CN102290332A - Method for preparing high-density silicon nanopore array - Google Patents

Abstract

The invention relates to a method for preparing a high-density silicon nanopore array. The method comprises the following steps: on the basis of taking a Pt nano crystal as a catalyst, and etching a silicon chip in a mixed solution of hydrofluoric acid and hydrogen peroxide by adopting a metal auxiliary chemical etching technology, thus the high-density silicon nanopore array is prepared, wherein the Pt nano crystal is obtained by carrying out high-temperature rapid hot annealing on an ultrathin Pt thin film which grows through magnetic control sputtering and has nano-scale thickness. According to the invention, the high-density silicon nanopore array is prepared by the metal auxiliary chemical etching technology, the technology is simple, wherein the high-temperature rapid hot annealing is performed for a short time, the thermal budget is low, simultaneously a power supply is not required to added additionally for the metal auxiliary chemical etching technology, power supply can be carried out spontaneously, the silicon nanopore array with the density exceeding 1.0*10<10>cm<-2> can be obtained, the preparation cost of the whole technology is lower, and the array can be manufactured on a large scale.

Description

A method for preparing a high-density silicon nanohole array

technical field

The invention belongs to the field of silicon-based nanomaterials and device manufacturing, and in particular relates to a process for preparing a high-density silicon nanohole array.

Background technique

Silicon nanopores are considered to be very promising processing templates in the fields of photovoltaics, biochemical sensors, and energy storage. Among the many fabrication methods, metal-assisted chemical etching has attracted extensive attention in the last decade because it can form silicon nanopore structures on silicon wafers through simple and inexpensive process steps. The basic mechanism of metal-assisted chemical etching to form silicon nanopores is: firstly, a layer of discontinuous heavy metal (Au, Ag, Pt or Pd) particles is covered on the silicon wafer, and then the silicon wafer is immersed in a solution containing hydrofluoric acid and an oxidant ( Hydrogen peroxide, ferric nitrate, potassium permanganate, etc.), since the etching rate of silicon covered with heavy metals is significantly higher than that of silicon without heavy metals, heavy metals will sink into the depth of bulk silicon to form Nanopores comparable in diameter and density to heavy metal particles.

At present, the main method of covering heavy metals on the surface of silicon wafers is electroless deposition. This method is more suitable for depositing Au and Ag particles with high density and good separation on the surface of silicon wafers, but it is not suitable for Pt. This is because as the deposition time increases, Pt is easy to form a dense film on the surface of the silicon wafer, which hinders the etching process. Therefore, the electroless plating method is generally only suitable for forming Pt particles with a very small density on the surface of the silicon wafer, and cannot be prepared. High-density silicon nanowell arrays. the

Therefore, there is a need to develop a method for fabricating high-density silicon nanopore arrays using heavy metal Pt-assisted chemical etching.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a high-density silicon nanohole array, which is suitable for silicon-based nanodevices, has low preparation cost, and is expected to be mass-produced. the

In order to achieve the above object, the present invention provides a method for preparing a high-density silicon nanohole array, using a metal-assisted chemical etching process, using Pt nanocrystals as a catalyst, and etching a silicon wafer in a mixed solution of hydrofluoric acid and hydrogen peroxide , so as to prepare a high-density silicon nanohole array; wherein, the Pt nanocrystals are obtained by high-temperature rapid thermal annealing of an ultra-thin Pt film grown by magnetron sputtering with a thickness of nanometers, and the Pt nanocrystals Size, shape and density can be controlled by changing the annealing temperature and annealing time. Moreover, before growing the ultra-thin Pt film, a layer of SiO ₂ needs to be thermally grown on the Si substrate, which is to prevent the Pt from reacting with the Si substrate during rapid thermal annealing of the Pt film.

The above-mentioned method for preparing a high-density silicon nanohole array comprises the following specific steps:

Step 1, thermally grow a layer of SiO ₂ with a thickness of 1-7 nm on the heavily doped p-type silicon wafer, wherein the thermal growth temperature is 800-1000°C, and the growth time is about 2 minutes, subject to the thickness meeting the requirements;

Step 2, growing an ultrathin Pt film with a thickness of 2 to 5 nanometers by magnetron sputtering on the above _SiO2 layer;

Step 3, performing high-temperature rapid thermal annealing on the ultra-thin Pt film obtained in step 2, wherein the annealing temperature is 700-800°C, the annealing time is 30-60s, and the high-temperature annealing atmosphere can be nitrogen or argon;

Step 4, putting the silicon wafer containing the ultra-thin Pt film obtained in step 3 into a mixed solution of hydrofluoric acid and hydrogen peroxide (ie, an etching solution) for etching, wherein the mass fraction of hydrofluoric acid is 50% , the mass fraction of hydrogen peroxide is 30%, the volume ratio of hydrofluoric acid and hydrogen peroxide is 2:1~10:1 (preferably 2:1~4:1); the etching solution can be diluted with water to reduce the etching rate , so as to reduce the surface roughness of the silicon wafer after etching; the etching time is generally 1 to 5 minutes, depending on the depth of the required silicon nanopore, and the lower the concentration of the etching solution for the same depth of hole, the longer the time required. longer.

Step 5, rinse the etched silicon wafer with deionized water, and then dry it in the air.

In the above-mentioned method for preparing a high-density silicon nanohole array, in step 1, the thickness of the SiO ₂ layer is 5-6 nanometers.

In the above-mentioned method for preparing a high-density silicon nanohole array, in step 2, the thickness of the ultra-thin Pt film is 3-4 nanometers.

In the above-mentioned method for preparing a high-density silicon nanohole array, in step 2, the magnetron sputtering power is 90W, the sputtering time is 48s, the sputtering pressure is 0.56Pa, and the sputtering temperature is room temperature.

The technical scheme of the present invention adopts a metal-assisted chemical etching process, uses Pt nanocrystals formed by high-temperature rapid thermal annealing as a catalyst, and etches silicon wafers in a mixed solution of hydrofluoric acid and hydrogen peroxide to form a high-density silicon nanopore array. By controlling the size and density of Pt nanocrystals, the diameter and density of silicon nanopores can be controlled.

The advantages of the method for preparing high-density silicon nanohole arrays proposed by the present invention:

1) The present invention uses metal-assisted chemical etching to prepare high-density silicon nanopore arrays. Compared with traditional anodic oxidation and reactive ion etching methods, it can be performed spontaneously without external power supply, so the process is simple and the preparation cost is low.

2) The present invention uses high-temperature rapid thermal annealing to obtain catalytic Pt nanocrystals, wherein the annealing duration is short and the thermal budget is low, and the size, shape and density of Pt nanocrystals can be controlled by changing the annealing temperature and annealing time.

3) The density of silicon nanopores prepared by the present invention is relatively high, exceeding 1.0×10 ¹⁰ cm ⁻² (that is, the number of nanopores exceeding 1.0×10 ¹⁰ per square centimeter).

4) The diameter and density of silicon nanopores prepared by the present invention are equivalent to those of Pt nanocrystals, so the diameter and density of silicon nanopores can be controlled by controlling the size and density of Pt nanocrystals.

High-temperature rapid thermal annealing is a self-assembly process through which ultra-thin heavy metal films can be processed to obtain heavy metal particles with very high density and good separation. Therefore, the present invention adopts the Pt nanocrystal obtained by the high-temperature rapid thermal annealing process as a catalyst, performs metal-assisted chemical etching on the silicon wafer, and prepares a silicon nanohole array with high density. The process of the invention is simple, in which the high-temperature rapid thermal annealing duration is short, the thermal budget is low, and the metal-assisted chemical etching can be carried out spontaneously without an external power supply, so the preparation cost of the whole process is low, and it is expected to be mass-produced.

Description of drawings

Fig. 1a is a scanning electron micrograph of Pt nanocrystals formed by annealing at 800°C for 45s according to an embodiment of the present invention.

Fig. 1b is a lateral diameter distribution diagram of Pt nanocrystals formed by annealing at 800°C for 45s according to an embodiment of the present invention.

Fig. 2a is a plan scanning electron micrograph of a silicon wafer after metal-assisted chemical etching according to an embodiment of the present invention.

Fig. 2b is a cross-sectional SEM image of a silicon wafer after metal-assisted chemical etching according to an embodiment of the present invention.

Detailed ways

The specific implementation manner of the present invention will be described in detail below in conjunction with the accompanying drawings and examples.

Example

Step 1, thermally grow a layer of SiO ₂ with a thickness of about 6 nanometers on a heavily doped p-type silicon wafer, wherein the thermal growth temperature is 1000° C., and the growth time is 2 minutes.

Step 2, grow an ultra-thin Pt film with a thickness of about 4 nanometers on the _SiO2 layer by magnetron sputtering, wherein the magnetron sputtering power is 90W, the sputtering time is 48s, the sputtering pressure is 0.56Pa, and the sputtering The temperature is room temperature.

Step 3, perform high-temperature rapid thermal annealing on the ultra-thin Pt film, the annealing conditions are: nitrogen atmosphere, temperature 800°C, time 45s. Figure 1a and Figure 1b are the scanning electron microscope pictures of the Pt nanocrystals formed after annealing and the corresponding lateral diameter distribution diagrams of the Pt nanocrystals, respectively. The density of Pt nanocrystals is 1.89×10 ¹⁰ cm ^-2 (that is, the number of Pt nanocrystal particles per square centimeter), and the average lateral diameter of nanocrystals is 39.97 nanometers.

Step 4, putting the silicon wafer into a mixed solution of hydrofluoric acid and hydrogen peroxide for etching, wherein the mass fraction of hydrofluoric acid is 50%, the mass fraction of hydrogen peroxide is 30%, and the volume ratio of hydrofluoric acid and hydrogen peroxide is 3 : 1, the etching time is 3min, and each Pt nanocrystal in step 3 corresponds to a nanopore after etching, that is, the obtained density is 1.89×10 ¹⁰ cm ^-2 (that is, the number of nanopores per square centimeter on the silicon wafer ) of high-density nanopore arrays. Figure 2a and Figure 2b are the planar scanning electron microscope pictures and cross-sectional scanning electron microscope pictures of the silicon wafer after metal-assisted chemical etching, respectively. It can be seen that the columnar nanopores with a diameter of about 40 nanometers are closely arranged.

In step 5, the etched silicon wafer is rinsed with deionized water for 5 minutes, and then dried in air to prepare the high-density silicon nanohole array of the present invention.

The present invention adopts high-temperature rapid thermal annealing to obtain Pt nanocrystals with catalytic effect, wherein the annealing duration is short and the thermal budget is low. In step 3, the size, shape and density of Pt nanocrystals can be improved by changing the annealing temperature and annealing time. control. The temperature and time required for Pt thin film annealing to form nanocrystals are also related to the thickness of the Pt thin film itself; With the increase of temperature, the density of Pt nanocrystals decreases gradually, the average lateral diameter of nanocrystals gradually decreases, and the shape of nanocrystals gradually approaches spherical; under the annealing condition of 800 °C, with the prolongation of annealing time, Pt nanocrystals The density of Pt nanocrystals increases first and then decreases, and the average horizontal diameter of nanocrystals first decreases and then increases, especially at 800°C and annealed for 45s, the density of Pt nanocrystals is the highest, and the separation between nanocrystals is the best.

Table 1: Size and density of Pt nanocrystals as a function of annealing temperature and annealing time

sample Nanocrystalline density (10 ¹⁰ /cm ² ) Average transverse diameter (nm) Anneal at 700℃ for 30s 1.68 52.32 Anneal at 750℃ for 30s 1.65 50.41 Anneal at 800℃ for 30s 1.63 43.71 Annealed at 800°C for 45s 1.89 39.97 Annealed at 800°C for 60s 1.85 42.28

The present invention adopts the Pt nanocrystal obtained by the high-temperature rapid thermal annealing process as a catalyst to carry out metal-assisted chemical etching on the silicon wafer, and prepares a silicon nanohole array with high density; the process is simple, and the duration of the high-temperature rapid thermal annealing is short , low thermal budget, and metal-assisted chemical etching can be carried out spontaneously without external power supply, so the preparation cost of the whole process is low, and it is expected to be mass-produced.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (5)

1. A method for preparing high-density silicon nanohole arrays, characterized in that, the method adopts Pt metal-assisted chemical etching process, uses Pt nanocrystals as a catalyst, and etches silicon wafers in a mixed solution of hydrofluoric acid and hydrogen peroxide , thereby preparing a high-density silicon nanohole array; the Pt nanocrystal is obtained by performing high-temperature rapid thermal annealing on an ultra-thin Pt film grown by magnetron sputtering with a thickness of nanometer scale; the high-density silicon nanocrystal A pore array refers to an array of silicon nanopores with a density exceeding 1.0×10 ¹⁰ cm ^-2 . 2. the method for preparing high-density silicon nanohole array as claimed in claim 1, is characterized in that, the method comprises the following specific steps: Step 1, thermally growing a layer of SiO ₂ with a thickness of 1-7 nm on the heavily doped p-type silicon wafer, wherein the thermal growth temperature is 800-1000°C; Step 2, growing an ultrathin Pt film with a thickness of 2 to 5 nanometers by magnetron sputtering on the above _SiO2 layer; Step 3, performing high-temperature rapid thermal annealing on the ultra-thin Pt film obtained in the above step 2, wherein the annealing temperature is 700-800°C, the annealing time is 30-60s, and the atmosphere for the high-temperature annealing is nitrogen or argon; Step 4, put the silicon chip obtained in step 3 into a mixed solution of hydrofluoric acid and hydrogen peroxide for etching, wherein the mass fraction of hydrofluoric acid is 50%, the mass fraction of hydrogen peroxide is 30%, and the hydrofluoric acid and hydrogen peroxide The volume ratio is 2:1~10:1; Step 5, rinse the etched silicon wafer with deionized water, and then dry it in the air. 3. The method for preparing a high-density silicon nanohole array as claimed in claim 2, characterized in that, in step 1, the thickness of the _SiO2 layer is 5 to 6 nanometers. 4. the method for preparing high-density silicon nanohole array as claimed in claim 2 or 3 is characterized in that, in step 2, the thickness of described ultra-thin Pt film is 3～4 nanometers, and wherein, magnetron sputtering The sputtering power was 90W, the sputtering time was 48s, the sputtering pressure was 0.56Pa, and the sputtering temperature was room temperature. 5. The method for preparing a high-density silicon nanopore array as claimed in claim 2 or 3, wherein in step 4, the volume ratio of the hydrofluoric acid and hydrogen peroxide is 2:1 to 4:1.

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