-55s), with the increase of exposure time, the remaining height h of the photoresist between the teeth of the bidental grating gradually decreases. After the exposure time is greater than 45s (including 45s), the ratio of the remaining height h of the photoresist between the teeth of the bidental grating to the total grating height H begins to be less than 1 / 2. After the exposure time is greater than 55s (including 55s), the remaining height h of the photoresist between the teeth of the bidental grating is equal to 0. Furthermore, from... Figure 12 As can be seen, changing the exposure time also affects the linewidth w2 of the bidental grating and the total height H of the grating.

[0092] As can be seen from the above analysis, under the condition that the material and period of the phase mask 30 are determined, the main factors affecting the structural parameters of the double-toothed grating include the ratio of the zero-order and first-order diffraction efficiencies of the phase mask, the distance between the phase mask and the sample coated with photoresist, and the exposure time of the photoresist. With two of these factors fixed, changing the third factor can control the groove profile of the obtained double-toothed grating. By controlling one, two, or all three factors, the groove profile of the double-toothed grating can be controlled to obtain the desired double-toothed grating structure.

[0093] The inventors further discovered that by changing the period d of the phase mask, photoresist patterns with different periods of bidental gratings can be obtained, which mainly changes the periodic characteristics of the bidental grating. It can be understood that since the bidental teeth in the bidental grating are arranged periodically, the periodic characteristic of the bidental grating is the distance from the starting position of one bidental tooth to the starting position of the next bidental tooth.

[0094] In the above embodiments, step S100 modulates the laser beam into a parallel beam within a preset plane, causing the parallel beam to be incident on a phase mask 30 with preset parameters. This is primarily illustrated by the example of modulating the laser beam into a parallel beam within a preset plane, causing the parallel beam to be perpendicularly incident on the phase mask 30 with preset parameters; that is, the parallel beam is incident orthogonally on the phase mask 30 within the preset plane. It should be noted that, as... Figure 3 As shown, the normal direction of the phase mask 30 is along the third direction Y. The parallel beam is incident perpendicularly on the phase mask 30 in the preset plane. That is, the angle between the transmission direction of the parallel beam in the preset plane and the normal direction of the phase mask 30 is 0°. The normal direction of the phase mask 30 is perpendicular to both the first direction Z and the second direction X.

[0095] It is understandable that when a parallel beam is incident on the phase mask 30 in the preset plane, the zero-order diffracted beam after passing through the phase mask 30 is symmetrically distributed along the third direction Y, the positive first-order diffracted beam and the negative first-order diffracted beam are symmetrically distributed along the third direction Y, so the final result is a symmetrical double-toothed grating.

[0096] Optionally, in other embodiments of this application, modulating the laser beam into a parallel beam within a preset plane, and incident the parallel beam onto a phase mask 30 having preset parameters, may further include:

[0097] The laser beam is modulated into a parallel beam within a preset plane, and the parallel beam is incident on a phase mask 30 with preset parameters at a preset angle. The preset angle is the angle between the transmission direction of the parallel beam (i.e., the third direction Y) and the normal direction of the phase mask 30, and the preset angle is not equal to 0°. The normal direction of the phase mask 30 is perpendicular to both the first direction Z and the second direction X.

[0098] In other words, when a parallel beam is incident non-normally onto the phase mask 30 within a preset plane, an asymmetric bidental grating is ultimately obtained. Specifically, the propagation direction of the parallel beam is incident on the phase mask 30 with preset parameters at angles of 0° (perpendicular or normal incidence), 5°, 10°, and 15° to the normal direction of the phase mask 30. The period d of the phase mask 30 is 666.7 nm, the depth s of the grating lines 31 is 280 nm, and the aspect ratio c / d of the grating lines 31 is 0.4. This corresponds to a zero-order diffraction efficiency and a first-order diffraction efficiency of 31% for the phase mask, with a ratio of 1 between the zero-order and first-order diffraction efficiencies. The simulation results of the resulting asymmetric bidental grating profile are as follows: Figure 13 As shown, from Figure 13 As can be seen, different asymmetric bidental gratings can be fabricated by changing the angle between the propagation direction of the parallel beam in the preset plane and the normal direction of the phase mask.

[0099] It is understandable that the teeth of a symmetrical bidental grating are arranged symmetrically, while the teeth of an asymmetrical bidental grating are distributed asymmetrically. Optionally, such as... Figure 13 As shown, the bitooth heights of the bitooth gratings are different in asymmetric bitooth gratings; other options, such as Figure 14a and Figure 14b As shown, the tooth width w2 of the two teeth in the asymmetric bitooth grating is different, where, Figure 14a To obtain scanning electron microscopy results of an asymmetric bidental grating using a phase mask with a period d of 1000 nm and a parallel beam incident at an angle of 2° (i.e., the angle between the propagation direction of the parallel beam and the normal direction of the phase mask is 2°), the exposure time was 55 s and the development time was 70 s. Figure 14b for Figure 14a The simulation results.

[0100] In summary, when fabricating a bitooth grating using the multi-tooth grating fabrication method and apparatus provided in this application embodiment, the bitooth grating can be controlled to be either a symmetrical or asymmetrical bitooth grating by adjusting the incident angle of the parallel beam's propagation direction in a preset plane relative to the normal direction of the phase mask. When the parallel beam is incident perpendicularly to the phase mask, it is used to fabricate a symmetrical bitooth grating; when the parallel beam is incident non-perpendicularly to the phase mask, it is used to fabricate an asymmetrical bitooth grating. Furthermore, by changing the period of the phase mask, bitooth gratings with different periods can be obtained. Under the condition that the material and period of the phase mask are determined, the groove profile of the bitooth grating can be controlled by adjusting at least one of the following three factors: the ratio of the zero-order to the first-order diffraction efficiency of the phase mask, the distance between the phase mask and the sample coated with photoresist, and the exposure time of the photoresist, to obtain the desired bitooth grating structure. Preferably, through the above-mentioned adjustment, considering that the bitooth grating includes multiple bitooth structures arranged periodically, the total height of the bitooth structure is H, and the height of the part between the bitooths in the bitooth structure is h, it can satisfy 0≤h / H≤1 / 2, thus obtaining a more obvious bitooth structure.

[0101] Therefore, the fabrication method and apparatus for multi-tooth gratings provided in this application can effectively control the near-field holographic light field of the phase mask, thereby reducing the reliance on direct electron beam writing to fabricate complex gratings. It allows for flexible and rapid adjustment and replacement of the phase mask to meet the needs of different applications. For example, the tooth width of a bitooth grating can be changed using the holographic fabrication method of the phase mask, which is of great significance for fabricating variable linewidth gratings and multi-frequency gratings.

[0102] The various parts of this manual are described in a combination of parallel and progressive methods. Each part focuses on the differences between the other parts, and the same or similar parts can be referred to each other.

[0103] The features described above regarding the disclosed embodiments can be substituted or combined with each other to enable those skilled in the art to implement or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not 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

1. A method for fabricating a multi-tooth grating, characterized in that, include: The laser beam is modulated into a parallel beam within a preset plane, and the parallel beam is incident on a phase mask with preset parameters. The phase mask has a plurality of grating lines extending along a first direction and periodically spaced along a second direction on its surface away from the parallel beam. The first direction and the second direction are perpendicular, and the preset plane is perpendicular to the first direction. The parallel beam is modulated into at least three diffracted beams using the phase mask. The at least three diffracted beams are located in the preset plane, and the at least three diffracted beams interfere with each other to form interference fringes with a multi-tooth grating pattern. The sample coated with photoresist at a preset distance from the phase mask is exposed for a preset time using the interference fringes, and then developed to form a multi-tooth grating on the sample.

2. The method for fabricating a multi-tooth grating according to claim 1, characterized in that, The multi-tooth grating is a double-tooth grating, and the phase mask is used to modulate the parallel beam into at least three diffraction beams, including: The parallel beam is modulated into three diffractive beams using the phase mask.

3. The method for fabricating a multi-tooth grating according to claim 2, characterized in that, Modulating the parallel beam into three diffracted beams using the phase mask includes: The parallel beam is modulated into a zero-order diffraction beam, a positive first-order diffraction beam, and a negative first-order diffraction beam using the phase mask.

4. The method for fabricating a multi-tooth grating according to claim 3, characterized in that, The preset parameters include the ratio of the zero-order to the first-order diffraction efficiency of the phase mask. The factors affecting the ratio of the zero-order to the first-order diffraction efficiency of the phase mask include the period of the phase mask, the grating aspect ratio, and the depth of the grating lines. The period of the phase mask is the sum of the width of the grating lines and the interval between two adjacent grating lines. The grating aspect ratio is the ratio of the width of the grating lines to the period of the phase mask.

5. The method for fabricating a multi-tooth grating according to claim 3, characterized in that, The preset distance includes multiple target distances arranged periodically. Under the same conditions, the same bidental grating structure is obtained on the samples at each of the target distances from the phase mask, and the interval between two adjacent target distances is 2d. 2 / λ, where λ is the wavelength of the laser beam, d is the period of the phase mask, and the period of the phase mask is the sum of the width of the grating lines and the interval between two adjacent grating lines.

6. The method for fabricating a multi-tooth grating according to any one of claims 1-5, characterized in that, The multi-tooth grating is a symmetrical bitooth grating that modulates the laser beam into a parallel beam within a preset plane, causing the parallel beam to be incident on a phase mask with preset parameters, including: The laser beam is modulated into a parallel beam within a preset plane, and the parallel beam is incident perpendicularly onto a phase mask with preset parameters.

7. The method for fabricating a multi-tooth grating according to any one of claims 1-5, characterized in that, The multi-tooth grating is an asymmetric double-tooth grating that modulates the laser beam into a parallel beam within a preset plane, causing the parallel beam to be incident on a phase mask with preset parameters, including: The laser beam is modulated into a parallel beam within a preset plane, and the parallel beam is incident on a phase mask with preset parameters at a preset angle. The preset angle is the angle between the transmission direction of the parallel beam and the normal direction of the phase mask, and the preset angle is not equal to 0°. The normal direction of the phase mask is perpendicular to both the first direction and the second direction.

8. The method for fabricating a multi-tooth grating according to any one of claims 1-5, characterized in that, The multi-tooth grating is a bitooth grating, and the bitooth grating includes multiple bitooth structures arranged at periodic intervals. The total height of the bitooth structures is H, and the height of the part between the bitooths in the bitooth structure is h, where 0 ≤ h / H ≤ 1 / 2.

9. An apparatus for fabricating a multi-tooth grating, characterized in that, It includes a laser, a modulation optical path, a phase mask, and a sample coated with photoresist arranged sequentially along the optical path transmission direction; The laser is used to generate a laser beam; The modulation optical path is used to modulate the laser beam into a parallel beam in a preset plane, so that the parallel beam is incident on the phase mask with preset parameters. The phase mask has a plurality of grating lines extending along a first direction and periodically spaced along a second direction on the surface opposite to the parallel beam. The first direction and the second direction are perpendicular, and the preset plane is perpendicular to the first direction. The phase mask is used to modulate the parallel beam into at least three diffracted beams, which are located in the preset plane and interfere with each other to form interference fringes with a multi-tooth grating pattern. The interference fringes are used to expose a photoresist-coated sample at a preset distance from the phase mask for a preset time, and then after development, a multi-tooth grating is formed on the sample.

10. The apparatus for fabricating a multi-tooth grating according to claim 9, characterized in that, The fabrication apparatus for the multi-tooth grating further includes a displacement stage, on which both the phase mask and the sample are located. The displacement stage is used to adjust the position of the phase mask, the position of the sample, and the distance between the phase mask and the sample.

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