CN110295358A - A kind of PECVD board saturation process of low EL blackspot - Google Patents

Abstract

The invention discloses a PECVD machine saturation process with low EL black spots, and relates to the field of silicon solar cell manufacturing. The Maya PECVD machine includes an alumina reaction chamber, a silicon nitride reaction chamber, and an alumina reaction chamber. The aluminum oxide film is coated on the surface of the silicon wafer, and the silicon nitride reaction chamber is used for coating the silicon nitride film on the surface of the aluminum oxide film, including the following steps: step 1, vacuum temperature rise treatment; step 2, process temperature parameter setting; step Three, gas flow parameter setting; step four, radio frequency power parameter setting; step five, after the parameter setting of steps two to three is completed, keep the graphite carrier plate continuously entering and leaving the Maya PECVD machine; step six, machine saturation , under the above parameter conditions, saturate the Maya PECVD machine for 1 hour, without affecting the output of the Maya PECVD machine, and reduce the EL black spots and black spots caused by the maintenance of the Maya PECVD machine without changing the equipment.

Description

A PECVD machine saturation process with low EL black spot

technical field

The invention relates to the field of manufacturing silicon solar cells, in particular to a PECVD machine saturation process with low EL black spots.

Background technique

PERC technology, that is, passivated emitter back contact, can greatly reduce the electrical recombination rate of the back surface by forming a passivation layer on the back of the solar cell, form a good internal optical back reflection mechanism, and increase the open circuit voltage and short circuit current of the battery, thereby improving The conversion efficiency of the battery. PERC solar cells have become the mainstream direction of high-efficiency solar cells. The core of the PERC battery is to coat a layer of aluminum oxide film on the back of the silicon wafer, and cover a layer of silicon nitride film on the aluminum oxide film to protect the aluminum oxide film. The function of the PECVD machine is to coat aluminum oxide and silicon nitride films. During the production process, the Maya PECVD machine needs regular maintenance, and the chamber body needs to be saturated after maintenance. After PERC solar cells are screen-printed, EL testing is required for the cells. Cells with normal EL tests are A-grade cells, and cells with abnormal EL tests need to be downgraded. EL black spots and black spots are a type of EL degraded cells, and the number of EL black spots and black spots directly affects the A-level rate of the cells.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, to provide a PECVD machine saturation process with low EL black spots, which does not affect the output of the Maya PECVD machine, and reduces the maintenance of the Maya PECVD machine without the need to modify the equipment. And the EL dark spot black spot problem.

In order to achieve the above object, the technical solution adopted in the present invention is: a PECVD machine saturation process with low EL black spots, carried out in the PECVD reaction chamber, and the PECVD machine includes an alumina reaction chamber and a silicon nitride reaction chamber Chamber, is characterized in that, comprises the following steps:

Step 1: Vacuumizing treatment. After the maintenance of the PECVD machine is completed, vacuumize the cover of each chamber body;

Step 2: Set the saturation process conditions of the machine. Set the process belt speed of the PECVD machine to 185cm/min to 200cm/min, the temperature of the alumina reaction chamber to 400°C to 450°C, and the pressure of the alumina reaction chamber to 0.11-0.14mbar, the temperature of the silicon nitride reaction chamber is set at 300°C, and the pressure of the silicon nitride reaction chamber is set at 0.11-0.14mbar;

Step 3: Set the reaction flow parameters in the machine. The alumina reaction chamber includes the first gas path and the second gas path. Set the nitrous oxide flow rate of the first gas path to 700sccm-900sccm, and the TMA flow rate to 0mg /min, the argon flow rate is set to 0sccm/min, the nitrous oxide flow rate of the second gas path is set to 700sccm~900sccm, the TMA flow rate is set to 0mg/min, and the argon flow rate is set to 0sccm/min;

Step 4: Set the radio frequency power and left and right duty ratio parameters in the machine, set the radio frequency power of the first gas path of the alumina reaction chamber to 2500W-2800W, and the left and right duty ratio of the first gas path of the alumina reaction chamber Set to 6/17 and 6/18 respectively, set the radio frequency power of the second gas path of the alumina reaction chamber to 2500W-2800W, and set the left and right duty ratios of the second gas path of the alumina reaction chamber to 6 respectively /17, 6/18;

Step 5, the machine is saturated. Under the process parameters of steps 2, 3, and 4, keep the graphite carrier plate continuously entering and leaving the PECVD machine, and let the PECVD machine stand for 1 hour.

In order to further optimize the present invention, the following technical solutions can be preferably selected:

Preferably, the PECVD machine adopts a Maya MAIA back-plating machine.

Preferably, the graphite carrier adopts a rectangular graphite carrier with a length of 6 pieces and a width of 4 pieces loaded with a total of 24 silicon chips.

Preferably, the silicon wafer is one of a P-type single crystal silicon wafer or a polycrystalline silicon wafer.

Preferably, in the second step, the process belt speed of the alumina reaction chamber is set to 185 cm/min, the temperature of the alumina reaction chamber is set to 450° C., and the pressure of the alumina reaction chamber is set to 0.14 mbar.

Preferably, in step 3, the nitrous oxide flow rate of the first gas path is set to 800 sccm, the TMA flow rate is set to 0 mg/min, the argon flow rate is set to 0 sccm/min, and the nitrous oxide flow rate of the second gas path is set to 800 sccm, The TMA flow rate was set to 0 mg/min, and the argon flow rate was set to 0 sccm/min.

Preferably, in the step four, the radio frequency power of the first gas path of the alumina reaction chamber is set to 2800W, and the left and right duty ratios of the first gas path of the alumina reaction chamber are set to 6/17 and 6/18 respectively, The radio frequency power of the second gas path of the alumina reaction chamber is set to 2800W, and the left and right duty ratios of the second gas path of the alumina reaction chamber are set to 6/17 and 6/18 respectively.

The beneficial effects of the present invention are:

(1) No need for equipment investment, the Maya PECVD machine is used to produce solar panels, through comprehensive optimization and adjustment of the three process parameters of gas flow, process temperature, and radio frequency power in the alumina cavity, while keeping the graphite carrier without silicon wafers. Entering and exiting the Maya PECVD machine, the problem of the high proportion of EL black spots and black spots in the first order after the maintenance of the PECVD machine can be realized.

(2) The PECVD machine only needs to adjust the process parameters in the alumina cavity. By increasing the radio frequency power, the ionization of the laughing gas is increased, and the cleaning effect of the chamber body is improved; the alumina powder is hygroscopic during the maintenance of the Maya machine. Increase the temperature during the process to reduce the water vapor content of the warehouse during maintenance. At the same time, the graphite carrier plate is continuously fed into and out of the Maya machine, so that the warehouse is continuously filled with nitrogen and vacuumized, and the impurity content in the warehouse is continuously pumped away, so as to achieve Reduce the problem of the high proportion of EL black spots and black spots in the first order after Maya maintenance. Compared with the existing technology, the proportion of EL black spots and black spots produced by the saturated Maya machine bin body of the present invention is reduced by about half, which can actively promote PERC batteries Advanced technological innovation and large-scale production have good economic and social benefits.

Detailed ways

A layer of silicon nitride film is deposited on the surface of the solar cell by PECVD (PlasmaEnhanced Chemical Vapor Deposition) technology. The working principle is that the high-frequency current ionizes the gas containing the constituent atoms of the film to form plasma locally. Plasma with strong chemical activity can easily react to form the desired film on the substrate. It can well reduce the reflection of sunlight on the surface of the silicon wafer and reduce the reflectivity. Before the process, the graphite boat should be saturated, and its function is to deposit a layer of silicon nitride film on the inner wall of the graphite boat, so that the inner wall is in the state of silicon nitride everywhere, which will make the silicon nitride deposition in the graphite boat. The speed tends to be consistent, and the flatness of the inner wall of the graphite boat is consistent. The function of the saturation process is to deposit a layer of silicon nitride film on the inner wall of the graphite boat, so that the inner wall is in the state of silicon nitride everywhere, so that the deposition rate of silicon nitride in the graphite boat tends to be consistent, and the graphite boat The flatness of the inner wall is consistent, and the difference in flatness will make the electric field distribution uneven.

The Maya MAIA back plating machine used in this example has two reaction chambers, one chamber is coated with aluminum oxide film, and the other chamber is coated with silicon nitride film. The Maya machine needs regular maintenance, and the maintenance cycle is 120 hours , during maintenance, it is necessary to open the two chambers to replace the quartz tubes in the chambers and clean up the aluminum oxide and silicon nitride deposited in the chambers. After the maintenance is completed, it is necessary to run the process to saturate the two chambers for about 1 hour to ensure The output silicon wafer efficiency EL and other indicators meet the production line requirements. Normally, the first single silicon wafer (1000 pieces) produced after Maya saturation has a relatively high proportion of EL black spots. , so that the EL black spot of the first single silicon wafer after Maya's maintenance reached the same level as the production line.

The first gas path and the second gas path in the alumina reaction chamber provide laughing gas, TMA, and argon. The laughing gas is nitrous oxide, and the molecular formula is N ₂ 0. After the laughing gas is ionized under the action of radio frequency, it is used for Cleaning of silicon wafer surface. TMA is trimethylaluminum, and its molecular formula is Al(CH ₃ ) ₃ . After ionization, TMA reacts with laughing gas to deposit aluminum oxide film on the surface of silicon wafer. The specific reaction is as follows:

2Al(CH ₃ ) ₃ +3N ₂ 0→Al ₂ O ₃ +3N ₂ +2CH ₄ +C+1/2H ₂

2Al(CH ₃ ) ₃ +5Ar+20N ₂ 0→Al ₂ O ₃ +2CO ₂ +4CO+9H ₂ O+20N ₂ +5Ar

Argon gas Ar is a carrier gas and does not participate in the reaction. When argon gas Ar exists, more laughing gas will be consumed to make TMA react completely.

The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

A PECVD machine saturation process with low EL black spots. The PECVD machine adopts Maya MAIA equipment. The Maya PECVD machine includes an alumina reaction chamber and a silicon nitride reaction chamber. The alumina reaction chamber is used for silicon wafers The surface is coated with an aluminum oxide film, and the silicon nitride reaction chamber is used to coat a silicon nitride film on the surface of the aluminum oxide film, including the following steps:

Step 1: Vacuum heating treatment. After the Maya PECVD machine is maintained, it is necessary to vacuumize and heat up the lids of each chamber.

Step 2: Set the process belt speed of the Maya PECVD alumina reaction chamber to 185cm/min, the chamber temperature to 300°C, the alumina reaction chamber pressure to 0.14mbar, and the silicon nitride reaction chamber temperature to 300°C, the pressure of the silicon nitride reaction chamber is set to 0.14mbar;

Step 3, flow parameter setting, the aluminum oxide chamber of Maya PECVD has two gas paths, the flow rate of the first gas path is 700 sccm, the flow rate of TMA is 400 mg/min, the flow rate of argon gas is 600 sccm/min, and the flow rate of the second gas path is 700 sccm/min. The nitrous oxide flow rate of the gas circuit is 700 sccm, the TMA flow rate is 400 mg/min, and the argon gas flow rate is 600 sccm/min.

Step 4, the radio frequency power of the first air path of the alumina cavity is 2300W, and the left and right duty ratios are 6/17 and 6/18 respectively. The RF power of the second gas path of the alumina cavity is 2300W, and the left and right duty ratios are 6/17 and 6/18 respectively. The pressure during the process was 0.14 mbar.

Step 5. After starting the process, keep the graphite carrier plate continuously entering and exiting the Maya PECVD machine, so that the chamber body is continuously filled with nitrogen and vacuumized, and the impurity content in the chamber body is continuously pumped away, thereby reducing the first EL black spot after Maya maintenance. To solve the problem of high dot ratio, the graphite carrier adopts a rectangular graphite carrier with a length of 6 pieces and a width of 4 pieces loaded with a total of 24 silicon wafers;

Step 6, saturate the machine, under the above parameter conditions, saturate the Maya PECVD machine for 1 hour.

Example 2

Step 1, vacuum heating treatment, after the maintenance of the Maya PECVD machine, it is necessary to carry out the vacuum heating process on the cover of each warehouse body;

Step 2: Set the process belt speed of the Maya PECVD alumina chamber to 185cm/min, the chamber temperature to 350°C, the pressure of the alumina reaction chamber to 0.14mbar, and the temperature of the silicon nitride reaction chamber to 300 ℃, the pressure of the silicon nitride reaction chamber is set to 0.14mbar;

Step 3, flow parameter setting, the aluminum oxide chamber of Maya PECVD has two gas paths, the flow rate of the first gas path is 720sccm, the flow rate of TMA is 300mg/min, the flow rate of argon is 600sccm/min, and the flow rate of the second gas path is 720sccm. The nitrous oxide flow rate of the gas circuit is 700 sccm, the TMA flow rate is 300 mg/min, and the argon gas flow rate is 600 sccm/min;

Step 4, the radio frequency power of the first air path of the alumina cavity is 2500W, and the left and right duty ratios are 6/17 and 6/18 respectively. The RF power of the second gas path of the alumina cavity is 2500W, the left and right duty ratios are 6/17 and 6/18 respectively, and the pressure during the process is 0.14mbar;

Step 5. After starting the process, keep the graphite carrier plate continuously entering and exiting the Maya PECVD machine, so that the chamber body is continuously filled with nitrogen and vacuumized, and the impurity content in the chamber body is continuously pumped away, thereby reducing the first EL black spot after Maya maintenance. To solve the problem of high dot ratio, the graphite carrier adopts a rectangular graphite carrier with a length of 6 pieces and a width of 4 pieces loaded with a total of 24 silicon wafers;

Step 6, saturate the machine, under the above parameter conditions, saturate the Maya PECVD machine for 1 hour.

Example 3

A PECVD machine saturation process with low EL black spots. The PECVD machine adopts Maya MAIA equipment. The Maya PECVD machine includes an alumina reaction chamber and a silicon nitride reaction chamber. The alumina reaction chamber is used for silicon wafers The surface is coated with an aluminum oxide film, and the silicon nitride reaction chamber is used to coat a silicon nitride film on the surface of the aluminum oxide film, including the following steps:

Step 1: Vacuum heating treatment. After the maintenance of the Maya PECVD machine is completed, the lids of each chamber are vacuumed and heated to set the process parameters, and the process parameters of the silicon nitride cavity remain unchanged;

Step 2: Set the process belt speed of the alumina reaction chamber to 185cm/min, the temperature of the alumina reaction chamber to 350°C, the pressure of the alumina reaction chamber to 0.14mbar, and the temperature of the silicon nitride reaction chamber to 300°C, the pressure of the silicon nitride reaction chamber is set to 0.14mbar;

Step 3, flow parameter setting, the alumina reaction chamber includes a first gas path and a second gas path, the nitrous oxide flow rate of the first gas path is set to 740 sccm, the TMA flow rate is set to 200 mg/min, and the argon gas flow rate is set to For 300sccm/min, the nitrous oxide flow rate of the second gas path is set to 740sccm, the TMA flow rate is set to 200mg/min, and the argon flow rate is set to 300sccm/min;

Step 4, parameter setting of radio frequency power and left and right duty cycle, set the radio frequency power of the first gas path of the alumina reaction chamber to 2600W, and set the left and right duty ratios of the first gas path of the alumina reaction chamber to 6/17 respectively , 6/18, set the radio frequency power of the second gas path of the alumina reaction chamber to 2600W, and set the left and right duty ratios of the second gas path of the alumina reaction chamber to 6/17 and 6/18 respectively;

Step 5. After starting the process, keep the graphite carrier plate continuously entering and exiting the Maya PECVD machine, so that the chamber body is continuously filled with nitrogen and vacuumized, and the impurity content in the chamber body is continuously pumped away, thereby reducing the first EL black spot after Maya maintenance. To solve the problem of high dot ratio, the graphite carrier adopts a rectangular graphite carrier with a length of 6 pieces and a width of 4 pieces loaded with a total of 24 silicon wafers;

Step 6, saturate the machine, under the above parameter conditions, saturate the Maya PECVD machine for 1 hour.

Example 4

A PECVD machine saturation process with low EL black spots. The PECVD machine adopts Maya MAIA equipment. The Maya PECVD machine includes an alumina reaction chamber and a silicon nitride reaction chamber. The alumina reaction chamber is used for silicon wafers The surface is coated with an aluminum oxide film, and the silicon nitride reaction chamber is used to coat a silicon nitride film on the surface of the aluminum oxide film, including the following steps:

Step 1: Vacuum heating treatment. After the maintenance of the Maya PECVD machine is completed, the lids of each chamber are vacuumed and heated to set the process parameters, and the process parameters of the silicon nitride cavity remain unchanged;

Step 2: Set the process belt speed of the alumina reaction chamber to 185cm/min, the temperature of the alumina reaction chamber to 450°C, the pressure of the alumina reaction chamber to 0.14mbar, and the temperature of the silicon nitride reaction chamber to 300°C, the pressure of the silicon nitride reaction chamber is set to 0.14mbar;

Step 3, flow parameter setting, the alumina reaction chamber includes a first gas path and a second gas path, the nitrous oxide flow rate of the first gas path is set to 800 sccm, the TMA flow rate is set to 0 mg/min, and the argon gas flow rate is set to 0sccm/min, the nitrous oxide flow rate of the second gas path is set to 800sccm, the TMA flow rate is set to 0mg/min, and the argon flow rate is set to 0sccm/min;

Step 4, parameter setting of radio frequency power and left and right duty cycle, set the radio frequency power of the first gas path of the alumina reaction chamber to 2800W, and set the left and right duty ratios of the first gas path of the alumina reaction chamber to 6/17 respectively , 6/18, set the radio frequency power of the second gas path of the alumina reaction chamber to 2800W, and set the left and right duty ratios of the second gas path of the alumina reaction chamber to 6/17 and 6/18 respectively;

Step 5. After starting the process, keep the graphite carrier plate continuously entering and exiting the Maya PECVD machine, so that the chamber body is continuously filled with nitrogen and vacuumized, and the impurity content in the chamber body is continuously pumped away, thereby reducing the first EL black spot after Maya maintenance. To solve the problem of high dot ratio, the graphite carrier adopts a rectangular graphite carrier with a length of 6 pieces and a width of 4 pieces loaded with a total of 24 silicon wafers;

Step 6, saturate the machine, under the above parameter conditions, saturate the Maya PECVD machine for 1 hour.

Example 5

A PECVD machine saturation process with low EL black spots. The PECVD machine adopts Maya MAIA equipment. The Maya PECVD machine includes an alumina reaction chamber and a silicon nitride reaction chamber. The alumina reaction chamber is used for silicon wafers The surface is coated with an aluminum oxide film, and the silicon nitride reaction chamber is used to coat a silicon nitride film on the surface of the aluminum oxide film, including the following steps:

Step 1: Vacuum heating treatment. After the maintenance of the Maya PECVD machine is completed, the lids of each chamber are vacuumed and heated to set the process parameters, and the process parameters of the silicon nitride cavity remain unchanged;

Step 2: Set the process belt speed of the alumina reaction chamber to 185cm/min, the temperature of the alumina reaction chamber to 500°C, the pressure of the alumina reaction chamber to 0.14mbar, and the temperature of the silicon nitride reaction chamber to 300°C, the pressure of the silicon nitride reaction chamber is set to 0.14mbar;

Step 3, flow parameter setting, the alumina reaction chamber includes a first gas path and a second gas path, the nitrous oxide flow rate of the first gas path is set to 850 sccm, the TMA flow rate is set to 0 mg/min, and the argon gas flow rate is set to 0sccm/min, the nitrous oxide flow rate of the second gas path is set to 850sccm, the TMA flow rate is set to 0mg/min, and the argon flow rate is set to 0sccm/min;

Step 4, parameter setting of radio frequency power and left and right duty ratio, set the radio frequency power of the first gas path of the alumina reaction chamber to 3000W, and set the left and right duty ratios of the first gas path of the alumina reaction chamber to 6/17 respectively , 6/18, set the radio frequency power of the second gas path of the alumina reaction chamber to 3000W, and set the left and right duty ratios of the second gas path of the alumina reaction chamber to 6/17 and 6/18 respectively;

Step 5. After starting the process, keep the graphite carrier plate continuously entering and exiting the Maya PECVD machine, so that the chamber body is continuously filled with nitrogen and vacuumized, and the impurity content in the chamber body is continuously pumped away, thereby reducing the first EL black spot after Maya maintenance. To solve the problem of high dot ratio, the graphite carrier adopts a rectangular graphite carrier with a length of 6 pieces and a width of 4 pieces loaded with a total of 24 silicon wafers;

Step 6, saturate the machine, under the above parameter conditions, saturate the Maya PECVD machine for 1 hour.

Effect of various parameters on machine saturation:

(1) Reaction chamber temperature: Since the alumina powder attached to the alumina chamber will absorb water vapor during maintenance, the water vapor will decompose into H ions and hydroxyl groups during the operation of the process, and enter the ALOx film layer. After the hydroxyl group is absorbed by ALOx, it will bring Positively charged H ions and negatively charged ALOx form an inward electric field, which affects the back passivation effect of ALOx, resulting in black spots under the EL, which will cause EL black spots and black spots. Raising the temperature is conducive to water vapor evaporation when the saturated process is running. , In this case, it will be drawn out of the chamber body with the vacuum pump. Theoretically, the higher the temperature of the saturation process, the more conducive to the evaporation and discharge of water vapor. Due to the hardware problems of the machine, if the temperature is too high, the heating plate of the machine will be deformed and the stability of the machine will be affected. Therefore, the temperature of the saturation process is not suitable. More than 450 degrees.

(2) Reaction power: The increase in power is more conducive to the ionization of nitrous oxide to generate plasma, but if the power is too high, it will easily cause damage to the sealing ring of the quartz tube. It is not appropriate to exceed 2800W, and the highest value of 2800 is selected as the experimental example.

(3) Nitrous gas flow rate: 1. During the normal process, the reaction between laughing gas and TMA will generate carbon, and the presence of carbon will also cause EL black spots and black spots on the cell. When running a saturated process, laughing gas will oxidize carbon Generated carbon dioxide is exhausted out of the chamber through a vacuum pump. 2. Laughing gas will generate plasma through ionization, and the plasma has a bombardment effect on the impurities attached to the chamber. The impurities will gradually fall off with the bombardment of the plasma, and will also be discharged out of the chamber through the vacuum pump.

(4) The flow rate of TMA and argon is zero: if TMA is fed into the saturated process, it will react with nitrous oxide to produce alumina, which will affect the cleaning effect of nitrous oxide on the chamber body. In addition, TMA exists in the form of liquid under normal pressure, and its When entering the alumina chamber, it is carried in by argon, so if the TMA flow is set to 0, the argon flow also needs to be set to 0.

Experimental content: 5,000 pieces in the previous process were divided into pieces, and re-divided into five 1,000 pieces. After one Maya machine was maintained, the Maya machine was used in Example 1, Example 2, Example 3, Example 4, and Example 5. The bin body is saturated for 1 hour. After the saturation is completed, 1000 pieces are produced. After the production is completed, five 1000 pieces are transmitted to the same path. After screen printing, the proportion of EL black spots and black spots is counted respectively, and the process of the present invention is displayed through 8 times of tracking. Compared with the original process, the proportion of EL black spots and black spots is reduced by about 50%.

Experimental data table 1:

Through the comparison of Example 1, Example 2, Example 3, Example 4, and Example 5, it can be clearly understood that by increasing the temperature, increasing the power, increasing the laughing gas flow, and adjusting the condition that the TMA and argon flow are zero Under this condition, the proportion of EL black spots and black spots can be greatly reduced, and the parameters of embodiment 4 are set to the optimized parameter setting values.

Finally, it should be noted that: the above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it still It is possible to modify the technical solutions recorded in the foregoing embodiments, or to perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. within the spirit and principles of the present invention shall be included in the within the protection scope of the present invention.

Claims (7)

1. a kind of PECVD machine saturation process of low EL dark spot, carry out in PECVD reaction chamber, described PECVD machine comprises aluminum oxide reaction chamber and silicon nitride reaction chamber, is characterized in that, comprises the following steps: Step 1: Vacuum treatment. After the maintenance of the PECVD machine is completed, vacuumize the lids of the alumina reaction chamber and the silicon nitride reaction chamber; Step 2: Set the saturation process conditions of the machine. Set the process belt speed of the PECVD machine to 185cm/min to 200cm/min, the temperature of the alumina reaction chamber to 400°C to 450°C, and the pressure of the alumina reaction chamber to 0.11-0.14mbar, the temperature of the silicon nitride reaction chamber is set at 300°C, and the pressure of the silicon nitride reaction chamber is set at 0.11-0.14mbar; Step 3: Setting the reaction flow parameters in the machine. The alumina reaction chamber includes the first gas path and the second gas path. Set the nitrous oxide flow rate of the first gas path to 700sccm-900sccm, and the TMA flow rate to 0mg /min, the argon flow rate is set to 0sccm/min, the laughing gas flow rate of the second gas path is set to 700sccm~900sccm, the TMA flow rate is set to 0mg/min, and the argon flow rate is set to 0sccm/min; Step 4: Set the radio frequency power and left and right duty ratio parameters in the machine, set the radio frequency power of the first gas path of the alumina reaction chamber to 2500W-2800W, and the left and right duty ratio of the first gas path of the alumina reaction chamber Set to 6/17 and 6/18 respectively, set the radio frequency power of the second gas path of the alumina reaction chamber to 2500W-2800W, and set the left and right duty ratios of the second gas path of the alumina reaction chamber to 6 respectively /17, 6/18; Step 5, the machine is saturated. Under the process parameters of steps 2, 3, and 4, keep the graphite carrier plate continuously entering and leaving the PECVD machine, and let the PECVD machine stand for 1 hour. 2. The PECVD machine saturation process of a kind of low EL black spot according to claim 1, it is characterized in that: the model that described PECVD machine adopts is Maya MAIA back plating machine. 3. the PECVD machine saturation process of a kind of low EL dark spot according to claim 1, it is characterized in that: described graphite support plate adopts the rectangular graphite support plate of long 6 pieces, wide 4 pieces to load 24 silicon wafers altogether . 4. A PECVD machine saturation process with low EL black spots according to claim 3, characterized in that: the silicon wafer is one of a P-type monocrystalline silicon wafer or a polycrystalline silicon wafer. 5. the PECVD machine saturation process of a kind of low EL dark spot according to claim 1, it is characterized in that: in described step 2, the process belt speed of alumina reaction chamber is set as 185cm/min, and alumina reaction The temperature of the chamber is set at 450° C., and the pressure of the alumina reaction chamber is set at 0.14 mbar. 6. The PECVD machine saturation process of a kind of low EL dark spot according to claim 1, it is characterized in that: described step 3 is set as 800sccm, TMA flow rate as 0mg/min with the laughing gas flow rate of the first gas path 1. The argon flow rate is set to 0 sccm/min, the nitrous oxide flow rate of the second gas path is set to 800 sccm, the TMA flow rate is set to 0 mg/min, and the argon gas flow rate is set to 0 sccm/min. 7. The PECVD machine saturation process of a kind of low EL dark spot according to claim 1, it is characterized in that: in described step 4, the radio frequency power of the first gas circuit of alumina reaction chamber is set to 2800W, and alumina The left and right duty ratios of the first gas path of the reaction chamber are set to 6/17 and 6/18 respectively, the radio frequency power of the second gas path of the alumina reaction chamber is set to 2800W, and the second gas path of the alumina reaction chamber The left and right duty ratios of the road are respectively set to 6/17 and 6/18.