Ion beam etching method of u-shaped groove grating based on mask shadow effect

Abstract

The application discloses a U-shaped groove grating ion beam etching method based on mask shadow effect, relates to the technical field of U-shaped groove etching, and comprises the following steps: an ion beam is inclinedly incident to a photoresist grating mask by placing a substrate with the photoresist grating mask in an inclined manner; the etching dose distribution of different regions on the surface of the substrate is regulated and controlled through the shadow effect of the photoresist grating mask on the ion beam, so that the etching dose of the center region of the groove bottom is greater than that of the two side regions, and a U-shaped groove with a smooth and gradually changing bottom profile is directly etched and formed. By constructing the smooth transition U-shaped groove bottom structure, the sharp corners are completely eliminated, the electric field concentration phenomenon is significantly relieved, the damage risk under high-power laser irradiation is effectively reduced, and the stability and service life of the grating under extreme environments are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of U-shaped groove etching, and particularly relates to a U-shaped groove grating ion beam etching method based on a mask shadow effect. BACKGROUND

[0002] As an important diffractive optical element, the performance of a surface relief grating directly depends on the geometric characteristics of its micro-nano structure. Among various diffractive elements, gratings are favored due to their design flexibility and controllable preparation. According to geometric shapes, there are step gratings, sinusoidal gratings, rectangular gratings, trapezoidal gratings, etc. Traditional etching processes are divided into wet and dry methods. Wet etching is limited by the crystal direction of the material and is prone to form V-shaped grooves. Dry etching, such as ion beam etching, usually forms rectangular grooves with steep sidewalls and nearly flat bottoms due to its good anisotropy. However, this angular structure will exhibit a significant aggregation effect under the action of electromagnetic fields, affecting the stability and reliability of the grating in extreme environments.

[0003] Existing research shows that under high-power density laser irradiation, electric field enhancement can induce device damage through multiple physical paths, and the dominant mechanism is closely related to the laser pulse width. For short pulse laser, local field amplification can significantly promote nonlinear processes such as avalanche ionization and multi-photon absorption, directly leading to the destruction of the electronic structure of the dielectric material. For long pulse or high repetition frequency laser, non-uniform energy absorption induced by electric field concentration will be converted into heat accumulation, which in turn causes material melting, cracking or delamination due to thermal stress concentration. SUMMARY

[0004] In view of the technical problems existing in the prior art, the application provides a U-shaped groove grating ion beam etching method based on a mask shadow effect to alleviate the electric field aggregation problem and improve the stability of the grating under high-power conditions.

[0005] The U-shaped groove grating ion beam etching method based on the mask shadow effect comprises the following steps:

[0006] The substrate with a photoresist grating mask is placed obliquely so that the ion beam hits the photoresist grating mask in an oblique incidence manner;

[0007] The shadow effect of the photoresist grating mask on the ion beam is used to regulate the etching dose distribution of different regions on the substrate surface, so that the etching dose of the center region of the groove bottom is greater than that of the two side regions, thereby directly etching a U-shaped groove with a smooth and gradually changing bottom profile.

[0008] Further, during the etching process, the substrate is alternately rotated to symmetric incident angles ±θ around the normal direction of the substrate, and the reciprocating scanning of the workbench is coordinated to perform alternating ion beam etching.

[0009] Further, the reciprocating scanning path of the workbench covers the Gaussian distribution area of the ion beam current density, and in one complete alternating etching cycle, the substrate is rotated to +θ angle for etching in one direction of the scanning stroke and rotated to -θ angle for etching in the return stroke.

[0010] Further, the initial incidence angle of the ion beam is determined according to the initial grating mask depth h0, the grating period d and the mask top width w2 .

[0011] Further, in the alternating etching process, the incidence angle of the ion beam is dynamically adjusted according to the mask remaining height h(t) and the groove bottom center etching depth D(t) at the moment t as the etching proceeds .

[0012] Further, the ion beam is generated by a strip-shaped radio frequency ion source, the etching gas used is a fluorine-based gas, the ion beam acceleration voltage is 400-600V, the beam current density is 0.3-0.7mA / cm 2 , and the ion beam divergence angle is 5-10°.

[0013] Further, the photoresist grating mask is prepared on a quartz substrate by a holographic lithography method, the grating period d is 600-700nm, the mask top width w2 is 180-220nm, and the mask depth is 500-700nm.

[0014] Further, the method further comprises a post-processing step after etching, including removing residual photoresist and characterizing the U-shaped groove morphology formed by etching.

[0015] Compared with the prior art, the beneficial effects of the present application are:

[0016] Firstly, the present application can fundamentally improve the electric field distribution and improve the device reliability: the traditional rectangular or trapezoidal grating has sharp corners at the junction of the groove bottom and the sidewall, which easily causes electric field concentration and becomes the source of laser damage. The present application constructs a smooth transition U-shaped groove bottom structure, completely eliminates the sharp corners, significantly alleviates the electric field concentration phenomenon, thereby effectively reduces the damage risk under high-power laser irradiation, and improves the stability and service life of the grating in extreme environments.

[0017] Secondly, the present application realizes high-precision and customizable complex groove machining: the present application converts the "mask shadow effect" in traditional processes, which is considered as a disadvantage, into a controllable forming tool. By precisely adjusting the ion beam incident angle and scanning path, the present application realizes the smooth curved surface structure that is difficult to directly process in the past. Combined with the dynamic angle adjustment mechanism, the system can compensate for the mask consumption and groove depth changes in real time, ensuring the stable formation of the U-shaped profile during etching. In addition, by adjusting the incident angle, the U-shaped amount can be flexibly adjusted to meet the customization needs of grating groove shape in different application scenarios.

[0018] At the same time, the present application solves the uniformity and consistency problem in large-scale manufacturing: by adopting the alternating etching strategy (combined with the reciprocating scanning of the workbench and the alternating positive and negative angles of the substrate), the present application effectively offsets the etching unevenness caused by the inherent Gaussian distribution of the ion beam. This strategy ensures excellent symmetry and uniformity of the grating groove in the entire substrate range, and is particularly suitable for the preparation of large-aperture gratings, providing a reliable process basis for batch manufacturing of high-performance gratings.

[0019] Finally, the present application has excellent process robustness and repeatability, and is easy to industrialize: the present application takes physical models and mathematical analysis as the core, and constructs an adaptive etching system that can dynamically compensate for the slight fluctuations of the initial process conditions, thereby significantly improving the process repeatability and yield. In addition, this process can be realized on a conventional ion beam etching equipment equipped with a programmable tilting sample stage, without the need for revolutionary equipment investment, which is conducive to the rapid upgrading and technical transformation of existing production lines, and has good industrialization application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Schematic diagram of ion beam alternating tilt etching photoresist grating mask;

[0021] Figure 2 Relationship diagram of substrate rotation direction and scanning position during ion beam etching process;

[0022] Figure 3 Schematic diagram of variable-angle ion beam tilt etching process;

[0023] Figure 4 Schematic diagram of atomic force test characterizing the groove shape after etching by the method. DETAILED DESCRIPTION

[0024] The technical solutions of the present application will be described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0025] The U-groove grating ion beam etching method based on mask shadowing effect provided by this invention includes the following steps:

[0026] The substrate with the photoresist grating mask is placed at an angle, so that the ion beam bombards the photoresist grating mask in an angled incident manner;

[0027] By using the shadowing effect of the ion beam produced by the photoresist grating mask, the etching dose distribution in different areas of the substrate surface is controlled, so that the etching dose in the center area of ​​the bottom of the trench is greater than that in the two sides, thereby directly etching to form a U-shaped trench with a smooth, gradient bottom contour.

[0028] To achieve a smooth, gradient-bottomed U-shaped groove, this embodiment proposes a method that utilizes the mask shadow effect to actively construct a non-uniform etching dose distribution, thereby directly etching the bottom curved surface of the U-shaped groove. By optimizing the process steps, this shadow effect is transformed from an unavoidable side effect into a precisely usable forming tool, achieving an etching depth at the center of the groove bottom greater than that on both sides, forming a smooth U-shaped transition. The specific technical solution is described below.

[0029] The substrate is tilted so that the ion beam is incident on the photoresist grating substrate at an angle. The shadow effect formed by the photoresist grating mask on the ion beam is used to actively control the bottom etching dose distribution. Since the ion beam itself has divergence, the shadowed area will also be etched to a certain extent, and the etching dose will be less as you go to the bottom of the mask.

[0030] like Figure 1 As shown, θ represents the ion beam incident angle, which is the angle between the ion beam incident direction and the substrate normal direction, w1 represents the bottom width of the mask, w2 represents the top width of the mask, h is the grating mask depth, and d is the grating period.

[0031] The ion beam incident direction 1 and ion beam incident direction 2 are symmetrical about the normal direction of the substrate. During the etching process, the U-shaped groove is achieved by alternating etching on both sides.

[0032] To ensure the quality of the bottom U-shaped groove, the following three points need to be guaranteed:

[0033] 1. Ion beam incident angle design

[0034] The intersection of the ion beam incident direction and the groove shape is set at the exact center of the groove bottom. This angle ensures that the etching dose distribution at the bottom decreases from the center outwards during subsequent etching. The ion beam incident angle must satisfy the following calculation formula. .

[0035] 2. Alternating ion beam etching

[0036] Ion beam etching adopts strip radio frequency ion source. In order to ensure the uniformity and size extensibility in the etching area, the worktable carrying the grating substrate needs to be reciprocatingly scanned. The ion beam flow at different positions of the worktable is usually Gaussian distribution. In order to ensure the complete symmetry of the etching groove type, an alternative etching scheme is proposed, as shown in Figure 2 The grating lines are vertically placed, and the O point and the A point are at the weakest positions of the ion beam flow.

[0037] When the worktable is scanned from the O point to the A point, the grating substrate is turned clockwise to the +θ angle, and the ion beam etching in this stroke is completed.

[0038] When the worktable is scanned from the A point to the O point, the grating substrate is turned counterclockwise to the -θ angle, and the ion beam etching in this stroke is completed.

[0039] Suppose the ion beam flow density distribution is wherein represents the peak density of the ion beam, is the standard deviation, and the sharpness of the reaction curve. When x is at the O point or the A point, the beam flow density is very small, and it can be considered that there is no etching effect on the substrate.

[0040] 3. Variable-angle ion beam oblique etching

[0041] During the etching process, due to the loss of the height of the photoresist mask and the formation of the quartz groove type, the overall depth changes. The etching rate of the photoresist is less than the etching rate of the quartz, and therefore the total depth is deepening, as shown in Figure 3 The solid arrow indicates the ion beam incident direction without change. It can be found that the shadow area is expanding, and the etching amount at the middle position is decreasing. h2 represents the U-shaped amount. If it is desired to change the U-shaped degree and increase the U-shaped amount, variable-angle oblique ion beam etching is needed. Taking the current position as an example, the ion beam incident direction needs to be adjusted to the dashed line position in the figure. Therefore, the etching amount at the middle position is the largest, and the etching amount at both sides is small, which can effectively increase h2.

[0042] The following key parameters are defined. h0 is the initial grating mask depth, Rm(θ) is the etching rate of the photoresist mask at the ion beam incident angle θ, Rq(θ) is the etching rate of the quartz substrate at the ion beam incident angle θ, t is the etching time, D(t) is the etching depth of the groove center at time t, D(t) = Rq(θ)*t, and h(t) is the remaining height of the mask at time t h0-Rm(θ))*t.

[0043] At the initial time t=0, in order to realize the dose gradient from the groove center to both sides, the ideal ion beam incident angle is the angle designed in the foregoing. With the etching, the position of the ion beam and the groove type changes. At any time t, the depth changes, and the width is considered to be unchanged (the change amount is small), and the ion beam incident angle should be corrected to

[0044] The U-shaped groove grating ion beam etching method based on the mask shadow effect mentioned in the present application comprises the following steps:

[0045] St1, photoresist grating mask preparation;

[0046] A 60mm*60mm*2mm quartz substrate is selected, and a positive photoresist AZ1500 is spin-coated on the substrate with a thickness of 600nm;

[0047] A holographic lithography method is used to manufacture a grating pattern, the grating period d is 667nm, the top width w2 of the photoresist grating mask is 195nm, the bottom width w1 is 300nm, and the groove depth (grating mask depth) h0 is 600nm.

[0048] St2, ion beam etching equipment debugging;

[0049] A strip-shaped radio frequency ion beam etching system (existing system) is used, and a programmable tilting sample table (existing system) is provided.

[0050] Fluorine-based gas is used as the etching gas, the ion beam acceleration voltage is 500V, the beam current density is 0.5mA / cm2, and the ion beam divergence angle is 7°.

[0051] St3, initial ion beam incident angle design: according to the formula, θ0 is 68.5°.

[0052] St4, variable-angle alternating ion beam etching;

[0053] St401, the substrate is rotated clockwise to 68.5°, and the workbench is scanned from O point to A point, and etching is performed in the process;

[0054] St402, the substrate is rotated counterclockwise to -68.5°, and the workbench is scanned from A point to O point, and etching is performed in the process;

[0055] St403, repeat the above steps, etch for 3 cycles, and then correct the angle; the correction amount is calculated according to the formula, the ion beam incident angle is adjusted to 70°, and the sample table is adjusted in real time;

[0056] St404, and so on until the etching depth requirement is reached.

[0057] St5, post-processing and characterization;

[0058] After the etching depth is completed, the surface photoresist residue is removed by acid washing and the like, and the topography is tested by atomic force and the like, the U-shaped amount and effect are confirmed by scanning the grating line topography by the atomic force equipment.

[0059] The above examples are only used to illustrate the technical method of the present application but not limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical method of the present application.

Claims

1. A U-groove grating ion beam etching method based on mask shadowing effect, characterized in that, Includes the following steps: The substrate with the photoresist grating mask is placed at an angle, so that the ion beam bombards the photoresist grating mask in an angled incident manner; By using the shadowing effect of the ion beam generated by the photoresist grating mask, the etching dose distribution in different areas of the substrate surface is controlled, so that the etching dose in the center area of ​​the bottom of the trench is greater than that in the two sides, thereby directly etching to form a U-shaped trench with a smooth, gradient bottom contour. During the etching process, the substrate is alternately rotated on both sides of its normal direction to a symmetrical incident angle ± θ And in conjunction with the reciprocating scanning of the worktable, alternating ion beam etching is performed; Based on the initial grating mask depth h 0. Grating period d and the top width of the mask w 2. Determine the initial incident angle of the ion beam. ; During alternating etching, as etching progresses, the time... t mask remaining height h ( t ) and the center etching depth of the trench bottom D ( t The incident angle of the ion beam is dynamically adjusted. .

2. The U-groove grating ion beam etching method based on mask shadowing effect according to claim 1, characterized in that, The reciprocating scanning path of the stage covers the Gaussian distribution region of the ion beam current density, and in one complete alternating etching cycle, the substrate rotates to + in one direction of the scanning stroke. θ The angle is etched, and during the return stroke, it rotates to - θ Etching is performed at an angle.

3. The U-groove grating ion beam etching method based on mask shadowing effect according to claim 1, characterized in that, The ion beam is generated by a strip-shaped radio frequency ion source, using a fluorine-based etching gas. The ion beam accelerating voltage is 400–600 V, and the beam current density is 0.3–0.7 mA / cm². 2 The ion beam divergence angle is 5~10°.

4. The U-groove grating ion beam etching method based on mask shadowing effect according to claim 1, characterized in that, The photoresist grating mask is fabricated on a quartz substrate using holographic lithography, with a grating period of... d The mask top width is 600~700nm. w 2 is 180~220nm, and the mask depth is 500~700nm.

5. The U-groove grating ion beam etching method based on mask shadowing effect according to claim 1, characterized in that, The method also includes post-processing steps after etching, including removing residual photoresist and characterizing the morphology of the U-shaped groove formed by etching.

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