CN109056049B - Preparation method of nano porous silicon biconcave lens - Google Patents
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Abstract
The invention discloses a preparation method of a nano porous silicon biconcave lens, which is characterized in that a platinum sheet which is conventionally used as an electrode is made into a hollow sphere, two symmetrical spherical crowns cut from the hollow sphere are made into electrodes, a silicon wafer is placed between the two spherical crown electrodes, two convex surfaces of the two spherical crown electrodes face the silicon wafer, and the silicon wafer divides corrosive liquid into two independent parts; firstly, a constant current source is adopted to carry out electric polishing on a silicon chip so that the front surface and the back surface of the silicon chip form the same concave spherical surface; and then two symmetrical spherical crown electrodes are replaced by parallel plate electrodes, and two surfaces of the silicon wafer are subjected to electrochemical corrosion to form the porous biconcave lens. The method can obtain the nano porous silicon biconcave lens, can be widely applied to micro-optical electromechanical systems, and makes a great contribution to the field of micro-optical electromechanical systems.
Description
Technical Field
The invention relates to the field of semiconductor technology and optical engineering, in particular to a preparation method of a nano porous silicon biconcave lens.
Background
In 1956, Uhlir found the existence of porous silicon when the silicon wafer was subjected to electrochemical polishing treatment in HF solution; in 1990, Canham discovered that porous silicon emits visible light at room temperature, which opens up a new era for the research of porous silicon, namely, the research stage of luminescent porous silicon at room temperature; the luminescence of porous silicon at room temperature shows the wide application prospect of silicon in the aspects of optoelectronics, optical devices, display technology and the like. Particularly, in 1996, the first realization of a silicon-based optoelectronic integrated prototype device by Hirschman is a milestone for the application and research of porous silicon.
The porous silicon film is a spongy porous material with a large specific surface area. The material has the advantages of low cost, good biocompatibility and complete compatibility with the existing integrated circuit process. Although porous silicon has attracted much attention as a high-quality sensor material since the 90 s in the 20 th century, the use of porous silicon materials for optical devices has been rare and is especially rare in the field of optical, mechanical and electrical integration research.
Micro-Electro-Mechanical systems (MEMS) are also called Micro-electromechanical systems, microsystems, micromachines, and the like. The micro-sensor micro-actuator is a high-tech device which integrates a micro-sensor, a micro-actuator, a micro-mechanical structure, a micro-power supply, a micro-energy source, a signal processing and control circuit, a high-performance electronic integrated device, an interface and communication into a whole, and has the size of several millimeters or less.
In recent years, with the rapid development of microelectronic technology, the sizes of electronic devices, MEMS accelerometers, MEMS microphones, micro motors, micro pumps, micro vibrators, MEMS optical sensors, MEMS pressure sensors, MEMS gyroscopes, MEMS humidity sensors, and MEMS gas sensors have become smaller and smaller. The micro-optical-mechanical-electrical system integration research is rapidly developing, silicon-based micro-optical, mechanical, electrical and integration technologies are highly regarded, micro-optical elements such as lenses, prisms and reflectors are important components of the micro-optical-mechanical-electrical system, and can convert, transmit and process micro-optical paths to achieve the purposes of light emission, light collection, light polarization, light interference and light scattering, but the research on the micro-optical elements such as micro-lenses, prisms and reflectors prepared by using porous silicon materials is still few.
There is a literature on a method for preparing an oxidized porous silicon optical waveguide prism by using polymethyl methacrylate (PMMA) to mask silicon and using a selective electrochemical etching process, so as to respectively prepare a converging lens and a diverging lens based on porous silicon. Such a waveguide prism can significantly converge and diverge the polarized light beam traveling in the waveguide. However, the method has complex process and low controllability, and is difficult to realize micro-opto-electro-mechanical system integration.
Disclosure of Invention
The invention aims to provide a preparation method of a nano porous silicon biconcave lens in order to realize the integration of silicon-based micro-optical, mechanical and electrical systems.
In order to achieve the purpose, the invention adopts the technical scheme that: a preparation method of a nanometer porous silicon biconcave lens is characterized in that a platinum sheet which is conventionally used as an electrode is made into a hollow sphere, two identical symmetrical spherical crowns cut from the hollow sphere are made into electrodes, two convex surfaces of the two spherical crowns face a silicon wafer, a silicon wafer is placed between the two spherical crown electrodes, the bottom surfaces of the two spherical crown electrodes are parallel to the plane where the silicon wafer is located, the central axis of the silicon wafer, the circle center of the spherical crown electrode and the central axis (three) of the spherical crown are superposed, the distances from the silicon wafer to the left spherical crown electrode and the right spherical crown electrode are equal, and the silicon wafer divides corrosive liquid into two independent parts; adopting a constant current source to perform electric polishing on the silicon chip so as to form the same concave spherical surface on the front and back surfaces of the silicon chip; and then replacing the two symmetrical spherical crown electrodes with parallel flat plate electrodes, and carrying out electrochemical corrosion on two surfaces of the silicon wafer to form the nano porous silicon concave lens.
The principle of the invention is as follows: the preparation of the nanometer porous silicon biconcave lens is divided into 2 processes, firstly, the silicon wafer is electropolished by using positive and negative large constant-current corrosion currents with the same size, on one hand, the front and the back surfaces of the silicon wafer are electropolished simultaneously under the condition of large constant-current corrosion current density (which is larger than the conventional electropolishing current of the silicon wafer), as the positive and negative constant corrosion currents with the same size are used and are spherical crown electrodes, the central axis of the two spherical crown electrodes is taken as the center, the farther away from the central axis, the smaller the corrosion current density is, and the slower the polishing speed of the silicon wafer is, the central axis of the silicon wafer is taken as the center, the shallower the polishing is the farther away from the central axis, and the same polishing current is applied to the front and the back surfaces of the silicon wafer, so that the same concave spherical surfaces are formed on the front. And secondly, after electropolishing is finished, replacing the two spherical crown electrodes with circular parallel plate electrodes, and simultaneously carrying out electrochemical corrosion on the front and back surfaces of the silicon wafer by using small positive and negative constant corrosion currents (which are smaller than the conventional electropolishing current of the silicon wafer) to form a porous silicon film until the whole silicon wafer is completely formed into a concave lens formed by porous silicon materials.
The radius of curvature of the two outer surfaces of the biconcave lens of the present invention can be varied by varying the radius R of the hollow sphere of the thin platinum sheet, the height H of the spherical cap, and the distance L between the planes of the bottoms of the two spherical caps, as well as the electropolishing conditions.
Preferably, the height H = 0.01-0.5R of the spherical crown of the platinum sheet used as the spherical crown electrode.
Preferably, the distance L =0.02~10R between the planes of the two platinum sheet spherical cap electrode bottoms.
The invention has the beneficial effects that: the method can obtain the nano porous silicon biconcave lens, can be widely applied to micro-optical electromechanical systems, and makes a great contribution to the field of micro-optical electromechanical systems.
Drawings
FIG. 1 is a schematic view of an electrolytic etching cell according to the present invention
The device comprises a sealing support, a corrosion groove, a silicon wafer, a spherical crown-shaped thin platinum sheet, a silicon wafer.
Detailed Description
The present invention will be further described with reference to the following examples. The present invention is not limited to the above-described embodiments, and any modifications and variations may be made by those skilled in the art without departing from the scope of the present invention. Therefore, the following embodiments may be modified or changed in a similar manner without departing from the scope of the invention.
Example one
The preparation method of the nano porous silicon biconcave lens specifically comprises the following steps:
1. selecting the silicon wafer type as P100A double-side polished circular silicon wafer having a resistivity of 0.01 Ω · cm and a thickness of 500 μm, two platinum (200 μm thick) spheres (radius of 2 cm) having a crown-bottom surface length = a silicon wafer diameter as an electrode; the silicon chip and the spherical crown-shaped thin platinum sheets 3 are completely immersed in electrolytic corrosion liquid for electrochemical corrosion, the plane where the silicon chip and the two spherical crown-shaped thin platinum sheets 3 are located is parallel, and the central axes of the silicon chip and the two spherical crown-shaped thin platinum sheets 3 are superposed, wherein the electrolytic corrosion liquid is prepared by the following steps of: the volume ratio of absolute ethyl alcohol to deionized water is 1:1: 2.
2. The circuit is connected, namely corrosive liquid is put in a corrosion tank 1, a silicon wafer 2 is fixed in the middle of the corrosion tank 1 through a sealing support 4, the silicon wafer 2 and the sealing support 4 divide the corrosive liquid in the corrosion tank 1 into two independent parts, 2 spherical crown-shaped thin platinum sheets 3 are symmetrically arranged at two ends in the corrosion tank 1 to serve as electrodes, the convex surfaces of the two spherical crown-shaped thin platinum sheets 3 face the silicon wafer 2, the distance L between the centers of the planes of the bottoms of the two spherical crown-shaped thin platinum sheets 3 is 0.25cm, the silicon wafer 2 and the spherical crown-shaped thin platinum sheets 3 (the corrosion diameter of the silicon wafer 2 is equal to the diameter of the circular plane projected by the bottom of the spherical crown-shaped thin platinum sheet 3 and is 2 cm) are all soaked in the corrosive liquid, the planes of the bottoms of the silicon wafer 2 and the two spherical crown-shaped thin platinum sheets 3 are parallel, the central axis of the silicon wafer 2 and the central axis of the spherical crown-shaped thin platinum sheets are superposed, a constant current source is arranged outside the corrosion tank 1, the constant current source is generated by any waveform generator G3101, the positive electrode and the negative electrode of the spherical crown-shaped thin platinum sheet are connected with a positive electrode through a positive electrode and a positive electrode, and a positive.
3. Polishing two sides of a silicon wafer to form concave silicon bodies: the constant current source is positive and negative square wave signals, the frequency is 10Hz, and the average polishing current is-120 mA/cm and 120mA/cm2The electropolishing time is 20Min, so that the silicon wafer is polished into a concave silicon body on the front and back surfaces simultaneously.
4. And (3) corroding the porous silicon on the surface of the silicon wafer for 20 minutes by using a 2% sodium hydroxide solution (prepared by sodium hydroxide and deionized water in a mass ratio of 1: 49) to form a two-sided concave silicon body.
5. Forming a porous silicon concave lens: two spherical crown electrodes are replaced by flat round platinum sheet electrodes (the thickness is 200 mu m), the constant current source is a positive square wave signal and a negative square wave signal, the frequency is 10Hz, and simultaneously, two groups of tests are carried out, the variation in the two groups of tests is the corrosion current density, and the corrosion current density is-50 mA/cm and 50mA/cm2-40 and 40mA/cm2And simultaneously forming porous silicon on two surfaces of the concave silicon body until the etching is finished to obtain the double-concave lens made of the porous silicon film material.
6. For convenience in studying the problem, we chose two sets of experiments whose experimental parameters and corresponding data are as follows:
| numbering | Polishing Current (mA/cm)2） | Polishing time (min) | Corrosion current (mA/cm)2） | Etching time (min) | Porosity degree | Center and edge thickness (mum) of porous silicon concave lens |
| ⑴ | 120 | 20 | 50 | 150 | 60% | ~325、420 |
| ⑵ | 120 | 20 | 40 | 187 | 55% | ~320、415 |
7. According to the relevant documents and combining the experimental conditions, the porosity of the double-sided concave lens formed by the two porous silicon thin films is about 60% and 55%, the thicknesses of the center and the edge of the double-sided concave lens are about 325 and 420 μm and about 320 and 415 μm respectively;
8. after the preparation of the nano porous silicon biconcave lens is finished, quickly putting the sample wafer of the porous silicon biconcave lens into high-purity deionized water for cleaning for 10 minutes to replace electrochemical corrosion liquid (hydrofluoric acid and water) and other reaction products in the porous silicon biconcave lens; then, soaking the porous silicon concave lens in a mixed solution of hydrogen peroxide and deionized water (the volume ratio is 2: 100) for post-treatment for 6 hours;
9. after the post-treatment is finished, washing with deionized water, and finally drying in the air;
10. and (5) obtaining a finished product after the product is qualified through inspection.
Example two
The preparation method of the nano porous silicon biconcave lens specifically comprises the following steps:
1. selecting the silicon wafer type as P100The double-sided polished round silicon wafer comprises a double-sided polished round silicon wafer with the resistivity of 0.01 omega cm and the thickness of 500 mu m, wherein the length of the crown bottom surfaces of two platinum sheets (with the thickness of 200 mu m) spheres (with the radius of 2 cm) is L = the diameter of the silicon wafer as an electrode, the silicon wafer and the spherical crown-shaped thin platinum sheet 3 are completely immersed in an electrolytic corrosion solution for electrochemical corrosion, the planes of the silicon wafer and the bottoms of the two spherical crown-shaped platinum sheets are parallel, the central axes of the silicon wafer and the spherical crown-shaped platinum sheet coincide, and the electrolytic corrosion solution is prepared from hydrofluoric acid, anhydrous ethanol and deionized water in a volume ratio of 1: 1.
2. And (3) connecting a circuit: the method is characterized in that corrosive liquid is placed in a corrosion tank 1, a silicon wafer 2 is fixed in the middle of the corrosion tank 1 through a sealing support 4, the silicon wafer 2 and the sealing support 4 divide the corrosive liquid in the corrosion tank 1 into two independent parts, two spherical crown-shaped thin platinum sheets 3 serving as electrodes are symmetrically arranged at two ends of the corrosion tank 1, the convex surfaces of the two spherical crown-shaped thin platinum sheets 3 face the silicon wafer 2, the distance between the centers of the planes where the bottoms of the two spherical crown-shaped thin platinum sheets 3 are located is 0.25cm, the silicon wafer 2 and the spherical crown-shaped thin platinum sheets 3 (the corrosion diameter of the silicon wafer 2 is equal to the diameter of the circular plane where the bottoms of the spherical crown-shaped thin platinum sheets 3 are located and is 2 cm) are all soaked in the corrosive liquid, the bottoms of the silicon wafer 2 and the two spherical crown-shaped thin platinum sheets 3 are parallel, and the central axis of the silicon wafer is coincident with the central. A constant current source is arranged outside the corrosion tank 1 and is generated by a TekVisa AFG3101 arbitrary waveform generator, the positive pole and the negative pole of the constant current source are connected with two spherical crown-shaped thin platinum sheet 3 electrodes by leads, and the positive pole and the negative pole of the current source form a current loop by corrosive liquid during work.
3. Polishing two sides of a silicon wafer to form concave silicon bodies: the constant current source is positive and negative square wave signals, the frequency is 10Hz, and the average polishing current is-100 mA/cm and 100mA/cm2The electropolishing time was 25Min, which allowed the silicon wafer to be simultaneously polished on both front and back sides to form a concave silicon body.
4. And (3) corroding the porous silicon on the surface of the silicon wafer for 20 minutes by using a 2% sodium hydroxide solution (prepared by sodium hydroxide and deionized water in a mass ratio of 1: 49) to form a two-sided concave silicon body.
5. Forming a porous silicon concave lens: two spherical crown electrodes are replaced by plane circular platinum sheet electrodes, the constant current source is a positive square wave signal and a negative square wave signal, the frequency is 10Hz, and simultaneously, two groups of tests are carried out, and the variation in the two groups of tests is the corrosion current density which is-50 mA/cm and 50mA/cm2-40 and 40mA/cm2And simultaneously forming porous silicon on both sides of the concave silicon body until the etching is finished to obtain the double-sided concave lens made of the porous silicon film material.
6. For convenience in studying the problem, we chose two sets of experiments whose experimental parameters and corresponding data are as follows:
| numbering | Polishing Current (mA/cm)2） | Polishing time (min) | Corrosion current (mA/cm)2） | Etching time (min) | Porosity degree | Center and edge thickness (mum) of porous silicon concave lens |
| ⑴ | 100 | 25 | 50 | 150 | 59% | ~315、410 |
| ⑵ | 100 | 25 | 40 | 185 | 54% | ~310、405 |
7. According to the relevant documents and combining the experimental conditions, the porosity of the concave lens formed by the two porous silicon films is about 59% and 54%, respectively, and the thicknesses of the center and the edge of the double concave lens are about 315 μm and 410 μm and 310 μm and 405 μm, respectively;
8. after the preparation of the nano porous silicon double-sided concave lens is finished, quickly putting the porous silicon double-sided concave lens sample into high-purity deionized water for cleaning for 10 minutes to replace electrochemical corrosion liquid (hydrofluoric acid and water) and other reaction products in the porous silicon double-sided concave lens; then, soaking the porous silicon double-sided concave lens in a mixed solution of hydrogen peroxide and deionized water (the volume ratio is 2: 100) for post-treatment for 6 hours;
9. after the post-treatment is finished, washing with deionized water, and finally drying in the air;
10. and (5) obtaining a finished product after the product is qualified through inspection.
Claims (3)
1. A preparation method of a nano porous silicon biconcave lens is characterized in that a platinum sheet which is conventionally used as an electrode is made into a hollow sphere, two symmetrical spherical crowns cut from the hollow sphere are made into electrodes, the height H = 0.01-0.5R of the spherical crown of the platinum sheet which is used as a spherical crown electrode is equal to the radius of the hollow sphere where the spherical crown electrode is located, a silicon wafer is placed between the two spherical crown electrodes, two convex surfaces of the two spherical crown electrodes face the silicon wafer, the bottom surfaces of the two spherical crown electrodes are parallel to the plane where the silicon wafer is located, the central axis of the silicon wafer and the circle center of the spherical crown electrode are superposed with the central axis of the spherical crown electrode, the distance between the silicon wafer and the left and right spherical crown electrodes is equal, the distance L = 0.02-10R between the bottoms of the two spherical crown electrodes is equal to the radius of the hollow sphere where the spherical crown electrode is located, a corrosion liquid is divided into two independent parts, the corrosion liquid is prepared from anhydrous ethanol and deionized water in a volume ratio of 1:1:2, the positive current and the negative current of the same and the positive current of the silicon wafer are changed into a positive current of the two concave crown electrodes and the negative current of the silicon wafer for polishing the silicon wafer, the two surfaces of the silicon wafer are changed into a constant current of the positive and the negative current of the positive and negative of the positive and the negative of the positive and negative.
2. The method for preparing a nanoporous silicon biconcave lens as claimed in claim 1, wherein the electropolishing comprises the steps of: firstly, electropolishing a silicon wafer by using positive and negative constant-current corrosion currents with the same size and larger than the conventional polishing current of the silicon wafer, on one hand, electropolishing the front and back surfaces of the silicon wafer simultaneously under the condition of normal large constant-current corrosion current density.
3. The method for preparing a nano-porous silicon biconcave lens according to claim 1 or 2, wherein the electrochemical etching comprises replacing two spherical cap electrodes with circular parallel plate electrodes after electropolishing, and simultaneously performing electrochemical etching on the front and back sides of the silicon wafer with constant etching current which is smaller than conventional silicon wafer polishing current and has the same positive and negative values to form a porous silicon film until the whole silicon wafer forms the biconcave lens made of porous silicon material.
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