A method for improving the electrical properties of silicon carbide-metal composite interfaces

Abstract

The present application relates to a kind of methods for improving silicon carbide-metal composite interface electrical performance, specific steps are as follows: 1) single crystal silicon carbide substrate is washed, and drying is obtained Clean single crystal silicon carbide substrate;2) the clean single crystal silicon carbide substrate obtained in step 1) is placed on laser galvanometer processing platform, and the surface of single crystal silicon carbide substrate is annealed using femtosecond laser;After annealing, metal layer is prepared on the surface of single crystal silicon carbide substrate according to needs.The method provided by the present application can effectively improve the electrical performance of silicon carbide-metal composite interface, and the carrier concentration and conductivity of the obtained sample are greatly improved.The method is simple to operate, and is more efficient than traditional annealing process.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, and specifically relates to a method for improving the electrical properties of silicon carbide-metal composite interfaces. Background Technology

[0002] The development of semiconductor science and technology has promoted progress and transformation in all sectors of society, and semiconductor materials are also the foundation of computer, network, and communication technologies. Starting with the first generation of semiconductor silicon materials, as industry has continuously progressed and matured, people have constantly sought breakthroughs in material properties to meet the needs of different fields.

[0003] Silicon carbide (SiC), as one of the representatives of third-generation semiconductor materials, has excellent physicochemical stability, making it a promising candidate for high-frequency, high-power devices. However, due to the complex surface states of SiC, numerous unsaturated dangling bonds exist on its surface. These bonds alter the energy states of the contact interface upon contact with a metal electrode, generating a Schottky barrier, which significantly impacts device stability. Existing methods often aim to achieve more stable contact interface properties by increasing carrier concentration or lowering the Schottky barrier, using ion implantation and high-temperature annealing, respectively. However, ion implantation inevitably leads to lattice distortion or defects, and high-temperature annealing can damage unmodified regions of the device, similarly affecting device lifespan. Therefore, developing new methods to improve the electrical properties of the SiC-metal contact interface is essential. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art by providing a method for improving the electrical properties of silicon carbide-metal composite interfaces. By using femtosecond laser technology and optimizing process parameters to anneal the surface of silicon carbide materials, the annealed surface not only has a high carrier concentration and conductivity, but also the spatial selectivity of the femtosecond laser ensures the stability of the unmodified region structure. The method is simple to operate.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0006] A method for improving the electrical properties of silicon carbide-metal composite interfaces is provided, with the following specific steps:

[0007] 1) Clean and dry the single-crystal silicon carbide substrate to obtain a clean single-crystal silicon carbide substrate;

[0008] 2) Place the clean single-crystal silicon carbide substrate obtained in step 1) on the laser galvanometer processing platform, and use a femtosecond laser to anneal the surface of the single-crystal silicon carbide substrate. After the annealing is completed, prepare a metal layer on the surface of the single-crystal silicon carbide substrate as needed.

[0009] According to the above scheme, the single-crystal silicon carbide substrate mentioned in step 1) is one of the following: N-type 4H-SiC substrate, 3C-SiC substrate, and 6H-SiC substrate.

[0010] According to the above scheme, the process conditions for annealing the surface of the single-crystal silicon carbide substrate using a femtosecond laser in step 2) are as follows: femtosecond laser wavelength of 1030 nm, repetition rate of 200 kHz, pulse width of 260 fs, and laser flux of 0.2–1.4 J / cm². 2 The scanning speed is 10–100 mm / s, and the scanning interval is 5–20 μm.

[0011] Preferably, the process conditions for annealing the surface of the single-crystal silicon carbide substrate using a femtosecond laser in step 2) are as follows: femtosecond laser wavelength of 1030 nm, repetition rate of 200 kHz, pulse width of 260 fs, and laser flux of 0.6 J / cm². 2 The scanning speed is 50 mm / s and the scanning interval is 10 μm.

[0012] According to the above scheme, step 2) involves preparing a metal layer on the surface of a single-crystal silicon carbide substrate by vacuum evaporation.

[0013] Preferably, the metal layer is a gold electrode layer with a thickness of 50–100 nm.

[0014] The present invention also includes semiconductor devices obtained by the above method.

[0015] This invention utilizes femtosecond laser annealing to induce a phase transition on the SiC surface through a photochemical reaction, breaking the original Si-C bonds on the material surface and generating plasma. During this plasma reaction, a portion of the Si element reacts with O element from the air to form SiO. x The structure, partly existing in the form of amorphous Si, is deposited on the modified surface. C is laser-induced to form a graphene structure on the modified SiC surface, in which SiO containing O vacancy defects... x The structure significantly improves the interfacial carrier concentration, and the generated graphene structure alters the bandgap at the interface between the original material and the electrode, improving the electrical transport properties of the SiC-metal interface, increasing the current magnitude, and enhancing device stability. Simultaneously, femtosecond laser annealing combines the advantages of high-temperature annealing and ion implantation, utilizing the high spatial selectivity of the laser to avoid defects in unmodified areas caused by thermal annealing, while also optimizing the process flow, making it more efficient and simpler compared to traditional annealing.

[0016] The beneficial effects of this invention are as follows: the method provided by this invention can effectively improve the electrical properties of the silicon carbide-metal composite interface, and the carrier concentration and conductivity of the obtained sample are significantly improved. The method is simple to operate and more efficient than the traditional annealing process. Attached Figure Description

[0017] Figure 1 The images show SEM images of the clean single-crystal SiC substrate obtained in step 1) and the single-crystal SiC substrate annealed under different laser fluxes in step 2).

[0018] Figure 2 The laser flux for Example 1 is 0.6 J / cm. 2 Cross-sectional SEM image of a single-crystal SiC substrate after lower annealing;

[0019] Figure 3 The images show the surface Raman spectra of the clean single-crystal SiC substrate (denoted as Pristine) obtained in step 1) of Example 1 and the single-crystal SiC substrate annealed under different laser fluxes in step 2).

[0020] Figure 4 The current-voltage characteristic curves of the five samples obtained in Example 2 are shown below;

[0021] Figure 5 The current-voltage characteristic curves of the four samples obtained in Example 3;

[0022] Figure 6 The graphs show the current-voltage characteristics of the four samples obtained in Example 4.

[0023] Figure 7 The current-voltage characteristic curves of the four samples obtained in Example 5 are shown below;

[0024] Figure 8 Comparison of Schottky barriers for samples obtained by depositing gold electrodes on the surface of SiC substrates annealed under different laser fluxes and clean single-crystal SiC substrates without annealing.

[0025] Figure 9 A comparison of carrier concentration on the surface of a clean single-crystal SiC substrate without annealing and on the surface of a SiC substrate obtained under optimal annealing process parameters;

[0026] Figure 10 A comparison of the electrical conductivity of a clean, unannealed single-crystal SiC substrate and a SiC substrate obtained under optimal annealing process parameters;

[0027] Figure 11 EDS spectra of a clean, unannealed single-crystal SiC substrate and a SiC substrate obtained under optimal annealing process parameters;

[0028] Figure 12 XPS energy dispersive spectroscopy comparison chart of a clean single-crystal SiC substrate without annealing and a SiC substrate obtained under optimal annealing process parameters. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] Example 1

[0031] A method for improving the electrical properties of silicon carbide-metal composite interfaces, comprising the following specific steps:

[0032] 1) Five N-type 4H-SiC substrates with a thickness of 500μm were ultrasonically cleaned with ethanol and deionized water for 15 minutes respectively, and then dried in an oven at 60℃ for 40 minutes to obtain clean single crystal SiC substrates.

[0033] 2) Take four single-crystal SiC substrates obtained in step 1) and place them on a laser galvanometer processing platform. Turn on the femtosecond laser to anneal the surface of the single-crystal SiC substrates. The femtosecond laser used has a wavelength of 1030 nm, a repetition frequency of 200 kHz, a pulse width of 260 fs, and a laser flux of 0.2 J / cm². 2 0.6J / cm 2 1.0 J / cm 2 1.4J / cm 2 The laser annealing process was completed by scanning at a speed of 100 mm / s with a scanning interval of 10 μm, and then the SiC substrate was removed.

[0034] Scanning electron microscopy (SEM) analysis was performed on the clean single-crystal SiC substrate obtained in step 1) and the single-crystal SiC substrate annealed at different laser fluxes in step 2) of this embodiment. The SEM images are shown below. Figure 1 As shown in the figure, (a) is the SEM image of the clean single-crystal SiC substrate surface obtained in step 1), and (b), (c), and (d) are the laser flux images obtained in step 2) with a flux of 0.2 J / cm. 2 0.6J / cm 2 1.0 J / cm 2 SEM images of the surface of a single-crystal SiC substrate after downward annealing, (e) and (f) are for laser flux of 1.4 J / cm². 2 The SEM image of the single-crystal SiC substrate after annealing shows a laser flux of 0.2 J / cm². 2 The surface modification effect on the time substrate was not obvious, while the excessive laser flux (1.4 J / cm) 2 This will generate amorphous clusters of material on the substrate surface, leading to the formation of modified layers with different orientations. The suitable laser flux is 0.6–1.0 J / cm². 2 .

[0035] Figure 2 The laser flux is 0.6 J / cm. 2The cross-sectional SEM image of the down-annealed single-crystal SiC substrate shows that the laser annealing treatment formed a modified layer with a thickness of 3μm on the surface of the single-crystal SiC substrate.

[0036] Figure 3 The images show the surface Raman spectra of the clean single-crystal SiC substrate (denoted as Pristine) obtained in step 1) and the single-crystal SiC substrate annealed at different laser fluxes in step 2) of this embodiment. It can be seen that as the laser flux increases, SiO with O vacancy defects is generated on the surface of the single-crystal SiC substrate. x Structure and graphite structure.

[0037] Example 2

[0038] A method for improving the electrical properties of silicon carbide-metal composite interfaces, comprising the following specific steps:

[0039] 1) Five N-type 4H-SiC substrates with a thickness of 500μm were ultrasonically cleaned with ethanol and deionized water for 15 minutes respectively, and then dried in an oven at 60℃ for 40 minutes to obtain clean single crystal SiC substrates.

[0040] 2) Take four single-crystal SiC substrates obtained in step 1) and place them on a laser galvanometer processing platform. Turn on the femtosecond laser to anneal the surface of the single-crystal SiC substrates. The femtosecond laser used has a wavelength of 1030 nm, a repetition frequency of 200 kHz, a pulse width of 260 fs, and a laser flux of 0.49 J / cm². 2 0.55J / cm 2 0.61 J / cm 2 0.67J / cm 2 The laser annealing process was completed at a speed of 100 mm / s with a scanning interval of 5 μm. After the laser annealing was completed, the SiC substrate was removed, and 80 nm thick gold electrodes were deposited on the surfaces of the four annealed SiC substrates and the clean single-crystal SiC substrate without annealing by vacuum evaporation.

[0041] The current-voltage characteristic curves of the five samples obtained in this embodiment are shown in the figure below. Figure 4 As shown, the unannealed single-crystal SiC substrate exhibits a high Schottky barrier at the Au / SiC interface, while the samples obtained after laser annealing show a reduction in the Schottky barrier at the Au / SiC interface. This indicates that the electrical properties of the laser-annealed SiC substrate are improved compared to the unannealed substrate, with a laser flux of 0.61 J / cm². 2 The electrical performance is best at the specified time, but it decreases when the laser flux is further increased thereafter.

[0042] Example 3

[0043] A method for improving the electrical properties of silicon carbide-metal composite interfaces, comprising the following specific steps:

[0044] 1) Four N-type 4H-SiC substrates with a thickness of 500μm were ultrasonically cleaned with ethanol and deionized water for 15 minutes, and then dried in an oven to obtain clean single-crystal SiC substrates.

[0045] 2) Place the single-crystal SiC substrates obtained in step 1) onto a laser galvanometer processing platform, and anneal the surface of the single-crystal SiC substrates using a femtosecond laser. The femtosecond laser wavelength is 1030 nm, the repetition frequency is 200 kHz, the pulse width is 260 fs, and the laser flux is controlled to be 0.49 J / cm². 2 0.55J / cm 2 0.61 J / cm 2 0.67J / cm 2 The laser annealing process was completed by scanning at a speed of 100 mm / s with a scanning interval of 10 μm. After the laser annealing was completed, the SiC substrate was removed and 80 nm thick gold electrodes were deposited on the surface of the four annealed SiC substrates by vacuum evaporation.

[0046] The current-voltage characteristic curves of the four samples obtained in this embodiment are shown in the figure below. Figure 5 As shown, the laser flux is 0.61 J / cm². 2 The sample obtained by time annealing has the best electrical properties. After that, if the laser flux is increased further, the slope of the sample curve will drop and the Schottky barrier will rise.

[0047] Example 4

[0048] A method for improving the electrical properties of silicon carbide-metal composite interfaces, comprising the following specific steps:

[0049] 1) Clean four N-type 4H-SiC substrates with a thickness of 500μm by ultrasonic cleaning with ethanol and deionized water, and then dry them in an oven to obtain clean single-crystal SiC substrates.

[0050] 2) Place the single-crystal SiC substrates obtained in step 1) onto a laser galvanometer processing platform, and anneal the surface of the single-crystal SiC substrates using a femtosecond laser. The femtosecond laser wavelength is 1030 nm, the repetition frequency is 200 kHz, the pulse width is 260 fs, and the laser flux is controlled to be 0.49 J / cm². 2 0.55J / cm 2 0.61 J / cm 2 0.67J / cm 2The laser annealing process was completed by scanning at a speed of 100 mm / s with a scanning interval of 15 μm. After the laser annealing was completed, the SiC substrate was removed and 80 nm thick gold electrodes were deposited on the surface of the four annealed SiC substrates by vacuum evaporation.

[0051] The current-voltage characteristic curves of the four samples obtained in this embodiment are shown in the figure below. Figure 6 As shown, the laser flux is 0.61 J / cm². 2 The sample obtained by time annealing has the best electrical properties. After that, if the laser flux is increased further, the slope of the sample curve will drop and the Schottky barrier will rise.

[0052] Example 5

[0053] A method for improving the electrical properties of silicon carbide-metal composite interfaces, comprising the following specific steps:

[0054] 1) Clean four N-type 4H-SiC substrates with a thickness of 500μm by ultrasonic cleaning with ethanol and deionized water, and then dry them in an oven to obtain clean single-crystal SiC substrates.

[0055] 2) Place the single-crystal SiC substrates obtained in step 1) onto a laser galvanometer processing platform, and anneal the surface of the single-crystal SiC substrates using a femtosecond laser. The femtosecond laser wavelength is 1030 nm, the repetition frequency is 200 kHz, the pulse width is 260 fs, and the laser flux is controlled to be 0.49 J / cm². 2 0.55J / cm 2 0.61 J / cm 2 0.67J / cm 2 The laser annealing process was completed by scanning at a speed of 50 mm / s (equivalent pulse number N = 100) with a scanning interval of 10 μm. After the laser annealing was completed, the SiC substrate was removed and 80 nm thick gold electrodes were deposited on the surface of the four annealed SiC substrates by vacuum evaporation.

[0056] The current-voltage characteristic curves of the four samples obtained in this embodiment are shown in the figure below. Figure 7 As shown, the laser flux is 0.61 J / cm². 2 The sample obtained by time annealing has the best electrical properties. After that, if the laser flux is increased further, the slope of the sample curve will drop and the Schottky barrier will rise.

[0057] Based on the above embodiments, the optimal annealing process parameters are: laser wavelength of 1030 nm, repetition frequency of 200 kHz, pulse width of 260 fs, and laser flux of 0.61 J / cm². 2The scanning interval was 10 μm and the scanning speed was 50 mm / s. Hall effect tests were performed on the annealed samples obtained under these conditions. The results showed that the carrier concentration on the silicon carbide surface (Si facet) reached 1.77 × 10⁻⁶ after femtosecond laser annealing. 18 cm -3 The conductivity reached 0.56×10 1 The S / m value indicates a Schottky barrier of 0.69 eV at the gold electrode interface, while the carrier concentration on the surface (Si face) of a clean, unannealed single-crystal SiC substrate is 5.40 × 10⁻⁶ eV. 13 cm -3 The conductivity is 1.71 × 10⁻⁶. -4 The S / m and the Schottky barrier at the interface with the gold electrode are 1.43 eV, indicating that the method of the present invention for improving the electrical properties of the silicon carbide-metal composite interface can significantly improve the electrical properties of the silicon carbide interface.

[0058] The method described in Example 1 was used for testing, except that the scanning speed was 50 mm / s. Then, 80 nm thick gold electrodes were deposited on the surfaces of four annealed SiC substrates and a clean, unannealed single-crystal SiC substrate using vacuum evaporation. The current-voltage characteristic curves of the five samples were then measured. The Schottky barrier comparison diagrams for the five samples are shown below. Figure 8 As shown, the SiC substrate can withstand a laser flux of 0.6 J / cm². 2 The sample obtained during annealing exhibits the lowest Schottky barrier height, requiring the least energy for electrons to transition from the semiconductor to the metal, i.e., a laser flux of 0.6 J / cm². 2 SiC substrates annealed at around 100°C exhibit the best electrical properties.

[0059] Figure 9 The image shows a comparison of carrier concentration on the surface of a clean, unannealed single-crystal SiC substrate (denoted as the original sample) and a SiC substrate obtained under optimal annealing process parameters (denoted as the femtosecond laser-annealed sample). The results show that the carrier concentration of the SiC substrate sample after laser annealing is significantly increased compared with the unannealed SiC substrate, indicating that the SiC substrate sample after laser annealing has a higher carrier mobility.

[0060] The conductivity of a clean, unannealed single-crystal SiC substrate (denoted as the original sample) and a SiC substrate obtained under optimal annealing parameters (denoted as the femtosecond laser-annealed sample) was measured using the four-probe method. The comparison is shown in the figure below. Figure 10 Compared with unannealed SiC substrates, the conductivity of SiC substrate samples after laser annealing is significantly improved.

[0061] Figure 11The two images show a clean, unannealed single-crystal SiC substrate (denoted as Pristine) and a SiC substrate obtained under optimal annealing parameters (denoted as 0.61 J / cm). 2 The EDS energy dispersive spectroscopy (EDS) spectrum of the substrate was analyzed. Statistical analysis of the percentage content of each element revealed that the surface of a clean, unannealed single-crystal SiC substrate contained almost only carbon and silicon. After femtosecond laser annealing, the oxygen content on the substrate surface increased significantly, from 0.83% to 17.01%, while the relative carbon content decreased considerably. Laser annealing resulted in a uniform oxygen distribution on the modified surface, which is beneficial for the stability of subsequent device performance.

[0062] To further investigate the effect of annealing on the electron binding energy of SiC surface, clean, unannealed single-crystal SiC substrates (denoted as Pristine) and SiC substrates obtained under optimal annealing parameters (denoted as 0.61 J / cm²) were compared. 2 XPS spectroscopy was performed, and the results are shown below. Figure 12 (a) compares the overall changes in XPS energy spectrum of the samples before and after laser annealing. The results show the peak values ​​of silicon (Si 2p and Si 2s), carbon (C 1s) and oxygen (O 1s). The appearance of the oxygen peak in the original sample in the full XPS spectrum is attributed to the surface oxidation of 4H-SiC in the air environment. It can be seen that after laser annealing, the O1s peak intensity of the 4H-SiC surface is significantly enhanced, while the corresponding Si 2s, Si 2p and C1s peak intensities are weakened. This well proves that the O element from the air reacted with the carbon and silicon elements on the sample surface. (b) Energy dispersive spectral peaks of the C1s orbital were determined. Si-C and CC bonds were found at 280.1 eV and 282.2 eV, respectively. The presence of the CC bond is likely due to impurities during growth. After laser annealing, the peak corresponding to the Si-C bond disappeared, indicating photodecomposition of SiC and breakage of the surface Si-C bonds. The significantly increased peak width of the CC bond at 282.2 eV reflects the increased disorder of surface C, inducing different carbon structures. Figure 3The Raman test results confirmed that the induced material was a graphite structure. (c) Energy dispersive spectroscopy analysis of the Si 2p orbitals before and after annealing showed that after annealing, the characteristic peak of the intrinsic Si-C bond at 102.4 eV disappeared, replaced by two new peaks at 100.8 eV and 103.5 eV, corresponding to Si-Si and Si-O bonds, respectively. This indicates that the SiC sample surface decomposed and underwent oxidation under the influence of laser. The Si-O bond originated from the high-energy Si plasma generated by the photochemical reaction, which reacted with oxygen in the air. The Si-Si bond at 100.8 eV indicates that elemental Si was generated simultaneously during laser annealing. (d) The O1s orbitals on the 4H-SiC surface before and after annealing were calibrated and analyzed. The sample surface without femtosecond laser annealing only had Si-O bonds, indicating the presence of SiO2. The source of SiO2 may be the oxide layer formed when the SiC surface is exposed to the atmospheric environment. After annealing, the characteristic peak at 533.2 eV corresponding to SiO2 disappeared, while a characteristic peak corresponding to SiOx / Si compounds was generated at 533.8 eV. This indicates that laser annealing can induce the formation of non-stoichiometric SiOx / Si compounds with oxygen vacancy defects on the sample surface. The formation mechanism can be expressed by the following formula:

[0063] SiC (s) +O 2(a) →SiO x(s) +Si (s) +C s +CO 2(a)

[0064] The formation of this compound is the cause Figure 11 The main reason for the increase in oxygen content in the EDS spectrum is the introduction of oxygen, while the decrease in carbon content is due to the breaking of existing Si-C bonds during annealing, leading to the escape of some elemental carbon or plasma, or the volatilization of CO2 formed from oxygen in the air. The overall silicon content did not change significantly, which can be attributed to the redeposition of amorphous silicon on the sample surface, bonding with C and O. The absence of Si-C bond peaks in the XPS spectrum after laser annealing indicates that the Si generated by the Si-C bond breakage exists in two forms: single crystals or SiOx / Si compounds. In this case, the surface oxygen content affects the SiOx / Si structure, leading to O vacancy defects on the SiC surface when the O content is insufficient. These defects affect the electrical transport properties of the sample surface.

Claims

1. A method for improving the electrical properties of silicon carbide-metal composite interfaces, characterized in that, The specific steps are as follows: 1) Clean and dry the single-crystal silicon carbide substrate to obtain a clean single-crystal silicon carbide substrate; 2) Place the clean single-crystal silicon carbide substrate obtained in step 1) on a laser galvanometer processing platform, and anneal the surface of the single-crystal silicon carbide substrate using a femtosecond laser. The process conditions for annealing the surface of the single-crystal silicon carbide substrate using a femtosecond laser are: femtosecond laser wavelength of 1030 nm, repetition rate of 200 kHz, pulse width of 260 fs, and laser flux of 0.49~0.61 J / cm². 2 The scanning speed is 10~100 mm / s, the scanning spacing is 5~20 μm, and after the annealing process is completed, a metal layer is prepared on the surface of the single crystal silicon carbide substrate as needed.

2. The method for improving the electrical properties of silicon carbide-metal composite interfaces according to claim 1, characterized in that, Step 1) The single-crystal silicon carbide substrate is one of the following: N-type 4H-SiC substrate, 3C-SiC substrate, and 6H-SiC substrate.

3. The method for improving the electrical properties of silicon carbide-metal composite interfaces according to claim 1, characterized in that, Step 2) The process conditions for annealing the surface of a single-crystal silicon carbide substrate using a femtosecond laser are as follows: femtosecond laser wavelength of 1030 nm, repetition rate of 200 kHz, pulse width of 260 fs, and laser flux of 0.6 J / cm². 2 The scanning speed is 50 mm / s and the scanning interval is 10 μm.

4. The method for improving the electrical properties of silicon carbide-metal composite interfaces according to claim 1, characterized in that, Step 2) The method for preparing a metal layer on the surface of a single-crystal silicon carbide substrate is as follows: vacuum evaporation is used.

5. The method for improving the electrical properties of silicon carbide-metal composite interfaces according to claim 1, characterized in that, The metal layer is a gold electrode layer with a thickness of 50~100 nm.

6. A semiconductor device obtained by the method according to any one of claims 1-5.

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