Method for improving edge burrs of Poly amorphous silicon film

Abstract

The invention discloses a process structure and a method for improving edge burrs of a Poly amorphous silicon film, and provides a solution without hardware modification aiming at the problem of edge burrs of a silicon wafer caused by blockage of silane particles in an air inlet pipe in an LPCVD (Low Pressure Chemical Vapor Deposition) process in preparation of a POLY layer on the back surface of an N-type TOPCON battery. The deposition temperature is reduced to 615 DEG C from 622 DEG C, the deposition time is prolonged to 1800 S from 1690 S, the optimized LPCVD technological process (including vacuumizing, segmented heating, pre-temperature-stabilizing, gas distribution control, gradient cooling and the like) is matched, the silane deposition rate is reduced, and the service life of a gas inlet pipe and the service life of a furnace pipe are prolonged. According to the process, gas is uniformly distributed by adopting the porous spraying pipe, the edge roughness of the silicon wafer is reduced after detection and adjustment, the film thickness uniformity is improved to + / -2% from + / -5%, the yield is improved by 6-10%, the edge burr problem is effectively solved, and the battery piece efficiency and the production line yield are improved.

Description

Technical Field

[0001] The present invention focuses on the technical field of industrial production data management, and in particular relates to a method for improving edge burrs of a Poly amorphous silicon film. Background Art

[0002] In the field of preparing the POLY layer on the back side of N-type TOPCON cells, the LPCVD process is widely used due to its deposition characteristics. In the existing process, the air intake structure inside the furnace tube is a combination of a straight-through pipe and a single-hole spray pipe. This structure has exposed significant technical defects in long-term use:

[0003] The existing air intake system utilizes a combined "straight-through pipe + single-hole spray" design, with the straight-through pipe responsible for the main airflow and the single-hole spray pipe providing localized air supply. This structure suffers from a naturally uneven flow field: the airflow at the straight-through pipe orifice is distributed in a jet-like pattern, while the gas diffusion range of the single-hole spray pipe is limited. This leads to inherent differences in gas flow velocity at different axial positions of the furnace tube, particularly at the edges of the silicon wafer, which can easily create airflow impact zones.

[0004] During the high-temperature LPCVD deposition process, silane gas undergoes thermal decomposition as it passes through a single-hole spray pipe, producing silicon particles that gradually accumulate at the opening. As the equipment ages, the single hole becomes clogged, reducing the cross-sectional area of ​​the ventilation system and forcing a compensatory increase in the gas flow rate at the through-hole. This sudden change in flow rate disrupts the equilibrium of deposition dynamics, causing abnormal fluctuations in gas concentration and deposition rate at the wafer's edge.

[0005] When the airflow rate at the straight-through nozzle increases abnormally, the adsorption and decomposition processes of silane at the wafer edge become unbalanced: supersaturated silane molecules rapidly deposit at the edge, forming a non-uniform film growth interface. This imbalance in deposition dynamics results in burr-like protrusions at the edge of the film, manifesting as disrupted crystal orientation, increased surface roughness, and the appearance of localized needle-like crystal defects.

[0006] Edge burrs directly impact the quality of TOPCON cell production. On the one hand, the film density in the burr-edged area decreases, leading to an increase in the interface recombination rate and weakening the cell's passivation effect. On the other hand, the irregular edge morphology complicates subsequent processes (such as etching and coating), easily leading to edge cracking or film shedding. Existing solutions involve high hardware modifications and long downtime, while simply adjusting process parameters makes it difficult to balance deposition uniformity and production efficiency, creating a technical bottleneck. Summary of the Invention

[0007] The present invention aims to provide a process method for improving burrs on the edges of silicon wafers caused by a fast deposition rate in an LPCVD tube, thereby improving the uniformity of Poly deposition and appearance consistency, thereby improving production line efficiency and yield.

[0008] The embodiment of the present application provides a process method for improving Poly amorphous silicon film edge burr, which comprises the following steps.

[0009] Step 1: Put the cleaned silicon wafer in the form of a small boat into an LPCVD furnace tube;

[0010] Step 2: Reduce the pressure in the furnace cavity to 10-100 Pa; slowly heat the furnace tube at a heating rate of 3-10 ℃ / min; maintain the target temperature for 10-20 minutes;

[0011] Step 3: introduce high-purity silane, and add nitrogen or argon as a carrier gas; the gas is distributed through a multi-hole spray pipe;

[0012] Step 4: carry out Poly deposition under a pressure of 50-300 Pa;

[0013] Step 5: stop introducing silane, continue vacuumizing; introduce a nitrogen protective atmosphere and gradually cool down;

[0014] Step 6: take out the silicon wafer after the furnace temperature is reduced to a safe range; reduce the deposition temperature from 622 ℃ to 615 ℃, and extend the deposition time from 1690 S to 1800 S.

[0015] In some embodiments of the present application, the multi-hole spray pipe has a hole diameter of 0.5-1 mm and a hole spacing of 10-15 mm.

[0016] In some embodiments of the present application, the silane gas flow is 150-200 sccm, and the nitrogen or argon carrier gas flow is 500-800 sccm.

[0017] In some embodiments of the present application, the temperature rising process is divided into three stages: 10 ℃ / min at 0-300 ℃, 5 ℃ / min at 300-600 ℃, and 3 ℃ / min at 600 ℃ to the target temperature.

[0018] In some embodiments of the present application, the cooling process is divided into two stages: 5 ℃ / min at 615 ℃-400 ℃, and 800 sccm of nitrogen flow; and 3 ℃ / min at 400 ℃-100 ℃, and 1200 sccm of nitrogen flow.

[0019] In some embodiments of the present application, the vacuumizing process is divided into three stages: first reduced to 100 Pa through a mechanical pump, and then to the target vacuum value through a molecular pump, and the pumping time is 8-12 minutes.

[0020] In some embodiments of the present application, the furnace tube axial temperature difference in the pre-stabilization temperature stage is ≤±1.5 ℃, which is monitored in real time through the built-in 5-point thermocouple in the furnace tube.

[0021] In some embodiments of the present application, the nitrogen gas is continuously introduced for 3-5 minutes after the deposition is stopped.

[0022] In some embodiments of the present application, the furnace temperature is less than 80℃ when the wafer is taken out, and a dust-free glove is used for the wafer taking process.

[0023] In some embodiments of the present application, the gas inlet pipe inside the LPCVD furnace tube is a porous spray pipe, which is used to guide the gas to the center of the furnace tube to form a uniform atmosphere.

[0024] The embodiments of the present application have at least the following advantages or benefits:

[0025] The present application adjusts the deposition temperature and prolongs the deposition time. Based on the kinetic characteristics of silane thermal decomposition, the low-temperature environment can avoid over-deposition in the edge area due to the high decomposition rate. Prolonging the deposition time can compensate for the insufficient film thickness caused by low temperature. Through kinetic balance control, the deposition rate of the whole silicon wafer tends to be consistent, fundamentally solving the problem of imbalance of edge deposition rate.

[0026] The present application uses a porous spray pipe to replace the original single-hole + straight pipe structure. After the gas is dispersed through the porous structure, the high-speed impact area of the straight pipe opening can be eliminated, and a symmetrical gas atmosphere field is formed in the center of the furnace tube, ensuring that the gas concentration deviation between the edge and the center of the silicon wafer is reduced, and the deposition uniformity is ensured.

[0027] The method involved in the present application divides the heating process into stages, which can avoid deformation of the furnace tube and silicon wafer due to thermal stress concentration, laying a temperature foundation for uniform deposition. The cooling process uses gradient cooling and is combined with nitrogen protection, which can match the silicon wafer temperature change rate with the film stress release rate, prevent film cracking or silicon wafer bending caused by thermal stress during the cooling stage, and improve the stability of the film structure.

[0028] The present application can ensure the purity of the furnace cavity atmosphere by precise vacuum gradient control, avoiding the interference of residual gas on silane decomposition; nitrogen sweeping can quickly remove residual silane and decomposition by-products, reduce the accumulation of edge particles caused by secondary deposition, and further optimize the surface quality of the film layer.

[0029] The present application reduces the silane deposition rate by optimizing process parameters, which can reduce the deposition amount of silane particles in the gas inlet pipe, prolong the single-hole clogging period, reduce the film accumulation rate on the inner wall of the furnace tube, prolong the furnace tube maintenance period, and reduce the equipment maintenance cost.

[0030] The present application can avoid hardware modification, reduce the modification cost of a single device, and does not affect the production capacity of the production line. At the same time, it is compatible with existing LPCVD equipment, has strong process migration, and can be quickly applied to mass production lines.

[0031] The present invention relates to a method that combines low-temperature, long-term deposition with uniform gas distribution, which can eliminate burr-like protrusions on the edge of a silicon wafer, improve the surface flatness of the film layer, and at the same time improve the consistency of the crystal orientation of the edge film layer, inhibit the disordered growth of columnar crystals, and improve the density of the film layer.

[0032] The optimized Poly film deposition process of the present invention can reduce the edge recombination rate, improve the conversion efficiency of the battery cell, reduce the proportion of edge dark areas in EL detection, and at the same time improve the film uniformity and yield, effectively reduce adverse phenomena such as edge cracking and film shedding, and improve the overall efficiency of the production line. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a schematic diagram of the air intake pipe structure of the equipment involved in the present invention;

[0035] Figure 2 The uniformity data table before the present invention is improved;

[0036] Figure 3 This is the improved uniformity data table of the present invention. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0039] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0040] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprises" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further limitations, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0041] In the description of the embodiments of the present invention, "a plurality of" means at least two.

[0042] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0043] like Figure 1-3 The embodiment of the present invention discloses a process for improving edge burrs of a Poly amorphous silicon film, which comprises the following steps:

[0044] Step 1: Place the cleaned silicon wafer into the LPCVD furnace in a small boat;

[0045] Step 2: Reduce the pressure in the furnace chamber to 10–100 Pa; slowly heat the furnace tube at a heating rate of 3–10°C / min; maintain the target temperature for 10–20 minutes;

[0046] Step 3: High-purity silane is introduced, and nitrogen or argon can be added as a carrier gas, and the gas is distributed through a porous spray pipe;

[0047] Step 4: Poly deposition at a pressure of 50–300 Pa;

[0048] Step 5: Stop introducing silane and continue evacuating; introduce nitrogen protective atmosphere and gradually reduce the temperature;

[0049] Step 6: After the furnace temperature drops to a safe range, remove the silicon wafer; lower the deposition temperature from 622°C to 615°C, and extend the deposition time from 1690S to 1800S.

[0050] In this embodiment, the aperture of the porous spray pipe is 0.5-1 mm, and the hole spacing is 10-15 mm.

[0051] In this embodiment, the flow rate of the silane gas is 150-200 sccm, and the flow rate of the nitrogen or argon carrier gas is 500-800 sccm.

[0052] In this embodiment, the above-mentioned heating process is divided into three stages: the rate is 10°C / min from 0 to 300°C, the rate is 5°C / min from 300 to 600°C, and the rate is 3°C / min from 600°C to the target temperature.

[0053] In this embodiment, the cooling process is divided into two stages: from 615°C to 400°C, the cooling rate is 5°C / min and the nitrogen flow rate is 800 sccm; from 400°C to 100°C, the cooling rate is 3°C / min and the nitrogen flow rate is 1200 sccm.

[0054] In this embodiment, the above vacuuming process is carried out in three stages. First, the pressure is reduced to 100 Pa by a mechanical pump, and then the molecular pump is started to reach the target vacuum value. The vacuuming time is 8-12 minutes.

[0055] In this embodiment, the axial temperature difference of the furnace tube in the pre-temperature stabilization stage is ≤±1.5° C., and is monitored in real time by five thermocouples built into the furnace tube.

[0056] In this embodiment, after stopping the deposition, 1000 sccm of nitrogen gas is continuously introduced for 3-5 minutes.

[0057] In this embodiment, the furnace temperature needs to be less than 80° C. when the slices are taken out of the furnace, and dust-free gloves are used during the process of taking the slices out.

[0058] In this embodiment, the air inlet pipe inside the LPCVD furnace tube is a multi-hole spray pipe, which is used to guide the gas to the center of the furnace tube to form a uniform atmosphere.

[0059] Example 1:

[0060] A process for improving the edge burrs of a Poly amorphous silicon film, comprising the following steps:

[0061] S1. Silicon wafer cleaning:

[0062] Deionized water (resistivity ≥ 18.2 MΩ·cm) was used for ultrasonic cleaning for 15 minutes, and ozone (concentration ≥ 15 mg / m 3 ) passivation treatment for 8 minutes to ensure that the surface particle size is less than 0.5μm.

[0063] S2. Boat loading:

[0064] The silicon wafers were vertically loaded into a 9-hole ceramic-coated boat (Al2O3 coating thickness ≥ 50 μm), with a distance of 15 mm between adjacent silicon wafers and ceramic columns used to support the contact points to avoid metal contamination.

[0065] S3 furnace tube vacuum pumping (PumpDown):

[0066] Three-stage vacuum control:

[0067] First stage vacuuming: Use a rotary vane mechanical pump (model RV-12) to reduce the furnace chamber pressure from atmospheric pressure to 100 Pa within 8 minutes;

[0068] Secondary vacuuming: Start the turbomolecular pump (model TMH-400) and continue to pump to 30 Pa, which takes 4 minutes;

[0069] Vacuum monitoring: A capacitive vacuum gauge (model CDG-522) is used to monitor pressure fluctuations in real time. After stabilization, the error is ≤±1Pa.

[0070] S4: RampUp

[0071] Staged temperature rise control:

[0072] 0-300℃ stage: heating at a rate of 10℃ / min, using a resistance heating wire wrapped around the furnace tube (power density 2.5W / cm 2 )heating;

[0073] 300-600℃ stage: the heating rate is reduced to 5℃ / min, and the auxiliary heating zone in the middle of the furnace tube is started;

[0074] 600-615℃ stage: rate 3℃ / min, closed-loop control through 5-point thermocouples (type K) built into the furnace tube, axial temperature difference ≤±1.5℃

[0075] S5: Pre-temperature stabilization (Soak)

[0076] Temperature uniformity control:

[0077] Maintain at 615°C for 15 minutes. The furnace tube adopts three-stage heating (inlet section, middle section, outlet section). The power deviation of each section is ≤±2%, and is adjusted in real time by the PLC temperature control system (model S7-300).

[0078] S6: Gas Introduction

[0079] Gas delivery system:

[0080] Silane (purity 99.999%) flow rate 180 sccm, controlled by a mass flow meter (model D07-19CM);

[0081] Nitrogen (99.99% purity) carrier gas flow rate 600 sccm was thoroughly mixed with silane in a mixing chamber (volume 500 mL);

[0082] Multi-hole spray pipe structure:

[0083] Made of 316L stainless steel, with a tube diameter of 12mm, it has 20 0.8mm diameter injection holes distributed axially, with a hole spacing of 12mm. The injection direction forms a 30° angle with the axis of the furnace tube to ensure that the gas is evenly distributed to the center area of ​​the furnace tube.

[0084] S7: Low-pressure deposition (Deposition)

[0085] Pressure and time control:

[0086] The furnace chamber pressure was maintained at 150 Pa by adjusting the pneumatic butterfly valve (model V501), the deposition time was 1800 s, and the pressure fluctuation was monitored in real time during the deposition process to be ≤±5 Pa.

[0087] S8: Gas Cut-off

[0088] Purge procedure:

[0089] After stopping the silane introduction, nitrogen purge (flow rate 1000 sccm) was immediately started and continued for 4 minutes. The purge gas was discharged through the exhaust pipe (diameter 25 mm) at the bottom of the furnace tube to ensure that the residual gas was emptied.

[0090] S9: CoolDown

[0091] Gradient cooling scheme:

[0092] 615℃-400℃ stage: cooling rate 5℃ / min, nitrogen flow rate 800sccm, start the furnace tube outer wall air cooling system;

[0093] 400℃-100℃ stage: cooling rate 3℃ / min, nitrogen flow rate increased to 1200sccm, until the furnace temperature stabilizes below 100℃;

[0094] Temperature monitoring: An infrared thermometer (RaytekMX4+) is used to monitor the surface temperature of the silicon wafer in real time.

[0095] S10: Unload

[0096] When the furnace temperature is less than 80°C, open the furnace door. In a Class 100 clean room environment, use silicon carbide tweezers to remove the silicon wafer, avoiding contact with the film surface.

[0097] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above and that the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present application is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A process for improving edge burrs of a Poly amorphous silicon film, characterized in that: The following steps are involved: Step 1: Place the cleaned silicon wafer into the LPCVD furnace in a small boat; Step 2: Reduce the pressure in the furnace chamber to 10–100 Pa; slowly heat the furnace tube at a heating rate of 3–10°C / min; maintain the target temperature for 10–20 minutes; Step 3: High-purity silane is introduced, and nitrogen or argon can be added as a carrier gas, and the gas is distributed through a porous spray pipe; Step 4: Poly deposition at a pressure of 50–300 Pa; Step 5: Stop introducing silane and continue evacuating; introduce nitrogen protective atmosphere and gradually reduce the temperature; Step 6: After the furnace temperature drops to a safe range, remove the silicon wafer; lower the deposition temperature from 622°C to 615°C, and extend the deposition time from 1690S to 1800S.

2. The process according to claim 1, characterized in that: The aperture of the porous spray pipe is 0.5-1 mm, and the hole spacing is 10-15 mm.

3. The process according to claim 1, characterized in that: The flow rate of the silane gas is 150-200 sccm, and the flow rate of the nitrogen or argon carrier gas is 500-800 sccm.

4. The process according to claim 1, characterized in that: The heating process is divided into three stages: the rate is 10°C / min from 0 to 300°C, the rate is 5°C / min from 300 to 600°C, and the rate is 3°C / min from 600°C to the target temperature.

5. The process according to claim 1, characterized in that: The cooling process is divided into two stages: from 615°C to 400°C, the cooling rate is 5°C / min and the nitrogen flow rate is 800sccm; from 400°C to 100°C, the cooling rate is 3°C / min and the nitrogen flow rate is 1200sccm.

6. The process according to claim 1, characterized in that: The vacuuming process is carried out in three stages. First, the pressure is reduced to 100 Pa by a mechanical pump, and then the molecular pump is started to reach the target vacuum value. The vacuuming time is 8-12 minutes.

7. The process according to claim 1, characterized in that: The axial temperature difference of the furnace tube in the pre-temperature stabilization stage is ≤±1.5° C. and is monitored in real time by 5 thermocouples built into the furnace tube.

8. The process according to claim 1, characterized in that: After stopping the deposition, 1000 sccm nitrogen gas was continuously introduced for 3-5 minutes.

9. The process according to claim 1, characterized in that: The oven temperature must be less than 80°C when the slices are taken out of the oven, and dust-free gloves must be used during the slice removal process.

10. The process according to any one of claims 1 to 9, characterized in that: The air inlet pipe inside the LPCVD furnace tube is a multi-hole spray pipe, which is used to guide the gas to the center of the furnace tube to form a uniform atmosphere.

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