Black silicon nano-forest structure, and preparation method and application thereof

Abstract

This invention belongs to the field of semiconductor material manufacturing technology, specifically relating to a black silicon nanoforest structure, its preparation method, and its applications. The invention involves depositing a silicon-rich silicon nitride thin film via PECVD, followed by chemical etching using gaseous HF (VHF) to form a uniform silicon forest structure. This method eliminates the need for metal catalysts and masks, removing metal contamination and physical damage. The process is simple and controllable, making it suitable for the industrial production of large-area black silicon.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor material manufacturing, and particularly relates to a black silicon nanoforest structure and a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in the background of the present application is only intended to increase the understanding of the overall background of the present application, and is not necessarily regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

[0003] Black silicon is a kind of silicon material with special nanostructure on the surface, and is named for its extremely low light reflectivity (dark black to the naked eye). The existing preparation technology of black silicon mainly includes:

[0004] (1) Femtosecond laser etching method: using ultra-short pulse laser to induce micro-nano structure on the surface of silicon, but the device is expensive (high-power femtosecond laser), the processing efficiency is low (usually point-by-point scanning, the scanning efficiency is less than 1 cm 2 / min), it is difficult to prepare uniformly in large area, and may introduce thermal damage or lattice defects, and the high cost limits its large-scale application.

[0005] (2) Metal catalytic chemical etching method: depositing metal catalyst (such as Ag, Au, Pt nanoparticles) on the surface of silicon, then etching in a mixed solution containing oxidant (such as H2O2) and fluoride (such as HF), using metal particles to catalyze the oxidation and dissolution of silicon, forming porous or nanowire structure, but this method needs to use metal catalyst (such as Ag, Au), which is easy to introduce metal impurities, form deep level recombination center, and reduce carrier lifetime; the process control is complex and the uniformity is poor.

[0006] (3) Reactive ion etching (RIE): using active ions (physical bombardment) and free radicals (chemical reaction) in plasma (usually generated by SF6, O2, CF4, etc.) to etch the surface of silicon anisotropically or isotropically, but the physical bombardment of high-energy ions on the surface of silicon is inevitable in the RIE process, which will introduce lattice damage, surface defects and dangling bonds. These damage points will become effective recombination centers for carriers, which will also deteriorate the electrical properties of the device (especially the minority carrier lifetime), and a mask process is required, which is complex and costly.

[0007] Therefore, the above-mentioned existing methods for preparing black silicon all have problems of metal contamination, physical damage, poor process controllability, etc., which limit the large-scale application of black silicon. The technical personnel in the field urgently seek a method which can realize the elimination of metal contamination and physical damage, does not need mask, has a simpler process, and can obtain large-area and high-uniformity black silicon nanostructure. SUMMARY

[0008] In view of the prior art, the present application aims to provide a black silicon nano-forest structure and a preparation method and application thereof. The present application relates to a black silicon preparation process which is completely free of metal catalysis and avoids high-energy ion physical bombardment. Specifically, the process uses mature semiconductor dry process equipment (PECVD, VHF) to realize large-area and high-uniformity black silicon nano-structure preparation (better than laser method and metal catalysis method) by precisely controlling parameters such as gas flow, ratio, power, and time; and the process is simpler without mask (solving the mask problem of RIE).

[0009] Specifically, the present application provides the following technical solutions:

[0010] In a first aspect, the present application provides a black silicon nano-forest structure, comprising: a silicon substrate and a silicon grass-like nano-forest layer on the surface of the silicon substrate.

[0011] The silicon grass-like nano-forest layer is formed by chemical conversion of silicon-rich silicon nitride in gaseous hydrofluoric acid and does not contain metal catalyst residues; wherein the atomic ratio of the silicon-rich silicon nitride is Si:N>3:4.

[0012] Preferably, the atomic ratio of the silicon-rich silicon nitride thin film is Si:N = 66:34.

[0013] Preferably, the silicon grass-like nano-forest layer presents uniformly distributed nano-scale grass-like protruding structures with a protruding height of 150-250 nm and a density of 80-120 roots / μm. 2 .

[0014] Preferably, the roughness of the black silicon nano-forest structure is ≥20 nm.

[0015] In a second aspect, the present application provides a preparation method of the above black silicon nano-forest structure, specifically comprising: first depositing a silicon-rich silicon nitride thin film on the surface of a silicon substrate by a plasma-enhanced chemical vapor deposition process (PECVD), and then performing chemical etching on the silicon-rich silicon nitride thin film by a gaseous HF process (VHF) to obtain the black silicon nano-forest structure.

[0016] Preferably, the gas flow ratio in the chemical deposition process is SiH4:N2:NH3= 45-55:780-820:20-25.

[0017] Preferably, the parameters of the chemical deposition process are as follows: chamber pressure is 120-150 Pa, radio frequency power is 150-200 W, deposition time is 60-70 seconds, and deposition thin film thickness is 180-220 nm.

[0018] Preferably, the flow rate of gaseous HF in the chemical etching is 450-550 sccm, and the processing time is 600-800 seconds.

[0019] Preferably, the gas flow rate ratio in the hydrofluoric acid vapor process is N2:EtOH:HF=1100-1200:350-450:500-550.

[0020] In a third aspect, the application provides an application of the black silicon nano-forest structure of the first aspect in the field of solar cells, photodetectors, sensors, etc.

[0021] The beneficial effects achieved by the above one or more technical solutions of the application are as follows:

[0022] (1) The application breaks through the bottleneck of mass production of black silicon by the innovative combination of "PECVD silicon-rich silicon nitride deposition + VHF vapor etching", and provides an industrialized feasible path for performance upgrading of optoelectronic devices at low cost, without pollution and high uniformity. The specific effects include:

[0023] 1) No metal pollution: abandoning metal catalytic etching (such as Ag / Au), eliminating deep level recombination centers, and protecting carrier lifetime;

[0024] 2) Zero physical damage: using pure chemical etching (VHF-HF vapor process), avoiding high-energy ion bombardment (such as RIE), and eliminating lattice damage and surface defects.

[0025] 3) No need for mask process: simplifying the process and reducing cost (traditional RIE requires a complex mask process).

[0026] (2) The application realizes uniform growth of nano-structures by precisely regulating the gas ratio (SiH4 / N2 / NH3), power, pressure and other parameters by PECVD, and the uniform nano-protrusions in the "silicon grass forest" structure prepared can effectively improve the light trapping capability. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of these drawings illustrate the embodiments of the application and, together with the description, serve to explain the application without imposing undue limitation on the application.

[0028] Figure 1 A scanning electron microscope image (scale 1 μm) of the black silicon nano-forest structure prepared in Example 1 of the application;

[0029] Figure 2 A scanning electron microscope image (scale 300 nm) of the black silicon nano-forest structure prepared in Example 1 of the application;

[0030] Figure 3An atomic force microscope image of the black silicon nanoforest structure prepared in Example 1 of this invention;

[0031] Figure 4 This is an atomic force microscope image of the black silicon nanoforest structure prepared in Comparative Example 1 of this invention;

[0032] Figure 5 This is an atomic force microscope image of the black silicon nanoforest structure prepared in Comparative Example 2 of this invention. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0035] Example 1 This embodiment provides a black silicon nanoforest structure, the preparation method of which includes the following steps:

[0036] (1) The silicon wafer was placed into the PECVD 350℃ chamber by a robot arm. After the chamber was evacuated, the process gas was introduced (the gas and flow rate ratio was SiH4:N2:NH3=50:800:22). The chamber pressure was set to 150 Pa. After stabilization, the RF power supply was turned on at 200 W and the deposition time was 66 s to obtain a 200 nm thick silicon-rich silicon nitride (atomic ratio was Si:N=66:34).

[0037] (2) Place the wafer with silicon nitride film into the VHF chamber (the gas and flow rate ratio is N2:EtOH:HF=1000:400:525), and simultaneously introduce gaseous hydrofluoric acid at a flow rate of 500 sccm for 700 s to obtain a rough silicon grass-like structure.

[0038] Comparative Example 1 This comparative example provides a black silicon nanoforest structure, the preparation method of which includes the following steps:

[0039] The difference between this comparative example and Example 1 is that in step (1), the gas and flow rate ratio is set to SiH4:N2:NH3=10:800:22, resulting in silicon nitride with a standard atomic ratio of Si:N=3:4. Other preparation methods are the same as in Example 1.

[0040] Comparative Example 2 This comparative example provides a black silicon nanoforest structure, the preparation method of which includes the following steps:

[0041] The difference between this comparative example and Example 1 is that step (2) was not performed, while the other preparation methods are the same as in Example 1.

[0042] Example 1 In this experiment, the structures of Example 1 and Comparative Examples 1-2 were measured.

[0043] like Figures 1-2 As shown in the scanning electron microscope image, after the VHF reaction, the surface silicon nitride and the smooth surface are transformed into a rough nanoforest-like structure.

[0044] like Figures 3-5 As shown, by measuring the structural roughness of the three materials, the data analysis shows that, compared with Comparative Example 3 (roughness Ra: 1.3 nm), the roughness of silicon nitride with standard atomic ratio hardly changed after the VHF process (roughness Ra: 1.505 nm), while the roughness of silicon-rich silicon nitride prepared in Example 1 of this application was significantly improved after the VHF process (roughness Ra: 21.51 nm). This is because silicon-rich silicon nitride has more defects, resulting in a larger roughness after the reaction. Specific test data are shown in Table 1.

[0045] Table 1

[0046]

[0047] Ra, Rq (root mean square roughness), and Rz (maximum profile height) are three common indicators for measuring surface roughness. Among them, Ra reflects the overall average height of the surface and is the most common and frequently used roughness indicator, providing a comprehensive and stable roughness overview. The smaller the Ra value, the smoother the surface.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A black silicon nanoforest structure, characterized in that, include: A silicon substrate and a layer of silicon grass-like nanoforests located on the surface of the silicon substrate; The silica-grass-like nanoforest layer is formed by the chemical conversion of silicon-rich silicon nitride with gaseous hydrofluoric acid and contains no metal catalyst residues; wherein the atomic ratio of the silicon-rich silicon nitride is Si:N>3:

4. The black silicon nanoforest structure is prepared by the following method: first, a silicon-rich silicon nitride film is deposited on the surface of a silicon substrate by plasma-enhanced chemical vapor deposition, and then the silicon-rich silicon nitride film is chemically etched by gaseous HF process to obtain the black silicon nanoforest structure. The gas flow rate ratio introduced during the plasma-enhanced chemical vapor deposition process is SiH4:N2:NH3 = 45~55:780~820:20~25; The parameters for plasma-enhanced chemical vapor deposition are: chamber pressure of 120-150 Pa, radio frequency power of 150-200 W, and deposition time of 60-70 seconds.

2. The black silicon nanoforest structure as described in claim 1, characterized in that, The atomic ratio of the silicon-rich silicon nitride thin film is Si:N = 66:

34.

3. The black silicon nanoforest structure as described in claim 1, characterized in that, The silica-grass-like nanoforest layer exhibits a uniformly distributed nanoscale grass-like protrusion structure, with a protrusion height of 150~250nm and a density of 80~120 stalks / μm. 2 .

4. The black silicon nanoforest structure as described in claim 1, characterized in that, The roughness of the black silicon nanoforest structure is ≥20 nm.

5. A method for preparing the black silicon nanoforest structure according to any one of claims 1 to 4, characterized in that, Specifically, a silicon-rich silicon nitride film is first deposited on the surface of a silicon substrate using a plasma-enhanced chemical vapor deposition process, and then the silicon-rich silicon nitride film is chemically etched using a gaseous HF process to obtain a black silicon nanoforest structure. The gas flow rate ratio introduced during the plasma-enhanced chemical vapor deposition process is SiH4:N2:NH3 = 45~55:780~820:20~25; The parameters for plasma-enhanced chemical vapor deposition are: chamber pressure of 120-150 Pa, radio frequency power of 150-200 W, and deposition time of 60-70 seconds.

6. The preparation method according to claim 5, characterized in that, The parameters for the plasma-enhanced chemical vapor deposition process are: the thickness of the deposited film is 180~220 nm.

7. The preparation method according to claim 5, characterized in that, The flow rate of gaseous HF introduced during the chemical etching is 450~550 sccm, and the processing time is 600~800 seconds.

8. The preparation method according to claim 5, characterized in that, The gas flow ratio in the gaseous HF process is N2:EtOH:HF = 1100~1200 : 350~450 : 500~550.

9. The application of the black silicon nanoforest structure according to any one of claims 1 to 4 in the fields of solar cells, photodetectors, and sensors.

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