TOPCon battery preparation method based on LPCVD (Low Pressure Chemical Vapor Deposition) process

Abstract

The invention relates to a TOPCon battery preparation method based on an LPCVD (Low Pressure Chemical Vapor Deposition) process, which comprises the following steps: carrying out first constant temperature operation after carrying out first vacuumizing operation and heating operation on a furnace tube, and carrying out second vacuumizing operation on the furnace tube in the constant temperature process. Therefore, the duration of vacuumizing is increased before oxygen is introduced into the furnace tube, so that foreign gas in the furnace tube can be cleared more thoroughly, and the quality of a tunneling oxide layer formed by oxidation is ensured. Moreover, the vacuumizing time is prolonged, so that the vacuum degree in the furnace tube is higher, the fitting degree of the furnace door can be enhanced, and the leakage rate of the furnace tube is lower. In this way, it can be ensured that the tunneling oxide layer and the polycrystalline silicon layer are formed in a stable environment. Therefore, the TOPCon battery preparation method based on the LPCVD process can effectively improve the battery performance.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to a method for preparing a TOPCon cell based on a LPCVD process. Background Art

[0002] TOPCon is a battery structure with high conversion efficiency, and is gradually becoming the mainstream technology in the solar cell industry. TOPCon batteries include an N-type silicon substrate, and an ultra-thin tunneling oxide layer and a polysilicon layer are formed on the back of the substrate, which together constitute a passivation contact structure. At present, the pre-treated silicon wafer is generally sent into the furnace tube, and after vacuuming and heating, oxygen is introduced to oxidize the tunneling oxide layer, and then the LPCVD process is used to form the polysilicon layer. However, in actual production, it is found that the thickness of the tunneling oxide layer is difficult to accurately control and the quality is difficult to guarantee, which affects the performance of the battery. Summary of the invention

[0003] Based on this, it is necessary to provide a TOPCon battery preparation method based on LPCVD process that can improve battery performance in response to the above problems.

[0004] A method for preparing a TOPCon battery based on an LPCVD process comprises the following steps:

[0005] Place the silicon substrate into the furnace tube and close the furnace door;

[0006] Performing a first vacuuming operation on the interior of the furnace tube;

[0007] Heating the furnace tube until the interior of the furnace tube reaches a desired process temperature;

[0008] Performing a first constant temperature operation on the furnace tube, and performing a second vacuuming operation on the furnace tube during the constant temperature process;

[0009] Performing leak detection on the furnace tube;

[0010] Performing a second constant temperature operation on the furnace tube;

[0011] Passing oxygen into the furnace tube to oxidize the surface of the silicon substrate to form a tunneling oxide layer;

[0012] A polysilicon layer is deposited on the surface of the tunnel oxide layer by using an LPCVD process.

[0013] In one embodiment, the vacuuming rate of the second vacuuming operation on the furnace tube is lower than the vacuuming rate of the first vacuuming operation.

[0014] In one embodiment, the constant temperature time of the first constant temperature operation on the furnace tube is longer than the constant temperature time of the second constant temperature operation on the furnace tube.

[0015] In one embodiment, the constant temperature time for the first constant temperature operation of the furnace tube is 350 seconds, and the constant temperature time for the second constant temperature operation of the furnace tube is 300 seconds.

[0016] In one embodiment, the thickness of the tunnel oxide layer is 1 nanometer to 2 nanometers.

[0017] In one embodiment, the thickness of the polysilicon layer is 50 nanometers to 200 nanometers.

[0018] In one embodiment, in the step of introducing oxygen into the furnace tube to oxidize the surface of the silicon substrate to form a tunneling oxide layer, the pressure of the oxygen in the furnace tube is lower than the normal pressure outside the furnace tube.

[0019] In one of the embodiments, between the step of introducing oxygen into the furnace tube to oxidize the surface of the silicon substrate to form a tunneling oxide layer and the step of depositing a polysilicon layer on the surface of the tunneling oxide layer using an LPCVD process, there is also a step of introducing nitrogen into the furnace tube for purging.

[0020] In one of the embodiments, in the step of depositing a polysilicon layer on the surface of the tunnel oxide layer using the LPCVD process, multiple reaction gases are blown into the furnace tube from multiple directions.

[0021] In one of the embodiments, in the step of depositing a polysilicon layer on the surface of the tunnel oxide layer using an LPCVD process, silane is introduced into the furnace tube as a reaction gas.

[0022] In the above-mentioned TOPCon battery preparation method based on the LPCVD process, after the first vacuuming operation and the temperature raising operation are performed on the furnace tube, the first constant temperature operation is first performed, and the furnace tube is vacuumed for the second time during the constant temperature process. In this way, the vacuuming time before oxygen is introduced into the furnace tube will be increased, so the impurity gas in the furnace tube can be cleaned more cleanly, thereby ensuring the quality of the tunneling oxide layer formed by oxidation. Moreover, since the vacuuming time is increased, the vacuum degree inside the furnace tube is higher, so the fit of the furnace door can be enhanced, so that the leakage rate of the furnace tube is lower. In this way, it can be ensured that the tunneling oxide layer and the polysilicon layer are formed in a stable environment. Therefore, the above-mentioned TOPCon battery preparation method based on the LPCVD process can effectively improve the battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a schematic flow chart of a method for preparing a TOPCon battery based on the LPCVD process in one embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0026] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply 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 understood as limiting the present invention.

[0027] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0028] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0030] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0031] See also Figure 1 , a TOPCon cell preparation method based on LPCVD process in one embodiment of the present invention includes steps S110 to S180. Among them:

[0032] Step S110, placing the silicon substrate into the furnace tube and closing the furnace door.

[0033] The silicon substrate can be an N-type silicon wafer or a P-type silicon wafer. Before the silicon substrate is sent into the furnace tube, it is generally necessary to pre-treat the silicon substrate. For example, the silicon substrate is cleaned to remove surface pollutants and oxide layers, and chemical treatment (such as RCA cleaning) is used to ensure that the surface of the silicon substrate is clean, so as to prepare for subsequent processes.

[0034] Step S120, performing a first vacuum operation on the interior of the furnace tube.

[0035] Specifically, the furnace tube is connected to an exhaust pipeline, and the exhaust pipeline is connected to a vacuum pumping device. By opening the valve on the exhaust pipeline and turning on the vacuum pumping device, the interior of the furnace tube can be vacuumed. Most of the air inside the furnace tube can be evacuated through the first vacuum pumping operation, thereby forming a negative pressure in the furnace tube. Usually, the first vacuum pumping has a faster exhaust rate and a shorter exhaust time. For example, in one embodiment, the exhaust time of the first vacuum pumping operation is 180 seconds.

[0036] Step S130, heating the furnace tube until the interior of the furnace tube reaches a desired process temperature.

[0037] Specifically, the heating can be performed by the electric heating tube built into the furnace tube, and the process temperature is generally between 500°C and 600°C. The heating operation generally adopts a slow heating method to make the temperature distribution inside the furnace tube as uniform as possible, so the heating operation generally takes a long time. For example, in one embodiment, the heating time of the heating operation is 660 seconds. Moreover, after heating the furnace tube, the residual air in the furnace tube can expand, and the internal air pressure will increase slightly, thereby facilitating the subsequent second vacuum operation.

[0038] Step S140, performing a first constant temperature operation on the furnace tube, and performing a second vacuum operation on the furnace tube during the constant temperature process.

[0039] The purpose of constant temperature can be achieved by continuously heating the inside of the furnace tube. The internal temperature of the furnace tube can be stabilized at the process temperature through the first constant temperature operation. Moreover, the second vacuuming operation of the furnace tube during the constant temperature process can increase the vacuuming time of the furnace tube, thereby further extracting the residual air in the furnace tube and improving the vacuum degree in the furnace tube, and the impurity gas in the furnace tube is cleaned more cleanly. Specifically, the second vacuuming operation can be performed in the same way as the first vacuuming operation, or another exhaust pipeline can be set to achieve the second vacuuming operation.

[0040] In this embodiment, the second vacuum pumping operation of the furnace tube has a lower exhaust rate than the first vacuum pumping operation. After the first vacuum pumping operation, the residual gas in the furnace tube is less and the vacuum degree is higher. At this time, the second vacuum pumping operation adopts a slow exhaust method, which can gradually exhaust the residual gas and protect the furnace tube, thereby preventing the furnace tube or the furnace door from being deformed due to excessive exhaust.

[0041] Step S150, leak detection of the furnace tube.

[0042] Specifically, generally, the presence of leakage in the furnace tube is determined by detecting the pressure change per unit time in the furnace tube, and the leakage rate is obtained. The leak detection operation in step S150 is the same as the leak detection method in the existing process, so it will not be described in detail here.

[0043] Moreover, since the second vacuuming operation was performed at the same time as the first constant temperature before the leak detection, the vacuuming time was increased, so the vacuum degree inside the furnace tube was higher, which can also enhance the fit of the furnace door and make the leakage rate of the furnace tube lower. In the actual production process, the proportion of furnace tubes with a leakage rate less than 3 increased from 45% to 89%. In other words, the inside of the furnace tube can maintain a more stable environment, so it can ensure that the subsequent tunneling oxide layer and polysilicon layer are formed in a more stable environment.

[0044] Step S160, performing a second constant temperature operation on the furnace tube.

[0045] The second constant temperature operation can be implemented in the same way as the first constant temperature operation, which can compensate for the heat damaged during the leak detection process so that the internal temperature of the furnace tube is stabilized at the process temperature. During the second constant temperature operation, the furnace tube is not evacuated. Due to the first constant temperature operation, the duration of the second constant temperature operation can be significantly shortened, which is conducive to improving efficiency.

[0046] Specifically, in one embodiment, the first constant temperature operation duration of the furnace tube is longer than the second constant temperature operation duration of the furnace tube. In order to maintain the furnace tube at the process temperature, the total constant temperature duration is substantially fixed, and by increasing the proportion of the first constant temperature operation duration in the total constant temperature duration, the vacuuming duration can be increased.

[0047] Further, in one embodiment, the constant temperature time for the first constant temperature operation on the furnace tube is 350 seconds, and the constant temperature time for the second constant temperature operation on the furnace tube is 300 seconds.

[0048] Step S170, introducing oxygen into the furnace tube to oxidize the surface of the silicon substrate to form a tunneling oxide layer.

[0049] By introducing oxygen into the furnace tube that forms a high-temperature environment, the surface of the silicon substrate can be quickly oxidized, and a tunneling oxide layer can be obtained by thermal oxidation. The chemical composition of the tunneling oxide layer is SiO 2 , its thickness is uniform and dense. Due to the two vacuuming operations, the impurity gas in the furnace tube is cleaned more cleanly, thus ensuring the quality of the tunneling oxide layer formed by oxidation.

[0050] Specifically in this embodiment, the thickness of the tunneling oxide layer is 1 nanometer to 2 nanometers. If the thickness of the tunneling oxide layer is too thin, too many pinholes may be generated, thereby reducing the passivation effect and increasing carrier recombination. On the contrary, if the thickness of the tunneling oxide layer is too thick, it will hinder the effective tunneling of electrons and affect the collection of current. The tunneling oxide layer with a thickness of 1 nanometer to 2 nanometers can take into account both reliability and electron tunneling requirements.

[0051] In one embodiment, in the above step S170, the pressure formed by the oxygen introduced into the furnace tube is lower than the normal pressure outside the furnace tube. When oxygen is introduced into the furnace tube, sufficient oxygen is not introduced to raise the pressure inside the furnace tube to the same as the external atmospheric pressure, but rather to maintain a slightly negative pressure environment inside the furnace tube.

[0052] In this way, excessive oxidation reaction caused by excessive oxygen concentration can be avoided, and the oxidation reaction can be carried out under relatively stable conditions, thereby improving the quality and stability of the tunneling oxide layer. In addition, since the air pressure inside the furnace tube will not gradually return to normal pressure, and a large amount of hot air flow will not be generated passing through the furnace door and the sealing ring, the impact and damage of the hot air flow on the furnace door can be avoided, which helps to further improve the stability of the internal environment of the furnace tube.

[0053] Step S180: using LPCVD process to deposit a polysilicon layer on the surface of the tunnel oxide layer.

[0054] After the tunnel oxide layer is obtained, the residual oxygen is extracted and the reaction gas is introduced to achieve the deposition of the polysilicon layer. Specifically, the reaction gas used for deposition can be silane (SiH 4 ), the gas pressure inside the furnace tube is low pressure (tens to hundreds of Pa), so that a polysilicon layer with uniform thickness and density is gradually deposited on the surface of the tunnel oxide layer.

[0055] Specifically, in one embodiment, the thickness of the polysilicon layer is 50 nanometers to 200 nanometers.

[0056] In one embodiment, in the above step S180, multiple reaction gases are blown into the furnace tube from multiple directions. By dividing the reaction gas into multiple paths and blowing them into the furnace tube from multiple different directions, the reaction gas can be more evenly distributed inside the furnace tube, thereby helping to improve the uniformity of the deposited polysilicon layer.

[0057] In addition, in one embodiment, between the above step S170 and step S180, there is also a step of introducing nitrogen into the furnace tube for purging.

[0058] Specifically, high purity nitrogen (N 2 ) is used as a purge gas, and its purity is required to reach more than 99.999%, and the purge time is usually tens of seconds to several minutes. Through nitrogen purge, the residual oxygen or other impurity gases in the furnace tube can be effectively discharged, so that the polysilicon layer can be formed in a purer environment, which helps to further improve the quality of the crystalline silicon layer.

[0059] It should be noted that in order to obtain a complete TOPCon cell, after the polysilicon layer is deposited, it is generally necessary to perform steps such as doping, annealing, back passivation and metallization, front texturing and passivation, and front metallization. The above steps are the same as the existing process, so they will not be repeated here.

[0060] In the above-mentioned TOPCon battery preparation method based on the LPCVD process, after the first vacuuming operation and the temperature raising operation are performed on the furnace tube, the first constant temperature operation is first performed, and the furnace tube is vacuumed for the second time during the constant temperature process. In this way, the vacuuming time before oxygen is introduced into the furnace tube will be increased, so the impurity gas in the furnace tube can be cleaned more cleanly, thereby ensuring the quality of the tunneling oxide layer formed by oxidation. Moreover, since the vacuuming time is increased, the vacuum degree inside the furnace tube is higher, so the fit of the furnace door can be enhanced, so that the leakage rate of the furnace tube is lower. In this way, it can be ensured that the tunneling oxide layer and the polysilicon layer are formed in a stable environment. Therefore, the above-mentioned TOPCon battery preparation method based on the LPCVD process can effectively improve the battery performance.

[0061] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a TOPCon battery based on LPCVD process, characterized in that: The following steps are involved: Place the silicon substrate into the furnace tube and close the furnace door; Performing a first vacuuming operation on the interior of the furnace tube; Heating the furnace tube until the interior of the furnace tube reaches a desired process temperature; Performing a first constant temperature operation on the furnace tube, and performing a second vacuuming operation on the furnace tube during the constant temperature process; Performing leak detection on the furnace tube; Performing a second constant temperature operation on the furnace tube; Passing oxygen into the furnace tube to oxidize the surface of the silicon substrate to form a tunneling oxide layer; A polysilicon layer is deposited on the surface of the tunnel oxide layer by using an LPCVD process.

2. The method for preparing a TOPCon battery based on the LPCVD process according to claim 1, characterized in that: The vacuuming rate of the second vacuuming operation on the furnace tube is lower than the vacuuming rate of the first vacuuming operation.

3. The method for preparing a TOPCon battery based on the LPCVD process according to claim 1, characterized in that: The constant temperature time length of the first constant temperature operation on the furnace tube is longer than the constant temperature time length of the second constant temperature operation on the furnace tube.

4. The method for preparing a TOPCon battery based on LPCVD process according to claim 3, characterized in that: The constant temperature time for the first constant temperature operation of the furnace tube is 350 seconds, and the constant temperature time for the second constant temperature operation of the furnace tube is 300 seconds.

5. The method for preparing a TOPCon battery based on LPCVD process according to claim 1, characterized in that: The thickness of the tunnel oxide layer is 1 nanometer to 2 nanometers.

6. The method for preparing a TOPCon battery based on LPCVD process according to claim 1, characterized in that: The thickness of the polysilicon layer is 50 nanometers to 200 nanometers.

7. The method for preparing a TOPCon battery based on LPCVD process according to claim 1, characterized in that: In the step of introducing oxygen into the furnace tube to oxidize the surface of the silicon substrate to form a tunneling oxide layer, the gas pressure formed by introducing oxygen into the furnace tube is lower than the normal pressure outside the furnace tube.

8. The method for preparing a TOPCon battery based on LPCVD process according to claim 1, characterized in that: Between the step of introducing oxygen into the furnace tube to oxidize the surface of the silicon substrate to form a tunneling oxide layer and the step of depositing a polysilicon layer on the surface of the tunneling oxide layer using the LPCVD process, there is also a step of introducing nitrogen into the furnace tube for purging.

9. The method for preparing a TOPCon battery based on LPCVD process according to claim 1, characterized in that: In the step of depositing a polysilicon layer on the surface of the tunnel oxide layer by using the LPCVD process, multiple reaction gases are blown into the furnace tube from multiple directions.

10. The method for preparing a TOPCon battery based on LPCVD process according to claim 1, characterized in that: In the step of depositing a polysilicon layer on the surface of the tunnel oxide layer by using the LPCVD process, silane is introduced into the furnace tube as a reaction gas.

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