JP2011061020A - Back contact solar cell element, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back contact solar cell element capable of reducing contact resistance while suppressing recombination loss of carriers, and to provide a method of manufacturing the same. <P>SOLUTION: This back contact solar cell element includes a silicon substrate 101 containing first conductivity type impurities at a first concentration, and first electrodes 110 and second electrodes 111 formed on a light non-reception surface 102b on the side opposite to a light reception surface 102a of the silicon substrate 101. In the solar cell element, the silicon substrate 101 includes, in a predetermined region of a surface layer part of the light non-reception surface 102b, a first conductivity type impurity region 104 containing the first conductivity type impurities at a second concentration higher than the first concentration, and a second conductivity type impurity region 105 containing second conductivity type impurities; the first electrode 110 is connected to the first conductivity type impurity region 104; the second electrode 111 is connected to the second conductivity type impurity region 105; a first silicide layer 108 is formed in a contact part between the first electrode 110 and the first conductivity type impurity region 104; and a second silicide layer 109 is formed in a contact part between the second electrode 111 and the second conductivity type impurity region 105. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a back contact solar cell element having no electrode on a light receiving surface and a method for manufacturing the same.

As a conventional back contact solar cell element using a crystalline silicon substrate having no electrode on the light receiving surface, a p ⁺ region and an n region are formed on a predetermined region of the non-light receiving surface opposite to the light receiving surface of the p-type silicon substrate. It has been proposed that a ⁺ region is formed and a first electrode and a second electrode that are in contact with these regions are formed on a p ⁺ region and an n ⁺ region (see, for example, Patent Document 1).
According to this back contact solar cell element, since there is no electrode on the light receiving surface, the light shadow area becomes zero, and a large amount of light necessary for power generation can be taken into the solar cell.

JP 2002-164556 A

In this back contact solar cell element, it is necessary to reduce the contact area between the first electrode and the p ⁺ region and the contact area between the second electrode and the n ⁺ region in order to suppress carrier recombination.
However, when the contact area decreases, the contact resistance increases and the power generation performance deteriorates.

  The present invention has been made in view of such conventional problems, and provides a back contact solar cell element capable of reducing contact resistance while suppressing carrier recombination loss, and a method for manufacturing the back contact solar cell element. Objective.

  Thus, according to the present invention, the silicon substrate containing the first conductivity type impurity at the first concentration, and the first electrode and the second electrode formed on the non-light-receiving surface opposite to the light-receiving surface of the silicon substrate. The silicon substrate has a first conductivity type impurity region containing a first conductivity type impurity at a second concentration higher than the first concentration in a predetermined region of a surface layer portion of the non-light-receiving surface; A second conductivity type impurity region containing a conductivity type impurity, the first electrode is connected to the first conductivity type impurity region, and the second electrode is connected to the second conductivity type impurity region, A first silicide layer is formed at a contact portion between the first electrode and the first conductivity type impurity region, and a second silicide layer is formed at a contact portion between the second electrode and the second conductivity type impurity region. Back contact solar cell element is provided .

  According to another aspect of the present invention, a second region higher than the first concentration is provided in a predetermined region of the non-light-receiving surface opposite to the light-receiving surface of the silicon substrate containing the first conductivity type impurity at the first concentration. Forming a first conductivity type impurity region containing a first conductivity type impurity and a second conductivity type impurity region containing a second conductivity type impurity at a concentration of, and on the first conductivity type impurity region; (B) forming a first silicide layer and forming a second silicide layer on the second conductivity type impurity region; forming a first electrode on the first silicide layer; and A method of manufacturing a back contact solar cell element including a step (C) of forming a second electrode on a layer is provided.

  According to the present invention, since there is no electrode on the light receiving surface, a large amount of light necessary for power generation can be taken in, and the contact resistance can be reduced while suppressing the recombination loss of the carrier. A back contact solar cell element with mainly improved curve factor and improved power generation efficiency can be obtained.

It is a schematic sectional drawing which shows Example 1 of the back contact type solar cell element of this invention. 2 is a conceptual diagram showing a positional relationship between first and second conductivity type impurity regions and first and second electrodes in a back contact solar cell element of Example 1. FIG. FIG. 3 is a process explanatory view showing a part of the manufacturing process of the back contact solar cell element according to Example 1; It is process explanatory drawing which shows the manufacturing process following the process of FIG. FIG. 5 is a process explanatory diagram showing a manufacturing process subsequent to the process of FIG. 4. It is process explanatory drawing which shows the manufacturing process following the process of FIG. FIG. 7 is a process explanatory diagram showing a manufacturing process subsequent to the process of FIG. 6.

  The back contact solar cell element of the present invention includes a silicon substrate containing a first conductivity type impurity at a first concentration, a first electrode formed on a non-light-receiving surface opposite to the light-receiving surface of the silicon substrate, A first conductivity type impurity region containing a first conductivity type impurity at a second concentration higher than the first concentration in a predetermined region of a surface layer portion of the non-light-receiving surface of the silicon substrate; And a second conductivity type impurity region containing a second conductivity type impurity, wherein the first electrode is connected to the first conductivity type impurity region, and the second electrode is connected to the second conductivity type impurity region. A first silicide layer is formed at a contact portion between the first electrode and the first conductivity type impurity region, and a second silicide is formed at a contact portion between the second electrode and the second conductivity type impurity region. A layer is formed.

Here, “first conductivity type” means n-type or p-type, and “second conductivity type” means p-type or n-type different from the first conductivity type.
Examples of p-type impurities include boron, aluminum, gallium, and indium. Examples of n-type impurities include phosphorus, arsenic, and antimony.
In this back contact solar cell element, the silicon substrate may be monocrystalline, polycrystalline, or amorphous, and the conductivity type may be n-type or p-type. The n-type is more preferable than the p-type because the resistance can be lowered at the same impurity concentration and the loss due to electric resistance is reduced.
For the first conductivity type impurity region, a mask (for example, silicon oxide film) having an opening in a predetermined region of the non-light-receiving surface of the silicon substrate is formed on the non-light-receiving surface, and a vapor phase diffusion method, a solid phase diffusion method, an ion implantation method, or the like Can be formed.
The method of forming the second conductivity type impurity region is the same as that of the first conductivity type impurity region.

  The first conductivity type impurity region and the second conductivity type impurity region are deep from the non-light-receiving surface so that high characteristics (short circuit current density, open circuit voltage, curvature factor, power generation efficiency, etc.) can be extracted from the back contact solar cell element. In addition, it is preferable to set the shape, arrangement, number, occupied area ratio with respect to the non-light-receiving surface, the interval between both adjacent regions, and the like in a plan view, and can be set as follows, for example.

[When n-type silicon substrate is used]
When an n-type silicon substrate is used, the n-type impurity concentration (first concentration) of the n-type silicon substrate is about 3 × 10 ^{14 to} 3 × 10 ¹⁵ cm ⁻³ , and the first conductivity type impurity region (n The concentration (second concentration) of the n-type impurity in the ⁺ region is about 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ , and the concentration of the p-type impurity in the second conductivity type impurity region (p ⁺ region) For example, about 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ .

The depth of the n-type impurity region from the non-light-receiving surface can be about 0.5 to 2 μm, and the depth of the p-type impurity region from the non-light-receiving surface can be about 0.5 to 2 μm.
The planar shape of each of the n-type and p-type impurity regions is not particularly limited. For example, the n-type and p-type impurity regions can be arranged in a dotted shape, a stripe shape, a meandering shape, a lattice shape, or the like.
The occupation area ratio of the n-type impurity region with respect to the non-light-receiving surface can be 5 to 20%, and the number of n-type impurity regions when the n-type impurity regions are scattered can be 100 to 1000.
The occupied area ratio of the p-type impurity region to the non-light-receiving surface can be 60 to 93%, and the number of p-type impurity regions when the p-type impurity regions are scattered can be 100 to 1000.
The interval between adjacent n-type impurity regions and p-type impurity regions can be 3 to 300 μm.

[When using a p-type silicon substrate]
When a p-type silicon substrate is used, the p-type impurity concentration (first concentration) of the p-type silicon substrate is about 3 × 10 ^{14 to} 3 × 10 ¹⁵ cm ⁻³ , and the first conductivity type impurity region (p The concentration (second concentration) of the p-type impurity in the ⁺ region is about 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ , and the concentration of the n-type impurity in the second conductivity type impurity region (n ⁺ region) For example, about 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ .

The depth of the p-type impurity region from the non-light-receiving surface can be about 0.5 to 2 μm, and the depth of the n-type impurity region from the non-light-receiving surface can be about 0.5 to 2 μm.
The shape of each of the p-type and n-type impurity regions in plan view is not particularly limited, and can be arranged in, for example, a dotted shape, a stripe shape, a meandering shape, a lattice shape, or a comb shape.
The occupied area ratio of the p-type impurity region to the non-light-receiving surface can be 5 to 20%, and the number of p-type impurity regions when the p-type impurity regions are scattered can be 100 to 1000.
The occupation area ratio of the n-type impurity region with respect to the non-light-receiving surface can be 60 to 93%, and the number of n-type impurity regions when the n-type impurity regions are scattered can be 100 to 1000.
The interval between adjacent p-type impurity regions and n-type impurity regions can be 3 to 300 μm.

From the viewpoint of reducing contact resistance while suppressing carrier recombination at the contact portion between the first electrode and the first conductivity type impurity region and at the contact portion between the second electrode and the second conductivity type impurity region, the first silicide the contact area between the contact area and the second conductive type impurity region of the second silicide layer of the first conductivity type impurity regions of the layer is preferably about 10 to 200 [mu] m ^2, about 30 to 80 [mu] m ² is more preferred. The materials constituting the first silicide layer and the second silicide layer may be the same or different, but the same material is preferable from the viewpoint of simplification of manufacturing, for example, nickel silicide, titanium silicide, cobalt silicide, palladium silicide, etc. Can be mentioned.
The first and second silicide layers are formed by forming a metal film of nickel, titanium, cobalt, palladium, etc. with a film thickness of about 30 to 70 nm on the first and second conductivity type impurity regions of the silicon substrate. It can be formed by performing a heat treatment for 1 to 30 minutes to cause a silicide reaction. At this time, depending on the material of the metal film, the silicide may be stabilized by performing a two-step heat treatment.
The metal film can be formed by a CVD method, a sputtering method, a vacuum evaporation method, or the like.

In addition, in this back contact solar cell element, an uneven structure may be formed on the light receiving surface of the silicon substrate in order to improve the light confinement effect due to the decrease in the reflectance of incident light.
When a (100) plane orientation single crystal silicon substrate is used, a pyramidal surface concavo-convex structure (texture structure) is obtained by immersing the silicon substrate in an alkaline aqueous solution such as NaOH, KOH, or NaCO ₃ and etching the light receiving surface. It is done.
In the case of a polycrystalline silicon substrate, it is composed of crystal grains of various plane orientations, and since alkali etching depends on the crystal plane orientation, a uniform texture structure as in the case of a single crystal cannot be obtained. It is difficult to reduce the reflectance as much as the case. Therefore, in the case of a polycrystalline silicon substrate, the concavo-convex structure can be uniformly formed by performing reactive ion etching on the light receiving surface regardless of the crystal plane orientation.
Even in the case of an amorphous silicon substrate, a uniform concavo-convex structure can be formed on the light receiving surface by reactive ion etching independent of the crystal plane orientation.

Furthermore, an antireflection film for suppressing recombination of carriers on the light receiving surface of the back contact solar cell element and further reducing the reflectance of incident light incident on the light receiving surface may be formed.
As the antireflection film, an insulating film such as a silicon nitride film or a silicon oxide film, and a laminated film of these insulating films can be used. When only the silicon oxide film is used, the antireflection film may be referred to as a surface passivation oxide film.
The film thickness of the antireflection film is set to a film thickness that reduces light reflection at the interface between the antireflection film and the silicon substrate. For example, the refractive index of the antireflection film to be used is 1.9 to 2.1. In this case, 50 to 80 nm is preferable, and 60 to 70 nm is more preferable. The antireflection film can be formed by a CVD method, a sputtering method, a vacuum deposition method, or the like.

In order to suppress recombination of carriers on the non-light-receiving surface of the silicon substrate of the back contact solar cell element, an insulating layer is provided in a region excluding the first silicide layer and the second silicide layer on the non-light-receiving surface of the silicon substrate. One layer or a plurality of layers may be formed.
As the insulating layer, a thermal oxide film (silicon oxide film) with a film thickness of about 10 to 100 nm can be used in the case of one layer, and a CVD film with a film thickness of about 250 to 1000 nm on the thermal oxide film in the case of two layers. A silicon oxide film can be formed.
This insulating layer functions as a mask for forming the first and second silicide layers in only the first and second conductivity type impurity regions in a self-aligned manner, and the first and second silicide layers are not formed. It also has a function of insulating the first and second electrodes so that the first and second electrodes do not directly contact the first and second conductivity type impurity regions.

The first electrode and the second electrode preferably have a shape of collecting current in contact with the plurality of first and second silicide layers. For example, the first electrode and the second electrode have a joining portion of each electrode along two opposing sides of a rectangular silicon substrate. It can be formed in a comb shape. In this case, each of the first and second silicide layers is arranged in a plurality of dots at positions overlapping with the comb-shaped first and second electrodes. The materials constituting the first and second electrodes may be the same or different, but the same materials are preferable from the viewpoint of simplification of production, and examples thereof include aluminum, an aluminum alloy, and silver.
The first and second electrodes also have a function of suppressing an increase in operating temperature due to reflection of incident light that has not been absorbed by the silicon substrate and has not generated carriers.
The first and second electrodes can be formed by a film forming technique such as a CVD method, a sputtering method, or a vacuum evaporation method, and a photo etching technique.

By providing a plurality of back contact solar cell elements, a back contact solar cell module can be configured.
In this case, for example, a plurality of back contact solar cell elements are arranged on a glass substrate with the light receiving surface facing the glass substrate side, and the first solar cell element adjacent to the first electrode of one solar cell element is arranged. A plurality of solar cells are formed by electrically connecting two electrodes to each other with a metal wire, covering a plurality of solar cell elements with a resin film in a sealed manner, and attaching a metal frame to the outer peripheral portion of the glass substrate. A back contact solar cell module in which elements are electrically connected in series can be manufactured. In addition, the 1st electrode and 2nd electrode of the solar cell element of both ends among the several back contact solar cell elements connected in series are electrically connected with the lead wire which takes out the electric power generated outside.

Example 1
<Structure of back contact solar cell element>
FIG. 1 is a schematic cross-sectional view showing Example 1 of a back contact solar cell element according to the present invention, and FIG. 2 shows first and second conductivity type impurity regions and first impurity regions in the back contact solar cell element of Example 1. -It is a conceptual diagram which shows the positional relationship with a 2nd electrode.
This back contact solar cell element includes a single crystal silicon substrate 101 containing phosphorus (P) as an n-type impurity at a first concentration of 2 × 10 ¹⁵ cm ⁻³ , and a side opposite to the light receiving surface 102 a of the silicon substrate 101. The first electrode 110 and the second electrode 111 are provided on the non-light-receiving surface 102b.
This silicon substrate 101 is a 9 cm square, has a thickness of 200 μm, and a low efficiency of 2.5 Ω · cm.

The silicon substrate 101 has a plurality of n ⁺ regions (first conductivity type impurity regions) 104 containing phosphorus at a second concentration 2 × 10 ¹⁹ cm ⁻³ higher than the first concentration in the surface layer portion of the non-light-receiving surface 102b. And a plurality of p ⁺ regions (second conductivity type impurity regions) 105 containing boron (B) as second conductivity type impurities at a concentration of 2 × 10 ¹⁹ cm ⁻³ .
As shown in FIG. 2, one n ⁺ region 104 has a dot shape with a depth of 0.5 μm and a diameter of 80 μm, and 600 dot rows 104 A are arranged in parallel with two opposite sides of the silicon substrate 101. Is arranged in.
One p ⁺ region 105 has a line shape with a depth of 0.5 μm and a width of 400 μm, and the line 105 A has a plurality of rows parallel to two opposite sides of the silicon substrate 101, and the dot rows of the n ⁺ region 104. Arranged between.
An interval L between the adjacent n ⁺ region 104 and the p ⁺ region 105 is 120 μm.

Further, the silicon substrate 101 has a pyramidal surface uneven structure on the light receiving surface 102a, and an antireflection film 103 made of a silicon nitride film having a film thickness of 65 nm is formed on the light receiving surface 102a.
Further, on the non-light-receiving surface 102 b of the silicon substrate 101, an insulating film 106 having an opening 107 with a diameter of 30 μm is formed in each n ⁺ region 104 and each p ⁺ region 105.
The insulating film 106 includes a 10 nm thick thermal oxide film formed on the non-light-receiving surface 102b of the silicon substrate 101, and a 750 nm thick non-doped silicon oxide film laminated thereon.

The first electrode 110 is formed on the insulating film 106 and has a comb-like portion 110a disposed at a position overlapping each dot row 104A in the n ⁺ region 104, and silicon extending in a direction perpendicular to the longitudinal direction of the dot row 104A. It is arranged in a position along one side of the substrate 101 and is formed in a comb shape including a connection portion 110b connected to the comb-like portion 110a.
The second electrode 111 is on the insulating film 106 and has a comb-like portion 111a disposed at a position overlapping the respective lines 105A of the p ⁺ region 105, and a silicon substrate 101 extending in a direction perpendicular to the longitudinal direction of the lines 105A. It is formed in the shape of a comb having a connecting portion 111b that is disposed at a position along the other side and connected to the comb-like portion 111a.
The first and second electrodes 110 and 111 are made of aluminum.

Further, a part of the comb-like portion 110 a of the first electrode 110 is embedded in each opening 107 of the insulating film 106, and nickel silicide (NiSi) is formed between the embedded portion and each n ⁺ region 104. A first silicide layer 108 is formed. That is, the first electrode 110 is connected to each n ⁺ region 104 through the first silicide layer 108.
A part of the comb-like portion 111 a of the second electrode 1110 is embedded in each opening 107 of the insulating film 106, and nickel silicide (NiSi) is formed between the embedded portion and each p ⁺ region 105. A second silicide layer 109 is formed. That is, the second electrode 111 is connected to the p ⁺ region 105 through the second silicide layer 109.
In Example 1 and Examples 2 to 4 to be described later, an example in which an n-type single crystal silicon substrate is used is illustrated, but an n-type polycrystalline, p-type single crystal, or p-type polycrystalline silicon substrate is used. Needless to say.

<Method for producing back contact solar cell element>
The back contact solar cell element of Example 1 has a higher concentration than the first concentration in a predetermined region of the non-light-receiving surface 102b of the single crystal silicon substrate 101 containing phosphorus at a first concentration of 2 × 10 ¹⁵ cm ⁻³ . and n ⁺ region 104 containing phosphorus at a second concentration 2 × 10 ¹⁹ cm ^-3, a step of forming a p ⁺ region 105 containing boron at a concentration of ^{2 × 10 19 cm -3 (a} ), n + region 104 A step (B) of forming a first silicide layer 108 on top and a second silicide layer 109 on a p ⁺ region 105; forming a first electrode 110 on the first silicide layer 108; It can be manufactured by a manufacturing method including the step (C) of forming the second electrode 111 on the silicide layer 109.

Further, in this method of manufacturing the back contact solar cell element, the insulating film 106 having the opening 107 in the predetermined region of the non-light-receiving surface 102b of the silicon substrate 101 is formed between the step (A) and the step (B). A step (B) in which a metal film made of nickel is deposited on the insulating film 106, the n ⁺ region 104 and the p ⁺ region 105 exposed from the opening 107, and heat treatment Then, by causing a silicide reaction between the n ⁺ region 104 and the metal film and between the p ⁺ region 105 and the metal film, the first silicide layer 108 and the second silicide layer 109 are formed. This is a step of removing the metal film of the reaction.

  Specifically, first, before the step (A), the n-type single crystal silicon substrate 101 is placed in an alkaline solution prepared by mixing potassium hydroxide and isopropyl alcohol at a molar ratio of 3: 1. By dipping for a minute, a pyramidal surface uneven structure was formed on the surface of the silicon substrate 101. At this time, a surface concavo-convex structure is formed on one surface serving as the light receiving surface 102a of the silicon substrate 101 and the other surface on the opposite side. Next, an antireflection film 103 made of a silicon nitride film having a thickness of 65 nm was formed on one surface serving as the light receiving surface 102a of the silicon substrate 101 having a surface uneven structure by a plasma chemical vapor reaction.

<Process (A)>
Next, a non-doped silicon oxide film is formed by a CVD method on the other surface to be the non-light-receiving surface 102b of the silicon substrate 101, and a photoresist film having an opening in a predetermined region is further formed thereon. Using the resist film as a mask, a part of the silicon oxide film was etched to form an opening. This opening is formed at a position and a size corresponding to the formation position of the n + region 104 to be formed later.
Thereafter, the photoresist film was removed by oxygen plasma.
Next, by using a silicon oxide film having an opening as a mask, phosphorus oxychloride (POCl ₃ ) is diffused in a gas phase to form a plurality of n ⁺ regions 104 on the non-light-receiving surface 102b of the silicon substrate 101 with the above-mentioned depth, The size, concentration, arrangement, etc. were used.
Thereafter, the silicon oxide film was removed by etching.

Next, a non-doped silicon oxide film is formed on the non-light-receiving surface 102b of the silicon substrate 101 by a CVD method, a photoresist film having an opening in a predetermined region is further formed thereon, and the photoresist film is used as a mask. An opening was formed by etching a part of the silicon oxide film. This opening is formed at a position and a size corresponding to the formation position of the p + region 105 to be formed later.
Thereafter, the photoresist film was removed by oxygen plasma.
Next, after depositing a boron-doped oxide film (BSG) on the silicon oxide film having an opening, solid phase diffusion is performed by heat treatment, so that the plurality of p ⁺ regions 105 are formed on the non-light-receiving surface 102b of the silicon substrate 101. The depth, size, concentration, arrangement, etc. were formed.
Thereby, the step (A) was completed, and then the boron-doped oxide film and the silicon oxide film were removed by etching.

Next, as shown in FIG. 3, the non-light-receiving surface 102b of the obtained silicon substrate 101 was subjected to thermal oxidation treatment at 900 ° C. for 60 minutes in a dry oxygen atmosphere, and then non-doped by CVD. The insulating film 106 was formed by depositing a silicon oxide film to a thickness of 750 nm.
Next, as illustrated in FIG. 4, a photoresist film having an opening in a predetermined region is formed over the insulating film 106, and a part of the insulating film 106 is formed with a 5% concentration hydrofluoric acid solution using the photoresist film as a mask. The opening 107 having a diameter of 30 μm was formed by etching.
Thereafter, the photoresist film was removed by oxygen plasma.

<Process (B)>
Next, as shown in FIG. 5, a nickel film having a film thickness of 50 nm is formed on the insulating film 106 and on the n ⁺ region 104 and the p ⁺ region 105 exposed from each opening 107 of the insulating film 106 by using a sputtering method. 189 was formed, and a first heat treatment was performed at 450 ° C. for 1 minute.
As a result, as shown in FIG. 6, the n ⁺ region 104 located in each opening 107 of the insulating film 106 and the nickel film 189 are silicided to select the first silicide layer 108 made of nickel silicide (Ni ₂ Si). The second silicide layer 109 made of nickel silicide (Ni ₂ Si) was selectively formed by silicidation between the p ⁺ region 105 located in each opening 107 of the insulating film 106 and the nickel film 189.
At this time, since the n ⁺ region 104 and the p ⁺ region 105 other than the opening 107 are covered with the insulating film 106, the silicide reaction does not occur.

Next, as shown in FIG. 7, the nickel film 189 is removed with a mixed solution of sulfuric acid and hydrogen peroxide solution to expose the first and second silicide layers 108 and 109, and then at 750 ° C. for 1 minute. A second heat treatment was performed. Thus, the composition of the first and second silicide layers 108 and 109 was changed from Ni ₂ Si to NiSi, and the process (B) was completed.
Since nickel silicide (NiSi) has a relatively low resistivity among various silicides, it is advantageous in reducing contact resistance.

<Process (C)>
Next, an aluminum film having a thickness of 2 μm is formed on the insulating film 106 and the first and second silicide layers 108 and 109 exposed from the openings 107 of the insulating film 106 by using a sputtering method. A photoresist film was formed in a predetermined pattern, and a part of the aluminum film was etched with a mixed solution of phosphoric acid, acetic acid, nitric acid, and pure water as a mask, and the photoresist was removed by oxygen plasma. .
As a result, as shown in FIG. 1, a comb-shaped first electrode 110 in contact with each first silicide layer 108 and a comb-shaped second electrode 111 in contact with each second silicide layer 109 are formed. ) Was completed, and the back contact solar cell element of Example 1 was completed.

<Evaluation of Example 1>
Table 1 shows the contact resistivity of the n ⁺ region 104 and the p ⁺ region 105 in the back contact solar cell of Example 1, and the measurement results of the power generation characteristics of this back contact solar cell element.
The contact resistivity was measured using the transmission line method (TLM method). Further, the power generation characteristics were performed at AM-1.5, the pseudo-sunlight irradiation conditions of 100W / cm ^2.
For comparison, a back contact solar cell (comparative example) similar to that of Example 1 except that the first and second silicide layers are not provided is manufactured. The power generation characteristics were measured, and the results are shown in Table 1.
In Table 1, “without silicide” means a comparative example, and “with silicide” means Example 1.

As shown in Table 1, the contact resistivity of the n ⁺ region and the p ⁺ region of the comparative example having no silicide was 0.017 Ω · cm ² .
On the other hand, the contact resistivities of the n ⁺ region 104 and the p ⁺ region 105 of Example 1 having the first and second silicide layers 108 and 109 are 0.004 Ω · cm ² and 0.006 Ω · cm ² , respectively. It was confirmed that the contact resistance was reduced.
The short-circuit current density, open-circuit voltage, fill factor, and power generation efficiency (photoelectric conversion efficiency) of the comparative example were 40.5 A / cm ² , 0.644 V, 0.646, and 16.8%, respectively.
On the other hand, the short-circuit current density, the open circuit voltage, the fill factor, and the power generation efficiency of Example 1 are 40.3 A / cm ² , 0.634 V, 0.795, and 20.3%, respectively. I understood that.

(Example 2)
A back contact solar cell element of Example 2 was completed in the same manner as Example 1 except for the step (B). Hereinafter, only a process (B) is demonstrated about the manufacturing method of Example 2. FIG.

<Process (B)>
A titanium film having a thickness of 50 nm is formed on the insulating film 106 and on the n ⁺ region 104 and the p ⁺ region 105 exposed from each opening 107 of the insulating film 106 by using a sputtering method. Heat treatment was performed (see FIG. 5).
As a result, the n ⁺ region 104 located in each opening 107 of the insulating film 106 and the titanium film are silicided to selectively form the first silicide layer 108 made of titanium silicide (TiSi ₂ ). A second silicide layer 109 made of nickel silicide (TiSi ₂ ) was selectively formed by silicidation of the p ⁺ region 105 located in each opening 107 and the titanium film (see FIG. 6).
At this time, since the n ⁺ region 104 and the p ⁺ region 105 other than the opening 107 are covered with the insulating film 106, the silicide reaction does not occur.
Next, the titanium film was removed with a mixed solution of sulfuric acid and hydrogen peroxide solution to expose the first and second silicide layers 108 and 109, and the process (B) was completed (see FIG. 7).

In the step (B) of Example 2, the heat treatment temperature was set to 600 ° C., but the heat treatment may be performed at 600 ° C. to 800 ° C. without diffusion to the silicon substrate side and without causing aggregation of titanium. Heat treatment in the range of ˜800 ° C. is preferable because a C54 phase of face-centered orthorhombic crystal is formed and the contact resistance is lowered.
Titanium silicide has relatively little influence of metal contamination on silicon among various silicides, is stable even in heat treatment at high temperature, and is easy to handle, which is advantageous for stability and mass productivity.

<Evaluation of Example 2>
The contact resistivity of the n ⁺ region 104 and the p ⁺ region 105 in the back contact solar cell of Example 2 and the power generation characteristics of the back contact solar cell element were measured in the same manner as in Example 1, and the results are shown in Table 1. It was shown in 2. For comparison, Table 1 also shows the measurement results of the comparative example that does not have the first and second silicide layers.
In Table 2, “without silicide” means a comparative example, and “with silicide” means Example 2.

As shown in Table 2, the contact resistivities of the n ⁺ region 104 and the p ⁺ region 105 of Example 2 having the first and second silicide layers 108 and 109 are 0.008 Ω · cm ² and 0.010 Ω · cm ² , respectively. It was confirmed that the contact resistance was reduced in the same area.
In addition, the short-circuit current density, the open-circuit voltage, the fill factor, and the power generation efficiency of Example 2 are 40.4 A / cm ² , 0.642 V, 0.781, and 20.3%, respectively. The fill factor is mainly improved and the power generation efficiency is improved. I understood that.

(Example 3)
A back contact solar cell element of Example 3 was completed in the same manner as Example 1 except for the step (B). Hereinafter, only a process (B) is demonstrated about the manufacturing method of Example 3. FIG.

<Process (B)>
A cobalt film having a thickness of 50 nm is formed on the insulating film 106 and on the n ⁺ region 104 and the p ⁺ region 105 exposed from each opening 107 of the insulating film 106 by using a sputtering method. A first heat treatment was performed (see FIG. 5).
As a result, the n ⁺ region 104 located in each opening 107 of the insulating film 106 and the cobalt film are subjected to a silicide reaction to selectively form a first silicide layer 108 made of cobalt silicide. A second silicide layer 109 made of cobalt silicide was selectively formed by silicidation between the p ⁺ region 105 and the cobalt film (see FIG. 6).
At this time, since the n ⁺ region 104 and the p ⁺ region 105 other than the opening 107 are covered with the insulating film 106, the silicide reaction does not occur.

Next, after removing the cobalt film with a mixed solution of sulfuric acid and hydrogen peroxide solution to expose the first and second silicide layers 108 and 109, a second heat treatment is performed at 800 ° C. for 1 minute. Then, the cobalt silicide (first and second silicide layers 108 and 109) was stabilized, and the step (B) was completed (see FIG. 7).
Cobalt silicide has relatively little formation region dependency among various silicides, and can reduce the resistivity even when the diameter of each opening 107 of the insulating film 106 is reduced to 50 μm or less. This is advantageous when performing the conversion.
In the step (B) of Example 3, only the cobalt film was formed by the sputtering method, but by depositing a titanium nitride film on the cobalt film, the surface of the cobalt film is oxidized during the first heat treatment. May be prevented.

<Evaluation of Example 3>
The contact resistivity of the n ⁺ region 104 and p ⁺ region 105 in the back contact solar cell of Example 3 and the power generation characteristics of this back contact solar cell element were measured in the same manner as in Example 1, and the results are shown in Table 1. It was shown in 3. For comparison, the measurement results of the comparative example having no first and second silicide layers are also shown in Table 3.
In Table 3, “without silicide” means a comparative example, and “with silicide” means Example 3.

As shown in Table 3, the contact resistivity of the n ⁺ region 104 and the p ⁺ region 105 of Example 3 having the first and second silicide layers 108 and 109 is 0.005 Ω · cm ² and 0.007 Ω · cm ² , respectively. It was confirmed that the contact resistance was reduced in the same area.
Further, the short-circuit current density, the open-circuit voltage, the fill factor, and the power generation efficiency of Example 3 are 40.5 A / cm ² , 0.640 V, 0.761, and 19.7%, respectively. The fill factor is mainly improved and the power generation efficiency is improved. I understood that.

Example 4
A back contact solar cell element of Example 4 was completed in the same manner as Example 1 except for the step (B). Hereinafter, only a process (B) is demonstrated about the manufacturing method of Example 4. FIG.

<Process (B)>
A palladium film having a film thickness of 50 nm is formed on the insulating film 106 and on the n ⁺ region 104 and the p ⁺ region 105 exposed from each opening 107 of the insulating film 106 by using a sputtering method. Heat treatment was performed (see FIG. 5).
As a result, the n ⁺ region 104 located in each opening 107 of the insulating film 106 and the palladium film are subjected to a silicide reaction to selectively form a first silicide layer 108 made of palladium silicide. A second silicide layer 109 made of palladium silicide was selectively formed by silicidation of the p ⁺ region 105 located and the palladium film (see FIG. 6).
At this time, since the n ⁺ region 104 and the p ⁺ region 105 other than the opening 107 are covered with the insulating film 106, the silicide reaction does not occur.
Next, the palladium film was removed with a mixed solution of sulfuric acid and hydrogen peroxide solution to expose the first and second silicide layers 108 and 109, and the process (B) was completed (see FIG. 7).

<Evaluation of Example 4>
The contact resistivity of the n ⁺ region 104 and the p ⁺ region 105 in the back contact solar cell of Example 4 and the power generation characteristics of this back contact solar cell element were measured in the same manner as in Example 1, and the results are shown in Table 1. This is shown in FIG. For comparison, Table 1 also shows the measurement results of the comparative example that does not have the first and second silicide layers.
In Table 4, “without silicide” means a comparative example, and “with silicide” means Example 4.

As shown in Table 4, the contact resistivity of the n ⁺ region 104 and the p ⁺ region 105 of Example 2 having the first and second silicide layers 108 and 109 is 0.005 Ω · cm ² and 0.008 Ω · cm ² , respectively. It was confirmed that the contact resistance was reduced in the same area.
In addition, the short-circuit current density, open-circuit voltage, fill factor, and power generation efficiency of Example 4 are 40.2 A / cm ² , 0.641 V, 0.790, and 20.4%, respectively. The fill factor is mainly improved and the power generation efficiency is improved. I understood that.

101 Silicon substrate 102a Light-receiving surface 102b Non-light-receiving surface 103 Antireflection film 104 n ⁺ region (first conductivity type impurity region)
105 p ⁺ region (second conductivity type impurity region)
106 Insulating film 107 Opening 108 First silicide layer 109 Second silicide layer 110 First electrode 111 Second electrode L Interval

Claims (7)

A silicon substrate containing a first conductivity type impurity at a first concentration, and a first electrode and a second electrode formed on a non-light-receiving surface opposite to the light-receiving surface of the silicon substrate;
The silicon substrate includes a first conductivity type impurity region containing a first conductivity type impurity at a second concentration higher than the first concentration, and a second conductivity type impurity in a predetermined region of a surface layer portion of the non-light-receiving surface. A second conductivity type impurity region containing,
The first electrode is connected to the first conductivity type impurity region, and the second electrode is connected to the second conductivity type impurity region,
A first silicide layer is formed at a contact portion between the first electrode and the first conductivity type impurity region, and a second silicide layer is formed at a contact portion between the second electrode and the second conductivity type impurity region. A back contact solar cell element characterized by being formed.   2. The back contact solar cell element according to claim 1, wherein the first silicide layer and the second silicide layer are made of one or two selected from nickel silicide, titanium silicide, cobalt silicide, and palladium silicide.   The back contact solar cell element according to claim 1 or 2, wherein the first conductivity type impurity is an n-type impurity, and the second conductivity type impurity is a p-type impurity.   The back contact solar cell element according to any one of claims 1 to 3, wherein an insulating layer is formed in a region excluding the first silicide layer and the second silicide layer on the non-light-receiving surface of the silicon substrate. . A predetermined region of the non-light-receiving surface opposite to the light-receiving surface of the silicon substrate containing the first conductivity-type impurity at the first concentration contains the first conductivity-type impurity at a second concentration higher than the first concentration. A step (A) of forming a first conductivity type impurity region and a second conductivity type impurity region containing a second conductivity type impurity;
(B) forming a first silicide layer on the first conductivity type impurity region and forming a second silicide layer on the second conductivity type impurity region;
And (C) forming a first electrode on the first silicide layer and forming a second electrode on the second silicide layer. A method of manufacturing a back contact solar cell element, comprising: Between the step (A) and the step (B), the method further includes a step of forming an insulating film having an opening in the predetermined region of the non-light-receiving surface of the silicon substrate on the non-light-receiving surface,
In the step (B), a metal film is deposited on the insulating film and on the first conductivity type impurity region and the second conductivity type impurity region exposed from the opening, and heat treatment is performed to thereby form a first conductivity type impurity. A silicide reaction is caused between the region and the metal film and between the second conductivity type impurity region and the metal film to form the first silicide layer and the second silicide layer, and then the unreacted metal The method for producing a back contact solar cell element according to claim 5, which is a step of removing the film.   The back surface contact type solar cell module provided with two or more back surface contact type solar cell elements as described in any one of Claims 1-4.

Images