CN109786511B - Diffusion method suitable for selective emitter - Google Patents
Diffusion method suitable for selective emitter Download PDFInfo
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- CN109786511B CN109786511B CN201910220247.7A CN201910220247A CN109786511B CN 109786511 B CN109786511 B CN 109786511B CN 201910220247 A CN201910220247 A CN 201910220247A CN 109786511 B CN109786511 B CN 109786511B
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Abstract
The invention discloses a diffusion method suitable for a selective emitter, which comprises multiple depositions and multiple drives, and the temperature in a furnace tube starts to decrease from the second drive of the step to the first drive. The three-step diffusion deposition and driving mode used in the invention enables a PSG layer with high phosphorus concentration to be formed on the surface of the silicon wafer, thereby being beneficial to pushing a phosphorus source in the PSG into the silicon wafer during heavy doping, forming a high-concentration heavy doping area and being beneficial to ohmic contact and improving FF; the relative concentration of the shallow doped region without heavy doping is a little lower, which is beneficial to improving the open-circuit voltage; the gradual cooling drive-in process enables gradient doping to be formed in the silicon wafer, the width of a P-N junction area is widened, the open-circuit voltage is improved, meanwhile, short-wave band spectrums in sunlight corresponding to shallow junctions are large in photon number contained in the spectrums within the range, good blue wave response can be obtained, and therefore the short-circuit current Isc is improved, and the gradual cooling drive-in process enables the square resistance uniformity to be good.
Description
Technical Field
The invention relates to the technical field of solar cell manufacturing, in particular to a diffusion method suitable for a selective emitter.
Background
Solar photovoltaic power generation has become a new industry which is concerned and developed intensively worldwide due to the characteristics of cleanness, safety, convenience, high efficiency and the like. Therefore, in recent years, the production of the crystalline silicon solar cell is rapidly developed, and the demand of the crystalline silicon solar cell in photovoltaic power stations and distributed applications is also very large.
The solar cell is developed in industrialization for more than ten years, the process is gradually matured and optimized, and the diffusion is used as a core step of the manufacturing process, and the improvement of the process directly influences the improvement of the cell efficiency.
At present, for a solar cell formed on the basis of a p-type silicon wafer, the technology for preparing a front surface emitter is mainly POCl3The diffusion method, which has been increasingly bottleneck in technical potential as the need for preparing high sheet resistance emitter increases,although a few manufacturers break through the process of preparing the emitter crystalline silicon battery with the sheet resistance of more than 100 omega/□ at present, the special slurry is expensive, the contact performance is not satisfactory, and the efficiency is not advantageous.
The Selective Emitter technology (Selective Emitter) is presented to solve the problem, and the SE technology is also common at present. Compared with various SE technologies, the development of diffusion processes in the core part is important.
Disclosure of Invention
In view of the above, in order to overcome the defects of the prior art, the present invention aims to provide a diffusion method suitable for a selective emitter, wherein a silicon wafer obtained by the diffusion method can effectively increase an open-circuit voltage and a short-circuit current.
In order to achieve the purpose, the invention adopts the following technical scheme:
a diffusion method for a selective emitter, the diffusion method comprising the steps of:
the method comprises the following steps: first surface deposition
Heating the temperature of the furnace tube to 790-810 ℃, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 400-600sccm, the flow rate of the large nitrogen is 700-900sccm, the flow rate of the oxygen is 500-700sccm, and the gas introduction time is 11-13 min;
step two: first drive in
Heating the temperature of the furnace tube to 870-;
step three: second drive in
Reducing the temperature of the furnace tube to 810-plus 830 ℃, introducing large nitrogen, oxygen and small nitrogen into the furnace tube, and continuously and slowly driving and diffusing the phosphorus source on the surface of the silicon wafer into the silicon wafer to ensure that the phosphorus source is uniformly distributed, wherein the flow rate of the large nitrogen is 1400-plus 1600sccm, the flow rate of the oxygen is 200-plus 400-sccm, the flow rate of the small nitrogen is 400-plus 600-sccm, and the gas introduction time in the furnace tube is 7-9 min;
step four: second deposition
Setting the temperature of the furnace tube to be consistent with the third step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing secondary phosphorus source deposition on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 700-plus-material 900sccm, the flow rate of the small nitrogen is 700-plus-material 900sccm, the flow rate of the oxygen is 400-plus-material 600sccm, and the gas introduction time is 8-11 min;
step five: third drive-in
Reducing the temperature of the furnace tube to 780-plus-800 ℃, and introducing large nitrogen, oxygen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited on the surface of the silicon wafer for the second time is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1400-plus-800 sccm, the flow rate of the oxygen gas is 200-plus-400 sccm, the flow rate of the small nitrogen gas is 400-plus-600 sccm, and the gas introduction time in the furnace tube is 8-10 min;
step six: third deposition
Setting the temperature of the furnace tube to be consistent with the fifth step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing third phosphorus source deposition on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 900-800 sccm, the flow rate of the small nitrogen is 600-800sccm, the flow rate of the oxygen is 200-400sccm, and the gas introduction time is 8-10 min;
step seven: the fourth drive in
Reducing the temperature of the furnace tube to 770-790 ℃, and introducing large nitrogen and small nitrogen gas into the furnace tube to ensure that the phosphorus source deposited for the third time on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen gas is 1400-1600sccm, the flow rate of the small nitrogen gas is 400-600sccm, and the operation time of the step is 4-6 min;
from the second first drive in of said step, the temperature in the furnace tube starts to decrease.
According to some preferred aspects of the present invention, the diffusion method further comprises the step of eight temperature swing gettering: reducing the temperature of the furnace tube to 650 plus 670 ℃, introducing large nitrogen gas and small nitrogen gas into the furnace tube to ensure that the phosphorus source deposited at the last on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, washing impurities in the silicon body into the phosphorosilicate glass, wherein the flow rate of the large nitrogen gas is 1400 plus 1600sccm, the flow rate of the small nitrogen gas is 700 plus 900sccm, and the gas introduction time in the furnace tube is 11-13 min.
According to some preferred aspects of the present invention, the furnace tube temperature at the first drive is lower than the furnace tube temperature at the first deposition, and the furnace tube temperature at the second drive is lower than the furnace tube temperature at the first drive.
Preferably, the set temperature of the furnace tube during the first driving is 870-; the set temperature of the furnace tube during the second driving is 810-; the temperature of the furnace tube during the first driving is uniformly and gradually reduced from 870 ℃ to 890 ℃ to 810 ℃ to 830 ℃.
According to some preferred aspects of the present invention, the furnace tube temperature at the second deposition is the same as the furnace tube temperature at the second drive, and the furnace tube temperature at the third drive is lower than the furnace tube temperature at the second deposition.
Preferably, the furnace set temperature during the third driving is 780-800 ℃, and the furnace temperature during the third driving is uniformly and gradually reduced from 780-800 ℃ to 770-790 ℃.
According to some preferred aspects of the present invention, the furnace tube temperature at the third deposition is the same as the furnace tube temperature at the third drive, and the furnace tube temperature at the fourth drive is lower than the furnace tube temperature at the third deposition.
Preferably, the temperature of the furnace tube during the fourth driving is set to 770-790 ℃, and the temperature of the furnace tube during the fourth driving is uniformly and gradually reduced from 770-790 ℃ to 650-670 ℃.
That is, in the second step, the temperature in the furnace tube is the highest, and from the second step, the temperature in the furnace tube is always decreased.
According to some preferred aspects of the invention, the large nitrogen is a shielding gas filling the furnace tube; the small nitrogen is nitrogen gas passing through a phosphorus oxychloride source bottle, but in the first step, the fourth step and the third stepThe phosphorus oxychloride source bottle is in an open state when deposition is carried out for six times and three times, and then the small nitrogen passes through the POCl3Source bottle and portable POCl3And (4) entering a furnace tube for deposition, wherein the phosphorus oxychloride source bottle in the second step, the third step, the fifth step and the seventh step is in a closed state, namely the small nitrogen does not carry phosphorus source when driving for four times, and the main function of the phosphorus oxychloride source bottle is only to exhaust air remained in the tube and dredge the tube.
Through the first step, the second step, the third step, the fourth step, the fifth step, the sixth step and the seventh step, a PSG layer with high phosphorus concentration is formed on the surface of the silicon wafer, so that a phosphorus source in the PSG is promoted into the silicon wafer during laser doping, and a high-concentration heavily doped region is formed; the gradual cooling drive-in process enables the gradual cooling drive-in process to be formed in the silicon wafer, so that gradient doping is formed in the silicon wafer, the width of a P-N junction area is widened, the open-circuit voltage is improved, short waves can be better absorbed by shallow junctions, short-wave band spectrums in sunlight corresponding to the shallow junctions are large in photon number contained in the spectrums within the range, better blue wave response can be obtained, and therefore short-circuit current is improved.
Compared with the prior art, the invention has the advantages that: the three-step diffusion deposition and driving mode used in the invention enables a PSG layer with high phosphorus concentration to be formed on the surface of the silicon wafer, thereby being beneficial to pushing a phosphorus source in the PSG into the silicon wafer during heavy doping, forming a high-concentration heavy doping area and being beneficial to ohmic contact and improving FF; the relative concentration of the shallow doped region without heavy doping is a little lower, which is beneficial to improving the open-circuit voltage; the gradual cooling drive-in process enables gradient doping to be formed in the silicon wafer, the width of a P-N junction area is widened, open-circuit voltage is improved, meanwhile, sunlight can be better absorbed by shallow junctions, short-wave-band spectrums in the sunlight corresponding to the shallow junctions are large in photon number contained in the spectrums within the range, better blue wave response can be obtained, accordingly, short-circuit current Isc is improved, and the gradual cooling drive-in process enables the square resistance uniformity to be better.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a graph showing the relationship between the diffusion sheet resistance, the surface concentration and the junction depth of the heavily doped region and the lightly doped region in preferred embodiment 1 of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not a whole embodiment. 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.
The invention relates to a diffusion method suitable for a selective emitter, which comprises the following steps:
the method comprises the following steps: first surface deposition
The temperature of the furnace tube is raised to 790-810 ℃, mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride is introduced into the furnace tube, the flow rate of the small nitrogen is 400-600sccm, the flow rate of the large nitrogen is 700-900sccm, the flow rate of the oxygen is 500-700sccm, and the gas introduction time is 11-13 min.
Step two: first drive in
And heating the temperature of the furnace tube to 870-.
Step three: second drive in
And reducing the temperature of the furnace tube to 810-plus 830 ℃, introducing large nitrogen, oxygen and small nitrogen into the furnace tube, and continuously and slowly driving and diffusing the phosphorus source on the surface of the silicon wafer into the silicon wafer to ensure that the phosphorus source is uniformly distributed, wherein the flow rate of the large nitrogen is 1400-plus 1600sccm, the flow rate of the oxygen gas is 200-plus 400sccm, the flow rate of the small nitrogen is 400-plus 600sccm, and the gas introduction time in the furnace tube is 7-9 min.
Step four: second deposition
Setting the temperature of the furnace tube to be consistent with the third step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing secondary phosphorus source deposition on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 700-plus-material 900sccm, the flow rate of the small nitrogen is 700-plus-material 900sccm, the flow rate of the oxygen is 400-plus-material 600sccm, and the gas introduction time is 8-11 min.
Step five: third drive-in
And reducing the temperature of the furnace tube to 780-plus-800 ℃, and introducing large nitrogen, oxygen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited on the surface of the silicon wafer for the second time is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1400-plus-800 sccm, the flow rate of the oxygen gas is 200-plus-400 sccm, the flow rate of the small nitrogen gas is 400-plus-600 sccm, and the gas introduction time in the furnace tube is 8-10 min.
Step six: third deposition
Setting the temperature of the furnace tube to be consistent with the fifth step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing third phosphorus source deposition on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 900-800 sccm, the flow rate of the small nitrogen is 600-800sccm, the flow rate of the oxygen is 200-400sccm, and the gas introduction time is 8-10 min.
Step seven: the fourth drive in
And reducing the temperature of the furnace tube to 770-790 ℃, and introducing large nitrogen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited for the third time on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1400-1600sccm, the flow rate of the small nitrogen is 400-600sccm, and the operation time of the step is 4-6 min.
Step eight: variable temperature gettering
Reducing the temperature of the furnace tube to 650 plus 670 ℃, introducing large nitrogen gas and small nitrogen gas into the furnace tube to ensure that the phosphorus source deposited at the last on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, washing impurities in the silicon body into the phosphorosilicate glass, wherein the flow rate of the large nitrogen gas is 1400 plus 1600sccm, the flow rate of the small nitrogen gas is 700 plus 900sccm, and the gas introduction time in the furnace tube is 11-13 min.
Example 1
The diffusion method for the selective emitter in the embodiment includes the following steps:
the method comprises the following steps: first surface deposition
And (3) heating the furnace tube to 800 ℃, introducing mixed gas consisting of small nitrogen, large nitrogen and oxygen carrying phosphorus oxychloride into the furnace tube, wherein the flow of the small nitrogen is 500sccm, the flow of the large nitrogen is 800sccm, the flow of the oxygen is 600sccm, and the operation time of the steps is 12 min.
Step two: first drive in
And (3) heating the furnace tube to 880 ℃, introducing big nitrogen, oxygen and small nitrogen into the furnace tube, and driving and diffusing the phosphorus source deposited on the surface of the silicon wafer into the silicon wafer under the high-temperature condition, wherein the flow rate of the big nitrogen is 800sccm, the flow rate of the small nitrogen is 500sccm, the flow rate of the oxygen is 300sccm, and the running time of the steps is 10 min.
Step three: second drive in
And (3) reducing the temperature of the furnace tube to 820 ℃, introducing large nitrogen gas, oxygen gas and small nitrogen gas into the furnace tube, and continuously and slowly driving and diffusing the phosphorus source on the surface of the silicon wafer into the silicon wafer to ensure that the phosphorus source is uniformly distributed, wherein the flow rate of the large nitrogen gas is 1500sccm, the flow rate of the oxygen gas is 300sccm, the flow rate of the small nitrogen gas is 500sccm, and the running time of the step is 8 min.
Step four: second deposition
Setting the temperature of the furnace tube to be the same as that in the fourth step, introducing mixed gas consisting of small nitrogen carrying phosphorus oxychloride, large nitrogen and oxygen into the furnace tube again, and performing secondary phosphorus source deposition on the surface of the silicon wafer, wherein the flow of the large nitrogen is 800sccm, the flow of the small nitrogen is 800sccm, the flow of the oxygen is 500sccm, and the operation time of the steps is 10 min.
Step five: third drive-in
And reducing the temperature of the furnace tube to 790 ℃, and introducing large nitrogen, oxygen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited for the second time on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1500sccm, the flow rate of the oxygen is 300sccm, the flow rate of the small nitrogen is 500sccm, and the running time of the step is 9 min.
Step six: third deposition
Setting the temperature of the furnace tube to be the same as that in the step six, introducing mixed gas consisting of small nitrogen carrying phosphorus oxychloride, large nitrogen and oxygen into the furnace tube again, and performing third phosphorus source deposition on the surface of the silicon wafer, wherein the flow of the large nitrogen is 1000sccm, the flow of the small nitrogen is 700sccm, the flow of the oxygen is 300sccm, and the operation time of the step is 9 min.
Step seven: the fourth drive in
And reducing the temperature of the furnace tube to 780 ℃, introducing large nitrogen and small nitrogen into the furnace tube, so that the phosphorus source deposited on the surface of the silicon wafer for the third time is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1500sccm, the flow rate of the small nitrogen is 500sccm, and the running time of the steps is 5 min.
Step eight: variable temperature gettering
And reducing the temperature of the furnace tube to 660 ℃, introducing large nitrogen gas, oxygen gas and small nitrogen gas into the furnace tube, wherein in the process of reducing the temperature, a small amount of impurities in the phosphorus silicon wafer are sucked into the phosphorus silicon glass on the surface of the silicon wafer, the flow rate of the large nitrogen gas is 1500sccm, the flow rate of the small nitrogen gas is 800sccm, the flow rate of the oxygen gas is 500sccm, and the operation time of the steps is 12 min.
That is, in the second step, the temperature in the furnace tube is the highest, and from the second step, the temperature in the furnace tube is always decreased.
The large nitrogen is protective gas filling the furnace tube; the small nitrogen is nitrogen passing through the phosphorus oxychloride source bottle, but the phosphorus oxychloride source bottle is in an open state when the small nitrogen passes through the POCl during the first step, the fourth step and the sixth step for deposition3Source bottle and portable POCl3And (4) entering a furnace tube for deposition, wherein the phosphorus oxychloride source bottle in the second step, the third step, the fifth step and the seventh step is in a closed state, namely the small nitrogen does not carry phosphorus source when driving for four times, and the main function of the phosphorus oxychloride source bottle is only to exhaust air remained in the tube and dredge the tube.
Through the first step, the second step, the third step, the fourth step, the fifth step, the sixth step and the seventh step, a PSG layer with high phosphorus concentration is formed on the surface of the silicon wafer, so that a phosphorus source in the PSG is promoted into the silicon wafer during laser doping, and a high-concentration heavily doped region is formed; the gradual cooling drive-in process enables the gradual cooling drive-in process to be formed in the silicon wafer, so that gradient doping is formed in the silicon wafer, the width of a P-N junction area is widened, the open-circuit voltage is improved, short waves can be better absorbed by shallow junctions, short-wave band spectrums in sunlight corresponding to the shallow junctions are large in photon number contained in the spectrums within the range, better blue wave response can be obtained, and therefore short-circuit current is improved.
Example 2
The diffusion method for the selective emitter in the embodiment includes the following steps:
the method comprises the following steps: first surface deposition
And heating the furnace tube to 790 ℃, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 400sccm, the flow rate of the large nitrogen is 700sccm, the flow rate of the oxygen is 500sccm, and the gas introduction time is 11 min.
Step two: first drive in
And (3) heating the furnace tube to 870 ℃, introducing large nitrogen, oxygen and small nitrogen into the furnace tube, and driving and diffusing the phosphorus source deposited on the surface of the silicon wafer into the silicon wafer at a high temperature, wherein the flow rate of the large nitrogen is 700sccm, the flow rate of the oxygen is 200sccm, the flow rate of the small nitrogen is 400sccm, and the gas introduction time in the furnace tube is 9 min.
Step three: second drive in
And reducing the temperature of the furnace tube to 810 ℃, introducing large nitrogen, oxygen and small nitrogen into the furnace tube, and continuously and slowly driving and diffusing the phosphorus source on the surface of the silicon wafer into the silicon wafer to ensure that the phosphorus source is uniformly distributed, wherein the flow rate of the large nitrogen is 1400sccm, the flow rate of the oxygen gas is 200sccm, the flow rate of the small nitrogen gas is 400sccm, and the gas introduction time in the furnace tube is 7 min.
Step four: second deposition
And (3) setting the temperature of the furnace tube to be consistent with the third step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing secondary phosphorus source deposition on the surface of the silicon wafer, wherein the flow of the large nitrogen is 700sccm, the flow of the small nitrogen is 700sccm, the flow of the oxygen is 400sccm, and the gas introduction time is 8 min.
Step five: third drive-in
And reducing the temperature of the furnace tube to 780 ℃, introducing large nitrogen, oxygen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited on the surface of the silicon wafer for the second time is more uniformly distributed on the surface of the silicon wafer, wherein the flow of the large nitrogen is 1400sccm, the flow of the oxygen is 200sccm, the flow of the small nitrogen is 400sccm, and the gas introduction time in the furnace tube is 8 min.
Step six: third deposition
And setting the temperature of the furnace tube to be consistent with the fifth step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing third phosphorus source deposition on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 900sccm, the flow rate of the small nitrogen is 600sccm, the flow rate of the oxygen is 200sccm, and the gas introduction time is 8 min.
Step seven: the fourth drive in
And reducing the temperature of the furnace tube to 770 ℃, and introducing large nitrogen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited on the surface of the silicon wafer for the third time is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1400sccm, the flow rate of the small nitrogen is 400sccm, and the running time of the step is 4 min.
Step eight: variable temperature gettering
And reducing the temperature of the furnace tube to 650 ℃, introducing large nitrogen gas and small nitrogen gas into the furnace tube to ensure that the phosphorus source deposited at the last on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, washing impurities in the silicon body into the phosphorosilicate glass, wherein the flow rate of the large nitrogen gas is 1400sccm, the flow rate of the small nitrogen gas is 700sccm, and the gas introduction time in the furnace tube is 11 min.
Example 3
The diffusion method for the selective emitter in the embodiment includes the following steps:
the method comprises the following steps: first surface deposition
Heating the furnace tube to 810 ℃, introducing mixed gas consisting of big nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 600sccm, the flow rate of the big nitrogen is 900sccm, the flow rate of the oxygen is 700sccm, and the gas introduction time is 13 min.
Step two: first drive in
And (3) heating the furnace tube to 890 ℃, introducing large nitrogen, oxygen and small nitrogen into the furnace tube, and driving and diffusing the phosphorus source deposited on the surface of the silicon wafer into the silicon wafer under the high-temperature condition, wherein the flow rate of the large nitrogen is 900sccm, the flow rate of the oxygen gas is 400sccm, the flow rate of the small nitrogen gas is 600sccm, and the gas introduction time in the furnace tube is 11 min.
Step three: second drive in
And reducing the temperature of the furnace tube to 830 ℃, introducing large nitrogen, oxygen and small nitrogen into the furnace tube, and continuously and slowly driving and diffusing the phosphorus source on the surface of the silicon wafer into the silicon wafer to ensure that the phosphorus source is uniformly distributed, wherein the flow rate of the large nitrogen is 1600sccm, the flow rate of the oxygen gas is 400sccm, the flow rate of the small nitrogen gas is 600sccm, and the gas introduction time in the furnace tube is 9 min.
Step four: second deposition
And (3) setting the temperature of the furnace tube to be consistent with the third step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing secondary phosphorus source deposition on the surface of the silicon wafer, wherein the flow of the large nitrogen is 900sccm, the flow of the small nitrogen is 900sccm, the flow of the oxygen is 600sccm, and the gas introduction time is 11 min.
Step five: third drive-in
And reducing the temperature of the furnace tube to 800 ℃, introducing big nitrogen, oxygen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited for the second time on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the big nitrogen is 1600sccm, the flow rate of the oxygen gas is 400sccm, the flow rate of the small nitrogen gas is 600sccm, and the gas introduction time in the furnace tube is 10 min.
Step six: third deposition
And setting the temperature of the furnace tube to be consistent with the fifth step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing third phosphorus source deposition on the surface of the silicon wafer, wherein the flow of the large nitrogen is 1100sccm, the flow of the small nitrogen is 800sccm, the flow of the oxygen is 400sccm, and the gas introduction time is 10 min.
Step seven: the fourth drive in
And reducing the temperature of the furnace tube to 790 ℃, introducing large nitrogen and small nitrogen into the furnace tube, so that the phosphorus source deposited on the surface of the silicon wafer for the third time is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1600sccm, the flow rate of the small nitrogen is 600sccm, and the operation time of the steps is 6 min.
Step eight: variable temperature gettering
And reducing the temperature of the furnace tube to 670 ℃, introducing large nitrogen gas and small nitrogen gas into the furnace tube to ensure that the phosphorus source deposited at the last on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, washing impurities in the silicon body into the phosphorosilicate glass, wherein the flow rate of the large nitrogen gas is 1600sccm, the flow rate of the small nitrogen gas is 900sccm, and the gas introduction time in the furnace tube is 13 min.
Comparative example 1
The method comprises the following steps: deposition of
Setting the temperature in the furnace tube to 785 ℃, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 1000sccm, the flow rate of the large nitrogen is 750sccm, the flow rate of the oxygen is 500sccm, and the gas introduction time is 15 min.
Step two: step of constant temperature
And (3) introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen without phosphorus oxychloride into the furnace tube at constant temperature, wherein the flow rate of the small nitrogen is 1000sccm, the flow rate of the large nitrogen is 800sccm, the flow rate of the oxygen is 200sccm, and the gas introduction time is 2 min.
Step three: first drive in
And raising the temperature of the furnace tube to 845 ℃, introducing mixed gas of big nitrogen and small nitrogen which does not carry phosphorus oxychloride into the furnace tube, wherein the flow of the big nitrogen is 800sccm, the flow of the small nitrogen is 1000sccm, and the gas introduction time is 2 min.
The process time is 6 min.
Step four: first oxidation
And (3) introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen without phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 500sccm, the flow rate of the large nitrogen is 400sccm, the flow rate of the oxygen is 200sccm, and the gas introduction time is 5 min.
Step five: second oxidation
And (3) introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen without phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 500sccm, the flow rate of the large nitrogen is 400sccm, the flow rate of the oxygen is 280sccm, and the gas introduction time is 7 min.
Step six: second drive in
And reducing the temperature in the furnace tube to 780 ℃, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen without phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 500sccm, the flow rate of the large nitrogen is 1000sccm, the flow rate of the oxygen is 600sccm, and the gas introduction time is 10 min.
Example 4 results and discussion
(1) The diffusion sheet resistance, surface concentration and junction depth of the heavily doped region and the lightly doped region obtained by the diffusion process of the invention in combination with the selective emitter process are shown in figure 1.
FIG. 1 shows that heavily doped regions and lightly doped regions have different concentrations and junction depths, and the high concentration and junction depth of the heavily doped regions facilitate contact and improve FF; the concentration of the shallow doped region is slightly lower than that of the heavily doped region, so that the open voltage is favorably improved; the driving process of gradually reducing the temperature of the concentration enables gradient doping to be formed in the silicon wafer, the width of a P-N junction area is widened, the open-circuit voltage is improved, meanwhile, the shallow junction can better absorb sunlight, the spectrum of the short wave band in the sunlight corresponding to the shallow junction contains more photons, and better blue wave response can be obtained, so that the short-circuit current Isc is improved, and the driving process of gradually reducing the temperature enables the square resistance uniformity to be better.
(2) The results of the tests performed on the battery pieces manufactured in the examples and the battery pieces manufactured in the conventional process of the first comparative example are shown in the following table:
TABLE 1 test results
| Group | Uoc(V) | Isc(A) | Rs(Ω) | Rsh(Ω) | FF(％) | Eta(％) |
| Example 1 | 0.6746 | 9.795 | 0.0005 | 0.0005 | 82.141 | 22.216 |
| Comparative example 1 | 0.6682 | 9.782 | 0.00066 | 0.00066 | 82.101 | 21.965 |
| Δ(SE-REF) | 0.0064 | 0.013 | -0.0002 | -0.0002 | 0.04 | 0.251 |
The Uoc is open-circuit voltage, the Isc is short-circuit current, the larger the Uoc is, the better the Isc is, the larger the Isc is, the better the Eta is conversion efficiency, the FF is a filling factor, the Rs is series resistance, and the Rsh is parallel resistance.
From the electrical property test results of table 1, it can be derived: compared with the conventional process in the comparative example 1, the diffusion process in the example 1 has significant gain in electrical performance, and table 1 shows experimental data of twenty thousand cells, wherein the open voltage of the cell prepared by the method in the example 1 is increased by 6.4mv, the short-circuit current is increased by 13mA, the FF is increased by 0.04%, and the efficiency is increased by 0.25% compared with the cell in the comparative example 1.
The three-step diffusion deposition and driving mode used in the invention enables a PSG layer with high phosphorus concentration to be formed on the surface of the silicon wafer, thereby being beneficial to pushing a phosphorus source in the PSG into the silicon wafer during heavy doping, forming a high-concentration heavy doping area and being beneficial to ohmic contact and improving FF; the relative concentration of the shallow doped region without heavy doping is a little lower, which is beneficial to improving the open-circuit voltage; the gradual cooling drive-in process enables gradient doping to be formed in the silicon wafer, the width of a P-N junction area is widened, open-circuit voltage is improved, meanwhile, sunlight can be better absorbed by shallow junctions, short-wave-band spectrums in the sunlight corresponding to the shallow junctions are large in photon number contained in the spectrums within the range, better blue wave response can be obtained, accordingly, short-circuit current Isc is improved, and the gradual cooling drive-in process enables the square resistance uniformity to be better.
The above embodiments are merely illustrative of the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the content of the present invention and implement the invention, and not to limit the scope of the invention, and all equivalent changes or modifications made according to the spirit of the present invention should be covered by the scope of the present invention.
Claims (6)
1. A diffusion method for a selective emitter, the diffusion method comprising the steps of:
the method comprises the following steps: first deposition
Heating the temperature of the furnace tube to 790-810 ℃, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube, wherein the flow rate of the small nitrogen is 400-600sccm, the flow rate of the large nitrogen is 700-900sccm, the flow rate of the oxygen is 500-700sccm, and the gas introduction time is 11-13 min;
step two: first drive in
Introducing large nitrogen, oxygen and small nitrogen gas into the furnace tube, and driving and diffusing the phosphorus source deposited on the surface of the silicon wafer into the silicon wafer under the high-temperature condition, wherein the flow rate of the large nitrogen gas is 700-plus-material 900sccm, the flow rate of the oxygen gas is 200-plus-material 400sccm, the flow rate of the small nitrogen gas is 400-plus-material 600sccm, and the gas introducing time in the furnace tube is 9-11 min;
step three: second drive in
Introducing large nitrogen, oxygen and small nitrogen gas into the furnace tube, and continuously driving and diffusing the phosphorus source on the surface of the silicon wafer into the silicon wafer to ensure that the phosphorus source is uniformly distributed, wherein the flow rate of the large nitrogen gas is 1400-plus-1600 sccm, the flow rate of the oxygen gas is 200-plus-400 sccm, the flow rate of the small nitrogen gas is 400-plus-600 sccm, and the gas introduction time in the furnace tube is 7-9 min;
step four: second deposition
Setting the temperature of the furnace tube to be consistent with the temperature of the furnace tube in the third step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing secondary phosphorus source deposition on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 700-plus-900 sccm, the flow rate of the small nitrogen is 700-plus-900 sccm, the flow rate of the oxygen is 400-plus-600 sccm, and the gas introduction time is 8-11 min;
step five: third drive-in
Introducing large nitrogen, oxygen and small nitrogen gas into the furnace tube to ensure that the phosphorus source deposited for the second time on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen gas is 1400-plus-material 1600sccm, the flow rate of the oxygen gas is 200-plus-material 400sccm, the flow rate of the small nitrogen gas is 400-plus-material 600sccm, and the gas introducing time in the furnace tube is 8-10 min;
step six: third deposition
Setting the temperature of the furnace tube to be consistent with the temperature of the furnace tube in the fifth step, introducing mixed gas consisting of large nitrogen, oxygen and small nitrogen carrying phosphorus oxychloride into the furnace tube again, and performing third phosphorus source deposition on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 900-800 sccm, the flow rate of the small nitrogen is 600-800sccm, the flow rate of the oxygen is 200-400sccm, and the gas introduction time is 8-10 min;
step seven: the fourth drive in
Introducing large nitrogen and small nitrogen into the furnace tube to ensure that the phosphorus source deposited for the third time on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, wherein the flow rate of the large nitrogen is 1400-plus-material 1600sccm, the flow rate of the small nitrogen is 400-plus-material 600sccm, and the operation time of the step is 4-6 min;
starting from the second first driving in step, the temperature in the furnace tube begins to decrease;
the furnace tube temperature during the first driving is higher than the furnace tube temperature during the first deposition, and the furnace tube temperature during the second driving is lower than the furnace tube temperature during the first driving; the furnace tube temperature during the second deposition is the same as the furnace tube temperature during the second drive, and the furnace tube temperature during the third drive is lower than the furnace tube temperature during the second deposition; the furnace tube temperature during the third deposition is the same as the furnace tube temperature during the third drive, and the furnace tube temperature during the fourth drive is lower than the furnace tube temperature during the third deposition.
2. The diffusion method for selective emitter according to claim 1, further comprising eight temperature swing gettering steps: reducing the temperature of the furnace tube to 650 plus 670 ℃, and introducing large nitrogen gas and small nitrogen gas into the furnace tube to ensure that the phosphorus source deposited at the last on the surface of the silicon wafer is more uniformly distributed on the surface of the silicon wafer, absorbing impurities in the silicon body into the phosphorosilicate glass, wherein the flow rate of the large nitrogen gas is 1400 plus 1600sccm, the flow rate of the small nitrogen gas is 700 plus 900sccm, and the gas introduction time in the furnace tube is 11-13 min.
3. The diffusion method for a selective emitter as claimed in claim 1, wherein the furnace set temperature for the first driving is 870-; the set temperature of the furnace tube during the second driving is 810-; the temperature of the furnace tube during the first driving is uniformly reduced from 870 ℃ to 890 ℃ to 810 ℃ to 830 ℃.
4. The diffusion method for a selective emitter as claimed in claim 1, wherein the temperature of the furnace during the third driving is 780-800 ℃, and the temperature of the furnace during the third driving is uniformly reduced from 780-800 ℃ to 770-790 ℃.
5. The diffusion method for a selective emitter as claimed in claim 1, wherein the temperature of the furnace during the fourth driving is set at 770-790 ℃, and the temperature of the furnace during the fourth driving is uniformly reduced from 770-790 ℃ to 650-670 ℃.
6. The diffusion method of claim 1, wherein the large nitrogen is a protective gas filling the furnace tube; the small nitrogen is nitrogen passing through a phosphorus oxychloride source bottle.
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