A method for preparing an inclined micro-nano structure

Abstract

The present invention provides a method for preparing an inclined micro-nano structure, which comprises the following steps: step S1, preparing a film layer of a material to be etched on a substrate; step S2, preparing a patterned mask layer on the film layer of the material to be etched; step S3, placing the sample prepared with the patterned mask layer in step S2 on the inclined surface of a slot carrier, placing the slot carrier on the lower electrode of a dry etching machine cavity with the inclined surface facing upward, and etching; in the slot carrier, the angle between the inclined surface and the horizontal plane is 5°-70°, and the opening of the slot carrier is covered with a metal isolation mesh; step S4, removing the residual mask layer. The etching method using the technical solution of the present invention can make the inclination angle of the micro-nano structure controllable at 5-70 degrees, and the finely controlled inclination angle can greatly reduce the preparation error of the designed micro-nano structure. Moreover, it is not limited by materials and is applicable to a variety of different dielectric materials.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-nano device preparation, and in particular relates to a method for preparing an inclined micro-nano structure. Background Art

[0002] Traditional bulk optical components rely on a certain thickness to produce sufficient phase changes to achieve functions such as light convergence, dispersion, and deflection. Such devices are often bulky and are not conducive to studying the interaction between light and matter at the subwavelength scale. With the development of micro-nano processing technology, a series of micro-nano optical components such as metasurfaces, photonic crystals, optical microcavities, and optical antennas have been realized, greatly improving people's ability to manipulate light using planar devices. The processing methods of micro-nano structures generally include maskless processing methods such as laser direct writing, nanoimprinting, and focused ion beam etching, as well as photolithography etching methods. In the photolithography etching method, dry etching plays a key role in transferring the mask pattern to the material. Although these processing techniques have successfully realized micro-nano optical devices such as metalenses, holographic metasurfaces, wave plates, and grating couplers based on different materials, these planar optical devices are usually uniform structures from top to bottom, which limits the expansion of optical component functions and the improvement of efficiency. Therefore, the development of dry etching processes for tilted micro-nano structures is of great significance.

[0003] Nanoimprinting is a processing method that can obtain tilted micro-nano structures. The principle of this method is to transfer the tilted micro-nano structure to the photoresist through the nanoimprinting master. However, this method can only form micro-nano structures on a limited number of imprinting adhesives. These imprinting adhesives generally have a low refractive index and poor ability to limit light. Therefore, various optical components based on imprinting adhesives are difficult to achieve high efficiency and good results. The laser direct writing method also has similar material limitations. The focused ion beam etching method can also obtain tilted micro-nano structures, and the applicable material range is wider than nanoimprinting and laser direct writing. However, this method has two defects: first, the use of gallium ions to etch silicon structures will produce ion doping in silicon materials, changing the optoelectronic properties of silicon; second, this maskless processing method has a slow preparation rate, which is not conducive to industrial processing. The dry etching method can overcome the limitations of material types and processing efficiency, and is a feasible solution for realizing tilted micro-nano structures. In previous studies, the ways to achieve tilted micro-nano structures using dry etching include using a tilted photoresist mask and placing the sample tilted in the cavity. The etching method based on the tilted photoresist mask is heavily dependent on the selectivity ratio of the photoresist and the structure, and due to the shadow effect of the tilted structure, it is difficult to obtain a small-sized structure with a precision of tens of nanometers while ensuring the etching depth. Directly placing the sample at an angle in the cavity cannot achieve the effect of controlling the angle due to the presence of the ion sheath. Summary of the invention

[0004] In view of the above technical problems, the present invention discloses a method for preparing an inclined micro-nano structure. By introducing a carrier of a specific shape into an etching cavity, the inclination angle of the micro-nano structure can be controlled within a range of 5°-70°, with small preparation error and high precision.

[0005] To this end, the technical solution adopted by the present invention is:

[0006] A method for preparing an inclined micro-nano structure comprises the following steps:

[0007] Step S1, preparing a film layer of material to be etched on a substrate;

[0008] Step S2, preparing a patterned mask layer on the material film layer to be etched;

[0009] Step S3, placing the sample with a patterned mask layer prepared in step S2 on the inclined surface of a slot carrier, placing the slot carrier on the lower electrode of the dry etching machine cavity with the inclined surface facing upward, and performing etching; in the slot carrier, the angle between the inclined surface and the horizontal plane is 5°-70°; an isolation net is provided above the opening of the slot carrier; Step S4, removing the residual mask layer.

[0010] This technical solution effectively controls the shape of the ion sheath, so that the direction of ion movement above the sample always tends to be perpendicular to the slope. The covered metal mesh further smoothes the sheath shape, so that the ion movement direction tends to be consistent with the sample angle and the slope of the stage. Compared with other non-slot-type carrier solutions, the tilt angle of the obtained micro-nano structure is controllable and the error is small.

[0011] As a further improvement of the present invention, the isolation net is made of metal.

[0012] As a further improvement of the present invention, in step S3, argon gas is introduced during the etching process, and the flow rate of the argon gas is 1 sccm-40 sccm. During the etching process, a series of adsorption and desorption reactions will occur on the substrate surface, including pure chemical reactions of uncharged fluorine atoms adsorbed on the substrate surface, etching reactions driven by ion energy, and so on. Moreover, the atomic gas model does not take the chemical reaction process and the collision process into account, and the etching morphology does not completely match the ion movement direction shown in the simulation results. By adopting this technical solution, through experiments on the flow rate of argon gas, when the flow rate is greater than 40 sccm, the bottom of the gap is rough, and grooves appear at the bottom corners of the grating. By adopting an appropriate flow rate of 1 sccm-40 sccm, the grating morphology is greatly improved.

[0013] As a further improvement of the present invention, in step S3, the RF source power of the dry etching machine is 50 W-400 W. The low RF source power of less than 50 W makes the narrow micro-nano structure gap narrower and narrower with the increase of etching depth, and the etching directionality is poor. The high RF source power of more than 400 W damages the chrome mask and makes the morphology rough.

[0014] As a further improvement of the present invention, the angle between the inclined plane and the horizontal plane is 5°-70°.

[0015] As a further improvement of the present invention, the dry etching machine is an inductively coupled plasma etching device or a reactive ion etching device. The principle of dry etching is to generate high-density plasma through a radio frequency coil under low pressure conditions. The ions bombard the sample surface along the direction of the sheath potential difference under the action of bias, producing physical sputtering and promoting chemical reactions. This method of combining chemical corrosion and physical bombardment can remove the material to be etched that is not protected by the mask, thereby obtaining a pattern consistent with the mask.

[0016] As a further improvement of the present invention, the etching material film layer is prepared by electron beam evaporation, chemical vapor deposition or spin coating. The materials of the etching material film layer mainly include titanium dioxide, silicon dioxide, silicon, silicon nitride, silicon carbide, perovskite and other materials. Further, before preparing the film layer, the substrate should be cleaned to prevent impurities from affecting the quality of the film layer. The cleaning step is to use acetone, isopropanol, and deionized water for ultrasonic treatment for about 15 minutes in sequence, and finally blow dry with a nitrogen gun. Electron beam evaporation technology bombards the target material with a high-energy electron beam to melt and vaporize the target material, and deposit it on the substrate at a constant speed to form a dense film, and the vacuum degree of the cavity is about 5 E-7 Torr. Further, the deposition method includes chemical vapor deposition, plasma-assisted chemical vapor deposition, metal oxide deposition and other methods.

[0017] As a further improvement of the present invention, the patterned mask layer comprises a photoresist mask film layer or a hard mask film layer. Furthermore, the hard mask film layer is a hard mask film layer such as Cr, Al, Ni, SiO2, etc. Among them, the photoresist mask film layer is prepared by spin coating, vitrification, electron beam exposure, and development. There are two ways of the hard mask layer: the stripping method and the etching method: the etching method first deposits the hard mask layer on the film layer to be engraved by evaporation, growth, etc., and then prepares a patterned photoresist on the hard mask layer, and then etches the hard mask layer with the photoresist as a mask to achieve the purpose of pattern transfer. The stripping method first prepares a patterned photoresist on the film layer to be engraved, and the pattern is the reverse structure of the desired micro-nano structure, and then evaporates the hard mask material on the top, and then soaks it in the photoresist stripping solution for a long time, and finally uses an acetone gun to strip the residual photoresist to obtain a hard mask pattern.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] First, the technical solution of the present invention is adopted. By placing the sample to be etched on the designed carrier, and then placing the carrier directly above the lower electrode in the cavity, dry etching is adopted to make the sample on the carrier obtain an inclined morphology. This etching method can make the inclination angle of the micro-nano structure controllable within 5-70 degrees. The finely controlled inclination angle can greatly reduce the preparation error of the designed micro-nano structure. Moreover, it is not limited by materials and is applicable to a variety of different dielectric materials. It can realize inclined micro-nano structures on any material that can be processed by dry etching technology. In particular, the use of this inclined etching process for titanium dioxide and silicon nitride, which are high refractive index materials in the visible light band, is conducive to the realization of micro-nano optical devices with richer functions and higher performance.

[0020] Second, this process is suitable for reactive ion etching equipment that can perform large-scale processing. It has low preparation costs, high production capacity, and has prospects for industrial development. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a preparation flow chart of a method for preparing an inclined micro-nano structure according to an embodiment of the present invention.

[0022] Figure 2 Schematic diagram of chromium grating masks with different duty ratios on a titanium dioxide film layer according to an embodiment of the present invention, wherein (a) to (c) are chromium gratings with duty ratios of 0.3, 0.6, and 0.8, respectively.

[0023] Figure 3 This is the placement position of the carrier in the RIE chamber of the embodiment of the present invention.

[0024] Figure 4 It is a schematic diagram of the carrier structure of an embodiment of the present invention.

[0025] Figure 5 The figure is a side view of a 45° slot-type carrier covered with a metal mesh in an embodiment of the present invention and the potential distribution above it, which reflects the improvement process and optimization effect of the carrier to control the sheath shape. (a) shows the potential distribution and ion movement above the sample when the sample is directly placed at an angle, (b) shows the potential distribution and ion movement above the sample without a metal mesh slot-type carrier, and (c) shows the potential distribution and ion movement above the sample with a metal mesh slot-type carrier.

[0026] Figure 6 It is a comparison diagram of the titanium dioxide grating etching morphology obtained in Example 1 of the present invention and Comparative Example 1, wherein (a) is Example 1 and (b) is Comparative Example 1.

[0027] Figure 7It is a comparison diagram of the titanium dioxide grating etching morphology obtained in Example 2 of the present invention and Comparative Example 2, wherein (a) is Example 2 and (b) is Comparative Example 2.

[0028] Figure 8 It is a schematic diagram of the etching morphology of titanium dioxide grating obtained in Comparative Examples 3 and 4 of the present invention.

[0029] Fig. 9 It is a schematic diagram of the titanium dioxide grating morphology with different duty cycles and different tilt angles in Example 3 of the present invention; wherein I, II, III and IV are the grating tilt angles corresponding to the normal line of 0 degrees, 15 degrees, 25 degrees and 45 degrees respectively.

[0030] Fig.10 This is a diagram showing the correspondence between the titanium dioxide grating morphology with different duty cycles and different tilt angles and the slope of the carrier in Example 3 of the present invention.

[0031] Fig.11 This is a topographic image of the titanium dioxide grating using a 70° groove-type carrier in Example 4 of the present invention.

[0032] Fig.12 This is the morphology image of the titanium dioxide grating using a 5° groove-type carrier in Example 5 of the present invention.

[0033] Fig.13 This is a morphology image of the titanium dioxide grating using a 15° grooved carrier in Example 6 of the present invention.

[0034] Fig.14 This is a diagram showing the large-angle anomalous refraction effect of titanium dioxide in Example 6 of the present invention.

[0035] Fig.15 These are morphological images of inclined gratings made of different materials using a slot-type carrier containing an isolation layer in Example 7 of the present invention, wherein (a) is silicon, (b) is silicon dioxide, and (c) is silicon nitride.

[0036] Fig.16 This is the left-right asymmetric silicon grating under the glue mask obtained in Example 8 of the present invention. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described in further detail below.

[0038] Example 1

[0039] A method for etching an inclined micro-nanostructure, such as Figure 1 As shown, it includes the following steps:

[0040] Step 1: preparing a film layer of material to be etched.

[0041] The film layer of the material to be etched is obtained by electron beam evaporation, chemical vapor deposition, spin coating and other methods, mainly including titanium dioxide, silicon dioxide, silicon, silicon nitride, silicon carbide, perovskite and other materials. Before preparing the film layer, the substrate must be cleaned to prevent impurities from affecting the quality of the film layer. The cleaning steps are acetone, isopropanol, and deionized water ultrasonically for 15 minutes in turn, and finally blown dry with a nitrogen gun. Electron beam evaporation technology bombards the target material with a high-energy electron beam to melt and vaporize the target material, and deposit it on the substrate at a constant speed to form a dense film. The vacuum degree of the chamber is about 5 E-7 Torr. Deposition methods include chemical vapor deposition, plasma-assisted chemical vapor deposition, metal oxide deposition and other methods.

[0042] Step 2, patterned mask preparation, mask materials include but are not limited to photoresist, chromium, nickel, silicon dioxide, and patterning methods include but are not limited to electron beam lithography, nanoimprinting, and laser direct writing.

[0043] The photoresist mask film layer is prepared by spin coating, vitrification, electron beam exposure and development. There are two ways to prepare the hard mask layer: stripping method and etching method: in the etching method, the hard mask layer is first deposited on the film layer to be etched by evaporation, growth, etc., and then a patterned photoresist is prepared on the hard mask layer, and then the hard mask layer is etched using the photoresist as a mask to achieve the purpose of pattern transfer; in the stripping method, a patterned photoresist is first prepared on the film layer to be etched, and the pattern is the reverse structure of the required micro-nano structure, and then a hard mask material is evaporated on it, and then it is immersed in a photoresist stripping solution for a long time, and finally the residual photoresist is stripped with an acetone gun to obtain a hard mask pattern.

[0044] Step 3, inclined dry etching, placing the designed slot carrier directly on the lower electrode of the dry etching machine cavity, the dry etching machine includes but is not limited to inductively coupled plasma etching equipment and reactive ion etching equipment. The slope of the sample in the slot carrier is 5-70 degrees (that is, the angle between the inclined surface in the carrier and the horizontal plane is 5°-70°). An isolation metal mesh is covered above the slot carrier opening. The argon gas flow rate is 2sccm. The RIE RF source power is 50 W.

[0045] The mask is transferred to the material to be etched using a dry etching process. The dry etching process is carried out in an inductively coupled plasma etching device or a reactive ion etching device. The principle of dry etching is to generate high-density plasma through a radio frequency coil under low pressure conditions. Under the action of bias, the ions bombard the sample surface along the direction of the sheath potential difference, producing physical sputtering and promoting chemical reactions. This method of combining chemical corrosion and physical bombardment can remove the material to be etched that is not protected by the mask, thereby obtaining a pattern consistent with the mask.

[0046] Step 4: remove the remaining mask layer.

[0047] The following describes the dry etching process of tilted micro-nanostructures using titanium dioxide grating as an example.

[0048] The morphology of the hard mask grating with different duty ratios on the titanium dioxide film layer is shown in Figure 2. Figure 2 The hard mask uses 27 nm thick chromium, which can be obtained by lift-off or etching.

[0049] In order to realize the angle-controllable tilted micro-nanostructure dry etching process, this embodiment adopts the following method: Figure 4 The schematic diagram of the slot-shaped carrier covered with a metal isolation mesh and placed on the lower electrode of the dry etching machine cavity is shown in FIG. Figure 3 In this embodiment, the sample with the patterned mask layer prepared in step 2 is placed on the inclined surface of the slot-shaped carrier, and the slot-shaped carrier is placed on the lower electrode of the dry etching machine cavity with the inclined surface facing upward; in the slot-shaped carrier, the angle between the inclined surface and the horizontal plane is 45 degrees, and the opening of the slot-shaped carrier is covered with a metal isolation mesh.

[0050] Side view of the 45° slot-type stage covered with a metal mesh and the potential distribution above it. Figure 5 As shown, when ions move along such an equipotential surface gradient, they can maintain a direction perpendicular to the lower electrode. At this time, they are bombarded obliquely relative to the sample surface placed on the slope in the groove, thereby achieving the purpose of inclined etching. Figure 5 The white lines in the figure indicate the direction of ion flow, and the thick arrows indicate the location of the sample. Figure 5 (a) shows the potential distribution and ion movement above the sample when the sample is placed directly at an angle, which can be imagined by a person skilled in the art. It can be seen that the direction of ion movement always tends to be perpendicular to the slope direction. Figure 5 (b) shows the case without the metal mesh slot-type carrier. It can be seen that the sheath shape is insensitive above the slot-type carrier. Figure 5 (c) shows the case of a metal mesh groove stage. It can be seen that this solution further smoothes the sheath shape, making the ion movement direction consistent with the sample angle and the stage slope. It can be seen that the sheath above the groove stage of this embodiment has smooth equipotential lines and is not sensitive to the narrow groove area.

[0051] In this embodiment, the grating is placed on the inclined surface of a slot-type carrier with a slope of 45° and covered with a metal isolation mesh. The etching result is as follows: Figure 6 As shown in (a), it can be seen that a titanium dioxide tilted grating structure with a tilt angle of 45° is achieved.

[0052] Comparative Example 1

[0053] In comparative example 1, the grating is directly placed on the lower electrode of the etching cavity at an angle of 45°. Figure 6As shown in (b), it can be seen that the final grating tilt angle (the angle between the grating side and the substrate normal) is 20°, which is much lower than the set tilt angle of 45°. It can be seen that the comparative example cannot achieve angle-controllable tilt etching.

[0054] Example 2

[0055] Based on Example 1, in this example, the argon gas flow rate is 40 sccm.

[0056] Comparative Example 2

[0057] Based on Example 1, in this comparative example, the argon gas flow rate is 45 sccm.

[0058] The titanium dioxide grating morphology obtained in Example 2 and Comparative Example 2 is compared. Figure 7 As shown. It can be seen that the bottom of the grating gap of Comparative Example 2 is rough, and grooves appear at the bottom corners of the grating. Compared with Comparative Example 2, the grating morphology of Example 2 is greatly improved.

[0059] Comparative Example 3

[0060] On the basis of Example 1, in this comparative example, the RIE RF source power used was 20 W.

[0061] Comparative Example 4

[0062] On the basis of Example 1, in this comparative example, the RIE RF source power used was 450 W.

[0063] The schematic diagram of the titanium dioxide grating etching morphology obtained in Comparative Examples 3 and 4 is shown in Figure 8 As shown, it can be seen that in comparative example 3, the low RF source power makes the narrow micro-nano structure gap narrower and narrower with the increase of etching depth, and the etching directionality is poor. In comparative example 4, the high RF source power damages the chrome mask and makes the morphology rough.

[0064] Example 3

[0065] On the basis of Example 1, in this example, the following is obtained by using the debugged process combined with trough-shaped carriers with different slopes: Fig. 9 The titanium dioxide grating structures with different tilt angles and different duty ratios are shown in the figure. The corresponding curves of the grating tilt angle and the stage slope are drawn, as shown in Fig.10 As shown, it can be seen that by adopting the technical solution of the present invention, the tilt angle of the etching process is controllable.

[0066] Example 4

[0067] Based on Example 1, in this example, the angle between the inclined surface and the horizontal plane in the slot-shaped carrier is 70°, and the obtained titanium dioxide grating morphology is as follows: Fig.11 shown.

[0068] Example 5

[0069] On the basis of Example 1, in this example, the angle between the inclined plane and the horizontal plane in the slot-shaped carrier is 0°, and the obtained titanium dioxide grating morphology is as follows: Fig.12 shown.

[0070] It can be seen that the angles of the samples obtained in Example 4 and Example 5 are precisely controllable and the preparation error is small.

[0071] Example 6

[0072] On the basis of Example 1, in this example, the angle between the inclined surface and the horizontal plane in the slot-shaped carrier is 15°, and the obtained titanium dioxide grating morphology is as follows: Fig.13 The product obtained is a titanium dioxide micro-nanostructure that can deflect a green light beam by 80° - a metagrating. The 80° deflection efficiency of this tilted metagrating can reach more than 80%, which is impossible for all previously published micro-nanostructures for large-angle anomalous transmission in the visible light band. The cross-sectional SEM image of the designed anomalous refractive titanium dioxide metagrating structure is shown in Fig.13 As shown in the figure, the grating tilt angle is 15°, corresponding to the carrier slope of 15°. The 80° large-angle anomalous refraction effect of the meta-grating is as follows: Fig.14 As shown in the figure, the thickness of the titanium dioxide film is 450 nm, and the narrowest gap of the structure is 70 nm. After the meta-grating is combined with the anti-reflection layer, the theoretical efficiency is 89.54%, and the experimentally measured efficiency is 83.6%. The similar efficiency values ​​between the experiment and the simulation prove that the tilted dry etching process described in the patent has the advantage of high sample quality, and the design of micro-nano structures based on this process can improve the performance of the optimization target.

[0073] Example 7

[0074] On the basis of Example 1, in this example, different materials are used to etch the inclined micro-nano structure according to the steps of Example 1, namely silicon, silicon dioxide and silicon nitride, and the obtained inclined morphology is as follows Fig.15 As shown, it can be seen that the slot-type carrier containing the isolation metal mesh of this embodiment can control the direction of ion movement in the dry etching chamber by manipulating the sheath potential above the carrier, and is suitable for any material with an anisotropic dry etching process.

[0075] Example 8

[0076] On the basis of Example 1, in this embodiment, by using the oblique etching step of Example 1 and combining different photoresist masks, a left-right asymmetric silicon grating structure can also be obtained, such as Fig.16 shown.

[0077] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for preparing an inclined micro-nano structure, characterized in that: It includes the following steps: Step S1, preparing a film layer of a material to be etched on a substrate; the material of the film layer of the material to be etched is titanium dioxide; Step S2, preparing a patterned mask layer on the material film layer to be etched; Step S3, placing the sample with the patterned mask layer prepared in step S2 on the inclined surface of the slot-shaped carrier, placing the slot-shaped carrier on the lower electrode of the dry etching machine cavity with the inclined surface facing upward, and performing etching; in the slot-shaped carrier, the angle between the inclined surface and the horizontal plane is 5°-70°, and the opening of the slot-shaped carrier is covered with a metal isolation mesh; Step S4, removing the remaining mask layer; Step S3: During the etching process, argon gas is introduced, and the flow rate of the argon gas is 1 sccm-40 sccm; In step S3, the radio frequency source power of the dry etching machine is 50 W-400 W.

2. The method for preparing an inclined micro-nano structure according to claim 1, characterized in that: The dry etching machine is an inductively coupled plasma etching device or a reactive ion etching device.

3. The method for preparing the inclined micro-nano structure according to claim 2, characterized in that: The etching material film layer is prepared by electron beam evaporation, chemical vapor deposition or spin coating.

4. The method for preparing the inclined micro-nano structure according to claim 3, characterized in that: The patterned mask layer includes a photoresist mask film layer or a hard mask film layer.

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