CN105655419A - Method for preparing black silicon material - Google Patents

Abstract

The invention belongs to the field of black silicon material preparation, and in particular relates to a method for preparing a selenium-silicon composite film by means of thermal evaporation and magnetron sputtering, and using femtosecond laser etching to prepare black silicon. The invention uses a layer of silicon film sputtered on the selenium film as a protective layer in the existing process, which reduces the volatilization of chalcogen elements in the femtosecond etching process, increases the doping content, and can prevent the introduction of laser pulse irradiation. The impurity Se diffuses to the grain boundary, so as to maintain its doping concentration on the surface, so as to improve the absorption rate of black silicon. The absorption rate of the black silicon prepared by using the method is higher than 95% in the 400-1100nm wave band, and the absorption rate in the 1100-2200nm wave band is higher than 90%. Compared with the black silicon material prepared by thermally evaporating a layer of selenium film without covering the silicon protective layer, the absorption rate of the black silicon prepared by the method in the near-infrared band is significantly improved.

Description

A kind of method for preparing black silicon material

technical field

The invention belongs to the field of black silicon material preparation, and in particular relates to a method for preparing a selenium-silicon composite film by means of thermal evaporation and magnetron sputtering, and using femtosecond laser etching to prepare black silicon.

Background technique

Crystalline silicon is rich in resources and has the advantages of easy acquisition, easy purification, high temperature resistance, and easy doping. It plays an important role in the semiconductor industry and has a wide range of applications in the fields of detectors, sensors, and solar cell preparation. However, the inherent defects of crystalline silicon limit its application in optoelectronic devices. Crystalline silicon is an indirect bandgap material with a forbidden band width of 1.124eV at room temperature and a cut-off wavelength of crystalline silicon absorption of 1100nm. When the incident light wavelength is greater than 1100nm, the absorption rate and responsivity of crystalline silicon will be greatly reduced. Therefore, when detecting these wave bands, germanium or III-V compound materials are often used to prepare detectors.

In 1998, Mazur et al. of Harvard University irradiated silicon wafers with a femtosecond laser in an atmosphere of sulfur hexafluoride (SF ₆ ), and formed a micron-scale orderly arrangement of pointed cone-like forest structures on the surface of silicon wafers. This structure Significantly reduces surface reflectivity. Due to its black appearance, this material is named "black silicon". Black silicon has an absorption rate higher than 90% in the near-ultraviolet-near-infrared (200-2500nm) band, has ultra-high photoconductive gain, and the photocurrent generated is hundreds of times that of traditional silicon materials, and it is different from existing silicon materials Good process compatibility. Therefore, black silicon is a very popular material at present, attracting many domestic and foreign researchers to conduct research.

The black silicon prepared by the traditional wet etching process has no doping, although the absorption rate in the visible light band is higher than 90%, the improvement of the absorption rate in the infrared band is not obvious. The absorption rate of black silicon prepared by using femtosecond laser under SF ₆ background gas in the near-infrared band can also reach more than 90%. Studies have shown that during the process of femtosecond laser scanning silicon substrates, supersaturated doped silicon materials with sulfur elements can be formed, and impurity energy bands can be formed in the silicon forbidden band and overlap with the silicon band tail, reducing the silicon forbidden band width to 0.4eV , Extend the absorption frequency band to achieve high absorption in the infrared band.

This doping method needs to be carried out in a gas environment, and the composition of doping elements is limited. In 2006, MichaelA.Sheehy spin-coated a layer of chalcogen powder on a silicon substrate as a doping source by means of powder spin coating, and used femtosecond etching to achieve doping of other chalcogen elements (selenium, tellurium) . Studies have shown that selenium and tellurium can also introduce impurity levels in the black silicon surface forbidden band to increase the absorption rate in the infrared band. In 2009, BrainR.Tull improved the preparation method of the chalcogen film layer, and used thermal evaporation to evaporate the chalcogen film layer on the silicon substrate as a doping source. Compared with the method of powder spin coating, the film prepared by thermal evaporation method has better contact with the silicon substrate and has better uniformity. However, during the femtosecond laser etching process, a large number of impurities absorb pulse energy and volatilize, which affects the doping content of black silicon.

Contents of the invention

In view of the above problems or deficiencies, on the basis of thermal evaporation coating, the present invention deposits a layer of silicon film as a protective layer by means of magnetron sputtering, and then performs femtosecond laser etching of silicon; the protective layer can reduce the amount of femtosecond laser The volatilization of impurity elements in the etching process increases the doping concentration, thereby achieving the purpose of increasing the infrared absorption rate.

The technical solutions disclosed by the invention include:

A method for preparing black silicon material, comprising the steps of:

Step 1, cleaning the silicon substrate to obtain a clean silicon substrate for use;

Step 2. Deposit a layer of selenium film on the surface of the silicon substrate by thermal evaporation as an impurity source, and the thickness of the selenium film is 50-300nm;

Step 3, using magnetron sputtering to prepare a layer of silicon film on the silicon substrate selenium film prepared in step 2 as a silicon protective layer, and the thickness of the silicon film is 50-150nm;

Step 4. Perform femtosecond laser etching on the silicon substrate prepared in step 3 in a nitrogen atmosphere of 0.2-0.8 atm. During femtosecond laser etching, the incident light energy density is 1-10kJ/m ² , and the scanning speed is 0.5-10mm /s.

Step 5, putting the silicon substrate after scan etching into hydrofluoric acid to remove the silicon oxide layer on the surface; washing it with deionized water and blowing it dry with nitrogen to obtain black silicon.

The silicon substrate is an N-type substrate;

The step 1 is specifically to clean the silicon substrate using the RCA standard cleaning method; then put the cleaned silicon substrate into acetone and ultrasonically remove the residual organic matter on the surface; finally, ultrasonically clean the silicon substrate in deionized water, and Blow dry under nitrogen atmosphere.

The absorption rate of the black silicon prepared by the above method is higher than 95% in the 400-1100nm wave band, and the absorption rate in the 1100-2200nm wave band is higher than 90%.

In the present invention, by introducing a silicon film as an impurity source protective layer on the basis of the existing technology, that is, the silicon film sputtered on the selenium film is used as a protective layer, which can reduce the volatilization of chalcogen elements in the femtosecond etching process and increase the doping rate. impurity content, and can prevent the impurity Se introduced by laser pulse irradiation from diffusing to the grain boundary, so as to maintain its doping concentration on the surface, so as to improve the absorption rate of black silicon.

In summary, the beneficial effect of the present invention is that the black silicon prepared by the method has an absorption rate higher than 95% in the 400-1100nm band, and an absorption rate higher than 90% in the 1100-2200nm band. Compared with the doped black silicon material prepared by thermally evaporating the selenium film without covering the silicon protective layer, the absorptivity of the doped black silicon prepared by the method in the near-infrared band is obviously improved.

Description of drawings

Fig. 1 is the process flow diagram of the method for manufacturing black silicon material of embodiment;

Fig. 2 is the schematic diagram after the thermal evaporation selenium film of embodiment and sputtering silicon film;

3 is a schematic cross-sectional view of the silicon substrate material after femtosecond laser etching in the embodiment;

Fig. 4 is the absorption spectrogram of silicon substrate material after femtosecond laser etching of embodiment;

Reference signs: 1—silicon substrate, 2—selenium film, 3—silicon film, 4—doped black silicon structure formed after laser scanning etching.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings.

FIG. 1 is a schematic flow diagram of this embodiment.

Step 1: Obtain a clean silicon substrate.

N-type silicon chip doped with phosphorus is selected as the substrate material. Then use the RCA standard cleaning method to clean the silicon substrate to remove the surface oxide. Then put the cleaned silicon substrate into acetone for 10 minutes to sonicate to remove the residual organic matter on the surface. Finally, the silicon substrate was sonicated in deionized water for 5 minutes and dried under nitrogen atmosphere.

Step 2: Thermally evaporated selenium film

Put the silicon substrate cleaned in step 1 on the workbench of the vacuum evaporation device, and evacuate the vacuum of the vacuum chamber to 6×10 ^-4 Pa. Start the evaporation unit, and evaporate a layer of 100nm selenium film on the polished surface of the silicon substrate as an impurity source.

Step 3: Magnetron sputtering silicon film

Put the silicon substrate prepared in step 2 on the walking unit in the vacuum chamber of the magnetron sputtering machine, first evacuate the vacuum degree of the vacuum chamber to 5×10 ^-4 Pa, and then pass in argon gas until the vacuum chamber is vacuumed. The degree is 5×10 ^-1 Pa. Turn on the power, adjust the power to argon ignition, turn on the walking unit, and sputter a layer of 50nm silicon film on the selenium film as a protective layer.

The material structure of the silicon substrate processed in step 3 is shown in FIG. 2 . The silicon substrate is 1, the selenium film is 2, and the silicon film is 3.

Step 4: Femtosecond laser scanning etching black silicon

Put the silicon substrate prepared in step 3 into a vacuum chamber, pump out the air in the chamber, and then inject nitrogen gas as a protective gas, and the nitrogen pressure is 0.5 atm. A femtosecond laser is used for scanning etching with an energy density of 3kJ/m ² and a scanning speed of 0.5mm/s, so as to form a microstructure and achieve doping on the silicon substrate. The silicon substrate etched by femtosecond laser scanning can form a doped black silicon structure on the surface. In this embodiment, a schematic cross-sectional view of the silicon substrate material after laser etching is shown in FIG. 3 , wherein 1 is a silicon substrate, and 4 is a doped black silicon structure formed after laser scanning etching.

Step 5: Remove the surface silicon oxide layer

The silicon substrate after scanning etching is immersed in hydrofluoric acid with a concentration of 5% for 5 minutes to remove the silicon oxide layer on the surface. Wash with deionized water and dry with nitrogen to prepare black silicon.

In this embodiment, the absorption spectrum of the laser-etched silicon substrate material is shown in FIG. 4 , which are respectively the absorption spectra of doped black silicon prepared by selenium-silicon composite film and doped black silicon prepared by thermally evaporating selenium film. Compared with the doped black silicon material prepared by thermally evaporating the selenium film without covering the silicon protective layer, the absorptivity of the doped black silicon prepared by the method in the near-infrared band is obviously improved.

Claims (4)

1. prepare a method for black silicon material, comprise the following steps:

Step 1, silicon substrate is cleaned, for subsequent use to obtain cleaning silicon substrate;

The mode of step 2, employing thermal evaporation deposits one layer of selenium film as impurity source in surface of silicon, and selenium film thickness is 50��300nm;

Step 3, adopting and prepare one layer of silicon fiml again as silicon protective layer on silicon substrate selenium film that the mode of magnetron sputtering prepared in step 2, silicon film thickness is 50��150nm;

Step 4, silicon substrate step 3 prepared carry out femtosecond laser etching under 0.2��0.8atm nitrogen atmosphere, and when femtosecond laser etches, incident light energy density is 1��10kJ/m², sweep velocity is 0.5��10mm/s;

Step 5, by scanning etching after silicon substrate put into hydrofluoric acid, remove surface silicon oxide layer; Clean with deionized water and blow with nitrogen dry, obtain black silicon.

2. prepare the method for black silicon material as claimed in claim 1, it is characterised in that: described silicon substrate is N-type silicon chip.

3. prepare the method for black silicon material as claimed in claim 1, it is characterised in that: described step 1 is specially and adopts RCA standard cleaning method to be cleaned by silicon substrate; The silicon substrate cleaned is put into the ultrasonic removing remained on surface organism of acetone again; Finally by silicon substrate ultrasonic clean in deionized water, and blow dry for subsequent use in a nitrogen atmosphere.

4. the black silicon adopting the arbitrary described method preparing black silicon material of claim 1-3 obtained, it is characterised in that: in the specific absorption of 400��1100nm wave band higher than 95%, in the specific absorption of 1100��2200nm wave band higher than 90%.