WO2012024847A1

WO2012024847A1 - Porous substrate and manufacturing method thereof

Info

Publication number: WO2012024847A1
Application number: PCT/CN2010/076713
Authority: WO
Inventors: 夏洋; 刘邦武; 李超波; 刘杰; 汪明刚; 李勇滔
Original assignee: 中国科学院微电子研究所
Priority date: 2010-08-23
Filing date: 2010-09-08
Publication date: 2012-03-01
Also published as: CN101964367A

Abstract

A porous substrate and manufacturing method thereof are provided. The surface topography of the substrate is disordered and porous. The depth of the holes is less than the thickness of the substrate; the holes are separate from each other and are not connected with each other. The method comprises: putting the substrate in the injection chamber of the preparation equipment of the substrate, adjusting the process parameter of the preparation equipment of the substrate into the preset range of value; injecting the reactive ions of the plasma generated by the preparation equipment of the substrate into the substrate, and the reactive ions reacting with the substrate to form the porous substrate. The bottoms of the holes in the porous substrate are not connected with each other. Using the porous substrate to make solar cells benefits to light absorption, carrier transport and collection. The method of manufacturing the porous substrate is simple in process, easy to control and it is not necessary to perform cleaning.

Description

Porous structure village bottom and preparation method thereof

Technical field

The invention relates to a semiconductor structure and a preparation method thereof, in particular to a substrate with a porous structure and a preparation method thereof. Background technique

At present, solar cells cannot replace traditional energy sources because of high production costs. Therefore, reducing the production cost of solar cells has become the biggest problem in this industry, and the production cost of solar cells is closely related to the efficiency of solar cells. Since the solar cell used in the current solar cell has a high refractive index and a reflection loss of more than 40%, the solar cell has a high light reflectance, thereby greatly reducing the photoelectric conversion efficiency of the solar cell.

One of the methods for reducing the light reflection efficiency of a solar cell is to make a pile structure on the incident surface of the substrate to reduce the reflection of incident light. Eric Mazur et al. of Harvard University in the United States used a femtosecond laser method to prepare a needle-like silicon material in 1996. As shown in Fig. 1, a solar cell was prepared, and the photoelectric conversion efficiency was 8.8% ~ 13.9%. . However, the silicon-based substrate of the needle structure prepared by this method has two disadvantages: a. The structure of the solar cell prepared from the silicon substrate of the needle structure is shown in FIG. 2, including the back electrode 1, the single crystal silicon 2 The silicon layer 3 of the needle structure, the passivation layer 4 and the gate 5, the photo-generated current of the solar cell flows through the silicon layer 3 of the needle-like structure is collected by the gate 5, and the silicon layer of the needle structure is disadvantageous to the photogeneration Current collection; b. The femtosecond laser is used in the method, the process is complicated, the process control is cumbersome, the equipment cost is extremely expensive, and the maintenance is inconvenient, which is not conducive to large-scale production.

Chinese patent CN 101673785 A (published on March 17, 2010) discloses a method for preparing porous silicon based on electrochemical etching. The main points of the method are as follows: First, a metal aluminum thin film anode electrode is prepared by screen printing on the back side of the silicon wafer, and aluminum and silicon have good ohmic contact, and platinum or platinum wire is used as a cathode electrode; then the silicon wafer front side is used. Immerse in an etching solution of HF: Η ₂ Ο = 1:10 for 1 minute at a temperature of 26 ° C; then place the front side of the wafer in a container with ultrasonic conditions at an ultrasonic frequency of 40 ~ 60 Hz, and Electrolytic etching treatment was carried out in a mixed solution of electrolyte HF: H ₂ 0: C ₂ H ₅ OH=2:1:1, and the electrolysis temperature was 40. (: The electrolytic corrosion current density is 5 ~ 10mA/cm ² and the time is 40 ~ 60s. However, the porous silicon prepared by the electrochemical etching method is spongy, and there are pores in the pores. After corrosion, in the porous silicon The residual electrolyte cannot be cleaned, affecting the final shape of the structure, making structural control difficult, which is not conducive to the preparation of solar cells. One of the objects of the present invention is to provide a substrate having a porous structure and a method for preparing the same, wherein the substrate of the porous structure does not have a string hole, and the solar cell is manufactured by using the substrate of the porous structure to facilitate light absorption and carriers. Transport and collection; The method of preparing a porous structure substrate is simple in process, convenient in control, and does not require removal of the electrolyte.

According to an aspect of the present invention, a substrate having a porous structure, the surface topography of the substrate is disorderly porous, the depth of the hole is smaller than the thickness of the substrate, and the holes are independent of each other. Each is not connected.

Further, the present invention has the following features: the pores have an average pore size of between 10 nanometers and 2 micrometers; an area density of the pores on the surface of the substrate is 0.01 to 0.91; an average pore depth of the pores Between 50 nm and 10 microns; the substrate is made of Si-based material, GaN-based material, InP-based material, GaAs-based material, Ge-based material, carbon-based material, SiN _x , Si0 ₂ , SiC, GeSi, ZnO, Made of Ti0 ₂ or CdS.

According to another aspect of the present invention, there is provided a method of preparing a substrate having a porous structure, comprising the steps of:

Place the bottom of the village in an injection chamber of the substrate preparation device;

Adjusting process parameters of the substrate preparation device into a preset range of values;

Injecting reactive ions in a plasma generated by the substrate preparation apparatus into the substrate; and reacting the reactive ions with the substrate to form a porous substrate; wherein a surface of the porous substrate The morphology is disordered porous, the depth of the holes is smaller than the thickness of the substrate, the holes are independent of each other, and the holes are not connected.

Further, the method further has the feature that placing the substrate in the implantation chamber of the substrate preparation apparatus further comprises electrically connecting the substrate to a power source to which a bias voltage is applied.

Further, the method further has the following feature: the adjusting the process parameters of the substrate preparation device into a preset numerical range includes:

Extracting the gas injection chamber, such that the injection pressure into the chamber base pressure range set in advance, the range of the base pressure set in advance to 10- ⁷ Pa ~ 1000Pa;

Filling the injection chamber with a mixed gas, adjusting the flow rate of the mixed gas, so that the pressure of the injection chamber enters a preset working pressure range, and the preset working pressure range is

10" ³ Pa ~ lOOOPa; and the volume ratio between the bodies enters a predetermined volume ratio range, and the predetermined volume ratio ranges from 0.01 to 100.

Further, the method has the following features: the gas having etching action includes SF ₆ , CF ₄ , CHF ₃ , C ₄ F ₈ , NF ₃ , SiF ₄ , C ₂ F ₆ , HF, BF ₃ , PF ₃ , Cl ₂ , HCl, SiH ₂ Cl ₂ , SiCl ₄ , BC1 ₃ or HBr, said passivated The gas of action includes 0 ₂ , N ₂ 0 or N ₂ .

Further, the method further has the following features: the pores have an average pore size between 100 nm and 2 microns; the ratio of the total area of the pores to the surface area of the substrate is 0.01 to 0.91; The pore depth is between 100 nm and 10 microns.

Compared with the prior art, the present invention has the following advantages:

A. Since the surface morphology of the porous structure of the present invention is disorderly porous, the pores are independent of each other, and the pores are not connected, that is, there is no string pore, because the porous substrate of the porous structure has Conducive to light absorption, carrier transport and collection, so the solar cell can be prepared by using the substrate, has high current collection rate, good electrical characteristics and long service life;

B. According to the method for preparing a porous structure substrate provided by the present invention, since the present invention uses a plasma immersion ion implantation process to prepare a substrate of a porous structure, that is, a filling chamber is filled with a mixed gas to meet a certain vacuum requirement, Under the action of the applied electric field, the generated plasma is injected into the substrate to react with the substrate, and the porous substrate can be prepared in one time, thereby avoiding cumbersome laser scanning processing, and the method is a thousand methods. The process does not need to add an electrolytic corrosion solution, so the process does not need to remove the electrolyte, so the structure control of the invention is convenient, and the finally formed structure is easy to control, which is beneficial to the preparation of the solar cell. DRAWINGS

1 is a schematic structural view of a conventional acicular porous structure of silicon;

2 is a schematic structural view of a conventional silicon solar cell having a porous structure;

3 is a schematic structural view of a bottom of a porous structure provided by an embodiment of the present invention;

4 is a schematic view showing the microstructure of a substrate having a porous structure according to an embodiment of the present invention; FIG. 5 is a schematic view showing the microstructure of a substrate having a porous structure according to an embodiment of the present invention; FIG. 7 is a schematic view showing another embodiment of a substrate process for preparing a porous structure according to the present invention; FIG. 8 is a further process for preparing a porous structure substrate of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 9 is a schematic view showing a process of preparing a porous structure by plasma immersion ion implantation according to the present invention; FIG. 10 is a schematic flow chart showing a first example of adjusting the injection process parameters in FIG. 9; A schematic flow diagram of a second example of adjusting the injection process parameters in FIG. 9; FIG. 12 is a flow diagram of the third example of adjusting the injection process parameters in FIG. detailed description The technical solutions of the present invention are further described below in conjunction with the accompanying drawings and embodiments.

Figure 3 is a schematic illustration of a substrate of a porous structure of the present invention. The holes 12 are arranged disorderly on the surface of the substrate 11, and the aperture sizes may be the same value or different values. Reference numerals 13, 15 are hole sections; reference numeral 14 is the height from the surface of the substrate to the bottom of the hole, that is, the hole depth. The depth of the holes 12 is smaller than the thickness of the substrate 11, and the holes 12 are independent of each other, and the holes are not connected to each other. 4 and FIG. 5 are micrographs of a specific embodiment of a porous structure of a porous structure according to the present invention under a scanning electron microscope. As can be seen from the figure, the number of holes on the substrate is large and the distribution is disordered. Independent of each other, the holes are not connected, that is, there is no string hole. The use of the porous structure of the village to manufacture solar cells is beneficial to light absorption, carrier transport and collection, so that the current collection rate of the solar cells is high. Good electrical characteristics and long service life.

The substrate 11 may be made of a Si-based material, a GaN-based material, an InP-based material, a GaAs-based material, a Ge-based material, a carbon-based material, SiN _x , SiO ₂ , SiC, GeSi, ZnO, Ti _{2 2} , CdS, or other equivalent substitutes. The substrate 11 can also be doped with a certain amount of B, P, Se and/or As.

In one embodiment, the substrate 11 formed to form the porous structure shown in FIG. 3 is a single crystal P-type doped substrate or an N-type doped substrate, and may also be a polycrystalline P-type doped substrate or N. Type doped substrate; holes 12 are independent of each other, and each hole is not connected; the average pore size can range from 10 nanometers to 2 micrometers, preferably from 100 nanometers to 1 micrometer, under certain process conditions, holes in the substrate The pores may have the same or very similar pore size, or under another process condition, the pore size of the pores on the substrate may be different, that is, the size of the average pore diameter may be controlled by the preparation method; the pores 12 are distributed on the surface of the substrate 11 Disorder; the area density of the hole on the surface of the substrate is 0.01~0.91, preferably 0.3~0.7. The area density reflects the distribution density of the hole on the bottom of the village. The larger the area density, the hole is on the bottom of the village. The larger the distribution, the area density can also be controlled by the preparation method; the shape of the hole in the direction perpendicular to the surface of the substrate can be cylindrical, truncated or other suitable hole shape, and the shape can also be prepared by the method. control The cross-sections of the cylindrical and truncated-shaped holes are respectively indicated by reference numerals 13 and 15 in Fig. 3; the average depth of the hole depth 14 is from 50 nm to 10 μm, preferably from 100 nm to 5 m, under certain process conditions. The holes in the substrate may have the same or very similar hole depths, or under another process condition, the holes in the substrate may have different hole depths, that is, the hole depth may be controlled by the preparation method. .

The present invention also provides a method of preparing a substrate of such a porous structure, mainly by placing a substrate in a preparation apparatus, and using a plasma immersion ion implantation process to prepare a substrate of a porous structure.

Plasma Immersion Ion Implantation (Calcium Immersion Ion Implantation) is sometimes referred to as plasma implantation, plasma doping, plasma immersion implantation, plasma source ion implantation, or plasma-based ion implantation in the semiconductor industry. . These kinds of scales represent the same process technology, that is, the sample to be injected is directly immersed in the plasma, and a bias voltage (also referred to as "injection voltage") is applied to the sample to form a sample and a plasma. Injecting sheath electric field; located in the infusion sheath The reactive ions in the electric field and from the plasma entering the sheathing electric field are directly injected into the sample under the acceleration of the electric field. Since a sheath is formed on the surface of the sample, the surface of the sample exposed to the plasma will be simultaneously injected at the same time.

A device for preparing a porous structure substrate (e.g., a plasma immersion ion implanter) includes an implantation chamber and a plasma source. Inside the injection chamber, there is a sample stage on which the sample can be placed. On the side opposite the sample stage, a plasma source is provided. The plasma source includes an evacuation system, a gas supply system, and a plasma power source. Wherein, the vacuum system can evacuate the injection chamber to a preset background pressure range. The gas supply system can charge the injection chamber with the required gas, and can adjust various parameters of the gas according to certain control rules, such as gas flow rate, extraction speed, gas composition ratio and concentration. After the gas is charged into the injection chamber, the pressure of the injection chamber can be brought to a predetermined working pressure range. The plasma power source can be a radio frequency power source, a microwave power source, or a direct current power source. These power supplies can also be powered in pulses, and the frequencies of these power supplies can be fixed or variable.

Alternatively, the apparatus for preparing a porous structure substrate further includes a power source to which a bias voltage can be applied. The power supply to which the bias voltage is applied is electrically coupled to the sample stage within the injection chamber. The type of power supply to which the bias voltage can be applied is similar to that of a plasma power source. It can be a radio frequency power supply, a microwave power supply, or a direct current power supply. These power supplies can also be supplied in pulses, or any combination of these power supplies, and thus can be supplied to the sample stage. The bias voltage composed of the bias voltage.

Alternatively, the apparatus for preparing a porous structure substrate may further include monitoring components for monitoring various process conditions in the injection chamber, such as monitoring electron temperature, plasma density, ion potential, ion mass spectrometry distribution, and emission spectrum in the chamber. Wait. The power of the plasma power source and the power source to which the bias voltage can be applied can be adjusted according to certain control rules. If the power is supplied in the form of a pulse, the frequency, duty cycle, and pulse width of the plasma power source and the power source to which the bias voltage can be applied It can also be adjusted according to certain control rules. A power supply that can apply a bias voltage can adjust its applied bias voltage according to certain control rules.

As shown in FIG. 6, FIG. 7 and FIG. 8, the present invention can directly prepare a porous structure by using only plasma immersion ion implantation, and can also be combined with other processes to prepare a porous structure. For example, the substrate may be pretreated (step 10) prior to plasma immersion ion implantation to prepare the porous structured substrate (step 20). After the plasma immersion ion implantation is performed to prepare the porous structure substrate (step 20), the prepared substrate of the porous structure may be subjected to post-treatment (step 30). These treatments can be selected according to actual needs. In Fig. 6, substrate pretreatment of the substrate pretreatment and the porous structure is used; in Fig. 7, only the substrate pretreatment is used; in Fig. 8, only the substrate post treatment of the porous structure is used. Among them, the manner of substrate pretreatment includes cleaning, polishing, doping, annealing, etching, texturing (also referred to as velvet) and/or patterning of the substrate. The manner of substrate post-treatment of the porous structure includes cleaning, polishing, doping, annealing, etching, texturing (also referred to as velvet) and/or patterning of the substrate of the porous structure. And other processes.

As shown in FIG. 9, the plasma immersion ion implantation provided by the embodiment of the present invention for preparing a substrate of a porous structure includes the following steps:

Step 201, placing the substrate in a porous structure substrate preparation device; the substrate may be subjected to cleaning, polishing, doping, annealing, etching, texturing (also referred to as fluffing), and/or patterning. The substrate obtained after the pretreatment may have a conventional shape such as a circle, a square or a rectangle, or any other complicated shape; the substrate preparation device of the porous structure may be a plasma immersion ion implanter. The substrate is placed in the injection chamber of the device and placed on the sample stage; in some embodiments, the substrate preparation device of the porous structure includes a power source to which a bias voltage can be applied, which allows the substrate to be electrically connected to the sample stage Since the sample stage is electrically connected to a power source to which a bias voltage can be applied, the substrate is electrically connected to a power source to which a bias voltage can be applied; under certain conditions, a power source to which a bias voltage can be applied can be applied to the substrate. Bias voltage

Step 202: Adjusting a process parameter of the porous structure of the substrate preparation device to achieve a plasma generating working condition; the process parameters may include a background pressure and a working pressure of the injection chamber, a flow rate of the injected gas, and a gas extraction Speed, mixed gas composition, composition ratio and concentration, output power and frequency of the plasma power supply, bias voltage applied by the power supply to which the bias voltage can be applied, pulse width, duty cycle and frequency if pulsed These process parameters can be preset according to the actual size of the substrate to be processed, the performance of the substrate of the prepared porous structure, or can be modified on-site during the processing; during the processing, these processes are monitored. The parameters are adjusted to meet the process requirements of the numerical range or the preset numerical range by adjusting the components of the porous structure of the substrate preparation device according to certain rules;

The background pressure of the injection chamber may range from 10 to ⁷ Pa to 100 OOPa, preferably from 10 to ⁵ Pa to 10 Pa, more preferably from 10 to ⁵ Pa to 10 to ³ Pa; and the working pressure of the injection chamber The range may be 10 - ³ Pa ~ lOOOPa, preferably O.OlPa ~ 100Pa, more preferably O.lPa ~ 50Pa;

The injection gas may be a mixed gas composed of an etching gas and a passivating gas, and the etching gas includes SF ₆ , CF ₄ , CHF ₃ , C ₄ F ₈ , NF ₃ , SiF ₄ , C ₂ F ₆ , HF, BF ₃ , PF ₃ , Cl ₂ , HCl, SiH ₂ Cl ₂ , SiCl ₄ , BC1 ₃ or HBr, the gas having a passivation comprising 0 ₂ , N ₂ 0 or N ₂ , preferably It may be composed of a plurality of gases having an etching action and a plurality of gases having a passivation effect, more preferably consisting of a gas having an etching action and a gas having a passivation effect, for example, by SF ₆ and 0. a mixed gas composed of ₂ , or a mixed gas composed of CF ₄ and N _{2 ,} which is composed of a gas having an etching action and a gas having a passivation and having etching The product ratio may also preferably be from 0.1 to 80, more preferably from 1 to 20; the flow rate of the mixed gas may be from 1 to 1000 sccm, preferably from 10 to 100 sccm, more preferably from 20 to 80 sccm;

The output power of the plasma power source is 1 to 100000 W, preferably 10 to 50000 W, and more preferably 300 to 5000 W; the applied bias voltage is -100,000 to 100,000 V, preferably -50,000 to 50,000 V, more Preferably, it may be -10000 to 0 V; the pulse width is 1 us ~ 1 s, preferably lus ~ 0.1 s, more preferably lus ~ 1 ms; the duty ratio is 1% ~ 99%, preferably 10 % ~ 90%, more preferably 20% - 80%; plasma power source frequency is DC ~ 10GHz, preferably 1MHz - 5GHz, more preferably 13.56MHz ~ 5GHz; bias voltage can be applied The frequency of the power supply is DC ~ 10GHz;

Step 203, after the plasma is generated and immersed in the bottom of the village, due to the application of a bias voltage to the substrate, the electric field of the sheath layer formed between the substrate and the plasma is accelerated, and is located in the sheath electric field and enters from the plasma. The reactive ions of the sheath electric field are directly injected into the village bottom;

Step 204, the reactive ions react with the substrate, for example, in the case where the injected gas is a mixed gas composed of SF ₆ and ₀₂ , after ionization, SF ₆ and 0 ₂ respectively generate an F* group and a 0* group. , wherein the F* group forms an etching effect on Si by forming SiF ₄ with Si; meanwhile, the 0* group forms Si _x O _y F _z on the surface of the etched wall to passivate the etched wall; Under the dual action of etching and passivation, a porous structure of a porous or network structure is finally formed.

In the method of the present invention for preparing a porous structure substrate by plasma immersion ion implantation, adjusting the process parameters of the porous structure of the substrate preparation apparatus is a very important step, and FIG. 10, FIG. 11 and FIG. Examples of several sub-steps of the steps, these sub-steps may be replaced, combined or cancelled, for example, adjusting the mixed gas composition ratio, the mixed gas flow rate, and the extraction speed may be adjusted or selected one or two to adjust, or may not adjust the mixed gas Various parameters. Therefore, for the sake of brevity, the combination of the sub-steps required to adjust the process parameters of the substrate-preparing device of the porous structure to achieve plasma generation will not be enumerated herein. It should be noted that the same reference numerals are used in the drawings and the drawings.

Through the above steps, a substrate having a porous structure as shown in Fig. 3 can be prepared. The surface morphology of the substrate is disordered porous, the depth of the holes is smaller than the thickness of the substrate, the holes are independent of each other, and the holes are not connected. The pores have an average pore size between 10 nanometers and 2 microns. The area density of the holes on the surface of the substrate is from 0.01 to 0.91. The pores have an average pore depth between 50 nanometers and 10 micrometers. The substrate may be made of a Si-based material, a GaN-based material, an InP-based material, a GaAs-based material, a Ge-based material, a carbon-based material, SiN _x , SiO ₂ , SiC, GeSi, ZnO, Ti _{2 2} , CdS, or other equivalent substitutes. And the substrate is doped with a certain amount of B, P, Se or As.

As shown in FIG. 10, the first embodiment of the process parameters of the substrate preparation apparatus for adjusting the porous structure is shown in FIG. Including the following steps:

Step 2022, the vacuuming system of the plasma source extracts the gas injected into the chamber;

Step 2024, the monitoring device in the vacuum system determines whether the pressure of the injection chamber enters a predetermined background pressure range, for example, whether it is in the range of l (T ⁵ Pa ~ 10" ³ Pa, and if yes, proceeds to step 2026. Otherwise, return to step 2022;

Step 2026, charging the injection chamber with a mixed gas, for example, a mixed gas composed of SF6 and 02; Step 2027, the monitoring device in the vacuum system determines whether the pressure of the injection chamber enters a preset working pressure range, for example, In the range of 0.1Pa ~ 50Pa, if yes, proceeds to step 2032, otherwise, proceeds to step 2029;

Step 2029, the gas supply device in the gas supply system adjusts the flow rate of the mixed gas and/or adjusts the extraction speed of the gas in the extraction injection chamber, for example, the valve in the flow meter or the air pump or the pipeline can be adjusted, and the returning step

2027;

Step 2032, starting a plasma power source to generate a plasma of a certain density and an electron temperature, and applying a bias voltage to the substrate placed on the sample stage by a power source capable of applying a bias voltage, the plasma power source being a radio frequency power source, the frequency For 13.56 MHz, the output power can be 800 W. The power supply with bias voltage can be pulsed DC power supply with a pulse width of 10 us, a duty cycle of 20%, a frequency of 20 kHz, and the applied bias voltage is - 20000V;

Step 2035, setting the injection time, starting the injection, and the injection time can be set according to specific conditions, such as the performance of the substrate to be prepared for the porous structure, the shape size of the substrate, the density of the plasma, and other process parameters. It has a certain impact on the injection time.

As shown in Fig. 11, another embodiment of the process parameters of the substrate preparation apparatus for adjusting the porous structure includes the following steps:

Step 2024, the monitoring device in the vacuum system determines whether the pressure of the injection chamber enters a predetermined background pressure range, for example, whether it is in the range of 10 Pa to 1000 Pa, and if so, proceeds to step 2026, otherwise, returns to step 2022. ;

Step 2026, charging the injection chamber with a mixed gas, for example, a mixed gas composed of CF ₄ and N ₂ ; Step 2028, the monitoring device in the gas supply system judges a gas having an etching effect in the mixed gas such as CF ₄ and N ₂ volume ratio is between 0.1 ~ 10, and if so, proceeds to step 2032, otherwise, proceeds to step 2030;

Step 2030, the gas supply device in the gas supply system adjusts the mixing ratio of the mixed gas, returning to step 2028; Step 2032, starting a plasma power source to generate a plasma of a certain density and an electron temperature, and applying a bias voltage to a substrate placed on the sample stage by a power source capable of applying a bias voltage, and the plasma power source may be a chopper power source. The frequency is 2.4 GHz, the output power can be 1000 W, and the power supply with bias voltage can be pulsed DC power supply with a pulse width of 25 us, a duty cycle of 50%, a frequency of 20 kHz, and the applied bias voltage is -2000V;

Step 2035, setting the injection time, starting the injection, and the injection time can be set according to specific conditions, for example, the performance of the substrate to be prepared for the porous structure, the shape and size of the substrate, the density of the plasma, and other process parameters. It has a certain impact on the injection time.

As shown in Fig. 12, a third embodiment of the process parameters for adjusting the substrate preparation apparatus of the porous structure includes the following steps:

Step 2024, the monitoring device in the vacuum system determines whether the pressure of the injection chamber enters a preset background pressure range, for example, whether it is in the range of 1 Pa to 100 Pa, and if yes, proceeds to step 2026, otherwise, returns to step 2022. ;

Step 2026, charging the injection chamber with a mixed gas, for example, a mixed gas composed of SF ₆ and 0 ₂ ; Step 2028, the monitoring device in the gas supply system determines that the gas having the etching effect in the mixed gas is blunt Whether the volume ratio between the chemical gases enters a predetermined volume ratio range, for example, whether the volume ratio of SF ₆ and 0 ₂ is between 0.5 and 20, and if so, proceeds to step 2032, otherwise, proceeds to step

2030;

Step 2030, the gas supply device in the gas supply system adjusts the mixing ratio of the mixed gas, and returns to step 2028;

Step 2032, starting a plasma power source to generate a plasma of a certain density and an electron temperature, and applying a bias voltage to a substrate placed on the sample stage by a power source capable of applying a bias voltage, the plasma power source being variable frequency RF power supply with a maximum frequency of 60 MHz and a maximum output power of 3000 W. The power supply with bias voltage can be a pulsed DC power supply with a minimum pulse width of lOO us, a duty cycle of 25%, and a maximum frequency of 2.5 kHz. The maximum bias voltage applied is -5000V;

Step 2033, the monitoring device of the plasma power source (for example, a monitoring device composed of a directional coupler and a controller) determines whether the output power and/or frequency of the plasma power source enters a preset value range (for example, the output power of the plasma power source). A monitoring device with a range of 2000W to 3000W and a plasma power supply frequency range of 10 MHz to 60 MHz) and a bias voltage can determine whether the pulse width, duty cycle, frequency, and/or applied bias voltage are Pre-set value range (for example, pulse width range is 100 us ~ 10 ms, duty cycle range is 25% ~ 50%, power supply frequency is 50Hz ~ 2.5 kHz, and the applied bias voltage range is -1000V ~ - 5000V), if the requirements are met, proceed to step 2038, otherwise, Go to step 2036;

Step 2034, according to certain control rules, adjust the corresponding plasma power supply output power, frequency, pulse width, duty cycle, frequency and / or bias voltage of the current that can apply the bias voltage, return to step 2053;

Step 2035, setting the injection time, starting the injection, and the injection time can be set in a specific situation, for example, the performance of the substrate for preparing the porous structure, the shape and size of the substrate, the density of the plasma, and other process parameters are all Injection time has a certain impact.

It should be noted that in the present invention, injecting reactive ions in the plasma into the substrate does not exclude the injection of non-reactive ions in the plasma into the substrate, because in some cases The plasma generated by the porous substrate preparation device includes ions that do not participate in the reaction, and these ions that do not participate in the reaction are injected into the substrate together during the immersion ion implantation process.

It should be noted that the control rules mentioned herein may be common feedback control algorithms, PID control algorithms, fuzzy control algorithms, genetic control algorithms, or expert systems designed according to certain empirical knowledge; control schemes may be implemented by electronic means. It can also be realized mechanically or by a technical solution suitable for actual adjustment. Among them, the electronic circuit control scheme includes hard-wired circuit logic control (such as a circuit composed of discrete components or a circuit composed of FPGA, CPLD or GAL), micro-controller control (such as single-chip microcomputer, DSP or ARM, etc.) and computer control.

It should be noted that, the numerical ranges mentioned herein and set in advance, inclusive of the range, for example, The base pressure in the range of ^{^{10- 7 Pa ~ lOOOPa, 10- 7}} Pa and lOOOPa also belong to the background pressure range. In the actual process, the preset value range can be adjusted by the control algorithm or manually adjusted by the operator according to the process requirements. In the present context, "and/or" means that more than two options can select not only one of them but also more than two options; the combination of multiple options is determined according to actual process conditions.

It should be noted that in the present invention, the step of adjusting the process parameters of the substrate preparation apparatus of the porous structure may be performed not only after the step of placing the substrate in the substrate preparation apparatus of the porous structure, but also by placing the substrate in the porous state. Before the step of the substrate preparation device of the structure, the initial value of the process parameter is adjusted in advance according to requirements; and, in the process of plasma generation and injection, the corresponding process parameters may be appropriately adjusted according to the process requirements and needs ( Includes manual adjustment and automatic adjustment to prepare a substrate that meets the performance requirements or better performance of the porous structure.

Since the invention adopts the plasma immersion ion implantation process to prepare the bottom of the porous structure, the dry process does not require the addition of the electrolytic corrosion solution, so the process does not need to remove the electrolyte, and the structure control is convenient, and the finally formed structure is easy to control; Moreover, compared with the cumbersome laser scanning processing, the method is convenient to control, and the operation cylinder is simple, which is advantageous for the preparation of batches of solar cells. The above-described embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above-described embodiments, and any other changes, modifications, substitutions, combinations, and combinations thereof may be made without departing from the spirit and scope of the invention. Simplifications, which are equivalent replacement means, are included in the scope of the present invention.

Claims

Claim

1. A porous structure of a village bottom, characterized by:

The surface topography of the substrate is disordered porous, the depth of the hole is smaller than the thickness of the substrate, the holes are independent of each other, and the holes are not connected.

2. The porous structure substrate according to claim 1, wherein:

The pores have an average pore size between 10 nanometers and 2 micrometers.

3. The porous structure substrate according to claim 1, wherein:

The pores have an area density on the surface of the substrate of 0.01 to 0.91.

4. The porous structure substrate of claim 1 wherein:

The pores have an average pore depth of between 50 nanometers and 10 meters.

The porous structure substrate according to any one of claims 1 to 4, wherein the substrate is made of a Si-based material, a GaN-based material, an InP-based material, a GaAs-based material, a Ge-based material, and carbon. Made of a base material, SiN _x , Si0 ₂ , SiC, GeSi, ZnO, Ti0 ₂ or CdS.

A method for preparing a substrate of a porous structure, comprising the steps of: placing the substrate in an injection chamber of the substrate preparation device;

Adjusting the process parameters of the village bottom preparation device into a preset numerical range;

Injecting reactive ions in a plasma generated by the substrate preparation device into the substrate; and reacting the reactive ions with the substrate to form a porous substrate; wherein, the surface of the porous substrate The morphology is disordered porous, the depth of the holes is smaller than the thickness of the substrate, the holes are independent of each other, and the holes are not connected.

7. The method according to claim 6, wherein placing the substrate in the injection chamber of the substrate preparation device further comprises:

The bottom of the village is electrically connected to a power source to which a bias voltage is applied.

The method according to claim 7, wherein the adjusting the process parameters of the substrate preparation device into a preset value range comprises: Extracting the gas injection chamber, such that the injection pressure into the chamber base pressure range set in advance, the range of the base pressure set in advance to 10- ⁷ Pa ~ 1000Pa;

Filling the injection chamber with a mixed gas, adjusting the flow rate of the mixed gas, so that the pressure of the injection chamber enters a preset working pressure range, and the preset working pressure range is 10" ³ Pa ~ lOOOPa And the volume ratio between the bodies enters a preset volume ratio range, and the preset volume ratio ranges from 0.01 to 100.

9. The method according to claim 8, wherein: the gas having etching action comprises SF ₆ , CF ₄ , CHF ₃ , C ₄ F ₈ , NF ₃ , SiF ₄ , C ₂ F ₆ , HF , BF ₃ , PF ₃ , Cl ₂ , HCl, SiH ₂ Cl ₂ , SiCl ₄ , BC1 ₃ or HBr, the passivating gas comprises 0 ₂ , N ₂ 0 or N ₂ .

10. A method according to any one of claims 6 to 9, characterized in that:

The pores have an average pore size between 10 nanometers and 2 micrometers; the pores have an areal density on the surface of the substrate of 0.01 to 0.91; and the pores have an average pore depth of between 50 nanometers and 10 nanometers. .