CN104183668A - Manufacturing method of solar cell unit - Google Patents

Abstract

The present invention provides a method of manufacturing a solar cell, which is a new method of manufacturing a solar cell using an ion implantation method. A method of manufacturing a solar cell unit according to an aspect of the present invention includes: a preparation step of preparing a solar cell substrate having a silicon layer of the first conductivity type and a coating film covering the silicon layer; and an emitter layer forming step of The film is irradiated with ions of the second conductivity type toward the silicon layer to form an emitter layer in a part of the light-receiving surface side of the silicon layer. In the emitter layer forming step, the ions are irradiated with energy such that the range of the ions is the distance from the surface of the coating film to the interface between the coating film and the silicon layer.

Description

Manufacturing method of solar cell

technical field

This application claims priority based on Japanese Patent Application No. 2013-110595 filed on May 27, 2013. The entire content of this application is incorporated in this specification by reference.

The invention relates to a method for manufacturing a solar cell unit.

Background technique

In solar cells, electron-hole pairs generated when semiconductor materials such as silicon absorb light pass through the electric field generated by the pn junction formed inside the cell, electrons move to the n-layer side, and holes move to the p-layer side, thereby flowing as a current to the p-layer side. External circuit output. When forming a pn junction or a contact layer, it is necessary to locally perform a process of varying the concentration or type of impurities. Furthermore, an antireflection film is formed on the light-receiving surface side of the silicon substrate in order to increase the light absorbed inside the solar cell as much as possible.

Specifically, there is known a solar cell manufacturing method in which an n-type layer (emitter layer) is formed on the surface of a p-type silicon substrate by doping n-type impurities at a high concentration by ion implantation, and then forming Anti-reflection film (for example, refer to Patent Document 1).

Patent Document 1: Japanese National Publication No. 2010-527163

However, when the emitter layer is formed by ion implantation, the range of implanted ions is a position (depth) that penetrates to a certain extent from the surface of the silicon substrate. Therefore, the concentration distribution of the dopant ions in the depth direction has a peak at a certain depth from the surface of the silicon substrate. The presence of such a peak in the impurity concentration hinders the movement of carriers, which is one of the causes of a decrease in power generation efficiency.

Contents of the invention

One of the exemplary objects of one aspect of the present invention is to provide a new method of manufacturing a solar cell using an ion implantation method.

In order to solve the above-mentioned problems, a method of manufacturing a solar cell according to an aspect of the present invention includes: a preparation step of preparing a substrate for a solar cell having a silicon layer of the first conductivity type and a coating film covering the silicon layer; and forming an emitter layer. In the step, the silicon layer is irradiated with ions of the second conductivity type through the coating film to form an emitter layer in a part of the light-receiving surface side of the silicon layer. In the emitter layer forming step, the ions are irradiated with energy such that the range of the ions is the distance from the surface of the cladding film to the interface between the cladding film and the silicon layer.

Another aspect of the present invention is a method of manufacturing a solar battery cell. This method includes: a preparation step of preparing a substrate for a solar cell having a silicon layer of the first conductivity type and a coating film covering the silicon layer; Type ions form an emitter layer in a part of the light-receiving side of the silicon layer. In the emitter layer forming step, the ions are irradiated with energy such that the peak position of the ion concentration distribution in the depth direction falls within the range of the depth D±10 nm from the interface between the coating film and the silicon layer.

Invention effect:

According to the present invention, it is possible to realize a new method of manufacturing a solar cell using an ion implantation method.

Description of drawings

FIG. 1 is a graph showing the results of doping concentration distribution when standard ion implantation is performed.

FIG. 2 is a diagram showing an example of a doping concentration distribution when ion implantation is performed into a silicon substrate through a mask.

FIG. 3 is a diagram showing an example of a doping concentration distribution inside a silicon substrate after removing a screen film.

Fig. 4 is a flowchart of a method of manufacturing a solar battery cell according to the first embodiment.

5( a ) to 5 ( f ) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing the solar battery cell according to the first embodiment.

6 is a flowchart of a method of manufacturing a solar battery cell according to the second embodiment.

7( a ) to 7 ( e ) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing a solar battery cell according to the second embodiment.

8 is a flowchart of a method of manufacturing a solar battery cell according to the third embodiment.

9( a ) to 9 ( e ) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing a solar battery cell according to the third embodiment.

10(a) to 10(b) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing a solar cell according to the third embodiment.

In the figure: 10-silicon substrate, 12-screen film, 14-emitter layer, 16-anti-reflection film, 18-light-receiving surface electrode, 20-back electrode, 24-mask, 26-contact area, 100, 200, 300 - Solar cell unit.

Detailed ways

Hereinafter, the form for carrying out this invention is demonstrated in detail. In addition, the structure described below is an illustration and does not limit the scope of the present invention at all. In addition, in the description of the drawings, the same reference numerals are attached to the same elements, and overlapping descriptions are appropriately omitted. In addition, in each cross-sectional view shown in the description of the manufacturing method, the thickness and size of the semiconductor substrate and other layers do not necessarily represent actual dimensions and ratios for the convenience of description.

(first embodiment)

Solar cells are designed in many types. For example, a crystalline Si-based solar cell ensures superiority over other types of solar cells by its features of simple structure and manufacturing method, high conversion efficiency, and the like. On the other hand, in order to obtain higher conversion efficiency in crystalline Si-based solar cells, it is very important to find out the conditions most suitable for each process unit and to differentiate them. Among them, the formation of the surface emitter layer mainly caused by the photoelectric effect is considered to be a very important factor, and it is considered that it preferably has the following characteristics.

However, the thermal diffusion method and the ion implantation method currently used as general manufacturing methods are difficult to simultaneously satisfy the following characteristics from the viewpoint of their characteristics.

(1) Shallow joint. Specifically, the internal diffusion potential is brought closer to the surface.

(2) Optimal doping concentration. Specifically, the emitter concentration has a certain higher concentration for contact with the electrodes and movement of majority carriers through the emitter layer. However, from the viewpoint of reducing the recombination of minority carriers, it is desirable that the concentration is not too high.

(3) There is no particular concentration peak inside the surface. Specifically, the high-low junction of a strong electric field that acts as a barrier to minority carrier movement does not exist on the inner side of the surface.

(4) There are some high and low joints on the outermost surface. Specifically, it has the effect of discharging minority carriers from the surface to the opposite surface.

Since the doping depth and concentration can be controlled, the ion implantation method is superior to the thermal diffusion method in terms of (1) and (2) above. On the other hand, when ion implantation is used, the depth corresponding to the acceleration energy of the ions has a peak of the doping concentration, and the doping concentration becomes a distribution that decreases from the peak position toward the surface layer.

FIG. 1 is a graph showing the results of doping concentration distribution when standard ion implantation is performed. In the ion implantation shown in FIG. 1 , phosphorus (P) was used as an implanted ion seed, and ions were implanted into a silicon substrate at an acceleration energy of 10 keV and a dose of 3×10 ¹⁵ ions/cm ² . As shown in FIG. 1 , according to ion implantation under such conditions, the doping concentration gradually increases from the surface S, reaches a peak at a depth D of about 0.015 μm (15 nm) from the surface S, and then decreases. That is, the implantation range Rp in this ion implantation is about 0.015 μm (15 nm).

This distribution Pr is slightly relaxed by the subsequent activation annealing, but the ion implantation method has room for improvement in the aforementioned point (3). In addition, low-energy ion implantation is required to form shallow junctions, but generally, the lower the energy, the lower the beam transmission efficiency and the lower the productivity.

The present invention realizes a new method of manufacturing a solar battery cell using the ion implantation method in consideration of these points. In the following method, considering the range of ions, before forming the emitter layer, any cladding film with a certain thickness is formed, and ion implantation is performed on the semiconductor layer through the cladding film to form an emitter with a preferred doping concentration distribution. The polar layer method is described. In addition, it is only necessary for the cover film to cover at least a part of the substrate, and it is not necessary to completely cover the substrate. In addition, the thickness of the entire covering film does not need to be the same, and the thickness of each region may be different.

In the present embodiment, a screen film is used as the coating film of the silicon (semiconductor) layer. As the screen film, an oxide film, a nitride film, or the like that is easily formed on a silicon substrate can be formed by a technique such as CVD or sputtering, or a printing technique or a coating technique. In addition, in consideration of the thickness of the screen film to be formed and the required ion implantation energy, it is preferable to form an oxide film or a nitride film by a technique such as CVD or sputtering. In addition, the material of the film is not particularly limited as long as ions are permeable, but a material having less influence on the inside of the silicon substrate due to impacts during ion implantation is preferable.

After the mask is formed, the energy of ion implantation is adjusted so that the ion implantation range Rp is near the interface between the mask and the silicon substrate, and ion implantation is performed on the silicon substrate through the mask. FIG. 2 is a diagram showing an example of a doping concentration distribution when ion implantation is performed into a silicon substrate through a mask. The screen film shown in FIG. 2 is an oxide film (SiO ₂ film) with a thickness of about 70 nm. Moreover, in the doping concentration distribution shown in Fig. 2, phosphorus (P) is used as implanted ion species, and the silicon substrate is ionized through the screen film under the conditions of acceleration energy of 60keV and dose of 3× ¹⁰¹⁵ / ^cm2 . injection.

The doping concentration profile Pr' shown in FIG. 2 is an ideal profile in which the doping concentration profile Pr' is gentle at least near the surface S' of the silicon substrate, and the concentration gradually and sharply decreases toward the inside of the substrate. In addition, the acceleration energy of about 60keV is the preferred energy for an ion implantation device that is accelerated as a stage to easily output a large current. Even if nearly half of the dose remains on the screen film, there is no problem in productivity. Therefore, the acceleration energy of implanted ions can be adjusted to 40 keV or more, more preferably 50 keV or more. In addition, the acceleration energy of implanted ions can be adjusted to, for example, 80 keV or less, more preferably 70 keV or less. In addition, the acceleration energy of implanted ions is not limited to the above example, and may be appropriately changed according to various conditions of the screen film or the silicon substrate.

After performing ion implantation under the above-mentioned conditions, the oxide film on the surface is removed by etching with buffered hydrofluoric acid or the like. FIG. 3 is a diagram showing an example of a doping concentration distribution inside a silicon substrate after removing a screen film. As shown in FIG. 3, the surface S' of the silicon substrate is exposed, and an ideal doping concentration distribution Pr'' is formed in the silicon substrate.

Fig. 4 is a flowchart of a method of manufacturing a solar battery cell according to the first embodiment. 5( a ) to 5 ( f ) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing the solar battery cell according to the first embodiment.

In the present embodiment, the case where a p-type single crystal silicon substrate is used as the semiconductor substrate is described, but the present invention can also be applied when using an n-type silicon substrate or a polycrystalline substrate, or other p-type or n-type compound semiconductor substrates. invention. Hereinafter, a method of manufacturing the solar battery cell according to the first embodiment will be described with reference to FIGS. 4 and 5 .

First, as shown in FIG. 5( a ), a p-type silicon substrate 10 is prepared by slicing a single crystal silicon ingot by a multi-wire method. Next, after removing damage caused by slicing the substrate surface with an alkaline solution, fine unevenness (texture: not shown in FIG. 5( a )) with a maximum height of about 10 μm is formed on the light-receiving surface (S10 in FIG. 4 ). The light-trapping effect is obtained by the scattering caused by the concave-convex structure, which contributes to the improvement of the conversion efficiency.

Next, as shown in FIG. 5(b), on the surface of the silicon substrate 10, a screen film 12 made of a film (or coating film) such as SiO ₂ is formed (S12 in FIG. 4). The thickness of the screen film 12 is, for example, about 10 to 100 nm. In this way, a solar cell substrate having a p-type (first conductivity type) silicon substrate 10 and a screen film 12 as a coating film covering the silicon substrate 10 is prepared. Next, as shown in FIG. 5(c), the silicon substrate 10 is irradiated with n-type (second conductivity type) ions of the opposite conductivity type to the silicon substrate 10 through the screen film 12, and the light-receiving surface side of the silicon substrate 10 Part of the region forms the emitter layer 14 (S14 in FIG. 4).

In the emitter layer forming process according to the present embodiment, as described in FIG. ') to irradiate ions with the energy of the distance (refer to FIG. 5(b)).

Next, as shown in FIG. 5(d), the screen film 12 is removed (S16 in FIG. 4), and an activation annealing treatment is performed to alleviate damage to the silicon substrate 10 caused by ion implantation (S18 in FIG. 4). In addition, the order of the removal of the screen film 12 and the activation annealing treatment may be reversed. Then, as shown in FIG. 5(e), an antireflection film 16 such as SiN or TiO ₂ is formed on the surface of the emitter layer 14 by CVD or the like (S20 in FIG. 4 ). The thickness of the antireflection film 16 is, for example, about 10 to 100 nm.

Next, as shown in FIG. 5(f), the direct light-receiving surface electrode 18 is formed on a predetermined region of the emitter layer 14 along the pattern of the antireflection film 16 (S22 in FIG. 4). The light-receiving surface electrode 18 is formed into a comb shape with a width of about 50 to 100 μm by, for example, printing or firing a paste for a light-receiving surface electrode mainly composed of silver (Ag). The height of the light-receiving surface electrode 18 is about 10 to 50 μm.

In addition, at this stage, the back electrode 20 is also formed by printing and firing using a paste for a back electrode whose main component is aluminum (Al). At this time, Al contained in the paste diffuses into the silicon substrate 10 to form the p+ layer 22 near the back electrode 20 . Thus, a BSF (Back Surface Field) effect can be obtained.

Through the above steps, the solar cell 100 is manufactured. In this solar battery cell 100 , since the peak of the concentration distribution of ions to be doped does not exist in the emitter layer 14 , carriers can easily move during power generation. That is, ion implantation is performed through the screen film 12 , thereby avoiding a doping concentration distribution that is generally common in ion implantation, specifically, a distribution in which the doping concentration increases once from the surface of the silicon substrate and then decreases. To describe in detail, in the emitter layer 14 of the solar cell 100 according to this embodiment, the doping concentration distribution is a gentle concentration gradient near the surface, and the concentration gradient gradually increases as it goes deeper from the surface. ideal shape. As a result, a solar battery cell with high power generation efficiency is obtained.

Moreover, when the processes of step S16 and step S18 shown in FIG. 4 are exchanged, and when the screen film is removed after the activation annealing treatment, in the high-concentration layer of dopant generated at the interface between the screen film and the silicon substrate, by removing the screen film Since a part is removed, it is possible to reduce recombination of carriers generated in the high-concentration layer and the like.

In addition, by appropriately selecting the film thickness of the screen film, in the ion implantation apparatus, the ion implantation process can be performed under the condition of high ion transmission efficiency, and the productivity can be improved. That is, by setting the thickness of the screen film to a predetermined value or more (for example, 10 nm or more), the acceleration energy of ions is increased, so that ion implantation efficiency becomes high. On the other hand, by setting the thickness of the screen film to a predetermined value or less (for example, 100 nm or less), useless ions that cannot reach the substrate and stay inside the screen film are reduced.

In addition, in this embodiment, the passivation film (anti-reflection film 16) is formed only on the surface side of the solar battery cell 100 (the side closer to the surface side than the silicon substrate 10), but it may be formed on the surface side of the solar battery cell 100 and Passivation films are formed on both sides of the back side. In addition, in this embodiment, the case of irradiating ions from the front side of the silicon substrate 10 has been described, but this method can also be applied to the case of irradiating ions from the back side or the case of irradiating ions from both the front side and the back side. invention.

(second embodiment)

In this embodiment, a case where an antireflection film is used as a screen film will be described. 6 is a flowchart of a method of manufacturing a solar battery cell according to the second embodiment. 7( a ) to 7 ( e ) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing a solar battery cell according to the second embodiment. In addition, the same code|symbol is attached|subjected to the same component or process as 1st Embodiment, and description is abbreviate|omitted suitably.

First, as shown in FIG. 7( a ), texture is formed on the light-receiving surface of the p-type silicon substrate 10 ( S10 in FIG. 6 ). Next, as shown in FIG. 7(b), an antireflection film 16 such as SiN or TiO ₂ is formed on the surface of the silicon substrate 10 by CVD or the like (S24 in FIG. 6). The thickness of the antireflection film 16 is, for example, about 10 to 100 nm. Thus, a solar cell substrate having a p-type (first conductivity type) silicon substrate 10 and an antireflection film 16 as a coating film covering the silicon substrate 10 is prepared.

Next, as shown in FIG. 7( c), the silicon substrate 10 is irradiated with n-type (second conductivity type) ions of the opposite conductivity type to the silicon substrate 10 through the anti-reflection film 16, and on the light-receiving surface side of the silicon substrate 10, Part of the region forms the emitter layer 14 (S26 in FIG. 6).

In the emitter layer forming process according to the present embodiment, as described in FIG. The energy irradiated ions at the distance to the surface S') (refer to Fig. 7(b))

Next, as shown in FIG. 7( d ), activation annealing is performed in order to alleviate damage to the silicon substrate 10 caused by ion implantation ( S28 in FIG. 6 ). Then, as shown in FIG. 7( e ), the light-receiving surface electrode 18 and the rear surface electrode 20 are formed by the same process as that of the first embodiment in step S22 .

Through the above steps, the solar cell 200 is manufactured. This solar cell 200 can obtain the same effects as those of the solar cell 100 according to the first embodiment. In addition, by using the antireflection film 16 as the screen film, it is possible to reduce the number of steps compared with the method of manufacturing the solar battery cell 100 according to the first embodiment. Furthermore, since no photoelectric reaction occurs in the antireflection film 16 , the doping concentration distribution in the antireflection film 16 does not affect the movement of minority carriers.

In addition, in this embodiment, the antireflection film 16 is directly formed on the silicon substrate 10 , but another passivation film may be formed between the silicon substrate 10 and the antireflection film 16 . At this time, another passivation film can be formed on the silicon substrate 10, and the anti-reflection film 16 can be formed after irradiating ions from the side of the other passivation film. The passivation film and the antireflection film 16 side are irradiated with ions.

(third embodiment)

In this embodiment mode, a case where an antireflection film is used as a screen film and a contact region is formed in addition to the emitter layer will be described. 8 is a flowchart of a method of manufacturing a solar battery cell according to the third embodiment. 9( a ) to 9 ( e ) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing a solar battery cell according to the third embodiment. 10(a) to 10(b) are schematic cross-sectional views of the semiconductor substrate in each step of the method of manufacturing a solar cell according to the third embodiment. In addition, the same code|symbol is attached|subjected to the same component or process as each above-mentioned embodiment, and description is abbreviate|omitted suitably.

First, as shown in FIG. 9( a ), texture is formed on the light-receiving surface of the p-type silicon substrate 10 ( S10 in FIG. 8 ). Next, as shown in FIG. 9(b), an antireflection film 16 such as SiN or TiO ₂ is formed on the surface of the silicon substrate 10 by CVD or the like (S24 in FIG. 8 ). Next, as shown in FIG. 9( c), the silicon substrate 10 is irradiated with n-type (second conductivity type) ions of the opposite conductivity type to the silicon substrate 10 through the anti-reflection film 16, and on the light-receiving surface side of the silicon substrate 10, A part of the region forms the emitter layer 14 (S26 in FIG. 8).

Next, as shown in FIG. 9( d ), a mask 24 patterned so that a predetermined region of the antireflection film 16 is exposed is formed ( S30 in FIG. 8 ). As the mask 24, a mask or a hard mask formed by a photolithography method or a printing method can be used.

Next, as shown in FIG. 9( e ), an n-type dopant having a conductivity type opposite to that of the substrate is implanted into the entire surface of the light-receiving surface side of the substrate again by ion implantation. At this time, ions are selectively implanted into a part of the emitter layer 14 below the predetermined region 16 a exposed to the antireflection film 16 not covered by the mask. As a result, a contact region 26 having a higher impurity concentration than other regions is formed in a predetermined region of the emitter layer 14 (S32 in FIG. 8 ). Such a method of selectively implanting ions into a part of the substrate to form a contact region with a high impurity concentration is called a selective emitter. In this way, by masking the portion where ion implantation is not required and performing ion implantation, a selective ion implantation pattern corresponding to the unmasked portion is formed in a predetermined region of the substrate.

Next, as shown in FIG. 10( a ), the mask 24 is removed from the silicon substrate 10 ( S34 in FIG. 8 ), and activation annealing is performed on the entire substrate ( S36 in FIG. 8 ). Then, as shown in FIG. 10( b ), the light-receiving surface electrode 18 and the rear surface electrode 20 are formed by the same process as that of the first embodiment in step S22 .

Through the above steps, the solar cell 300 is manufactured. This solar battery cell 300 can obtain the same effect as the solar battery cell according to each of the above-mentioned embodiments.

In addition, in this embodiment, the antireflection film 16 is directly formed on the silicon substrate 10 , but another passivation film may be formed between the silicon substrate 10 and the antireflection film 16 . At this time, another passivation film can be formed on the silicon substrate 10, and the anti-reflection film 16 can be formed after irradiating ions from the side of the other passivation film. The passivation film and the antireflection film 16 side are irradiated with ions.

In the solar cell according to each of the above-mentioned embodiments, ions are irradiated (implanted) to the substrate via the screen film 12 or the antireflection film 16 , thereby enabling shallow junctions on the surface of the substrate without reducing energy too much. In addition, since ion implantation is completed without reducing the energy too much, reduction in beam transmission efficiency is avoided, and productivity is improved.

In addition, the peak position of the doping concentration distribution is not necessarily inside the screen film 12 or the antireflection film 16 . For example, in the emitter layer forming step, ions may be irradiated with energy such that the peak position of the concentration distribution of the ions in the depth direction becomes the depth D±10 nm up to the interface between the screen film 12 or the antireflection film 16 and the silicon substrate 10. range. As a result, the peak of the concentration distribution of the doped ions exists near the interface between the screen film or the anti-reflection film 16 and the silicon substrate 10 , so that carriers can easily move during power generation.

As mentioned above, although this invention was demonstrated with reference to said each embodiment, this invention is not limited to the above-mentioned embodiment, About the form which suitably combines or replaces the structure of each embodiment, it is also included in this invention. In addition, according to the knowledge of those skilled in the art, various modifications such as design changes can be added to the embodiments in the ion implantation apparatus, transfer container, etc. in each embodiment, and such embodiments with added modifications are also included in within the scope of the present invention.

In each of the above-mentioned embodiments, the case where a new coating film is formed on the silicon substrate has been described, but it is also possible to process the surface of the silicon substrate to modify the surface layer into a silicon oxide film, and perform ion implantation using this as a coating film. .

Claims (4)

1. A method for manufacturing a solar cell unit, comprising: a preparation step of preparing a solar cell substrate having a silicon layer of the first conductivity type and a coating film covering the silicon layer; and an emitter layer forming step of irradiating the silicon layer with ions of the second conductivity type through the coating film to form an emitter layer in a part of the light-receiving surface side of the silicon layer, In the emitter layer forming step, the ions are irradiated with energy such that the range of the ions is the distance from the surface of the coating film to the interface between the coating film and the silicon layer. 2. The method of manufacturing a solar cell unit according to claim 1, wherein The coating film is an anti-reflection film. 3. The method for manufacturing a solar cell unit according to claim 1, further comprising: a removing step of removing the cover film after forming the emitter layer; and An antireflection film forming step is to form an antireflection film on the emitter layer after the removal step. 4. A method for manufacturing a solar cell unit, comprising: a preparation step of preparing a solar cell substrate having a silicon layer of the first conductivity type and a coating film covering the silicon layer; and an emitter layer forming step of irradiating the silicon layer with ions of the second conductivity type through the coating film to form an emitter layer in a part of the light-receiving surface side of the silicon layer, In the emitter layer forming step, the ions are irradiated with energy such that the peak position of the concentration distribution of the ions in the depth direction becomes a depth D±10 nm from the interface between the coating film and the silicon layer. scope.