A method of passivating defects on a silicon surface

Abstract

The application provides a method for passivating silicon surface defects, and belongs to the fields of information technology and solar cells; the application utilizes the polarization charge on the surface of a ferroelectric film to controllably generate a surface electric field with a certain intensity on the silicon surface, and then efficiently and controllably passivates the silicon surface defects; the application utilizes the HfO2 ferroelectric film to passivate the silicon surface defects, and in the process of efficiently passivating the silicon surface defects, the HfO2 ferroelectric film does not hinder the transmission of carriers in a silicon-based heterojunction device; the method for passivating the silicon surface defects can increase the carrier lifetime of the silicon surface by nearly 1.8 times, and has strong industrial practicability.

Description

Technical Field

[0001] The invention belongs to the fields of information technology and solar cells, and particularly relates to a method for passivating silicon surface defects. Background Art

[0002] Currently, there are two methods for passivating silicon surface defects: chemical passivation and field effect passivation. Chemical passivation is a process that uses a heat treatment process to form an interface phase of compounds such as silicon oxygen and silicon nitrogen at the interface between silicon and the dielectric layer. This method passivates the dangling bonds on the silicon surface to a certain extent. However, due to the lattice mismatch and thermal mismatch between the deposited dielectric layer and the silicon substrate, chemical passivation cannot completely passivate surface defects and may even introduce new defects. Field effect passivation uses the charged space charge in the dielectric layer or the dielectric layer / silicon interface to form a surface electric field on the silicon surface, causing an imbalance of carriers on the silicon surface, which greatly improves the carrier lifetime on the silicon surface. Because field effect passivation can tolerate a high surface trap density, field effect passivation can effectively passivate silicon surface defects. Compared with chemical passivation, the effect of field effect passivation is very significant.

[0003] In existing field-effect passivation methods, the silicon surface electric field is primarily caused by defects in the dielectric layer or at the dielectric / silicon interface, resulting in low and uncontrollable field-effect passivation effectiveness. Therefore, developing an efficient and controllable field-effect passivation technology is crucial for the development of high-performance silicon-based microelectronics and optoelectronics. Summary of the Invention

[0004] To address some of the shortcomings of the prior art, the present invention provides a method for passivating silicon surface defects. The method utilizes polarized charges on the surface of a ferroelectric film to controllably generate a surface electric field of a certain intensity on the silicon surface, thereby efficiently and controllably passivating the silicon surface defects. The method utilizes an HfO2 ferroelectric film to passivate silicon surface defects, effectively passivating the silicon surface defects while not hindering carrier transport in silicon-based heterojunction devices. The method can increase the silicon surface carrier lifetime by nearly 1.8 times, demonstrating strong industrial applicability.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A method for passivating silicon surface defects comprises: forming an HfO2 ferroelectric film on the surface of a silicon wafer to passivate the Si surface defects.

[0007] Preferably, the method specifically includes:

[0008] (1) placing a cleaned silicon wafer into an atomic layer deposition device, and cyclically alternatingly depositing HfO2 and an oxide material to form a thin film structure on the surface of the silicon wafer; the oxide material includes Al2O3, ZrO2 or SiO2;

[0009] (2) performing a rapid annealing treatment on the thin film structure formed on the surface of the silicon wafer in step (1), so that a HfO2 ferroelectric thin film is formed on the surface of the silicon wafer.

[0010] Preferably, in step (1), the processing steps of the silicon wafer include:

[0011] S1. Ultrasonic cleaning of the silicon wafer using acetone, anhydrous ethanol, and deionized water in sequence to remove oil and other stains on the surface of the silicon wafer, followed by drying with nitrogen gas;

[0012] S2. Soak the silicon wafer in hydrofluoric acid to remove the natural oxide layer on the silicon surface;

[0013] S3. Clean the silicon wafer with ethanol and deionized water in sequence to remove hydrofluoric acid impurities on the surface of the silicon wafer, and then dry it with nitrogen to obtain a clean silicon wafer.

[0014] Preferably, in S1, the ultrasonic cleaning time is 5 to 8 minutes;

[0015] In S2, the volume fraction of hydrofluoric acid is 5%, and the immersion time is 1-3 minutes;

[0016] In S3, the silicon wafer is immersed in anhydrous ethanol for 5 minutes, and then the surface of the silicon wafer is continuously rinsed with deionized water to remove hydrofluoric acid impurities on the silicon surface. Finally, the silicon wafer is blown dry with a nitrogen gun to obtain a clean silicon wafer.

[0017] Preferably, in step (1), when the metal oxide is Al2O3, 17-21 layers of HfO2 material and 1 layer of Al2O3 material are deposited in each cycle, and the cycle is repeated 7-10 times to form (HfO2) on the surface of the silicon wafer. x (Al2O3) y Thin film, wherein x:y=17-21:1.

[0018] Preferably, in step (1), when the metal oxide is ZrO2, one layer of HfO2 material and one layer of ZrO2 material are deposited in each cycle, and the cycle is repeated 40-60 times to form (HfO2) on the surface of the silicon wafer. x (ZrO2) y Thin film, where x:y = 0.5:0.5.

[0019] Preferably, the conditions of the rapid annealing treatment are: annealing atmosphere is nitrogen, annealing temperature is 450-1000° C., annealing time is 45-75 seconds, and HfO 2 ferroelectric thin film is formed.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention uses ferroelectric thin film materials to passivate silicon surface defects. This method utilizes polarized charges on the surface of the ferroelectric film, whose magnitude and polarity can be controlled by an external electric field. This method can controllably generate a surface electric field of a certain intensity on the silicon surface, thereby efficiently and controllably passivating silicon surface defects. Furthermore, during the preparation of the ferroelectric thin film material, Al or Zr impurities are doped. This doping modulates the crystal structure of HfO2, resulting in an HfO2 material with a ferroelectric phase.

[0022] The ferroelectric properties of the HfO2 ferroelectric film described in the present invention are not limited by size effects, exhibiting strong ferroelectricity even at a thickness of 10 nm. Therefore, the HfO2 ferroelectric film effectively passivates silicon surface defects while not hindering carrier transport in silicon-based heterojunction devices. Compared to non-ferroelectric passivation layer materials such as HfO2 and Al2O3, the HfO2 ferroelectric film improves the silicon surface carrier lifetime by nearly 1.8 times, and by over 70% compared to prior art literature reports. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure after HfO2 ferroelectric film is prepared on the silicon wafer surface; in the figure: 1-cleaned silicon wafer; 2-HfO2 ferroelectric film.

[0024] Figure 2 This is the AFM test result of the HfO2 ferroelectric film surface.

[0025] Figure 3 The hysteresis loop of HfO2 ferroelectric thin film and the corresponding volt-ampere characteristic curve.

[0026] Figure 4 PFM test results of HfO2 ferroelectric thin film.

[0027] Figure 5 This is a data graph of the maximum lifetime of minority carriers on the silicon surface.

[0028] Figure 6 Statistical distribution of minority carrier lifetime on the silicon surface. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0030] Example 1:

[0031] Take a p-type silicon wafer with a thickness of 500μm and a resistivity of 1-10Ω·cm. Use acetone and anhydrous ethanol to ultrasonically clean the silicon wafer for 5 minutes, then use deionized water to continuously rinse the silicon wafer surface. Finally, use a nitrogen gun to blow dry the silicon wafer.

[0032] The silicon wafer was immersed in 5% hydrofluoric acid for 1 minute, then immersed in anhydrous ethanol for 5 minutes. Finally, the surface of the silicon wafer was continuously rinsed with deionized water. Finally, the silicon wafer was blown dry with a nitrogen gun to obtain a clean silicon wafer free of oxide layer and oil stains.

[0033] The cleaned silicon wafer is placed in the atomic layer deposition system reaction chamber, the reaction chamber is evacuated, and then HfO2 and Al2O3 materials are alternately deposited on the silicon wafer surface. In one cycle, HfO2 material is 19 layers and Al2O3 material is 1 layer. The cycle is repeated 7 times to form (HfO2) on the silicon wafer surface. x (Al2O3) y film, x:y=19:1. Then the formed (HfO2) x (Al2O3) y The silicon wafer with the thin film was placed in a rapid annealing furnace and annealed at 950℃ for 1 minute to obtain the following Figure 1 The silicon wafer material shown has a HfO2 ferroelectric thin film passivation layer.

[0034] Figure 2 This is the AFM test result of the HfO2 ferroelectric film surface. It can be seen from the figure that the surface of the HfO2 ferroelectric film is very smooth and the surface roughness is only 0.471nm. Figure 3 and Figure 4 The results of the ferroelectric test of HfO2 ferroelectric film show that the ferroelectricity of HfO2 ferroelectric film is excellent. Among them, the remanent polarization 2Pr is 22.9μC / cm 2 , the coercive field 2Ec is 8.7MV / cm.

[0035] Figure 5 The results of transient photoconductivity measurement of Si surface carrier lifetime are shown. Figure 6 is the statistical result of the carrier lifetime measurement on the Si surface. Figure 5 and Figure 6 It can be seen that HfO2 ferroelectric films can passivate defects on the Si surface and extend the lifetime of Si surface carriers. Furthermore, the passivation effect of HfO2 ferroelectric films is superior to that of non-ferroelectric HfO2 films. Compared with non-ferroelectric HfO2 films, the passivation effect of HfO2 ferroelectric films increases the Si surface carrier lifetime by nearly 1.8 times. Compared with existing literature reports, the carrier lifetime of silicon surface is increased by more than 70%.

[0036] Example 2:

[0037] Take a p-type silicon wafer with a thickness of 500μm and a resistivity of 1-10Ω·cm. Use acetone and anhydrous ethanol to ultrasonically clean the silicon wafer for 5 minutes, then use deionized water to continuously rinse the silicon wafer surface. Finally, use a nitrogen gun to blow dry the silicon wafer.

[0038] The silicon wafer was immersed in 5% hydrofluoric acid for 1 minute, then immersed in anhydrous ethanol for 5 minutes. Finally, the surface of the silicon wafer was continuously rinsed with deionized water. Finally, the silicon wafer was blown dry with a nitrogen gun to obtain a clean silicon wafer free of oxide layer and oil stains.

[0039] The cleaned silicon wafer is placed in the atomic layer deposition system reaction chamber, the reaction chamber is evacuated, and then HfO2 and Al2O3 materials are alternately deposited on the silicon wafer surface. In one cycle, HfO2 material is 21 layers and Al2O3 material is 1 layer. The cycle is repeated 10 times to form (HfO2) on the silicon wafer surface. x (Al2O3) y Thin film, x:y=21:1. Then (HfO2) will be formed x (Al2O3) y The silicon wafer with the thin film is placed in a rapid annealing furnace and annealed at 900° C. for 75 seconds to obtain a silicon wafer material with a HfO2 ferroelectric thin film passivation layer.

[0040] Example 3:

[0041] Take a p-type silicon wafer with a thickness of 500μm and a resistivity of 1-10Ω·cm. Use acetone and anhydrous ethanol to ultrasonically clean the silicon wafer for 5 minutes, then use deionized water to continuously rinse the silicon wafer surface. Finally, use a nitrogen gun to blow dry the silicon wafer.

[0042] The silicon wafer was immersed in 5% hydrofluoric acid for 1 minute, then immersed in anhydrous ethanol for 5 minutes. Finally, the surface of the silicon wafer was continuously rinsed with deionized water. Finally, the silicon wafer was blown dry with a nitrogen gun to obtain a clean silicon wafer free of oxide layer and oil stains.

[0043] The cleaned silicon wafer is placed in the reaction chamber of the atomic layer deposition system, and the reaction chamber is evacuated to vacuum. Then, HfO2 and ZrO2 materials are alternately deposited on the surface of the silicon wafer. In one cycle, HfO2 material is 1 layer and ZrO2 material is 1 layer. The cycle is repeated 40 times to form (HfO2) on the surface of the silicon wafer. x (ZrO2) y film, x:y=0.5:0.5. Then the formed (HfO2) x (ZrO2) yThe thin-film silicon wafer is placed in a rapid annealing furnace and annealed at 450°C for 1 minute to obtain a silicon wafer material with a HfO2 ferroelectric thin-film passivation layer.

[0044] Example 4:

[0045] A p-type silicon wafer with a thickness of 500 μm and a resistivity of 1-10 Ω·cm is ultrasonically cleaned with acetone and anhydrous ethanol in sequence, with a cleaning time of 5 minutes, then the surface of the silicon wafer is continuously rinsed with deionized water, and finally the silicon wafer is blown dry using a nitrogen gun.

[0046] The above silicon wafer is immersed in 5% hydrofluoric acid for 1 minute, then immersed in anhydrous ethanol for 5 minutes, and finally the surface of the silicon wafer is continuously rinsed with deionized water. Finally, the silicon wafer is blown dry using a nitrogen gun to obtain a clean silicon wafer without an oxide layer or oil stains.

[0047] The clean silicon wafer is placed in a reaction chamber of an atomic layer deposition system, the reaction chamber is pumped to vacuum, and then HfO2 and ZrO2 materials are cyclically and alternately deposited on the surface of the silicon wafer, wherein in one cycle, 1 layer of HfO2 material and 1 layer of ZrO2 material are deposited, and the cycle is repeated 60 times to form a (HfO2) x (ZrO2) y thin film on the surface of the silicon wafer, with x:y = 0.5:0.5. Then the formed (HfO2) x (ZrO2) y The thin-film silicon wafer is placed in a rapid annealing furnace and annealed at 500°C for 45 seconds to obtain a silicon wafer material with a HfO2 ferroelectric thin-film passivation layer.

[0048] The above examples are preferred embodiments of the present application, but the present application is not limited to the above embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.

Claims

1. A method for passivating silicon surface defects, characterized in that: Si surface defects are passivated by forming a HfO2 ferroelectric film on the surface of a silicon wafer; the method comprises: (1) placing a cleaned silicon wafer into an atomic layer deposition device, and cyclically depositing HfO2 and an oxide material to form a thin film structure on the surface of the silicon wafer; the oxide material includes Al2O3, ZrO2 or SiO2; When the metal oxide is Al2O3, 17-21 layers of HfO2 material and 1 layer of Al2O3 material are deposited in each cycle, and the cycle is repeated 7-10 times to form (HfO2) on the surface of the silicon wafer. x (Al2O3) y Thin films, where x:y=17~21:1; When the metal oxide is ZrO2, one layer of HfO2 material and one layer of ZrO2 material are deposited in each cycle, and the cycle is repeated 40-60 times to form (HfO2) on the surface of the silicon wafer. x (ZrO2) y Thin film, where x:y=0.5:0.5; (2) performing a rapid annealing treatment on the thin film structure formed on the surface of the silicon wafer in step (1), so that a HfO2 ferroelectric thin film is formed on the surface of the silicon wafer; The conditions of the rapid annealing treatment are: the annealing atmosphere is nitrogen, the annealing temperature is 450-1000 o C, annealing time is 45-75 seconds to form HfO2 ferroelectric thin film.

2. The method for passivating silicon surface defects according to claim 1, wherein: In step (1), the processing steps of the silicon wafer include: S1. Ultrasonic cleaning of the silicon wafer using acetone, anhydrous ethanol, and deionized water to remove oil from the surface of the silicon wafer, followed by nitrogen drying. S2. Soak the silicon wafer in hydrofluoric acid to remove the natural oxide layer on the silicon surface; S3. Clean the silicon wafer with ethanol and deionized water to remove hydrofluoric acid impurities on the surface of the silicon wafer. Then dry it with nitrogen to obtain a clean silicon wafer.

3. The method for passivating silicon surface defects according to claim 2, wherein: In S1, the ultrasonic cleaning time is 5 to 8 minutes; In S2, the volume fraction of hydrofluoric acid is 5%, and the immersion time is 1-3 minutes; In S3, the silicon wafer is immersed in anhydrous ethanol, and then the surface of the silicon wafer is continuously rinsed with deionized water to remove hydrofluoric acid impurities on the silicon surface. Finally, the silicon wafer is blown dry with a nitrogen gun to obtain a clean silicon wafer.

Images