JP2014086589A - Method for manufacturing solar cell and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solar cell capable of manufacturing a solar cell having excellent electric characteristics with high manufacturing efficiency and in a high yield, and to provide a solar cell.SOLUTION: An opening 14 is provided in a diffusion prevention mask layer formed on a surface of a semiconductor substrate 11 by irradiating the diffusion prevention mask layer with a laser beam. A portion exposed from the opening 14 of the diffusion prevention mask layer 12 is etched using an alkaline solution 15, and then an impurity is diffused into the semiconductor substrate using the diffusion prevention mask layer 12 as a mask.

Description

  The present invention relates to a method for manufacturing a solar battery cell and a solar battery cell.

  In recent years, solar cells that directly convert solar energy into electrical energy have been increasingly expected as next-generation energy sources, particularly from the viewpoint of global environmental problems. There are various types of solar cells, such as those using compound semiconductors and those using organic materials, but the mainstream in recent years is that using silicon crystals.

  Among them, the solar cell that has been produced and sold most recently has a structure in which an n-electrode is provided on a light-receiving surface that receives sunlight and a p-electrode is provided on the back surface. In the solar battery cell having such a structure, the n-electrode provided on the light receiving surface side is necessary for taking out current. However, since sunlight does not enter the lower part of the n electrode of the substrate, no power is generated in the lower part. Therefore, when the electrode area is large, the conversion efficiency of the solar battery cell is lowered. Such a loss due to the electrode on the light receiving surface side of the solar battery cell is called a shadow loss.

  On the other hand, there is also a solar cell in which there is no electrode on the light receiving surface and both the p electrode and the n electrode are formed on the back surface, which is called a back electrode type solar cell. In the back electrode type solar cell, since there is no electrode on the light receiving surface, there is no shadow loss due to the electrode, and almost all incident sunlight can be taken into the substrate, so in principle high conversion Efficiency can be realized. However, since the back electrode type solar cell needs to be formed on the back surface of the substrate by patterning all the electrodes and the diffusion region, the manufacturing process becomes more complicated than the conventional solar cell. The complexity of the manufacturing process inevitably increases the manufacturing cost and decreases the mass productivity, making it difficult to mass-produce for commercial use.

  Thus, for example, Patent Document 1 has developed a method of manufacturing a back electrode type solar cell in which an impurity diffusion region is formed on the back surface of a substrate using an etching paste. For example, when an n-type silicon substrate is used, a diffusion mask is formed on the back surface of the n-type silicon substrate, and an opening is provided by etching the diffusion mask with an etching paste applied on the diffusion mask. N-type impurities are diffused from n to form an n-type impurity diffusion region on the back surface of the n-type silicon substrate. Here, in order to obtain a high conversion efficiency for the back electrode type solar cell, it is necessary to thin the n-type impurity diffusion region. However, when an etching paste is used, the n-type impurity diffusion region is thinned. Has its limits.

  For example, in Patent Document 2, the etching mask layer provided on the surface of the silicon substrate is patterned using laser light, and the silicon substrate exposed from the opening of the etching mask layer is etched using an alkaline aqueous solution. A method for manufacturing a solar cell is disclosed in which a groove is formed and a buried electrode is formed in the groove.

  However, in the method for manufacturing a solar cell described in Patent Document 2, the manufacturing time of the solar cell is lowered due to the long etching time for forming the groove, and further, the yield is lowered due to breakage of the silicon substrate. There is a problem.

JP 2008-186927 A JP 2007-103572 A

  In view of the above circumstances, an object of the present invention is to provide a solar cell manufacturing method and a solar cell that can manufacture solar cells having good electrical characteristics with high manufacturing efficiency and high yield. There is.

  The present invention includes a first step of forming a diffusion prevention mask layer on the surface of a semiconductor substrate, and a step of providing an opening at a laser light irradiation portion of the diffusion prevention mask layer by irradiating the diffusion prevention mask layer with laser light. 2, a third step of etching the portion exposed from the opening of the diffusion prevention mask layer using an alkaline solution, and diffusing impurities into the semiconductor substrate using the diffusion prevention mask layer as a mask after the third step. It is a manufacturing method of the photovoltaic cell including a 4th process. With such a configuration, a damage layer that causes a leak path such as an oxide film generated when laser light is irradiated on the surface of the semiconductor substrate when an opening is formed in the diffusion prevention mask layer and heat is generated. Can be etched using an alkaline solution, so that solar cells having good electrical characteristics can be produced with high production efficiency and high yield.

  Here, the solar cell manufacturing method of the present invention includes a fifth step of removing the diffusion prevention mask layer after the fourth step, and a passivation layer on the surface of the semiconductor substrate after the removal of the diffusion prevention mask layer. A sixth step of forming an opening, a seventh step of irradiating the passivation layer with laser light to provide an opening at the laser light irradiation portion, and a portion exposed from the opening of the passivation layer with an alkaline solution It is preferable to include the 8th process etched using. With such a configuration, damage that increases contact resistance with an electrode such as an oxide film caused by heat generated by irradiating the surface of the semiconductor substrate with laser light when an opening is formed in the passivation layer. Since the layer can be etched using an alkaline solution, solar cells having good electrical characteristics can be manufactured with high yield.

  Moreover, in the manufacturing method of the photovoltaic cell of this invention, it is preferable that the etching depth from the surface of the semiconductor substrate in a 3rd process is 10 nm or more. With such a configuration, the damaged layer generated on the surface of the semiconductor substrate can be sufficiently etched.

  Moreover, the manufacturing method of the photovoltaic cell of this invention is exposed from the opening part of a diffusion prevention mask layer at the timing of at least one between the 3rd process and the 4th process, and the 8th process. It is preferable to further include a ninth step of hydrofluoric acid treating at least one of the portion and the portion exposed from the opening of the passivation layer. With such a configuration, the generation caused by etching using the alkaline solution after forming the opening to the diffusion prevention mask layer and / or etching using the alkaline solution after forming the opening to the passivation layer Since a substance can be sufficiently removed by hydrofluoric acid treatment, a solar battery cell having good electrical characteristics can be manufactured with a high yield.

  Furthermore, the present invention is a solar battery cell manufactured by any one of the solar battery manufacturing methods described above, and having a laser beam irradiation trace on a semiconductor substrate. By setting it as such a structure, it can manufacture with high manufacturing efficiency and a high yield, and can also be set as the photovoltaic cell which has a favorable electrical property.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a photovoltaic cell and a photovoltaic cell which can manufacture the photovoltaic cell which has a favorable electrical property with high manufacturing efficiency and a high yield can be provided.

It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is typical sectional drawing illustrating the manufacturing process of the manufacturing method of the photovoltaic cell of embodiment. It is the figure which compared the conversion efficiency of the back surface electrode type photovoltaic cell of Example 1 and Comparative Example 1. FIG. It is the figure which compared the leakage current amount of the back surface electrode type photovoltaic cell of Example 1 and Comparative Example 1. FIG. (A) is an optical microscope photograph of the surface of the back surface side of the n-type silicon substrate before formation of the n-type impurity diffusion region of Comparative Example 1, and (b) is before formation of the n-type impurity diffusion region of Example 1. It is an optical microscope photograph of the surface on the back side of the n-type silicon substrate after etching. (A) is the SEM photograph of the surface of the back surface side of the n-type silicon substrate before the formation of the n-type impurity diffusion region of Comparative Example 1, and (b) is the state before the formation of the n-type impurity diffusion region of Example 1. It is the SEM photograph of the surface of the back surface side of the n-type silicon substrate after etching. (A) is a composite diagram of the EBIC image and SEM image of the surface on the back surface side of the n-type silicon substrate before the formation of the n-type impurity diffusion region of Comparative Example 1, and (b) is the n-type impurity of Example 1. FIG. 3 is a composite diagram of an EBIC image and an SEM image of the surface on the back surface side of an n-type silicon substrate after etching before formation of a diffusion region. It is a figure which shows the relationship between the pulse width (ps) of the laser beam irradiated to an n-type silicon substrate, and the thermal diffusion length (m) which generate | occur | produces in an n-type silicon substrate. It is a figure which shows the relationship between the etching depth Y (micrometer) and immersion time X (minute) when changing the solution temperature and immersion time of sodium hydroxide aqueous solution whose sodium hydroxide concentration is 30 mass%. (A) is the optical microscope photograph of the surface of the back surface side of the n-type silicon substrate after the etching of Example 2 and before the hydrofluoric acid treatment, and (b) is the hydrofluoric acid treatment following the etching of Example 2. It is an optical microscope photograph of the surface of the back surface side of the n-type silicon substrate after performing.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

  1 to 11 are schematic cross-sectional views illustrating manufacturing steps of a solar cell manufacturing method according to an embodiment which is an example of the solar cell manufacturing method of the present invention. First, as shown in FIG. 1, a diffusion prevention mask layer 12 is formed on each of the light receiving surface side and the back surface side of the semiconductor substrate 11. The diffusion prevention mask layer 12 may be formed on at least one surface of the light receiving surface side and the back surface side of the semiconductor substrate 11.

As the semiconductor substrate 11, for example, an n-type or p-type silicon substrate can be used. Here, when a silicon substrate is used as the semiconductor substrate 11, in order to remove the slice damage of the silicon wafer sliced to a desired thickness, a thickness of about 10 to 20 μm per side is mixed with hydrofluoric acid and nitric acid or What was etched with alkaline solutions, such as sodium hydroxide, can be used. Although the size and shape of the semiconductor substrate 11 are not particularly limited, the semiconductor substrate 11 may have a pseudo-rectangular surface with a thickness of 100 to 300 μm and an outer shape of 100 to 150 mm on a side. Further, the impurity concentration of the n-type impurity or the p-type impurity in the semiconductor substrate 11 can be, for example, 1 × 10 ¹⁵ pieces / cm ³ or more and 1 × 10 ¹⁶ pieces / cm ³ .

  As the diffusion prevention mask layer 12, for example, at least one of an oxide layer and a nitride layer can be used. As the oxide layer, for example, a silicon oxide layer or the like can be used. As the nitride layer, for example, a silicon nitride layer can be used. Therefore, as the diffusion prevention mask layer 12, for example, a single layer of a silicon oxide layer, a single layer of a silicon nitride layer, or a stacked body of a silicon oxide layer and a silicon nitride layer can be used.

  Although the thickness of the diffusion prevention mask layer 12 is not particularly limited, for example, it can be set to a thickness of 200 nm or more and 400 nm or less, respectively.

  The method for forming the diffusion prevention mask layer 12 is not particularly limited, but for example, atmospheric pressure CVD (Chemical Vapor Deposition) method, plasma CVD method, steam oxidation method, or SOG (Spin on Glass) coating / firing may be used. it can. Note that, from the viewpoint of increasing the manufacturing efficiency of the solar battery cell, it is preferable to use a natural oxide film as the diffusion prevention mask layer 12.

  Next, as shown in FIG. 2, the diffusion prevention mask layer 12 on the back surface side of the semiconductor substrate 11 is irradiated with the laser beam 13, so that the diffusion prevention mask layer at the irradiated portion of the laser beam 13 as shown in FIG. 3. 12 is removed, and an opening 14 is formed in the diffusion preventing mask layer 12.

  As the laser beam 13, it is preferable to use a laser beam having a short wavelength and a short pulse width. In this case, damage to the surface of the semiconductor substrate 11 when the semiconductor substrate 11 is irradiated with the laser beam 13 can be reduced. Here, the wavelength of the laser light 13 having a short wavelength and a short pulse width is preferably 1000 nm or less, and more preferably 355 nm or less. The pulse width of the laser light 13 having a short wavelength and a short pulse width is preferably 10 ns (nanoseconds) or less, and more preferably 15 ps (pico) seconds or less. When such a laser beam 13 having a short wavelength and a short pulse width is used, damage to the surface of the semiconductor substrate 11 can be reduced. On the other hand, the laser beam 13 is applied to the surface of the semiconductor substrate 11. A damage layer that causes a leak path such as an oxide film generated by the generation of heat by irradiation is generated.

  Next, as shown in FIG. 4, the portion exposed from the opening 14 of the diffusion prevention mask layer 12 is etched using an alkaline solution 15. As a result, when the opening 14 is formed in the diffusion prevention mask layer 12, a damage layer that causes a leak path such as an oxide film generated by the surface of the semiconductor substrate 11 being irradiated with the laser beam 13 to generate heat is removed. can do. Therefore, in a later step, a damaged layer that can be a mask when diffusing impurities on the surface of the semiconductor substrate 11 can be removed by the alkaline solution 15 at this stage. Therefore, a solar cell having good electrical characteristics can be obtained. It becomes possible to manufacture with high manufacturing efficiency and high yield.

  The alkaline solution 15 is not particularly limited as long as the damaged layer can be removed. For example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution can be used.

  The etching depth from the surface of the semiconductor substrate 11 is preferably 10 nm or more. In this case, since the damaged layer generated on the surface of the semiconductor substrate 11 by the irradiation of the laser beam 13 can be sufficiently removed by etching, solar cells having better electrical characteristics are manufactured with a higher yield. be able to.

  In addition, after the etching using the alkaline solution 15 described above, it is preferable to treat the portion exposed from the opening 14 of the diffusion prevention mask layer 12 with hydrofluoric acid. After the etching, it is preferable to perform cleaning using pure or the like, but even after the cleaning, a substance such as silicon constituting the semiconductor substrate 11 reacts with the alkaline solution 15 during the etching. The reaction product such as silicate may adhere to the opening 14 of the diffusion prevention mask layer 12 and / or the surface of the semiconductor substrate 11. Therefore, the reaction product such as silicate can be removed by hydrofluoric acid treatment of the portion exposed from the opening 14 of the diffusion prevention mask layer 12 after the etching using the alkaline solution 15. Solar cells having good electrical characteristics can be manufactured with a higher yield.

  Next, as shown in FIG. 5, an n-type impurity diffusion region 21 is formed by diffusing an n-type impurity into the semiconductor substrate 11 using the diffusion prevention mask layer 12 after the etching as a mask.

The n-type impurity diffusion region 21 is formed by, for example, vapor phase diffusion using POCl ₃ containing phosphorus as an n-type impurity or coating diffusion in which a solvent containing phosphorus is spin-coated and annealed at a high temperature. it can.

The n-type impurity diffusion region 21 is formed by vapor phase diffusion so that the n-type impurity concentration in the n-type impurity diffusion region 21 is 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ¹⁹ / cm ^3. In this case, for example, it is preferable to diffuse the n-type impurity in the semiconductor substrate 11 at a temperature of 800 ° C. or higher and 900 ° C. or lower for a time of 30 minutes or longer and 60 minutes or shorter. Further, an FSF (front surface field) is formed by diffusing n-type impurities on the light receiving surface side of the semiconductor substrate 11 without forming the diffusion prevention mask layer 12 on the light receiving surface side surface of the semiconductor substrate 11. May be.

  Further, after the formation of the n-type impurity diffusion region 21, the PSG (phosphor silicate glass) layer and the diffusion prevention mask layer 12 formed by the diffusion of the n-type impurity are removed.

  Thereafter, as shown in FIG. 6, the p-type impurity diffusion region 22 is formed in the same manner as the n-type impurity diffusion region 21. That is, when forming the p-type impurity diffusion region 22, (i) a step of forming a diffusion prevention mask layer 21 on the surface of the semiconductor substrate 11, and (ii) diffusion by irradiating the diffusion prevention mask layer 21 with the laser beam 13. (Iii) a step of etching the portion exposed from the opening 14 of the diffusion prevention mask layer 21 using the alkaline solution 15 (more preferably It is preferable that a step of hydrofluoric acid treatment after the etching) and (iv) a step of diffusing p-type impurities into the semiconductor substrate 11 using the diffusion prevention mask layer 12 after the etching as a mask.

The p-type impurity diffusion region 22 is formed by, for example, vapor phase diffusion using BBr ₃ containing boron as a p-type impurity, or coating diffusion in which a solvent containing boron is spin-coated and annealed at a high temperature. it can.

The p-type impurity diffusion region 22 is formed by vapor phase diffusion so that the p-type impurity concentration in the p-type impurity diffusion region 22 is 1 × 10 ¹⁸ / cm ³ or more and 1 × 10 ¹⁹ / cm ^3. In this case, it is preferable to diffuse the p-type impurity at a temperature of 900 ° C. or higher and 1000 ° C. or lower for a time period of 30 minutes or longer and 60 minutes or shorter.

  Further, after the formation of the p-type impurity diffusion region 22, the BSG (boron silicate glass) layer and the diffusion prevention mask layer formed by the diffusion of the p-type impurity are removed.

  Next, as shown in FIG. 7, a passivation layer 23 is formed on each of the light receiving surface side and the back surface side of the semiconductor substrate 11. The passivation layer 23 may be formed on at least one surface of the light receiving surface side and the back surface side of the semiconductor substrate 11. Alternatively, the texture layer may be formed by performing texture etching on the light receiving surface of the semiconductor substrate 11 using the passivation layer 23 as a texture etching mask. Further, the passivation layer 23 provided on the light receiving surface side of the semiconductor substrate 11 may be used as an antireflection film, or a new antireflection film may be formed after the formation of the texture structure.

  As the passivation layer 23, for example, at least one of an oxide layer and a nitride layer can be used. As the oxide layer, for example, a silicon oxide layer or the like can be used. As the nitride layer, for example, a silicon nitride layer can be used. Therefore, as the passivation layer 23, for example, a single layer of a silicon oxide layer, a single layer of a silicon nitride layer, or a stacked body of a silicon oxide layer and a silicon nitride layer can be used.

  As the silicon oxide layer used for the passivation layer 23, for example, a layer having a thickness of 300 nm or more and 800 nm or less formed by a steam oxidation method, an atmospheric pressure CVD method, or SOG coating / firing can be used. Further, as the silicon nitride layer, for example, a layer formed by plasma CVD or atmospheric pressure CVD and having a thickness of 60 nm to 100 nm can be used.

  Next, as shown in FIG. 8, the passivation layer 23 on the back surface side of the semiconductor substrate 11 is irradiated with the laser beam 13, thereby removing the passivation layer 23 at the irradiated portion of the laser beam 13 as shown in FIG. 9. Thus, an opening 24 is formed in the passivation layer 23. Here, the opening 24 is formed so that a part of the surface of the n-type impurity diffusion region 21 and a part of the surface of the p-type impurity diffusion region 22 are exposed. The description of the laser beam 13 is the same as described above, and thus the description thereof is omitted here.

  Next, as shown in FIG. 10, the portion exposed from the opening 24 of the passivation layer 23 is etched using an alkaline solution 15. As a result, when the opening 24 is formed in the passivation layer 23, the damage layer that causes a leak path such as an oxide film generated when the surface of the semiconductor substrate 11 is irradiated with the laser beam 13 to generate heat is removed. Can do. Therefore, a damaged layer that may cause an increase in contact resistance when an electrode is formed on the surface of the semiconductor substrate 11 in a later step can be removed by the alkaline solution 15 at this stage. The battery cell can be manufactured with higher manufacturing efficiency and higher yield.

  In addition, after the etching using the alkaline solution 15 described above, it is preferable to treat the portion exposed from the opening 24 of the passivation layer 23 with hydrofluoric acid. After the etching, it is preferable to perform cleaning using pure or the like, but even after the cleaning, a substance such as silicon constituting the semiconductor substrate 11 reacts with the alkaline solution 15 during the etching. In some cases, the reaction product such as silicate adhered to the portion exposed from the opening 24 of the passivation layer 23 and / or the surface of the semiconductor substrate 11. Therefore, a reaction product such as a silicate can be removed by hydrofluoric acid treatment of the portion exposed from the opening 24 of the passivation layer 23 after the etching using the alkaline solution 15, which is better. Solar cells having electrical characteristics can be manufactured with a higher yield.

  In addition, since the description about the etching depth from the surface of the semiconductor substrate 11 and the alkaline solution 15 is the same as the above, the description is abbreviate | omitted here.

  Thereafter, as shown in FIG. 11, the n-electrode 25 that contacts the surface of the n-type impurity diffusion region 21 and the p-electrode 26 that contacts the surface of the p-type impurity diffusion region 22 are formed. The back electrode solar cell of the form is completed. The back electrode solar cell according to the embodiment thus manufactured has an irradiation trace of the laser beam 13 on the surface of the semiconductor substrate 11.

  The n electrode 25 and the p electrode 26 can be formed by, for example, baking at a temperature of 500 ° C. or more and 600 ° C. or less after applying a silver paste.

  In addition, the size of the opening 24 of the passivation layer 23 is preferably smaller than the n electrode 25 and the p electrode 26. For example, when the width of the linear opening 24 in the passivation layer 23 is 80 μm, the width of the linear n electrode 25 and the p electrode 26 may be 100 μm.

  As described above, in the method for manufacturing a solar cell according to the embodiment, a damage layer that causes a leak path such as an oxide film generated when the surface of the semiconductor substrate 11 is irradiated with the laser beam 13 to generate heat. Can be removed by etching using the alkaline solution 15, so that solar cells having good electrical characteristics can be manufactured with high manufacturing efficiency and high yield.

  In particular, when the surface of the semiconductor substrate 11 is irradiated with laser light 13 having a short wavelength and a short pulse width in order to reduce damage to the surface of the semiconductor substrate 11, a leak path such as an oxide film is formed on the surface of the semiconductor substrate 11. Since the damage layer which becomes the factor of this becomes easy to produce | generate, the manufacturing method of the photovoltaic cell of embodiment becomes more effective.

  Furthermore, by making the etching depth from the surface of the semiconductor substrate 11 10 nm or more and / or performing hydrofluoric acid treatment after etching using the alkaline solution 15, a solar battery cell having better electrical characteristics can be obtained. It becomes possible to manufacture with a high yield.

  For the above reasons, according to the method for manufacturing a solar cell according to the embodiment, a method for manufacturing a solar cell that can manufacture a solar cell having good electrical characteristics with high manufacturing efficiency and high yield, and A solar battery cell can be provided.

  This is because the present inventors irradiate the diffusion prevention mask layer 12 provided on the surface of the semiconductor substrate 11 with the laser beam 13 and partially remove the diffusion prevention mask layer 12 in the irradiated portion of the laser beam 13. As a result of paying attention to the manufacturing process of the back electrode type solar cell that forms the opening 14, a damage layer caused by the irradiation of the laser beam 13 such as an oxide film is formed on the surface of the semiconductor substrate 11, and this damage layer becomes an impurity diffusion. This is because it has been found that it also functions as a leak path for conducting the pn junction part.

  This is also the case when the inventors form the opening 24 by irradiating the passivation layer 23 provided on the surface of the semiconductor substrate 11 with the laser beam 13 to partially remove the passivation layer 23. Similarly, a damaged layer such as an oxide film is formed on the surface of the semiconductor substrate 11, and this damaged layer has also been found to cause an increase in contact resistance between the impurity diffusion region on the surface of the semiconductor substrate 11 and the electrode. It is.

<Preparation of Back Electrode Solar Cell of Example 1>
First, a natural oxide film was formed on each of the light receiving surface side and the back surface side of the n-type silicon substrate. Next, the natural oxide film on the back surface side of the n-type silicon substrate was irradiated with laser light having a short wavelength and a short pulse width a plurality of times, thereby forming a linear opening at the laser light irradiation portion of the natural oxide film. . Here, the shape of the opening of the natural oxide film was matched with the shape of the formation region of the n-type impurity diffusion region.

  Here, the wavelength of the laser light applied to the natural oxide film is 532 nm, the pulse width is 4 ns, the irradiation energy per pulse is 25 μJ, the processing diameter per pulse is 35 μm, The width of the opening was 210 μm.

  Next, the portion exposed from the opening of the natural oxide film was etched with an aqueous sodium hydroxide solution. Here, the sodium hydroxide concentration of the aqueous sodium hydroxide solution is 30% by mass, the immersion time of the n-type silicon substrate in the aqueous sodium hydroxide solution is 1 to 3 minutes, and the temperature of the aqueous sodium hydroxide solution is 75. ° C.

Next, after cleaning the n-type silicon substrate after the etching with pure water, using the natural oxide film as a mask, POCl ₃ containing phosphorus as an n-type impurity is used to remove phosphorus from the opening of the natural oxide film. An n-type impurity diffusion region was formed in the n-type silicon substrate by performing vapor phase diffusion on the n-type silicon substrate. After the formation of the n-type impurity diffusion region, the natural oxide film and the PSG layer generated by phosphorus diffusion were removed.

Next, in the same manner as described above, a p-type impurity diffusion region was formed in a region between the n-type impurity diffusion regions on the surface of the n-type silicon substrate. Laser light irradiation conditions and etching conditions using a sodium hydroxide aqueous solution were the same as described above. The p-type impurity diffusion region was formed by vapor phase diffusion using BBr ₃ containing boron as a p-type impurity. After the formation of the p-type impurity diffusion region, the natural oxide film and the BSG layer produced by boron diffusion were removed.

  Next, an opening serving as a contact hole was formed in a linear shape using an etching paste. At this time, the width of the opening was 80 μm.

  Thereafter, by applying and baking silver paste, a linear n-electrode that contacts the surface of the n-type impurity diffusion region is formed, and a linear p-electrode that contacts the surface of the p-type impurity diffusion region is formed. The back electrode type solar battery cell of Example 1 was produced. Here, the width of the linear n-electrode and p-electrode was 100 μm.

<Preparation of Back Electrode Solar Cell of Comparative Example 1>
The back electrode solar cell of Comparative Example 1 is the same as Example 1 except that the portion exposed from the opening of the natural oxide film is not etched with an aqueous sodium hydroxide solution before the n-type impurity diffusion region is formed. A cell was produced.

<Comparison of electrical characteristics>
For comparison of the electrical characteristics of the back electrode type solar cells of Example 1 and Comparative Example 1, 1SUN pseudo-sunlight having a spectral distribution of AM1.5 and an energy density of 100 mW / cm ² was obtained using Example 1 and a solar simulator. The back electrode type solar cell of Comparative Example 1 was irradiated to create a current-voltage curve, and from the results, conversion efficiency (%) and leakage current of the back electrode type solar cell of Example 1 and Comparative Example 1 The amount (A) was calculated. The results are shown in FIG. 12 (conversion efficiency) and FIG. 13 (leakage current amount).

  As shown in FIG. 12, the conversion efficiency of the back electrode solar cell of Comparative Example 1 was 15.4%, whereas the conversion efficiency of the back electrode solar cell of Example 1 was 17.4%. Met. Therefore, the effect of improving the conversion efficiency by etching the portion exposed from the opening of the natural oxide film with an aqueous sodium hydroxide solution before the formation of the n-type impurity diffusion region was confirmed.

  Further, as shown in FIG. 13, it is confirmed that the leakage current amount of the back electrode solar cell of Example 1 is reduced to about 1/8 of the leakage current amount of the back electrode solar cell of Comparative Example 1. It was done.

  From the results shown in FIG. 12 and FIG. 13, it was confirmed that the back electrode type solar battery cell of Example 1 was superior to the back electrode type solar battery cell of Comparative Example 1 in electrical characteristics.

<Comparison of surface conditions>
FIG. 14A shows an optical micrograph of the surface on the back side of the n-type silicon substrate before the formation of the n-type impurity diffusion region of Comparative Example 1, and FIG. 14B shows the n-type impurity of Example 1. The optical microscope photograph of the surface of the back surface side of the n-type silicon substrate after formation of the diffusion region and after etching is shown.

  FIG. 15A shows an SEM (Scanning Electron Microscope) photograph of the back surface of the n-type silicon substrate before the formation of the n-type impurity diffusion region of Comparative Example 1, and FIG. 2 shows an SEM photograph of the surface on the back surface side of the n-type silicon substrate before the formation of the n-type impurity diffusion region of Example 1 and after the etching.

  As shown in FIGS. 14 and 15, in Example 1, it was confirmed that the unevenness of the laser light irradiation portion 41 on the surface on the back surface side of the n-type silicon substrate was reduced as compared with Comparative Example 1. it can. Further, in Example 1, as compared with Comparative Example 1, the laser light non-irradiated portion 42 on the surface on the back surface side of the n-type silicon substrate is also etched.

<Comparison of leakage path of pn junction>
FIG. 16A shows an image obtained by EBIC (Electron Beam Induced Current) on the back surface side of the n-type silicon substrate before the formation of the n-type impurity diffusion region of Comparative Example 1 and an SEM. FIG. 16B shows an EBIC image and an SEM image of the surface on the back surface side of the n-type silicon substrate before the formation of the n-type impurity diffusion region of Example 1 and after the etching. The figure which synthesize | combined is shown. The applied voltage used for acquiring the EBIC image was 10 kV.

  As is clear from a comparison between FIG. 16A and FIG. 16B, FIG. 16A is more likely to be between the p-type impurity diffusion region 61 and the n-electrode 63 than FIG. 16B. It can be seen that the n-type impurity diffusion region 62 is brightened. This means a leak path of a pn junction which is a junction between the p-type impurity diffusion region 61 and the n-type impurity diffusion region 62. Therefore, as in Example 1, etching is performed before the formation of the n-type impurity diffusion region. It can be seen that the leakage path of the pn junction can also be reduced when the above is performed.

<Relationship between pulse width and thermal diffusion length>
FIG. 17 shows the pulse width (ps (picoseconds)) of the laser beam irradiated to the n-type silicon substrate and the diffusion length (thermal diffusion length) of the heat generated in the n-type silicon substrate by the laser beam irradiation. The unit is m). The slope of the straight line shown in FIG. 17 showing the relationship between the thermal diffusion length in the depth direction of the n-type silicon substrate and the pulse width of the laser light is calculated by the following equation (I). In the following formula (I), Xth represents the thermal diffusion length, k0 represents the thermal conductivity of the n-type silicon substrate, tp represents the pulse width of the laser beam, and Ci represents the heat capacity of the n-type silicon substrate. Show.

Xth = (2 × k0 × tp / Ci) ^ (0.5) (I)
As shown in FIG. 17, when the n-type silicon substrate was irradiated with laser light with a pulse width of 1 ps or more, the thermal diffusion length in the depth direction of the n-type silicon substrate was 10 nm or more. That is, when a laser beam having a pulse width of 1 ps or more is irradiated onto an n-type silicon substrate, a region having a depth of 10 nm or more of the n-type silicon substrate may be damaged by heat and become an oxide film. Therefore, when the etching depth from the surface of the n-type silicon substrate is 10 nm or more, the oxide film generated on the surface of the n-type silicon substrate by the laser light irradiation can be sufficiently removed.

<Relationship between etching depth and immersion time>
The etching depth of the n-type silicon substrate can be adjusted by changing conditions such as solution concentration, solution temperature, and immersion time. FIG. 18 shows etching when the solution temperature (60 ° C., 75 ° C., 90 ° C.) and the dipping time (1 minute, 3 minutes, 5 minutes) of a 30% by weight sodium hydroxide aqueous solution are changed. The relationship between depth Y (micrometer) and immersion time X (minutes) is shown. Note that the etching depth of the n-type silicon substrate was calculated by measurement using a step gauge.

  As shown in FIG. 18, the etching rates of the aqueous solution of sodium hydroxide at 60 ° C., 75 ° C., and 90 ° C. are changed to 0.3 μm / min, 1.1 μm / min, and 2.2 μm / min, respectively. I understand. That is, a desired etching depth can be obtained by changing the etching conditions.

<Production of Back Electrode Solar Cell of Example 2>
Before forming the n-type impurity diffusion region, the portion exposed from the opening of the natural oxide film was etched with a sodium hydroxide aqueous solution and then treated with hydrofluoric acid. An electrode type solar cell was produced.

  FIG. 19A shows an optical micrograph of the surface on the back surface side of the n-type silicon substrate after the etching in Example 2 and before the hydrofluoric acid treatment, and FIG. 19B shows the etching in Example 2. The optical microscope photograph of the surface of the back surface side of an n-type silicon substrate after performing a hydrofluoric acid process succeedingly is shown.

  In FIG. 19A, it can be seen that silicic acid represented by a color different from that of the n-type silicon substrate as the base adheres in the laser light irradiation portion 41. On the other hand, in FIG. 19B, it is understood that silicic acid is removed when hydrofluoric acid treatment is performed to such an extent that the natural oxide film that becomes the diffusion preventing mask layer is not removed. Here, the hydrofluoric acid treatment conditions were such that the hydrofluoric acid concentration was 1% by volume, the immersion time of the n-type silicon substrate in hydrofluoric acid was 10 seconds, and the hydrofluoric acid temperature was normal temperature.

That is, when an n-type silicon substrate is etched with an alkaline solution and then the next n-type silicon substrate is etched with an alkaline solution, silicic acid may adhere to the surface of the n-type silicon substrate. That is, when a sodium hydroxide aqueous solution is used as the etching solution, sodium silicate (Na ₂ SiO ₃ ) is generated by the following chemical reaction formula (II).

Si + 2NaOH + H ₂ O → Na ₂ SiO ₃ + 2H ₂ ↑ (II)
If the silicate as described above adheres to the n-type silicon substrate and / or the natural oxide film, the silicate is removed even if it is washed with pure water after etching using an alkaline solution. Have difficulty. It is effective to remove silicate by hydrofluoric acid treatment after etching with an alkaline solution and before impurity diffusion and / or electrode formation, thereby having better electrical properties Solar cells can be manufactured with higher yield.

  The present invention includes a first step of forming a diffusion prevention mask layer on the surface of a semiconductor substrate, and a step of providing an opening at a laser light irradiation portion of the diffusion prevention mask layer by irradiating the diffusion prevention mask layer with laser light. 2, a third step of etching the portion exposed from the opening of the diffusion prevention mask layer using an alkaline solution, and diffusing impurities into the semiconductor substrate using the diffusion prevention mask layer as a mask after the third step. It is a manufacturing method of the photovoltaic cell including a 4th process. With such a configuration, a damage layer that causes a leak path such as an oxide film generated when laser light is irradiated on the surface of the semiconductor substrate when an opening is formed in the diffusion prevention mask layer and heat is generated. Can be etched using an alkaline solution, so that solar cells having good electrical characteristics can be produced with high production efficiency and high yield.

  The manufacturing method of the photovoltaic cell of the present invention includes a fifth step of removing the diffusion prevention mask layer after the fourth step, and a passivation layer formed on the surface of the semiconductor substrate after removing the diffusion prevention mask layer. A sixth step, a seventh step of providing an opening in the laser light irradiation portion of the passivation layer by irradiating the passivation layer with the laser light, and a portion exposed from the opening of the passivation layer using an alkaline solution And an eighth step of etching. With such a configuration, damage that increases contact resistance with an electrode such as an oxide film caused by heat generated by irradiating the surface of the semiconductor substrate with laser light when an opening is formed in the passivation layer. Since the layer can be etched using an alkaline solution, solar cells having good electrical characteristics can be manufactured with high yield.

  In the solar cell manufacturing method of the present invention, the etching depth from the surface of the semiconductor substrate in the third step is preferably 10 nm or more. With such a configuration, the damaged layer generated on the surface of the semiconductor substrate can be sufficiently etched.

  The method for manufacturing a solar battery cell of the present invention includes a portion exposed from the opening of the diffusion prevention mask layer at least one timing between the third step and the fourth step and after the eighth step. It is preferable that the method further includes a ninth step of performing hydrofluoric acid treatment on at least one of the portions exposed from the opening of the passivation layer. With such a configuration, the generation caused by etching using the alkaline solution after forming the opening to the diffusion prevention mask layer and / or etching using the alkaline solution after forming the opening to the passivation layer Since a substance can be sufficiently removed by hydrofluoric acid treatment, a solar battery cell having good electrical characteristics can be manufactured with a high yield.

  The present invention is a solar cell manufactured by any one of the solar cell manufacturing methods described above, and has a semiconductor substrate having a laser beam irradiation trace. By setting it as such a structure, it can manufacture with high manufacturing efficiency and a high yield, and can also be set as the photovoltaic cell which has a favorable electrical property.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICATION This invention can be utilized for the manufacturing method and photovoltaic cell of a photovoltaic cell, and can be suitably utilized especially for the manufacturing method and back electrode type photovoltaic cell of a back electrode type photovoltaic cell.

  DESCRIPTION OF SYMBOLS 11 Semiconductor substrate, 12 Diffusion prevention mask layer, 13 Laser beam, 14 Opening part, 15 Alkaline solution, 21 n-type impurity diffusion area, 22 p-type impurity diffusion area, 23 Passivation layer, 24 opening part, 25 n electrode, 26 p Electrode, 41 Laser light irradiation location, 42 Laser light non-irradiation location, 61 p-type impurity diffusion region, 62 n-type impurity diffusion region, 63 n electrode.

Claims (5)

A first step of forming a diffusion prevention mask layer on the surface of the semiconductor substrate;
A second step of irradiating the diffusion prevention mask layer with laser light to provide an opening at the laser light irradiation portion of the diffusion prevention mask layer;
A third step of etching a portion exposed from the opening of the diffusion prevention mask layer using an alkaline solution;
And a fourth step of diffusing impurities into the semiconductor substrate using the diffusion prevention mask layer as a mask after the third step. A fifth step of removing the diffusion prevention mask layer after the fourth step;
A sixth step of forming a passivation layer on the surface of the semiconductor substrate after removing the diffusion prevention mask layer;
A seventh step of providing an opening at the laser light irradiation portion of the passivation layer by irradiating the passivation layer with laser light;
The manufacturing method of the photovoltaic cell of Claim 1 including the 8th process of etching the part exposed from the said opening part of the said passivation layer using an alkaline solution.   The manufacturing method of the photovoltaic cell of Claim 1 or 2 whose etching depth from the said surface of the said semiconductor substrate is 10 nm or more.   A portion exposed from the opening of the diffusion prevention mask layer and the opening of the passivation layer at least at one timing between the third step and the fourth step and after the eighth step. The manufacturing method of the photovoltaic cell of any one of Claim 1 to 3 which further includes the 9th process of hydrofluoric-acid-treating at least one of the part exposed from a part. A solar battery cell manufactured by the method for manufacturing a solar battery cell according to any one of claims 1 to 4,
The solar cell which has the irradiation trace of the said laser beam on the said semiconductor substrate.