CN115403002B

CN115403002B - A method for preparing an inclined micro-nano structure

Info

Publication number: CN115403002B
Application number: CN202210982168.1A
Authority: CN
Inventors: 肖淑敏; 刘怡麟; 王雨杰; 宋清海
Original assignee: Harbin Institute of Technology Shenzhen
Current assignee: Harbin Institute of Technology Shenzhen
Priority date: 2022-08-16
Filing date: 2022-08-16
Publication date: 2025-04-01
Anticipated expiration: 2042-08-16
Also published as: CN115403002A

Abstract

The invention provides a preparation method of an inclined micro-nano structure, which comprises the following steps of S1, S2, S3, placing a sample of the patterned mask layer prepared in the step S2 on an inclined plane of a groove-shaped carrier, placing the groove-shaped carrier on a lower electrode of a dry etching machine cavity, and etching the inclined plane upwards, wherein the inclined plane and the horizontal plane form an included angle of 5-70 degrees in the groove-shaped carrier, a metal isolation net is covered on an opening of the groove-shaped carrier, and S4, and removing the residual mask layer. By adopting the etching method of the technical scheme of the invention, the inclination angle of the micro-nano structure can be controlled at 5-70 degrees, and the preparation error of the designed micro-nano structure can be greatly reduced by finely controlling the inclination angle. And is not limited by materials, and is applicable to a plurality of different dielectric materials.

Description

Preparation method of inclined micro-nano structure

Technical Field

The invention belongs to the technical field of micro-nano device preparation, and particularly relates to a preparation method of an inclined micro-nano structure.

Background

Conventional bulk optics rely on a certain thickness to produce enough phase change to achieve the functions of focusing, dispersing, deflecting, etc. of light. Such devices tend to be bulky and are disadvantageous for studying the interaction of light with matter at sub-wavelength scales. With the development of micro-nano processing technology, a series of micro-nano optical elements such as a super-structured surface, a photonic crystal, an optical microcavity, an optical antenna and the like are realized, so that the light control capability of people by using a planar device is greatly improved. Methods for processing micro-nano structures generally comprise maskless processing methods such as laser direct writing, nanoimprint lithography, focused ion beam etching and the like, and photoetching methods. In the photolithographic etching method, dry etching plays a key role in transferring a mask pattern to a material. Although the processing processes successfully realize micro-nano optical devices such as super-structured lenses, holographic super-structured surfaces, wave plates, grating couplers and the like based on different materials, the plane optical devices are generally of uniform structures, which limits the expansion of functions of optical elements and the improvement of efficiency, so that the development of the inclined micro-nano structure dry etching process has important significance.

Nanoimprinting is a processing method that can obtain inclined micro-nano structures. The principle of this method is to transfer the tilted micro-nano structure onto the photoresist through the nanoimprint master. However, this method can only form micro-nano structures on a limited number of imprint gels, and these imprint gels have low general refractive indexes and poor light limiting capability, so that it is difficult to achieve high efficiency and good effect of various optical elements based on the imprint gels. Laser direct writing methods also have similar material limitations. The method of focused ion beam etching can also obtain an inclined micro-nano structure, and the applicable material range is wider than that of nano imprinting and laser direct writing. However, the method has two defects that firstly, the silicon structure is etched by gallium ions, ion doping is generated in the silicon material, the photoelectric property of the silicon is changed, and secondly, the maskless processing method is low in preparation speed and is not beneficial to industrial processing. The dry etching method can overcome the limitation of material types and processing efficiency, and is a feasible scheme for realizing the inclined micro-nano structure. In previous studies, approaches to achieve tilted micro-nano structures using dry etching included both using tilted photoresist masks and placing samples tilted in cavities. The etching method based on the inclined photoresist mask is seriously dependent on the selection ratio of photoresist and structure, and due to the shadow effect of the inclined structure, the small-size structure with the accuracy of tens of nanometers is difficult to obtain on the premise of ensuring the etching depth. The sample is directly placed in the cavity in an inclined way, so that the effect of controllable angle cannot be achieved due to the existence of the ion sheath layer.

Disclosure of Invention

Aiming at the technical problems, the invention discloses a preparation method of an inclined micro-nano structure, which leads a carrier with a specific shape into an etching cavity to ensure that the inclination angle of the micro-nano structure is controllable at 5-70 degrees, and has small preparation error and high precision.

In this regard, the invention adopts the following technical scheme:

a preparation method of an inclined micro-nano structure comprises the following steps:

step S1, preparing a material film layer to be etched on a substrate;

S2, preparing a patterned mask layer on the material film layer to be etched;

And S3, placing the sample of the patterned mask layer prepared in the step S2 on an inclined plane of a groove-shaped carrier, placing the groove-shaped carrier on a lower electrode of a cavity of a dry etching machine, and etching the inclined plane upwards, wherein an included angle between the inclined plane and the horizontal plane in the groove-shaped carrier is 5-70 degrees, an isolation net is arranged above an opening of the groove-shaped carrier, and step S4, removing the residual mask layer.

By adopting the technical scheme, the shape of the ion sheath layer is effectively regulated, so that the ion movement direction above the sample always tends to be perpendicular to the slope direction. The covered metal net further smoothes the sheath shape, so that the ion movement direction is consistent with the included angle of the sample and the gradient of the carrier, and compared with other non-groove carrier schemes, the obtained micro-nano structure has controllable inclination angle and small error.

As a further improvement of the invention, the isolation net is made of metal.

As a further improvement of the invention, argon is introduced in the etching process in the step S3, and the flow rate of the argon is 1sccm-40sccm. During the etching process, a series of adsorption and desorption reactions occur on the surface of the substrate, and the uncharged fluorine atoms are adsorbed on the surface of the substrate to generate a pure chemical reaction, an ion energy driven etching reaction and the like. The atomic gas model does not consider the chemical reaction process and the collision process, the etching morphology is not completely matched with the ion movement direction shown in the simulation result, and by adopting the technical scheme, when the flow of argon is more than 40sccm, the bottom in the gap is rough, and grooves appear at the bottom angle of the grating. And the grating morphology is greatly improved by adopting the proper flow of 1sccm-40sccm.

As a further improvement of the invention, in step S3, the radio frequency source power of the dry etching machine is 50W-400W. The low radio frequency source power of less than 50W makes the narrow micro-nano structure gap narrower and narrower along with the increase of etching depth, and the etching directivity is poor. While high rf source power greater than 400W causes damage to the chrome mask, making the topography rough.

As a further improvement of the invention, the inclined plane forms an angle of 5-70 degrees with the horizontal plane.

As a further improvement of the invention, the dry etching machine is an inductively coupled plasma etching device or a reactive ion etching device. The dry etching principle is that under the condition of low pressure, the gas glow generates high density plasma through the radio frequency coil, and the ions bombard the surface of the sample along the potential difference direction of the sheath layer under the action of bias voltage, thereby generating physical sputtering action and promoting chemical reaction. This method of combining chemical etching and physical bombardment allows removal of the material to be etched from the portions not protected by the mask, thereby obtaining a pattern consistent with the mask.

As a further improvement of the invention, the etching material film layer is prepared by adopting methods such as electron beam evaporation, chemical vapor deposition or spin coating and the like. The etching material film layer mainly comprises titanium dioxide, silicon nitride, silicon carbide, perovskite and other materials. Furthermore, before the film layer is prepared, the substrate is cleaned, so that impurities are prevented from affecting the quality of the film layer. The cleaning step is that acetone, isopropanol and deionized water are adopted to sequentially carry out ultrasonic treatment for about 15 min, and finally a nitrogen gun is used for drying. The electron beam evaporation technology bombards the target material with high-energy electron beam to make the target material melt and gasify, and deposit on the substrate at constant speed to form compact film with cavity vacuum degree of 5E-7 Torr. Further, the deposition method comprises chemical vapor deposition, plasma-assisted chemical vapor deposition, metal oxide deposition and the like.

As a further refinement of the invention, the patterned mask layer comprises a photoresist mask film layer or a hard mask film layer. Further, the hard mask film layer is Cr, al, ni, siO ₂ or other hard mask film layers. The photoresist mask film layer is prepared by spin coating, vitrification, electron beam exposure and development. The hard mask layer has two ways of stripping method and etching method, namely, the etching method is to deposit the hard mask layer on the film layer to be etched in the modes of vapor deposition, growth and the like firstly, then prepare patterned photoresist above the hard mask layer, and then etch the hard mask layer by taking the photoresist as a mask, thereby realizing the purpose of pattern transfer. The stripping method comprises the steps of firstly preparing patterned photoresist on a film layer to be etched, wherein the pattern is an inverse structure of a required micro-nano structure, evaporating a hard mask material above the patterned photoresist, soaking the patterned photoresist in photoresist stripping liquid for a long time, and finally stripping residual photoresist by using an acetone gun to obtain the hard mask pattern.

Compared with the prior art, the invention has the beneficial effects that:

Firstly, by adopting the technical scheme of the invention, the sample to be etched is placed on the designed carrier, then the carrier is directly placed above the lower electrode in the cavity, and dry etching is adopted, so that the sample on the carrier obtains an inclined shape, the inclination angle of the micro-nano structure can be controlled at 5-70 degrees by adopting the etching method, and the preparation error of the designed micro-nano structure can be greatly reduced by finely controlling the inclination angle. And the material is not limited, and the method is applicable to various dielectric materials, and can realize an inclined micro-nano structure on any material which can be processed by a dry etching process. In particular, the inclined etching process is adopted for titanium dioxide and silicon nitride which are materials with high refractive indexes in the visible light wave band, so that the micro-nano optical device with richer functions and higher performance can be realized.

Secondly, the process is suitable for reactive ion etching equipment capable of carrying out mass processing, has low preparation cost and high productivity, and has industrial development prospect.

Drawings

Fig. 1 is a preparation flow chart of a preparation method of an inclined micro-nano structure according to an embodiment of the invention.

FIG. 2 is a schematic diagram of a chromium grating mask with different duty ratios on a titanium dioxide film layer according to an embodiment of the present invention, wherein (a) - (c) are chromium gratings with duty ratios of 0.3, 0.6, and 0.8, respectively.

Fig. 3 is a table placement position within the RIE chamber according to an embodiment of the invention.

Fig. 4 is a schematic view of a stage structure according to an embodiment of the invention.

Fig. 5 is a side view of a 45 ° trough-shaped carrier covered with a metal mesh and its upper potential distribution, which show the improvement process and optimization effect of the shape of the carrier regulation sheath. Wherein (a) is the situation of directly placing the sample obliquely, the situation of electric potential distribution and ion movement above the sample, (b) is the situation of electric potential distribution and ion movement above the sample without adopting a metal mesh slot type carrier, and (c) is the situation of electric potential distribution and ion movement above the sample with a metal mesh slot type carrier.

FIG. 6 is a graph showing the comparison of the etched patterns of the titanium dioxide gratings obtained in example 1 and comparative example 1 according to the present invention, wherein (a) is example 1 and (b) is comparative example 1.

FIG. 7 is a graph showing the comparison of the etched features of the titanium dioxide gratings obtained in example 2 and comparative example 2 according to the present invention, wherein (a) is example 2 and (b) is comparative example 2.

FIG. 8 is a schematic diagram of the etched profile of the titanium dioxide grating obtained in comparative example 3 and comparative example 4 of the present invention.

FIG. 9 is a schematic diagram of the morphology of a titanium dioxide grating with different duty ratios and different tilt angles according to embodiment 3 of the present invention, wherein I, II, III and IV are 0 degrees, 15 degrees, 25 degrees and 45 degrees of the grating tilt angles corresponding to the normal line, respectively.

FIG. 10 is a graph showing the relationship between the morphology of the titanium dioxide grating and the gradient of the carrier for different duty cycles and different tilt angles according to example 3 of the present invention.

FIG. 11 is a graph of the morphology of a titanium dioxide grating using a 70℃slot stage according to example 4 of the present invention.

FIG. 12 is a graph of the morphology of a titanium dioxide grating using a 5℃slot stage according to example 5 of the present invention.

FIG. 13 is a graph of the morphology of a titanium dioxide grating employing a 15℃slot type stage according to example 6 of the present invention.

FIG. 14 is a graph showing the large angle extraordinary refraction effect of titanium dioxide of example 6 of the present invention.

FIG. 15 is a topography of a tilted grating using different materials for the spacer-containing channel carrier of example 7 of the present invention, wherein (a) is silicon, (b) is silicon dioxide, and (c) is silicon nitride.

Fig. 16 is a left-right asymmetric silicon grating under a glue mask obtained in example 8 of the present invention.

Detailed Description

Preferred embodiments of the present invention are described in further detail below.

Example 1

An etching method of an inclined micro-nano structure, as shown in figure 1, comprises the following steps:

and step1, preparing a material film to be etched.

The material film layer to be etched is obtained by methods such as electron beam evaporation, chemical vapor deposition, spin coating and the like and mainly comprises materials such as titanium dioxide, silicon nitride, silicon carbide, perovskite and the like. Before the film is prepared, the substrate is cleaned, so that impurities are prevented from affecting the quality of the film. The cleaning step is that acetone, isopropanol and deionized water are sequentially subjected to ultrasonic treatment for 15 min, and finally are dried by a nitrogen gun. The electron beam evaporation technology bombards the target material with high-energy electron beams to make the target material melt and gasify, and deposit on the substrate at constant speed to form a compact film. The vacuum degree of the cavity is about 5E-7 Torr. Deposition methods include chemical vapor deposition, plasma-assisted chemical vapor deposition, metal oxide deposition, and the like.

Step 2, preparing a patterned mask, wherein mask materials comprise photoresist, chromium, nickel and silicon dioxide, and patterning methods comprise electron beam lithography, nanoimprint and laser direct writing.

The photoresist mask film layer is prepared by spin coating, vitrification, electron beam exposure and development. The hard mask layer has two ways of stripping method and etching method, namely the etching method is to deposit the hard mask layer on the film layer to be etched by vapor deposition, growth and the like firstly, then prepare patterned photoresist above the hard mask layer, then etch the hard mask layer by taking the photoresist as a mask to realize the purpose of pattern transfer, the stripping method is to prepare patterned photoresist on the film layer to be etched, the pattern is the inverse structure of the required micro-nano structure, then vapor deposit the hard mask material above, then soak the hard mask material in photoresist stripping liquid for a long time, and finally strip the residual photoresist by an acetone gun to obtain the hard mask pattern.

And 3, inclined dry etching, namely directly placing the designed groove-shaped carrier on a lower electrode of a cavity of a dry etching machine, wherein the dry etching machine comprises but is not limited to inductively coupled plasma etching equipment and reactive ion etching equipment. The slope of the sample in the groove-shaped carrier is 5-70 degrees (namely, the included angle between the inclined plane in the carrier and the horizontal plane is 5-70 degrees). An isolating metal net is covered above the opening of the groove-shaped carrier. The argon flow was 2sccm. The RIE rf source power was 50W.

The mask is transferred to the material to be etched using a dry etching process. The dry etching process is performed in an inductively coupled plasma etching apparatus or a reactive ion etching apparatus. The dry etching principle is that under the condition of low pressure, the gas glow generates high density plasma through the radio frequency coil, and the ions bombard the surface of the sample along the potential difference direction of the sheath layer under the action of bias voltage, thereby generating physical sputtering action and promoting chemical reaction. This method of combining chemical etching and physical bombardment allows removal of the material to be etched from the portions not protected by the mask, thereby obtaining a pattern consistent with the mask.

And 4, removing the residual mask layer.

The dry etching process of the inclined micro-nano structure is described below by taking a titanium dioxide grating as an example.

The hard mask grating morphology of different duty cycles on the titanium dioxide film layer is shown in fig. 2. The hard mask is made of chromium with a thickness of 27 nm a and can be obtained by a stripping method or an etching method.

In order to realize the dry etching process of the angle-controllable inclined micro-nano structure, the embodiment adopts a groove-shaped carrier which is shown in fig. 4 and covers a metal isolation net, and a schematic diagram of the groove-shaped carrier which is placed on a lower electrode of a cavity of a dry etching machine is shown in fig. 3. In the embodiment, the sample with the patterned mask layer prepared in the step 2 is placed on the inclined plane of the groove-shaped carrier, the groove-shaped carrier is placed on the lower electrode of the dry etching machine cavity, the inclined plane faces upwards, the inclined plane and the horizontal plane in the groove-shaped carrier form an included angle of 45 degrees, and the opening of the groove-shaped carrier is covered with the metal isolation net.

The side view of the 45-degree groove-shaped carrier covered with the metal mesh and the potential distribution above the side view are shown in fig. 5, when ions move along the gradient of the equipotential surface, the direction perpendicular to the lower electrode can be kept, and at the moment, oblique incidence bombardment is carried out relative to the surface of a sample placed on a slope in the groove, so that the purpose of oblique etching is achieved. The white line in fig. 5 indicates the ion flow direction, the thick arrow indicates the sample placement position, and fig. 5 (a) indicates the potential distribution and ion movement situation above the sample when the sample is directly placed obliquely as can be expected by those skilled in the art, and it can be seen that the ion movement direction always tends to be perpendicular to the slope direction. Fig. 5 (b) shows the case without metal mesh channel type carrier, it can be seen that the sheath shape is insensitive above the channel type carrier. Fig. 5 (c) shows the case of a metal-containing mesh-channel type stage, and it can be seen that this approach further smoothes the sheath shape, bringing the ion movement direction into agreement with the sample angle and stage gradient. It can be seen that the sheath over the slotted carrier of this embodiment has a smooth equipotential line and is not sensitive to the narrow recess region.

In this embodiment, the grating is placed on the inclined plane of the groove-type stage with a 45 ° gradient and covered with a metal isolation net, and the etching result is shown in fig. 6 (a), and it can be seen that a titanium dioxide inclined grating structure with a 45 ° inclination angle is realized.

Comparative example 1

In comparative example 1, the grating was placed directly on the etched cavity bottom electrode at 45 ° tilt. As shown in fig. 6 (b), the etching result shows that the final grating tilt angle (the angle between the grating side and the substrate normal) is 20 ° and is far lower than the set tilt angle of 45 °, and the comparative example cannot realize the tilt etching with controllable angle.

Example 2

Based on example 1, the argon flow rate was 40sccm in this example.

Comparative example 2

In this comparative example, the argon flow was 45sccm based on example 1.

The pair of titanium dioxide grating morphologies obtained in example 2 and comparative example 2 is shown in fig. 7. It can be seen that the bottom in the grating gap of comparative example 2 was rough and grooves were present at the grating bottom corners. The grating profile of example 2 is greatly improved over that of comparative example 2.

Comparative example 3

Based on example 1, in this comparative example, an RIE rf source power of 20W was used.

Comparative example 4

Based on example 1, in this comparative example, an RIE rf source power of 450W was used.

The schematic etching morphology of the titanium dioxide gratings obtained in comparative example 3 and comparative example 4 is shown in fig. 8, and it can be seen that in comparative example 3, the low rf source power makes the narrow micro-nano structure gap narrower as the etching depth increases, and the etching directivity is poor. Comparative example 4, high rf source power causes damage to the chrome mask, roughening the topography.

Example 3

Based on embodiment 1, in this embodiment, a process of debugging is adopted to combine with groove-shaped carriers with different gradients to obtain a titanium dioxide grating structure with different inclination angles and different duty ratios as shown in fig. 9. And the inclination angle of the grating and the gradient of the carrier are correspondingly drawn to form a curve, as shown in fig. 10, the inclination angle of the etching process can be controlled by adopting the technical scheme of the invention.

Example 4

Based on embodiment 1, in this embodiment, the included angle between the inclined plane and the horizontal plane in the groove-shaped carrier is 70 °, and the obtained titanium dioxide grating morphology chart is shown in fig. 11.

Example 5

Based on embodiment 1, in this embodiment, the included angle between the inclined plane and the horizontal plane in the groove-shaped carrier is 0 °, and the obtained titanium dioxide grating morphology chart is shown in fig. 12.

It can be seen that the samples obtained in example 4 and example 5 are accurate and controllable in angle and small in preparation error.

Example 6

Based on embodiment 1, in this embodiment, the included angle between the inclined plane and the horizontal plane in the groove-shaped carrier is 15 °, and the obtained titanium dioxide grating morphology chart is shown in fig. 13. The obtained product is a titanium dioxide micro-nano structure-super-structure grating capable of deflecting green light beams by 80 degrees. The 80-degree deflection efficiency of the inclined super-structured grating can reach more than 80%, and the effect cannot be achieved by the micro-nano structure of all visible light wave bands for the large-angle abnormal transmission function, which is published before. The cross-sectional SEM image of the ultra-structured grating structure of the abnormally-refracted titanium dioxide obtained by design is shown in fig. 13, the inclination angle of the grating is 15 degrees, and the gradient of the corresponding carrier is 15 degrees. The 80-degree large-angle abnormal refraction effect of the super-structured grating is shown in fig. 14, the thickness of the titanium dioxide film layer is 450 nm, and the narrowest gap of the structure is 70 nm. After the super-structured grating is combined with the anti-reflection layer, the theoretical efficiency is 89.54%, and the efficiency is measured to be 83.6% through experiments. The efficiency values of the experiment and the simulation are similar, and the inclined dry etching process disclosed by the patent has the advantage of high sample quality, and the performance of an optimization target can be improved by designing the micro-nano structure based on the process.

Example 7

Based on embodiment 1, in this embodiment, different materials are used to perform etching of the inclined micro-nano structure according to the steps of embodiment 1, and the obtained inclined morphology is shown in fig. 15, and it can be seen that the slot-shaped carrier containing the isolated metal mesh of this embodiment can regulate and control the movement direction of ions in the dry etching cavity by controlling the sheath potential above the carrier, and is suitable for any material with anisotropic dry etching process.

Example 8

In this embodiment, based on embodiment 1, the oblique etching step of embodiment 1 is used in combination with different photoresist masks, and a silicon grating structure with asymmetric left and right can be obtained as shown in fig. 16.

The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.

Claims

1. A preparation method of an inclined micro-nano structure is characterized by comprising the following steps:

Step S1, preparing a material film layer to be etched on a substrate, wherein the material of the material film layer to be etched is titanium dioxide;

S2, preparing a patterned mask layer on the material film layer to be etched;

Step S3, placing the sample of the patterned mask layer prepared in the step S2 on an inclined plane of a groove-shaped carrier, placing the groove-shaped carrier on a lower electrode of a cavity of a dry etching machine, and etching the inclined plane upwards, wherein the inclined plane and the horizontal plane form an included angle of 5-70 degrees in the groove-shaped carrier, and a metal isolation net is covered on an opening of the groove-shaped carrier;

Step S4, removing the residual mask layer;

step S3, argon is introduced in the etching process, wherein the flow rate of the argon is 1sccm-40sccm;

in step S3, the radio frequency source power of the dry etching machine is 50W-400W.

2. The method of claim 1, wherein the dry etching tool is an inductively coupled plasma etching apparatus or a reactive ion etching apparatus.

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

4. The method of manufacturing a tilted micro-nano structure according to claim 3, wherein the patterned mask layer comprises a photoresist mask layer or a hard mask layer.