A method for improving the life of hot filaments in a hoFCVD apparatus for depositing silicon nitride

Abstract

The application relates to a method for prolonging the life of a hot wire in a HoFCVD device during deposition of silicon nitride, comprising: preheating the hot wire with a small current; increasing the small current to a large current without ammonia gas, so that the temperature of the hot wire rapidly rises above 1950 DEG C; keeping the hot wire heated with the large current, controlling the pressure in the reaction chamber, and introducing silane and ammonia gas to deposit silicon nitride; continuing the state of the hot wire heated with the large current, and not controlling the pressure in the reaction chamber; and adjusting the large current of the hot wire to the small current for buffering. The application can effectively inhibit the increase of the resistance of the hot wire, and successfully maintain the high repeatability of the process. The application precisely controls the temperature of the hot wire at the key node, avoids the diffusion of nitrogen atoms to the inside of the hot wire in the low-temperature stage of the hot wire, greatly reduces the rising rate of the resistance of the hot wire compared with the process before optimization, greatly prolongs the life of the hot wire, and reduces the number of equipment downtime maintenance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor material preparation and processing, and more particularly, relates to a method for prolonging the hot filament life in HoFCVD equipment when depositing silicon nitride. BACKGROUND

[0002] At present, the application demand of silicon nitride in the photovoltaic field is increasing, and the silicon nitride film can act as an anti-corrosion layer. In long-term outdoor tests, the battery without using silicon nitride protection may have obvious performance degradation in harsh environments (such as high temperature and high humidity, high salt fog area) in 5-10 years, and the battery with silicon nitride protection can maintain a high level in 15-20 years. This is because the silicon nitride film effectively prevents the damage of corrosive media to the inside of the battery, slowing down the speed of battery performance decline. In the manufacturing process of crystalline silicon solar cells, silicon nitride can also be used as a surface passivation layer. It can reduce the dangling bonds on the surface of crystalline silicon, reduce the surface recombination rate, and at the same time, it can also reduce the reflection of light on the surface of the battery, increase the light utilization rate, and thus improve the short-circuit current density.

[0003] Hot filament chemical vapor deposition (HoFCVD) as an important thin film preparation technology has many advantages in the preparation of silicon nitride film. Because the temperature during the decomposition of hot filament is basically 1800-2200℃, the active particles decomposed have very high energy, so even at a lower substrate temperature, dense silicon nitride films can be prepared. HoFCVD decomposes neutral active particles, which eventually "float" to the substrate to form a film, and it is a relatively gentle plating method without plasma damage. HoFCVD equipment has a fast deposition rate, uses vertical load plate plating, has high production capacity, and the equipment cost is not high, so it is the first choice for depositing silicon nitride film.

[0004] In HoFCVD equipment, the hot filament plays a key role. The hot filament generates high temperature by applying a large current, catalytically decomposes the reaction gas into active particles, and finally deposits a film on the substrate. However, the hot filament faces severe life challenges during long-term operation, which not only affects the continuous and stable operation of the equipment, but also increases the production cost and maintenance frequency. With the increasingly strict control of costs by the industry, higher requirements for the efficient and stable operation of HoFCVD equipment are put forward, and prolonging the life of the hot filament has become a key problem that needs to be solved urgently.

[0005] The current HoFCVD device prolongs the life of the hot wire mainly through the hot wire pretreatment process, which allows the internal atoms of the hot wire to have enough time to adjust their positions, reduces the lattice distortion and dislocation in the initial stage, and makes the hot wire more flexible in the subsequent long-term use, thereby increasing the service life of the hot wire. In the process of preparing a crystalline silicon heterojunction cell, the service life of the hot wire of the HoFCVD device can maintain the stability of the cell efficiency within 30 days.

[0006] However, research has found that even after the hot wire is pretreated, the resistance of the hot wire still rises rapidly when preparing silicon nitride, resulting in poor repeatability of the process, a significant reduction in the service life of the hot wire, and the need to frequently replace the hot wire to maintain the stability of the process, which seriously restricts the production efficiency of the device, the device cannot operate stably for a long time, and brings great obstacles to large-scale industrial production. Therefore, in the actual application of the HoFCVD device for depositing silicon nitride, the problem of rapid rise of the resistance of the hot wire has become a key difficulty that needs to be solved urgently. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for improving the service life of the hot wire of the HoFCVD device when depositing silicon nitride. The method is essentially to solve the problem of rapid rise of the resistance of the hot wire when depositing a silicon nitride film by the HoFCVD device through an optimized silicon nitride process formula.

[0008] In order to solve the above technical problems or achieve the above purposes, the present application adopts the following technical solutions:

[0009] According to an aspect of the present application, a method for improving the service life of the hot wire of the HoFCVD device when depositing silicon nitride is provided, comprising:

[0010] The hot wire is preheated with a small current;

[0011] Without introducing ammonia, the small current is increased to a large current, so that the temperature of the hot wire is rapidly raised to higher than 1950℃;

[0012] The hot wire is heated with a large current, the pressure in the reaction chamber is controlled, and silane and ammonia are introduced to deposit silicon nitride;

[0013] The state of the large current heating of the hot wire is continued, and the reaction chamber is not controlled in pressure;

[0014] The large current of the hot wire is adjusted to a small current for buffering.

[0015] In an embodiment of the present application, the small current is 6-8A and the large current is 30-36A.

[0016] In an embodiment of the present application, the duration of the preheating of the hot wire with a small current is 5-6s.

[0017] In one embodiment of the present application, the small current is increased to the large current for 6-8s to rapidly increase the hot wire temperature to above 1950 DEG C.

[0018] In one embodiment of the present application, the duration of maintaining the hot wire large current heating is 20-30s.

[0019] In one embodiment of the present application, the duration of continuing the hot wire large current heating state is 6-8s.

[0020] In one embodiment of the present application, the duration of the hot wire large current adjustment to the small current buffer is 10-12s.

[0021] In one embodiment of the present application, the pressure in the reaction chamber is controlled at 1-1.5Pa.

[0022] In one embodiment of the present application, the flow rate of silane is 50-60sccm, and the flow rate of ammonia is 500-600sccm.

[0023] In one embodiment of the present application, the large current is 32A to rapidly increase the hot wire temperature to 2100 DEG C.

[0024] The technical solution provided by the present application has the following advantages compared with the prior art:

[0025] The present application can effectively inhibit the increase of hot wire resistance, and through the unique process step design, especially the precise control of the hot wire temperature at the key node, the diffusion of nitrogen atoms to the inside of the hot wire in the low temperature stage of the hot wire is avoided, the hot wire resistance increase rate is greatly reduced (for example, reduced by about 90%) compared with the prior art process, the hot wire life is greatly prolonged, and the number of equipment downtime maintenance is reduced.

[0026] The present application avoids the low temperature coating stage through the front and rear large current heating mode, and the composition accuracy of the deposited silicon nitride film layer is better. BRIEF DESCRIPTION OF DRAWINGS

[0027] The drawings incorporated into the specification and forming a part thereof, illustrate embodiments consistent with the present application and together with the description serve to explain the principles of the application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced as follows, and obviously, other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0029] Figure 1A flowchart of a method for prolonging the life of a hot filament in a HoFCVD device for depositing silicon nitride is shown. DETAILED DESCRIPTION

[0030] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the embodiments of the present application will be further described below. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0031] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a variety of ways beyond the specific details set forth herein; obviously, the embodiments described in the specification are only a part of the embodiments of the present application and not all the embodiments.

[0032] As shown in the drawings, Figure 1 The present application provides a method for prolonging the life of a hot filament in a HoFCVD device for depositing silicon nitride, which comprises the following steps:

[0033] S11: preheat the hot filament with a small current;

[0034] S12: increase the small current to a large current without introducing ammonia, so that the temperature of the hot filament rapidly rises above 1950℃;

[0035] S13: keep the hot filament heated with the large current, control the pressure in the reaction chamber, and introduce silane and ammonia to deposit silicon nitride;

[0036] S14: continue the state of the hot filament heated with the large current, and do not control the pressure in the reaction chamber;

[0037] S15: reduce the large current of the hot filament to a small current for buffering.

[0038] The present application can effectively inhibit the increase of the resistance of the hot filament. By unique process step design, especially precise control of the temperature of the hot filament at the key node, the present application avoids the diffusion of nitrogen atoms to the inside of the hot filament at the low temperature stage of the hot filament, greatly reduces the rate of increase of the resistance of the hot filament (for example, about 90% reduction), greatly prolongs the life of the hot filament, and reduces the number of equipment downtime maintenance.

[0039] In the method of the above-mentioned embodiments, in steps S11-S15, the small current is 6-8A, preferably 6A; the large current is 30-36A, preferably 32A.

[0040] In the method of the above-mentioned embodiments, in step S11, the duration of preheating the hot filament with a small current is 5-6s, preferably 5s.

[0041] In the method of the above embodiment, in step S12, the small current is increased to the large current for 6-8s to rapidly increase the hot wire temperature to above 1950℃, preferably for 6s, and the large current is 32A to rapidly increase the hot wire temperature to 2100℃.

[0042] In the method of the above embodiment, in step S13, the duration of the hot wire large current heating is maintained for 20-30s, preferably for 20s.

[0043] In the method of the above embodiment, in step S14, the duration of the hot wire large current heating state is continued for 6-8s, preferably for 6s.

[0044] In the method of the above embodiment, in step S15, the duration of the hot wire large current adjustment to the small current buffer is 10-12s, preferably for 10s.

[0045] In the method of the above embodiment, in step S13, the pressure in the reaction chamber is controlled at 1-1.5Pa, preferably 1Pa; the flow rate of silane is 50-60sccm, preferably 50sccm; and the flow rate of ammonia is 500-600sccm, preferably 500sccm.

[0046] The above technical solutions of the present application will be described in detail through specific embodiments.

[0047] In the process of depositing a silicon nitride film, when the hot wire temperature is lower than or equal to 1950℃, nitrogen atoms will diffuse into the hot wire, which is the fundamental reason for the rapid rise of the hot wire resistance. Conversely, when the temperature is higher than 1950℃, the diffusion of nitrogen atoms into the hot wire will be significantly slowed down. Based on this, the embodiments of the present application provide a method for improving the service life of the hot wire or the hot wire life when depositing silicon nitride in a HoFCVD device, and the specific steps are as follows.

[0048] First step: preheat the hot wire with a small current of 6-8A for 5-6s.

[0049] This step aims to gently start the hot wire and gradually enter the preliminary activation stage from the normal temperature state.

[0050] Second step: increase the hot wire current to 30-36A for 6-8s to rapidly increase the hot wire temperature to above 1950℃, and no ammonia gas is passed during this stage.

[0051] By passing a large current in advance, the hot wire temperature is rapidly increased to a specific range. During this stage, due to the rapid rise of the hot wire temperature, the diffusion of nitrogen atoms into the hot wire during the low temperature stage is effectively avoided.

[0052] Third step: keep the heating of the hot filament with large current 30-36 A, and continue the process for 20-30 s, while the pressure in the reaction chamber is precisely controlled at 1-1.5 Pa, to deposit the silicon nitride film. During this period, the silane is introduced at 50-60 sccm, and the ammonia is introduced at 500-600 sccm, and the reaction gas is orderly decomposed under the catalysis of the hot filament at high temperature, to gradually deposit the high-quality silicon nitride film on the substrate.

[0053] Fourth step: continue the heating of the hot filament with large current 30-36 A for 6-8 s, and the reaction chamber is not controlled in pressure during this period.

[0054] In this step, the large current is continuously supplied during the gas evacuation after the deposition is completed, to avoid the diffusion of the residual active nitrogen atoms to the inside of the hot filament during the evacuation.

[0055] Fifth step: reduce the large current 30-36 A of the hot filament to small current 6-8 A, and maintain for 10-12 s.

[0056] This step is a buffer stage, which can relieve the elongation deformation of the hot filament caused by the long-time large current and the high temperature of the silicon wafer caused by the irradiation of the hot filament.

[0057] Example 1

[0058] A method for improving the service life of the hot filament of a HoFCVD device during the deposition of silicon nitride, and the specific steps are as follows:

[0059] First step: preheat the hot filament with small current 6 A, and continue the process for 5 s.

[0060] Second step: increase the current of the hot filament to 32 A, and continue the process for 6 s, to rapidly increase the temperature of the hot filament to 2100℃, and no ammonia is introduced during this period.

[0061] Third step: keep the heating of the hot filament with large current 32 A, and continue the process for 20 s, while the pressure in the reaction chamber is precisely controlled at 1 Pa, and during this period, the silane is introduced at 50 sccm, and the ammonia is introduced at 500 sccm, to deposit the silicon nitride film.

[0062] Fourth step: continue the heating of the hot filament with large current 32 A for 6 s, and the reaction chamber is not controlled in pressure during this period.

[0063] Fifth step: reduce the large current 32 A of the hot filament to small current 6 A, and maintain for 10 s.

[0064] The specific optimization parameters of the above example 1 are shown in table 1 below:

[0065] Table 1: Process parameters of each step in example 1

[0066] Step First step Second step Third step Fourth step Fifth step Time (s) 5 6 20 6 10 Gas pressure (Pa) —— —— 1 —— —— Silane (sccm) —— —— 50 —— —— Ammonia (sccm) —— —— 500 —— —— Hot wire current (A) 6 32 32 32 6

[0067] Before the optimization, the hot filament showed a voltage of 182V at 32A current at the beginning of the replacement (after the replacement of the new hot filament, the stage when the hot filament just started to be used). However, after seven days of continuous silicon nitride film deposition, the voltage of the hot filament increased significantly to 220V at the same given 32A current, resulting in a significant decrease in the repeatability of the process. After the optimization adjustment in the above-mentioned embodiment 1, the voltage of the hot filament only increased to 198V at 32A current after 30 days of silicon nitride film deposition, and the high repeatability of the process was successfully maintained, meeting the use requirements of hot filament life of mass production equipment.

[0068] Embodiment 2

[0069] A method for improving the hot filament life of a HoFCVD device during silicon nitride deposition, the specific steps are as follows:

[0070] First step: preheat the hot filament with a small current of 7A for 5.5s of process time;

[0071] Second step: increase the hot filament current to 30A for 7s of process time, so that the hot filament temperature quickly rises to 1980℃, and no ammonia gas is passed during this stage.

[0072] Third step: keep the hot filament at a large current of 30A for 25s of process time, while the reaction chamber pressure is precisely controlled at 1.2Pa, and during this period, 55sccm of silane and 560sccm of ammonia are passed to deposit silicon nitride film.

[0073] Fourth step: continue the hot filament at a large current of 30A for 7s of process time, and the reaction chamber is not controlled during this stage.

[0074] Fifth step: reduce the hot filament from a large current of 30A to a small current of 7A for 11s.

[0075] The specific optimization parameters of the above-mentioned embodiment 2 are shown in Table 2 below:

[0076] Table 2: Process parameters of each step in embodiment 2

[0077] Step First step Second step Third step Fourth step Fifth step Time (s) 5.5 7 25 7 11 Gas pressure (Pa) —— —— 1.2 —— —— Silane (sccm) —— —— 55 —— —— Ammonia (sccm) —— —— 560 —— —— Hot wire current (A) 7 30 30 30 7

[0078] Before the optimization, the hot filament showed a voltage of 175V at 30A current at the beginning of the replacement (after the replacement of the new hot filament, the stage when the hot filament just started to be used). However, after seven days of continuous silicon nitride film deposition, the voltage of the hot filament increased significantly to 210V at the same given 30A current, resulting in a significant decrease in process repeatability. After the optimization adjustment in the above-mentioned embodiment 2, the voltage of the hot filament only increased to 186V at 30A current after 30 days of silicon nitride film deposition, and the high repeatability of the process was successfully maintained, meeting the use requirements of hot filament life of mass production equipment.

[0079] Embodiment 3

[0080] A method for improving the hot filament life of a HoFCVD device during silicon nitride deposition, the specific steps are as follows:

[0081] First step: preheat the hot filament with a small current of 8A for 6s of process time;

[0082] Second step: increase the hot filament current to 36A for 8s of process time, quickly raise the hot filament temperature to 2200℃, and no ammonia gas is passed during this stage.

[0083] Third step: keep the hot filament at a large current of 36A for 30s of process time, and accurately control the reaction chamber pressure at 1.5Pa, and during this period, pass in 60sccm of silane and 600sccm of ammonia for silicon nitride film deposition.

[0084] Fourth step: continue the hot filament at a large current of 36A for 8s of process time, and the reaction chamber is not pressure-controlled during this stage.

[0085] Fifth step: reduce the hot filament from a large current of 36A to a small current of 8A for 12s.

[0086] The specific optimization parameters of the above-mentioned embodiment 3 are shown in Table 3 below:

[0087] Table 3: Process parameters of each step in embodiment 3

[0088] Step First step Second step Third step Fourth step Fifth step Time (s) 6 8 30 8 12 Gas pressure (Pa) —— —— 1.5 —— —— Silane (sccm) —— —— 60 —— —— Ammonia (sccm) —— —— 600 —— —— Hot wire current (A) 8 36 36 36 8

[0089] Before the optimization, the hot wire showed a voltage of 196V at a current of 36A in the initial replacement stage (the stage when the hot wire is just put into use after the replacement of a new hot wire). However, after a continuous seven-day silicon nitride film deposition process, the voltage of the hot wire was significantly increased to 232V at the same given current of 36A, resulting in a significant reduction in the repeatability of the process. After the optimization adjustment in the above-mentioned embodiment 3, the voltage of the hot wire was only mildly increased to 201V at a current of 36A after a silicon nitride film deposition for up to 30 days, and the high repeatability of the process was successfully maintained, meeting the use requirements of the hot wire life of the mass production equipment.

[0090] As can be seen from the above-mentioned embodiments 1-3, compared with before the optimization, the voltage of the hot wire of the present application is only mildly increased after a silicon nitride film deposition for up to 30 days at a large current, that is, the increase in the resistance of the hot wire is effectively inhibited, and the high repeatability of the process is successfully maintained. Therefore, the present application can effectively inhibit the increase in the resistance of the hot wire, the present application precisely controls the temperature of the hot wire at the key node, avoids the diffusion of nitrogen atoms to the inside of the hot wire in the low-temperature stage of the hot wire, greatly reduces the rate of the increase in the resistance of the hot wire compared with the process before the optimization, greatly prolongs the life of the hot wire, and reduces the number of equipment downtime maintenance.

[0091] It should be noted that, in this document, relational terms such as“first” and“second”, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms“comprises”,“comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element preceded by“comprises a” does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0092] The above description is only the embodiments of the present application, which enable those skilled in the art to understand and implement the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and features disclosed herein.

Claims

1. A method for increasing the hot filament lifetime of a HoFCVD apparatus when depositing silicon nitride, characterized in that, The method comprises the following steps: Preheating the hot wire with a small current; Increasing the small current to a large current without ammonia gas, so that the temperature of the hot wire rapidly rises above 1950℃; Keeping the hot wire heated with the large current, controlling the pressure in the reaction chamber at 1-1.5Pa, and introducing silane and ammonia gas to deposit silicon nitride, the flow rate of the silane being 50-60sccm, and the flow rate of the ammonia gas being 500-600sccm; Continuing the state of the hot wire heated with the large current, and not controlling the pressure in the reaction chamber; Adjusting the large current of the hot wire to a small current for buffering; The small current is 6-8A, and the large current is 30-36A.

2. The method of increasing the hot filament life of a HoFCVD apparatus for deposition of silicon nitride according to claim 1, wherein, The duration of the preheating of the hot wire with the small current is 5-6s.

3. The method of increasing the hot filament life of a HoFCVD apparatus for deposition of silicon nitride according to claim 1, wherein, The duration of increasing the small current to the large current is 6-8s to rapidly raise the temperature of the hot wire above 1950℃.

4. The method of increasing the hot filament life of a HoFCVD apparatus for deposition of silicon nitride according to claim 1, wherein, The duration of keeping the hot wire heated with the large current is 20-30s.

5. The method of increasing the hot filament life of a HoFCVD apparatus for deposition of silicon nitride according to claim 1, wherein, The duration of continuing the state of the hot wire heated with the large current is 6-8s.

6. The method of increasing the hot filament life of a HoFCVD apparatus for deposition of silicon nitride of claim 1, wherein, The duration of adjusting the large current of the hot wire to the small current for buffering is 10-12s.

7. The method of increasing the hot filament life of a HoFCVD apparatus for deposition of silicon nitride of claim 1, wherein, The large current is 32A to rapidly raise the temperature of the hot wire to 2100℃.

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