Method for oxidizing porous silicon

Abstract

The application provides a porous silicon oxidation method and relates to the technical field of material processing. The method comprises the following steps: obtaining porous silicon; and performing electrochemical oxidation treatment on the porous silicon through a dynamic current regulation process to obtain oxidized porous silicon. The electrochemical oxidation treatment on the porous silicon through the dynamic current regulation process can avoid the oxidation interruption phenomenon, so that the porous silicon can obtain uniform and complete passivation effect, and the problems of uneven oxidation and incomplete local passivation of the porous silicon in traditional constant current / constant voltage electrochemical oxidation are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material processing, and in particular to a method for oxidizing porous silicon. BACKGROUND

[0002] Porous silicon, as a new type of functional material with strategic significance, has shown a wide application prospect in the fields of information technology, biomedical engineering, environmental engineering and energy conversion due to its excellent electrical and optical properties. It is necessary to actively perform passivation treatment on 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 steam annealing, etc. However, these methods generally have the disadvantages of complex process, high cost or the need for high temperature and high pressure conditions, and the latter can also cause irreversible damage to the microstructure of the porous silicon. In contrast, the electrochemical oxidation method has attracted much attention due to its advantages of simple operation, low cost and the ability to realize 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: the one-way oxidation mechanism can easily lead to uneven oxidation of thick-layer porous silicon, i.e., over-oxidation on one side and insufficient oxidation on the other side. This problem of local incomplete passivation seriously restricts the practical application effect of the technology, and further limits the application potential of porous silicon materials in a wider range of fields. SUMMARY

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

[0004] One aspect of the present application provides a method for oxidizing porous silicon, comprising: obtaining porous silicon; performing electrochemical oxidation treatment on the porous silicon through a dynamic current regulation process to obtain oxidized porous silicon.

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

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

[0007] According to an embodiment of the present application, the electrochemical oxidation treatment on the porous silicon through the dynamic current regulation process comprises: performing electrochemical oxidation treatment on the porous silicon for a target time length in a continuous current increase or a stepwise current increase manner.

[0008] According to an embodiment of the present application, the target time length is less than or equal to 60 min.

[0009] According to the embodiment of the present application, 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.

[0010] According to the embodiment of the present application, the electrochemical oxidation treatment of the porous silicon by the dynamic current regulation process further comprises: irradiating the porous silicon by a light source.

[0011] According to the embodiment of the present application, the method for oxidizing the porous silicon further comprises: performing a thermal annealing treatment on the oxidized porous silicon.

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

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

[0014] The present application can avoid the oxidation truncation phenomenon by the dynamic current regulation process to electrochemically oxidize the porous silicon, so that the porous silicon can obtain a uniform and complete passivation effect, and the problems of non-uniform oxidation and incomplete local passivation of the porous silicon in the traditional constant current / constant voltage electrochemical oxidation are solved. BRIEF DESCRIPTION OF DRAWINGS

[0015] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0016] Figure 1 a flow chart of the method for oxidizing the porous silicon according to the embodiment of the present application is schematically shown;

[0017] Figure 2 a dynamic current waveform diagram of the method for oxidizing the porous silicon according to the embodiment of the present application and a constant current waveform diagram of a control group are schematically shown;

[0018] Figure 3 a scanning electron microscope (SEM) morphology comparison diagram of the method for oxidizing the porous silicon according to the embodiment of the present application is schematically shown;

[0019] Figure 4 a micro-oxidation principle comparison diagram of the method for oxidizing the porous silicon according to the embodiment of the present application is schematically shown. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to specific embodiments and the accompanying drawings.

[0021] It is to be noted that similar or identical parts are denoted by the same reference numerals in the drawings or the description. The technical features in the example embodiments described in the specification can be freely combined in the absence of conflicts to form new solutions, and the shape or thickness of the embodiments can be exaggerated in the drawings for simplicity or convenience. Furthermore, elements or implementations not depicted or described in the drawings are in forms known to those skilled in the art. In addition, although examples can be provided herein including parameters with specific values, it should be understood that the parameters need not be exactly equal to the corresponding values, but can be approximately equal to the corresponding values within an acceptable error range or design constraint.

[0022] Unless there is a technical obstacle or contradiction, the above various embodiments of the present application can be freely combined to form additional embodiments, which are all within the scope of protection of the present application.

[0023] Although the present application is illustrated with reference to the accompanying drawings, the embodiments disclosed in the drawings are intended to exemplarily illustrate the preferred embodiments of the present application and should not be construed as a limitation of the present application. The dimensional proportions in the drawings are merely illustrative and should not be construed as a limitation of the present application.

[0024] Although some embodiments of the general inventive concept have been shown and described, it will be understood by those having ordinary skill in the art that changes can be made to these embodiments without departing from the principles and spirit of the general inventive concept.

[0025] Figure 1 A flowchart of a method of oxidizing porous silicon according to an embodiment of the present application is schematically shown.

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

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

[0028] According to an embodiment of the present application, obtaining the porous silicon includes preparing the 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, the porous silicon can be prepared by the electrochemical etching method. An n-type <100> silicon wafer with a resistance of 0.01 Ω·cm is selected and placed in a mixed solution of a mixture ratio of 1:1 of an HF (hydrogen fluoride) solution and ethanol for an anodization treatment, wherein the HF solution can be a solution with a hydrogen fluoride content of 40%, and an anodization current density of 30 mA / cm 2 2 is applied for 3 min.

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

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

[0032] The porous silicon has unique advantages as a structure isolation layer in the field of integrated circuits due to its high specific surface area and easy oxidation characteristics. In order to achieve the best isolation performance, the porous silicon layer usually needs to maintain a thickness of 5 μm or more. In addition, the excellent electroluminescence performance of the material opens up a new way for the development of all-silicon-based optoelectronic integration technology, and when it is used as a device functional layer, a relatively thick structure is usually required to obtain good voltage resistance and stability. Finally, the significant high specific surface area and adjustable pore size structure characteristics of the porous silicon make it an ideal candidate material for supercapacitor electrode materials and advanced energy storage systems, and a thicker porous silicon layer structure design is also required to optimize ion transport kinetics and improve energy storage capacity.

[0033] Compared with traditional thermal oxidation, high-temperature water vapor annealing or high-temperature thermal carbonization, the electrochemical oxidation in the embodiment of the present application has the advantages of simple operation, low cost and large-area processing at room temperature. However, it is usually difficult to fully oxidize the porous silicon layer with a thickness greater than 5 μm using conventional constant current / constant voltage oxidation, so the present application provides a method for uniformly electrochemically oxidizing a thick porous silicon layer, which meets the application requirements in different fields.

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

[0035] According to an embodiment of the present application, the electrochemical oxidation of the porous silicon by the dynamic current regulation process includes immersing the porous silicon in an electrolyte. The porous silicon is electrochemically oxidized by the dynamic current regulation process.

[0036] According to an embodiment of the present application, 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 oxidation method of the porous silicon according to the embodiment of the present application and the constant current waveform diagram of the control group are schematically shown.

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

[0039] The samples in Group A are embodiments of the present application, and can be subjected to electrochemical oxidation by using Figure 2 The dynamic current shown in the left graph of FIG. 2 linearly increases, and the specific current density range is 0-30 mA / cm 2 , and the oxidation time is 20 min.

[0040] The samples in Group B are control groups, and can be subjected to electrochemical oxidation by using a constant current, with a current density of 20 mA / cm 2 , and the oxidation time is 15 min. The oxidation current waveforms used for the samples in Group A and Group B are shown in Figure 2 .

[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 x A x t, where j is the oxidation current density, A is the area of the porous silicon oxidation zone, and t is the duration of the oxidation. Therefore, in order to facilitate comparison, the exchanged charge corresponding to the current waveforms used in the two different oxidation methods in the present embodiment is equal (18 C / cm 2 ).

[0042] According to an embodiment of the present application, the target time length is less than or equal to 60 min.

[0043] The electrochemical oxidation time can be determined according to the porosity, physical thickness, and microstructure of the porous silicon layer, and is usually not more than 60 min.

[0044] Figure 3 The scanning electron microscope morphology contrast diagram of the oxidation method of porous silicon according to an embodiment of the present application is schematically shown. Figure 4 The micro-oxidation principle contrast diagram of the oxidation method of porous silicon according to an embodiment of the present application is schematically shown.

[0045] According to an embodiment of the present application, the electrochemical oxidation treatment of the porous silicon by dynamic current regulation process includes: continuously increasing the current or increasing the current in a stepwise manner to electrochemically oxidize the porous silicon for a target time length.

[0046] Please refer to Figure 3 , Figure 3The cross-section and surface scanning electron microscope morphologies of porous silicon samples using dynamic current oxidation (Group A samples) and constant current oxidation (Group B samples) are 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, indicating that the oxidation process is incomplete (the arrow in the lower right of the figure indicates the oxidation direction). In addition, the surface morphologies of the two groups of samples also show significant differences: the surface pore size of Group A samples is significantly reduced, confirming that the oxidation layer has completely covered the material surface, while Group B samples still have larger pore sizes, indicating that the surface layer region is less oxidized or not fully oxidized. The above differences in morphology characteristics 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, controlled oxidation effects can be achieved for porous silicon with different structural characteristics, thereby meeting the needs of specific application scenarios for material performance.

[0047] Please refer to Figure 4 , Figure 4 The reaction mechanisms of the two different oxidation modes are illustrated through an electrochemical oxidation model diagram. The study shows that the electrochemical oxidation process of porous silicon relies 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, the initial oxidation current density is high and remains constant, resulting in a significant accumulation of hole concentration at the porous silicon / substrate interface, and the electric field strength at the electrolyte / porous silicon interface is enhanced, thereby triggering rapid initial oxidation kinetics. This high-speed oxidation process causes the formation of a dense and continuous oxidation layer at the bottom of the porous silicon, completely blocking the hole transport channel (i.e., the oxidation cutoff effect), which prevents holes from migrating to the surface layer along the nanosilicon pillars, ultimately leading to the premature termination of the oxidation reaction. In contrast, when using the linearly varying current oxidation mode, the low current density at the initial stage maintains the interface electric field strength and hole injection concentration at a low level, thereby achieving a controlled slow oxidation kinetics. This progressive oxidation characteristic causes the oxidation reaction to occur preferentially in the pore bottom region (field enhancement effect dominant), and the formed oxidation layer is non-continuous and non-dense, thus maintaining the unobstructed hole transport channel, ensuring the continuous transport of holes to the upper layer of the porous silicon, and ultimately achieving full-layer complete oxidation.

[0048] It can be understood that, to achieve the above effects, the dynamic regulation of current needs to meet the following conditions: one, the current density needs to achieve a time sequence change from low to high, and this process should be gradually completed within a reasonable time scale, two, the regulation mode is not limited to continuous linear growth, and a stepwise incremental strategy can be used.

[0049] The core mechanism is that: by maintaining a low current density in the initial stage, the interface electric field strength and hole injection concentration are effectively controlled, so as to suppress the oxidation rate at a low level. Thus, the initial formed oxide layer presents a non-continuous and non-dense characteristic, thereby maintaining the conductivity of the hole transport channel, ensuring the continuous transportation of holes to the upper layer of porous silicon, and finally realizing the full oxidation of the material layer.

[0050] This embodiment shows that under the condition of the same total exchange charge, different oxidation current waveforms will result in completely different oxidation effects. Compared with the constant current oxidation mode, the use of low-to-high dynamic current regulation technology can achieve a higher oxidation degree. This finding shows that for thick 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, simply extending the oxidation time cannot further improve the oxidation effect and make the porous silicon layer more fully oxidized due to the existence of the oxidation cutoff effect. This fact further confirms the technical advantages of dynamic current regulation technology in achieving deep and uniform oxidation of porous silicon.

[0051] It should be particularly noted that in this embodiment, based on the unique topographic structure characteristics of the selected porous silicon layer, a dynamic current regulation strategy in a linear increasing mode is used for electrochemical oxidation treatment. However, for porous silicon systems with different structural characteristics (such as pulsed multilayer structures), dynamic current regulation technology can also use various current increasing modes such as stepwise increasing, exponential increasing, etc. Regardless of the dynamic current regulation mode used, the core principle is to ensure a low oxidation rate in the initial stage of oxidation, thereby effectively suppressing the oxidation cutoff phenomenon in the electrochemical oxidation process and ensuring that the porous silicon layer can achieve complete and uniform oxidation.

[0052] Compared with the traditional constant current or constant voltage electrochemical oxidation method, the small-to-large variable current oxidation method of the present application can avoid the oxidation cutoff phenomenon, so that the porous silicon layer can obtain a uniform and complete passivation effect.

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

[0054] In order to improve the oxidation rate, the porous silicon can be irradiated with a light source, and the light source used can be a tungsten lamp, the power of the light source used can be not more than 1000 W, and the distance between the light source and the sample can be not more than 50 cm.

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

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

[0057] The annealing step can remove residual electrolyte in the pores and further improve the quality of the SiO2 film layer obtained by electrochemical oxidation. The thermal annealing used can be furnace thermal annealing or rapid thermal annealing, the annealing temperature can be between 500°C and 1200°C, and the annealing time is not more than 120 minutes.

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

[0059] The annealing can be performed in a 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 minutes in a furnace chamber to remove residual electrolyte in the pores and improve the quality of the SiO2 film layer obtained by electrochemical oxidation. All samples can use N2 as a protective gas during thermal annealing, and cool to room temperature after annealing.

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

[0062] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an exemplary method. Based on design preferences, it is understood that the specific order or hierarchy of steps in the processes can be rearranged while remaining within the scope of the present application.

[0063] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only for specific embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An oxidation method for completely passivating porous silicon with a thickness greater than or equal to 5 μm by avoiding oxidation cutoff, characterized in that, include: Obtain porous silicon; The porous silicon is subjected to electrochemical oxidation treatment by a dynamic current control process to obtain oxidized porous silicon. The electrochemical oxidation treatment of the porous silicon using a dynamic current control process includes: The porous silicon is subjected to electrochemical oxidation treatment for a target duration by continuously increasing the current, so that the porous silicon is fully and uniformly oxidized, thereby preventing oxidation cutoff during the electrochemical oxidation process.

2. The method according to claim 1, characterized in that... The electrochemical oxidation treatment of the porous silicon using a dynamic current control process includes: The porous silicon is immersed in an electrolyte; The porous silicon is subjected to electrochemical oxidation treatment using a dynamic current control 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 using a dynamic current control process includes: The porous silicon is subjected to electrochemical oxidation treatment for a target duration by stepwise increasing the current.

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 process of obtaining porous silicon includes: The porous silicon is prepared by at least one of electrochemical etching, chemical etching, galvanic cell etching, and hydrothermal etching.

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

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

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

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