Oxidation method of porous silicon

Abstract

The invention provides an oxidation method of porous silicon, and relates to the technical field of material treatment. The method comprises the following steps: obtaining porous silicon; and performing electrochemical oxidation treatment on the porous silicon through a dynamic current regulation and control process to obtain the oxidized porous silicon. According to the method, electrochemical oxidation treatment is carried out on the porous silicon through a dynamic current regulation and control process, so that an oxidation cut-off phenomenon can be avoided, the porous silicon can obtain a uniform and thorough passivation effect, and the problems of non-uniform porous silicon oxidation and incomplete local passivation in traditional constant-current / constant-voltage electrochemical oxidation are solved.

Description

Technical Field

[0001] The invention relates to the technical field of material processing, and in particular to an oxidation method for porous silicon. Background Art

[0002] As a new functional material with strategic significance, porous silicon has shown broad application prospects in information technology, biomedicine, environmental engineering and energy conversion due to its excellent electrical and optical properties. It is necessary to actively passivate the porous silicon layer after its preparation, which can not only improve its stability and effectively avoid performance degradation, but also further improve its chemical, optical and electrical properties. Common treatment methods include high-temperature thermal oxidation, low-temperature air annealing, surface nitridation, high-temperature thermal carbonization, multiple annealing, high-pressure water vapor annealing, etc. However, these methods generally have the disadvantages of complex process, high cost or high temperature and high pressure conditions, and the latter will also cause irreversible damage to the microstructure of porous silicon. In contrast, electrochemical oxidation has attracted much attention due to its advantages such as simple operation, low cost and large-area treatment at room temperature. This method realizes the oxidation passivation of porous silicon by applying a specific electric field in the electrolyte. However, the traditional constant current / constant voltage electrochemical oxidation has obvious limitations: its unidirectional oxidation mechanism easily leads to uneven oxidation of thick porous silicon, that is, overoxidation on one side and insufficient oxidation on the other side. This problem of incomplete local passivation seriously restricts the practical application of this technology, and thus limits the application potential of porous silicon materials in a wider range of fields. Summary of the invention

[0003] In view of the above problems, an embodiment of the present invention provides a method for oxidizing porous silicon.

[0004] One aspect of the present invention provides a method for oxidizing porous silicon, comprising: obtaining porous silicon; and electrochemically oxidizing the porous silicon through a dynamic current control process to obtain oxidized porous silicon.

[0005] According to an embodiment of the present invention, performing electrochemical oxidation treatment on porous silicon through a dynamic current regulation process includes: immersing the porous silicon in an electrolyte; and performing electrochemical oxidation treatment on the porous silicon through a dynamic current regulation process.

[0006] According to an embodiment of the present invention, the electrolyte includes: a sulfuric acid solution, a nitric acid solution and a sodium hydroxide solution.

[0007] According to an embodiment of the present invention, electrochemical oxidation treatment of porous silicon by a dynamic current control process includes: electrochemical oxidation treatment of porous silicon for a target time by increasing current continuously or stepwise.

[0008] According to an embodiment of the present invention, the target duration is less than or equal to 60 minutes.

[0009] According to an embodiment of the present invention, obtaining porous silicon includes: preparing porous silicon by at least one of an electrochemical etching method, a chemical etching method, a galvanic cell method and a hydrothermal etching method.

[0010] According to an embodiment of the present invention, the electrochemical oxidation treatment of porous silicon by the dynamic current control process further includes: irradiating the porous silicon with a light source.

[0011] According to an embodiment of the present invention, the method for oxidizing porous silicon further includes: performing thermal annealing on the oxidized porous silicon.

[0012] According to an embodiment of the present invention, performing thermal annealing on the oxidized porous silicon includes: performing thermal annealing on the oxidized porous silicon in an inert gas atmosphere, a nitrogen atmosphere or a vacuum environment.

[0013] According to an embodiment of the present invention, the thickness of the porous silicon is greater than or equal to 5 μm.

[0014] The present invention uses a dynamic current control process to electrochemically oxidize porous silicon, which can avoid oxidation truncation and enable the porous silicon to obtain a uniform and thorough passivation effect, solving the problems of uneven oxidation of porous silicon and incomplete local passivation in traditional constant current / constant voltage electrochemical oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above contents and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0016] Figure 1 A flowchart schematically shows a method for oxidizing porous silicon according to an embodiment of the present invention;

[0017] Figure 2 Schematically showing a dynamic current waveform diagram of a porous silicon oxidation method according to an embodiment of the present invention and a constant current waveform diagram of a control group;

[0018] Figure 3 A scanning electron microscope morphology comparison diagram schematically shows a method for oxidizing porous silicon according to an embodiment of the present invention;

[0019] Figure 4 A comparison diagram of the microscopic oxidation principle of the oxidation method of porous silicon according to an embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0021] It should be noted that in the drawings or descriptions, similar or identical parts use the same figure numbers. The technical features in the various embodiments exemplified in the specification can be freely combined to form new solutions without conflict, and in the drawings, the shape or thickness of the embodiments can be expanded and simplified or conveniently indicated. Furthermore, the elements or implementations not shown or described in the drawings are in a form known to ordinary technicians in the relevant technical field. In addition, although demonstrations of parameters containing specific values ​​may be provided herein, it should be understood that the parameters do not need to be exactly equal to the corresponding values, but can be approximated to the corresponding values ​​within an acceptable error tolerance or design constraint.

[0022] Unless there are technical obstacles or contradictions, the above-mentioned various embodiments of the present invention can be freely combined to form other embodiments, and these other embodiments are all within the protection scope of the present invention.

[0023] Although the present invention is described in conjunction with the accompanying drawings, the embodiments disclosed in the drawings are intended to exemplify the preferred embodiments of the present invention and should not be construed as limiting the present invention. The size ratios in the drawings are merely illustrative and should not be construed as limiting the present invention.

[0024] Although some embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the present general disclosed concept.

[0025] Figure 1 The flowchart of the method for oxidizing porous silicon according to an embodiment of the present invention is schematically shown.

[0026] like Figure 1 As shown, an embodiment of the present invention provides a method for oxidizing porous silicon, including operations S110 and S120.

[0027] In operation S110 , porous silicon is obtained.

[0028] According to an embodiment of the present invention, obtaining porous silicon includes: preparing porous silicon by at least one of an electrochemical etching method, a chemical etching method, a galvanic cell method and a hydrothermal etching method.

[0029] For example, porous silicon can be prepared by electrochemical etching. <100> The silicon wafer is placed in a mixed solution of HF (hydrogen fluoride) solution and ethanol in a ratio of 1:1 for anodization treatment, wherein the HF solution may be a solution containing 40% hydrogen fluoride, and the applied anodization current density is 30 mA / cm 2 , the power-on time is 3 min.

[0030] Among them, porous silicon can be prepared on single crystal silicon, or on epitaxial polycrystalline silicon or amorphous silicon. The prepared porous silicon can be a single-layer structure with a fixed porosity, or a multi-layer structure with a variable porosity. The doping type of the material can be n-type, p-type silicon or intrinsic.

[0031] According to an embodiment of the present invention, the thickness of the porous silicon is greater than or equal to 5 μm.

[0032] Porous silicon, with its high specific surface area and easy oxidation properties, has shown unique advantages as a structural isolation layer in the field of integrated circuits. To achieve optimal isolation performance, the porous silicon layer usually needs to maintain a thickness of more than 5 μm. In addition, the excellent electroluminescent properties of this material have opened up new avenues for the development of all-silicon-based optoelectronic integration technology. When it is used as a device functional layer, in order to obtain good pressure resistance and stability, a thicker structure is usually required. Finally, the significantly high specific surface area and adjustable pore size structure characteristics of porous silicon make it an ideal candidate material for supercapacitor electrode materials and advanced energy storage systems. In order to optimize the ion transport kinetics and increase the energy storage capacity, a thicker porous silicon layer structure design is also required.

[0033] Compared with traditional thermal oxidation, high temperature steam annealing or high temperature thermal carbonization, the electrochemical oxidation in the embodiment of the present invention has the advantages of simple operation, low cost and large area processing at room temperature. However, porous silicon layers with a thickness greater than 5 μm are usually difficult to fully oxidize using conventional constant current / constant voltage oxidation. Therefore, the present invention provides a method for achieving uniform electrochemical oxidation of thick porous silicon layers to meet the application requirements of different fields.

[0034] In operation S120, the porous silicon is electrochemically oxidized by a dynamic current control process to obtain oxidized porous silicon.

[0035] According to an embodiment of the present invention, the electrochemical oxidation treatment of porous silicon by a dynamic current regulation process includes: immersing the porous silicon in an electrolyte. The electrochemical oxidation treatment of porous silicon by a dynamic current regulation process.

[0036] According to an embodiment of the present invention, the electrolyte includes: a sulfuric acid solution, a nitric acid solution and a sodium hydroxide solution.

[0037] Figure 2 The dynamic current waveform diagram of the porous silicon oxidation method according to the embodiment of the present invention and the constant current waveform diagram of the control group are schematically shown.

[0038] For example, the porous silicon obtained in operation S110 may be divided into group A samples and group B samples, and both group A samples and group B samples are placed in, for example, a 1 mol / L sulfuric acid solution for electrochemical oxidation treatment.

[0039] Group A samples are examples of the present invention, and can be used Figure 2 The left figure shows a linear increase in the dynamic current for electrochemical oxidation, with a specific current density range of 0-30 mA / cm 2 , the oxidation time is 20 min.

[0040] The samples in group B were used as the control group, and the electrochemical oxidation method with a constant current density of 20 mA / cm 2 The oxidation time was 15 min, and the oxidation current waveforms used by samples in group A and group B were as follows: Figure 2 shown.

[0041] It is worth noting that the electrochemical oxidation process of porous silicon is completed by the exchange of charges between the porous silicon layer and the electrolyte. The exchanged charge Q (defined as the amount of charge flowing through the electrode) can be quantitatively calculated by Q=j×A×t, where j is the oxidation current density, A is the area of ​​the porous silicon oxidation zone, and t is the duration of oxidation. Therefore, for the sake of comparison, the exchanged charge corresponding to the current waveforms used in the two different oxidation methods in this embodiment is equal (18 C / cm 2 ).

[0042] According to an embodiment of the present invention, the target duration is less than or equal to 60 minutes.

[0043] The electrochemical oxidation time can be determined according to the porosity, physical thickness and micromorphology of the porous silicon layer, and usually does not exceed 60 min.

[0044] Figure 3 The scanning electron microscope morphology comparison diagram of the oxidation method of porous silicon according to an embodiment of the present invention is schematically shown. Figure 4 A comparison diagram of the microscopic oxidation principle of the oxidation method of porous silicon according to an embodiment of the present invention is schematically shown.

[0045] According to an embodiment of the present invention, electrochemical oxidation treatment of porous silicon by a dynamic current control process includes: electrochemical oxidation treatment of porous silicon for a target time by increasing current continuously or stepwise.

[0046] See also Figure 3 , Figure 3The cross-sectional and surface scanning electron microscope morphology comparison of porous silicon samples using dynamic current oxidation (Group A samples) and constant current oxidation (Group B samples) is shown. The results show that Group A samples exhibit uniform oxidation characteristics throughout the entire porous silicon layer, while Group B samples have obvious oxidation interface stratification inside, indicating that the oxidation process is incomplete (the lower right arrow in the figure indicates the oxidation direction). In addition, the surface morphology of the two groups of samples also shows significant differences: the surface pore size of Group A samples is significantly reduced, confirming that the oxidation layer has completely covered the surface of the material, while Group B samples still maintain a larger pore size, indicating that the degree of oxidation in the surface area is low or not fully oxidized. The above differences in morphological features confirm the decisive influence of different current waveforms on the oxidation behavior of porous silicon, and further indicate that by precisely controlling the current waveform parameters during the electrochemical oxidation process, a controllable oxidation effect can be achieved for porous silicon with different structural characteristics, thereby meeting the requirements for material performance in specific application scenarios.

[0047] See also Figure 4 , Figure 4 The reaction mechanisms of two different oxidation modes are explained by the schematic diagram of the electrochemical oxidation model. Studies have shown that the electrochemical oxidation process of porous silicon depends on the continuous supply of holes to maintain the reaction. Under the action of an external electric field, holes are injected from the substrate and drive the oxidation reaction from bottom to top. In the constant current oxidation mode, due to the high and constant initial oxidation current density, the hole concentration at the porous silicon / substrate interface accumulates significantly, and the electrolyte / porous silicon interface electric field strength is enhanced, which triggers rapid initial oxidation kinetics. This high-speed oxidation process promotes the formation of a dense and continuous oxide layer at the bottom of the porous silicon, resulting in a complete blockage of the hole transport channel (i.e., the oxidation truncation effect), which makes it impossible for holes to migrate along the nano-silicon pillars to the surface, and ultimately leads to the premature termination of the oxidation reaction. In contrast, when the linear gradient current oxidation mode is adopted, the lower current density in the initial stage keeps the interface electric field strength and hole injection concentration at a low level, thereby achieving controllable slow oxidation kinetics. This progressive oxidation characteristic causes the oxidation reaction to occur preferentially in the bottom region of the hole (dominated by the field enhancement effect). The formed oxide layer is discontinuous and non-dense, thus maintaining the smooth flow of hole transport channels and ensuring that holes are continuously transported to the upper region of the porous silicon, ultimately achieving complete oxidation of the entire layer.

[0048] It is understandable that in order to achieve the above effects, the dynamic regulation of current must meet the following conditions: First, the current density must achieve a time-series change from low to high, and the process should be completed gradually within a reasonable time scale; second, the regulation mode is not limited to continuous linear growth, and a step-by-step increase strategy can be adopted.

[0049] The core mechanism is to effectively control the interface electric field strength and hole injection concentration by maintaining a low current density in the initial stage, thereby suppressing the oxidation rate at a low level. This ensures that the oxide layer formed in the early stage is discontinuous and non-dense, thereby maintaining the conductivity of the hole transmission channel, ensuring that holes continue to be transported to the upper layer of porous silicon, and finally achieving full oxidation of the entire layer of the material.

[0050] This embodiment shows that under the condition of the same total exchange charge, completely different oxidation effects will be obtained by using different oxidation current waveforms. Compared with the constant current oxidation mode, the use of low to high dynamic current control technology can achieve a higher degree of oxidation. This finding shows that for thick-layer porous silicon structures, the uniformity and sufficiency of the oxidation process can be effectively improved by optimizing the oxidation current waveform parameters. It should be emphasized that in the constant current oxidation mode used in this embodiment, due to the existence of the oxidation cutoff effect, simply extending the oxidation time cannot further improve the oxidation effect and enable the porous silicon layer to obtain more sufficient oxidation. This fact further confirms the technical advantages of dynamic current control technology in achieving deep and uniform oxidation of porous silicon.

[0051] It should be noted that in this embodiment, based on the unique morphological and structural characteristics of the selected porous silicon layer, the experiment adopted a dynamic current control strategy in a linear increasing mode for electrochemical oxidation treatment. However, for porous silicon systems with different structural characteristics (such as pulsed multilayer structures), the dynamic current control technology can also adopt a variety of different current increase modes such as step increase and exponential increase. Regardless of the dynamic current control method adopted, the core principle is that a sufficiently low oxidation rate must be ensured in the initial stage of oxidation, so as to effectively suppress the oxidation truncation phenomenon during the electrochemical oxidation process and ensure that the porous silicon layer can achieve a complete and uniform oxidation effect.

[0052] Compared with the conventional constant current or constant voltage electrochemical oxidation method, the variable current oxidation method from small to large in the present invention can avoid oxidation truncation phenomenon, so that the porous silicon layer can obtain a uniform and thorough passivation effect.

[0053] According to an embodiment of the present invention, the electrochemical oxidation treatment of porous silicon by the dynamic current control process further includes: irradiating the porous silicon with a light source.

[0054] In order to increase the oxidation rate, a light source may be used to irradiate the porous silicon. The light source may be a tungsten lamp. The power of the light source may not exceed 1000 W. The distance between the light source and the sample may not exceed 50 cm.

[0055] For example, the electrochemical oxidation process of group A samples and group B samples can be carried out under the illumination of a 500 W tungsten lamp to provide the holes required for the reaction, and the samples are set at a distance of 20 cm from the tungsten lamp.

[0056] According to an embodiment of the present invention, the method for oxidizing porous silicon further includes: performing thermal annealing on the oxidized porous silicon.

[0057] The annealing step can remove the residual electrolyte in the pores and further improve the SiO 2 The thermal annealing used can be furnace thermal annealing or rapid thermal annealing, the annealing temperature can be between 500℃-1200℃, and the annealing time does not exceed 120 mins.

[0058] According to an embodiment of the present invention, performing thermal annealing on the oxidized porous silicon includes: performing thermal annealing on the oxidized porous silicon in an inert gas atmosphere, a nitrogen atmosphere or a vacuum environment.

[0059] Annealing can be performed under vacuum or in an inert gas atmosphere such as nitrogen or argon.

[0060] For example, both groups of samples can be annealed at 550°C for 60 min in a furnace chamber to remove residual electrolyte in the pores and improve the quality of the silicon dioxide film obtained by electrochemical oxidation. 2 As a protective gas, it cools down to room temperature after annealing.

[0061] It is understood that the above-used substrate type, preparation method, porous silicon layer structure, electrolyte concentration, current waveform, oxidation time, light intensity of the light source and distance from the sample can be appropriately selected by those skilled in the art according to specific needs and ultimate goals. The variable current electrochemical oxidation method adopted is not limited by the structure and thickness of the porous silicon layer, and the current waveform can be flexibly adjusted as needed to meet the application needs of different fields.

[0062] It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based on design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged without departing from the scope of the present invention.

[0063] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for oxidizing porous silicon, characterized in that: include: obtaining porous silicon; The porous silicon is subjected to electrochemical oxidation treatment through a dynamic current regulation process to obtain oxidized porous silicon.

2. The method according to claim 1, characterized in that The electrochemical oxidation treatment of the porous silicon by the dynamic current control process comprises: immersing the porous silicon in an electrolyte; The porous silicon is subjected to electrochemical oxidation treatment through a dynamic current regulation process.

3. The method according to claim 2, characterized in that The electrolyte includes: sulfuric acid solution, nitric acid solution and sodium hydroxide solution.

4. The method according to claim 1 or 2, characterized in that: The electrochemical oxidation treatment of the porous silicon by the dynamic current control process comprises: The porous silicon is subjected to electrochemical oxidation treatment for a target time by increasing the current continuously or stepwise.

5. The method according to claim 4, characterized in that The target duration is less than or equal to 60 minutes.

6. The method according to claim 1, characterized in that The obtaining of porous silicon comprises: The porous silicon is prepared by at least one of an electrochemical etching method, a chemical etching method, a galvanic cell method and a hydrothermal etching method.

7. The method according to claim 1, characterized in that The electrochemical oxidation treatment of the porous silicon by the dynamic current control process further comprises: The porous silicon is irradiated with a light source.

8. The method according to claim 1, characterized in that: The method further comprises: The oxidized porous silicon is subjected to thermal annealing treatment.

9. The method according to claim 8, characterized in that The thermal annealing treatment of the oxidized porous silicon comprises: The oxidized porous silicon is subjected to thermal annealing treatment in an inert gas atmosphere, a nitrogen atmosphere or a vacuum environment.

10. The method according to claim 1, characterized in that The thickness of the porous silicon is greater than or equal to 5 μm.

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