Aluminum-doped zinc oxide thin film and method for manufacturing the same

Abstract

The application relates to the technical field of film layers, in particular to an ALD stacked gradient film layer and a passivation process thereof, a to-be-deposited silicon wafer is loaded, put into a boat, vacuumized, preheated at a temperature of 230-250 DEG C, pretreated for a specified time; a reaction cavity is water pretreated; gaseous precursors TMA and H2O are alternately pulsed into the reaction cavity to perform cyclic deposition; the cavity is excessively purged to remove impurities and by-products; the cavity is purged and cooled after deposition; the silicon wafer is discharged and the vacuum cavity is broken; the ALD system upgrading scheme has strong compatibility and can be directly adapted to the existing TOPCon production line transformation; through accurate regulation and control of the TMA / water flow ratio, deposition temperature and pulse time of each layer, the technical pain points that the film layer uniformity is poor, the adhesion is insufficient, the passivation effect and the conductive performance are difficult to be considered in the traditional single film layer ALD process are solved; the passivation quality of the emitter is significantly improved, the interface recombination rate is reduced, the battery conversion efficiency is improved, meanwhile, the film layer uniformity and the process stability meet the mass production requirements.

Description

Technical Field

[0001] This invention relates to the field of film-related technologies, and in particular to an ALD stacked gradient film and its passivation process. Background Technology

[0002] TOPCon cells, as a new generation of high-efficiency photovoltaic cell technology, have become the mainstream development direction of the photovoltaic industry due to their high conversion efficiency, excellent temperature coefficient, and long-term reliability. The passivation film is the core functional layer of a TOPCon cell; its density, passivation effect, and interface compatibility directly determine the cell's interfacial recombination rate, open-circuit voltage, and fill factor. Atomic layer deposition (ALD) technology, with its atomic-level film thickness control precision and excellent three-dimensional conformal coverage capability, has become a key technology for preparing TOPCon cell passivation films. Trimethylaluminum (TMA) and water, as typical precursor combinations, are widely used in the deposition process of alumina-based passivation films.

[0003] Currently, most ALD passivation film preparation processes in TOPCon workshops within the industry employ a single-layer film and fixed process parameters. This involves maintaining constant parameters such as the TMA-to-water flow ratio, deposition temperature, and reaction pressure throughout the deposition process to form a homogeneous single alumina film. While this approach is simple and easy to control in mass production, it has revealed several intractable technical shortcomings in practical applications, as follows: 1. Functional requirements are difficult to balance. A single film layer cannot simultaneously meet the multiple requirements of "high density barrier, efficient passivation, and good interface matching". If high density is pursued to block impurity diffusion, the proportion of TMA and the deposition temperature need to be increased, which will lead to increased internal stress of the film layer and reduced passivation sites. If passivation performance is emphasized and the proportion of TMA is reduced, the film layer density will be insufficient, making it susceptible to moisture erosion during long-term use and affecting the reliability of the battery.

[0004] 2. Poor compatibility between the film layer and subsequent processes. The surface roughness of the film deposited by a single parameter is relatively high, which makes it less compatible with subsequent metallization processes. It can easily increase the metal contact resistance and reduce the cell fill factor. At the same time, the adhesion between the film and the silicon substrate is limited by a single parameter. In the subsequent high-temperature sintering process, problems such as film cracking and peeling are likely to occur, resulting in a decrease in cell yield.

[0005] In summary, the existing ALD passivation film preparation process for TOPCon cells can no longer meet the mass production requirements of high-efficiency and high-reliability TOPCon cells. Designing an ALD coating process with a stacked gradient structure has become an urgent need for the development of the photovoltaic industry. Summary of the Invention

[0006] The purpose of this invention is to provide an ALD stacked gradient film layer and its passivation process to solve the problems mentioned in the background art.

[0007] The technical solution adopted in this invention is: An ALD (Alternating Layer Degradation) layer and its passivation process are disclosed, comprising a multilayer gradient film structure, wherein the multilayer gradient film structure consists of a dense transition layer, a passivation functional layer and an interface matching layer.

[0008] Optionally, the multilayer gradient membrane uses TMA and water as core precursors.

[0009] A passivation process for an ALD (Alternating Layer) multilayer gradient film includes the following steps: S1: loading the silicon wafer to be deposited, feeding it into the boat, evacuating the vacuum, preheating to 230-250°C, and pretreatment for a specified time; S2: water pretreatment in the reaction chamber; S3: cyclic deposition by alternately introducing gaseous precursor TMA and H2O pulses into the reaction chamber; S4: excessive purging of the chamber to remove impurities and byproducts; S5: post-deposition chamber purging and cooling; S6: silicon wafer unloading and vacuum cavity breaking.

[0010] Optionally, in S3, the total number of cycles is 30 to 35.

[0011] Optionally, in S3, the deposition reaches the target thickness range of 4.5 nm to 5.1 nm.

[0012] Optionally, the preprocessing time in S1 is 510 to 580 seconds.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. The ALD system upgrade solution has strong compatibility and can be directly adapted to the transformation of existing TOPCon production lines; 2. Using TMA and water as the core precursors, a multi-layer gradient film structure of "dense transition layer - passivation functional layer - interface matching layer" is constructed. Each layer solves the technical pain points of poor film uniformity, insufficient adhesion, and difficulty in achieving both passivation effect and conductivity in the traditional single-layer ALD process by precisely controlling the TMA / water flow ratio, deposition temperature and pulse time. 3. The quality of emitter passivation is significantly improved, the interfacial recombination rate is reduced, and the battery conversion efficiency is improved. At the same time, the film uniformity and process stability meet the requirements for mass production. Detailed Implementation

[0014] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship shown, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0015] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0016] Example 1 The conventional single-stage ALD process (without layering design, no water pretreatment / simplified pretreatment) was adopted, with a total of 32 cycles. Other auxiliary / equipment parameters were kept at the industry standard. This was used to compare the effects of water pretreatment and layered circulation stacking design on passivation effect and membrane quality.

[0017] Experimental group: The specific process steps have been described in the technical solution. During the experiment, the preheating temperature, preheating time, and TMA flow rate were designed to be consistent with the control group (preheating temperature 230–250 ℃, pretreatment time 510–580 seconds). The pulse time and process flow rate of the water treatment were adjusted, and the following gradient verification was performed:

[0018] I. Film Thickness Comparison The experimental and control groups were simultaneously verified on the same TOPCon solar cells. After the ALD process, ellipsometry was used to measure five points: the center and four corners. The corner points were taken within 1-2 cm from the edge of the silicon wafer. U% = (max-min) / 2 / Average. The film thickness test data are shown in Table 1 below: Control group - ALD device film thickness data

[0019] Experimental group 1-ALD film thickness data

[0020] Experimental group 2-ALD film thickness data

[0021] Experimental group 3-ALD film thickness data

[0022] Experimental group 4-ALD film thickness data

[0023] II. Efficiency Comparison The experimental and control groups were applied to the same TOPCon solar cells, and the electrical performance data of the TOPCon solar cells were then tested. The specific test data are shown in Table 2 below:

[0024] Tables 1 and 2 present the performance evaluation results of the thin films prepared under the conditions of the embodiments of the present invention and the control. Referring to Table 1, the alumina thin films prepared in the embodiments of the present invention underwent process optimization by adjusting the water pulse time and process flow rate. Using the same amount of TMA, as the number of stacking process cycles increased, a multi-layer gradient film structure of "dense transition layer - passivation functional layer - interface matching layer" was constructed, resulting in higher chemical utilization and more uniform film compared to the control group. Referring to Table 2, it is shown that the alumina prepared by the present invention can achieve a synergistic unity of high film density, excellent passivation effect, and good compatibility with subsequent processes, reducing the interfacial recombination rate of the battery, increasing the open-circuit voltage and fill factor, and improving the overall efficiency of the battery cell.

[0025] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ALD (Alternating Layer) stacked gradient film layer, characterized in that, It includes a multilayer gradient membrane structure, which consists of a dense transition layer, a passivation functional layer, and an interface matching layer.

2. The ALD stacked gradient film layer according to claim 1, characterized in that, The multilayer gradient membrane uses TMA and water as core precursors.

3. A passivation process for an ALD stacked gradient film, wherein the ALD stacked gradient film is described in any one of claims 1-2, characterized in that, Includes the following steps: S1: The silicon wafer to be deposited is loaded into the boat, vacuumed, preheated to 230-250℃, and pretreated for a specified time. S2: Water pretreatment in the reaction chamber; S3: Cyclic deposition is performed by alternately introducing gaseous precursor TMA and H2O pulses into the reaction chamber; S4: Excessive purging of the chamber to remove impurities and byproducts; S5: Post-deposition chamber purging and cooling; S6: Silicon wafer unloading and vacuum breaking chamber.

4. The passivation process for an ALD stacked gradient film layer according to claim 3, characterized in that, In S3, the total number of cycles is 30 to 35.

5. The ALD stacked gradient film layer and its passivation process according to claim 3, characterized in that, In S3, the deposition reaches the target thickness range of 4.5 nm to 5.1 nm.

6. The ALD stacked gradient film layer and its passivation process according to claim 3, characterized in that, The preprocessing time in S1 is 510 to 580 seconds.

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