CN113206002A - Method for preparing high-uniformity ultrathin oxide layer - Google Patents
Method for preparing high-uniformity ultrathin oxide layer Download PDFInfo
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- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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- H01L21/02107—Forming insulating materials on a substrate
- H01L21/02109—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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Abstract
The invention discloses a method for preparing a high-uniformity ultrathin oxide layer, which comprises the steps of loading silicon wafers in a boat, controlling the pressure in a furnace tube to be 300-760 torr after the boat is put into the boat and heated, heating, introducing oxygen after the temperature is stabilized at 400-450 ℃, and carrying out SiO once2Growing, opening a vacuum pump to vacuumize the furnace tube to below 1000mtorr, heating to 500-2Growing, cooling, and taking out the boat to finish the oxidation process. The preparation method of the invention can overcome the defect of SiO in the prior art2Too fast growth and non-uniformity. In the invention, SiO is carried out for a plurality of times according to the growth rule of an oxide layer2Grow in different low-temperature environments, obviously improve SiO2Uniformity of thicknessAnd (4) sex.
Description
Technical Field
The invention relates to the technical field of solar cells, in particular to a method for preparing an ultrathin oxide layer with high uniformity.
Background
High efficiency and low cost are the two most important directions for the research of solar cells. For the crystalline silicon solar cell, along with the improvement of the crystalline silicon manufacturing technology, the service life of a bulk carrier of a substrate silicon wafer is continuously prolonged, and the bulk carrier is no longer a key factor for restricting the improvement of the cell efficiency. The passivation of the cell surface has an increasingly significant effect on the conversion efficiency. In the production process of the solar cell, the cost of the substrate silicon wafer accounts for the highest proportion of the whole production cost, so that the production cost is reduced, the photovoltaic electricity price 'flat-price internet connection' is realized as soon as possible, the market competitiveness is improved, the silicon wafer is thinned to be the necessary trend, and the problem of serious cell surface recombination is generated. This poses a challenge to the surface passivation technology of the solar cell, and the research on the surface passivation technology of the crystalline silicon solar cell is necessary in order to keep the high conversion efficiency of the cell during the thinning process of the silicon wafer. Therefore, the research on the surface passivation technology of the crystalline silicon solar cell is indispensable for improving the conversion efficiency of the solar cell and reducing the production cost of the solar cell.
The tunneling oxide layer passivation contact technology (tunneloxidized passive) is published by the research institute of Germany Fraunhofeise, the structure of the tunneling oxide layer passivation contact technology is composed of an ultrathin oxide layer and a heavily doped polycrystalline silicon layer, selective passing of current carriers can be achieved, many photons can penetrate through the two passivation layers, few photons are blocked, passivation contact of the whole surface of a battery can be achieved, and conversion efficiency of the battery is improved. Cell based on TOPCon structure, Fraunhofer at 4cm2The FZ silicon wafer of (a) obtained a conversion efficiency of 25.7%. Based on mass production, the efficiency of the HBC battery reaches more than 25%, and the open-circuit voltage of the battery reaches more than 720 mV.
However, in practical manufacturing, it is difficult to manufacture an ultra-thin oxide layer with high uniformity and high quality, and a tunneling oxide layer with poor uniformity can greatly reduce the tunneling effect of the solar cell, so that it is very necessary to manufacture an ultra-thin oxide layer with high uniformity.
Disclosure of Invention
In view of the above, the present invention provides a method for preparing an ultra-thin oxide layer with high uniformity to overcome the defects of the prior art.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for preparing a highly uniform ultra-thin oxide layer, comprising the steps of:
(1) loading the silicon wafer with the polished surface into a boat, pushing the boat into an oxidation device with the internal temperature of 400-;
(2) the temperature is stabilized at 400 ℃ and 450 ℃, and O is introduced2Carrying out the first SiO2Growing;
(3) after the step (2) is finished, vacuumizing to enable the pressure in the oxidation device to be less than 1000 mtorr;
(4) after the temperature is controlled stably, O is introduced2Carrying out a second SiO2Growing, wherein the temperature control range is 500-600 ℃;
(5) after the oxidation is finished, opening a vacuum pump to enable the atmosphere of the oxidation device to be in a low-pressure state below 100 mtorr;
(6) cooling, breaking vacuum and taking out the boat from the oxidation device;
(7) and taking the silicon wafer off the boat.
Further, in step (1), the pressure is controlled to be 500-.
Further, in the step (2), the pressure is controlled to be 300-760 torr, and O is introduced2The flow range is 5-30slm, and the time is 5-30 minutes.
Further, in the step (2), the pressure is controlled to be 450-650 torr, and O is introduced2The flow range is 10-20slm, and the time is 10-20 minutes.
Further, in the step (3), the pressure in the oxidation device is less than 100 mtorr.
Further, in the step (4), O is introduced2The flow range is 5-30slm, and the holding time is 2-30 minutes.
Further, in the step (4), the temperature control range is 500-.
Further, in the step (4), O is introduced2The flow range is 10-20slm, and the holding time is 3-10 minutes.
Further, in the step (6), the temperature is reduced to 400-570 ℃, and the boat is taken out of the oxidation device after vacuum breaking.
Further, in step (6), the temperature is reduced to 500 ℃ and the boat is taken out from the oxidation device after the vacuum is broken.
Furthermore, the number of the single tube carrier slides ranges from 800 to 2800.
The invention has the beneficial effects that:
(1) the invention loads silicon wafers in a boat, controls the pressure in a furnace tube to be 300-760 torr after the boat is put into the boat and heated, heats the furnace tube, introduces oxygen after the temperature is stabilized at 400-2Growing, opening a vacuum pump to vacuumize the furnace tube to below 1000mtorr, heating to 500-2Growing, cooling, and taking out the boat to finish the oxidation process. The preparation method of the invention can overcome the defect of SiO in the prior art2Too fast growth and non-uniformity. In the invention, SiO is carried out for a plurality of times according to the growth rule of an oxide layer2Grow in different low-temperature environments, obviously improve SiO2Uniformity of thickness.
(2) The invention uses a low-pressure low-temperature growth mode to further control the impurity pollution of the ultrathin oxidation tunneling layer of the solar cell, obviously controls the particle pollution in the furnace tube under low pressure, and greatly promotes the growth of a high-quality tunneling passivation layer.
(3) The invention uses low-pressure low-temperature oxidation method, and the process of compacting the initial natural oxide layer is firstly carried out at a low temperature of below 450 ℃. For silicon real surface only
And silicon atoms on the inner surfaces of the left and right natural oxide layers form covalent bonds with atoms in the body and are adjacent to oxygen or silicon atoms in the natural oxide layers. When oxygen atoms have certain kinetic energy and impact the outer surface of the natural oxide layer, the oxygen atoms are captured by free silicon in the natural oxide layer, and the physical process is a densification process of the natural oxide layer. The temperature of the densification process is low, the kinetic energy of oxygen atoms is not enough to continue to be combined with the surface of the bottom layer Si, and the natural oxide layer on the surface of the silicon wafer can be ensured to finish dense growth under sufficient time.The key precondition of forming a good passivation tunneling layer when the natural oxide layer is uniform and compact. Temperature of oxidation>And at 500 ℃, oxygen ions and holes penetrate through the compact layer to reach the silicon interface to grow an oxide medium layer. With the continuous thickening of the oxide layer, the penetration probability of oxygen atoms decreases exponentially, and when the oxygen atoms diffuse inwards and diffuse outwards from the oxide layer to reach dynamic balance, the growth of the oxide layer is in a saturation state. Therefore, the second oxidation is controlled at 500-600 ℃, so that the thickness of the required oxide layer can be accurately and effectively controlled, the saturated state is achieved at the required temperature, the oxide layer in the saturated state grows with better growth consistency, the kinetic energy of O atoms reaches the equilibrium state at the temperature, and the SiO atoms at the temperature are ensured to be in the equilibrium state at the temperature2And (4) growth uniformity. The uniform oxide layer is a good TOPCon solar cell tunneling oxidation passivation layer, the good passivation layer can greatly prolong the minority carrier lifetime of the cell, and the open-circuit voltage and the filling factor of the cell are improved.
(4) The invention provides a method for preparing a high-uniformity ultrathin oxide layer, which is particularly suitable for being used as a tunneling oxidation passivation layer in an N-type solar cell and is beneficial to rapid popularization of a high-quality N-type photovoltaic cell.
Drawings
Fig. 1 is a flow chart of a conventional method for preparing an oxide layer of a solar cell.
Fig. 2 is a flow chart of a method for preparing an oxide layer of a solar cell according to the present invention.
Detailed Description
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, and it should be noted that the detailed description is only for describing the present invention, and should not be construed as limiting the present invention.
Example 1
As shown in fig. 2, the present invention provides a method for preparing an ultra-thin oxide layer with high uniformity, comprising the following steps:
(1) loading the silicon wafer with the polished surface into a quartz boat, pushing the quartz boat into an oxidation furnace quartz tube with the internal temperature of 410 ℃, and then opening a vacuum pump to pump vacuum so that the vacuum atmosphere of the furnace tube is in a low-pressure state of 600 torr;
(2) the temperature was stabilized to 440 ℃ and 20slm (L/min) of O was passed through2Keeping the gas for 15min, and carrying out SiO for the first time2Growing;
(3) after the step (2) is finished, opening a vacuum pump to enable the furnace tube atmosphere to be in a 100mtorr low-pressure state;
(4) heating to 550 ℃, stabilizing and introducing 15slm (L/min) of O2Gas, keeping for 5min, performing SiO for the second time2Growing;
(5) after the oxidation is finished, opening a vacuum pump to enable the furnace tube atmosphere to be in a low-pressure state of 100 mtorr;
(6) cooling and discharging: reducing the temperature to 450 ℃, breaking the vacuum, and taking out the quartz boat from the quartz tube of the oxidation furnace;
(7) unloading the sheet: and taking down the silicon wafer from the quartz boat.
In this embodiment, the number of silicon wafers carried by a single boat is 1800 wafers.
Example 2
As shown in fig. 2, the present invention provides a method for preparing an ultra-thin oxide layer with high uniformity, comprising the following steps:
(1) loading the silicon wafer with the polished surface into a quartz boat, pushing the quartz boat into an oxidation furnace quartz tube with the internal temperature of 400 ℃, and then opening a vacuum pump to enable the vacuum atmosphere of the furnace tube to be in a low-pressure state of 500 torr;
(2) the temperature was stabilized to 430 ℃ and 10slm (L/min) of O was passed through2Gas, keeping for 20min, performing SiO for the first time2Growing;
(3) after the step (2) is finished, opening a vacuum pump to enable the furnace tube atmosphere to be in a low-pressure state of 50 mtorr;
(4) heating to 510 ℃, introducing 10slm of O after stabilization2Gas, keeping for 5min, performing SiO for the second time2Growing;
(5) after the oxidation is finished, opening a vacuum pump to enable the furnace tube atmosphere to be in a low-pressure state of 30 mtorr;
(6) cooling and discharging: reducing the temperature to 500 ℃, breaking the vacuum, and taking out the quartz boat from the quartz tube of the oxidation furnace;
(7) unloading the sheet: and taking down the silicon wafer from the quartz boat.
In this embodiment, the number of silicon wafers carried by a single boat is 2000.
Example 3
As shown in fig. 2, the present invention provides a method for preparing an ultra-thin oxide layer with high uniformity, comprising the following steps:
(1) loading the silicon wafer with the polished surface into a quartz boat, pushing the quartz boat into an oxidation furnace quartz tube with the internal temperature of 400 ℃, and then opening a vacuum pump to enable the vacuum atmosphere of the furnace tube to be in a low-pressure state of 500 torr;
(2) the temperature was stabilized to 450 ℃ and 20slm (L/min) of O was passed through2Gas, keeping for 10min, performing SiO for the first time2Growing;
(3) after the step (2) is finished, opening a vacuum pump to enable the furnace tube atmosphere to be in a low-pressure state of 50 mtorr;
(4) heating to 550 ℃, introducing 10slm of O after stabilization2Gas, keeping for 10min, performing SiO for the second time2Growing;
(5) after the oxidation is finished, opening a vacuum pump to enable the furnace tube atmosphere to be in a low-pressure state of 40 mtorr;
(6) cooling and discharging: reducing the temperature to 400 ℃, breaking the vacuum, and taking out the quartz boat from the quartz tube of the oxidation furnace;
(7) unloading the sheet: and taking down the silicon wafer from the quartz boat.
In this embodiment, the number of silicon wafers carried by a single boat is 1000.
Example 4
A method for preparing a highly uniform ultra-thin oxide layer, comprising the steps of:
(1) loading the silicon wafer with the polished surface into a quartz boat, pushing the quartz boat into an oxidation furnace quartz tube with the internal temperature of 420 ℃, and then opening a vacuum pump to enable the vacuum atmosphere of the furnace tube to be in a low-pressure state of 500 torr;
(2) the temperature was stabilized to 440 ℃ and 25slm (L/min) of O was passed through2Gas, keeping for 10min, performing SiO for the first time2Growing;
(3) after the step (2) is finished, opening a vacuum pump for vacuum pumping to enable the furnace tube atmosphere to be in a low-pressure state of 80 mtorr;
(4) heating to 530 ℃, introducing 25slm of O after stabilization2Gas, keeping for 3min, performing SiO for the second time2Growing;
(5) after the oxidation is finished, opening a vacuum pump to enable the furnace tube atmosphere to be in a low-pressure state of 50 mtorr;
(6) cooling and discharging: reducing the temperature to 400 ℃, breaking the vacuum, and taking out the quartz boat from the quartz tube of the oxidation furnace;
(7) unloading the sheet: and taking down the silicon wafer from the quartz boat.
In this embodiment, the number of silicon wafers carried by a single boat is 1500.
Example 5
In order to confirm the effect of the high-uniformity ultrathin oxide layer, the TOPCon battery efficient tunneling oxide layer doped amorphous silicon passivation monitoring sample is prepared by the method, and the actual effect of the method is represented by testing the minority carrier lifetime of the sample.
The key point of the TOPCon cell is that the contact formed by the ultra-thin silicon oxide and the doped amorphous silicon layer is passivated, so that the good quality amorphous silicon also has a great effect in the TOPCon cell; the TOPCon cell uses high quality ultra-thin silicon oxide and doped polysilicon layer to realize high efficiency passivation and carrier selective collection of the whole back surface. The full-area passivation surface enables no silicon/metal contact interface, which is beneficial to improving Open circuit voltage (Voc), and the full-area collection of carriers can reduce the lifetime sensitivity and is beneficial to improving Fill Factor (FF). In addition, the cell has 1) no need for laser drilling; 2) n-type silicon chips are adopted without optical attenuation; 3) compatible medium-high temperature sintering; 4) strong expansibility of technology and the like.
The preparation of the high-efficiency tunneling oxide layer doped amorphous silicon passivation monitoring sample comprises the following steps:
a. a monocrystalline silicon wafer prepared by a solar-grade N-type Czochralski method with a sample substrate having a thickness of 190 μm and a resistivity of 3-7 omega cm is used;
b. putting the silicon chip into a polishing and cleaning machine, and utilizing HNO3Polishing the surface of the silicon wafer by using/HF mixed solution, and processing the silicon waferThe surface reflectivity is 30-40%;
c. carrying out RCA cleaning on the sample; the RCA cleaning is a conventional method in the prior art, and the RCA cleaning method is not improved;
d. putting the sample obtained in the step (c) into LPCVD equipment, and carrying out high-uniformity tunneling oxide layer growth, wherein the oxide layer growth is prepared by using the method;
e. continuing to perform double-sided doped amorphous silicon growth on the sample after the oxide layer growth is completed, wherein the doped amorphous silicon growth mode is an LPCVD (low pressure chemical vapor deposition) method and PH (potential of hydrogen) is utilized3&SiH4The growth is carried out at low pressure of 500mtorr, and the thickness of the doped amorphous silicon thin film is between 50 and 200 nm. The LPCVD method is conventional in the art and is not modified by the present invention.
f. And finishing the manufacture of the high-efficiency tunneling oxide layer doped amorphous silicon passivation monitoring sample and carrying out minority carrier lifetime test.
The method of the present invention is used to prepare the oxide layer in step d, the specific process is shown in fig. 2, and the specific steps are as described in example 1.
And f, performing characterization test on the sample, wherein the used test equipment is a WCT120 minority carrier lifetime tester.
The minority carrier lifetime is an important parameter for representing the quality of semiconductor materials and devices, and accurate measurement of the minority carrier lifetime can not only judge the quality of the materials, but also guide process adjustment. Minority carriers refer to minority carriers relative to majority carriers. The minority carrier lifetime refers to the average lifetime τ of the non-equilibrium minority carriers, i.e., the time taken for the concentration of the non-equilibrium carriers to decrease to 1/e of the original value.
The value of minority carrier lifetime is determined by a composite mechanism. Recombination can be classified into radiative recombination and non-radiative recombination, and auger recombination, depending on the energy release pattern. Radiative recombination is inevitable with auger recombination, and non-radiative recombination is associated with defects and impurities of the material. Recombination occurs both at the surface and in vivo, and passivation is primarily intended to minimize surface recombination.
The contact passivation formed by the ultrathin silicon oxide and the doped amorphous silicon layer is used for reducing the recombination on the surface of the photovoltaic cell, and the higher the minority carrier lifetime is, the smaller the recombination is, and the higher the cell efficiency is.
The high-efficiency tunneling oxide layer doped amorphous silicon passivation monitoring sample prepared by the invention is tested, and the result is shown in table 3. Table 3 shows that the minority carrier lifetime of the sample prepared by the method can reach more than 2000 mus through testing, and the battery structure has good passivation performance.
Comparative example 1
The conventional method for growing the oxide layer of the solar cell is shown in fig. 1 and comprises the following steps:
(1) loading the silicon wafer with the polished surface into a quartz boat, pushing the quartz boat into an oxidation furnace quartz tube with the internal temperature of 430 ℃, wherein the furnace tube pressure is 760torr normal pressure state;
(2) heating to 630 ℃, introducing 10L/min of O after stabilization2Gas, SiO2Growing and keeping for 10 min;
(3) after the oxidation in the step (2) is finished, cooling and discharging: reducing the temperature to 460 ℃, breaking the vacuum, and taking out the quartz boat from the furnace tube of the oxidation furnace;
(4) unloading the sheet: and taking the silicon wafer off the boat.
Comparative example 2
Preparing a passivation monitoring sample of TOPCon battery tunneling oxide layer doped amorphous silicon, and characterizing the passivation effect of the battery structure under the scheme by testing the minority carrier lifetime of the sample.
The preparation of the passivation monitoring sample of the tunneling oxide layer doped with amorphous silicon comprises the following steps:
A. a monocrystalline silicon wafer prepared by a solar-grade N-type Czochralski method with a sample substrate of 190 μm thickness and a resistivity of 3-7 omega cm is used;
B. putting the silicon chip into a polishing and cleaning machine, and utilizing HNO3Polishing the surface of the silicon wafer by using the/HF mixed solution, wherein the reflectivity of the surface of the silicon wafer after the polishing is 30-40%;
C. carrying out RCA cleaning on the sample; the RCA cleaning is a conventional method in the prior art, and the RCA cleaning method is not improved;
D. putting the sample obtained in the step (C) into LPCVD equipment, and carrying out high-uniformity tunneling oxide layer growth, wherein the oxide layer growth is prepared by using a conventional oxidation method;
E. continuing to perform double-sided doped amorphous silicon growth on the sample after the oxide layer growth is completed, wherein the doped amorphous silicon growth mode is an LPCVD (low pressure chemical vapor deposition) method and PH (potential of hydrogen) is utilized3&SiH4Growth was carried out at a low pressure of 500 mtorr;
F. and finishing the manufacture of the high-efficiency tunneling oxide layer doped amorphous silicon passivation monitoring sample, and performing minority carrier lifetime test by using the WCT 120.
In this comparative example, the method for growing the oxide layer of the conventional solar cell is shown in fig. 1, and the specific steps are as described in comparative example 1. Other conditions during the monitoring of the sample preparation were consistent with example 5. The minority carrier lifetime under this protocol was tested and compared to the test results in example 5, with the comparison results shown in table 4.
Table 2 shows thickness uniformity data of the oxide layers prepared in example 1 and comparative example 1, and table 1 shows thickness data and uniformity data of the silicon wafers at different positions of the boat in example 2; table 3 shows passivation data of the tunnel oxide layer prepared in example 5.
TABLE 1
TABLE 2
TABLE 3
Note: life represents minority carrier Lifetime, J0Representing current density, I-Voc representing open circuit voltage, I-FF representing fill factor,PL indicates the photoluminescence intensity, with higher intensity indicating greater passivation.
TABLE 4
As is apparent from tables 1 and 2, the oxide layers obtained in examples 1-2 were uniform in thickness and the SiO produced was uniform as compared with comparative example 12The film is thin. The thickness uniformity of the oxide layer of the silicon chip (the furnace mouth, the furnace and the furnace tail) is greatly improved. This shows that the preparation method of the invention can overcome the SiO in the prior art2Too fast growth and non-uniformity. In the invention, SiO is carried out for a plurality of times according to the growth rule of an oxide layer2Grow in different low-temperature environments, obviously improve SiO2Uniformity of thickness.
The nature of the low-temperature oxidation growth of the ultrathin oxide layer is compact and growth. From an energy perspective, it should first be dense and then grown, but as the temperature changes, the correspondence between the two changes. Low-temperature oxidation at the temperature of less than 450 ℃, and densification is the main reason for forming the ultrathin dielectric layer; the thickness of the ultrathin medium layer is determined by densification and growth at the temperature of 500-600 ℃; above 600 ℃, the effect of densification on oxide thickness is replaced by growth. This is because the average kinetic energy 3/2kT of oxygen atoms is proportional to the oxidation temperature. If the formed dielectric layer is regarded as a potential barrier, the oxygen atoms can jump over the potential barrier only when the average kinetic energy of the oxygen atoms is larger than the height of the potential barrier, namely the oxygen atoms penetrate through the dielectric layer to reach a silicon interface and then are combined with the silicon atoms to form an oxide layer.
The invention uses low-pressure low-temperature oxidation method, and the process of compacting the initial natural oxide layer is firstly carried out at a low temperature of below 450 ℃. For silicon real surface only
The silicon atoms on the inner surfaces of the left and right native oxide layers form covalent bonds with the atoms in the body and simultaneously with oxygen in the native oxide layer or oxygen in the native oxide layerThe silicon atoms are adjacent. When oxygen atoms have certain kinetic energy and impact the outer surface of the natural oxide layer, the oxygen atoms are captured by free silicon in the natural oxide layer, and the physical process is a densification process of the natural oxide layer. The temperature of the densification process is low, the kinetic energy of oxygen atoms is not enough to continue to be combined with the surface of the bottom layer Si, and the natural oxide layer on the surface of the silicon wafer can be ensured to finish dense growth under sufficient time. A uniform and dense native oxide layer is a key prerequisite for the formation of a good passivation tunneling layer. Temperature of oxidation>And at 500 ℃, oxygen ions and holes penetrate through the compact layer to reach the silicon interface to grow an oxide medium layer. With the continuous thickening of the oxide layer, the penetration probability of oxygen atoms decreases exponentially, and when the oxygen atoms diffuse inwards and diffuse outwards from the oxide layer to reach dynamic balance, the growth of the oxide layer enters a saturated state. Therefore, the second oxidation is controlled at 500-600 ℃, so that the thickness of the required oxide layer can be accurately and effectively controlled, the saturated state is achieved at the required temperature, the oxide layer in the saturated state grows with better growth consistency, the kinetic energy of O atoms reaches the equilibrium state at the temperature, and the SiO atoms at the temperature are ensured to be in the equilibrium state at the temperature2And (4) growth uniformity. The uniform oxide layer is a good TOPCon solar cell tunneling oxidation passivation layer, the good passivation layer can greatly prolong the minority carrier lifetime of the cell, and the open-circuit voltage and the filling factor of the cell are improved.
The invention uses a low-pressure low-temperature growth mode to further control the impurity pollution of the ultrathin oxidation tunneling layer of the solar cell, obviously controls the particle pollution in the furnace tube under low pressure, greatly promotes the growth of a high-quality tunneling passivation layer, prolongs the minority carrier lifetime, and promotes the open-circuit voltage and the filling factor of the cell, as shown in table 3.
The results in table 4 show that the minority carrier lifetime of the sample prepared by the conventional scheme is shorter than that of the sample prepared by the method provided by the invention, and further show that the preparation method provided by the invention is beneficial to the growth of the efficient tunneling oxide layer, the formation of the efficient tunneling oxide layer doped amorphous silicon contact passivation structure and the improvement of the conversion efficiency of contact batteries such as TOPcon.
In conclusion, the invention adopts a low-pressure low-temperature oxidation process to improve the thickness uniformity and repeatability of the ultrathin oxide layer, greatly improves the tunneling passivation layer effect of the N-type solar cell, and is beneficial to large-scale popularization of the novel solar cell.
Particularly, for a novel HBC battery, growth of P & lt + & gt and n & lt + & gt doped amorphous silicon and different annealing processes need to be carried out on the back surface of the battery, and a uniform and stable oxidation process is particularly critical under the process. The doped layers with different properties on the whole surface need to have extremely high thickness consistency of the oxide layer so as to prevent the penetration phenomenon from more serious subsequent treatment, thereby reducing the passivation performance.
It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Claims (10)
1. A method for preparing an ultrathin oxide layer with high uniformity is characterized by comprising the following steps:
(1) loading the silicon wafer with the polished surface into a boat, pushing the boat into an oxidation device with the internal temperature of 400-;
(2) the temperature is stabilized at 400 ℃ and 450 ℃, and O is introduced2Carrying out the first SiO2Growing;
(3) after the step (2) is finished, vacuumizing to enable the pressure in the oxidation device to be less than 1000 mtorr;
(4) after the temperature is controlled stably, O is introduced2Carrying out a second SiO2Growing, wherein the temperature control range is 500-600 ℃;
(5) after the oxidation is finished, opening a vacuum pump to enable the atmosphere of the oxidation device to be in a low-pressure state below 100 mtorr;
(6) cooling, breaking vacuum and taking out the boat from the oxidation device;
(7) and taking the silicon wafer off the boat.
2. The method as claimed in claim 1, wherein the pressure in step (1) is controlled to be 500-.
3. The method of claim 1, wherein in the step (2), the pressure is controlled to be 300-760 torr, and O is introduced into the chamber2The flow range is 5-30slm, and the time is 5-30 minutes.
4. The method as claimed in claim 3, wherein in the step (2), the pressure is controlled to be 450-650 torr, and O is introduced2The flow range is 10-20slm, and the time is 10-20 minutes.
5. The method as claimed in claim 1, wherein the pressure in the oxidation apparatus is less than 100mtorr in step (3).
6. The method for preparing an ultra-thin oxide layer with high uniformity as claimed in claim 1, wherein in the step (4), O is introduced2The flow range is 5-30slm, and the holding time is 2-30 minutes.
7. The method as claimed in claim 1, wherein the temperature control range in step (4) is 500-550 ℃.
8. The method for preparing an ultra-thin oxide layer with high uniformity as claimed in claim 1, wherein in the step (4), O is introduced2The flow range is 10-20slm, and the holding time is 3-10 minutes.
9. The method of claim 1, wherein in the step (6), the temperature is reduced to 400-570 ℃, and the boat is taken out of the oxidation apparatus after vacuum breaking.
10. The method as claimed in claim 9, wherein in step (6), the temperature is reduced to 450-500 ℃, and the boat is taken out from the oxidation apparatus after the vacuum is broken.
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