KR20140139959A - Method for manufacturing solar cell - Google Patents

Abstract

A method for manufacturing a solar cell using an ion implanting method is provided. The method for manufacturing the solar cell according to one aspect comprises a preparation process of preparing for a substrate for the solar cell having a first conduction type silicon layer and a coated film covering the silicon layer; and an emitter layer forming process of forming an emitter layer on a partial area of a light receiving surface of the silicon layer by scanning a second conduction type ion toward the silicon layer via the coated film. In the emitter layer forming process, the ion is scanned with energy making an ion arrival distance become a distance from a surface of the coated film to an interface between the coated film and the silicon layer.

Description

[0001] The present invention relates to a method for manufacturing a solar cell,

The present application claims priority based on Japanese Patent Application No. 2013-110595, filed on May 27, 2013. The entire contents of which are incorporated herein by reference.

The present invention relates to a method of manufacturing a solar cell.

In a solar cell, electrons and holes move to the n-layer side and the p-layer side, respectively, by an electric field caused by a pn junction or the like formed in the inside of a cell when a semiconductor material such as silicon absorbs light. And is taken out as a current. the formation of the pn junction and the contact layer requires a treatment for locally varying the concentration or type of the impurity. In order to increase the amount of light entering the interior of the solar cell as much as possible, an antireflection film is formed on the light receiving surface side of the silicon substrate.

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

Prior art literature

(Patent Literature)

Patent Document 1: JP-A-2010-527163

However, when the emitter layer is formed using the ion implantation method, the reaching distance of the ions to be implanted is a position (depth) advanced to some extent from the surface of the silicon substrate. As a result, the concentration profile of the doping 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 of the impurity concentration is an obstacle to the movement of the carrier, which is one of the factors that causes a decrease in power generation efficiency.

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

According to an aspect of the present invention, there is provided a method of manufacturing a solar cell including a preparation step of preparing a substrate for a solar cell having a silicon layer of a first conductivity type and a coating film covering the silicon layer; And an emitter layer forming step of irradiating ions of a 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. The emitter layer forming step irradiates the ions with energy such that the ion reaching distance is the distance from the surface of the coating film to the interface between the coating film and the silicon layer.

Another aspect of the present invention is a method of manufacturing a solar cell. This method comprises a preparation step of preparing a substrate for a solar cell having a silicon layer of a first conductivity type and a coating film covering the silicon layer and a step of irradiating ions of a second conductivity type toward the silicon layer through the coating film, And an emitter layer forming step of forming an emitter layer in a part of the light receiving surface side. In the emitter layer forming step, the ions are irradiated with energy such that the peak position of the concentration profile in the depth direction of the ions is within the range (D) ± 0 nm to the interface between the coating film and the silicon layer.

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

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a result of a doping concentration profile when standard ion implantation is performed. FIG.
2 is a diagram showing an example of a doping concentration profile when ion implantation is performed on a silicon substrate through a screen film.
3 is a diagram showing an example of the doping concentration profile in the silicon substrate after the screen film is removed.
4 is a flowchart of a manufacturing method of the solar cell according to the first embodiment.
5A to 5F are schematic cross-sectional views of a semiconductor substrate in each step of the method for manufacturing a solar cell according to the first embodiment.
6 is a flowchart of a method of manufacturing a solar cell according to the second embodiment.
In Fig. 7, Figs. 7A to 7E are schematic sectional views of the semiconductor substrate in each step of the method for manufacturing a solar cell according to the second embodiment.
8 is a flowchart of a manufacturing method of the solar cell according to the third embodiment.
In Fig. 9, Figs. 9 (a) to 9 (e) are schematic sectional views of the semiconductor substrate in each step of the method for manufacturing a solar cell according to the third embodiment.
10 (a) to 10 (b) are schematic cross-sectional views of a semiconductor substrate in each step of the method for manufacturing a solar cell according to the third embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the configurations described below are illustrative and do not limit the scope of the present invention at all. In the description of the drawings, the same elements are denoted by the same reference numerals and redundant explanations are appropriately omitted. In each of the cross-sectional views illustrating the manufacturing method, the thickness and size of the semiconductor substrate and other layers are for convenience of explanation, and do not necessarily indicate actual dimensions or ratios.

(First Embodiment)

There are various types of solar cells. For example, a crystalline Si-based solar cell maintains superiority to other types of solar cells due to its simple structure, manufacturing method, and high conversion efficiency. On the other hand, in order to obtain a higher conversion efficiency in a crystalline Si-based solar cell, finding the optimum condition for each process unit is very important for differentiation. Among them, the formation of a surface emitter layer in which the photoelectric effect appears dominant is considered to be a very important factor, and it is considered desirable to have the following characteristics.

However, at present, both the thermal diffusion method and the ion implantation method which are used as a general manufacturing method are difficult to satisfy the following characteristics at the same time from their characteristics.

(1) shallow junction. Specifically, the internal diffusion potential should be closer to the surface.

(2) Optimum doping concentration. Specifically, the emitter concentration should have a predetermined high concentration for the contact with the electrodes and the movement of the majority carriers through the emitter layer. On the other hand, the concentration should not be too high in view of reducing recombination of minority carriers.

(3) Do not have a specific concentration peak inside the surface. Specifically, the high-low junction of the strong electric field enough to become a barrier of the movement of the minority carriers does not exist inside the surface.

(4) Have some high-low junction on top surface. Specifically, it should have the effect of emitting a minority carrier from the surface to the opposite surface.

The feature of the ion implantation method for the thermal diffusion method is very advantageous in terms of the above-mentioned (1) and (2) in that the doping depth and concentration can be controlled. On the other hand, when ion implantation is used, the doping concentration decreases from the peak position toward the surface layer with a peak corresponding to the depth of the ion acceleration energy.

Fig. 1 is a diagram showing a result of a doping concentration profile when standard ion implantation is performed. The ion implantation shown in Fig. 1 is performed on a silicon substrate under the condition that phosphorus (P) is used as an ion species to be implanted and the acceleration energy is 10 keV and the dose amount is 3 x 10 ¹⁵ ions / cm ² . 1, the doping concentration gradually increases from the surface S, and the doping concentration reaches a peak at a depth D of about 0.015 mu m (15 nm) from the surface S. As a result, , And then the doping concentration decreases. That is, the ion implantation depth Rp in the ion implantation is about 0.015 mu m (15 nm).

This profile Pr is somewhat alleviated by the subsequent activation annealing, but the ion implantation method has room for further improvement from the viewpoint of the above-mentioned (3). Further, in order to form a shallow junction, ion implantation of low energy is required, but generally, the lower the energy is, the lower the transport efficiency of the beam, and the productivity is lowered.

In view of this point, the present invention realizes a method of manufacturing a new solar cell using an ion implantation method. In the following embodiments, a coating film having a predetermined thickness is formed before the formation of the emitter layer in consideration of the ion reaching distance, and ion implantation is performed on the semiconductor layer through the coating film to form an emitter layer having a desired doping concentration profile Will be described. However, the coating film needs to cover at least a part of the substrate and does not need to completely cover the substrate. The thickness of the coating film is not necessarily uniform on the whole, and the thickness may be different for each region.

In this embodiment, a screen film is used as a coating film of a silicon (semiconductor) layer. As the screen film, an oxide film or a nitride film which is easily formed on a silicon substrate may be formed by a technique such as CVD or sputtering, or may be formed by a printing technique or a coating technique. However, considering the thickness of the screen film to be produced 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. The material of the film is not particularly limited as long as it can permeate ions, but it is preferable that the effect on the inside of the silicon substrate due to the knock-on occurred during ion implantation is small.

After the screen film is formed, the energy of the ion implantation is adjusted so that the ion implantation depth Rp is near the interface between the screen film and the silicon substrate, and the silicon substrate is ion-implanted through the screen film. 2 is a diagram showing an example of a doping concentration profile when ion implantation is performed on a silicon substrate through a screen film. The screen film shown in Fig. 2 is an oxide film (SiO ₂ film) having a thickness of about 70 nm. Then, the dopant concentration profile shown in Figure 2, the implantation ion species as a by using a (P), the acceleration energy is 60keV, dose amount is 3 × 10 ¹⁵ gae / cm ² is ion-implanted with respect to the silicon substrate through the membrane screen under the conditions Is performed.

The doping concentration profile Pr 'shown in FIG. 2 is an ideal profile in which at least the vicinity of the surface S' of the silicon substrate is gentle, and the concentration is gradually decreased steeply toward the inside of the substrate. However, the acceleration energy of about 60 keV is an energy for one stage acceleration of ion implantation, which is a suitable energy which is likely to take out large current, and there is no problem in productivity even if it remains on the screen film at half the dose. Therefore, the acceleration energy of the implanted ions may be adjusted to be 40 keV or more, more preferably 50 keV or more. The acceleration energy of the implanted ions may be adjusted to be, for example, 80 keV or less, more preferably 70 keV or less. However, the acceleration energy of the implanted ions is not limited to the above example, and may be appropriately changed according to various conditions of the screen film and the silicon substrate.

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

4 is a flowchart of a manufacturing method of a solar cell according to the first embodiment. 5A to 5F are schematic cross-sectional views of a semiconductor substrate in each step of the method for manufacturing a solar cell according to the first embodiment.

In the present embodiment, a case where a p-type single crystal silicon substrate is used as the semiconductor substrate is described. However, even when an n-type silicon substrate, a polycrystalline substrate, or another p-type or n-type compound semiconductor substrate is used, can do. Hereinafter, a manufacturing method of the solar cell according to the first embodiment will be described with reference to Figs. 4 and 5. Fig.

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, the damage caused by the slice on the substrate surface is removed with an alkali solution, and fine irregularities (texture: not shown in Fig. 5A) with a maximum height of about 10 mu m are formed on the light receiving surface (S10 in Fig. 4) . The light scattering effect is obtained by scattering by the concavo-convex structure, thereby contributing to the improvement of the conversion efficiency.

To form Next, the screen film 12 formed on the surface of the silicon substrate 10, a film (or coating film) of SiO _2, etc. as shown in Fig. 5 (b) (S12 in Fig. 4). The thickness of the screen film 12 is, for example, about 10 to 100 nm. Thereby, a substrate for a solar cell having a silicon substrate 10 of p-type (first conductivity type) and a screen film 12 as a coating film covering the silicon substrate 10 is prepared. Next, as shown in Fig. 5 (c), an n-type (second conductive type) semiconductor layer 10 is formed so as to face the silicon substrate 10 through the screen film 12, ) To form an emitter layer 14 in a part of the light receiving surface side of the silicon substrate 10 (S14 in Fig. 4).

2, the ion implantation depth Rp is set such that the ion implantation depth Rp is equal to the sum of the ion implantation depth Rp from the surface S of the screen film 12 to the surface of the screen film 12 and the silicon substrate 10 Ions are irradiated with an energy that is a distance to the interface (surface S 'of the silicon substrate 10) (see Fig. 5 (b)).

Next, as shown in Fig. 5 (d), the screen film 12 is removed (S16 in Fig. 4), and an activation annealing process is performed to alleviate the damage of the silicon substrate 10 by ion implantation 4, S18). However, the order of the removal of the screen film 12 and the activation annealing process may be changed. 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.

5 (f), the light receiving surface electrode 18 is formed directly on the 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 by printing and firing a light-receiving surface electrode paste containing silver (Ag) as a main component, for example, in a comb shape having a width of about 50 to 100 mu m. The height of the light receiving surface electrode 18 is about 10 to 50 mu m.

In this step, the back electrode 20 is also formed by printing and firing using a back electrode paste mainly composed of aluminum (Al). At this time, Al contained in the paste is diffused into the silicon substrate 10 to form the p + layer 22 in the vicinity of the back electrode 20. As a result, a BSF (Back Surface Field) effect can be obtained.

By the above process, the solar cell 100 is manufactured. In this solar cell 100, since the peak of the concentration profile of the doped ions is not present in the emitter layer 14, the carrier is likely to move during power generation. That is, by doping ions through the screen film 12, it is possible to avoid the doping concentration profile seen in general ion implantation, specifically, the profile in which the doping concentration increases once from the silicon substrate surface and then decreases. As described above, in the emitter layer 14 of the solar cell 100 according to the present embodiment, the doping concentration profile becomes an ideal shape with a gradual concentration gradient in the vicinity of the surface and a gradual gradient in concentration from the surface . As a result, a solar cell having high power generation efficiency can be obtained.

When the process of steps S16 and S18 shown in Fig. 4 is changed to remove the screen film after performing the activation annealing process, the high concentration layer of the dopant, which is considered to be generated at the interface between the screen film and the silicon substrate, Since the part is removed by removal, carrier recombination due to the high concentration layer is reduced.

In addition, by appropriately selecting the film thickness of the screen film, the ion implantation process can be performed under conditions where the ion transport efficiency is high in the ion implantation apparatus, and the productivity is 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 the ions can be increased, so that the ion implantation efficiency is enhanced. On the other hand, when the thickness of the screen film is set to a predetermined value or less (for example, 100 nm or less), unnecessary ions staying in the screen film without reaching the substrate can be reduced.

In this embodiment, the passivation film (antireflection film 16) is formed only on the front surface side (the surface side of the silicon substrate 10) of the solar cell 100, And a passivation film may be formed on both sides of the back surface. In the present embodiment, the case of irradiating ions from the surface side of the silicon substrate 10 has been described. However, in the case of irradiating ions from the back surface side or irradiating ions from both the front surface side and the back surface side, Can be applied.

(Second Embodiment)

In the present embodiment, a case where the antireflection film is used as a screen film will be described. 6 is a flowchart of a manufacturing method of a solar cell according to the second embodiment. 7A to 7E are schematic cross-sectional views of a semiconductor substrate in each step of the method for manufacturing a solar cell according to the second embodiment. However, the same reference numerals are given to the same components and processes as those of the first embodiment, and the description thereof will be appropriately omitted.

First, as shown in Fig. 7 (a), a texture is formed on the light receiving surface of the p-type silicon substrate 10 (S10 in Fig. 6). Next, Fig. 7 (b) as shown in, to form the anti-reflection film 16 of on the surface of the silicon substrate (10), SiN or TiO _2, etc., by CVD method (S24 in Fig. 6). The thickness of the antireflection film 16 is, for example, about 10 to 100 nm. Thereby, a substrate for a solar cell 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), an n-type (second conductivity type) ion which is opposite in conductivity to the silicon substrate 10 is applied to the silicon substrate 10 through the antireflection film 16 And the emitter layer 14 is formed in a part of the light receiving surface side of the silicon substrate 10 (S26 in Fig. 6).

In the emitter layer forming step according to the present embodiment, the ion implantation depth Rp is set such that the ion implantation depth Rp of the antireflection film 16 from the surface S of the antireflection film 16 to the silicon substrate 10 Ions are irradiated with an energy that is a distance to the interface (surface S 'of the silicon substrate 10) (see Fig. 7 (b)).

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

By the above process, the solar cell 200 is manufactured. This solar cell 200 has the same effect as the solar cell 100 according to the first embodiment. In addition, the use of the antireflection film 16 as the screen film can reduce the number of steps compared with the method of manufacturing the solar cell 100 according to the first embodiment. Since the photoelectric reaction does not occur in the antireflection film 16, the doping concentration profile in the antireflection film 16 does not affect the movement of the minority carriers.

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. [ In this case, another passivation film may be formed on the silicon substrate 10 and the antireflection film 16 may be formed after the ions are irradiated from the other passivation film side. Alternatively, another passivation film and antireflection film 16 may be formed on the silicon substrate 10, Ions may be irradiated from the other passivation film and antireflection film 16 side.

(Third Embodiment)

In the present embodiment, a case where the antireflection film is used as a screen film and the contact region is formed in addition to the emitter layer will be described. 8 is a flowchart of a manufacturing method of the solar cell according to the third embodiment. 9 (a) to 9 (e) are schematic sectional views of a semiconductor substrate in each step of the method for manufacturing a solar cell according to the third embodiment. 10 (a) to 10 (b) are schematic sectional views of a semiconductor substrate in each step of the method for manufacturing a solar cell according to the third embodiment. However, the same reference numerals are given to the same constituent elements and processes as those of the above-described embodiments, and the description thereof will be omitted as appropriate.

First, as shown in Fig. 9 (a), a texture is formed on the light receiving surface of the p-type silicon substrate 10 (S10 in Fig. 8). Next, Figure 9 (b) as shown in, to form the anti-reflection film 16 of on the surface of the silicon substrate (10), SiN or TiO _2, etc., by CVD method (S24 in Fig. 8). Next, as shown in Fig. 9 (c), an n-type (second conductivity type) ion which is opposite in conductivity to the silicon substrate 10 is applied to the silicon substrate 10 through the antireflection film 16 And the emitter layer 14 is formed on a part of the light receiving surface side of the silicon substrate 10 (S26 in Fig. 8).

Next, as shown in Fig. 9 (d), a patterned mask 24 is formed so as to expose a predetermined region of the antireflection film 16 (S30 in Fig. 8). The mask 24 is formed by a photolithography method or a printing method, but a hard mask can be used.

Next, as shown in Fig. 9 (e), an n-type dopant which is opposite in conductivity to the substrate is again injected into the light receiving surface side of the substrate by ion implantation. At this time, ions are selectively implanted into a region of a part of the emitter layer 14 under the antireflection film 16, which is not covered by the mask, through the exposed predetermined region 16a of the antireflection film 16. Thus, a contact region 26 having a higher impurity concentration than the other impurity concentration is formed in a predetermined region of the emitter layer 14 (S32 in Fig. 8). The method of selectively implanting ions into a part of the substrate as described above to form a contact region having a high impurity concentration is also referred to as a selective emitter. According to this method, after the portion where ion implantation is unnecessary is performed, ion implantation is performed, so that a selective ion implantation pattern corresponding to a portion which is not masked is formed in a predetermined region of the substrate.

Next, as shown in Fig. 10A, the mask 24 is removed from the silicon substrate 10 (S34 in Fig. 8), and the entire substrate is subjected to activation annealing (S36 in Fig. 8). Then, as shown in Fig. 10 (b), the light receiving surface electrode 18 and the back electrode 20 are formed by the process of step S22, which is the same as that of the first embodiment.

By the above process, the solar cell 300 is manufactured. The solar cell 300 has the same effect as the solar cell according to each of the above-described embodiments.

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. [ In this case, another passivation film may be formed on the silicon substrate 10 and the antireflection film 16 may be formed after the ions are irradiated from the other passivation film side. Alternatively, another passivation film and antireflection film 16 may be formed on the silicon substrate 10, Ions may be irradiated from the other passivation film and antireflection film 16 side.

The solar cell according to each of the embodiments described above can irradiate (inject) ions to the substrate through the screen film 12 and the antireflection film 16 to realize shallow junctions in the surface layer of the substrate without significantly lowering the energy have. Further, since the energy at the time of ion implantation is not reduced so much, the decrease in the transport efficiency of the beam can be avoided, and the productivity is improved.

However, the peak position of the doping concentration profile does not necessarily have to be inside the screen film 12 or the anti-reflection film 16. For example, in the emitter layer forming step, the peak position of the concentration profile in the depth direction of the ions is set to a depth (D) of 10 nm to the interface between the screen film 12 and the antireflection film 16 and the silicon substrate 10 The ions may be irradiated with energy in the range of As a result, the peak of the concentration profile of the doped ions exists in the vicinity of the interface between the screen film and the antireflection film 16 and the silicon substrate 10, so that the carrier tends to move at the time of power generation.

Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above-described embodiments, but the present invention is not limited to the above embodiments. It is also possible to add various modifications to the embodiment in the ion implantation apparatus, the transport container, and the like in each embodiment based on the knowledge of those skilled in the art, and embodiments in which such modifications are added are also within the scope of the present invention .

In each of the above-described embodiments, the coating film is newly formed on the silicon substrate. However, the surface of the silicon substrate may be treated to change the surface layer into a silicon oxide film, and the coating film may be ion-implanted.

10: silicon substrate
12: Screen membrane
14:
16: Antireflection film
18: Light receiving surface electrode
20: back electrode
24: Mask
26: contact area
100, 200, 300: solar cell

Claims (4)

A preparation step of preparing a substrate for a solar cell having a silicon layer of a first conductivity type and a coating film covering the silicon layer;
And an emitter layer forming step of irradiating ions of a second conductivity type toward the silicon layer through the coating film to form an emitter layer in a part of the light receiving surface side of the silicon layer,
Wherein the ion implantation depth in the emitter layer forming step is such that the ions are irradiated with energy such that the ion implantation depth is a distance from a surface of the coating film to an interface between the coating film and the silicon layer Way. The method according to claim 1,
Wherein the coating film is an antireflection film. The method according to claim 1,
A removing step of removing the coating film after the emitter layer is formed,
Further comprising an antireflection film forming step of forming an antireflection film on the emitter layer after the removing step. A preparation step of preparing a substrate for a solar cell having a silicon layer of a first conductivity type and a coating film covering the silicon layer;
And an emitter layer forming step of irradiating ions of a second conductivity type toward the silicon layer 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 profile in the depth direction of the ions is within a range (D) ± 10 nm from the interface between the coating film and the silicon layer Wherein the method comprises the steps of:

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