Method for manufacturing blazed grating

Abstract

The present invention provides a method for manufacturing a blazed grating, comprising the following steps: forming a pattern on a grating substrate; forming an etching mask on the grating substrate by using a mask material, the mask material filling the voids in the pattern of the grating substrate; removing the etching mask on the surface of the grating substrate until the pattern of the grating substrate is exposed, and the mask material filled in the voids of the pattern of the grating substrate will not be removed; performing inclined angle etching on the grating substrate to obtain a required blazed grating structure; removing the remaining mask material. By the method of the present invention, the manufacturing of a grating with a nanoscale size can be achieved, and the formed pattern has higher precision; this method has high repeatability, the grating height can be determined or controlled by the etching rate and time, and the width is determined by the distance between the mask materials on both sides.

Description

Technical Field

[0001] The present invention belongs to the technical field of gratings, and in particular relates to a method for manufacturing a blazed grating. Background Art

[0002] When the grating is scribed into a sawtooth-shaped groove cross-section, the light energy of the grating is concentrated in a predetermined direction, that is, on a certain spectral order. When detected from this direction, the intensity of the spectrum is the largest. This phenomenon is called blazing, and such a grating is called a blazed grating. Blazed gratings have functions such as spectroscopy and filtering, and are widely used in ultra-precision measurement systems, spectrometers, semiconductor lasers, display technology, and other technical fields.

[0003] Existing blazed grating manufacturing technologies include mechanical scribing method, grayscale electron beam lithography method, wet etching method, holographic exposure plus ion beam etching method.

[0004] Among them, the mechanical scribing method uses a specific machine for cutting. Although the operation is simple, the surface of the scribed sample is rough, the error is large, and ghost lines often appear, affecting the device performance.

[0005] The grayscale electron beam lithography method relies on electron beam lithography at different doses to form a set 3D structure, which is theoretically feasible. However, in the actual application process, the selection of photoresist and developer is very complicated, and there are extremely strict requirements for the development environment. For the blazed grating structure, a continuous series of extremely small but numerous steps need to be obtained, with poor repeatability, low production efficiency and high cost.

[0006] The wet etching method relies on a specific etching solution. Commonly, a KOH solution can be used as the etching solution for silicon. The application range of wet etching is limited, and the blazed angle generated is strictly limited by the single crystal silicon crystal plane.

[0007] The invention patent with the publication number CN110133779B discloses a method for forming a blazed grating. The method includes: preparing a passivation layer on a grating substrate; forming a plurality of passivation layer trenches on the passivation layer, the plurality of passivation layer trenches having the same width in the height direction and being equally spaced from each other; transferring the pattern on the passivation layer to the grating substrate, so as to form a plurality of substrate trenches on the grating substrate, the plurality of substrate trenches having the same width in the height direction and being equally spaced from each other; bombarding one side of the plurality of substrate trenches with an inclined ion beam. This invention adopts the holographic exposure plus ion beam etching method, which can prepare blazed gratings with high integration and high precision, and can achieve high-precision preparation of the diffraction angle of diffraction gratings. However, its repeatability is poor, and multiple simulations are required to determine the etching time and the incident angle of the plasma beam. And there is still an error of about ten percent between the data simulated based on the existing model and the actual situation, and the evolution of the anti-blazing edge is difficult to control and difficult to apply to the manufacture of nano-scale gratings. Summary of the Invention

[0008] The present invention aims to solve the technical problems that the grating pattern size manufactured by the existing blazed grating manufacturing technology is not precise enough, the structural evolution of the right-angle anti-blaze angle is relatively complex, the etching process of the grating structure has poor repeatability and is difficult to precisely control, and provides a manufacturing method for a blazed grating.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A manufacturing method for a blazed grating, comprising the following steps:

[0011] Form a pattern on the grating substrate;

[0012] Use a mask material to form an etching mask on the grating substrate, and the mask material fills the voids in the grating substrate pattern;

[0013] Remove the etching mask on the surface of the grating substrate until the pattern of the grating substrate is exposed, and the mask material filled in the voids of the grating substrate pattern will not be removed;

[0014] Perform inclined angle etching on the grating substrate to obtain the required blazed grating structure;

[0015] Remove the remaining mask material.

[0016] As a preferred technical solution, the grating substrate is a SiO2 layer deposited on a silicon substrate; or the grating substrate is a silicon substrate.

[0017] As a preferred technical solution, the mask material is Al2O3.

[0018] As a preferred technical solution, the method for forming a pattern on the grating substrate includes:

[0019] Spin-coat a layer of resist on the grating substrate, expose and develop the resist layer to form a resist layer with a pattern;

[0020] Evaporate and deposit a metal layer on the grating substrate by electron beam evaporation. The thickness of the metal layer is less than the thickness of the resist layer, and the metal layer is deposited in the voids and on the top of the resist layer pattern;

[0021] Remove the remaining resist to strip the metal to form a metal layer with a pattern;

[0022] Transfer the pattern of the metal layer to the grating substrate by etching.

[0023] As a preferred technical solution, the resist is polymethyl methacrylate PMMA, and the metal layer is a Cr metal layer.

[0024] As a preferred technical solution, the method for etching the grating substrate at an inclined angle is: performing inclined reactive ion beam etching.

[0025] As a preferred technical solution, the method for etching the grating substrate at an inclined angle is: placing the grating substrate in a Faraday cage, and guiding the etching plasma to enter perpendicular to the surface of the Faraday cage to achieve inclined angle reactive ion etching.

[0026] As a preferred technical solution, during the process of etching the grating substrate at an inclined angle, when partial gratings appear during etching, the grating substrate is taken out, and an enhanced mask layer is deposited on the sidewalls exposed by the mask material by using an inclined electron beam, and then the grating substrate is continuously etched at an inclined angle.

[0027] As a preferred technical solution, the enhanced mask layer is a Cr enhanced mask layer.

[0028] After adopting the above technical solution, the present invention has the following advantages:

[0029] The manufacturing of nano-scale gratings can be realized by this method, and the formed pattern has higher precision; this method has high repeatability, the grating height can be determined or controlled by the etching rate and time, and the width is determined by the distance between the mask materials on both sides. Description of the Drawings

[0030] Figure 1 It is a flowchart of the steps of the manufacturing method of the blazed grating in Embodiment 1;

[0031] Figure 2 It is a flowchart of the steps of the manufacturing method of the blazed grating in Embodiment 2;

[0032] 1 - grating substrate; 2 - SiO2 layer; 3 - PMMA layer; 4 - electron beam; 5 - Cr metal layer; 6 - etching mask; 7 - Faraday cage; 8 - silicon wafer; 9 - etching plasma; 10 - Faraday cage inclination angle. Detailed Embodiments

[0033] The following further describes the present invention in detail with reference to the drawings and specific embodiments.

[0034] Embodiment 1

[0035] As Figure 1 shown, the manufacturing method of the blazed grating includes the following steps:

[0036] 1. Select a single-sided polished silicon wafer as the grating substrate 1;

[0037] 2. Deposit a 200-nm SiO2 layer 2 on the surface of the grating substrate using a plasma-enhanced chemical vapor deposition system (PECVD).

[0038] 3. Spin-coat a 100-nm PMMA layer 3 on the SiO2 layer 2 as a resist layer and bake it on a hot plate at 180 °C for 10 minutes. Thus, a stack composed of SiO2 and PMMA is formed on the silicon substrate (as shown in Figure 1 a);

[0039] PMMA, namely polymethyl methacrylate, is a resist used for electron beam lithography. It belongs to high molecular polymers and its properties are similar to those of photoresists in optical lithography, that is, irradiation can cause chemical or physical changes to form patterns.

[0040] 4. Expose using an electron beam 4 with an acceleration voltage of 100 kV and an exposure dose of 1000 μC / cm 2 , and expose PMMA as a positive resist with the electron beam 4 to form a designed pattern (here the PMMA pattern size is 10 nm wide and the period is 310 nm);

[0041] 5. Immerse the sample in IPA:MIBK = 3:1 at room temperature to develop the PMMA for 1 minute, and then rinse and dry it with IPA. (As shown in Figure 1 b);

[0042] IPA is isopropyl alcohol and MIBK is methyl isobutyl ketone.

[0043] 6. Evaporate and deposit a 10-nm-thick Cr metal layer 5 on the developed PMMA layer 3 using electron beam evaporation (as shown in Figure 1 c);

[0044] 7. Place the sample in PG-remover to perform the lift-off process to achieve pattern transfer (as shown in Figure 1 d);

[0045] PG-remover is a stripping solution and its main component is 1-methyl-2-pyrrolidone (NMP).

[0046] The lift-off process, that is, the lift-off process, can save the etching step and reduce costs.

[0047] 8. Under the following etching conditions, transfer the pattern in the Cr metal layer 5 to the SiO2 layer 2 (as shown in Figure 1 e):

[0048] Reactive ion etching conditions: 15 sccm O2, 40 sccm C4F8, 10 mTorr, 200 W RF, 2500 W ICP, 50 °C;

[0049] 9. Deposit 5 nm of Al2O3 on top of the SiO2 layer 2 using atomic layer deposition (ALD) technology (as shown in Figure 1 Figure f), forming an etching mask 6. The formed Al2O3 trench has a width of 10 nm and a height of 200 nm;

[0050] Al2O3 is used as a mask material to form an etching mask on the grating substrate. The voids in the SiO2 layer 2 pattern should also be filled with Al2O3 to ensure a uniform sample surface.

[0051] 10. Apply plasma etching to the Al2O3 layer on the surface to obtain a SiO2 trench structure filled with Al2O3 (as shown in Figure 1 Figure g);

[0052] Al2O3 etching conditions:

[0053] 20 sccm Cl2, 60 sccm BCl3, 70 mTorr, RF 250 W, 50 °C.

[0054] 11. Perform inclined ion beam etching on the remaining structure, and the blazed grating structure evolves into the structure shown in Figure 1 Figure h;

[0055] For SiO2 gratings, a mixture of CF4 and Ar is usually used for reactive ion beam etching. During the actual operation, the sample will be placed at a certain inclination angle with respect to the reactive ions to achieve inclined angle reactive ion beam etching. The design of this angle is related to the formed blaze angle.

[0056] In this embodiment, the SiO2 reactive ion beam etching conditions are:

[0057] Ion energy 500 eV, ion current 120 mA, Ar 3 sccm, CF4 5 sccm, inclination angle 45°.

[0058] 12. Considering that the 10 nm Al2O3 mask may not be sufficient to support the appearance of the entire blazed grating structure, the sample is taken out when partial gratings appear during etching, and a 20 nm Cr layer is deposited on the sidewalls of the exposed alumina by inclined electron beam evaporation as an enhanced mask (as shown in Figure 1 Figure i):

[0059] 13. Tilt the ion beam etching on the remaining structure until a complete blazed grating structure appears, and place the etched sample in a metal etching solution for wet etching to remove the remaining Al2O3 and Cr, obtaining the final SiO2 blazed grating sample. The SiO2 blazed grating structure has a height of 200 nm, a width of 300 nm, and a blaze angle close to 45° (as Figure 1 shown in j);

[0060] Implementing according to this example can truly achieve the batch preparation of nano-scale blazed gratings with both right-angle anti-blaze angles and controllable blaze angles. Due to the introduction of the Cr-enhanced mask, the width of the Al2O3 trench in this example can be narrower in actual design, thus achieving a more continuous blazed grating structure.

[0061] Example 2

[0062] As Figure 2 shown, a method for manufacturing a blazed grating includes the following steps:

[0063] 1. Select a single-sided polished silicon wafer as the grating substrate;

[0064] 2. Spin-coat a 100-nm PMMA thin film and bake it on a hot plate at 180 °C for 10 minutes;

[0065] 3. Use electron beam lithography with an acceleration voltage of 100 kV and an exposure dose of 1000 μC / cm 2 , and use PMMA as a positive resist to form a designed pattern by electron beam lithography. Here, the PMMA pattern has a width of 300 nm and a period of 310 nm;

[0066] 4. Immerse the sample in IPA:MIBK = 3:1 at room temperature to develop the PMMA for 1 minute, and then rinse and dry it with IPA. (As Figure 2 shown in b);

[0067] 6. Use reactive ion etching for pattern transfer (as Figure 2 shown in c);

[0068] Reactive ion etching conditions: 22 sccm SF6, 38 sccm C4F8, 10 mTorr, 10 W RF, 1200 W ICP, 15 °C.

[0069] 9. Use atomic layer deposition (ALD) technology to deposit 5 nm of Al2O3 on top of the silicon wafer (as Figure 2 shown in d);

[0070] 10. Apply plasma etching to the Al2O3 layer on the surface to obtain a Si trench structure protected on the side (as Figure 2As shown in e), the Al2O3-filled trench is 10 nm wide and 200 nm high;

[0071] Al2O3 etching conditions:

[0072] 20 sccm Cl2, 60 sccm BCl3, 70 mTorr, RF 250 W, 50 °C, bias 327 V.

[0073] 11. Place the sample in the Faraday cage 7. The Faraday cage 7 can guide the etching plasma 9 to enter perpendicularly to the surface of the Faraday cage 7, thereby realizing inclined-angle reactive ion etching (as shown in Figure 2 h). Here, the Faraday cage 7 can cover a quarter-sized area of the 4-inch silicon wafer 8. The designed inclination angle is 56°. The structure obtained after etching is as shown in Figure 2 f;

[0074] A common Faraday cage is made of copper mesh and can be a triangular prism structure with a right-angled triangle cross-section. When the sample is placed in the Faraday cage and the etching plasma is broken down, an equipotential potential will be formed at the boundary of the Faraday cage. An electric-field-free region will be formed inside the Faraday cage, thereby guiding the ions in the plasma to etch the sample in a direction perpendicular to the inclined plane. The inclination angle of the Faraday cage and the blaze angle of the blazed grating satisfy a complementary relationship. The common silicon grating etching gas can be selected as a combination of SF6 + C4F8 or SF6 + O2.

[0075] In this embodiment, the reactive ion etching conditions are: 22 sccm SF6, 38 ccm C4F8, 10 mTorr, 10 W RF, 1200 W ICP, 15 °C.

[0076] 12. Place the etched sample in an Al etching solution for wet etching to remove the remaining Al2O3, obtaining the final Si blazed grating sample (as shown in Figure 2 g). The Si blazed grating structure is 200 nm high and 300 nm wide, and the blaze angle is close to 45°.

[0077] Implementing according to this embodiment can truly realize the batch preparation of nano-scale blazed gratings with both a right-angled anti-blaze angle and a controllable blaze angle. When designing the inclination angle 10 of the Faraday cage, 20° to 70° is usually easy to design, and the corresponding range of the blaze angle should also be 20° to 70°.

[0078] To achieve a blazed grating structure with a right-angled anti-blazed angle, this technical solution first forms a groove structure about 10 nm wide, and then uses ALD technology to fill it with alumina. The alumina on the surface is removed, but the alumina structure of the groove plasma beam is retained as the etching mask on the side. Due to the protection of alumina, the anti-blazed edge and anti-blazed angle will not be affected during the etching process.

[0079] For the etching of the finally formed blazed grating structure, if the material is SiO2, reactive ion beam etching technology can be used to achieve inclined angle etching, and the silicon substrate can be used as the etching stop layer to ensure the height of the grating, and the width is determined by the alumina on both sides. If the material is Si, the Faraday cage can be used to guide the direction of the reactive plasma etching during the etching process. The reactive plasma etching has high repeatability, the grating height can be controlled by the etching rate and time, and the width is still determined by the distance between the alumina on both sides.

[0080] In addition to the above preferred embodiments, the present invention has other implementation manners. Those skilled in the art can make various changes and deformations according to the present invention. As long as they do not depart from the spirit of the present invention, they shall fall within the scope defined by the appended claims of the present invention.

Claims

1. A method for manufacturing a blazed grating, characterized in that: Including the following steps: Form a pattern on the grating substrate; Use a masking material to form an etching mask on the grating substrate, and the masking material fills the voids in the pattern of the grating substrate; Remove the etching mask on the surface of the grating substrate until the pattern of the grating substrate is exposed, and the masking material filled in the voids of the grating substrate pattern will not be removed; Perform etching at an inclined angle on the grating substrate to obtain the required blazed grating structure; Remove the remaining masking material; The method for performing etching at an inclined angle on the grating substrate is: perform inclined ion beam etching; During the process of performing etching at an inclined angle on the grating substrate, take out the grating substrate when partial gratings appear during etching, use an inclined electron beam to deposit a reinforcing mask layer on the sidewalls where the masking material is exposed, and then continue to perform etching at an inclined angle on the grating substrate.

2. The manufacturing method of the blazed grating according to claim 1, characterized in that, The grating substrate is a SiO2 layer deposited on a silicon substrate; or the grating substrate is a silicon substrate.

3. The manufacturing method of the blazed grating according to claim 1, characterized in that, The masking material is one of Al2O3, HfO2, Ga2O3, AlN, Ir, Pt.

4. The manufacturing method of the blazed grating according to any one of claims 1-3, characterized in that The method for forming a pattern on the grating substrate includes: Spin-coat a resist layer on the grating substrate using a resist, expose and develop the resist layer to form a patterned resist layer; Deposit a metal layer on the grating substrate by electron beam evaporation, the thickness of the metal layer is less than the thickness of the resist layer, and the metal layer is deposited in the voids in the pattern of the resist layer; Remove the remaining resist to form a patterned metal layer; Use an etching method to transfer the pattern of the metal layer to the grating substrate.

5. The manufacturing method of the blazed grating according to claim 4, characterized in that, The resist is polymethyl methacrylate PMMA, and the metal layer is a Cr metal layer.

6. The manufacturing method of the blazed grating according to claim 1, characterized in that, The reinforcing mask layer is a Cr reinforcing mask layer.

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