Method for prolonging service life of hot filament in process of depositing silicon nitride by HoFCVD (HooF Chemical Vapor Deposition) equipment

Abstract

The invention relates to a method for prolonging the service life of a hot filament during silicon nitride deposition of HoFCVD equipment. The method comprises the following steps: preheating the hot filament by adopting small current; under the condition that ammonia gas is not introduced, the small current is increased to the large current, so that the temperature of the hot wire is rapidly increased to be higher than 1950 DEG C; heating the hot wire by adopting large current, controlling the pressure in the reaction chamber, and introducing silane and ammonia gas to deposit silicon nitride; continuing the high-current heating state of the heating wire, and not controlling the pressure of the reaction chamber; and the high current of the hot wire is reduced to low current for buffering. According to the invention, the resistance of the hot wire can be effectively prevented from rising, and the high repeatability of the process is successfully maintained. According to the method, the temperature of the hot wire is accurately controlled at a key node, diffusion of nitrogen atoms into the hot wire in the low-temperature stage of the hot wire is avoided, the resistance rising rate of the hot wire is greatly reduced compared with that of a process before optimization, the service life of the hot wire is greatly prolonged, and the shutdown maintenance frequency of equipment is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material preparation and processing, and more specifically, relates to a method for improving the service life of a hot filament during the deposition of silicon nitride by a HoFCVD device. Background Art

[0002] At present, the application demand for silicon nitride in the photovoltaic field is increasing day by day. The silicon nitride thin film can act as an anti-corrosion layer. In long-term outdoor tests, the cells without silicon nitride protection may show obvious performance degradation in 5 - 10 years in harsh environments (such as high temperature and high humidity, high salt fog areas), while the cells with silicon nitride protection can still maintain a high level of performance in 15 - 20 years. This is because the silicon nitride thin film effectively prevents the damage of corrosive media to the inside of the cell and slows down the rate of cell performance decline. During 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, lower the surface recombination rate, and at the same time act as an antireflection layer, reducing the reflection of light on the cell surface, increasing the light utilization rate, and thus enhancing 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 thin films. Since the temperature during the decomposition of the hot filament is basically between 1800°C and 2200°C, the decomposed active particles have very high energy, and a silicon nitride thin film with good densification can be prepared even at a relatively low substrate temperature. HoFCVD decomposes into neutral active particles, which finally "float" onto the substrate to form a film. It is a relatively gentle coating method without plasma damage. The HoFCVD device has a high deposition rate, uses a vertical carrier plate for coating, has a large production capacity, and the equipment cost is not high, making it the first choice for depositing silicon nitride thin films.

[0004] In a HoFCVD device, the hot filament plays a key role. The hot filament generates high temperature by applying a large current, catalytically cracks 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. As the industry's control over costs becomes more stringent, higher requirements are put forward for the efficient and stable operation of HoFCVD devices, and extending the service life of the hot filament has become a key problem that urgently needs to be solved.

[0005] Currently, the main way to extend the life of the hot wire in the HoFCVD equipment is through the hot wire pretreatment process, which allows sufficient time for the internal atoms of the hot wire to adjust their positions in advance, reducing lattice distortion and dislocations in the initial stage, making it more resilient during subsequent repeated long-term use, and thus increasing the service life of the hot wire. During the preparation process of crystalline silicon heterojunction batteries, the hot wire life of the HoFCVD equipment can maintain the stability of battery efficiency within 30 days.

[0006] However, research has found that even after the hot wire pretreatment process, when depositing silicon nitride, the resistance of the hot wire still rises rapidly, resulting in very poor process repeatability, a significant shortening of the hot wire life, and the need to frequently replace the hot wire to maintain process stability. This severely restricts the production efficiency of the equipment, and the equipment cannot operate stably for a long time, bringing great obstacles to large-scale industrial production. Therefore, in the practical application of the silicon nitride deposition process using the HoFCVD equipment, the problem of rapid increase in hot wire resistance has become a key difficulty that urgently needs to be solved. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for improving the hot wire life when depositing silicon nitride using the HoFCVD equipment. This method essentially solves the problem of rapid increase in hot wire resistance when depositing silicon nitride thin films using the HoFCVD equipment through an optimized silicon nitride process formula.

[0008] To solve the above technical problems or achieve the above purpose, the present invention adopts the following technical solutions:

[0009] According to an aspect of the present invention, there is provided a method for improving the hot wire life when depositing silicon nitride using the HoFCVD equipment, including:

[0010] Preheating the hot wire with a small current;

[0011] Without introducing ammonia, increasing the small current to a large current to rapidly raise the temperature of the hot wire to above 1950 °C;

[0012] Maintain the hot wire heated with a large current, control the pressure in the reaction chamber, and introduce silane and ammonia for the deposition of silicon nitride;

[0013] Continue the hot wire in the large current heating state and do not control the pressure of the reaction chamber;

[0014] Lower the large current of the hot wire to a small current for buffering.

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

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

[0017] In one embodiment of the present invention, a small current is increased to a large current and maintained for 6 - 8 s to rapidly raise the temperature of the heating wire to above 1950 °C.

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

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

[0020] In one embodiment of the present invention, the duration of reducing the large current of the heating wire to a small current buffer is 10 - 12 s.

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

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

[0023] In one embodiment of the present invention, when the large current is 32 A, the temperature of the heating wire rapidly rises to 2100 °C.

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

[0025] The present invention can effectively inhibit the increase in the resistance of the heating wire. Through the unique design of process steps, especially the precise control of the heating wire temperature at key nodes, the diffusion of nitrogen atoms into the heating wire during the low - temperature stage of the heating wire is avoided. The rising rate of the heating wire resistance is greatly reduced compared with the process before optimization (for example, reduced by about 90%), which greatly extends the service life of the heating wire and reduces the number of equipment shutdowns for maintenance.

[0026] By the way of heating with large current before and after, the present invention avoids the low - temperature coating stage, and the composition accuracy of the deposited silicon nitride thin film layer is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present invention and, together with the specification, are used to explain the principles of the present invention.

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other accompanying drawings can also be obtained based on these drawings without creative efforts.

[0029] Figure 1The flowchart shows a method for improving the hot filament life during silicon nitride deposition in a HoFCVD device provided by an embodiment of the present invention. Detailed implementation manners

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

[0031] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0032] As Figure 1 shown, an embodiment of the present invention provides a method for improving the hot filament life during silicon nitride deposition in a HoFCVD device, including the following steps:

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

[0034] S12: Without introducing ammonia, increase the small current to a large current to quickly raise the hot filament temperature to higher than 1950 °C;

[0035] S13: Keep the hot filament heated with a large current, control the pressure in the reaction chamber, and introduce silane and ammonia for silicon nitride deposition;

[0036] S14: Continue the hot filament large current heating state and do not control the pressure of the reaction chamber;

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

[0038] The present invention can effectively inhibit the increase of the hot filament resistance. Through the unique design of the process steps, especially the precise control of the hot filament temperature at key nodes, the diffusion of nitrogen atoms into the hot filament interior at the low temperature stage of the hot filament is avoided, and the hot filament resistance rise rate is greatly reduced compared with the process before optimization (for example, reduced by about 90%), greatly extending the hot filament life and reducing the number of equipment shutdowns for maintenance.

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

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

[0041] In the method of the above embodiment, in step S12, the small current is increased to a large current and maintained for 6 - 8 s to rapidly raise the temperature of the heating wire to above 1950 °C. The preferred duration is 6 s. When the large current is 32 A, the temperature of the heating wire rapidly rises to 2100 °C.

[0042] In the method of the above embodiment, in step S13, the duration of maintaining the large current heating of the heating wire is 20 - 30 s, and the preferred duration is 20 s.

[0043] In the method of the above embodiment, in step S14, the duration of continuing the large current heating state of the heating wire is 6 - 8 s, and the preferred duration is 6 s.

[0044] In the method of the above embodiment, in step S15, the duration of reducing the large current of the heating wire to a small current buffer is 10 - 12 s, and the preferred duration is 10 s.

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

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

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

[0048] The first step: Pass a small current of 6 - 8 A through the heating wire for preheating, and maintain the process duration for 5 - 6 s.

[0049] This step aims to gently start the heating wire and gradually bring it from the normal temperature state into the preliminary activation stage.

[0050] The second step: Increase the current of the heating wire to 30 - 36 A, and maintain the process duration for 6 - 8 s to rapidly raise the temperature of the heating wire to above 1950 °C, and ammonia is not introduced in this stage.

[0051] By introducing a large current in advance, the temperature of the heating wire is rapidly raised to a specific range. In this stage, due to the rapid rise in the temperature of the heating wire, the diffusion of nitrogen atoms into the heating wire at the low temperature stage is effectively avoided.

[0052] Step 3: Maintain the hot wire at a high current of 30 - 36 A for heating, with a continuous process duration of 20 - 30 s. Meanwhile, precisely control the pressure in the reaction chamber at 1 - 1.5 Pa to deposit the silicon nitride thin film. During this period, introduce 50 - 60 sccm of silane and 500 - 600 sccm of ammonia. Under the high-temperature catalysis of the hot wire, the reaction gases decompose orderly, and a high-quality silicon nitride thin film is gradually deposited on the substrate.

[0053] Step 4: Continue to heat the hot wire at a high current of 30 - 36 A for 6 - 8 s. The pressure in the reaction chamber is not controlled at this stage.

[0054] In this step, during the gas evacuation stage after deposition, continuously supply high current to prevent the residual active nitrogen atoms from diffusing into the hot wire during the evacuation stage.

[0055] Step 5: Reduce the high current of the hot wire from 30 - 36 A to a low current of 6 - 8 A and maintain it for 10 - 12 s.

[0056] This step serves as a buffer stage to relieve problems such as the elongation deformation of the hot wire caused by long-term high current and the excessive temperature of the silicon wafer irradiated by the hot wire.

[0057] Example 1

[0058] A method for improving the lifespan of the hot wire during the deposition of silicon nitride by a HoFCVD device, the specific steps are as follows:

[0059] Step 1: Preheat the hot wire by passing a low current of 6 A for 5 s;

[0060] Step 2: Increase the hot wire current to 32 A for 6 s to rapidly raise the temperature of the hot wire to 2100 °C, and no ammonia is introduced at this stage.

[0061] Step 3: Maintain the hot wire at a high current of 32 A for heating, with a continuous process duration of 20 s. Meanwhile, precisely control the pressure in the reaction chamber at 1 Pa. During this period, introduce 50 sccm of silane and 500 sccm of ammonia to deposit the silicon nitride thin film.

[0062] Step 4: Continue to heat the hot wire at a high current of 32 A for 6 s. The pressure in the reaction chamber is not controlled at this stage.

[0063] Step 5: Reduce the high current of the hot wire from 32 A to a low current of 6 A and maintain it for 10 s.

[0064] The specific optimized 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 The first step The second step The third step The fourth step The fifth step Time (s) 5 6 20 6 10 Air pressure (Pa) —— —— 1 —— —— Silane (sccm) —— —— 50 —— —— Ammonia (sccm) —— —— 500 —— —— Hot wire current (A) 6 32 32 32 6

[0067] Before optimization, the hot wire exhibited a voltage of 182 V at a current of 32 A in the initial stage after replacement (the stage when the hot wire was just put into use after replacing with a new one). However, after seven consecutive days of silicon nitride thin film deposition, with the same given current of 32 A, the voltage of the hot wire significantly increased to 220 V, resulting in a substantial reduction in the process repeatability. After the optimization adjustment in Example 1 above, at a current of 32 A, after up to 30 days of silicon nitride thin film deposition, the voltage of the hot wire only mildly increased to 198 V, and the high repeatability of the process was successfully maintained, meeting the usage requirements of the hot wire life for mass production equipment.

[0068] Example 2

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

[0070] The first step: Pass a small current of 7 A through the hot wire for preheating, with a continuous process duration of 5.5 s;

[0071] The second step: Increase the hot wire current to 30 A, with a continuous process duration of 7 s, so that the temperature of the hot wire rapidly rises to 1980 °C, and ammonia is not introduced in this stage.

[0072] The third step: Keep the hot wire heated at a large current of 30 A, with a continuous process duration of 25 s. At the same time, accurately control the pressure of the reaction chamber at 1.2 Pa. And during this period, introduce 55 sccm of silane and 560 sccm of ammonia for silicon nitride thin film deposition.

[0073] The fourth step: Continue to heat the hot wire at a large current of 30 A, with a continuous process duration of 7 s. The pressure of the reaction chamber is not controlled in this stage.

[0074] The fifth step: Lower the large current of the hot wire from 30 A to a small current of 7 A and maintain it for 11 s.

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

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

[0077] Step The first step The second step The third step The fourth step The fifth step Time (s) 5.5 7 25 7 11 Air pressure (Pa) —— —— 1.2 —— —— Silane (sccm) —— —— 55 —— —— Ammonia (sccm) —— —— 560 —— —— Hot wire current (A) 7 30 30 30 7

[0078] Before optimization, the hot wire exhibited a voltage of 175V at a current of 30A in the initial stage after replacement (the stage when the hot wire was first put into use after replacing with a new one). However, after seven consecutive days of silicon nitride thin film deposition, with the same given current of 30A, the voltage of the hot wire significantly increased to 210V, resulting in a substantial reduction in the process repeatability. After the optimization adjustment in Example 2 above, at a current of 30A, after up to 30 days of silicon nitride thin film deposition, the voltage of the hot wire only mildly increased to 186V, and the high repeatability of the process was successfully maintained, meeting the service life requirements of the hot wire for mass production equipment.

[0079] Example 3

[0080] A method for improving the service life of the hot wire during silicon nitride deposition by HoFCVD equipment, the specific steps are as follows:

[0081] The first step: Pass a small current of 8A through the hot wire for preheating, lasting for a process duration of 6s;

[0082] The second step: Increase the hot wire current to 36A, lasting for a process duration of 8s, so that the temperature of the hot wire rapidly rises to 2200°C, and ammonia is not introduced in this stage.

[0083] The third step: Keep the hot wire heated at a large current of 36A, lasting for a process duration of 30s. At the same time, accurately control the pressure of the reaction chamber at 1.5Pa. And during this period, introduce 60sccm of silane and 600sccm of ammonia for silicon nitride thin film deposition.

[0084] The fourth step: Continue to heat the hot wire at a large current of 36A, lasting for a process duration of 8s. The pressure of the reaction chamber is not controlled in this stage.

[0085] The fifth step: Lower the large current of the hot wire from 36A to a small current of 8A and maintain it for 12s.

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

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

[0088] Step The first step The second step The third step The fourth step The fifth step Time (s) 6 8 30 8 12 Air pressure (Pa) —— —— 1.5 —— —— Silane (sccm) —— —— 60 —— —— Ammonia (sccm) —— —— 600 —— —— Hot wire current (A) 8 36 36 36 8

[0089] Before optimization, the hot wire exhibited a voltage of 196 V at a current of 36 A during the initial stage of replacement (the stage when the hot wire was just put into use after replacing with a new one). However, after the deposition of silicon nitride thin films for seven consecutive days, with the same given current of 36 A, the voltage of the hot wire increased significantly to 232 V, resulting in a substantial reduction in the process repeatability. After the optimization adjustment in Example 3 above, at a current of 36 A, after the deposition of silicon nitride thin films for up to 30 days, the voltage of the hot wire only increased mildly to 201 V, and the high repeatability of the process was successfully maintained, meeting the usage requirements of the hot wire life for mass production equipment.

[0090] As can be seen from Examples 1 - 3 above, compared with before optimization, the hot wire of the present invention only showed a mild increase in voltage after the deposition of silicon nitride thin films for up to 30 days at a high current, that is, the increase in the resistance of the hot wire was effectively inhibited, and the high repeatability of the process was successfully maintained. Therefore, the present invention can effectively inhibit the increase in the resistance of the hot wire. The present invention precisely controls the temperature of the hot wire at key nodes, avoiding the diffusion of nitrogen atoms into the hot wire during the low-temperature stage of the hot wire. The rate of increase in the resistance of the hot wire is greatly reduced compared with the process before optimization, greatly extending the life of the hot wire and reducing the number of equipment shutdowns for maintenance.

[0091] It should be noted that in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to the said process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the said element.

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

Claims

1. A method for improving the life of a hot wire when depositing silicon nitride using a HoFCVD device, characterized in that: include: Preheat the hot wire with a small current; Without introducing ammonia, the small current is increased to a large current, so that the temperature of the hot wire rises rapidly to above 1950°C; The hot wire is kept heated by a large current, the pressure in the reaction chamber is controlled, and silane and ammonia are introduced to deposit silicon nitride; Continue the high current heating state of the hot wire and do not control the pressure of the reaction chamber; Reduce the high current of the hot wire to a low current for buffering.

2. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The small current is 6-8A, and the large current is 30-36A.

3. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The duration of the small current preheating of the hot wire is 5-6s.

4. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The small current is increased to a large current and the current is maintained for 6-8 seconds to allow the temperature of the hot wire to rise rapidly to above 1950°C.

5. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The duration of high current heating of the hot wire is maintained for 20-30s.

6. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The duration of the high current heating state of the hot wire is 6-8s.

7. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The duration of the hot wire high current being reduced to a low current buffer is 10-12s.

8. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The pressure in the reaction chamber was controlled at 1-1.5 Pa.

9. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 1, characterized in that: The flow rate of silane is 50-60 sccm, and the flow rate of ammonia is 500-600 sccm.

10. The method for improving the life of the hot wire when depositing silicon nitride by HoFCVD equipment according to claim 2, characterized in that: When the high current is 32A, the temperature of the hot wire rises rapidly to 2100℃.

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