Semiconductor process apparatus and wafer boat cleaning method

Abstract

The application provides a semiconductor process equipment, which comprises a tubular process chamber for accommodating a wafer boat; an air inlet and an air outlet are arranged at two ends of the tubular process chamber in the axial direction respectively; an in-situ plasma source is arranged on the side of the tubular process chamber where the air outlet is located and is electrically connected with the wafer boat in the tubular process chamber, and is used for loading radio frequency power to the wafer boat to etch the deposits between each two adjacent wafer sheets of the wafer boat; and a remote plasma source is arranged on the side of the tubular process chamber where the air inlet is located, and is used for providing plasma into the tubular process chamber to etch the deposits on the wafer sheets located at the outer side among all the wafer sheets of the wafer boat and the wafer feet. The scheme of the application does not need to disassemble the wafer boat, and can shorten the cleaning time and reduce the cleaning cost.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and in particular to a semiconductor process equipment and a wafer boat cleaning method. Background Art

[0002] The production of crystalline silicon solar cells involves a plasma-enhanced chemical vapor deposition (PECVD) coating process. During this process, a film layer of a certain thickness (generally greater than 10 μm) is deposited on a wafer boat, which serves as a carrier for wafers (e.g., silicon wafers). This requires the boat to be cleaned. Existing boat cleaning processes generally use traditional wet cleaning, which involves immersing the boat in a cleaning tank filled with HF / HCl solution or an alkaline solution, rinsing it with clean water after 4-8 hours, and then drying it at high temperature for a long time.

[0003] During wet cleaning, the wafer boat must be disassembled to thoroughly clean the wafers without leaving any blind spots. Frequent disassembly increases the risk of boat breakage. Furthermore, long, high-temperature drying is required after cleaning, resulting in lengthy cleaning times. Furthermore, when cleaning amorphous silicon and polycrystalline silicon from the wafer boat, large amounts of HNO₃ must be added, leading to high wastewater treatment costs and environmental concerns, resulting in high cleaning costs. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art, and proposes a semiconductor process equipment and a wafer boat cleaning method, which does not require disassembly of the wafer boat and can shorten the cleaning time and reduce the cleaning cost.

[0005] To achieve the purpose of the present invention, a semiconductor process equipment is provided, comprising:

[0006] A tubular process chamber is used to accommodate a wafer boat; an air inlet and an air extraction port are respectively provided at two axial ends of the tubular process chamber;

[0007] an in-situ plasma source disposed on one side of the tubular process chamber where the gas pumping port is located and electrically connected to the wafer boat in the tubular process chamber, for applying radio frequency power to the wafer boat to etch deposits between two adjacent wafer boats of the wafer boat;

[0008] A remote plasma source is arranged on the side of the gas inlet of the tubular process chamber, and is used to provide plasma into the tubular process chamber to etch the outer boat slices of all the wafer carrier boat slices and the deposits on the boat feet.

[0009] Optionally, the in-situ plasma source includes a radio frequency power supply, and a positive electrode and a negative electrode of the radio frequency power supply are electrically connected to two adjacent boats in the wafer carrier boat.

[0010] Optionally, the semiconductor process equipment also includes an exhaust device, which includes an exhaust pipeline, a residual gas detection unit and an exhaust pump, wherein the two ends of the exhaust pipeline are respectively connected to the exhaust port and the exhaust pump, and the residual gas detection unit is arranged on the exhaust pipeline to detect whether the gas flowing through the exhaust pipeline contains the deposits.

[0011] Optionally, the semiconductor process equipment is used to perform a cleaning process on the wafer carrier boat; or, the semiconductor process equipment is used to perform a deposition process on the wafers on the wafer carrier boat and a cleaning process on the wafer carrier boat.

[0012] As another technical solution, the present invention further provides a wafer boat cleaning method, which is applied to the semiconductor process equipment provided by the present invention, and the method comprises:

[0013] introducing a first cleaning gas into the tubular process chamber through the gas inlet, and extracting the gas in the tubular process chamber through the gas extraction port to maintain the pressure of the tubular process chamber at a first pressure value;

[0014] Turning on the in-situ plasma source and applying radio frequency power to the wafer carrier boat to excite the first cleaning gas between two adjacent wafers of the wafer carrier boat to form a plasma capable of etching the deposits at the position;

[0015] After a first cleaning time has elapsed, the first cleaning gas is stopped from being introduced, and the in-situ plasma source is turned off;

[0016] Turning on the remote plasma source to supply plasma generated by the second cleaning gas into the tubular process chamber, and maintaining the pressure of the tubular process chamber at a second pressure value to etch the outer boats of all the boats in the wafer carrier boat and deposits on the boat legs;

[0017] After the second cleaning time has elapsed, the remote plasma source is turned off.

[0018] Optionally, the first cleaning gas includes a fluorine-containing gas and at least one of an inert gas and oxygen.

[0019] Optionally, the second cleaning gas includes at least one of chlorine, hydrogen chloride and hydrogen bromide.

[0020] Optionally, after stopping the introduction of the first cleaning gas and turning off the in-situ plasma source, and before turning on the remote plasma source; and after the second cleaning time has elapsed and the remote plasma source has been turned off, the method further includes:

[0021] A purge gas is introduced into the tubular process chamber through the gas inlet to purge the tubular process chamber.

[0022] Optionally, before the first cleaning gas is introduced into the tubular process chamber through the gas inlet, the method further includes:

[0023] Allowing the temperature of the wafer boat to reach a preset temperature;

[0024] The preset temperature is greater than or equal to 200° C. and less than or equal to 500° C.

[0025] Optionally, the first pressure value is greater than or equal to 0.5 Torr and less than or equal to 2 Torr; the second pressure value is greater than or equal to 0.1 Torr and less than or equal to 3 Torr.

[0026] The present invention has the following beneficial effects:

[0027] In the technical solutions of the semiconductor process equipment and the wafer boat cleaning method provided by the present invention, by respectively arranging an air inlet and an air exhaust port at both ends of the tubular process chamber in the axial direction, the cleaning gas introduced from the air inlet can flow from the front boat foot of the wafer boat to the rear boat foot of the wafer boat, and then be discharged through the air exhaust port, thereby ensuring that the cleaning gas can pass through the entire wafer boat and reach between each adjacent boat piece of the wafer boat, thereby ensuring that the wafer boat is fully cleaned.

[0028] By combining the use of an in-situ plasma source and a remote plasma source, the in-situ plasma source can be used to load radio frequency power to the carrier boat to etch the deposits between each two adjacent boat slices of the carrier boat, and then the remote plasma source can be used to provide plasma into the tubular process chamber to etch the deposits on the outer boat slices and the boat feet of all the boat slices of the carrier boat, so that all the boat slices and the boat feet of the carrier boat can be cleaned. Compared with the existing technology, there is no need to disassemble the carrier boat, and there is no need to dry the carrier boat at high temperature for a long time, which can shorten the cleaning time and reduce the cleaning cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic structural diagram of a semiconductor process equipment provided by an embodiment of the present invention;

[0030] Figure 2 A structural diagram of a wafer boat used in an embodiment of the present invention;

[0031] Figure 3 Flowchart of a wafer boat cleaning method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solution of the present invention, the semiconductor process equipment and the wafer boat cleaning method provided by the present invention are described in detail below with reference to the accompanying drawings.

[0033] See also Figure 1 An embodiment of the present invention provides a semiconductor process equipment, including a tubular process chamber 1, an in-situ plasma source 2, and a remote plasma source 3, wherein the tubular process chamber 1 is used to accommodate a wafer boat 4, and the cavity of the tubular process chamber 1 is, for example, a quartz tube, and the quartz tube can be horizontal or vertical. The quartz tube is provided with a front flange and a rear flange at both ends of the axial direction, respectively, for sealing the internal space of the quartz tube to form a closed space. Moreover, an air inlet 11 and an air exhaust port 12 are provided at both ends of the axial direction of the tubular process chamber 1, respectively, and the two are provided, for example, at the front flange and the rear flange, respectively, wherein the air inlet 11 is used to introduce a cleaning gas or a purge gas into the tubular process chamber 1; the air exhaust port 12 is used to be connected to a gas exhaust device to extract the gas in the tubular process chamber 1. By arranging an air inlet 11 and an air exhaust port 12 at both ends of the tubular process chamber 1 in the axial direction, the cleaning gas introduced from the air inlet can flow from the front boat foot (left boat foot) of the wafer carrier boat 4 to the rear boat foot (right boat foot) of the wafer carrier boat 4, and then be discharged through the air exhaust port 12, thereby ensuring that the cleaning gas can pass through the entire wafer carrier boat 4 and reach between each adjacent boat sheet of the wafer carrier boat 4, thereby ensuring that the wafer carrier boat 4 is fully cleaned.

[0034] The in-situ plasma source 2 is disposed on one side of the tubular process chamber 1 where the exhaust port 12 is located, and is electrically connected to the wafer boat 4 in the tubular process chamber 1, for example, by way of an RF electrode 21 provided through a rear flange. The in-situ plasma source 2 is used to apply RF power to the wafer boat 4 to excite the cleaning gas between each adjacent pair of wafer boats in the wafer boat 4 to form a plasma, which can etch the deposits between each adjacent pair of wafer boats. In some optional embodiments, the in-situ plasma source 2 includes an RF power supply, the positive and negative electrodes of which are electrically connected to each adjacent pair of wafer boats in the wafer boat 4. Specifically, a wafer carrier boat 4 made of graphite is typically used to carry the wafer. The wafer carrier boat 4 includes a plurality of spaced-apart boats (e.g., graphite sheets). During the coating process, the wafer is carried between two adjacent boats. During the cleaning process, the two adjacent boats are connected to the positive and negative electrodes of an RF power supply, respectively. The RF power (e.g., pulsed RF) provided by the RF power supply excites the cleaning gas between the two adjacent boats to generate a glow discharge plasma. The plasma is accelerated between the two adjacent boats by applying opposite alternating voltages to the two adjacent boats, thereby etching the boats, i.e., etching the deposits between each adjacent boat of the wafer carrier boat 4. It is understood that the above-mentioned in-situ plasma source can be a plasma source originally used for a normal process (e.g., a deposition process) reused as a plasma source for the cleaning process, or a plasma source specifically used for the cleaning process.

[0035] The remote plasma source 3 is arranged on the side where the air inlet 11 of the tubular process chamber 1 is located, and is used to provide plasma into the tubular process chamber 1 to etch the boat slices located on the outside of all the boat slices of the carrier boat 4 and the deposits on the boat feet. By arranging the remote plasma source 3 on the side where the air inlet 11 of the tubular process chamber 1 is located, the plasma can flow from the front boat foot of the carrier boat 4 to the rear boat foot of the carrier boat 4 with the air flow, thereby ensuring that the plasma can pass through the entire carrier boat 4 and reach the boat slices and boat feet located on the outside of the carrier boat 4, thereby ensuring that the carrier boat is fully cleaned. The so-called boat slices located on the outside of all the boat slices of the carrier boat 4, such as Figure 2 The boat foot is the outermost boat piece B1 in the multi-layer structure of the boat pieces arranged at intervals. Figure 2 The portion of the wafer boat 4 in the area B2 and B3. Figure 2 The portion of the wafer boat 4 in area A.

[0036] By combining the in-situ plasma source 2 and the remote plasma source 3, the in-situ plasma source 2 can first be used to load radio frequency power to the wafer boat 4 to etch the deposits between each adjacent two boat slices of the wafer boat 4, and then the remote plasma source 3 can be used to provide plasma into the tubular process chamber 1 to etch the boat slices located on the outside of all the boat slices of the wafer boat 4 and the deposits on the boat legs, so that all the boat slices and boat legs of the wafer boat 4 can be cleaned. Moreover, compared with the wet cleaning method in the prior art, there is no need to disassemble the wafer boat 4, and there is no need to dry the wafer boat 4 at a high temperature for a long time, thereby shortening the cleaning time and reducing the cleaning cost. In addition, compared with the use of the in-situ plasma source alone for the cleaning process, the use of the in-situ plasma source alone can effectively clean the deposits between each adjacent two boat slices of the wafer boat, but the cleaning rate of the boat slices located on the outside of the wafer boat and the deposits on the boat legs is slower and the cleaning effect is poorer, which ultimately leads to a longer overall cleaning time and increased cleaning costs. Compared to using a remote plasma source alone for the cleaning process, using a remote plasma source alone requires a larger amount of gas, much higher than the amount of cleaning gas used during in-situ plasma cleaning, resulting in higher cleaning costs. In addition, because the deposits on the outer boats and boat legs are less than the deposits between each adjacent boat of the wafer boat, the deposits between each adjacent boat of the wafer boat 4 can be first removed using the in-situ plasma source 2, and then the deposits on the outer boats and boat legs can be removed using the remote plasma source 3. This cleaning sequence has higher cleaning efficiency, is more conducive to shortening cleaning time, and reduces cleaning costs.

[0037] In some optional embodiments, the semiconductor process equipment further includes a gas extraction device, which includes a gas extraction pipeline 31, a residual gas detection unit 33, and a gas extraction pump 32. The two ends of the gas extraction pipeline 31 are respectively connected to the gas extraction port 12 and the gas extraction pump 32. The residual gas detection unit 33 is provided on the gas extraction pipeline 31 to detect whether the gas flowing through the gas extraction pipeline 31 contains sediment, thereby determining the cleaning effect and whether the cleaning process can be terminated. In addition, a flow control valve is also provided on the gas extraction pipeline 31 to adjust the exhaust volume, thereby controlling the pressure of the tubular process chamber.

[0038] In some optional embodiments, the semiconductor processing equipment is used to perform a cleaning process on a wafer carrier boat. In this case, the in-situ plasma source is a plasma source specifically used for the cleaning process. Alternatively, the semiconductor processing equipment is used to perform a deposition process on wafers on a wafer carrier boat or to perform a cleaning process on the wafer carrier boat. For example, the semiconductor processing equipment may be a PECVD device, such as that used to prepare amorphous silicon thin films for heterojunction solar cells, and may also be reused for cleaning amorphous silicon deposits on a wafer carrier boat. In this case, the in-situ plasma source may be a plasma source originally used for a normal process (e.g., a deposition process) that is reused as a plasma source for the cleaning process.

[0039] As another technical solution, see Figure 3 The present invention also provides a wafer boat cleaning method, which is applied to the semiconductor process equipment provided in the embodiment of the present invention. Figure 1 Taking the semiconductor process equipment shown in FIG. 1 as an example, the method includes:

[0040] S1, introducing a first cleaning gas into the tubular process chamber 1 through the gas inlet 11, and extracting the gas in the tubular process chamber 1 through the gas extraction port 12 to maintain the pressure of the tubular process chamber 1 at a first pressure value;

[0041] S2, turning on the in-situ plasma source 2, applying radio frequency power to the wafer carrier boat 4, to excite the first cleaning gas between each two adjacent wafer carrier boats 4 to form a plasma capable of etching the deposits at that position;

[0042] S3, after the first cleaning time has elapsed, stopping the introduction of the first cleaning gas and turning off the in-situ plasma source 2;

[0043] S4, turning on the remote plasma source 3 to supply plasma generated by the second cleaning gas into the tubular process chamber 1, and maintaining the pressure of the tubular process chamber 1 at the second pressure value to etch the outer boats of all the boats in the wafer carrier boat 4 and the deposits on the boat legs;

[0044] S5. After the second cleaning time has passed, turn off the remote plasma source 3.

[0045] In some optional embodiments, the first cleaning gas includes a fluorine-containing gas and at least one of an inert gas and oxygen. The fluorine-containing gas includes, for example, a combination of one or more gases selected from the group consisting of NF3, SF6, CF4, and F2. The inert gas includes, for example, Ar. Fluorine radicals in the plasma formed by the fluorine-containing gas can react with the deposits between each of two adjacent boats to generate gaseous reactants, which are then discharged from the tubular process chamber along with the gas flow. The plasma formed by the fluorine-containing gas can etch deposits such as intrinsic amorphous silicon, phosphorus / boron doped amorphous silicon, intrinsic polysilicon, phosphorus / boron doped polysilicon, etc. For example, the first cleaning gas includes SF6 and Ar, wherein the gas flow rate of SF6 is 6000 sccm to 9000 sccm, and the gas flow rate of Ar is 2000 sccm to 3000 sccm.

[0046] In some optional embodiments, the second cleaning gas includes at least one of chlorine (Cl2), hydrogen chloride (HCl), and hydrogen bromide (HBr). The plasma formed by these gases does not react with the quartz tube or other quartz components in the tubular process chamber. Preferably, the Cl2 gas flow rate is 3,000 sccm to 80,000 sccm.

[0047] In addition, since the bond energy of the chemical bond Si-Cl is 381KJ / mol and the bond energy of the chemical bond Si-Br is 310KJ / mol, the bond energies of both are greater than the bond energy of the chemical bond Si-Si (222KJ / mol) and less than the bond energy of the chemical bond Si-O (452KJ / mol), therefore, plasma containing Cl or Br can only etch the chemical bond Si-Si, but cannot etch the chemical bond Si-O. In addition, since the bond energy of the chemical bond Si-F is 565KJ / mol, plasma containing F can etch both the chemical bond Si-Si and the chemical bond Si-O. Therefore, the wafer boat cleaning method provided in the embodiment of the present invention can be used to clean silicon oxide or silicon nitride, and can also be used to clean amorphous silicon or polycrystalline silicon.

[0048] In some optional embodiments, after the above step S3 and before the above step S4; and after the second cleaning time has passed and the remote plasma source 3 is turned off, the method further includes:

[0049] A purge gas is introduced into the tubular process chamber 1 through the gas inlet to purge the tubular process chamber 1 .

[0050] By purging the tubular process chamber 1, gaseous reactants generated by the deposition reaction and excess cleaning gas can be discharged from the tubular process chamber 1 to prevent them from being retained in the tubular process chamber. Optionally, the purge gas includes at least one of N2 and Ar, with a flow rate of 10,000 sccm to 50,000 sccm.

[0051] In some optional embodiments, before the above step S1, the following steps are further included:

[0052] Making the temperature of the slide boat 4 reach a preset temperature;

[0053] The preset temperature is greater than or equal to 200° C. and less than or equal to 500° C., preferably greater than or equal to 200° C. and less than or equal to 220° C.

[0054] The temperature of the wafer boat 4 can be brought to the preset temperature by heating. In addition, optionally, after the temperature of the wafer boat reaches the preset temperature, the tubular process chamber is evacuated.

[0055] In some optional embodiments, the first pressure value is greater than or equal to 0.5 Torr and less than or equal to 2 Torr, preferably greater than or equal to 0.5 Torr and less than or equal to 1 Torr; the second pressure value is greater than or equal to 0.1 Torr and less than or equal to 3 Torr, preferably greater than or equal to 2 Torr and less than or equal to 3 Torr.

[0056] In some optional embodiments, the first cleaning time can be set according to the thickness of the deposit between two adjacent boat slices collected and the etching rate of the above-mentioned step S2, and the second cleaning time can be set according to the thickness of the deposit on the boat slice located outside the carrier boat and the etching rate of the above-mentioned step S4.

[0057] In some optional embodiments, in the above step S2, the power frequency of the in-situ plasma source 2 can be selected to be 40MHz~13.56MHz, preferably 13.56MHz, and the RF power can be selected to be 10KW~30KW, preferably 10KW~15KW, to ensure a higher etching rate.

[0058] In some optional embodiments, in the above step S4, the power frequency of the remote plasma source 3 can be selected to be 13.56MHz~20MHz, preferably 20MHz, and the radio frequency power can be selected to be 5KW~10KW, preferably 6KW~8KW, to ensure that the gas ionization rate is greater than 95%.

[0059] To sum up, in the technical solutions of the semiconductor process equipment and the wafer boat cleaning method provided by the embodiments of the present invention, by respectively arranging an air inlet and an air exhaust port at both ends of the tubular process chamber in the axial direction, the cleaning gas introduced from the air inlet can flow from the front boat foot of the wafer boat to the rear boat foot of the wafer boat, and then be discharged through the air exhaust port, thereby ensuring that the cleaning gas can pass through the entire wafer boat and reach between each adjacent boat piece of the wafer boat, thereby ensuring that the wafer boat is fully cleaned.

[0060] By combining the use of an in-situ plasma source and a remote plasma source, the in-situ plasma source can be used to load radio frequency power to the carrier boat to etch the deposits between each two adjacent boat slices of the carrier boat, and then the remote plasma source can be used to provide plasma into the tubular process chamber to etch the deposits on the outer boat slices and the boat feet of all the boat slices of the carrier boat, so that all the boat slices and the boat feet of the carrier boat can be cleaned. Compared with the existing technology, there is no need to disassemble the carrier boat, and there is no need to dry the carrier boat at high temperature for a long time, which can shorten the cleaning time and reduce the cleaning cost.

[0061] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A semiconductor process equipment, characterized in that: include: a tubular process chamber for accommodating a wafer boat; An air inlet and an air extraction port are respectively provided at both ends of the tubular process chamber in the axial direction; an in-situ plasma source disposed on one side of the tubular process chamber where the gas pumping port is located and electrically connected to the wafer boat in the tubular process chamber, for applying radio frequency power to the wafer boat to etch deposits between two adjacent wafer boats of the wafer boat; A remote plasma source is arranged on the side of the gas inlet of the tubular process chamber, and is used to provide plasma into the tubular process chamber to etch the outer boat slices of all the wafer carrier boat slices and the deposits on the boat feet.

2. The semiconductor process equipment according to claim 1, wherein: The in-situ plasma source includes a radio frequency power supply, and a positive electrode and a negative electrode of the radio frequency power supply are electrically connected to two adjacent boats in the wafer carrier boat.

3. The semiconductor process equipment according to claim 1 or 2, characterized in that: The semiconductor process equipment also includes an exhaust device, which includes an exhaust pipeline, a residual gas detection unit and an exhaust pump, wherein the two ends of the exhaust pipeline are respectively connected to the exhaust port and the exhaust pump, and the residual gas detection unit is arranged on the exhaust pipeline to detect whether the gas flowing through the exhaust pipeline contains the deposits.

4. The semiconductor process equipment according to claim 1, wherein: The semiconductor process equipment is used to perform a cleaning process on the wafer carrier boat; or, the semiconductor process equipment is used to perform a deposition process on the wafers on the wafer carrier boat and a cleaning process on the wafer carrier boat.

5. A method for cleaning a slide boat, characterized in that: Applied to the semiconductor process equipment according to any one of claims 1 to 4, the method comprising: introducing a first cleaning gas into the tubular process chamber through the gas inlet, and extracting the gas in the tubular process chamber through the gas extraction port to maintain the pressure of the tubular process chamber at a first pressure value; Turning on the in-situ plasma source and applying radio frequency power to the wafer carrier boat to excite the first cleaning gas between each two adjacent wafer carrier boats to form a plasma capable of etching the deposits between each two adjacent wafer carrier boats; After a first cleaning time has elapsed, the first cleaning gas is stopped from being introduced, and the in-situ plasma source is turned off; Turning on the remote plasma source to supply plasma generated by the second cleaning gas into the tubular process chamber, and maintaining the pressure of the tubular process chamber at a second pressure value to etch the outer boats of all the boats in the wafer carrier boat and deposits on the boat legs; After the second cleaning time has elapsed, the remote plasma source is turned off.

6. The method for cleaning a wafer boat according to claim 5, wherein: The first cleaning gas includes a fluorine-containing gas and at least one of an inert gas and oxygen.

7. The method for cleaning a wafer boat according to claim 5, wherein: The second cleaning gas includes at least one of chlorine, hydrogen chloride, and hydrogen bromide.

8. The method for cleaning a wafer boat according to claim 5, wherein: After the first cleaning gas is stopped and the in-situ plasma source is turned off, and before the remote plasma source is turned on; and after the second cleaning time has passed and the remote plasma source is turned off, the method further includes: A purge gas is introduced into the tubular process chamber through the gas inlet to purge the tubular process chamber.

9. The method for cleaning a wafer boat according to claim 5, wherein: Before the first cleaning gas is introduced into the tubular process chamber through the gas inlet, the method further includes: Allowing the temperature of the wafer boat to reach a preset temperature; The preset temperature is greater than or equal to 200° C. and less than or equal to 500° C.

10. The method for cleaning a wafer boat according to claim 5, wherein: The first pressure value is greater than or equal to 0.5 Torr and less than or equal to 2 Torr; the second pressure value is greater than or equal to 0.1 Torr and less than or equal to 3 Torr.

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