Method for removing parasitic silicon carbide

Abstract

The application provides a method for removing parasitic silicon carbide, which comprises using silane and an oxygen-free cleaning gas containing hydrogen and hydrogen fluoride gas, keeping the cleaning temperature in a cleaning chamber not lower than 1300 DEG C, and removing the parasitic silicon carbide under a cleaning pressure not lower than 100 mbar, so as to improve the cleaning rate. The hydrogen gas plays a dilution role on the hydrogen fluoride gas, and meanwhile, the cleaning efficiency is considered, so as to prevent over-etching. The silicon species generated by the decomposition of silane can generate gaseous silicon tetrafluoride with fluorine, and is adsorbed on the surface of exposed graphite basal body after cleaning, so as to reduce the significant damage of the hydrogen fluoride gas to the surface of exposed graphite basal body after cleaning. In the later cleaning stage, the silane is switched to propane, so as to improve the silicon-rich atmosphere formed in the cleaning chamber due to the introduction of silane, reduce or avoid the problem that the silicon species adsorbed on the surface of the graphite basal body is difficult to be taken away by the flow field of the purge gas, and make the surface of the epitaxial wafer appear obvious cluster phenomenon.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor device processing equipment, in particular to a method for removing parasitic silicon carbide. BACKGROUND

[0002] With the rapid growth of high-frequency, high-power radio frequency and power electronics demand such as 5G and new energy, the physical limit bottleneck of silicon-based semiconductor devices gradually emerges, and how to limit the increase of device size, control the increase of device heat and control the rapid expansion of cost while improving power has become a key concern in the semiconductor industry. The third generation of semiconductor materials, led by silicon carbide, gradually moves from research to industrialization under this trend, and becomes an explicit trend to replace some silicon-based power devices. In order to promote the practicality of SiC devices, it is indispensable to establish a high-quality epitaxial growth technology.

[0003] The silicon carbide epitaxial equipment is a continuous production equipment, and frequent shutdown for cleaning will reduce the yield, affect the production efficiency, and increase the process fluctuation risk, affecting the process stability. After the current process is completed, parasitic silicon carbide will be formed in the growth chamber, which will continue to grow using the source gas in the next cycle growth process, affecting the effective epitaxial growth on the substrate, and causing the growth rate to decrease. In addition, the parasitic silicon carbide structure is loose, and when accumulated to a certain extent, the parasitic silicon carbide is easy to peel off from the surface of the parts in the growth chamber and fall on the silicon carbide epitaxial layer under the action of the gas flow field in the growth chamber, affecting the growth quality.

[0004] For the parasitic silicon carbide on the graphite parts in the growth chamber, in the prior art, fluorine-containing gases such as fluorine, carbon trifluoride, hydrogen fluoride gas are usually plasmaized, and the high-activity fluorine radicals generated by the plasma are used to quickly chemically remove the parasitic silicon carbide. However, fluorine-containing gases such as fluorine, carbon trifluoride, hydrogen fluoride gas have strong oxidizing properties, and the degree of reaction with parasitic silicon carbide is intense and difficult to control, and the safety is poor; the strong oxidizing fluorine-containing gas is easy to cause excessive etching damage to the graphite parts, for example, the surface of the local area compared with other areas appears significant color difference, and the roughness increases. Taking the graphite part as a flow guide cover or a base as an example, the process gas flow field flowing through this place is easy to be disturbed in the subsequent process, and the parasitic particles are also more likely to accumulate and fall off in this place, affecting the growth quality of the silicon carbide epitaxial layer.

[0005] Therefore, it is urgent to provide a new method which can effectively remove the parasitic silicon carbide without easy over-etching. SUMMARY

[0006] To achieve the above-mentioned purpose, the present application provides a method for removing parasitic silicon carbide, which is beneficial to quickly remove the parasitic silicon carbide on the surface of the graphite part, and reduces or even avoids excessive damage to the surface of the graphite part.

[0007] The method for removing parasitic silicon carbide of the present application comprises the following steps:

[0008] S1: obtaining a reference etching time length by cleaning a reference graphite piece formed with parasitic silicon carbide by hydrogen fluoride gas at a cleaning temperature and a cleaning pressure, wherein the cleaning temperature is not lower than 1300℃, and the cleaning pressure is not lower than 100 mbar;

[0009] S2: placing a graphite piece to be cleaned formed with parasitic silicon carbide in a cleaning chamber, exposing the surface of the graphite piece to be cleaned formed with parasitic silicon carbide to the environment in the cleaning chamber, and controlling the cleaning chamber to reach the cleaning temperature and the cleaning pressure;

[0010] S3: introducing silane and an oxygen-free cleaning gas containing the hydrogen fluoride gas and hydrogen into the cleaning chamber, controlling the flow ratio of the hydrogen and the hydrogen fluoride gas to be between 10:1 and 50:1, the flow ratio of the hydrogen fluoride gas and the silane to be between 10:1 and 100:1, and the first time length of introducing the silane and the oxygen-free cleaning gas to be less than the reference etching time length and not less than 70% of the reference etching time length;

[0011] S4: controlling the flow of the oxygen-free cleaning gas to be constant, stopping the introduction of the silane, introducing propane into the cleaning chamber, and controlling the second time length of introducing the oxygen-free cleaning gas and the propane to be less than the first time length.

[0012] Optionally, the cleaning temperature is between 1300℃ and 1500℃, and the cleaning pressure is between 500 mbar and 1000 mbar.

[0013] Optionally, in step S3, the flow of the hydrogen fluoride gas introduced is not less than 1000 sccm, and the flow of the silane introduced is not less than 50 sccm.

[0014] Optionally, in step S3, the flow of the hydrogen fluoride gas introduced is between 1000 sccm and 5000 sccm, and the flow of the silane introduced is between 50 sccm and 500 sccm.

[0015] Optionally, in step S3, the first time length is controlled to be not more than 90% of the reference etching time length.

[0016] Optionally, the first time length is controlled to be not less than 75% of the reference etching time length.

[0017] Optionally, in step S4, the flow of the propane introduced is controlled to be less than 1 in terms of the carbon-silicon ratio of the flow of the silane introduced in step S3.

[0018] Optionally, in step S4, the propane flow rate is between 10 sccm and 50 sccm.

[0019] Optionally, the second duration shall not exceed 60% of the first duration.

[0020] Optionally, in step S1, the graphite part to be cleaned has the same dimensions and manufacturing process as the reference graphite part.

[0021] Optionally, in step S1, the step of obtaining the reference etching time for cleaning a reference graphite part with parasitic silicon carbide formed by cleaning with hydrogen fluoride gas at a cleaning temperature and cleaning pressure includes:

[0022] The reference graphite part with parasitic silicon carbide is placed into the cleaning chamber, and the cleaning temperature and cleaning pressure are controlled to be reached in the cleaning chamber.

[0023] The hydrogen fluoride gas is introduced into the cleaning chamber until the reference etching time is reached to remove the parasitic silicon carbide covering the body surface of the reference graphite part.

[0024] Optionally, the graphite part to be cleaned includes an exposed body surface without parasitic silicon carbide formation, and before placing the graphite part to be cleaned into the cleaning chamber, the exposed body surface is further shielded using a shielding structure composed of sacrificial material.

[0025] Optionally, the sacrificial material is a corrosion-resistant carbon-based material.

[0026] Optionally, both the reference graphite part and the graphite part to be cleaned are bases, flow guides, or heat shields made of graphite-based materials.

[0027] The method for removing parasitic silicon carbide of the present invention has the following beneficial effects:

[0028] Using an oxygen-free cleaning gas containing hydrogen and hydrogen fluoride, and maintaining a temperature of no less than 1300℃ and a pressure of no less than 100 mbar within the cleaning chamber, enhances the activity of the oxygen-free cleaning gas and slows down the airflow within the cleaning chamber, thus improving the cleaning rate. Under the aforementioned temperature and pressure, controlling the flow ratio of hydrogen to hydrogen fluoride between 10:1 and 50:1 allows the hydrogen gas, which has a certain etching effect on silicon carbide but a low etching rate, to dilute the highly oxidizing hydrogen fluoride gas, while simultaneously ensuring cleaning efficiency. This helps to regulate the appropriate reaction rate between parasitic silicon carbide and hydrogen fluoride, preventing over-etching.

[0029] Silane is introduced, and the flow ratio of hydrogen fluoride gas to silane is controlled between 10:1 and 100:1 to further dilute the hydrogen fluoride gas. The silicon species (such as Si and SiH3) produced by the decomposition of silane (SiH4) are utilized. + The ability to react with fluorine to form gaseous silicon tetrafluoride, and the property of adsorbing onto the surface of the graphite substrate after cleaning, reduces the significant damage of hydrogen fluoride gas to the surface of the graphite substrate after cleaning.

[0030] Furthermore, in the later stage of cleaning, the parasitic silicon carbide removal method of this application switches silane to propane, which improves the silicon-rich atmosphere formed in the cleaning chamber due to the introduction of silane, and reduces or avoids the problem that silicon species adsorbed on the surface of the graphite substrate are difficult to be carried away by the purging gas flow, resulting in obvious clustering on the surface of the epitaxial wafer. Attached Figure Description

[0031] Figure 1 The diagram shows the growth chamber of a silicon carbide epitaxial device.

[0032] Figure 2 The diagram shown is of the base.

[0033] Figure 3 The diagram shows a flow chart of the method for removing parasitic silicon carbide according to the present invention.

[0034] Figure 4 The diagram shows a shielding structure installed on the base.

[0035] Figure 5 The diagram shows a shielding structure installed in the fairing.

[0036] Figure 6 The image shown is of the surface of a reference graphite part after undergoing HF treatment in Example 4.

[0037] Figure 7 The image shown is of the surface of the graphite part to be cleaned after cleaning, as shown in Example 4.

[0038] Figure 8 The image shown is a surface morphology diagram of a silicon carbide epitaxial wafer obtained by silicon carbide epitaxial growth after cleaning the substrate bearing substrate with parasitic silicon carbide using the removal method of Embodiment 4 of this application.

[0039] Figure 9 The image shown is a surface morphology diagram of a silicon carbide epitaxial wafer obtained by removing parasitic silicon carbide from a substrate using the comparative method of Embodiment 4 of this application and then performing silicon carbide epitaxial growth. Detailed Implementation

[0040] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0041] like Figure 1 As shown, the silicon carbide epitaxial apparatus of the present invention has a growth chamber 5, and a base 1 for supporting a substrate 200 is disposed within the growth chamber 5. During the silicon carbide epitaxial growth process, the substrate to be epitaxially grown, such as a silicon carbide substrate, a doped silicon carbide substrate, an alumina substrate, or an aluminum nitride substrate, is supported by the base 1. The growth chamber 5 is also provided with a gas injection mechanism 4 for supplying process gas into the growth chamber 5. The gas injection mechanism 4 is disposed opposite to the base 1. Specifically, the outlet side of the gas injection mechanism 4 is disposed opposite to the top surface 11 of the base 1 for supporting the substrate 200. A heating device 2 is also disposed on the bottom surface of the base 1, which can heat the base 1 and heat the substrate 200 it supports through heat transfer from the base 1. A flow guide shroud 7 is also disposed between the gas injection mechanism 4, the base 1, and the sidewall of the growth chamber 5. The flow guide shroud 7, the base 1, and the gas injection mechanism 4 form a reaction space. A heat insulation ring 6 is also provided on the outside of the heating device 2. This heat insulation ring 6 allows as much heat from the heating device 2 as possible to be transferred to the base 1, thereby improving the heat transfer efficiency of the base 1 to the substrate 200. Figure 1 As shown, the epitaxial growth apparatus of the present invention also includes a rotary drive device 3, which is disposed in the growth chamber 5 in a dynamic sealing manner and fixedly connected to the middle part of the base 1, so as to drive the base 1 to drive the substrate 200 to rotate around the rotation axis T2 during the epitaxial reaction.

[0042] like Figure 2 As shown, the top surface 11 of the base 1 has a plurality of recesses 100, which are recessed from the top surface 11 to the bottom surface 12 of the base 1. The size and number of the recesses 100, as well as their distribution on the base 1, can be designed according to the size, thickness, and number of the substrate 200 that needs to be supported and held, as well as the size of the base 1. For a substrate 200 that is typically disc-shaped, the recesses 100 are designed with circular openings, and the opening size corresponds to the size of the substrate 200.

[0043] In this embodiment, the base 1, the flow guide 7, and the heat insulation ring 6 are all graphite components.

[0044] During silicon carbide epitaxial growth, the growth chamber 5 maintains a specific process temperature and pressure. The gas injection mechanism 4 injects source gas containing carbon and silicon sources into the growth chamber 5. This source gas grows a silicon carbide epitaxial film on the surface of the substrate 200. During this process, the surfaces through which the source gas flows, for example... Figure 1 Parasitic silicon carbide will be formed on the surface of the flow guide shroud 7 exposed inside the growth chamber 5, the surface of the base 1 exposed inside the growth chamber 5, and the outer surface of the heat insulation ring 6.

[0045] Parasitic silicon carbide is a polycrystalline silicon carbide with high defect rate and loose structure. The monocrystalline silicon carbide coating on the surface of graphite parts has ordered atomic arrangement, low surface energy, and strong chemical inertness. If the thickness of parasitic silicon carbide on the graphite part exceeds a certain limit and is not cleaned, it is easily affected by the process flow field and process gases during the epitaxial growth process and falls onto the substrate, affecting the quality of the epitaxial film.

[0046] The epitaxial growth equipment is a continuous production line. When the cumulative thickness of parasitic silicon carbide on the surface of the graphite part reaches a certain value, the graphite part needs to be disassembled and cleaned to remove the parasitic silicon carbide. In this invention, during the epitaxial growth process, the thickness of the epitaxial layer grown in each round of epitaxial processes is counted. Once the cumulative thickness of this epitaxial layer reaches a certain value, the epitaxial growth equipment is stopped, and the graphite part with parasitic silicon carbide is disassembled for subsequent cleaning.

[0047] Existing technologies use oxygen-containing cleaning gases. For example, when the cleaning gas contains oxygen, the Si formed from the decomposition of parasitic silicon carbide reacts with O to form silicon oxide, which easily re-adsorbs onto the surface of the cleaned object. In subsequent silicon carbide epitaxial growth, silicon oxide becomes a heterogeneous nucleus, leading to epitaxial defects. Furthermore, the free O generated by its decomposition under process conditions can react with the carbon source in the source gas introduced during epitaxial growth, altering the carbon-to-silicon ratio and interfering with the growth efficiency and balance of the epitaxial wafer.

[0048] Therefore, the parasitic silicon carbide removal method of this application uses an oxygen-free cleaning gas to avoid the above-mentioned problems.

[0049] Parasitic silicon carbide is a polycrystalline silicon carbide with high defect content and a loose structure. Even if the thickness of parasitic silicon carbide is uniform throughout the graphite part, the structural morphology will not be uniform. Although the reaction between the gas used in chemical cleaning and parasitic silicon carbide is isotropic, the degree of reaction will not be uniform in different areas. This is why the local areas of the graphite-based surface of the graphite part show significant damage and increased roughness compared to other areas.

[0050] Hydrogen fluoride (HF) gas has strong oxidizing properties. If used alone as an oxygen-free cleaning gas, it can easily cause over-etching in localized areas of the graphite parts after cleaning. Hydrogen also has an etching effect on parasitic silicon carbide, but under the same process conditions as HF cleaning, its cleaning efficiency is much slower than that of hydrogen fluoride gas, and its use alone will significantly affect the cleaning efficiency. For example, for graphite substrates of the same batch and specifications, with parasitic silicon carbide covering the surface (240 mm between the bearing surfaces, and the parasitic silicon carbide thickness exceeding 1000 micrometers), cleaning was performed using HF and hydrogen at 1500°C and 1000 mbar. The HF treatment took about 1 hour, while the hydrogen treatment took more than 3 hours.

[0051] Therefore, the parasitic silicon carbide removal method of this application uses an oxygen-free cleaning gas containing hydrogen and hydrogen fluoride. The hydrogen gas, which has a certain etching effect on silicon carbide but a low etching rate, dilutes the highly oxidizing hydrogen fluoride gas, while taking into account the cleaning efficiency. This is beneficial for regulating the reaction rate of parasitic silicon carbide and hydrogen fluoride and preventing over-etching.

[0052] Furthermore, addressing the issues that using hydrogen fluoride gas alone can easily lead to over-etching, while excessive dilution with hydrogen gas significantly affects cleaning efficiency, and insufficient dilution can easily cause significant damage to the graphite surface, the parasitic silicon carbide removal method of this application also introduces silane to further participate in the dilution of hydrogen fluoride gas. It also utilizes silicon species (Si, SiH3) generated from the decomposition of silane. + It can react with fluorine to form gaseous silicon tetrafluoride and adsorb onto the surface of the graphite substrate after cleaning, reducing the significant damage of hydrogen fluoride gas to the surface of the graphite substrate after cleaning.

[0053] Furthermore, the introduction of silane creates a silicon-rich atmosphere within the cleaning chamber. Some of the silicon species produced by the decomposition of silane adsorb onto the surface of the graphite substrate and are difficult to remove by purging. These adsorbed silicon species react with the carbon-containing source gas during the epitaxial growth process to form silicon carbide particles. These particles are dispersed by the gas flow, resulting in significant clustering on the epitaxial wafer surface. Therefore, the parasitic silicon carbide removal method of this application switches silane to propane in the later stages of cleaning, utilizing the reaction between propane and silicon species to improve the silicon-rich atmosphere.

[0054] Based on the above, the present invention provides a method for removing parasitic silicon carbide, such as... Figure 3 As shown, the method for removing parasitic silicon carbide of the present invention includes steps S1 to S4, specifically:

[0055] S1: Obtain a reference etching time for cleaning a reference graphite part with parasitic silicon carbide formed by cleaning with hydrogen fluoride gas at a cleaning temperature and a cleaning pressure, wherein the cleaning temperature is not less than 1300°C and the cleaning pressure is not less than 100 mbar.

[0056] S2: The graphite part to be cleaned, on which parasitic silicon carbide has formed, is placed in the cleaning chamber. The surface of the graphite part on which parasitic silicon carbide has grown is exposed to the environment inside the cleaning chamber, and the cleaning temperature and the cleaning pressure are controlled to be reached inside the cleaning chamber.

[0057] S3: Introduce silane and an oxygen-free cleaning gas containing hydrogen fluoride and hydrogen into the cleaning chamber;

[0058] S4: Control the flow rate of the oxygen-free cleaning gas to remain constant, stop the introduction of silane, and introduce propane into the cleaning chamber.

[0059] In some embodiments, step S1 further includes obtaining a reference etching time for cleaning a reference graphite part with parasitic silicon carbide formed by using hydrogen fluoride gas at a cleaning temperature and cleaning pressure. This reference etching time can serve as a reference for selecting the inlet time in step S3, so that the parasitic silicon carbide can be effectively removed in step S3 while avoiding significant damage to the exposed graphite-based surface of the graphite part.

[0060] In some specific embodiments, the step of obtaining the reference etching time for cleaning a reference graphite part with parasitic silicon carbide formed by hydrogen fluoride gas at a cleaning temperature and cleaning pressure includes: placing the reference graphite part with parasitic silicon carbide formed into the cleaning chamber, performing step S2, and then introducing the hydrogen fluoride gas into the cleaning chamber until the reference etching time is reached so that the body surface of the reference graphite part is exposed.

[0061] In some embodiments, the cleaning chamber is a graphite tube chamber housed within a tubular furnace, its inner wall covered with a silicon carbide coating, and the graphite components are placed inside the graphite tube. The specific implementation of the tubular furnace follows conventional techniques in the art. Specifically, one end of the tubular furnace provides oxygen-free cleaning gas to the opening of the graphite tube, while the other end is equipped with an exhaust device to control the pressure inside the chamber and the exhaust gas. Components in direct contact with the gas during intake and exhaust are treated with anti-corrosion measures, for example, using graphite components, single-crystal silicon carbide components, or components protected by a single-crystal silicon carbide coating. The inner wall of the tubular furnace is filled with graphite felt for protection, and a heating device installed on the furnace wall heats the graphite tube chamber using long-distance heating methods such as radio frequency.

[0062] In some embodiments, in steps S1 and S2, the cleaning temperature is not lower than 1300 degrees Celsius, and the cleaning pressure is not lower than 100 mbar. The cleaning temperature and pressure used in step S2 are respectively equal to those in step S1.

[0063] In the following description of this application, the term "between" is used to define the endpoint values ​​of the defined numerical range.

[0064] In some specific embodiments, in step S2, the cleaning temperature is between 1300℃ and 1500℃, and the cleaning pressure is between 500 mbar and 1000 mbar, which is beneficial to accelerate the etching reaction and slow down the flow of air in the growth chamber, thus improving the cleaning rate.

[0065] In step S3 of some embodiments, the flow ratio of hydrogen gas to hydrogen fluoride gas is controlled to be between 10:1 and 50:1, and the flow ratio of hydrogen fluoride gas to silane is between 10:1 and 100:1.

[0066] In step S3 of some embodiments, the first duration for introducing the oxygen-free cleaning gas and the silane is controlled to be less than the reference etching duration and not less than 70% of the reference etching duration. As mentioned earlier, using hydrogen fluoride gas (HF) alone as an oxygen-free cleaning gas results in a high reaction rate and short time, but it can easily cause significant damage to localized surface areas of the graphite part. Therefore, not only by diluting HF with hydrogen and silane to reduce the intensity of the reaction and improve etching controllability, but more importantly, by limiting the first duration to be less than the reference etching duration and not less than 70% of the reference etching duration, this step achieves the removal of at least nearly half of the parasitic silicon carbide to improve cleaning efficiency, while also effectively protecting the exposed graphite-based surface of the graphite part to reduce or avoid significant damage.

[0067] In step S4 of some embodiments, since the first time duration is controlled to be less than the reference etching time and not less than 70% of the reference etching time in step S3, at least nearly half of the parasitic silicon carbide is removed. Therefore, in step S4, while introducing propane to improve the silicon-rich atmosphere in the chamber, it also dilutes HF, maintains the flow rate of the oxygen-free cleaning gas, removes the remaining parasitic silicon carbide, and controls the second time duration of introducing the oxygen-free cleaning gas and the propane to be less than the first time duration, so as to minimize the significant damage to the exposed graphite-based surface of the graphite part.

[0068] In some embodiments, in step S3, the flow rate of the hydrogen fluoride gas is between 1000 sccm and 5000 sccm.

[0069] In some embodiments, in step S3, the hydrogen flow rate is between 45,000 sccm and 55,000 sccm.

[0070] In some embodiments, in step S3, the flow rate of the silane is between 50 sccm and 500 sccm.

[0071] In some embodiments, in step S3, the first duration does not exceed 90% of the reference etching duration, so as to avoid significant damage caused by excessive time in this step, resulting in too little remaining parasitic silicon carbide, too much exposed graphite base surface of the graphite part, and excessive contact time between HF and graphite base surface during the execution of step S4.

[0072] In some embodiments, in step S3, the first duration is not less than 75% of the reference etching duration.

[0073] In some embodiments, the first duration is not less than 40 minutes.

[0074] In order to remove parasitic silicon carbide, as mentioned above, the first duration should not be too short.

[0075] In some embodiments, in step S4, the carbon-to-silicon ratio of the propane flow rate to the silane flow rate in step S3 is controlled to be less than 1, so as to avoid unnecessary carbon deposition on the exposed graphite-based surface caused by excessive propane decomposing in the cavity.

[0076] In some embodiments, the propane flow rate does not exceed 50 sccm.

[0077] In some embodiments, the propane flow rate is between 10 sccm and 50 sccm.

[0078] In some embodiments, the second duration does not exceed 60% of the first duration.

[0079] In some embodiments, the graphite part to be cleaned includes an exposed body surface. Taking a graphite base as an example, such as... Figure 1 In the silicon carbide epitaxial apparatus shown, the base 1 is shielded by a heat insulation ring 6. During the growth process, the recesses 100 on the graphite base are shielded by the substrate 200, and there is no parasitic silicon carbide below the base 1 or within the recesses 100. Since HF and hydrogen in the oxygen-free cleaning gas also have a certain etching effect on the surface of the graphite base, if these surfaces are not shielded in the cleaning chamber, significant damage such as whitening will occur. Therefore, before placing the graphite part to be cleaned into the cleaning chamber, the process further includes: using a shielding structure composed of sacrificial materials to shield the exposed surfaces of the graphite part where no parasitic silicon carbide has grown. For example, a shielding structure composed of sacrificial materials is used to shield the surfaces of the graphite part to be cleaned where no parasitic silicon carbide has grown. Figure 4and Figure 5 The shielding structure 10 shown.

[0080] In some embodiments, such as Figure 5 As shown, the graphite part to be cleaned is a flow guide 7. Parasitic silicon carbide is grown on the inner surface of the flow guide 7. The shielding structure 10 is a graphite barrel. The graphite barrel is sleeved on the outside of the flow guide 7. The inner wall of the graphite barrel and the outer wall of the flow guide 7 are in contact, so that the surface of the flow guide 7 covered by parasitic silicon carbide is exposed.

[0081] In some embodiments, such as Figure 4 As shown, the graphite part to be cleaned is a base 1, and parasitic silicon carbide is grown on the top surface and sidewalls of the base 1. The shielding structure 10 is a graphite barrel, and one side of the bottom surface of the base 1 is placed on top of the graphite barrel, so that the surface of the base 1 covered by parasitic silicon carbide is exposed.

[0082] In some embodiments, such as Figure 2 As shown, the top surface of the base 1 is provided with a recess 100 for supporting the substrate 200. Step S1 further includes placing a supporting sheet in the recess 100. The supporting sheet can be a graphite sheet with a size equivalent to the recess, or a discarded substrate.

[0083] The method for removing parasitic silicon carbide of the present invention is explained in detail through the following examples and comparative examples.

[0084] The reference graphite parts and the graphite parts to be cleaned used in the following embodiments are all graphite bases with the same dimensions and manufacturing process. Specifically, they are graphite bases with a bearing surface diameter of 240 mm, with recesses located in the center of the graphite base, and are sized to accommodate a 6-inch diameter substrate. The manufacturing process for each reference graphite part and the graphite part to be cleaned is as follows: at a growth temperature and pressure of 1550°C and 100 mbar, the graphite base is rotated at 600 rpm. In each process cycle, 70 sccm~155 sccm of propane (carbon source), 200 sccm~400 sccm of silane (silicon source), and 2000 sccm~5000 sccm of hydrogen chloride (conditioning gas) are introduced to grow a silicon carbide epitaxial layer on the substrate. The designed thickness of the silicon carbide epitaxial layer to be grown in a single process is 7 μm~11 μm. After multiple rounds of continuous production, if the cumulative designed thickness of the silicon carbide epitaxial layer exceeds 1500 μm, epitaxial growth is stopped, and the graphite parts are disassembled and cleaned after shutdown.

[0085] Example 1

[0086] The method for removing parasitic silicon carbide in this embodiment specifically includes the following steps:

[0087] S1: Provide two graphite bases of the same specifications and process history as a reference graphite part and a graphite part to be cleaned, respectively. The top surface of the two graphite parts, except for the recessed area, is covered with parasitic silicon carbide, and the sidewalls are covered with parasitic silicon carbide within a height range of about 2 cm (from the top surface downwards).

[0088] Place the reference graphite piece on Figure 4 Above the shielding structure 10 shown, the shielding structure 10 can specifically be a graphite barrel. A graphite sheet is placed in the recess of the base. The reference graphite part, together with the graphite barrel and the graphite sheet, is placed in the cleaning chamber of the graphite tube structure (surface coated with single crystal silicon carbide) of the tube furnace, so that the top and side walls of the base with parasitic silicon carbide can be exposed to the atmosphere of oxygen-free cleaning gas. The cleaning temperature in the cleaning chamber is controlled at 1350°C, the cleaning pressure is 500 mbar, HF is introduced at a flow rate of 5000 sccm, and the reference etching time is controlled at 80 min.

[0089] After the reference graphite part is cleaned, stop the flow of HF and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80°C. Then, transfer the cleaned reference graphite part out of the cleaning chamber.

[0090] S2: Place the graphite base to be cleaned as described above. Figure 4 Above the shielding structure 10 shown, after placing the auxiliary piece in the recess, it is transferred into the cleaning chamber; the cleaning temperature in the cleaning chamber is controlled at 1350℃ and the cleaning pressure is 500mbar.

[0091] S3: Introduce hydrogen fluoride gas, hydrogen gas, and silane into the clean chamber, and control the inlet flow rate of hydrogen gas to be 50,000 sccm, the inlet flow rate of hydrogen fluoride gas to be 5,000 sccm, and the inlet flow rate of silane to be 500 sccm. The first inlet duration of each gas is 65 min.

[0092] S4: Keep the flow rates of hydrogen fluoride and hydrogen constant, stop the flow of silane, and introduce propane into the clean chamber at a flow rate of 45 sccm. The second duration of the above-mentioned gas introduction in this step is 35 min.

[0093] After S4 is completed, stop the flow of hydrogen fluoride gas, hydrogen and propane, and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80 degrees Celsius. Then, transfer the cleaned graphite parts to be cleaned out of the cleaning chamber.

[0094] Example 2

[0095] The method for removing parasitic silicon carbide in this embodiment specifically includes the following steps:

[0096] S1: Provide two graphite bases of the same specifications and process history as a reference graphite part and a graphite part to be cleaned, respectively. The top surface of the two graphite parts, except for the recessed area, is covered with parasitic silicon carbide, and the sidewalls are covered with parasitic silicon carbide within a height range of about 2 cm (from the top surface downwards).

[0097] Place the reference graphite piece on Figure 4 Above the shielding structure 10 shown, the shielding structure 10 can specifically be a graphite barrel. A graphite sheet is placed in the recess of the base. The reference graphite piece, together with the graphite barrel and the graphite sheet, is placed in the cleaning chamber of the graphite tube structure of the tube furnace in Embodiment 1, so that the top and sidewalls of the base with parasitic silicon carbide can be exposed to the atmosphere of oxygen-free cleaning gas. The cleaning temperature in the cleaning chamber is controlled at 1400°C, the cleaning pressure is 950 mbar, HF is introduced at a flow rate of 2500 sccm, and the reference etching time is controlled at 75 min.

[0098] After the reference graphite part is cleaned, stop the flow of HF and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80°C. Then, transfer the cleaned reference graphite part out of the cleaning chamber.

[0099] S2: Place the graphite base to be cleaned as described above. Figure 4 Above the shielding structure 10 shown, after placing the supporting piece in the recess, it is transferred into the cleaning chamber;

[0100] The cleaning temperature in the cleaning chamber is controlled at 1400℃, and the cleaning pressure is controlled at 950 mbar.

[0101] S3: Introduce hydrogen fluoride gas, hydrogen gas, and silane into the clean chamber, and control the inlet flow rate of hydrogen gas to be 50,000 sccm, the inlet flow rate of hydrogen fluoride gas to be 2,500 sccm, and the inlet flow rate of silane to be 250 sccm. The first inlet duration of each gas is 65 min.

[0102] S4: Keep the flow rates of hydrogen fluoride and hydrogen constant, stop the flow of silane, and introduce propane into the clean chamber at a flow rate of 20 sccm. The second duration of the above-mentioned gas introduction in this step is 30 min.

[0103] After S4 is completed, stop the flow of hydrogen fluoride gas, hydrogen and propane, and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80 degrees Celsius. Then, transfer the cleaned graphite parts to be cleaned out of the cleaning chamber.

[0104] Example 3

[0105] The method for removing parasitic silicon carbide in this embodiment specifically includes the following steps:

[0106] S1: Provide two graphite bases of the same specifications and process history as a reference graphite part and a graphite part to be cleaned, respectively. The top surface of the two graphite parts, except for the recessed area, is covered with parasitic silicon carbide, and the sidewalls are covered with parasitic silicon carbide within a height range of about 2 cm (from the top surface downwards).

[0107] Place the reference graphite piece on Figure 4 Above the shielding structure 10 shown, the shielding structure 10 can specifically be a graphite barrel. A graphite sheet is placed in the recess of the base. The reference graphite piece, together with the graphite barrel and the graphite sheet, is placed in the cleaning chamber of the graphite tube structure of the tube furnace in Embodiment 1, so that the top and sidewalls of the base with parasitic silicon carbide can be exposed to the atmosphere of oxygen-free cleaning gas. The cleaning temperature in the cleaning chamber is controlled at 1400°C, the cleaning pressure is 1000 mbar, HF is introduced at a flow rate of 1000 sccm, and the reference etching time is controlled at 140 min.

[0108] After the reference graphite part is cleaned, stop the flow of HF and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80°C. Then, transfer the cleaned reference graphite part out of the cleaning chamber.

[0109] S2: Place the graphite base to be cleaned as described above. Figure 4 Above the shielding structure 10 shown, after placing the supporting piece in the recess, it is transferred into the cleaning chamber;

[0110] The cleaning temperature in the cleaning chamber is controlled at 1400℃, and the cleaning pressure is controlled at 1000 mbar.

[0111] S3: Introduce hydrogen fluoride gas, hydrogen gas, and silane into the clean chamber, and control the inlet flow rate of hydrogen gas to be 50,000 sccm, the inlet flow rate of hydrogen fluoride gas to be 1,000 sccm, and the inlet flow rate of silane to be 50 sccm. The first inlet duration of each gas is 120 min.

[0112] S4: Keep the flow rates of hydrogen fluoride and hydrogen constant, stop the flow of silane, and introduce propane into the clean chamber at a flow rate of 15 sccm. The second duration of the above-mentioned gas introduction in this step is 20 min.

[0113] After S4 is completed, stop the flow of hydrogen fluoride gas, hydrogen and propane, and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80 degrees Celsius. Then, transfer the cleaned graphite parts to be cleaned out of the cleaning chamber.

[0114] Example 4

[0115] The method for removing parasitic silicon carbide in this embodiment includes the following:

[0116] S1: Provide two graphite bases of the same specifications and process history as a reference graphite part and a graphite part to be cleaned, respectively. The top surface of the two graphite parts, except for the recessed area, is covered with parasitic silicon carbide, and the sidewalls are covered with parasitic silicon carbide within a height range of about 2 cm (from the top surface downwards).

[0117] Place the reference graphite piece on Figure 4 Above the shielding structure 10 shown, the shielding structure 10 can specifically be a graphite barrel. A graphite sheet is placed in the recess of the base. The reference graphite piece, together with the graphite barrel and the graphite sheet, is placed in the cleaning chamber of the graphite tube structure of the tube furnace in Embodiment 1, so that the top and sidewalls of the base with parasitic silicon carbide can be exposed to the atmosphere of oxygen-free cleaning gas. The cleaning temperature in the cleaning chamber is controlled at 1500°C, the cleaning pressure is 1000 mbar, HF is introduced at a flow rate of 5000 sccm, and the reference etching time is controlled at 60 min.

[0118] After the reference graphite part is cleaned, stop the flow of HF and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80°C. Then, transfer the cleaned reference graphite part out of the cleaning chamber.

[0119] S2: Place the graphite base to be cleaned as described above. Figure 6 Above the shielding structure 10 shown, after placing the supporting piece in the recess, it is transferred into the cleaning chamber;

[0120] The cleaning temperature in the cleaning chamber is controlled at 1500℃, and the cleaning pressure is controlled at 1000 mbar.

[0121] S3: Introduce hydrogen fluoride gas, hydrogen gas, and silane into the clean chamber, and control the inlet flow rate of hydrogen gas to be 50,000 sccm, the inlet flow rate of hydrogen fluoride gas to be 5,000 sccm, and the inlet flow rate of silane to be 50 sccm. The first inlet duration of each gas is 45 min.

[0122] S4: Keep the flow rates of hydrogen fluoride and hydrogen constant, stop the flow of silane, and introduce propane into the clean chamber at a flow rate of 10 sccm. The second duration of the above-mentioned gas introduction in this step is 15 min.

[0123] After S4 is completed, stop the flow of hydrogen fluoride gas, hydrogen and propane, and introduce purging gas Ar into the cleaning chamber to cool the cleaning chamber to below 80 degrees Celsius. Then, transfer the cleaned graphite parts to be cleaned out of the cleaning chamber.

[0124] The surface of the reference graphite part after undergoing the HF treatment described in step S1 of Example 4 is compared with the surface of the graphite part to be cleaned after undergoing the cleaning in steps S2 to S4.Figure 7 As shown, the reference graphite part after HF treatment exhibits significant color difference in localized areas, indicating that significant over-etching has increased roughness. Meanwhile, as... Figure 6 As shown, after the graphite parts were cleaned, the surface was smooth and no abnormalities were observed. Figure 8 The obvious over-etching marks are shown. It is evident that the method of this invention, while removing parasitic silicon carbide, can effectively protect the surface of the graphite substrate, preventing damage caused by over-etching.

[0125] After the execution of Embodiment 4 of this application is completed, the cleaned graphite substrate is installed into the silicon carbide epitaxial equipment, which has been cleaned and has its flow guide and heat shield replaced. The wafer in the recess is replaced with a 6-inch silicon carbide substrate, which is placed in the growth chamber of the epitaxial equipment. The silicon carbide epitaxial layer is grown at 1550 degrees Celsius and 100 mbar. Specifically, the substrate rotation speed is controlled at 600 rpm, the carbon source propane flow rate is 125 sccm, the silicon source silane flow rate is 350 sccm, the hydrogen chloride flow rate is 3800 sccm, and the growth thickness of the silicon carbide epitaxial layer is 10 μm. After the epitaxial process is completed, the surface defects of the silicon carbide epitaxial wafer are inspected using an Olympus microscope, such as... Figure 9 As shown, no significant clustering phenomenon was observed on the surface of the epitaxial wafer.

[0126] This application also provides a comparative example of Example 4, which differs from Example 4 in that silane is not introduced during S4. The cleaned graphite substrate is installed in a silicon carbide epitaxial wafer with a cleaned flow guide and heat shield. The wafer in the recess is replaced with a 6-inch silicon carbide substrate, which is placed in the growth chamber of the epitaxial wafer. A silicon carbide epitaxial layer is grown at the same 1550°C and 100 mbar as described above. Specifically, the substrate rotation speed remains at 600 rpm, and the flow rates of propane, silane, hydrogen chloride, and the growth thickness of the silicon carbide epitaxial layer are the same as described above. After the epitaxial process is completed, surface defects of the silicon carbide epitaxial wafer are inspected using an Olympus microscope, such as... ​ As shown, the surface of the epitaxial wafer exhibits obvious particle clustering.

[0127] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for removing parasitic silicon carbide, characterized in that, Includes the following steps: S1: Obtain a reference etching time for cleaning a reference graphite part with parasitic silicon carbide formed by cleaning with hydrogen fluoride gas at a cleaning temperature and a cleaning pressure, wherein the cleaning temperature is not less than 1300°C and the cleaning pressure is not less than 100 mbar. S2: The graphite part to be cleaned, on which parasitic silicon carbide has formed, is placed in a cleaning chamber, the surface of the graphite part on which parasitic silicon carbide has grown is exposed to the environment inside the cleaning chamber, and the cleaning temperature and the cleaning pressure inside the cleaning chamber are controlled to be reached. S3: Introduce silane and an oxygen-free cleaning gas containing hydrogen fluoride and hydrogen into the cleaning chamber, controlling the flow ratio of hydrogen to hydrogen fluoride to be between 10:1 and 50:1, the flow ratio of hydrogen fluoride to silane to be between 10:1 and 100:1, and the first duration of introducing the silane and the oxygen-free cleaning gas is less than the reference etching duration and not less than 70% of the reference etching duration; S4: Control the flow rate of the oxygen-free cleaning gas to remain constant, stop the flow of the silane, and introduce propane into the cleaning chamber. Control the second duration of the flow of the oxygen-free cleaning gas and the propane to be less than the first duration.

2. The method for removing parasitic silicon carbide according to claim 1, characterized in that, The cleaning temperature is between 1300℃ and 1500℃, and the cleaning pressure is between 500 mbar and 1000 mbar.

3. The method for removing parasitic silicon carbide according to claim 1, characterized in that, In step S3, the flow rate of the hydrogen fluoride gas is not less than 1000 sccm, and the flow rate of the silane is not less than 50 sccm.

4. The method for removing parasitic silicon carbide according to claim 3, characterized in that, In step S3, the flow rate of the hydrogen fluoride gas is between 1000 sccm and 5000 sccm, and the flow rate of the silane is between 50 sccm and 500 sccm.

5. The method for removing parasitic silicon carbide according to claim 1, characterized in that, In step S3, the first duration is controlled to not exceed 90% of the reference etching duration.

6. The method for removing parasitic silicon carbide according to claim 1, characterized in that, The first etching duration is controlled to be no less than 75% of the reference etching duration.

7. The method for removing parasitic silicon carbide according to claim 1, characterized in that, In step S4, the carbon-silicon ratio of the propane flow rate to the silane flow rate in step S3 is controlled to be less than 1.

8. The method for removing parasitic silicon carbide according to claim 7, characterized in that, In step S4, the propane flow rate is between 10 sccm and 50 sccm.

9. The method for removing parasitic silicon carbide according to claim 1, characterized in that, The second duration shall not exceed 60% of the first duration.

10. The method for removing parasitic silicon carbide according to claim 1, characterized in that, In step S1, the graphite part to be cleaned has the same dimensions and manufacturing process as the reference graphite part.

11. The method for removing parasitic silicon carbide according to claim 1, characterized in that, Step S1, the step of obtaining the reference etching time for cleaning a reference graphite part with parasitic silicon carbide formed by cleaning with hydrogen fluoride gas at cleaning temperature and cleaning pressure, includes: The reference graphite part with parasitic silicon carbide is placed into the cleaning chamber, and the cleaning temperature and cleaning pressure are controlled to be reached in the cleaning chamber. The hydrogen fluoride gas is introduced into the cleaning chamber until the reference etching time is reached to remove the parasitic silicon carbide covering the body surface of the reference graphite part.

12. The method for removing parasitic silicon carbide according to claim 1, characterized in that, The graphite part to be cleaned includes an exposed body surface where parasitic silicon carbide has not formed. Before placing the graphite part to be cleaned into the cleaning chamber, the exposed body surface is also shielded using a shielding structure composed of sacrificial material.

13. The method for removing parasitic silicon carbide according to claim 12, characterized in that, The sacrificial material is a corrosion-resistant carbon-based material.

14. The method for removing parasitic silicon carbide according to claim 1, characterized in that, Both the reference graphite component and the graphite component to be cleaned are bases, flow guides, or heat insulation covers made of graphite-based materials.

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