A SiC substrate pretreatment method to improve surface morphology

Abstract

This invention provides a SiC substrate pretreatment method to improve surface morphology. During in-situ etching, carbon and silicon sources are introduced to avoid carbon or silicon enrichment that could degrade the surface morphology. The auxiliary treatment effects of carbon and silicon sources can improve surface damage repair, reduce surface roughness, and inhibit atomic step aggregation, thereby providing a substrate surface with a regular atomic step structure and improving the quality of epitaxial growth.

Description

Technical Field

[0001] This invention relates to the field of SiC epitaxial technology, and in particular to a SiC substrate pretreatment method for improving surface morphology. Background Technology

[0002] SiC materials possess characteristics such as a wide bandgap, high critical breakdown field strength, high thermal conductivity, and high carrier saturation velocity, making them promising candidates for power devices. In device fabrication using SiC as a substrate, epitaxy is an indispensable and crucial step due to limitations imposed by substrate defects, low impurity diffusion coefficients, and limited implantation depth. Chemical vapor deposition (CVD) is commonly used to deposit high-quality SiC, GaN, and AlGaN materials on SiC substrates to meet the material quality and structural design requirements of devices. The quality of these epitaxial materials is significantly influenced by the substrate surface morphology and plays a vital role in the performance of subsequently fabricated devices. Therefore, before starting epitaxial growth, a clean, polished substrate must undergo surface pretreatment to remove surface damage caused by polishing and obtain a regular atomic step structure.

[0003] In current epitaxial growth processes using SiC substrates, the mainstream surface pretreatment method involves in-situ etching of the SiC substrate surface within the epitaxial growth equipment's reaction chamber using hydrogen gas or a mixture of hydrogen and a small amount of hydrogen chloride at high temperatures. After this step, silicon and carbon sources can be introduced to begin epitaxial material growth. During the in-situ etching process, additional silicon or carbon sources can be introduced for auxiliary treatment, depending on the substrate's processing requirements. Carbon-assisted treatment (e.g., propane, ethylene) helps improve the repair of surface scratches and other damage, but in a carbon-rich atmosphere, it can lead to increased surface roughness and the aggregation of atomic steps into giant steps, affecting the subsequent epitaxial growth quality. Silicon-assisted treatment (e.g., silane) helps reduce surface roughness and suppress atomic step aggregation, but in a silicon-rich atmosphere, it easily forms silicon clusters, causing epitaxial defects. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a SiC substrate pretreatment method to improve surface morphology. During in-situ etching, a pulsed method is used to introduce carbon and silicon sources to avoid carbon or silicon enrichment that could degrade the surface morphology. The auxiliary treatment effects of carbon and silicon sources can improve surface damage repair, reduce surface roughness, and suppress atomic step aggregation, thereby providing a substrate surface with a regular atomic step structure and improving the quality of epitaxial growth.

[0005] The present invention adopts the following technical solution:

[0006] This invention provides a SiC substrate pretreatment method for improving surface morphology, the method comprising:

[0007] Step S100: The SiC substrate for epitaxial growth is placed into the reaction chamber, heated to a certain temperature and pressure is set in a hydrogen atmosphere.

[0008] Step S200: While maintaining the flow of hydrogen, an auxiliary gas is introduced into the reaction chamber in a pulsed manner.

[0009] In step S300, after the pulse-assisted treatment is completed, continue to introduce hydrogen gas, stop introducing auxiliary gas, maintain the temperature and pressure in the reaction chamber, introduce a small amount of hydrogen chloride gas, and continue in-situ etching for 1 to 10 minutes; the ratio of hydrogen chloride gas flow rate to hydrogen gas flow rate is 0.01% to 0.1%.

[0010] Step S400: In-situ etching ends, epitaxial layer growth begins.

[0011] Furthermore, in step S100, the temperature is raised to 1500-1650°C in a hydrogen atmosphere, and the pressure is set to 40-200 mbar.

[0012] Furthermore, in step S100, the substrate is an off-axis conductive or semi-insulating SiC substrate with an off-axis angle of 0.1° to 8° along the <11-20> direction.

[0013] Furthermore, in step S200, a time period T includes different air intake time periods Δt1 and Δt2 and a time interval Δt'. Two different auxiliary gases are introduced in Δt1 and Δt2 respectively, and the introduction of auxiliary gases is stopped in Δt'. Temperature and pressure are maintained to perform the pulse-assisted in-situ etching process.

[0014] Furthermore, in step S200, the pulse-assisted in-situ etching process is performed for 5 to 60 minutes, the air intake time intervals Δt1 and Δt2 are within the range of 1s ≤ Δt1 ≤ 60s and 1s ≤ Δt2 ≤ 60s, and the time interval Δt' is within the range of 1s ≤ Δt' ≤ 20s.

[0015] Furthermore, in step S200, the auxiliary gas is a silicon source and a carbon source. The types of silicon sources include silane, trichlorosilane, and dichlorosilane. The ratio of silicon source gas flow rate to hydrogen flow rate is in the range of 0.004% to 0.1%. The types of carbon sources include propane, ethylene, methane, and acetylene. The molar ratio of carbon to silicon between the carbon source and the silicon source satisfies 0.6 ≤ C / Si ≤ 1.6.

[0016] Furthermore, in step S300, the in-situ etching time is 1 to 10 minutes, and the ratio of hydrogen chloride gas flow rate to hydrogen gas flow rate is 0.01% to 0.1%.

[0017] Compared with the prior art, the technical solution of the present invention can achieve the following beneficial technical effects:

[0018] This invention features pulsed alternating introduction of carbon and silicon sources. The carbon pulse can improve the repair effect of substrate surface damage, while the silicon pulse can reduce surface free energy and suppress the increase in surface roughness and atomic step coalescence caused by the carbon pulse.

[0019] This invention reduces the reaction between silicon and carbon residues by increasing the interval between the pulsed alternation of carbon and silicon sources and performing pure hydrogen etching.

[0020] This invention removes silicon carbide byproducts formed during the pulse etching process by using a mixture of hydrogen and a small amount of hydrogen chloride gas for in-situ etching after the pulse-assisted in-situ etching is completed, thus providing a good substrate surface and reaction chamber environment for subsequent epitaxial growth. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the pulse-assisted in-situ etching method of the present invention.

[0022] Figure 2 This is a schematic diagram of gas introduction during the substrate pretreatment process of Embodiment 1 of this application.

[0023] Figure 3 This is a schematic diagram of gas introduction during the substrate pretreatment process in Embodiment 2 of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0025] During in-situ etching of SiC substrates, the etching gas exhibits varying etching rates on the microstructures. For instance, it has a higher etching rate on protrusions, thus enabling surface damage repair through selective etching. During high-temperature etching, hydrogen more readily combines with carbon to form hydrocarbons, leading to a faster rate of carbon consumption on the substrate surface.

[0026] On the one hand, introducing a carbon source during in-situ etching increases the partial pressure of hydrocarbons on the substrate surface, which helps suppress the combination of hydrogen and carbon, thus balancing the etching rates of carbon and silicon and better repairing surface damage. However, in a carbon-rich atmosphere, silicon carbide has a high surface free energy. The atomic steps on the SiC material surface will reduce the surface free energy by merging into giant steps, leading to increased surface roughness and affecting epitaxial quality.

[0027] On the other hand, introducing a silicon source during in-situ etching helps reduce the surface free energy of silicon carbide, thereby suppressing the coalescence of atomic steps and reducing surface roughness. However, the introduction of a silicon source cannot solve the problem of uneven carbon-silicon consumption, and silicon clusters are easily generated in a silicon-rich atmosphere, which also affects the epitaxial quality.

[0028] If a pulsed air intake method is used for auxiliary treatment, alternating between carbon and silicon sources, problems such as giant step aggregation or silicon clusters caused by carbon or silicon richness can be effectively avoided.

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0030] This invention provides a SiC substrate pretreatment method to improve surface morphology; specifically, it is a pulse-assisted in-situ etching method for SiC substrate pretreatment. For example... Figure 1 As shown, it includes the following steps:

[0031] Step S100: The SiC substrate for epitaxial growth is placed into the reaction chamber and heated to 1500-1650°C in a hydrogen atmosphere, with a pressure of 40-200 mbar. The substrate is an off-axis (0001) conductive or semi-insulating SiC substrate with an off-axis (0001) deflection angle of 0.1°-8° along the <11-20> direction.

[0032] In step S200, while maintaining the flow of hydrogen, a small amount of auxiliary gas is introduced. The auxiliary gas is introduced into the reaction chamber in a pulsed manner, that is, within a time period T, there are different gas inlet time periods Δt1 and Δt2 and a time interval Δt'. Two different auxiliary gases are introduced in Δt1 and Δt2 respectively, and the gas inlet is stopped in Δt'. The temperature and pressure are maintained, and the above-mentioned pulsed assisted in-situ etching process is performed for 5 to 60 minutes. The gas inlet time periods Δt1 and Δt2 satisfy 1s≤Δt1≤60s, 1s≤Δt2≤60s, and the time interval Δt' satisfies 1s≤Δt'≤20s. The auxiliary gases are silicon and carbon sources. The silicon sources include silane, trichlorosilane, and dichlorosilane. The ratio of silicon source gas flow rate to hydrogen flow rate is 0.004% to 0.1%. The carbon sources include propane, ethylene, methane, acetylene, etc. The molar ratio of carbon to silicon between the carbon and silicon sources satisfies 0.6 ≤ C / Si ≤ 1.6.

[0033] In step S300, after the pulse-assisted treatment is completed, continue to introduce hydrogen gas, stop introducing auxiliary gas, maintain the temperature and pressure in the reaction chamber, introduce a small amount of hydrogen chloride gas, and continue in-situ etching for 1 to 10 minutes; the ratio of hydrogen chloride gas flow rate to hydrogen gas flow rate is 0.01% to 0.1%.

[0034] Step S400: In-situ etching ends, epitaxial layer growth begins.

[0035] In steps S100 to S400, the flow rate of hydrogen is 20 to 160 slm.

[0036] The advantage of this invention is that by adjusting the surface morphology of the substrate through a pulse-assisted in-situ etching process before epitaxial growth, it can repair surface damage, reduce surface roughness, and suppress atomic step aggregation, while avoiding the problems caused by in-situ etching in carbon-rich and silicon-rich atmospheres.

[0037] Example 1, such as Figure 2 As shown:

[0038] Step 1: The SiC substrate for epitaxial growth is placed into the reaction chamber and heated to 1600°C in a hydrogen atmosphere. The hydrogen flow rate is set to 40 slm and the pressure to 150 mbar.

[0039] Step 2: While keeping hydrogen gas flowing in, alternately introduce silane and ethylene as auxiliary gases.

[0040] Silane and ethylene are alternately introduced in a pulsed manner within a 40s cycle. Ethylene is introduced at time t0 with a flow rate of 4 sccm and is stopped at time t0+15s. Silane is introduced at time t0+20s with a flow rate of 8 sccm and is stopped at time t0+35s. Ethylene is introduced at time t0+40s with a flow rate of 4 sccm, and then the cycle repeats in a 40s cycle.

[0041] During the pretreatment process, the temperature and pressure of step 1 are kept constant, and in-situ etching is performed for 10 minutes.

[0042] Step 3: Maintain hydrogen flow, stop the flow of silane and ethylene, maintain constant temperature and pressure in the reaction chamber, introduce hydrogen chloride gas at 10 sccm, and continue in-situ etching for 5 minutes.

[0043] Step 4: Pretreatment complete, epitaxial growth begins.

[0044] The schematic diagram of the gas introduced during the pretreatment stage of this embodiment changes over time is shown below. Figure 2As shown in the figure. This embodiment avoids carbon and silicon enrichment by alternately introducing carbon and silicon sources, while simultaneously improving the surface damage repair effect and inhibiting the aggregation of giant steps.

[0045] Example 2, as Figure 3 As shown:

[0046] Step 1: The SiC substrate for epitaxial growth is placed into the reaction chamber and heated to 1600°C in a hydrogen atmosphere. The hydrogen flow rate is set to 40 slm and the pressure to 150 mbar.

[0047] Step 2: While keeping hydrogen gas flowing in, alternately introduce silane and ethylene as auxiliary gases.

[0048] Silane and ethylene are alternately introduced in a pulsed manner within a 45s cycle. Ethylene is introduced at time t0 with a flow rate of 5 sccm and is stopped at time t0+20s. Silane is introduced at time t0+25s with a flow rate of 8 sccm and is stopped at time t0+40s. Ethylene is introduced at time t0+45s with a flow rate of 4 sccm, and then the cycle repeats in 45s.

[0049] During the pretreatment process, the temperature and pressure of step 1 are kept constant, and in-situ etching is performed for 15 minutes.

[0050] Step 3: Maintain hydrogen flow, stop the flow of silane and ethylene, maintain constant temperature and pressure in the reaction chamber, introduce hydrogen chloride gas at 10 sccm, and continue in-situ etching for 5 minutes.

[0051] Step 4: Pretreatment complete, epitaxial growth begins.

[0052] The schematic diagram of the gas introduced during the pretreatment stage of this embodiment changes over time is shown below. Figure 3 As shown. When the auxiliary gas is alternately introduced in a pulsed manner, the introduction time of the carbon source and silicon source can be adjusted according to actual needs. This embodiment is for substrates with obvious surface damage such as scratches. By slightly increasing the introduction flow rate and duration of the carbon source, the surface damage repair effect can be improved.

[0053] In summary, this invention provides a SiC substrate pretreatment method for improving surface morphology, comprising: step S100, placing the SiC substrate for epitaxial growth into a reaction chamber, heating it to a certain temperature and setting a pressure in a hydrogen atmosphere; step S200, introducing an auxiliary gas while maintaining hydrogen flow, the auxiliary gas being introduced into the reaction chamber in a pulsed manner; step S300, after the pulsed auxiliary treatment is completed, maintaining hydrogen flow, stopping the auxiliary gas flow, maintaining the temperature and pressure in the reaction chamber, introducing a small amount of hydrogen chloride gas, and continuing in-situ etching; step S400, after the in-situ etching is completed, epitaxial layer growth begins. The introduction of carbon and silicon sources during the in-situ etching process avoids carbon or silicon enrichment that could degrade the surface morphology. The auxiliary treatment effects of carbon and silicon sources improve surface damage repair, reduce surface roughness, and inhibit atomic step aggregation, thereby providing a substrate surface with a regular atomic step structure and improving the quality of epitaxial growth.

[0054] The specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for pretreatment of SiC substrates to improve surface morphology, characterized in that, The method includes: Step S100: The SiC substrate for epitaxial growth is placed into the reaction chamber, heated to a certain temperature and pressure is set in a hydrogen atmosphere; the temperature is raised to 1500-1650℃ in a hydrogen atmosphere and the pressure is set to 40-200mbar; the substrate is an off-axis conductive or semi-insulating SiC substrate with an off-axis deflection angle of 0.1°-8° along the <11-20> direction. Step S200: While maintaining the hydrogen flow, an auxiliary gas is introduced into the reaction chamber in a pulsed manner. Within a time period T, there are different gas inlet time intervals Δt1 and Δt2, and a time interval Δt'. Two different auxiliary gases are introduced during Δt1 and Δt2 respectively, and the gas flow is stopped during Δt'. Temperature and pressure are maintained, and pulsed assisted in-situ etching is performed. The duration of the pulsed assisted in-situ etching process is 5–60 minutes. The ranges of Δt1 and Δt2 satisfy 1s≤Δt1≤60s, 1s≤Δt2≤60s, and the range of time interval Δt' satisfies 1s≤Δt'≤20s; the auxiliary gas is a silicon source and a carbon source. The types of silicon sources include silane, trichlorosilane, and dichlorosilane. The ratio of silicon source gas flow rate to hydrogen flow rate is in the range of 0.004% to 0.1%. The types of carbon sources include propane, ethylene, methane, and acetylene. The molar ratio of carbon to silicon between the carbon source and the silicon source satisfies 0.6≤C / Si≤1.

6. In step S300, after the pulsed auxiliary treatment is completed, hydrogen gas is continuously introduced, the auxiliary gas is stopped, the temperature and pressure in the reaction chamber are maintained, a small amount of hydrogen chloride gas is introduced, and in-situ etching continues; the in-situ etching time is 1 to 10 minutes, and the ratio of hydrogen chloride gas flow rate to hydrogen gas flow rate is 0.01% to 0.1%. Step S400: In-situ etching ends, epitaxial layer growth begins.

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