Silicon nitride thin film deposition method and vertical LPCVD (Low Pressure Chemical Vapor Deposition) equipment

Abstract

The invention discloses a silicon nitride thin film deposition method and vertical LPCVD equipment. The method comprises the steps that S1, the standby temperature of a process cavity is set; s2, the wafer boat rises to a process position at a constant speed, and nitrogen is introduced between the inner pipe and the outer pipe; s3, closing the nitrogen, and vacuumizing the cavity; s4, introducing nitrogen into the cavity, and keeping the pressure in the cavity at P3; s5, evacuating the nitrogen in the cavity, and introducing ammonia gas; s6, under the condition that only ammonia gas flows, the pressure in the cavity is kept at P4; s7, introducing dichlorosilane into the cavity, and carrying out silicon nitride film deposition; s8, closing the dichlorosilane, keeping the ammonia gas flow unchanged, and consuming residual dichlorosilane; s9, removing ammonia gas; and S10, the process cavity recovers to normal pressure, the wafer boat descends at a constant speed, and nitrogen is introduced between the inner pipe and the outer pipe. The method has the characteristics of simple principle, high film forming stability, low pollution degree and the like, and overcomes the defect that the surface of the existing silicon nitride film is easily polluted by particles.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to a method for depositing a silicon nitride thin film and a vertical LPCVD apparatus. Background Art

[0002] For the insulating layer, dielectric layer, and passivation layer of the third-generation semiconductor GaN and SiC devices, a silicon nitride (SiN) thin film is inevitably used. A typical method for forming such a thin film is plasma enhanced chemical vapor deposition (PECVD). This method exposes the device to plasma, which can cause plasma damage to the device surface.

[0003] With the development of low-pressure chemical vapor deposition (LPCVD) silicon nitride technology, in more and more compound semiconductor process fields, the LPCVD method is gradually used to replace PECVD for depositing SiN thin films. LPCVD can deposit a SiN film under low pressure (preferably 10 Pa to 100 Pa) and high temperature (preferably higher than 700 °C). Due to the high deposition temperature, the deposited SiN film becomes dense and compact, having good quality. When depositing SiN by LPCVD, in order to reduce the thickness non-uniformity within the wafer and between adjacent wafers, a high-speed source gas (preferably dichlorosilane SiCl2H2 and ammonia NH3) is usually introduced. Therefore, the flow rates and gas ratios of SiCl2H2 and NH3 will affect the thickness uniformity, refractive index, and stress of the SiN thin film. To obtain a SiN thin film that meets the design quality, a large amount of experimental work needs to be carried out on process conditions such as the flow rate and ratio of the source gas, the deposition temperature, and the process chamber pressure. This process consumes a large amount of time and cost. Therefore, the process method and steps for depositing LPCVD SiN thin films are of great value.

[0004] During the LPCVD SiN deposition, thin film particle contamination will occur. Particle contamination can cause serious defects in the integrated circuit and semiconductor device manufacturing processes. The circuit may experience open circuits, short circuits, leakage, electrical drift, etc. to varying degrees, and even lead to chip scrapping, causing huge economic losses. By analyzing the reasons for product failure, it is found that failures caused by contaminants account for 60% of the total failure factors. Therefore, special attention needs to be paid to the contaminants that may be introduced in each link during the process production. Among various contaminants, particle contamination is the most common and has the greatest impact on product yield.

[0005] In the furnace tube LPCVD process, the particle contamination problem in the SiN process is the most difficult to control. The traditional method is mainly to perform periodic preventive maintenance cleaning (PM) on the LPCVD furnace tube to reduce particle contamination. The first commonly used preventive maintenance cleaning method is to remove quartz parts such as process tubes and boats inside the furnace tube for pickling, and then reinstall them after washing; the second commonly used preventive maintenance cleaning method is to introduce a fluorine-containing gas into the furnace tube to etch the SiN film deposited on the tube wall and vacuum pipeline, and the peeled-off SiN film is sucked into the factory end through the vacuum pipeline. The first method requires disassembling and assembling equipment components, which is time-consuming and laborious, resulting in a significant reduction in equipment usage efficiency; after multiple etching and cleaning operations using the second method, fluoride ions will corrode the vacuum metal pipeline, bringing new contamination to the wafers. Therefore, it is necessary to optimize the process steps and process parameters to reduce the particles generated during the LPCVD SiN deposition process, and combined with regular PM, the final particle contamination can be better controlled.

[0006] In addition, the crystallization at the furnace mouth (manifold) during LPCVD SiN deposition has always been an important factor affecting the deposition quality of the SiN film. Fluororubber sealing rings are provided on the upper and lower surfaces of the furnace mouth flange for process chamber sealing to ensure vacuum sealing conditions, and circulating cooling water is passed through the inside of the furnace mouth flange for furnace mouth cooling to protect the sealing ring from damage due to high temperature. It is precisely due to the flow of the cooling circulating water that the temperature inside the furnace mouth flange is relatively low, and the reaction by-product NH4Cl of SiCl2H2 and NH3 is likely to condense here, resulting in furnace mouth crystallization. When the furnace mouth crystallization is severe, it will cause particles to appear on the surface of the wafer after depositing the SiN film, seriously affecting the film quality. The traditional method to solve the furnace mouth crystallization is to reduce the flow rate of the cooling circulating water. For example, the cooling water flow rate is controlled between 0.5 slm and 0.8 slm. However, this method is difficult to completely avoid furnace mouth crystallization, and when the number of processes accumulates to a certain extent, crystallization will still occur at the furnace mouth. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiency that the surface of the existing silicon nitride film is easily contaminated by particles, and to provide a silicon nitride film deposition method and a vertical LPCVD device with simple principle, convenient operation, high film formation stability and low pollution degree.

[0008] To solve the above technical problem, the technical solution adopted by the present invention is as follows:

[0009] A silicon nitride film deposition method includes the following steps:

[0010] Step S1, set the standby temperature of the process chamber to 600 °C to 650 °C;

[0011] Step S2: The susceptor is uniformly raised to the process position at a speed of 0.8 mm / s to 1.2 mm / s, and nitrogen gas is introduced between the inner tube and the outer tube of the process chamber during the raising of the susceptor at a flow rate of 15 slm to 25 slm. This nitrogen gas flow rate is denoted as L1;

[0012] Step S3: After the susceptor is raised to the process position, the nitrogen gas is turned off, the inside of the process chamber is evacuated to a vacuum, and a vacuum leak rate test is performed;

[0013] Step S4: Nitrogen gas is introduced into the process chamber. This nitrogen gas flow rate is denoted as J2, and at the same time, the pressure inside the chamber is maintained at P3;

[0014] Step S5: The nitrogen gas inside the process chamber is evacuated, and ammonia gas is introduced. This ammonia gas flow rate is J2;

[0015] Step S6: With only ammonia gas flowing, the pressure inside the process chamber is maintained at P4;

[0016] Step S7: At a pressure of P4, dichlorosilane (SiCl2H2) is introduced into the process chamber to deposit a silicon nitride thin film;

[0017] Step S8: The dichlorosilane is turned off, and the ammonia gas flow rate is adjusted to H1 to consume the residual dichlorosilane in the process chamber;

[0018] Step S9: The ammonia gas supply is stopped, the inside of the chamber is evacuated, and then nitrogen gas with a flow rate of J1 is introduced;

[0019] Step S10: The process chamber is restored to atmospheric pressure, and then the susceptor is uniformly lowered at a speed of 0.8 mm / s to 1.2 mm / s. During the lowering of the susceptor, nitrogen gas is introduced between the inner tube and the outer tube of the process chamber at a flow rate of 15 slm to 25 slm. This nitrogen gas flow rate is denoted as L1.

[0020] As a further improvement of the present invention, in step S2, 1.0 slm to 2.0 slm of nitrogen gas is introduced into the inner tube. This nitrogen gas flow rate is denoted as J1.

[0021] As a further improvement of the present invention, in step S3, the inside of the process chamber is evacuated from atmospheric pressure P1 to a low pressure P2. After the inside of the chamber is evacuated to the low pressure P2, P2 is preferably < 1.0 Pa, and the vacuum evacuation continues for > 30 min. After the vacuum evacuation is completed, the leak rate of the chamber is detected. The leak rate requirement is < 2 Pa / min. Subsequently, the temperature of the process chamber is raised to the silicon nitride deposition process temperature. The process temperature is preferably 780 °C to 800 °C, and the heating rate is controlled at 5 °C to 6 °C / min.

[0022] As a further improvement of the present invention, in step S4, the nitrogen flow rate J2 is preferably 0.5 slm to 1.0 slm, so that the chamber pressure reaches P3, P3 is preferably 30 Pa to 133 Pa, the purging duration is 5 min to 10 min. After the purging is completed, the nitrogen is closed, and the vacuum is pumped for 3 min to 5 min to pump the chamber pressure to P2.

[0023] As a further improvement of the present invention, in step S6, P4 is preferably 20 Pa to 40 Pa, and the pressure control duration is preferably 10 min to 20 min.

[0024] As a further improvement of the present invention, in step S7, the flow rate D1 of dichlorosilane is preferably 30 sccm to 35 sccm, and the flow rate of ammonia is reduced from J2 to H2, H2 is preferably 170 sccm to 200 sccm.

[0025] As a further improvement of the present invention, in step S8, the ammonia flow rate H1 = J2, which is 0.5 slm to 1.0 slm, and the ammonia purging duration is preferably 5 min to 6 min.

[0026] As a further improvement of the present invention, in step S9, the vacuum pumping duration is preferably 5 min to 6 min, and the nitrogen purging duration is preferably 5 min to 6 min; step S9 is repeated more than twice to remove ammonia in the chamber.

[0027] As a further improvement of the present invention, in step S10, nitrogen with a flow rate of J2 is first introduced for 5 min to 6 min, then nitrogen with a flow rate of J1 is introduced for 5 min to 6 min, and finally nitrogen with a flow rate of J3 is introduced until the chamber returns to normal pressure; J1 is preferably 1.0 slm to 2.0 slm, J2 is preferably 0.5 slm to 1.0 slm, and J3 is preferably 2 slm to 5 slm.

[0028] As a general technical concept, the present invention also provides a vertical LPCVD device for implementing the above silicon nitride thin film deposition method, including a furnace body, an outer tube, an inner tube, a furnace mouth flange, a SiCl2H2 inlet pipe, an NH3 inlet pipe, a sandwich inlet pipe, a wafer boat, and a vacuum pumping assembly;

[0029] The furnace body, the outer tube, and the inner tube are nested in sequence. The wafer boat is used to load the wafers and drive the wafers to lift in the inner tube to complete the coating process; the furnace mouth flange is arranged at the bottom of the furnace body, and the SiCl2H2 inlet pipe, the NH3 inlet pipe, and the sandwich inlet pipe are all connected to the furnace mouth flange to realize gas transportation; a gas path V2 is connected in parallel to the SiCl2H2 inlet pipe, a gas path V3 is connected in parallel to the NH3 inlet pipe, and the sandwich inlet pipe communicates with the sandwich between the outer tube and the inner tube. The gas path V2, the gas path V3, and the sandwich inlet pipe can all be used to transport nitrogen;

[0030] The furnace mouth flange includes an upper water-cooling flange and a lower water-cooling flange, the cooling water paths of the upper water-cooling flange and the lower water-cooling flange are arranged in parallel, and a solenoid valve is provided on the cooling water control circuit of the lower water-cooling flange, and the solenoid valve is linked with the control system; during the process, the upper water-cooling flange remains in a normally open state, and the solenoid valve is in a closed state, and when the process is completed, the solenoid valve automatically opens.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] 1. In the silicon nitride film deposition method of the present invention, during the uniform ascent and descent of the wafer boat, nitrogen is introduced into the interlayer between the inner tube and the outer tube of the process chamber for purging, and the gas flow rate of the process chamber is adjusted to balance the air pressure and reduce convection during the process, so as to maintain a slightly positive pressure state in the process chamber when the wafer boat rises and descends, and avoid the particle contaminants that are easy to peel off on the wall of the tail pipe from flowing back into the cavity, thereby preventing the wafer surface from being contaminated and improving the quality stability of the silicon nitride film.

[0033] 2. The vertical LPCVD equipment of the present invention improves the circulating water structure of the furnace mouth flange, and sets the upper water-cooling flange and the lower water-cooling flange as parallel water channels. During the process, the upper water-cooling flange is in a normally open state to reduce the flange temperature and protect the sealing ring. By adding a solenoid valve to the cooling water control loop of the lower water-cooling flange and linking with the process control software, the circulating water of the lower water-cooling flange is automatically closed during the execution of the process, ensuring that the inner wall of the flange is at a higher temperature. After the process is completed, the circulating water is automatically turned on, so that the NH4Cl by-product generated during the process cannot crystallize inside the flange. Moreover, after the process is completed, the by-product has been completely discharged from the tail exhaust pipe. At this time, opening the lower circulating water will not produce crystals, avoiding the furnace mouth crystals from falling onto the wafer, thereby ensuring the film formation quality of the silicon nitride film on the wafer surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structural principle of a vertical LPCVD device in a specific embodiment of the present invention;

[0035] Figure 2 It is a schematic diagram of the process of depositing a silicon nitride film in a specific embodiment of the present invention;

[0036] Figure 3 It is a curve diagram of pressure variation during the deposition of silicon nitride film in a specific embodiment of the present invention;

[0037] Figure 4 It is a curve diagram of flow rate changes of various process gases during silicon nitride film deposition in a specific embodiment of the present invention;

[0038] Figure 5Schematic diagram of particle backflow during the upward or downward movement of the susceptor in a specific embodiment of the present invention;

[0039] Figure 6 Particle distribution diagram of the silicon nitride thin film process in a specific embodiment of the present invention; wherein, Fig. (a) is the particle distribution on the surface of the silicon nitride thin film of the wafer at the top of the process chamber, Fig. (b) is the particle distribution on the surface of the silicon nitride thin film of the wafer in the middle of the process chamber, and Fig. (c) is the particle distribution on the surface of the silicon nitride thin film of the wafer at the bottom of the process chamber;

[0040] Figure 7 Particle change diagram during the entire PM cycle of the process chamber in a specific embodiment of the present invention;

[0041] Figure 8 Schematic diagram of the structural principle of the furnace port flange in a specific embodiment of the present invention;

[0042] Figure 9 Schematic diagram of the water path control of the furnace port flange in a specific embodiment of the present invention;

[0043] Legend: 1. Furnace body; 2. Outer tube; 3. Inner tube; 4. Heat preservation barrel; 5. Furnace port flange; 6. SiCl2H2 inlet pipe; 7. NH3 inlet pipe; 8. Interlayer inlet pipe; 9. Vacuum pump; 10. Cold trap; 11. Butterfly valve; 12. Vacuum pipeline; 13. Vacuum gauge; 14. Susceptor; 15. Heating wire; 16. Wafer; 17. Thermocouple; 18. Carrier table; 19. Control valve; 20. MFC (Mass Flow Controller); 51. Upper water-cooled flange; 52. Lower water-cooled flange; 53. Cooling water joint; 54. Inlet pipe interface; 55. Exhaust port; 56. Outer tube sealing surface; 57. Inner tube mounting seat; 58. Thermocouple mounting port; 59. Solenoid valve. Detailed implementation manners

[0044] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0045] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "side", "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0046] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, the meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0047] Embodiment 1

[0048] In this embodiment, a vertical LPCVD apparatus is provided for implementing a silicon nitride thin film deposition method. As Figure 1 shown, the vertical LPCVD apparatus includes: a furnace body 1, an outer tube 2, an inner tube 3, a furnace mouth flange 5, a SiCl2H2 inlet pipe 6, an NH3 inlet pipe 7, a sandwich inlet pipe 8, a wafer boat 14, and a vacuum pumping assembly.

[0049] The furnace body 1, the outer tube 2, and the inner tube 3 are nested in sequence to form a process chamber. The wafer boat 14 is disposed on a heat preservation barrel 4, and the heat preservation barrel 4 is disposed on a carrier 18. The carrier 18 can drive the heat preservation barrel 4 and the wafer boat 14 to move up and down in the vertical direction to enter and exit the process chamber. The wafer boat 14 is used to load wafers 16 and drive the wafers 16 to move up and down in the inner tube 3 to complete the coating process. The furnace mouth flange 5 is disposed at the bottom of the furnace body 1, and the furnace mouth flange 5 is also connected to the vacuum pumping assembly. The SiCl2H2 inlet pipe 6, the NH3 inlet pipe 7, and the sandwich inlet pipe 8 are all connected to the furnace mouth flange 5 to achieve gas delivery. A gas path V2 is connected in parallel to the SiCl2H2 inlet pipe 6, a gas path V3 is connected in parallel to the NH3 inlet pipe 7, and the sandwich inlet pipe 8 communicates with the sandwich between the outer tube 2 and the inner tube 3. The gas path V2, the gas path V3, and the sandwich inlet pipe 8 can all be used to deliver nitrogen. That is, the SiCl2H2 inlet pipe 6 can be used to deliver SiCl2H2 and / or nitrogen, and the NH3 inlet pipe 7 can be used to deliver NH3 and / or nitrogen. It can be understood that a control valve 19 and an MFC 20 are provided on each inlet pipe, and the flow rate of the gas is controlled by the respective control valve 19 and the gas flow meter MFC 20.

[0050] As Figure 1 shown, in this embodiment, the vacuum pumping assembly includes a vacuum pump 9, a cold trap 10, a butterfly valve 11, a vacuum pipeline 12, and a vacuum gauge 13. The vacuum pipeline 12 is respectively connected to the vacuum pump 9 and the furnace mouth flange 5 to evacuate the inside of the process chamber. The cold trap 10, the butterfly valve 11, and the vacuum gauge 13 are sequentially disposed on the vacuum pipeline 12 to monitor and control the vacuum state inside the process chamber in real time.

[0051] As Figure 8 and Figure 9As shown in the figure, the furnace mouth flange 5 includes an upper water-cooled flange 51, a lower water-cooled flange 52, a cooling water joint 53, an inlet gas pipe interface 54, an exhaust port 55, an outer pipe sealing surface 56, an inner pipe mounting seat 57, and a thermocouple mounting port 58. A plurality of inlet gas pipe interfaces 54 are respectively connected to the SiCl2H2 inlet gas pipe 6, the NH3 inlet gas pipe 7, and the sandwich inlet gas pipe 8. A sealing ring is provided at the connection between the outer pipe sealing surface 56 and the outer pipe 2, and a sealing ring is also provided at the connection between the inner pipe mounting seat 57 and the inner pipe 3. The thermocouple 17 passes through the thermocouple mounting port 58 and extends into the inner pipe 3.

[0052] In this embodiment, the upper water-cooled flange 51 and the lower water-cooled flange 52 are respectively provided with independent cooling water joints 53 to realize the parallel setting of the cooling water circuits of the upper water-cooled flange 51 and the lower water-cooled flange 52. And a solenoid valve 59 is provided on the cooling water control loop of the lower water-cooled flange 52, and the solenoid valve 59 is linked with the control system. During the process, the upper water-cooled flange 51 remains in the open state, and the solenoid valve 59 is in the closed state; when the process ends, the solenoid valve 59 automatically opens.

[0053] In this embodiment, by improving the circulating water structure of the furnace mouth flange 5, the upper water-cooled flange 51 and the lower water-cooled flange 52 are set as a parallel water circuit. During the process, the upper water-cooled flange 51 is in the open state, and the cooling water flow rate can be set to 0.5 slm to reduce the flange temperature and protect the sealing ring. By adding a solenoid valve 59 to the cooling water control loop of the lower water-cooled flange 52 and linking it with the process control software, the circulating water of the lower water-cooled flange 52 is automatically closed during the process, ensuring that the inner wall of the flange is at a relatively high temperature. After the process ends, the circulating water is automatically opened, so that the NH4Cl by-product generated during the process cannot crystallize inside the flange, and the by-product has been completely discharged from the tail exhaust pipe after the process ends. At this time, opening the lower circulating water will no longer cause crystallization, avoiding the furnace mouth crystals from falling onto the wafer, and thus ensuring the film forming quality of the silicon nitride film on the wafer surface.

[0054] Furthermore, a heating tape (not shown in the figure) can be additionally installed outside the furnace mouth flange 5. The outside of the furnace mouth flange 5 is heated by the heating tape to keep the furnace mouth flange 5 within the temperature range of 150°C to 200°C and reduce crystallization at the furnace mouth. After adopting the above transformation measures, the problem of furnace mouth crystallization is completely solved, and no furnace mouth crystallization phenomenon has occurred during the entire maintenance cycle of the equipment.

[0055] Embodiment 2

[0056] As Figure 2 shown, the method for depositing a silicon nitride film of the present invention is implemented based on the vertical LPCVD equipment in Embodiment 1, and includes the following steps:

[0057] Step S1: Set the standby temperature of the process chamber to 600°C - 650°C.

[0058] Step S2: Raise the susceptor at a constant speed of 0.8 mm / s - 1.2 mm / s to the process position. During the susceptor raising process, introduce 15 slm - 25 slm of nitrogen between the inner tube and the outer tube of the process chamber, and this nitrogen flow rate is denoted as L1. Meanwhile, introduce 1.0 slm - 2.0 slm of nitrogen into the inner tube, and this nitrogen flow rate is denoted as J1. The key during the susceptor raising process is to introduce nitrogen with a flow rate of L1 into the interlayer between the inner tube 3 and the outer tube 2 through the air inlet V1 of the interlayer inlet pipe 8, and introduce nitrogen with a flow rate of J1 into the inner tube 3 through V2 or V3. Introducing nitrogen into the interlayer can maintain a slightly positive pressure in the process chamber when the susceptor is rising, avoiding the backflow of easily exfoliated particulate contaminants on the tail exhaust pipe wall back into the chamber and contaminating the wafer.

[0059] Step S3: After the susceptor rises to the process position, close the nitrogen, open the vacuum valve, evacuate the inside of the process chamber to vacuum, and perform a vacuum leak rate test. Specifically, first evacuate the inside of the process chamber from atmospheric pressure P1 to low pressure P2. After the chamber is evacuated to low pressure P2, continue to evacuate for > 30 min. After the evacuation is completed, detect the leak rate of the chamber, and the leak rate requirement is < 2 Pa / min. Subsequently, raise the temperature of the process chamber to the silicon nitride deposition process temperature. P2 is preferably < 1.0 Pa, the process temperature is preferably 780°C - 800°C, and the heating rate is controlled at 5°C - 6°C / min.

[0060] Step S4: After the chamber reaches the process temperature, introduce nitrogen with a flow rate of J2 into the process chamber through V2 or V3, and keep the pressure inside the chamber at P3. Specifically, the nitrogen flow rate J2 is preferably 0.5 slm - 1.0 slm, P3 is preferably 30 Pa - 133 Pa, the purging duration is 5 min - 10 min. After the purging is completed, close the nitrogen, evacuate for 3 min - 5 min, and evacuate the pressure inside the chamber to P2. Further introduce nitrogen (nitrogen flow rate J2 = H2 + D1) and control the pressure inside the process chamber at a stable pressure value P4 through the butterfly valve 11. P4 is preferably 20 Pa - 40 Pa, and the pressure control time is 10 min - 20 min.

[0061] Step S5: Evacuate the nitrogen inside the process chamber and introduce ammonia, and this ammonia flow rate is J2. The chamber pressure is stable at P4, and the ammonia introduction time is preferably 5 min. At this time, all the nitrogen inside the process chamber has been replaced by ammonia.

[0062] Step S6: Keep the pressure inside the process chamber at P4 with only ammonia flowing. P4 is preferably 20 Pa - 40 Pa, and the pressure control duration is preferably 10 min - 20 min.

[0063] Step S7: Introduce dichlorosilane (SiCl2H2) into the process chamber under a pressure of P4 to deposit a silicon nitride thin film. In step S7, the flow rate D1 of dichlorosilane is preferably 30 sccm to 35 sccm. The flow rate of ammonia gas is reduced from J2 to H2, and H2 is preferably 170 sccm to 200 sccm. J2 = H2 + D1, that is, by controlling the gas flow rate, the pressure in the chamber is kept constant. Adjust the time for introducing dichlorosilane according to the required thickness of the silicon nitride thin film.

[0064] Step S8: Close dichlorosilane and adjust the ammonia gas flow rate to H1 to consume the residual dichlorosilane in the process chamber. In step S8, the ammonia gas flow rate H1 = J2, which is 0.5 slm to 1.0 slm, and the ammonia gas purge duration is preferably 5 minutes. At the same time, as Figure 1 shown, introduce full-scale nitrogen gas through V2. By adjusting the control valve 19, use nitrogen gas to purge the residual SiCl2H2 gas between the MFC20 and the control valve 19 into the vacuum pump 9 through the pipeline 21 to avoid directly introducing it into the furnace body.

[0065] Step S9: Stop introducing ammonia gas, open the vacuum valve to evacuate, and after evacuating the residual ammonia gas in the chamber, then introduce nitrogen gas with a flow rate of J1. Specifically, the evacuation duration is preferably 5 minutes, and the nitrogen gas purge duration is preferably 5 minutes. Repeat this step more than twice to completely remove the ammonia gas in the chamber.

[0066] Step S10: Restore the process chamber to atmospheric pressure, and then lower the susceptor at a constant speed of 0.8 mm / s to 1.2 mm / s. During the descent of the susceptor, introduce 15 slm to 25 slm of nitrogen gas between the inner tube and the outer tube of the process chamber, and this nitrogen gas flow rate is denoted as L1. At this point, a silicon nitride thin film with a uniform thickness and particle contamination ≤ 30 ea can be deposited on the wafer surface. The particle distribution is as Figure 6 shown. It can be clearly seen from Figure 6 that there are fewer particles on the surface of the silicon nitride thin film of the wafers at the top, middle, and bottom of the process chamber, and the number of particles on the surface of the silicon nitride thin film of the wafers at the top and middle of the process chamber is significantly less than that on the surface of the silicon nitride thin film of the wafers at the bottom. In this embodiment, the specific operation for restoring the process chamber to atmospheric pressure is as follows: First, introduce nitrogen gas with a flow rate of J2 for 5 minutes, then introduce nitrogen gas with a flow rate of J1 for 5 minutes, and finally introduce nitrogen gas with a flow rate of J3 until the chamber returns to atmospheric pressure; J1 is preferably 1.0 slm to 2.0 slm, J2 is preferably 0.5 slm to 1.0 slm, and J3 is preferably 2 slm to 5 slm.

[0067] The key during the process of lowering the susceptor is to introduce 15 slm to 25 slm (L1) of nitrogen gas into the interlayer between the inner tube 3 and the outer tube 2 through V1, and introduce 1.0 - 2.0 slm (J1) of nitrogen gas into the inner tube 3 through V2 or V3. Introducing nitrogen gas into the interlayer can ensure that the process chamber maintains a slightly positive pressure when the susceptor descends, avoiding the backflow of easily exfoliated particulate contaminants on the wall of the exhaust pipe into the chamber, thereby contaminating the wafer. The backflow of particulate contaminants is as shown in Figure 5 as shown. In this embodiment, the pressure change and various process gas flow rate changes during the deposition process of the silicon nitride thin film are as shown in Figure 3 and Figure 4 as shown.

[0068] During the process of lifting and lowering the susceptor, the air pressure is unbalanced between the inner chamber of the tube and the transfer chamber, as well as between the exhaust pipes, resulting in convection at the furnace mouth position and the exhaust port position. The particles carried in the convective gas are likely to adhere to the surface of the wafer. Therefore, in this embodiment, during the process of lifting / lowering the susceptor, a large amount of nitrogen gas is introduced through V1 into the interlayer between the inner tube 3 and the outer tube 2. The main treatment principle is to adjust the gas flow rate in the process chamber, balance the air pressure, reduce the convection during the process to maintain a slightly positive pressure state in the process chamber when the susceptor rises and descends, avoid the backflow of easily exfoliated particulate contaminants on the wall of the exhaust pipe into the chamber, thereby preventing the surface of the wafer from being contaminated and improving the quality stability of the silicon nitride thin film.

[0069] After the single deposition process of the silicon nitride thin film is completed, according to the above process, the deposition of the silicon nitride thin film is repeated. As the cumulative thickness of the thin film in the process chamber increases, the change in the incremental amount of process particles of the silicon nitride thin film is as shown in Figure 7 as shown. When the cumulative thickness of the thin film in the process chamber reaches about 5.0 um, the process particles of the silicon nitride gradually exceed the OOS standard; when the cumulative thickness reaches about 5.5 um, the process particles of the silicon nitride gradually exceed the OOC standard.

[0070] The above description is only the preferred embodiment of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for depositing a silicon nitride thin film, characterized in that, It includes the following steps: Step S1: Set the standby temperature of the process chamber to 600°C - 650°C; Step S2: Raise the susceptor at a uniform speed of 0.8 mm / s - 1.2 mm / s to the process position, and introduce 15 slm - 25 slm of nitrogen between the inner tube and the outer tube of the process chamber during the susceptor rising process. This nitrogen flow rate is denoted as L1; Step S3: After the susceptor rises to the process position, close the nitrogen, evacuate the inside of the process chamber to vacuum, and conduct a vacuum leak rate test; Step S4: Introduce nitrogen into the process chamber. This nitrogen flow rate is denoted as J2, and at the same time, maintain the chamber pressure at P3; Step S5: Evacuate the nitrogen in the process chamber and introduce ammonia. The ammonia flow rate is J2; Step S6: Maintain the pressure in the process chamber at P4 when only ammonia is flowing; Step S7: Introduce dichlorosilane (SiCl2H2) into the process chamber under the pressure of P4 to deposit a silicon nitride thin film; Step S8: Close dichlorosilane and adjust the ammonia flow rate to H1 to consume the remaining dichlorosilane in the process chamber; Step S9: Stop introducing ammonia, evacuate the chamber to vacuum, and then introduce nitrogen with a flow rate of J1; Step S10: Restore the process chamber to atmospheric pressure, and then lower the susceptor at a uniform speed of 0.8 mm / s - 1.2 mm / s. During the susceptor lowering process, introduce 15 slm - 25 slm of nitrogen between the inner tube and the outer tube of the process chamber. This nitrogen flow rate is denoted as L1.

2. The method for depositing a silicon nitride thin film according to claim 1, wherein In step S2, introduce 1.0 slm - 2.0 slm of nitrogen into the inner tube. This nitrogen flow rate is denoted as J1.

3. The method for depositing a silicon nitride thin film according to claim 1, wherein In step S3, evacuate the inside of the process chamber from atmospheric pressure P1 to low pressure P2. After the chamber is evacuated to low pressure P2, preferably P2 < 1.0 Pa, continue to evacuate to vacuum for more than 30 min. After the vacuum evacuation is completed, conduct a leak rate detection on the chamber. The leak rate requirement is < 2 Pa / min. Then raise the temperature of the process chamber to the silicon nitride deposition process temperature. The process temperature is preferably 780°C - 800°C, and the heating rate is controlled at 5°C - 6°C / min.

4. The silicon nitride thin film deposition method according to claim 1, wherein In step S4, the nitrogen flow rate J2 is preferably 0.5 slm - 1.0 slm to make the chamber pressure reach P3. P3 is preferably 30 Pa - 133 Pa. The purging duration is 5 min - 10 min. After the purging is completed, close the nitrogen and evacuate to vacuum for 3 min - 5 min to evacuate the chamber pressure to P2.

5. The method for depositing a silicon nitride thin film according to claim 1, characterized in that, In step S6, P4 is preferably 20 Pa - 40 Pa, and the pressure control duration is preferably 10 min - 20 min.

6. The method for depositing a silicon nitride thin film according to claim 4, wherein In step S7, the flow rate D1 of dichlorosilane is preferably 30 sccm - 35 sccm, and reduce the ammonia flow rate from J2 to H2. H2 is preferably 170 sccm - 200 sccm.

7. The method for depositing a silicon nitride thin film according to any one of claims 1 to 6, characterized in that, In step S8, the ammonia flow rate H1 = J2, which is 0.5 slm - 1.0 slm, and the ammonia purging duration is preferably 5 min - 6 min.

8. The method for depositing a silicon nitride thin film according to any one of claims 1 to 6, characterized in that, In step S9, the vacuum evacuation duration is preferably 5 min - 6 min, and the nitrogen purging duration is preferably 5 min - 6 min; Repeat step S9 more than twice to remove ammonia in the chamber.

9. The method for depositing a silicon nitride thin film according to any one of claims 1 to 6, characterized in that, In the step S10, nitrogen with a flow rate of J2 is introduced for 5 to 6 minutes, then nitrogen with a flow rate of J1 is introduced for 5 to 6 minutes, and finally nitrogen with a flow rate of J3 is introduced until the pressure in the chamber returns to normal pressure; J1 is preferably 1.0 slm to 2.0 slm, J2 is preferably 0.5 slm to 1.0 slm, and J3 is preferably 2 slm to 5 slm.

10. A vertical LPCVD apparatus for implementing the silicon nitride thin film deposition method according to any one of claims 1 to 9, characterized in that, Including: a furnace body (1), an outer tube (2), an inner tube (3), a furnace mouth flange (5), a SiCl2H2 inlet pipe (6), an NH3 inlet pipe (7), a sandwich inlet pipe (8), a susceptor (14) and a vacuum pumping assembly; The furnace body (1), the outer tube (2) and the inner tube (3) are nested in sequence. The susceptor (14) is used to load the wafer (16) and drive the wafer (16) to lift and lower in the inner tube (3) to complete the coating process; the furnace mouth flange (5) is arranged at the bottom of the furnace body (1), and the SiCl2H2 inlet pipe (6), the NH3 inlet pipe (7) and the sandwich inlet pipe (8) are all connected to the furnace mouth flange (5) to realize gas transportation; a gas path V2 is connected in parallel to the SiCl2H2 inlet pipe (6), a gas path V3 is connected in parallel to the NH3 inlet pipe (7), and the sandwich inlet pipe (8) communicates with the sandwich between the outer tube (2) and the inner tube (3). The gas path V2, the gas path V3 and the sandwich inlet pipe (8) can all be used to transport nitrogen. The furnace mouth flange (5) includes an upper water-cooled flange (51) and a lower water-cooled flange (52). The cooling water paths of the upper water-cooled flange (51) and the lower water-cooled flange (52) are connected in parallel, and a solenoid valve (59) is arranged on the cooling water control loop of the lower water-cooled flange (52). The solenoid valve (59) is linked with the control system; during the process, the upper water-cooled flange (51) remains in an open state, and the solenoid valve (59) is in a closed state. When the process ends, the solenoid valve (59) automatically opens.

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