阅读说明：本技术 一种超高深宽比的硅纳米针阵列的制备方法 (Preparation method of silicon nanoneedle array with ultra-high depth-to-width ratio ) 是由 涂学凑 孟庆雨 刘梦欣 康琳 张蜡宝 贾小氢 赵清源 陈健 吴培亨 于 2019-10-30 设计创作，主要内容包括：本发明公开了一种超高深宽比的硅纳米针阵列的制备方法,在硅衬底上旋涂MMA和PMMA A2双层光刻胶；对涂覆MMA和PMMA A2双层光刻胶的硅衬底进行电子束曝光,在硅衬底上制作抗蚀剂图形；对形成抗蚀剂图形的硅衬底进行电子束蒸发,在硅衬底上沉积一层Al薄膜；对沉积Al薄膜后的硅衬底进行剥离,得到沉积在硅衬底上的Al薄膜阵列,为后续ICP刻蚀工艺提供掩膜；对覆盖Al掩膜的硅衬底进行ICP硅刻蚀,制作硅纳米针阵列结构。通过本发明工艺流程能够稳定地获得超高深宽比的硅纳米针阵列结构,单个硅纳米针形态良好,侧壁光滑,最小针尖直径达到10nm,深宽比可达1450。(The invention discloses a preparation method of a silicon nanoneedle array with an ultra-high aspect ratio, which comprises the steps of spin-coating MMA and PMMA A2 double-layer photoresist on a silicon substrate; carrying out electron beam exposure on the silicon substrate coated with the MMA and PMMA A2 double-layer photoresist, and manufacturing a resist pattern on the silicon substrate; carrying out electron beam evaporation on the silicon substrate with the resist pattern formed, and depositing an Al film on the silicon substrate; stripping the silicon substrate on which the Al film is deposited to obtain an Al film array deposited on the silicon substrate and provide a mask for a subsequent ICP etching process; and carrying out ICP silicon etching on the silicon substrate covered with the Al mask to manufacture the silicon nanoneedle array structure. The process flow can stably obtain the silicon nanometer needle array structure with ultra-high depth-to-width ratio, the single silicon nanometer needle has good state and smooth side wall, the minimum needle point diameter reaches 10nm, and the depth-to-width ratio can reach 1450.)

1. A preparation method of a silicon nanoneedle array with ultra-high aspect ratio is characterized by comprising the following steps:

step 1, spin coating MMA and PMMA A2 double-layer photoresist on a silicon substrate;

step 2, carrying out electron beam exposure on the silicon substrate coated with the MMA and PMMA A2 double-layer photoresist, and manufacturing a resist pattern on the silicon substrate;

step 3, performing electron beam evaporation on the silicon substrate with the resist pattern, and depositing an Al film on the silicon substrate;

step 4, stripping the silicon substrate on which the Al film is deposited to obtain an Al film array deposited on the silicon substrate, and providing a mask for a subsequent ICP etching process;

and 5, performing ICP silicon etching on the silicon substrate covered with the Al mask to manufacture the silicon nanoneedle array structure.

2. The method for preparing the silicon nanoneedle array with ultra-high aspect ratio as claimed in claim 1, wherein before the double-layer photoresist of MMA and PMMA A2 is spin-coated on the silicon substrate, the pure silicon substrate is ultrasonically cleaned with acetone, alcohol and deionized water for 5-8 minutes, and then the residual moisture on the surface is blow-dried by a nitrogen gun.

3. The method for preparing the silicon nanoneedle array with ultra-high aspect ratio as claimed in claim 1, wherein in step 1, an MMA photoresist is spin-coated on a silicon substrate, and then the silicon nanoneedle array is placed on a constant temperature baking platform to be baked, and then a layer of PMMA a2 photoresist is spin-coated and baked.

4. The method for preparing the silicon nanoneedle array with ultra-high aspect ratio as claimed in claim 1, wherein only one exposure is required in step 2, and the exposure dose of the electron beam exposure step is optimized to 750 μ C/cm²。

5. The method for preparing the silicon nanoneedle array with ultra-high aspect ratio as claimed in claim 1, wherein the sample after electron beam exposure is placed in a solution of methyl isobutyl (methyl) ketone and isopropanol at a ratio of 1:3 for development for 3min, then placed in IPA solution for fixation for 1min, finally immersed in deionized water for 10s, taken out and dried with a nitrogen gun to remove residual moisture on the surface of the sample, and then subjected to electron beam evaporation to prepare the Al thin film.

6. The method as claimed in claim 1, wherein in step 3, the thickness of the Al thin film is controlled to be 300-350 nm.

7. The method for preparing the silicon nanoneedle array with ultra-high aspect ratio as claimed in claim 1, wherein in step 4, the sample is immersed in the N-methylpyrrolidone solution, heated in a water bath at 80 ℃ for 60min, and then ultrasonically stripped by sequentially placing the sample in acetone, alcohol and deionized water, and finally the Al thin film array deposited on the silicon substrate is left.

8. The method as claimed in claim 1, wherein in step 5, the pressure in ICP silicon etching is controlled at 20mtorr, the temperature is 10 ℃, the RF power is 700-.

9. The method as claimed in claim 1, wherein in step 5, the gas for ICP silicon etching is SF₆And C₄F₈Wherein, SF₆The gas flow rate is 32Sccm, C₄F₈The gas flow was 40 Sccm.

Technical Field

The invention relates to the technical field of semiconductors, in particular to a method for preparing a silicon nanometer needle tip array with an ultra-high depth-to-width ratio by comprehensively using electron beam lithography, electron beam evaporation and Inductively Coupled Plasma (ICP).

Background

The nano-scale needle tip has very important and wide application in the fields of biomedical cell probes, single photon sources, electromagnetic wave absorbers, anti-reflection structures, quantum device preparation and the like. For example, in 2015, foreign scientists (NatureMaterials,14 (5)), 532-. The absorption rate of the broadband terahertz wave absorbing material based on the silicon nanoneedle array in 2016 (Chinese invention patent with application number of 201611243901.9) to terahertz waves is as high as 90%, and the defects of narrow absorption band width, poor stability, high manufacturing cost and the like of the existing terahertz wave absorber are overcome.

At present, the means for preparing the silicon nano needle is limited, and the common method is dry etching. When dry etching silicon, photoresist is usually used as an etching mask, but this method has many defects. If the positive photoresist polymethyl methacrylate (PMMA) is used as an etching mask, the exposure area is large, the exposure time is long, the etching resistance is poor, and the etching depth of more than 5 mu m is difficult to achieve. The negative photoresist Hydrogen Silsesquioxane (HSQ) is used as an etching mask, although the etching resistance is better than that of PMMA, molecular polymers formed after exposure and development are not easy to remove, the next process is polluted, the HSQ is expensive, the quality guarantee period is short, the process stability is poor, and the etching depth is less than 10 mu m. Other preparation methods, such as wet etching, thermal evaporation and focused ion milling, also have the problems of complex process, high preparation cost, difficult batch production and the like.

Disclosure of Invention

The invention aims to provide a preparation method of a silicon nanoneedle array with an ultra-high aspect ratio.

The technical solution for realizing the purpose of the invention is as follows: a preparation method of a silicon nanoneedle array with ultra-high aspect ratio comprises the following steps:

step 1, spin coating MMA and PMMAA2 double-layer photoresist on a silicon substrate;

step 2, carrying out electron beam exposure on the silicon substrate coated with the MMA and PMMAA2 double-layer photoresist, and manufacturing a resist pattern on the silicon substrate;

step 3, performing electron beam evaporation on the silicon substrate with the resist pattern, and depositing an Al film on the silicon substrate;

step 4, stripping the silicon substrate on which the Al film is deposited to obtain an Al film array deposited on the silicon substrate, and providing a mask for a subsequent ICP etching process;

and 5, performing ICP silicon etching on the silicon substrate covered with the Al mask to manufacture the silicon nanoneedle array structure.

Compared with the prior art, the invention has the remarkable advantages that: 1) the silicon nano needle array structure with ultra-high depth-to-width ratio can be stably obtained through the process flow, a single silicon nano needle has good state and smooth side wall, the minimum needle point diameter reaches 10nm, and the depth-to-width ratio can reach 1450; 2) the Al used as the mask has the advantages of long etching resistance time, stable process and the like, can realize the batch preparation of the silicon nanoneedle array structure with the ultrahigh depth-to-width ratio, and has lower preparation cost; 3) according to the invention, silicon nano-needle array structures with different heights and different needle point sizes can be conveniently obtained by changing the parameters of layout design and ICP etching.

Drawings

FIG. 1 is a schematic view of the process flow for preparing the silicon nanoneedle array with ultra-high aspect ratio of the present invention.

FIG. 2 is a design layout required for the electron beam exposure process steps of the present invention.

FIG. 3 is a Scanning Electron Microscope (SEM) image of the surface of a sample which has been subjected to deposition of an Al thin film but has not been subjected to exfoliation in accordance with the present invention.

FIG. 4 is a Scanning Electron Microscope (SEM) image of the surface of a sample after peeling according to the present invention.

FIG. 5 is a Scanning Electron Microscope (SEM) image of the overall topography of a sample etched under different etching conditions in accordance with the present invention.

FIG. 6 is a Scanning Electron Microscope (SEM) image of the overall morphology of a sample at various etching stages of the invention.

Fig. 7 is a Scanning Electron Microscope (SEM) image of the silicon nanoneedle array fabricated after etching according to the present invention.

FIG. 8 is a Scanning Electron Microscope (SEM) image of the tip of a silicon nanoneedle fabricated according to the present invention.

FIG. 9 is a Scanning Electron Microscope (SEM) image of the silicon nanoneedle tip size measurement made by the present invention.

Detailed Description

The invention is further illustrated by the following examples in conjunction with the accompanying drawings.

The preparation method of the silicon nanoneedle array with the ultra-high depth-to-width ratio mainly comprises the following micro-nano processing steps:

(1) ultrasonically cleaning a pure silicon wafer substrate by acetone, alcohol and deionized water for 5-8 minutes, then drying the residual moisture on the surface by a nitrogen gun, observing the surface under an optical microscope, and confirming that the surface is clean and has no obvious particles or impurities. If the substrate surface is not clean enough, the subsequent fabrication of the resist structure will be affected.

(2) MMA photoresist was spin-coated on the above silicon substrate, and then baked on a constant temperature bake table for the purpose of removing residual moisture in the photoresist. Then spin-coat a layer of PMMAA2 photoresist again in the same way and bake. Through a large number of experiments, the MMA and PMMAA2 are preferably spin-coated and baked by using the parameters in the table 1, and under the condition of the parameters, the MMA and PMMA glue layers are moderate in thickness, good in uniformity and strong in adhesive force. The double-layer photoresist process used in the step can bring great convenience to the subsequent stripping step.

TABLE 1 Electron Beam lithography Condition Table

(3) The sample is exposed by an electron beam, and FIG. 2 is a layout used in the electron beam exposure step of the present invention, the layout is made by L-Edit software, the radius of the circle in the layout is 900nm, and the period is 5 μm. Although a bilayer resist is used, MMA and PMMA have similar exposure doses and therefore require only one exposure step. Through multiple exposure dose test experiments, the exposure dose of the electron beam exposure step is finally optimized to 750 mu C/cm². Under the exposure dose, the layout graph can be fully exposed, and the developed resist graph has high contrast and good quality. The preparation of the silicon nano needles with different heights can be realized by adjusting the size of the circular radius in the layout design, and the distance between circle centers can be adjusted for the preparation of the silicon nano needle array structures with different periods.

(4) And (3) placing the sample subjected to electron beam exposure into a solution with the ratio of methyl isobutyl (methyl) ketone (MIBK) to isopropyl alcohol (IPA) being 1:3 for development for 3min, then placing the solution into the IPA solution for fixation for 1min, finally immersing the solution into deionized water for 10s, taking the solution out, drying the residual moisture on the surface of the sample by using a nitrogen gun, and blowing the sample by using the air gun until the air outlet quantity of the air gun is not too large so as to avoid collapse of a resist pattern. Since MMA and PMMA are both positive photoresists, the circular pattern array region exposed by electron beams on the two layers of photoresist after development and fixation will be removed and other regions not exposed by electron beams will be retained under the exposure dose condition in the step (3).

(5) An Al thin film with the thickness of 300-350nm is evaporated on the sample by means of electron beam evaporation. FIG. 3 shows a scanning electron microscope image of the surface of the sample after deposition of the Al thin film, in which the circular depressed regions are deposited

The Al film is deposited on the silicon substrate, and the Al film is deposited on the double-layer photoresist in other areas.

(6) Immersing the sample in N-methylpyrrolidone solution, heating in water bath at 80 ℃ for 60min, then sequentially putting the sample into acetone, alcohol and deionized water, and stripping the Al film deposited on the photoresist by using an ultrasonic machine, and finally leaving the round Al film deposited on the silicon substrate. When the ultrasonic machine is used for stripping, attention must be paid to the fact that the power cannot be too high so as to avoid causing the shedding of Al deposited on the silicon substrate. Fig. 4 is a scanning electron microscope image of the surface of the sample after the stripping step, and it can be seen that only circular Al thin film arrays are left on the surface of the silicon substrate, and these Al thin film arrays will provide the required mask for the subsequent etching step.

(7) And carrying out ICP silicon etching on the sample with the surface covered with the circular array Al mask, wherein the specific etching conditions comprise gas type, gas flow, ICP power, RF power, pressure, temperature, etching time and the like. During etching, a thin layer of silicone grease can be coated on the back of the sample to increase heat conduction.

The silicon nanoneedle can be integrally manufactured into two parts, wherein one part is used for manufacturing a needle point structure at the top, and the other part is used for manufacturing a columnar supporting structure below the needle point. In ICP dry etching, different technological parameters can form structures with different appearances, and the design structure can be manufactured by utilizing the technical parameters. In the ICP etching process used by the invention, SF is adopted₆As an etching gas, at the same time, it is necessary to introduce C in an appropriate ratio due to the isotropic etching characteristic exhibited in the ICP dry etching₄F₈The gas is passivated.

A large number of process experiments find that the flow and the proportion of etching gas have the most obvious influence on the etching morphology, and particularly, when the flow proportion of the etching gas and the passivation gas is small, the column shape integrally presents a state of being thin at the top and thick at the bottom, and otherwise presents a state of being thick at the top and thin at the bottom. After a large number of experiments, four groups of stable and representative process parameters are summarized, and table 2 is data of the four groups of process parameters. The pictures marked with numbers 1, 2, 3 and 4 in fig. 5 respectively correspond to the sample morphology scanning electron microscope pictures of four groups of ICP etching comparative experiments in table 2. By adjusting the etching process parameters, the control of the overall shape of the silicon nano needle can be realized.

TABLE 2 Effect of different etching conditions on morphology

(8) The etched sample is observed by a scanning electron microscope, the appearance of the sample is observed, key parameter information is measured, process parameters are optimized according to results, and through a large number of experiments, the optimal process conditions used in the method are shown in table 3. Fig. 6 is a scanning electron microscope picture of the overall morphology of the silicon nanoneedle array after 8min, 25min, 45min and 55min of etching in the manufacturing process using the process parameters of table 3, and it can be seen that there are significant differences in the morphology at different etching stages. Fig. 7 is a scanning electron microscope picture of the silicon nanoneedle array prepared using the process conditions in table 3, and it can be seen that the prepared silicon nanoneedle array has smooth sidewall, complete morphology, uniform overall height and reached 14.5 μm. Fig. 8 is a scanning electron microscope picture of the tip portion of the silicon nanoneedle prepared using the process conditions in table 3. Fig. 9 is a scanning electron microscope photograph of a measurement of a tip portion of a silicon nanoneedle prepared using the process conditions in table 3, and it can be seen that the minimum size of the tip can reach 10 nm.

TABLE 3ICP etching Condition Table