CN110098283A - A kind of ion implanting phosphorus diffusion method of matching laser selective doping - Google Patents

Abstract

The invention relates to a novel ion implantation process, in particular to an ion implantation phosphorus diffusion method for matching laser selective doping. The method includes the following steps: ① Phosphorus is ion-implanted for the first time on the surface of the P-type silicon wafer after texturing, and a low dose of phosphorus is selected for implantation, and a high acceleration voltage is selected for the implantation; ② Annealing activates + pushes the junction to diffuse the formed phosphorus The doping concentration on the junction surface is low, and the effective phosphorus doping concentration distribution changes smoothly with depth, forming a light expansion area with a square resistance of 140‑180ohm/sq; The purpose is to form a high-concentration phosphorus diffusion layer near the surface of the silicon wafer; ④ laser doping: the laser selectively activates the phosphorus implanted in the second ion implantation; ⑤ cleaning. The invention further improves the efficiency of the PERC battery by reducing the recombination in the phosphorus diffusion junction of the battery, improving the uniformity of the phosphorus diffusion square resistance and reducing the loss of the series resistance of the battery.

Description

A Phosphorous Diffusion Method of Ion Implantation Matching Laser Selective Doping

technical field

The invention relates to a novel ion implantation process, in particular to an ion implantation phosphorus diffusion method matched with laser selective doping, and belongs to the technical field of photovoltaic power generation.

Background technique

With the gradual depletion of fossil energy, clean energy has attracted more and more attention. Photovoltaic power generation technology, as a mainstream technology for utilizing solar energy resources, has been market-oriented and commercialized. In order to further promote the utilization and promotion of photovoltaic battery products, it is necessary to gradually improve battery efficiency and reduce the cost of electricity.

At present, the mainstream phosphorus diffusion junction preparation method for photovoltaics is high-temperature thermal diffusion. Its main disadvantages are mainly three points. Diffusion square resistance uniformity is low. Second, the amount of diffusion source cannot be precisely controlled during the diffusion process, resulting in poor process stability. 3. The power of thermal diffusion push junction comes from temperature and concentration gradient at different depths, resulting in high phosphorus doping concentration on the silicon wafer surface, high Auger recombination in this area, and low open circuit voltage of the battery.

Contents of the invention

The object of the present invention is an ion-implantation phosphorus diffusion method matched with laser selective doping, which can prepare high-quality phosphorus diffusion selective emitter and improve the conversion efficiency of solar cells.

The technical solution adopted by the present invention to solve its technical problems is:

A method for ion implantation phosphorus diffusion matching laser selective doping, the method comprising the following steps:

①Phosphorus is first ion-implanted on the surface of the P-type silicon wafer after texturing, and a low dose of phosphorus is selected for implantation. At the same time, a high acceleration voltage is selected for implantation. The amount of phosphorus implanted is 8×10 ¹⁴ to 10×10 ¹⁴ cm ^-2 , The accelerating voltage is 10-14kV;

②Annealing activation + pushing junction, so that the surface doping concentration of the formed phosphorus diffusion junction is low, and the distribution of effective phosphorus doping concentration varies with depth more smoothly, forming a light expansion area with a square resistance of 140-180ohm/sq;

③Phosphorus ion implantation for the second time: This time, the implantation dose is high-phosphorus phosphorus, the implantation amount of phosphorus is 4×10 ¹⁵ to 6×10 ¹⁵ cm ^-2 , and the accelerating voltage is 4-6KV, the purpose is to form High concentration phosphorus diffusion layer;

④Laser doping: The laser selectively activates the phosphorus in the second ion implantation to form a re-expansion area in the contact area of the subsequent metallized grid line. The square resistance of the re-expansion area is 20-40ohm/sq;

⑤Cleaning: Cleaning away the phosphorus-containing layer of the second ion implantation in the light expansion area that is not activated by laser, and finally forming a complete selective phosphorus diffusion emitter.

The method of the present invention is applied to the preparation of high-efficiency PERC cells that can be mass-produced today. Due to its excellent back passivation and laser slotting process, the mass production efficiency of PERC cells is close to 22%. The invention improves the uniformity of phosphorus diffusion square resistance and reduces the loss of battery series resistance by reducing the recombination in the phosphorus diffusion junction of the battery. battery efficiency.

In the present invention, the ion implantation technique excites gas discharge to generate plasma, and the positive ions in the plasma are extracted by the accelerated extraction battery to form an ion beam with a certain initial velocity. By testing the ion beam current density per unit time and the movement speed of the silicon wafer on the transmission belt, the implantation amount of dopant ions in the silicon wafer can be precisely controlled. By controlling the extraction acceleration voltage of the plasma, the energy of the extracted ion beam can be affected, and then the implantation depth of the dopant element can be affected. The square resistance uniformity of the prepared diffusion junction can be ensured by ensuring that the extracted ion beam is uniform within the entire movement range of the silicon wafer.

Through the reasonable design of ion implantation process and laser selective doping technology, the light expansion area has good square resistance uniformity, low phosphorus doping concentration on the surface, and low Auger recombination. High-efficiency PERC cells with low square resistance in the re-expansion area and low contact resistance between subsequent metallization and silicon wafer surface.

As a preference, the specific process of step ② annealing activation + pushing junction is: in the high-temperature annealing furnace tube, activate the phosphorus atoms implanted in the silicon wafer in the ion implantation-1, adopt an annealing process at 850±50°C, 30±5min, and the whole process is in Annealed in 10±2 L/min N ₂ and 1±0.2 L/min O ₂ atmosphere to form a lightly expanded junction with a square resistance of 160±20 ohm/sq.

Preferably, the specific process of cleaning in step ⑤ is: use 60±5°C hydrogen peroxide + hydrochloric acid (1:1 volume ratio) to clean the silicon wafer for 15-20 minutes, and then clean the oxide layer on the surface of the silicon wafer with hydrofluoric acid. The mass concentration of hydrochloric acid is 6-14%.

Preferably, the method specifically includes the following steps:

①Ion implantation-1: The first ion implantation is carried out on the surface of the P-type silicon wafer after texturing. Firstly, the phosphorus implantation dose is selected as 9×10 ¹⁴ cm ^-2 , and the acceleration voltage is 12kV to form the first phosphorus atom implantation layer;

The main purpose: to implant low-dosage phosphorus elements, and form light expansion junctions with low surface doping phosphorus concentration but deep junctions in the subsequent annealing process. At the same time, near the space charge region formed by the PN junction, the phosphorus doping concentration is higher, which enhances the light-splitting efficiency of the PN junction.

②Annealing+push junction: Activate the phosphorus atoms implanted in the silicon wafer in the high-temperature annealing furnace tube in ion implantation-1, adopt an annealing process of 850±50°C, 30±5min, and the whole process is at 10±2 L/min N ₂ Annealed with 1±0.2 L/minO ₂ atmosphere to form a light expansion junction with a square resistance of 160±20 ohm/sq;

③Ion implantation-2: The implantation dose of phosphorus is 4×10 ¹⁵ cm ^-2 , and the acceleration voltage is 6kV, and the second phosphorus atom implantation is carried out;

Main purpose: Implant high doses of phosphorus atoms on the shallow surface of silicon wafers, and activate the implanted phosphorus atoms in the laser treatment area in the subsequent laser selective doping process to form phosphorus junctions with high phosphorus doping concentration on the surface, and subsequent battery preparation In the metallization process in the process, the metal grid line covers the laser treatment area to form a good metal-semiconductor ohmic contact and improve the fill factor of the battery.

④Laser doping: The square resistance of phosphorous junction expansion in the laser treatment area is 30ohm/sq;

⑤Cleaning: Use 60°C hydrogen peroxide + hydrochloric acid (1:1) to clean the above-mentioned silicon wafer for 15 minutes, and then clean the oxide layer on the surface of the silicon wafer with hydrofluoric acid. The mass concentration of hydrochloric acid is about 10%.

The main purpose: to clean away the surface phosphorus atoms implanted in the ion implantation-2 step of the area not treated by the laser in step 3, and retain the light expansion junction formed in the ion implantation-1 step.

Compared with prior art, the beneficial effect of the present invention is:

1. The square resistance uniformity of the formed light expansion area is good;

2. The effective doping concentration on the surface of the light expansion area is low, the Auger recombination is low, and the open circuit voltage is high;

3. The doping concentration of the light expansion region changes smoothly with the depth. Near the space charge region of the PN junction, the effective phosphorus doping concentration is higher, and the potential difference on both sides of the formed space charge region is higher, which is conducive to the effective light splitting of the PN junction. Form a high open circuit voltage;

4. The square resistance of the re-expansion area is low, the contact resistance between the metal and the silicon wafer surface is low, and the battery fill factor is high.

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 production process flow chart of the present invention.

Detailed ways

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.

In the present invention, unless otherwise specified, all parts and percentages are in weight units, and the equipment and raw materials used can be purchased from the market or commonly used in the field. The methods in the following examples, unless otherwise specified, are conventional methods in the art.

Example 1:

A method for ion implantation phosphorus diffusion matching laser selective doping, the process flow chart of the method is shown in Figure 1, and the specific steps of the method are as follows:

1. Ion implantation-1: The first ion implantation is carried out on the surface of the P-type silicon wafer after texturing. Firstly, the phosphorus implantation dose is selected to be 9×10 ¹⁴ cm ^-2 , and the acceleration voltage is 12kV to form the first phosphorus atom implantation layer. .

The main purpose: to implant low-dosage phosphorus elements, and form light expansion junctions with low surface doping phosphorus concentration but deep junctions in the subsequent annealing process. At the same time, near the space charge region formed by the PN junction, the phosphorus doping concentration is higher, which enhances the light-splitting efficiency of the PN junction.

2. Annealing + pushing junction: activate the phosphorus atoms implanted in the silicon wafer in ion implantation-1 in the high temperature annealing furnace tube. Using 850℃, 30min annealing process, annealing in 10 L/min N ₂ and 1 L/min O ₂ atmosphere throughout the process, forming a light expansion junction with a square resistance of 160 ohm/sq.

3. Ion implantation-2: the implantation dose of phosphorus is 4×10 ¹⁵ cm ^-2 , and the acceleration voltage is 7kV, and the second phosphorus atom implantation is performed.

Main purpose: Implant high doses of phosphorus atoms on the shallow surface of silicon wafers, and activate the implanted phosphorus atoms in the laser treatment area in the subsequent laser selective doping process to form phosphorus junctions with high phosphorus doping concentration on the surface, and subsequent battery preparation In the metallization process in the process, the metal grid line covers the laser treatment area to form a good metal-semiconductor ohmic contact and improve the fill factor of the battery. The square resistance of phosphorous junction expansion in the laser treatment area is 30ohm/sq.

4. Laser doping: The laser selectively activates the phosphorous ion implanted for the second time to form a re-expansion area in the contact area of the subsequent metallized grid line. The square resistance of the re-expansion area is 20-40ohm/sq;

5. Cleaning: Use 60°C hydrogen peroxide + hydrochloric acid (volume ratio: 1:1) to clean the above-mentioned silicon wafer for 15 minutes, and then clean the oxide layer on the surface of the silicon wafer with hydrofluoric acid. The mass concentration of hydrochloric acid is 10%.

The main purpose: to clean away the surface phosphorus atoms implanted in the ion implantation-2 step of the area not treated by the laser in step 3, and retain the light expansion junction formed in the ion implantation-1 step.

Comparative example Selective emitter made by phosphorus thermal diffusion method (BaseLine group)

1. Thermal diffusion: Phosphorus-doped thermal diffusion is performed on the surface of the P-type silicon wafer after texturing; a phosphorus diffusion junction with a square resistance of 110-130ohm/sq is formed as a light expansion junction.

2. Laser doping: laser selective activation to form a re-expansion area in the contact area of the subsequent metallized grid line, and the square resistance of the re-expansion area is 50-60ohm/sq;

3. Cleaning: Use hydrofluoric acid and hydrochloric acid (1:1 volume ratio) to clean the silicon wafer for 5 minutes to remove the phosphosilicate glass on the surface and form a complete SE structure. The mass concentration of hydrochloric acid is 10%.

Through the above process steps, a complete ion-implanted phosphorus diffusion selective emitter is obtained. After passivation, screen printing, and sintering processes, a solar cell is prepared. The battery performance test is shown in the table below, where Baseline uses phosphorus thermal diffusion, laser Selective doping to form phosphorus diffusion selective emitter, after passivation, screen printing, and sintering process, the performance parameters of the solar cell are shown in Table 1.

Table 1

Group Voc Isc FF Eta BaseLine 672mV 40.15mA/cm² 81.52% 21.92% Example 1 680mV 40.18mA/cm² 81.74% 22.33%

It can be seen from Table 1 that compared with the BaseLine group, the ion implantation process of the present invention can increase the open circuit voltage (Voc) of the battery by 8mV, while the fill factor (FF) is also increased by 0.22%, and the conversion efficiency (Eta) of the battery is increased by 0.41%. significant improvement.

The embodiment described above is only a preferred solution of the present invention, and does not limit the present invention in any form. There are other variations and modifications on the premise of not exceeding the technical solution described in the claims.

Claims (5)

1. a kind of ion implanting phosphorus diffusion method of matching laser selective doping, it is characterised in that this method includes following step It is rapid:

1. the P-type wafer surface first time ion implanting phosphorus after making herbs into wool, the phosphorus of selection injection low dosage, injection simultaneous selection are high Acceleration voltage, the injection rate of phosphorus are 8 × 10¹⁴To 10 × 10¹⁴ cm^-2, acceleration voltage 10-14kV；

2. activation+knot of annealing, keeps the phosphorus diffusion knot surface dopant concentration to be formed low, available phosphorus doping concentration distribution becomes with depth Change is more gentle, forms the area Qing Kuo that sheet resistance is 140-180ohm/sq；

3. second of phosphonium ion injection: the phosphorus of this implantation dosage high phosphorus, the injection rate of phosphorus are 4 × 10¹⁵To 6 × 10¹⁵ cm^-2, add Fast voltage is 4-6KV, it is therefore an objective to form the phosphorus-diffused layer of high concentration in silicon wafer near surface；

4. laser doping: laser selective activates the phosphorus of second of ion implanting, forms subsequent metallisation grid line contact area Area is re-expanded, re-expand area's sheet resistance is 20-40ohm/sq；

5. cleaning: washing the area Qing Kuo not by second of ion implanting of laser active containing phosphorous layer, ultimately form complete choosing Selecting property phosphorus diffusion emitter.

2. the ion implanting phosphorus diffusion method of matching laser selective doping according to claim 1, it is characterised in that: step Suddenly 2. annealing activation+knot detailed process is: the phosphorus being infused in active ions injection -1 in silicon wafer in high annealing boiler tube Atom, using 850 ± 50 DEG C, the annealing process of 30 ± 5min, whole process is in 10 ± 2 L/min N₂With 1 ± 0.2 L/min O₂Atmosphere Interior annealing is enclosed, the light expansion that sheet resistance is 160 ± 20 ohm/sq is formed and ties.

3. the ion implanting phosphorus diffusion method of matching laser selective doping according to claim 1, it is characterised in that: step Suddenly the detailed process 5. cleaned is: using 60 ± 5 DEG C of hydrogen peroxide+hydrochloric acid cleaning silicon chip 15-20min, subsequent hydrofluoric acid clean Silicon chip surface oxide layer.

4. the ion implanting phosphorus diffusion method of matching laser selective doping according to claim 3, it is characterised in that: double The volume ratio of oxygen water and hydrochloric acid is 1:1-2, and the mass concentration of hydrochloric acid is 6-14%.

5. the ion implanting phosphorus diffusion method of matching laser selective doping according to claim 1, it is characterised in that should Method specifically includes the following steps:

1. ion implanting -1: the P-type wafer surface after making herbs into wool carries out first time ion implanting, and selecting phosphorus implantation dosage first is 9 ×10¹⁴ cm^-2, acceleration voltage 12kV, formation first time phosphorus atoms implanted layer；

2. annealing+knot: the phosphorus atoms being infused in active ions injection -1 in high annealing boiler tube in silicon wafer, using 850 ± 50 DEG C, the annealing process of 30 ± 5min, whole process is in 10 ± 2 L/min N₂With 1 ± 0.2 L/minO₂Annealing in atmosphere, forms The light expansion that sheet resistance is 160 ± 20 ohm/sq is tied；

3. ion implanting -2: using phosphorus implantation dosage for 4 × 10¹⁵ cm^-2, acceleration voltage 6kV, second of phosphorus atoms note of progress Enter；

4. laser doping: it is 30ohm/sq that laser treated regions phosphorus, which expands knot sheet resistance,；

5. cleaning: cleaning above-mentioned silicon wafer 15min, subsequent hydrofluoric acid clean silicon chip surface using 60 DEG C of hydrogen peroxide+hydrochloric acid (1:1) Oxide layer.