A method for manufacturing a high-line-to-space deep groove triangular blazed grating

Abstract

The application discloses a preparation method of a high-line-to-depth groove triangular blazed grating, and belongs to the technical field of micro-nano grating precision machining, and comprises the following steps: step S1, substrate pretreatment and photoresist spin coating; step S2, ultraviolet photoetching exposure; step S3, wet development grating mask preparation; and step S4, directional static argon plasma synchronous etching. The application discloses a preparation method of a triangular blazed grating with the advantages of simple overall process, conventional photoetching, etching equipment, high process stability, large-scale batch production capacity, and stable batch preparation of 2000 lines / mm and groove depth greater than or equal to 400 nm.

Description

Technical Field

[0001] This invention relates to the field of precision fabrication technology for micro-nano gratings, and in particular to a method for fabricating a high-line-to-deep-groove triangular blazed grating. Background Technology

[0002] The 2000 lines / mm diffraction grating has a theoretical period of 500 nm, classifying it as a submicron high-density grating. The triangular blazed grating, relying on its tilted sidewalls, concentrates light energy in the target wavelength band to the first diffraction order, making it a core component for spectral detection. Research indicates that when the grating trench depth reaches 400 nm or more, it can broaden the efficient diffraction band and reduce polarization correlation loss.

[0003] The mainstream fabrication processes for triangular blazed gratings currently include:

[0004] 1. Mechanical diamond scribing process: The extremely small grid line spacing of 500nm will cause the diamond tool to wear out quickly, resulting in a long processing cycle, high production cost, and periodic ghost lines on the finished product; due to the limitation of the tool etching limit, the maximum processing depth of the trench is only 280nm, which cannot meet the requirement of ≥400nm depth.

[0005] 2. Metal hard mask ion beam etching process: This route requires multiple processes to be completed sequentially, the process flow is long, precious metal masks are continuously consumed, and the procurement and maintenance costs of supporting high-precision ion beam equipment are high, which is not conducive to small and medium-sized mass production.

[0006] 3. Single-layer photoresist mask combined with conventional ion beam etching: Ion beam etching (IBE) is a purely physical sputtering mechanism. The etching rate of photoresist is usually higher than that of quartz substrates, and the etching margin is limited. When the line density increases to 2000 lines / mm, the gate line width drops to less than 200nm. Lateral sputtering of the ion beam will rapidly narrow the mask line width, and the trench depth is difficult to exceed 350nm under conventional processes. Moreover, conventional etching solutions in the industry generally adopt a stage rotation mode with a uniform speed, and the ion beam bombards uniformly from multiple angles, which can only produce flat-bottomed trapezoidal trenches or arc-shaped trenches, and cannot form controllable triangular blaze slopes.

[0007] Therefore, developing a method for fabricating high-line-density deep-groove triangular blazed gratings that does not require a metal hard mask, has a simplified process, and can be stably mass-produced has significant industrial value. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to propose a method for fabricating high line-to-pair deep trench triangular blazed gratings. Through the synergistic effect of low duty cycle thick photomask and static directional ion beam etching, a one-step forming of deep trench triangular blazed gratings above 400nm is achieved in a single-layer photoresist system. The process is simple, the equipment is highly versatile, and the production cost is low.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] This invention provides a method for fabricating a high-line-to-deep-groove triangular blazed grating, comprising the following steps:

[0011] Step S1, Substrate pretreatment and photoresist spin coating: Spin coat the diluted UV positive photoresist onto the surface of the cleaned and wiped substrate, and then complete the pre-baking and cooling process in sequence.

[0012] Step S2, UV lithography exposure: High-resolution UV lithography is used, and the duty cycle of the grating after development is controlled by adjusting the exposure time;

[0013] Step S3, wet development to prepare grating mask: wet development is used to remove the photoresist in the unexposed areas to obtain a photoresist rectangular grating mask with a duty cycle of less than 0.4;

[0014] Step S4, Directional Static Argon Plasma Synchronous Etching: Using the photoresist pattern as a mask, the substrate is fixed on the stage of the ion beam etching equipment, so that the extension direction of the grating lines is perpendicular to the incident plane of the argon ion beam. The argon ion beam is incident at a preset tilt angle. The stage remains stationary and does not rotate throughout the etching process. The argon ion beam simultaneously etches the photoresist mask and the substrate, and continues etching until the photoresist mask is completely etched and removed without residue, forming a triangular blazed grating structure on the surface of the substrate.

[0015] A preferred embodiment of the present invention is that the grating line density is 2000 lines / mm, corresponding to a grating period of 500nm.

[0016] A preferred embodiment of the present invention is that the trench depth after etching the triangular blazed grating is ≥400nm.

[0017] A preferred embodiment of the present invention is that the photoresist thickness is obtained by diluting the stock solution, and the photoresist thickness is controlled between 500nm and 550nm.

[0018] A preferred embodiment of the present invention is that, in step S3, the duty cycle of the developed photoresist is controlled to be less than 0.4, corresponding to a photoresist gate line width of less than 200 nm.

[0019] A preferred embodiment of the present invention is that the process parameters for argon ion beam etching are: ion energy 400–600 eV, beam current density 0.9–1.2 mA / cm², and working vacuum degree. Argon flow rate: 5-10 sccm.

[0020] A preferred embodiment of the present invention is that the incident tilt angle of the ion beam is 45°.

[0021] A preferred embodiment of the present invention is that, in step S4, the argon plasma continuous etching time is 25 min to 35 min to ensure that there is no photoresist residue.

[0022] A preferred embodiment of the present invention is that, in step S1, a light-shielding film is pasted on the back of the substrate to eliminate the influence of back-reflected light on exposure.

[0023] A preferred embodiment of the present invention is that the substrate thickness is less than 4 mm and the material is any one of quartz, borosilicate glass or monocrystalline silicon.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. Streamlined process and improved production turnover efficiency: This invention achieves simultaneous etching of photoresist mask and substrate through synchronous plasma etching, and the photoresist can be completely removed in one go during the etching process, eliminating the need for the additional independent wet or plasma photoresist removal process in traditional processes; compared with the multiple pattern transfer and stripping processes of metal hard mask etching, the overall processing flow is greatly shortened and the production time per batch is significantly reduced.

[0026] 2. No hard metal mask required, strong process compatibility: This invention can be processed using only general-purpose high-resolution ultraviolet lithography equipment and conventional argon ion beam etching equipment, without the need for high-end special equipment such as electron beam or focused ion beam; no precious metal hard mask is used throughout the process, avoiding material consumption and morphology errors in metal sputtering and stripping processes, and can be achieved with ordinary optical processing production lines.

[0027] 3. Significantly improved core structural indicators: This invention can stably fabricate triangular blazed gratings with 2000 lines / mm and a trench depth ≥400nm. The grating trench sidewalls are continuous and smooth, without obvious serrations or burrs. Compared with the flat-bottomed trapezoidal groove and shallow trench gratings produced by conventional single-layer adhesive processes, the regular deep triangular groove structure can extend the efficient diffraction working band of the grating, reduce the polarization correlation loss of the optical system, reduce spectral stray light, and improve the signal-to-noise ratio of spectral detection.

[0028] 4. High process controllability and good consistency in mass production: The photoresist dilution ratio, exposure time and ion beam etching time of this invention are all set with clear and controllable process parameter ranges. By relying on the coordinated control of parameters, the target triangular trench morphology can be stably reproduced. The trench depth and morphology of different batches of products are consistent, which can meet the basic requirements of mass production. Attached Figure Description

[0029] Figure 1 This is a process flow diagram provided in a specific embodiment of the present invention;

[0030] Figure 2This is a SEM characterization image of the cross-section of the triangular grating trench prepared according to Example 1 of the present invention.

[0031] Figure 3 This is a SEM characterization image of the cross-section of the triangular grating trench prepared according to Example 2 of the present invention.

[0032] Figure 4 This is a SEM characterization image of the cross-section of the triangular grating trench prepared according to Example 3 of the present invention.

[0033] Figure 5 This is a comparative example provided in a specific embodiment of the present invention: a SEM image of the cross-section of a grating after etching on a rotating stage.

[0034] Figure 6 These are SEM images of the cross-section of the grating after etching with a high duty cycle mask, provided in a specific embodiment of the present invention.

[0035] Figure 7 This is a comparative example of a grating cross-section after etching using three thin-film photomasks, provided in a specific embodiment of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0037] The following examples and comparative examples all used argon ion beam etching equipment. The basic process parameters were: ion energy 600 eV, beam current density 1.14 mA / cm², and working vacuum degree. Argon flow rate 10 sccm, ion beam incident angle 45°

[0038] Example 1

[0039] A method for fabricating a high-line-to-deep-groove triangular blazed grating, used to fabricate a triangular blazed grating with 2000 lines / mm and a groove depth of 460nm, is disclosed below. The specific process steps are as follows:

[0040] Step S1, Pretreatment of substrate 1 and spin coating of photoresist: Select a 2mm thick quartz optical substrate 1, wipe it with lint-free paper, perform plasma cleaning for 30 minutes, and cool to room temperature. Mix the stock solution of type 701 ultraviolet positive photoresist 2 with positive photoresist diluent at a volume ratio of 2:1. Spin coat the substrate with a spin coater to obtain a 530nm photoresist layer. Preheat the substrate to 110℃ for 90 seconds, and allow it to cool naturally. Apply a light-shielding film to the back of substrate 1 for matting treatment.

[0041] Step S2, UV lithography exposure: Place the corresponding periodic photomask and substrate 1 with a resist thickness of 530nm on the photolithography equipment, set the exposure gap between the photomask and substrate 1 according to the equipment process specifications, expose for 66s, bake at 130℃ for 90s after exposure, and then cool naturally to room temperature.

[0042] Step S3 Wet development: Immerse substrate 1 completely in the developer solution, soak for 40 seconds, rinse with flowing deionized water for 50 seconds, and dry with nitrogen to obtain a photoresist grating mask with a duty cycle of 0.37 and a grating line width of 185nm.

[0043] Step S4, Static Oriented Argon Ion Beam Synchronous Etching: Fix the substrate 1 tightly to the etching stage, adjust the placement angle so that the direction of the grating lines is perpendicular to the incident plane of the argon ion beam 3, keep the stage stationary and do not rotate throughout the entire processing, turn on the argon ion beam 3 etching source and continuously etch for 30 minutes, and over-etch appropriately to ensure that the photoresist 2 is completely removed without residue.

[0044] Test results:

[0045] like Figure 2 As shown, after etching, scanning electron microscopy testing revealed that the depth of the substrate grating trench was 465 nm, the trench sidewalls were smooth, and the cross-section was a regular triangular blazed groove.

[0046] Example 2

[0047] After the photoresist 2 was prepared, it was spin-coated to a thickness of 500 nm, the exposure time was 58 s, the duty cycle after development was 0.32, and the argon ion beam 3 was etched for 25 min. The other parameters were the same as in Example 1.

[0048] Test results:

[0049] like Figure 3 As shown, after etching, scanning electron microscopy testing showed that the depth of the substrate grating trench was 405nm, and the triangular bevel was complete and smooth, meeting the usage index of 400nm depth.

[0050] Example 3

[0051] After the photoresist 2 was prepared, it was spin-coated to a thickness of 550 nm, the exposure time was 72 s, the duty cycle after development was 0.39, and the argon ion beam 3 was etched for 35 min. The other parameters were the same as in Example 1.

[0052] Test results:

[0053] like Figure 4 As shown, after etching, scanning electron microscopy testing revealed that the depth of the substrate grating trench was 487 nm, and the triangular bevel morphology was uniform and defect-free.

[0054] Comparative Example 1

[0055] The remaining process parameters are completely consistent with those in Example 1, except that the etching stage adopts a uniform rotation mode of the machine at 10 rpm for 30 minutes.

[0056] Test results:

[0057] like Figure 5 As shown, SEM observation after etching reveals that the bottom of the trench is curved, the sidewalls are steep, there is no scintillation, and the maximum depth of the trench is only 238nm, which cannot meet the requirement of a deep trench of more than 400nm.

[0058] Comparative Example 2

[0059] Adjust the exposure time, and after development, the duty cycle of photoresist 2 is 0.52. The remaining steps are the same as in Example 1, and etching is performed for 30 minutes.

[0060] Test results:

[0061] like Figure 6 As shown, SEM observation after etching reveals that the top has triangular serrations with a depth of 210nm, while the lower part has a rectangular structure. The spacing between the lower trenches is narrow, making it impossible to deepen them further and failing to meet the requirement of trenches deeper than 400nm.

[0062] Comparative Example 3

[0063] The photoresist 2 was diluted to a thickness of 420 nm, and the remaining steps were the same as in Example 1.

[0064] Test results:

[0065] like Figure 7 As shown, after 22 minutes of etching, the photoresist 2 was completely consumed, and the trench depth was only 326nm, which could not reach the ≥400nm specification.

[0066] The key parameters and test results of each embodiment and comparative example are summarized in Table 1:

[0067] The test results of the above embodiments and comparative examples show that the present invention can stably prepare 2000 lines / mm triangular blazed gratings with trench depth ≥400nm by the synergistic effect of static directional ion beam etching and low duty cycle thick photomask, breaking through the depth limit of conventional processes, and the trench shape is regular and controllable.

[0068] In this invention, the spatial orientation of the substrate 1 is fixed throughout the process, and the argon ion beam 3 continuously bombards the substrate at a single fixed angle. The lateral uniform retreat of the photoresist mask is synchronized with the etching depth of the substrate trench. The directional ion beam continuously trims the two sidewalls of the trench, and the sidewalls transition smoothly and continuously from top to bottom. No additional chemical trimming or secondary etching process is required, and a regular triangular blazing slope can be spontaneously formed. At the same time, the synchronous etching can completely remove the photoresist 2 in one go, eliminating the need for a separate photoresist removal process and shortening the processing flow.

[0069] The low duty cycle thick photoresist mask supports deep trench etching at high line density by improving both the equivalent selectivity and etching capacity. During argon ion beam etching, the photoresist 2 etch rate is faster than the substrate. For a high line density grating of 2000 lines / mm, this invention prepares a 500nm–550nm thick photoresist layer by diluting the photoresist 2, providing sufficient etching capacity for vertical etching. Simultaneously, the duty cycle is controlled below 0.4, reducing the bombardment area on the top surface of the photoresist and increasing the exposed area of ​​the substrate, thus optimizing the equivalent etching selectivity and matching the photoresist layer consumption rate with the etching depth rate of the substrate 1. The low duty cycle also provides sufficient space for lateral retreat during etching, preventing premature lateral mask failure. Together, these two factors support etching depths above 400nm in a single-layer photoresist system.

[0070] In summary, this invention breaks through the conventional technical understanding that "high line density deep trench triangular gratings must rely on hard metal masks" by combining the synergistic effect of low duty cycle thick photomask and static directional ion beam etching. Both are indispensable, and the two features are coupled and synergistic, producing a technical effect of 1+1>2. Only by combining the two can the two major goals of "deep trenches above 400nm" and "regular triangular blazed slopes" be achieved simultaneously.

[0071] This invention has been described through preferred embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. This invention is not limited to the specific embodiments disclosed herein; other embodiments falling within the scope of the claims are also within the protection scope of this invention.

Claims

1. A method for fabricating a high-line-to-deep-groove triangular blazed grating, characterized in that: Includes the following steps: Step S1, Pretreatment of substrate (1) and spin coating of photoresist: Spin coating of diluted UV positive photoresist (2) onto the surface of substrate (1) after cleaning and wiping, and then pre-baking and cooling are completed in sequence; Step S2, UV lithography exposure: High-resolution UV lithography is used, and the duty cycle of the grating after development is controlled by adjusting the exposure time; Step S3, wet development to prepare grating mask: wet development is used to remove the photoresist in the unexposed area (2) to obtain a photoresist rectangular grating mask with a duty cycle of less than 0.4; Step S4, Directional Static Argon Plasma Synchronous Etching: Using the photoresist (2) pattern as a mask, the substrate (1) is fixed on the stage of the ion beam etching equipment, so that the extension direction of the grating lines is perpendicular to the incident plane of the argon ion beam (3). The argon ion beam (3) is incident at a preset tilt angle. The stage remains stationary and does not rotate throughout the etching process. The argon ion beam (3) simultaneously etches the photoresist mask and the substrate (1). The etching continues until the photoresist mask is completely etched and removed without residue, forming a triangular blazed grating structure on the surface of the substrate (1).

2. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: The grating has a line density of 2000 lines / mm and a corresponding grating period of 500nm.

3. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: The trench depth after etching the triangular blazed grating is ≥400nm.

4. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: The thickness of the photoresist (2) is obtained by diluting the original solution, and the thickness of the photoresist (2) is controlled between 500nm and 550nm.

5. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: In step S3, the duty cycle of the developed photoresist (2) is controlled to be less than 0.4, and the corresponding photoresist gate line width is less than 200nm.

6. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: The process parameters for argon ion beam etching (3) are: ion energy 400-600 eV, beam current density 0.9-1.2 mA / cm², and working vacuum degree. Argon flow rate: 5-10 sccm.

7. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: The incident tilt angle of the argon ion beam (3) is 45°.

8. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: In step S4, the argon plasma etching time is 25 min to 35 min to ensure that there is no residue of photoresist (2).

9. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: In step S1, a light-shielding film is pasted on the back of the substrate (1) to eliminate the influence of back-reflected light on exposure.

10. The method for fabricating a high-line-to-deep-groove triangular blazed grating according to claim 1, characterized in that: The substrate (1) has a thickness of less than 4 mm and is made of any one of quartz, borosilicate glass or monocrystalline silicon.

Images