CN108054088A - N-type silicon chip Boron diffusion method, crystal silicon solar energy battery and preparation method thereof - Google Patents

Abstract

The present application provides a boron diffusion method for N-type silicon wafers, a crystalline silicon solar cell and a manufacturing method thereof. Two boron diffusions are used, and the doping concentration of the second boron diffusion is greater than that of the first boron diffusion, and also That is, boron diffusion is formed by the first light expansion and the second re-expansion. Due to the first light expansion, the junction depth is deeper, the doping concentration of boron is lower, and the ohmic contact is poor, but it can reduce the recombination of the diffusion layer. The second re-expansion, the junction depth is shallower, and the doping concentration of boron is higher. , to ensure that the surface of the silicon wafer is in contact with the metal electrode to form a good ohmic contact. That is to say, the boron diffusion method of the N-type silicon wafer provided by the present invention ensures good battery contact resistance Rs while reducing diffusion recombination.

Description

N-type silicon wafer boron diffusion method, crystalline silicon solar cell and manufacturing method thereof

technical field

The invention relates to the technical field of making solar cells, in particular to a method for boron diffusion on an N-type silicon wafer, a crystalline silicon solar cell and a manufacturing method thereof.

Background technique

Conventional fossil fuels are being exhausted day by day. Among the existing sustainable energy sources, solar energy is undoubtedly the cleanest, most common and most potential alternative energy source. At present, among all solar cells, silicon solar cells are one of the solar cells that have been widely commercialized. This is due to the extremely abundant reserves of silicon materials in the earth's crust. With excellent electrical and mechanical properties, silicon solar cells occupy an important position in the field of photovoltaics. Therefore, developing cost-effective silicon solar cells has become one of the main research directions of photovoltaic companies in various countries.

N-type crystalline silicon cells have become an ideal substrate for high-efficiency crystalline silicon cells due to their advantages such as high minority carrier lifetime, good response to weak light, low light attenuation, and strong anti-PID ability. N-type batteries generally use boron diffusion as their emitter junction. Improving the quality of boron diffusion junctions and reducing their recombination is one of the important ways to improve battery efficiency.

Therefore, how to improve the quality of boron diffusion has become an urgent problem to be solved.

Contents of the invention

In view of this, the present invention provides a boron diffusion method for N-type silicon wafers, a crystalline silicon solar cell and a manufacturing method thereof, so as to solve the problem of low boron diffusion quality in the prior art.

To achieve the above object, the present invention provides the following technical solutions:

A boron diffusion method for an N-type silicon wafer, comprising:

Put the silicon wafer after texturing and cleaning into the diffusion furnace tube, and raise the temperature to the first temperature;

performing the first deposition to form a first boron diffusion on the surface of the silicon wafer;

raising the temperature to a second temperature and pushing the junction, the second temperature being higher than the first temperature;

performing a second deposition to form a second boron diffusion on the surface of the silicon wafer;

annealing and cooling down, and taking out the silicon wafer from the diffusion furnace tube;

Wherein, on the surface of the silicon wafer, the doping concentration of the second boron diffusion is greater than the doping concentration of the first boron diffusion, and the depth of the second boron diffusion is smaller than the depth of the first boron diffusion.

Preferably, the first deposition is performed to form a first boron diffusion on the surface of the silicon wafer, which specifically includes:

Feed nitrogen, oxygen, and boron-carrying source nitrogen into the diffusion furnace tube to perform the first deposition, and the first deposition time is 20min-60min, including the endpoint value;

Wherein, the gas flow rate of the nitrogen is 9000 sccm;

The gas flow rate of oxygen is 50sccm-100sccm, including the endpoint value;

The flow rate of the boron-carrying nitrogen gas is 50 sccm-150 sccm, including endpoints.

Preferably, the second deposition is performed to form a second boron diffusion on the surface of the silicon wafer, which specifically includes:

Feed nitrogen, oxygen, and boron-carrying source nitrogen into the diffusion furnace tube to perform a second deposition, and the second deposition time is 10min-20min, including endpoint values;

Wherein, the gas flow rate of the nitrogen is 9000 sccm;

The gas flow rate of oxygen is 100sccm-200sccm, including the endpoint value;

The flow rate of the boron-carrying nitrogen gas is 200sccm-400sccm, inclusive.

Preferably, the silicon wafers after texturing and cleaning are put into the diffusion furnace tube and heated to the first temperature, which specifically includes:

Put the silicon wafer after texturing and cleaning into the diffusion furnace tube;

Introduce nitrogen, the flow rate of nitrogen gas is 9000sccm;

At a rate of 10°C/min, the temperature was raised to 850°C-900°C, inclusive.

Preferably, the temperature is raised to a second temperature, and the junction is pushed, and the second temperature is higher than the first temperature, specifically including:

Pass into nitrogen, and described nitrogen gas flow rate is 9000sccm;

According to the heating rate of 10°C/min, the temperature is raised to 950°C-1000°C, including the endpoint value;

And pass through nitrogen and oxygen for 30min-70min to push the knot, including the endpoint value;

Wherein, the nitrogen gas flow rate is 9000 sccm, and the oxygen gas flow rate is 500 sccm-1000 sccm, including the endpoint values.

Preferably, the annealing is performed to lower the temperature, and the silicon wafer is taken out from the diffusion furnace tube, which specifically includes:

Nitrogen was introduced to lower the temperature, the flow rate of nitrogen gas was 9000sccm, and the cooling rate was 10°C/min;

After the temperature inside the diffusion furnace tube dropped to 800° C., the silicon wafer was taken out.

The present invention also provides a method for manufacturing a crystalline silicon solar cell, comprising a boron diffusion step, wherein the boron diffusion step adopts any one of the boron diffusion methods described above.

The present invention also provides a crystalline silicon solar cell, which is manufactured by the above-mentioned crystalline silicon solar cell manufacturing method.

It can be seen from the above-mentioned technical scheme that the boron diffusion method of N-type silicon wafer, crystalline silicon solar cell and its manufacturing method provided by the present invention adopts two boron diffusions, and the doping concentration of the second boron diffusion is higher than that of the first boron diffusion. Doping concentration, that is, the boron diffusion is formed by the first light expansion and the second re-expansion. Due to the first light expansion, the junction depth is deeper, the doping concentration of boron is lower, and the ohmic contact is poor, but it can reduce the recombination of the diffusion layer. The second re-expansion, the junction depth is shallower, and the doping concentration of boron is higher. , to ensure that the surface of the silicon wafer is in contact with the metal electrode to form a good ohmic contact. That is to say, the boron diffusion method of the N-type silicon wafer provided by the present invention ensures good battery contact resistance Rs while reducing diffusion recombination.

Based on the boron diffusion method provided above, the present invention also provides a crystalline silicon solar cell and a manufacturing method thereof. Due to the improvement in the quality of the boron diffusion junction, the performance of the crystalline silicon solar cell can also be improved accordingly.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 is a kind of N-type silicon chip boron diffusion method flow schematic diagram provided by the present invention;

Fig. 2 is a distribution diagram of boron atoms obtained by adopting the boron diffusion method of an N-type silicon wafer provided by the present invention.

Detailed ways

As mentioned in the background section, improving boron diffusion is one of the effective ways to improve the efficiency of solar cells. However, the quality of the boron diffusion junction formed by the boron diffusion method in the prior art is poor, which seriously affects the efficiency of the battery.

The inventors found that the reason for the above situation is that in the prior art, one-time boron diffusion is usually used to form the emitter junction. That is, one deposition and one pushing junction; if the diffusion concentration is high, the diffusion recombination is large, and the open circuit voltage Voc of the solar cell is low, resulting in low photoelectric conversion efficiency of the solar cell; and if the diffusion concentration is low, the solar cell’s After the emitter and the surface electrode are sintered, the contact resistance Rs is relatively high, and the efficiency of the solar cell is also low.

Based on this, the present invention provides a method for boron diffusion of N-type silicon wafers, comprising:

Put the silicon wafer after texturing and cleaning into the diffusion furnace tube, and raise the temperature to the first temperature;

performing the first deposition to form a first boron diffusion on the surface of the silicon wafer;

raising the temperature to a second temperature and pushing the junction, the second temperature being higher than the first temperature;

performing a second deposition to form a second boron diffusion on the surface of the silicon wafer;

annealing and cooling down, and taking out the silicon wafer from the diffusion furnace tube;

Wherein, on the surface of the silicon wafer, the doping concentration of the second boron diffusion is greater than the doping concentration of the first boron diffusion, and the depth of the second boron diffusion is smaller than the depth of the first boron diffusion.

The N-type silicon chip boron diffusion method provided by the present invention adopts two boron diffusions, and the doping concentration of the second boron diffusion is greater than the doping concentration of the first boron diffusion, that is, the first light diffusion is adopted, and the second Boron diffusion is formed by way of re-expansion. Due to the first light expansion, the junction depth is deeper, the doping concentration of boron is lower, and the ohmic contact is poor, but it can reduce the recombination of the diffusion layer. The second re-expansion, the junction depth is shallower, and the doping concentration of boron is higher. , to ensure that the surface of the silicon wafer is in contact with the metal electrode to form a good ohmic contact. That is to say, the boron diffusion method of the N-type silicon wafer provided by the present invention ensures good battery contact resistance Rs while reducing diffusion recombination.

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. 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.

Please refer to Fig. 1, Fig. 1 is the flow chart of the N-type silicon wafer boron diffusion method provided by the embodiment of the present invention; the N-type silicon wafer boron diffusion method includes:

S101: Put the silicon wafer after texturing and cleaning into the diffusion furnace tube, and heat up to the first temperature;

In this embodiment, put the silicon wafer after texturing and cleaning into the diffusion furnace tube; feed nitrogen gas, the flow rate of nitrogen gas is 9000 sccm; according to the heating rate of 10 ° C / min, the temperature is raised to 850 ° C - 900 ° C, including the endpoint value .

It should be noted that in order to prevent the surface of the silicon wafer from being oxidized at high temperature in the diffusion furnace tube, it is necessary to pass inert gas or a gas that is not easy to react with the silicon wafer at high temperature into the diffusion furnace tube to remove the oxygen and air in the diffusion furnace tube. , to protect the silicon wafer. Considering the production cost of the silicon wafer, the cost of nitrogen gas is relatively low, therefore, in this embodiment, optionally, the gas introduced is nitrogen gas.

S102: performing the first deposition to form a first boron diffusion on the surface of the silicon wafer;

After the temperature in the diffusion furnace tube rises to a predetermined temperature, that is, the first temperature, nitrogen, oxygen and boron-carrying source nitrogen are introduced into the diffusion furnace tube to perform the first deposition, and the first deposition The time is 20min-60min, including the endpoint value; wherein, the gas flow rate of the nitrogen gas is 9000sccm; the oxygen gas flow rate is 50sccm-100sccm, including the endpoint value; the nitrogen gas flow rate carrying the boron source is 50sccm-150sccm, including the endpoint value .

The purpose of this step is to deposit a relatively small amount of boron on the surface of the silicon wafer, form a light diffusion on the surface of the silicon wafer, and avoid the high concentration of boron diffusion and large recombination. It should be noted that although the doping concentration of boron is low in this step, the junction depth is relatively deep, thereby forming a deep emitter junction and providing a basis for subsequent formation of an ohmic contact.

S103: heating up to a second temperature, and pushing the junction, the second temperature is higher than the first temperature;

It should be noted that after the boron element is deposited on the surface of the silicon wafer, in order to accelerate the entry of boron atoms into the silicon wafer, the embodiment of the present invention also needs to add a push-in step after the first deposition. Described push knot step specifically comprises:

Nitrogen is passed into the diffusion furnace tube, and the nitrogen gas flow rate is 9000 sccm;

According to the heating rate of 10°C/min, the temperature is raised to 950°C-1000°C, including the endpoint value;

And pass through nitrogen and oxygen for 30min-70min to push the knot, including the endpoint value;

Wherein, the nitrogen gas flow rate is 9000 sccm, and the oxygen gas flow rate is 500 sccm-1000 sccm, including the endpoint values.

For N-type semiconductors, the Auger recombination (Auger recombination) lifetime of minority carriers (holes) is inversely proportional to the square of the majority carrier (electron) concentration. When heavily doped, the electron concentration is very high, and the value of the Auger recombination lifetime of the minority carriers is very small, that is, the Auger recombination makes the lifetime of the minority carriers greatly reduced.

However, in this embodiment, the boron atoms deposited on the surface of the silicon wafer for the first time are pushed into the interior of the silicon wafer by high temperature and activated. At this time, due to the low doping concentration of boron deposited for the first time, the doping concentration of boron atoms activated in the silicon wafer is low, resulting in less Auger recombination and ensuring the lifetime of minority carriers.

S104: performing a second deposition to form a second boron diffusion on the surface of the silicon wafer;

Due to the low Auger recombination of the first boron diffusion and the low concentration of boron diffusion, good ohmic contact with the subsequently formed metal electrodes cannot be formed. In the embodiment of the present invention, a second deposition is also performed to form a high-concentration boron diffusion.

In this embodiment, the second deposition mainly forms boron diffusion with shallower junction depth but higher boron doping concentration, so as to ensure good ohmic contact between the surface of the silicon wafer and the metal electrode, reduce the contact resistance Rs, and improve the performance of the solar cell. conversion efficiency.

In this embodiment, as long as the boron diffusion of the second deposition is heavier than the boron diffusion of the first deposition, that is, the boron doping concentration of the second boron diffusion is higher than that of the first boron diffusion. The embodiment does not limit the specific implementation method, which may be to increase the diffusion temperature, increase the boron source or prolong the boron diffusion time, etc. In this embodiment, in order to ensure the production efficiency of the silicon wafer, the optional process conditions for the second deposition are:

Feed nitrogen, oxygen, and boron-carrying source nitrogen into the diffusion furnace tube to perform a second deposition, and the second deposition time is 10min-20min, including endpoint values;

Wherein, the gas flow rate of the nitrogen is 9000 sccm;

The gas flow rate of oxygen is 100sccm-200sccm, including the endpoint value;

The flow rate of the boron-carrying nitrogen gas is 200sccm-400sccm, inclusive.

S105: annealing and cooling down, and taking out the silicon wafer from the diffusion furnace tube;

In this embodiment, the specific process steps of annealing and cooling are not limited. Optionally, nitrogen gas is introduced to lower the temperature. The flow rate of nitrogen gas is 9000 sccm, and the cooling rate is 10°C/min; when the temperature in the diffusion furnace tube drops to 800°C, The silicon wafer is taken out.

Nitrogen can also be replaced by other gases, as long as it can protect the silicon wafer from being oxidized.

In the embodiment of the present invention, a boron diffusion method for N-type silicon wafers is provided. Two boron diffusions are used, and the doping concentration of the second boron diffusion is greater than that of the first boron diffusion, that is, the first light diffusion is adopted. The boron diffusion is formed by the way of the second re-expansion. Due to the first light expansion, the junction depth is deeper, the doping concentration of boron is lower, and the ohmic contact is poor, but it can reduce the recombination of the diffusion layer. The second re-expansion, the junction depth is shallower, and the doping concentration of boron is higher. , to ensure that the surface of the silicon wafer is in contact with the metal electrode to form a good ohmic contact. That is to say, the boron diffusion method of the N-type silicon wafer provided by the present invention ensures good battery contact resistance Rs while reducing diffusion recombination.

An embodiment of the present invention also provides a method for manufacturing a crystalline silicon solar cell, including a boron diffusion step, which is the boron diffusion method described in the above embodiment using two different doping concentrations.

The embodiment of the present invention also provides a crystalline silicon solar cell, which is formed by the above-mentioned crystalline silicon solar cell manufacturing method, and the boron diffusion curve with low recombination but good contact resistance Rs is obtained through experimental detection, as shown in Figure 2, and the abscissa is etching The depth of the silicon wafer, the ordinate is the doping concentration of boron atoms, as can be seen from Figure 2, on the surface of the silicon wafer (that is, the position where the abscissa is smaller), the doping concentration of boron is higher, and as the junction depth The deeper (that is, the position with larger abscissa), the lower the boron doping concentration, thereby reducing the diffusion recombination and ensuring good battery contact resistance Rs. Corresponding to Figure 2, the boron diffusion formed by the second deposition mainly contributes to its junction depth of 0-0.1 μm. Compared with the first deposition, the boron doping concentration is increased to ensure good ohmic contact performance. Thereby improving the efficiency of solar cells.

It should be noted that each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. For the same and similar parts in each embodiment, refer to each other, that is, Can.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (8)

1. A method for boron diffusion of an N-type silicon wafer, characterized in that, comprising: Put the silicon wafer after texturing and cleaning into the diffusion furnace tube, and raise the temperature to the first temperature; performing the first deposition to form a first boron diffusion on the surface of the silicon wafer; raising the temperature to a second temperature and pushing the junction, the second temperature being higher than the first temperature; performing a second deposition to form a second boron diffusion on the surface of the silicon wafer; annealing and cooling down, and taking out the silicon wafer from the diffusion furnace tube; Wherein, on the surface of the silicon wafer, the doping concentration of the second boron diffusion is greater than the doping concentration of the first boron diffusion, and the depth of the second boron diffusion is smaller than the depth of the first boron diffusion. 2. The boron diffusion method of N-type silicon wafer according to claim 1, characterized in that, the first deposition is carried out to form the first boron diffusion on the surface of the silicon wafer, specifically comprising: Feed nitrogen, oxygen, and boron-carrying source nitrogen into the diffusion furnace tube to perform the first deposition, and the first deposition time is 20min-60min, including the endpoint value; Wherein, the gas flow rate of the nitrogen is 9000 sccm; The gas flow rate of oxygen is 50sccm-100sccm, including the endpoint value; The flow rate of the boron-carrying nitrogen gas is 50 sccm-150 sccm, including endpoints. 3. The boron diffusion method of N-type silicon wafer according to claim 2, characterized in that, the second deposition is carried out to form the second boron diffusion on the surface of the silicon wafer, specifically comprising: Feed nitrogen, oxygen, and boron-carrying source nitrogen into the diffusion furnace tube to perform a second deposition, and the second deposition time is 10min-20min, including endpoint values; Wherein, the gas flow rate of the nitrogen is 9000 sccm; The gas flow rate of oxygen is 100sccm-200sccm, including the endpoint value; The flow rate of the boron-carrying nitrogen gas is 200sccm-400sccm, inclusive. 4. The method for boron diffusion of N-type silicon wafers according to claim 1, characterized in that, the silicon wafers after the texturing and cleaning are put into the diffusion furnace tube, and the temperature is raised to the first temperature, which specifically includes: Put the silicon wafer after texturing and cleaning into the diffusion furnace tube; Introduce nitrogen, the flow rate of nitrogen gas is 9000sccm; At a rate of 10°C/min, the temperature was raised to 850°C-900°C, inclusive. 5. The method for boron diffusion of N-type silicon wafers according to claim 4, wherein the temperature is raised to a second temperature, and the junction is pushed, and the second temperature is higher than the first temperature, specifically comprising : Pass into nitrogen, and described nitrogen gas flow rate is 9000sccm; According to the heating rate of 10°C/min, the temperature is raised to 950°C-1000°C, including the endpoint value; And pass through nitrogen and oxygen for 30min-70min to push the knot, including the endpoint value; Wherein, the nitrogen gas flow rate is 9000 sccm, and the oxygen gas flow rate is 500 sccm-1000 sccm, including the endpoint values. 6. The method for boron diffusion of N-type silicon wafers according to any one of claims 1-5, wherein the annealing is performed to lower the temperature, and the silicon wafers are taken out from the diffusion furnace tube, specifically comprising: Nitrogen was introduced to lower the temperature, the flow rate of nitrogen gas was 9000sccm, and the cooling rate was 10°C/min; After the temperature inside the diffusion furnace tube dropped to 800° C., the silicon wafer was taken out. 7. A method for manufacturing a crystalline silicon solar cell, comprising a boron diffusion step, characterized in that the boron diffusion step adopts the boron diffusion method according to any one of claims 1-6. 8. A crystalline silicon solar cell, characterized in that it is formed by the manufacturing method of a crystalline silicon solar cell according to claim 7.