A manufacturing method of triple lithography based on a three-layer hybrid mask to realize the manufacturing of a fractal micro-nano structure with aerodynamic drag reduction imitating sand ridges

Abstract

The present invention discloses a method for manufacturing a fractal micro-nano structure with aerodynamic drag reduction imitating sand dunes by using triple lithography based on a three-layer hybrid mask. In this method, a special lithography sequence is designed by selecting three-layer mask materials with gradually decreasing chemical activity, and a hybrid mask sequence combination of metal and non-metal materials such as silicon oxide, aluminum, and photoresist is selected as the etching mask for the fractal micro-nano structure with aerodynamic drag reduction imitating sand dunes. The selection of this mask material comprehensively considers the compatibility of the metal mask in the inductively coupled plasma etching process, the controllability and precision of the process effect, the complexity of the process, and the cost of the process. Different from the idea of performing lithography once and etching once in the traditional process, the present invention proposes that after the three-layer hybrid mask is prepared by spin-coating lithography process, the cycle of repeating etching and removing the mask is carried out by utilizing the property that the chemical activity of the designed three-layer hybrid mask decreases successively, so as to complete the preparation of the three-layer composite micro-nano structure.

Description

Technical Field

[0001] The present invention relates to a technology based on MEMS (Micro-Electro-Mechanical System), and particularly to a method for fabricating a multi-scale multi-layer composite micro-nano structure array in micro-nano electronic processes. Background Art

[0002] In practical engineering problems, many industries often face challenges brought by fluid resistance and biological contamination. The patent with publication number CN108357665A titled "A Pneumatic Drag Reduction Fractal Micro-Nano Structure Imitating Sand Ripples" points out that the pneumatic drag reduction fractal micro-nano structure imitating sand ripples has the characteristic of good drag reduction performance. Therefore, realizing the fabrication of the pneumatic drag reduction fractal micro-nano structure imitating sand ripples is of great significance for solving engineering application problems in industries such as biomedicine, ships, pipelines, energy, aircraft, and biological contamination.

[0003] The manufacturing methods of micro-nano structures depend on many factors, such as precision, cost, geometry, scale, substrate, and sample size. Patents represented by manufacturing technologies such as the patent with publication number CN113635553A titled "A 3D Printing System and Method", the patent with publication number CN113547206A titled "A Laser Etching Device, Method, and System", the patent with publication number CN108102913A titled "A Three-Dimensional Cell Culture Chip Based on Soft Lithography Technology, Its Preparation Method, and Application", and the patent with publication number CN113707835A titled "A Method for Preparing Nanoimprint Patterning Quantum Dot LEDs" have fabricated micro-nano structures with various morphologies. However, the pneumatic drag reduction fractal micro-nano structure imitating sand ripples is a three-dimensional multi-layer composite micro-nano structure array, with the structural scale ranging from nanometers to hundreds of micrometers, and the side length dimension of the sample for drag reduction research should be at least on the order of 10 cm. Existing methods are difficult to achieve. How to realize the fabrication of such a complex-shaped pneumatic drag reduction fractal micro-nano structure imitating sand ripples is an important problem faced by its scientific research and practical applications.

[0004] Therefore, the present invention proposes a triple lithography method based on a three-layer hybrid mask to achieve precise and controllable fabrication of the pneumatic drag reduction fractal micro-nano structure imitating sand ripples. A combination of three mask materials with gradually decreasing chemical activity, namely silicon oxide, aluminum, and photoresist, is selected as the etching mask for the pneumatic drag reduction fractal micro-nano structure imitating sand ripples, and corresponding special lithography sequences are designed according to the different chemical activities of different materials. By solving the uniformity and lateral etching problems of the aluminum mask, the wet etching process of metallic aluminum under the influence of the hybrid mask is optimized. The invention can provide an effective means for scientific research or industrial production of drag reduction structures. Summary of the Invention

[0005] The present invention provides a method for precisely controllably preparing a multi-scale multi-layer composite micro-nano structure. The feature is that a triple photolithography method based on a three-layer hybrid mask with sequentially decreasing chemical activity is adopted by the spin coating process to achieve a high degree of selectivity in the process, thus solving the manufacturing problem of the aerodynamic drag reduction fractal micro-structure imitating sand dunes and providing a technical basis for realizing the preparation of more complex cross-scale multi-layer composite micro-nano functional structures.

[0006] The technical solution of the present invention is: a method for fabricating a multi-layer composite micro-nano functional structure, including the following steps:

[0007] In the present invention, the following definitions are made. The aerodynamic drag reduction fractal micro-nano structure imitating sand dunes is defined as the first, second, and third layer structures from top to bottom, and the three-layer hybrid mask is defined as the first, second, and third layer etching masks from the inside to the outside.

[0008] Step 1: Clean the silicon wafer using the standard cleaning process.

[0009] Step 2: Deposit a silicon oxide layer with a thickness of hundreds of nanometers on the surface of the silicon wafer. The deposition method is preferably low-pressure chemical vapor deposition (LPCVD).

[0010] Step 3: Spin coat a layer of photoresist with a thickness of several micrometers on the surface of the silicon wafer, and do so for each photolithography hereafter. Using the mask plate of the first layer structure pattern, after the first photolithography, dry-etch the silicon oxide with the patterned photoresist as the mask to pattern the silicon oxide, remove the photoresist, and use the patterned silicon oxide as the first layer etching mask. The etching method is preferably reactive ion etching (RIE).

[0011] Step 4: After completing Step 3, sputter a layer of aluminum metal with a thickness of hundreds of nanometers on its surface using a magnetron sputtering instrument.

[0012] Step 5: Using the mask plate of the second layer structure pattern, after the second photolithography, pattern the aluminum metal with the second patterned photoresist as the mask by wet etching and use it as the second layer etching mask. The traditional aluminum wet etching process needs to be carried out at a reaction temperature of 80 °C and in an ultrasonic environment. In order to minimize the influence of temperature on the mask and the influence of the adhesion between mask layers on the process, in this wet etching process of aluminum, first soak the photolithographed silicon wafer in deionized water at room temperature, and then put the silicon wafer into the aluminum etching solution. During this period, gently brush the surface of the silicon wafer with a soft brush in the same direction, so as to pattern the aluminum metal without affecting other mask layers.

[0013] Step 6: Using the mask plate of the third layer structure pattern, after the third photolithography, pattern the photoresist for the third time and use it as the third layer etching mask. After this step, the composite preparation of the three-layer metal and non-metal material hybrid mask with sequentially decreasing chemical activity from the third layer mask material to the first layer mask material is completed.

[0014] Step 7: Using the inductively coupled plasma etching system (ICP) with the third-layer etching mask as a mask for etching, the third-layer structure is formed, and the third-layer etching mask is removed. Due to the previously designed decreasing order of chemical properties from the third-layer mask material to the first-layer mask material, only the third-layer etching mask will be removed in this step.

[0015] Step 8: After completing Step 7, using the inductively coupled plasma etching system (ICP) with the second-layer etching mask as a mask for etching, the second-layer structure is formed, and the second-layer etching mask is removed with aluminum etchant. Due to the previously designed decreasing order of chemical properties, only the second-layer etching mask will be removed in this step.

[0016] Step 9: After completing Step 8, using the inductively coupled plasma etching system (ICP) with the first-layer etching mask as a mask for etching, the first-layer structure is formed, and the first-layer etching mask is removed. Due to the previously designed decreasing order of chemical properties, only the first-layer etching mask will be removed in this step, and finally the preparation of the silicon-based aerodynamic drag reduction fractal micro-nano structure imitating sand dunes is completed.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. In order to realize the preparation of a three-dimensional aerodynamic drag reduction fractal micro-nano structure imitating sand dunes, a three-layer photolithography method based on a three-layer hybrid mask is proposed. Three mask materials with sequentially decreasing chemical activities are selected to design a special photolithography sequence, and a mixed mask sequence combination of metal and non-metal materials such as silicon oxide, aluminum, and photoresist is selected as the etching mask for the aerodynamic drag reduction fractal micro-nano structure imitating sand dunes. The selection of this mask material comprehensively considers the compatibility of the metal mask in the inductively coupled plasma etching process, the controllability and accuracy of the process effect, the complexity of the process, and the cost of the process. Different from the idea of lithography once and etching once in the traditional process, the present invention proposes to use the spin-coating photolithography process to complete the compound preparation of the three-layer hybrid mask, and then use the property of sequentially decreasing chemical activities of the designed three-layer hybrid mask to repeat the cycle of etching and removing the mask to complete the preparation of the three-layer composite micro-nano structure. During this process, according to the design of sequentially decreasing chemical activities of the three-layer hybrid mask, it can be ensured that when etching is completed using each layer of mask, removing the corresponding mask will not affect the remaining masks. The present invention provides a new direction for accurately and controllably preparing aerodynamic drag reduction fractal micro-nano structures imitating sand dunes that can be used in scientific research and practical applications.

[0019] 2. The present invention optimizes the wet etching process of metallic aluminum under the influence of a hybrid mask. The traditional wet etching process of aluminum requires a reaction temperature of 80 °C and an ultrasonic environment. Different from the traditional process, in order to minimize the influence of temperature on the mask and the influence of the adhesion between mask layers on the process, the process of wet etching metallic aluminum in this process is carried out at room temperature and in a non-ultrasonic environment. To solve the problems of uniformity and lateral etching during the aluminum mask etching process at room temperature and in a non-ultrasonic environment, the present invention proposes to first soak the silicon wafer in ionized water to form a water film on the surface. Since water has good fluidity, it is beneficial for the discharge of the gas generated during the initial reaction. At the same time, during the etching process, low-frequency perturbation is used to replace high-frequency vibration to timely release the generated gas and balance the local concentration of the etchant. This invention can provide an effective means for scientific research or industrial production of drag reduction structures. Detailed implementation mode

[0020] Implementation case:

[0021] In this embodiment, a preparation method of a sand dune-like pneumatic drag reduction fractal micro-nano structure is given, including the following steps:

[0022] Step 1: Wash the silicon wafer with H 2 SO 4 and H 2 O 2 with a volume ratio of 4:1, and dry it at 150 °C for 10 minutes to clean the 4-inch silicon wafer.

[0023] Step 2: Deposit a 200-nm-thick silicon oxide layer on the surface of the silicon wafer using a low-pressure chemical vapor deposition device (LPCVD).

[0024] Step 3: Spin-coat about 3 μm thick photoresist EPI680 on the silicon wafer, and then perform soft baking on a hot plate at 110 °C for 30 s. Then irradiate with ultraviolet light to form a micro-nano structure graphic array, develop it in MIF700 developer for 30 s, rinse with deionized water, and dry with nitrogen. Then perform hard baking on a hot plate at 120 °C for 3 minutes. Using the mask plate of the first-layer structure pattern, after the first lithography, use a reactive ion etching device (RIE) to dry-etch the silicon oxide with the patterned photoresist as the mask to pattern the silicon oxide, remove the photoresist, and use the patterned silicon oxide as the first-layer etching mask.

[0025] Step 4: After completing Step 3, sputter a 150-nm-thick metallic aluminum layer on its surface using a magnetron sputtering instrument.

[0026] Step 5: Using the mask of the second-layer structure pattern, after repeating the photolithography process in Step 3, soak the photolithographed silicon wafer in deionized water at room temperature. Stir the poured aluminum etchant evenly, then place the silicon wafer into it. There are obvious bubbles generated during the etching process. During this period, gently brush the surface of the silicon wafer with a soft brush in the same direction. After about 200 s, accompanied by an obvious darkening in color, the patterning of the metal aluminum is completed with the second-patterned photoresist as the mask and used as the second-layer etching mask.

[0027] Step 6: Using the mask of the third-layer structure pattern, repeat the photolithography process in Step 3 again, and pattern the photoresist for the third time, which is used as the third-layer etching mask. In this way, the composite preparation of the three-layer metal and non-metal material hybrid mask with the chemical activity decreasing successively from the third-layer mask material to the first-layer mask material is completed.

[0028] Step 7: Use an inductively coupled plasma etching system (ICP) to vertically etch the silicon to a depth of 40 μm with the third-layer etching mask (patterned photoresist) as the mask, and the third-layer structure is formed. Then use acetone and alcohol to wet-etch the photoresist, and these two solvents will not affect the silicon oxide and metal aluminum masks.

[0029] Step 8: After completing Step 7, use the inductively coupled plasma etching system (ICP) to vertically etch the silicon for the second time by 20 μm with the second-layer etching mask (patterned metal aluminum) as the mask, and the second-layer structure is formed. Then use the aluminum etchant to remove the remaining metal aluminum. The aluminum etchant does not react with silicon oxide and will not affect the silicon oxide mask.

[0030] Step 9: After completing Step 8, use the inductively coupled plasma etching system (ICP) to vertically etch the silicon for the third time by 10 μm with the first-layer etching mask (patterned silicon oxide) as the mask, and the first-layer structure is formed. Then use hydrofluoric acid to remove the remaining silicon oxide, and finally the preparation of the silicon-based aerodynamic drag reduction fractal micro-nano structure imitating sand dunes is completed.

Claims

1. A manufacturing method of triple lithography based on a three - layer hybrid mask to achieve a fractal micro - nano structure for aerodynamic drag reduction of sand - dune - like patterns, characterized in that, the fractal micro - nano structure for aerodynamic drag reduction of sand - dune - like patterns is defined as the first, second, and third layer structures from top to bottom, and the three - layer hybrid mask is defined as the first, second, and third etching masks from inside to outside. The manufacturing method includes the following steps: Step 1: Clean the silicon wafer using the standard cleaning process. Step 2: Deposit a silicon oxide layer with a thickness of hundreds of nanometers on the silicon wafer surface. Step 3: Spin - coat a photoresist layer with a thickness of several micrometers on the silicon wafer surface, and do the same for each subsequent lithography. Use the mask of the first - layer structure pattern. After the first lithography, dry - etch the silicon oxide with the patterned photoresist as the mask to pattern the silicon oxide, remove the photoresist, and use the patterned silicon oxide as the first - layer etching mask. Step 4: After completing Step 3, sputter a metal aluminum layer with a thickness of hundreds of nanometers on the silicon wafer surface. Step 5: Use the mask of the second - layer structure pattern. After the second lithography, pattern the metal aluminum with the second - patterned photoresist as the mask by wet etching method, and use it as the second - layer etching mask. Step 6: Use the mask of the third - layer structure pattern. After the third lithography, pattern the photoresist for the third time and use it as the third - layer etching mask. So far, the composite preparation of the three - layer metal - and - non - metal material hybrid mask with the chemical activity decreasing successively from the third - layer mask material to the first - layer mask material is completed. Step 7: Use the inductively coupled plasma etching system (ICP) to etch with the third - layer etching mask as the mask to form the third - layer structure, and remove the third - layer etching mask. Due to the previously designed sorting of the chemical properties decreasing successively from the third - layer mask material to the first - layer mask material, only the third - layer etching mask will be removed in this step. Step 8: Use the inductively coupled plasma etching system (ICP) to etch with the second - layer etching mask as the mask to form the second - layer structure, and remove the second - layer etching mask with aluminum etching solution. Due to the previously designed sorting of the chemical properties decreasing successively, only the second - layer etching mask will be removed in this step. Step 9: Use the inductively coupled plasma etching system (ICP) to etch with the first - layer etching mask as the mask to form the first - layer structure, and remove the first - layer etching mask. Due to the previously designed sorting of the chemical properties decreasing successively, only the first - layer etching mask will be removed in this step. So far, the preparation of the silicon - based fractal micro - nano structure for aerodynamic drag reduction of sand - dune - like patterns is completed.

2. A manufacturing method of triple lithography based on a three - layer hybrid mask to achieve a fractal micro - nano structure for aerodynamic drag reduction of sand - dune - like patterns as described in claim 1, characterized in that, the deposition method in Step 2 is preferably low - pressure chemical vapor deposition (LPCVD).

3. A manufacturing method of triple lithography based on a three - layer hybrid mask to achieve a fractal micro - nano structure for aerodynamic drag reduction of sand - dune - like patterns as described in claim 1, characterized in that, the etching method in Step 2 is preferably reactive ion etching (RIE).

4. A manufacturing method of triple lithography based on a three - layer hybrid mask to achieve a fractal micro - nano structure for aerodynamic drag reduction of sand - dune - like patterns as described in claim 1, It is characterized in that The specific process of the wet etching of aluminum in step 5 is as follows: at room temperature, first soak the lithographed silicon wafer in deionized water, and then put the silicon wafer into the aluminum etching solution. During this period, gently brush the surface of the silicon wafer with a soft brush in the same direction.