Method of manufacturing solar cell

Abstract

To provide a method of manufacturing a solar cell having a selection emitter structure with a long carrier lifetime generated by light, simply.SOLUTION: A method of manufacturing a solar cell having impurity diffusion layers with two or more different impurity concentrations on a semiconductor substrate includes the following steps (a) to (d) in this order: (a) applying an impurity diffusion composition (A) onto a semiconductor substrate to form an impurity diffusion composition film (B); (b) diffusing the impurity of the impurity diffusion composition film (B) into the semiconductor substrate to form an impurity diffusion layer (C); (c) removing the impurity diffusion composition film (B) by etching; and (d) heating the etched semiconductor substrate in a gas atmosphere containing boron and phosphorus, diffusing the boron or phosphorus into the semiconductor substrate to form an impurity diffusion layer (D) in a region in the semiconductor substrate where the impurity diffusion composition film (B) is not formed, and simultaneously promoting the diffusion of the impurity diffusion layer (C).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In the manufacture of a conventional solar cell having a pn junction, for example, an n-type impurity is diffused into a p-type semiconductor substrate such as silicon to form an n-type diffusion layer, thereby forming a pn junction.

[0003] In recent years, solar cells having a selective emitter structure have been disclosed in order to reduce the contact resistance with electrodes and suppress carrier recombination (see, for example, Non-Patent Document 1). For example, in a solar cell having a selective emitter structure based on an n-type silicon substrate, in the p-type diffusion layer on the light-receiving surface side, a high-concentration p-type diffusion layer (p ++ layer) is formed, and a low-concentration to medium-concentration p-type diffusion layer (p + layer) is formed on the light-receiving surface other than directly under the electrode. In order to form a selective emitter structure, it is known that a complicated process combining multiple diffusions and partial etching by masking is required (see, for example, Patent Document 1). Furthermore, for the purpose of simplifying the process, a method of separately applying diffusion agents of multiple impurity concentrations to a substrate by an inkjet method and diffusing the impurities (see, for example, Patent Document 2), a method of selectively forming a pattern on a substrate using a coating solution containing an impurity diffusion component and heat-treating the patterned substrate in a doping gas atmosphere to form diffusion layers of multiple impurity concentrations (see, for example, Patent Documents 3 to 5), a method of selectively forming a pattern on a substrate using a coating solution containing an impurity diffusion component and forming diffusion layers of multiple impurity concentrations by utilizing the out-diffusion phenomenon from the pattern by heat treatment (see, for example, Patent Documents 6 to 7), etc. have been proposed.

[0004] Also, a method for providing a method for manufacturing a semiconductor element that can be manufactured by a simple method without requiring a complicated apparatus and has excellent in-plane uniformity of impurity concentration, and a method for manufacturing a solar cell (see, for example, Patent Document 8) have also been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the method described in Patent Document 1, processes for patterning and etching are required to form the selective emitter structure, and the number of processes tends to increase. Further, in the inkjet method described in Patent Document 2, a dedicated apparatus having a plurality of heads is required, and the control of the ejection from each head becomes complicated. Further, the diffusion paste described in Patent Documents 3 to 5 has a problem that the out-diffusion suppression of impurities from the paste film is insufficient, and thus there is a large variation in the impurity diffusion concentration in portions other than the pattern formation portion. Furthermore, the methods described in Patent Documents 6 and 7 are difficult to control out-diffusion, and also have a problem that there is a large variation in the impurity concentration in portions other than the pattern formation portion.

[0008] In the method described in Patent Document 8, these problems are overcome, but it has been demanded to make the lifetime of carriers generated by light longer and further improve the power generation efficiency of the solar cell.

[0009] The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a method for manufacturing a solar cell having a selective emitter structure by a simple method without requiring a complicated apparatus and to provide a method for manufacturing a solar cell having a long lifetime of carriers generated by light.

Means for Solving the Problems

[0010] In order to solve the above problems, the method for manufacturing a solar cell of the present invention mainly has the following configuration. A method for manufacturing a solar cell having impurity diffusion layers with different impurity concentrations of two levels or more on a semiconductor substrate, the method for manufacturing a solar cell including the following steps (a) to (d) in this order. (a) A step of applying an impurity diffusion composition (A) to a semiconductor substrate to form an impurity diffusion composition film (B) partially. (b) A step of diffusing the impurities in the impurity diffusion composition film (B) into the semiconductor substrate to form an impurity diffusion layer (C). (c) A step of removing the impurity diffusion composition film (B) by etching. (d) Heating the semiconductor substrate in a gas atmosphere containing boron or phosphorus, diffusing boron or phosphorus into the semiconductor substrate to form an impurity diffusion layer (D) in a portion where the impurity diffusion composition film (B) of the semiconductor substrate is not formed, and simultaneously further advancing the diffusion of the impurity diffusion layer (C).

Effect of the Invention

[0011] According to the present invention, a solar cell having a selective emitter structure and a long carrier lifetime generated by light can be manufactured by a simple method without requiring a complicated apparatus.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] Hereinafter, a method for manufacturing a solar cell of the present invention will be described with reference to the drawings. Note that the following embodiments are examples, and the present invention is not limited to these embodiments.

[0014] The method for manufacturing a solar cell of the present invention is a method for manufacturing a solar cell having impurity diffusion layers with different impurity concentrations of two levels or more on a semiconductor substrate, and includes the following steps (a) to (d) in this order. (a) A step of applying an impurity diffusion composition (A) to a semiconductor substrate to partially form an impurity diffusion composition film (B). (b) A step of diffusing the impurities in the impurity diffusion composition film (B) into the semiconductor substrate to form an impurity diffusion layer (C). (c) A step of removing the impurity diffusion composition film (B) by etching. (d) Heating the semiconductor substrate after etching in a gas atmosphere containing boron or phosphorus to diffuse boron or phosphorus into the semiconductor substrate to form an impurity diffusion layer (D) in a portion where the impurity diffusion composition film (B) was not formed, and simultaneously further advancing the diffusion of the impurity diffusion layer (C).

[0015] The different impurity concentrations of two levels or more referred to here mean that the impurity concentration difference is 1×10 17 atoms / cm 3 or more, and it means that the difference in the sheet resistance value of the substrate surface in the portion where the impurity diffusion layer is formed is 10 Ω / sq or more.

[0016] Examples of the semiconductor substrate include an n-type single crystal silicon, polycrystalline silicon, and a crystal silicon substrate in which other elements such as germanium and carbon are mixed, with an impurity concentration of 10 15 ~10 16 atoms / cm 3 It is also possible to use a p-type single crystal silicon or a semiconductor other than silicon.

[0017] The semiconductor substrate preferably has a thickness of 50 to 300 μm and an outer shape that is approximately square with a side length of 100 to 300 mm. Also, in order to remove slice damage and the natural oxide film, it is preferable to etch the surface of the semiconductor substrate with a hydrofluoric acid solution, an alkaline solution, or the like. At this time, innumerable uneven texture shapes with a typical width of 20 to 100 μm and a depth of about 1 to 4 μm are formed on the surface of the semiconductor substrate. Hereinafter, the etching process of the semiconductor substrate surface may be referred to as the texture processing process of the semiconductor substrate.

[0018] FIG. 1 shows a process flowchart of an example of the method for manufacturing a solar cell according to the present invention. First, in the process shown in (a), an impurity diffusion composition (A) is partially applied onto a semiconductor substrate 1 to form a pattern 2 of an impurity diffusion composition film (B). Next, in the process shown in (b-1) or (b-2), impurities are diffused from the pattern 2 of the impurity diffusion composition film (B) into the semiconductor substrate 1 to form an impurity diffusion layer (C). (b-1) shows the process of forming the impurity diffusion layer (C) by heating in a heating furnace, and (b-2) shows the process of forming the impurity diffusion layer (C) by laser irradiation 3. A layer (E) containing silicon oxide may be formed on the semiconductor substrate 1. Next, in the process shown in (c), the pattern of the impurity diffusion composition film (B) is removed from the substrate on which the impurity diffusion layer (C) is formed by etching. When the layer (E) containing silicon oxide is formed in the process shown in (b), it is preferable that the layer (E) containing silicon oxide is also removed in the process shown in (c). Next, in the process shown in (d), the semiconductor substrate 1 after etching is heated in an impurity diffusion component-containing gas 4, that is, a gas atmosphere containing boron or phosphorus, to diffuse boron or phosphorus into the semiconductor substrate, and an impurity diffusion layer (D) is formed in a portion where the impurity diffusion composition film (B) was not formed. Also, the diffusion of the impurity diffusion layer (C) further proceeds. At this time, a layer (F) containing borosilicate glass or phosphosilicate glass may be formed due to oxidation of the surface of the semiconductor substrate 1. In this case, next, in the process shown in (e), it is preferable to remove the layer (F) containing borosilicate glass or phosphosilicate glass by etching. Also, it is preferable to include a process (not shown) including a process of laser-irradiating a portion of the impurity diffusion layer (C) after the process of (c).

[0019] Hereinafter, each process of the present embodiment will be described in detail.

[0020] <Step of applying the impurity diffusion composition (A) to the semiconductor substrate to partially form the impurity diffusion composition film (B)> The impurity diffusion composition (A) preferably contains (A-1) a hydroxyl group-containing polymer and (A-2) an impurity diffusion component. Further, the impurity diffusion composition (A) preferably contains (A-3) a polymer of a silane compound, (A-4) a silane compound, and / or (A-5) particles containing a Group 13 element or a Group 15 element. Two or more of these may be included. It is more preferable to include these together with (A-1) the hydroxyl group-containing polymer and (A-2) the impurity diffusion component.

[0021] (A-1) The hydroxyl group-containing polymer is a component that forms a complex with (A-2) the impurity diffusion component and forms a uniform film during coating.

[0022] Specific examples of (A-1) the hydroxyl group-containing polymer include vinyl alcohol derivatives such as polyvinyl alcohol (including modified polyvinyl alcohol), polyvinyl acetal, and polyvinyl butyral; polyalkylene oxides such as polyethylene oxide and polypropylene oxide; polyhydroxy acrylates such as hydroxyethyl cellulose, polyhydroxymethyl acrylate, polyhydroxyethyl acrylate, and polyhydroxypropyl acrylate. Two or more of these may be included. Among them, when (A-2) the impurity diffusion component described below is a Group 13 element compound, particularly preferably a boron compound, polyvinyl alcohol (hereinafter sometimes simply referred to as PVA) is preferable in terms of the ability to form a complex with the boron compound, the stability of the formed complex, and the storage stability of the p-type impurity diffusion composition.

[0023] The saponification degree of PVA is preferably 20 mol% or more and less than 70 mol%. By setting the saponification degree within this range, the complex stability with (A-2) the impurity diffusion component is enhanced, and the diffusibility and diffusion uniformity are improved.

[0024] (A-1) The average degree of polymerization of the hydroxyl group-containing polymer is preferably 150 to 1000 in terms of solubility and complex stability. In the present invention, both the average degree of polymerization of the hydroxyl group-containing polymer and the saponification degree of PVA are values measured in accordance with JIS K 6726 (1994). The saponification degree is a value measured by the back titration method among the methods described in the said JIS.

[0025] In terms of good heat diffusion and suppression of organic residues on the substrate after removal of the composition, the amount of (A-1) the hydroxyl group-containing polymer is preferably 1 to 20% by mass, more preferably 5 to 15% by mass in the impurity diffusion composition.

[0026] (A-2) The impurity diffusion component is a component for forming an impurity diffusion layer in the semiconductor substrate. These are compounds that are uniformly dissolved in the impurity diffusion composition (A), and are distinguished from the particles containing a Group 13 element or a Group 15 element (A-5) described later. As the p-type impurity diffusion component, a compound containing an element of Group 13 is preferable, and among them, a boron compound is preferable. As the n-type impurity diffusion component, a compound containing a Group 15 element is preferable, and among them, a phosphorus compound is preferable.

[0027] Examples of the boron compound include boric acid, diboron trioxide, methylboronic acid, phenylboronic acid, trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, trioctyl borate, triphenyl borate, etc. Two or more of these may be included. Among them, boric acid and diboron trioxide are more preferable from the viewpoint of doping property.

[0028] Examples of the phosphorus compound include phosphate esters such as diphosphorus pentoxide, phosphoric acid, polyphosphoric acid, methyl phosphate, dimethyl phosphate, trimethyl phosphate, ethyl phosphate, diethyl phosphate, triethyl phosphate, propyl phosphate, dipropyl phosphate, tripropyl phosphate, butyl phosphate, dibutyl phosphate, tributyl phosphate, phenyl phosphate, diphenyl phosphate, and triphenyl phosphate; and phosphite esters such as methyl phosphite, dimethyl phosphite, trimethyl phosphite, ethyl phosphite, diethyl phosphite, triethyl phosphite, propyl phosphite, dipropyl phosphite, tripropyl phosphite, butyl phosphite, dibutyl phosphite, tributyl phosphite, phenyl phosphite, diphenyl phosphite, and triphenyl phosphite. Two or more of these may be included. Among them, phosphoric acid, diphosphorus pentoxide, and polyphosphoric acid are preferable from the viewpoint of doping property.

[0029] The amount of the (A-2) impurity diffusion component contained in the impurity diffusion composition can be arbitrarily determined according to the resistance value required for the semiconductor substrate, and is preferably 0.1 to 10% by mass.

[0030] From the viewpoint of diffusion uniformity, the mass ratio of the (A-1) hydroxyl group-containing polymer to the (A-2) impurity diffusion component is preferably 1:1 to 20:1, and more preferably 4:1 to 10:1.

[0031] From the viewpoint that the carrier lifetime of the solar cell becomes longer, the impurity diffusion composition (A) used in the present invention preferably contains a polymer of a silane compound represented by the following general formula (1).

[0032]

Chemical formula

[0033] In the general formula (1), R 1 and R 2 each represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms, and a plurality of R1 and R 2 may be the same or different, respectively. l represents an integer from 1 to 10,000. From the viewpoint of the toughness of the film after film formation, l is preferably from 5 to 10,000, more preferably from 10 to 10,000.

[0034] R in the general formula (1) 1 and R 2 The alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, the alkenyl group having 2 to 10 carbon atoms, the acyl group having 2 to 6 carbon atoms, and the aryl group having 6 to 15 carbon atoms in may each be either an unsubstituted form or a substituted form, and can be selected according to the properties of the impurity diffusion composition.

[0035] Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a t-butyl group, an n-hexyl group, a trifluoromethyl group, a 3,3,3-trifluoropropyl group, a 3-glycidoxypropyl group, a 2-(3,4-epoxycyclohexyl)ethyl group, a [(3-ethyl-3-oxetanyl)methoxy]propyl group, a 3-aminopropyl group, a 3-mercaptopropyl group, a 3-isocyanatepropyl group, and the like.

[0036] Specific examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group, a tert-butoxy group, and the like.

[0037] Specific examples of the alkenyl group having 2 to 10 carbon atoms include a vinyl group, a 3-acryloxypropyl group, a 3-methacryloxypropyl group, and the like.

[0038] Specific examples of the acyl group having 2 to 6 carbon atoms include an acetyl group and the like.

[0039] Specific examples of the aryl group having 6 to 15 carbon atoms include a phenyl group, a tolyl group, a p-hydroxyphenyl group, a p-styryl group, a p-methoxyphenyl group, a 1-(p-hydroxyphenyl)ethyl group, a 2-(p-hydroxyphenyl)ethyl group, a 4-hydroxy-5-(p-hydroxyphenylcarbonyloxy)pentyl group, a naphthyl group, and the like.

[0040] From the viewpoint of suppressing out-diffusion from the impurity diffusion composition, R 1 and R 2 at least one of which is preferably any one of an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms.

[0041] More preferably, R 1 is any one of an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms, and R 2 is either a hydroxyl group or an alkoxy group having 1 to 6 carbon atoms.

[0042] The terminal group of the polymer of the silane compound represented by the general formula (1) is preferably any one of hydrogen, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, and an alkenyl group having 2 to 10 carbon atoms.

[0043] From the viewpoint of suppressing out-diffusion from the impurity diffusion composition, it is preferable that the polymer of the (A-3) silane compound is a polymer of a silane compound represented by the following general formula (2).

[0044]

Chemical formula

[0045] In the general formula (2), R 3 represents an aryl group having 6 to 15 carbon atoms, and a plurality of R 3 may be the same or different from each other. R 4represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms, and a plurality of Rs 4 may be the same or different from each other. R 5 and R 6 represent any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an acyl group having 2 to 6 carbon atoms, and a plurality of Rs 5 and R 6 may be the same or different from each other. n and m represent integers from 1 to 9,999, n + m is from 2 to 10,000, and n:m = 95:5 to 25:75. From the viewpoint of the toughness of the film after film formation, the preferable range of (n + m) is from 5 to 10,000, more preferably from 10 to 10,000.

[0046] The alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, the alkenyl group having 2 to 10 carbon atoms, the acyl group having 2 to 6 carbon atoms, and the aryl group having 6 to 15 carbon atoms in R 3 ~R 6 in the general formula (2) may be either an unsubstituted form or a substituted form, and can be selected according to the properties of the impurity diffusion composition. Specific examples thereof include the same ones as those in R 1 and R 2 .

[0047] The polymer of the silane compound represented by the general formula (2) is a polysiloxane in which the unit containing an aryl group having 6 to 15 carbon atoms is 25 to 95 mol% in terms of Si atoms. That is, n:m = 95:5 to 25:75. By being in this range, the effect of suppressing the out-diffusion of impurity diffusion components and reducing organic residues when removing impurity diffusion components after heat treatment is improved. Also, by being in this range, even in an impurity diffusion composition to which a thermal decomposition component such as a thickener is added, due to the reflow effect of the silane compound, it becomes possible to fill the pores generated by thermal decomposition, and a dense film with few pores can be formed. Therefore, it is less likely to be affected by the atmosphere during diffusion, and a high masking property against other impurities can be obtained. From the viewpoint of further improving out-diffusion suppression and masking property, the unit containing an aryl group having 6 to 15 carbon atoms is more preferably 35 mol% or more, and even more preferably 40 mol% or more. Also, in order not to generate residues regardless of the atmosphere and film thickness, it is preferable that the unit containing an aryl group is 80 mol% or less. That is, it is particularly preferable that n:m = 80:20 to 40:60.

[0048] The polymer of the silane compound represented by the general formula (2) only needs to contain each constituent component in the above-mentioned predetermined ratio, and may be a block copolymer or a random copolymer.

[0049] The terminal group of the polymer of the silane compound represented by the general formula (2) is preferably any one of hydrogen, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an acyloxy group having 1 to 6 carbon atoms, and an alkenyl group having 2 to 10 carbon atoms.

[0050] The polymer of the silane compound represented by the general formula (1) or (2) can be obtained, for example, by hydrolyzing an organosilane compound and then subjecting the hydrolyzate to a condensation reaction in the presence of a solvent or without a solvent. Various conditions of the hydrolysis reaction, such as acid concentration, reaction temperature, reaction time, etc., can be appropriately set in consideration of the reaction scale, the size and shape of the reaction vessel, etc. For example, in a solvent, after adding an acid catalyst and water to the organosilane compound over 1 to 180 minutes, it is preferable to react at room temperature to 110 °C for 1 to 180 minutes. By carrying out the hydrolysis reaction under such conditions, a rapid reaction can be suppressed. The reaction temperature is more preferably 30 to 130 °C.

[0051] The hydrolysis reaction is preferably carried out in the presence of an acid catalyst. In the present invention, from the viewpoint of doping properties, the acid catalyst preferably contains as few atoms other than silicon, hydrogen, carbon, oxygen, nitrogen, and phosphorus as possible, and it is preferable to use phosphoric acid, formic acid, acetic acid, or a carboxylic acid-based acid catalyst. Among them, phosphoric acid is preferable.

[0052] The preferable content of the acid catalyst is preferably 0.1 part by mass to 5 parts by mass with respect to 100 parts by mass of the total organosilane compound used during the hydrolysis reaction. By setting the amount of the acid catalyst within the above range, the hydrolysis reaction can be easily controlled to proceed as required and sufficiently.

[0053] The solvent used for the hydrolysis reaction of the organosilane compound and the condensation reaction of the hydrolyzate is not particularly limited, and can be appropriately selected in consideration of the stability, coatability, volatility, etc. of the resin composition. Also, two or more solvents may be combined, or the reaction may be carried out without a solvent.

[0054] From the point that the carrier lifetime of the solar cell becomes longer, the impurity diffusion composition (A) used in the present invention preferably contains a silane compound represented by the following general formula (3).

[0055]

Chemical formula

[0056] In general formula (3), R 7 ~R 10 represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms. Preferably, two or more of R 7 ~R 10 are any one of a hydroxyl group and an alkoxy group having 1 to 6 carbon atoms, and more preferably, three or more of R 7 ~R 10 are any one of a hydroxyl group and an alkoxy group having 1 to 6 carbon atoms.

[0057] Specific examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, the alkenyl group having 2 to 10 carbon atoms, the acyl group having 2 to 6 carbon atoms, and the aryl group having 6 to 15 carbon atoms are the same as those in R 1 and R 2 .

[0058] From the viewpoint that the carrier lifetime of the solar cell becomes longer, the impurity diffusion composition (A) used in the present invention preferably contains particles containing a Group 13 element or a Group 15 element. The p-type impurity diffusion composition (A) preferably contains particles containing a Group 13 element, and the n-type impurity diffusion composition (A) preferably contains particles containing a Group 15 element.

[0059] Examples of the particles containing a Group 13 element include, for example, B 2 O 3 , Al 2 O 3 , Ga 2 O 3In addition to oxides of group 13 elements such as the like, glass compounds containing glass components (hereinafter, sometimes referred to as glass particles or glass particles containing group 13 elements), boron, silicon particles doped with aluminum, boron nitride, boron-containing silicon oxide compounds, and the like can be mentioned. Among these, glass particles containing group 13 elements, boron nitride, and boron-containing silicon oxide compounds are preferable, and glass particles containing group 13 elements are more preferable.

[0060] Glass particles containing group 13 elements can be formed, for example, by including oxides of group 13 elements and glass components. As the oxides of group 13 elements used to introduce group 13 elements into glass particles, it is preferable that the compound contains one or more selected from the group consisting of B 2 O 3 , Ga 2 O 3 and Al 2 O 3 , and it is more preferable to contain B 2 O 3 .

[0061] The content rate of the oxides of group 13 elements in glass particles containing group 13 elements varies depending on the situation where the desired effect can be obtained. For example, from the viewpoint of the diffusibility of group 13 elements, it is preferably 0.5 mass% or more and 100 mass% or less, and more preferably 2 mass% or more and 80 mass% or less.

[0062] When the compound containing group 13 elements is glass particles, the components of the glass particles can be components generally used. For example, the glass softening point can be set within a desired range, and from the viewpoint of reducing the difference from the thermal expansion coefficient of the semiconductor substrate, the components SiO 2 , K 2 O, Na 2 O, Li 2 O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl 2 O, V 2 O 5 , SnO, ZrO 2 , WO 3 , MoO3 , Y 2 O 3 , CsO 2 , TiO 2 , TeO 2 , La 2 O 3 , Nb 2 O 5 , Ta 2 O 5 , GeO 2 , Lu 2 O 3 and at least one selected from the group consisting of MnO can be used.

[0063] Specific examples of the glass particles include glass particles containing both an oxide of a Group 13 element and the glass component. B 2 O 3 -SiO 2 system (described in the order of the oxide of the Group 13 element - glass component, the same applies hereinafter), B 2 O 3 -ZnO system, B 2 O 3 -PbO system, etc., systems containing B 2 O 3 as the oxide of the Group 13 element, Al 2 O 3 -SiO 2 system, etc., systems containing Al 2 O 3 as the oxide of the Group 13 element, Ga 2 O 3 -SiO 2 system, etc., systems containing Ga 2 O 3 are exemplified. In the above, glass particles containing one or two components were exemplified, but B 2 O 3 -SiO 2 -CaO, etc., glass particles containing three or more components may also be used. Also, Al 2 O 3 -B 2 O 3 systems, etc., glass particles containing two or more Group 13 elements are also preferably used. Among these, at least B 2 O 3It is preferably glass particles containing B, 2 O 3 It is more preferably contained in an amount of 0.1 to 100 mol%, still more preferably contained in an amount of 10 to 80 mol%, and most preferably contained in an amount of 20 to 70 mol%.

[0064] The softening point of the glass particles containing Group 13 elements is preferably 400°C to 900°C, more preferably 400°C to 850°C, and still more preferably 400°C to 800°C. When the softening point of the glass particles is 400°C or higher, it is possible to prevent excessive out-diffusion from the glass particles when diffusing Group 13 elements. When the temperature is 900°C or lower, the out-diffusion does not become too small, and there is a tendency to make the diffusion to the portion where the p-type diffusion layer forming composition is not applied uniform.

[0065] The softening point of the glass particles can be measured by a thermogravimetric measurement-differential thermal analyzer (DTA) with a heating rate of about 10°C / min, and can be measured as the temperature at the inflection point of the DTA curve associated with the softening flow that appears on the high-temperature side of the glass transition point Tg.

[0066] The content rate of the compound containing Group 13 elements (A-2) and / or the particles containing Group 13 elements (A-5) in the p-type impurity diffusion composition (A) is determined in consideration of coatability, diffusibility of the compound containing Group 13 elements, particles, etc. Generally, the total content rate of the compound containing Group 13 elements and the particles in the p-type impurity diffusion composition (A) is preferably 0.1 mass% or more and 95 mass% or less, more preferably 1 mass% or more and 90 mass% or less, still more preferably 1 mass% or more and 80 mass% or less, particularly preferably 2 mass% or more and 50 mass% or less, and most preferably 5 mass% or more and 20 mass% or less. When the total content rate of the compound containing Group 13 elements and the particles in the p-type impurity diffusion composition (A) is 0.1 mass% or more, an impurity diffusion layer can be sufficiently formed. When it is 95 mass% or less, the dispersibility of the compound containing Group 13 elements and the particles in the p-type impurity diffusion composition (A) becomes good, and the coatability on the semiconductor substrate is improved.

[0067] The content rate of the compound containing a Group 15 element and / or the particles containing a Group 15 element in the n-type impurity diffusion composition (A) is determined in consideration of coatability, the compound containing a Group 15 element, diffusibility of the particles, etc. Generally, the total content rate of the compound containing a Group 15 element and the particles in the n-type impurity diffusion composition (A) is preferably 0.1% by mass or more and 95% by mass or less, more preferably 1% by mass or more and 90% by mass or less, still more preferably 1% by mass or more and 80% by mass or less, particularly preferably 2% by mass or more and 50% by mass or less, and most preferably 5% by mass or more and 20% by mass or less. When the total content rate of the compound containing a Group 15 element and the particles in the n-type impurity diffusion composition (A) is 0.1% by mass or more, an impurity diffusion layer can be sufficiently formed, and when it is 95% by mass or less, the dispersibility of the compound containing a Group 15 element and the particles in the p-type impurity diffusion composition (A) becomes good, and the coatability onto the semiconductor substrate is improved.

[0068] The impurity diffusion composition (A) preferably further contains a solvent. Particularly from the viewpoint of further improving printability when using a screen printing method, a spin coating method, or the like, a solvent having a boiling point of 100°C or higher is preferable. When the boiling point is 100°C or higher, for example, when the impurity diffusion composition is printed on a printing plate used in the screen printing method, it is easy to suppress the impurity diffusion composition from drying and adhering on the printing plate.

[0069] The content of the solvent with a boiling point of 100 °C or higher is preferably 20% by mass or more based on the total amount of the solvent. Examples of the solvent with a boiling point of 100 °C or higher include diethylene glycol methyl ethyl ether (boiling point 176 °C), diacetone alcohol (boiling point 169 °C), propylene glycol monomethyl ether acetate (boiling point 145 °C), 3-methoxy-3-methyl-1-butanol (boiling point 174 °C), dipropylene glycol monomethyl ether (boiling point 188 °C), γ-butyrolactone (boiling point 204 °C), N-methyl-2-pyrrolidone (boiling point 204 °C), N,N-dimethylimidazolidinone (boiling point 226 °C), dipropylene glycol methyl ether acetate (boiling point 213 °C), 1,3-butylene glycol diacetate (boiling point 232 °C), and the like.

[0070] The impurity diffusion composition (A) may contain a surfactant. By containing a surfactant, coating unevenness can be improved and a uniform coating film can be obtained. As the surfactant, a fluorine-based surfactant, a silicone-based surfactant, an acrylic-based surfactant, etc. are preferably used.

[0071] When containing a surfactant, the content is preferably 0.0001 to 1% by mass in the impurity diffusion composition.

[0072] The impurity diffusion composition (A) preferably contains a thickener for viscosity adjustment. Thereby, it can be applied with a more precise pattern by a printing method such as screen printing.

[0073] From the viewpoints of dense film formation and residue reduction, the thickener preferably has a 90% thermal decomposition temperature of 400 °C or lower. Specifically, polyethylene glycol, polyethylene oxide, polypropylene glycol, polypropylene oxide, and various acrylate resins are preferred. Among them, polyethylene oxide, polypropylene oxide, or acrylate resin is particularly preferred. From the viewpoint of storage stability, acrylate resin is particularly preferred. Here, the 90% thermal decomposition temperature is the temperature at which the weight of the thickener decreases by 90% due to thermal decomposition. The 90% thermal decomposition temperature can be measured using a thermogravimetric analyzer (TGA) or the like.

[0074] From the viewpoint of screen printability, the impurity diffusion composition (A) preferably contains a thixotropic agent that imparts thixotropy. Here, imparting thixotropy means increasing the ratio (η1 / η2) of the viscosity (η1) at low shear stress to the viscosity (η2) at high shear stress. By containing a thixotropic agent, the pattern accuracy of screen printing can be improved. This is presumably due to the following reasons. That is, the impurity diffusion composition containing a thixotropic agent has a low viscosity at high shear stress, so clogging of the screen is less likely to occur during screen printing, and has a high viscosity at low shear stress, so bleeding immediately after printing and thickening of the pattern line width are less likely to occur.

[0075] Specific examples of the thixotropic agent include cellulose derivatives, polysaccharides, hydrogenated castor oil-based polyethylene oxides, fatty acid-based polyvalent carboxylic acids, phosphate ester-based surfactants, montmorillonite, fine particle silicon oxides, colloidal alumina, calcium carbonate, and the like. The thixotropic agent can be used alone, but it is also possible to combine two or more thixotropic agents. Moreover, it is more preferably used in combination with the thickener, and a higher effect can be obtained.

[0076] There is no restriction on the viscosity of the impurity diffusion composition (A), and it can be appropriately changed according to the printing method and film thickness. Here, for example, in the case of the screen printing method, which is one of the preferable printing forms, the viscosity of the impurity diffusion composition is preferably 5,000 mPa·s or more. More preferably, it is 10,000 mPa·s or more. There is no particular upper limit, but from the viewpoints of storage stability and handleability, it is preferably 100,000 mPa·s or less. Here, when the viscosity is less than 1,000 mPa·s, it is the value measured at a rotational speed of 20 rpm using an E-type digital viscometer based on JIS Z 8803 (1991) "Solution Viscosity - Measurement Method", and when the viscosity is 1,000 mPa·s or more, it is the value measured at a rotational speed of 20 rpm using a B-type digital viscometer based on JIS Z 8803 (1991) "Solution Viscosity - Measurement Method". Thixotropy can be determined as the thixotropy index from the ratio of viscosities at different rotational speeds obtained by the above viscosity measurement method. In the present invention, the ratio (η2 / η20) of the viscosity (η20) at a rotational speed of 20 rpm to the viscosity (η2) at a rotational speed of 2 rpm is defined as thixotropy. In order to form a pattern with good accuracy in screen printing, the thixotropy is preferably 2 or more, and more preferably 3 or more.

[0077] There is no particular restriction on the solid content concentration of the impurity diffusion composition (A), but a range of 1 mass% or more to 90 mass% or less is a preferable range. If it is lower than this concentration range, the coating film thickness may become too thin and it may be difficult to obtain the desired doping property and masking property. If it is higher than this concentration range, the storage stability may decrease.

[0078] Examples of the coating method of the impurity diffusion composition (A) include spin coating method, screen printing method, inkjet printing method, slit coating method, spray coating method, relief printing method, intaglio printing method, etc.

[0079] After coating the impurity diffusion composition (A) by these methods, it is preferable to dry the semiconductor substrate coated with the impurity diffusion composition (A) at 50 to 300 °C for 30 seconds to 30 minutes using a hot plate, oven, etc. to form a pattern of the impurity diffusion composition film (B).

[0080] From the viewpoint of the diffusibility of impurities, the film thickness of the dried impurity diffusion composition film (B) is preferably 100 nm or more, and from the viewpoint of the residue after etching, it is preferably 20 μm or less. More preferably, it is 15 μm or less, and still more preferably 10 μm or less.

[0081] <(b) Step of diffusing the impurities in the impurity diffusion composition film (B) into the semiconductor substrate to form an impurity diffusion layer (C)> As a method for diffusing the impurities in the impurity diffusion composition film (B) into the semiconductor substrate, known diffusion methods can be used. For example, methods such as heating by electricity or infrared rays using a heating furnace, laser irradiation, and microwave irradiation can be used. From the viewpoint of diffusion uniformity, heating by a heating furnace or laser irradiation is preferred. At this time, in addition to the impurity diffusion composition film (B), a layer (E) containing silicon oxide may be formed.

[0082] When forming the impurity diffusion layer (C) by heating with a heating furnace, from the viewpoint of promoting the decomposition and removal of the organic matter in the impurity diffusion composition film (B) and improving the carrier lifetime after diffusion, it is preferable to set the inside of the heating furnace to 700 - 850 °C and the oxygen concentration to 10 - 50% in advance and then insert the semiconductor substrate. If the temperature and oxygen concentration are lower than this, the organic matter will not be sufficiently removed. If the temperature and oxygen concentration are higher than this, when the impurity diffusion composition (A) does not contain a silane compound, (A-2) volatilization of the impurity diffusion component occurs and the amount of the impurity diffusion component in the impurity diffusion composition film (B) decreases. When the impurity diffusion composition (A) contains a silane compound, before the organic matter is removed, due to the reflow effect of the silane compound, the impurity diffusion composition film (B) becomes a dense film with few voids, so the organic matter is trapped in the impurity diffusion composition film (B) and the removal becomes insufficient. Also, when the temperature is raised to 700 - 850 °C after inserting the semiconductor substrate, (A-2) volatilization of the impurity diffusion component and the organic matter being trapped in the impurity diffusion composition film (B) occur as described above.

[0083] After the semiconductor substrate is introduced into the heating furnace, it is preferably processed at 700 to 850 °C and an oxygen concentration of 10 to 50% for 5 to 200 minutes, and then the temperature is raised to promote the diffusion of impurities. The time and temperature at that time can be appropriately set so as to obtain desired diffusion characteristics such as impurity concentration and diffusion depth. For example, by heating and diffusing at 800 °C or higher and 1200 °C or lower for 1 to 120 minutes, the surface impurity concentration is 10 19 ~10 21 atoms / cm 3 of the diffusion layer can be formed. The atmosphere during diffusion is not particularly limited, and it may be carried out in the atmosphere, or the amount of oxygen in the atmosphere may be appropriately adjusted using an inert gas such as nitrogen or argon. From the viewpoint of shortening the diffusion time, the oxygen concentration in the atmosphere during diffusion is preferably 3% or less.

[0084] When forming the impurity diffusion layer (C) by laser irradiation, there is no particular limitation on the laser light source, and a known one can be used. For example, the fundamental wave (1064 [nm]), second harmonic wave (532 [nm]), third harmonic wave (355 [nm]) of the Nd:YAG laser or Nd:YVO 4 laser, or laser light such as the XeCl excimer laser (308 [nm]), KrF excimer laser (248 [nm]), ArF excimer laser (198 [nm]) can be used. This is irradiated at an oscillation frequency of 5 to 100 kHz and a pulse width of 10 to 200 nsec so that the temperature within the beam diameter is heated to 800 to 1000 °C, and the surface impurity concentration is 10 19 ~10 21 atoms / cm 3 of the diffusion layer is preferably formed.

[0085] In addition, heat treatment may be further added after laser irradiation to promote the impurity diffusion of the impurity diffusion layer (C).

[0086] <(c) Step of removing the impurity diffusion composition film (B) by etching> After forming the impurity diffusion layer (C) in this way, the pattern 2 of the impurity diffusion composition film (B) and, in some cases, the layer (E) containing silicon oxide formed on the surface are etched and removed. The material used for etching is not particularly limited. For example, it preferably contains at least one of hydrogen fluoride, ammonium, phosphoric acid, sulfuric acid, and nitric acid as an etching component, and contains water, an organic solvent, etc. as other components. Also, the outermost surface of the substrate may be etched with an alkali used for texture processing.

[0087] In the present invention, after forming the impurity diffusion layer (C), the impurity diffusion composition film (B) is removed by etching, and then an impurity diffusion layer (D) having an impurity concentration different from that of the impurity diffusion layer (C) is formed in a portion where the impurity diffusion layer (C) is not formed. By this method, it is possible to improve the carrier lifetime without being affected by the boron silicide component formed at the interface between the impurity diffusion composition film (B) and the impurity diffusion layer (C), or a small amount of carbon or boron component adhering to a portion where the impurity diffusion layer (C) is not formed from the impurity diffusion composition film (B) when forming the impurity diffusion layer (C).

[0088] <(d) Step of heating the etched semiconductor substrate in a gas atmosphere containing boron or phosphorus, diffusing boron or phosphorus into the semiconductor substrate to form an impurity diffusion layer (D) in a portion where the impurity diffusion composition film (B) of the semiconductor substrate was not formed, and simultaneously further advancing the diffusion of the impurity diffusion layer (C)> By heating the etched semiconductor substrate in a gas atmosphere containing boron or phosphorus, an impurity diffusion layer (D) is formed in a portion where the impurity diffusion composition film (B) of the semiconductor substrate was not formed.

[0089] For example, in the case of p-type, boron bromide (BBr 3 ), and in the case of n-type, phosphorus oxychloride (POCl 3 ) is bubbled, and N 2There is a method of heating a semiconductor substrate at 800 to 1,000 °C in an atmosphere containing an impurity diffusion component by flowing. At this time, due to the oxidation of the substrate surface, a layer containing boron silicate glass in the case of p-type and phosphorus silicate glass in the case of n-type is formed, and impurities are diffused into the semiconductor substrate.

[0090] At this time, it is preferable that the impurity diffusion layer (C) and the impurity diffusion layer (D) of the semiconductor substrate have the same type of conductivity. That is, it is preferable to heat in a gas atmosphere containing boron when the impurity diffusion layer (C) is p-type, and in a gas atmosphere containing phosphorus when the impurity diffusion layer (C) is n-type. The impurity concentration of the impurity diffusion layer (D) can be set by setting the gas pressure and heating conditions at this time.

[0091] Furthermore, when the impurity diffusion layer (C) and the impurity diffusion layer (D) have the same type of conductivity, the diffusion of the impurity diffusion layer (C) further proceeds by this process.

[0092] <(e) Step of removing the layer containing boron silicate glass or phosphorus silicate glass on the semiconductor substrate by etching> After thus forming impurity diffusion layers with two or more different impurity concentrations, it is preferable to remove the layer (F) containing boron silicate glass or phosphorus silicate glass formed on the surface.

[0093] For the removal, a method similar to the removal of the pattern of the impurity diffusion composition film (B) and the layer (E) containing silicon oxide described in (c) is preferably used. <(f) Step of further promoting the diffusion of the impurity diffusion layer (C) by irradiating the impurity diffusion layer (C) with a laser> From the viewpoint of making the carrier lifetime of the solar cell longer, it is preferable to include a step of further advancing the diffusion of the impurity diffusion layer (C) by irradiating the impurity diffusion layer (C) with a laser after the step (c). The step (f) may be included, for example, between the steps (c) and (d), between the steps (d) and (e), or after the step (e), or may be included two or more times. This makes it possible to selectively advance the diffusion in the region of the impurity diffusion layer (C). From the viewpoint of making the carrier lifetime of the solar cell longer, it is more preferable to include the step (f) between the steps (d) and (e).

[0094] Regarding the light source and conditions of the laser irradiation in the step (f), the same method as in the case of forming the impurity diffusion layer (C) by laser irradiation described in (b) is preferably used.

[0095] <Back surface formation step> The method for manufacturing a solar cell of the present invention may include a back surface formation step. After the step (e) above, when there is a step (f) thereafter, it is preferable to have a back surface formation step thereafter, and the back surface can be simultaneously cleaned by etching.

[0096] For example, when forming a p-type impurity diffusion layer with two or more different impurity concentrations on the surface of a semiconductor substrate and forming an n-type impurity diffusion layer on the back surface, the surface is protected with an SiO 2 film or the like so that n-type impurities do not penetrate into the surface. The preferable film thickness for obtaining the protection effect is 100 to 1,000 nm, and it is preferably formed by plasma CVD with a high film formation rate at a low temperature in order to suppress the influence on the p-type diffusion layer on the surface of the semiconductor substrate. More specifically, it is formed under the conditions that the mixed gas flow rate ratio SiH 4 / N 2 O is 0.01 to 5.0, the pressure in the reaction chamber is 0.1 to 4 Torr, and the temperature during film formation is 300°C to 550°C.

[0097] Thereafter, phosphorus oxychloride (POCl 3 ) is bubbled into the back surface, and N 2While flowing, heat the semiconductor substrate at 800 to 900 °C in an atmosphere containing an impurity diffusion component. At this time, an n-type impurity diffusion layer is formed on the back surface of the semiconductor substrate, and at the same time, a layer containing silicon oxide, such as a phosphorus silicate glass layer, is formed on the outermost surface of the back surface by oxidation.

[0098] Next, remove the inorganic film on the surface of the semiconductor substrate and the layer containing silicon oxide on the back surface by etching. For the removal, the same method as the removal of the pattern of the impurity diffusion composition film (B) and the layer (E) containing silicon oxide described in (c) is preferably used.

[0099] <Passivation step> In the method for manufacturing a solar cell of the present invention, after the step of (e), if there is a step of (f) and a back surface forming step, it is preferable to provide a passivation film for suppressing surface recombination and preventing light reflection on the front and back surfaces of the semiconductor substrate. For example, as the passivation film of the p-type diffusion layer, SiO obtained by heat treatment in a high-temperature oxygen atmosphere of 700 °C or higher 2 And, in order to protect this film, a silicon nitride film may be provided. Also, only a SiN x film may be formed. In this case, it can be formed by a plasma CVD method using a mixed gas of SiH 4 and NH 3 as raw materials. At this time, hydrogen diffuses into the crystal, and the orbit that does not contribute to the bond of silicon atoms, that is, the dangling bond and hydrogen are bonded to inactivate the defect (hydrogen passivation). More specifically, the mixed gas flow rate ratio NH 3 / SiH 4 is 0.05 to 5.0, the pressure in the reaction chamber is 0.1 to 4 Torr, and it is formed under the condition that the temperature during film formation is 300 °C to 550 °C.

[0100] <Electrode formation step> Next, a metal paste is screen-printed on the high-concentration impurity diffusion layer among the two-level impurity diffusion layers from above the passivation film, dried, and an electrode is formed. The metal paste for the electrode contains metal particles and glass particles as essential components, and may contain a resin binder, other additives, etc. as required. Regarding the metal particles used at this time, Ag and Al are preferably used.

[0101] <Electrode firing process> Next, the electrode is heat-treated (fired) to complete the solar cell. When heat-treated (fired) in the range of 600 °C to 900 °C for several seconds to several minutes, on the light-receiving surface side, the antireflection film, which is an insulating film, melts due to the glass particles contained in the metal paste for the electrode, and further, a part of the silicon surface also melts, and the metal particles (for example, silver particles) in the paste form a contact portion with the semiconductor substrate and solidify. As a result, the formed light-receiving surface electrode and the semiconductor substrate are electrically connected. This is called firing through.

[0102] The light-receiving surface electrode generally consists of a busbar electrode and finger electrodes intersecting with the busbar electrode. Such a light-receiving surface electrode can be formed by means such as screen printing of the above-mentioned metal paste, plating of the electrode material, or vapor deposition of the electrode material by electron beam heating in a high vacuum. The busbar electrode and the finger electrodes can be formed by known methods.

Example

[0103] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. Among the compounds used, those using abbreviations are shown below.

[0104] KBM-13: Methyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) KBM-103: Phenyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) GBL: γ-Butyrolactone (manufactured by Mitsubishi Chemical Corporation).

[0105] <Evaluation method> <Carrier Lifetime Measurement> For the solar cells obtained in Examples 1 to 8 and Comparative Example 1, using a solar simulator having a spectral distribution of AM1.5, under 25 °C, simulated sunlight was irradiated at an energy density of 100 mW / cm 2 , and the open-circuit voltage V OC (Voltage Open Circuit) was measured. The higher the V OC , the longer the carrier lifetime, and it can be said that the solar cell has good characteristics.

[0106] (Production Example 1) <Preparation of p-Type Impurity Diffusion Composition> 1.3 g of boric acid (manufactured by Fujifilm Wako Pure Chemical Corporation), 11.6 g of polyvinyl alcohol with a saponification degree of 49 mol% (manufactured by Nippon Gohsei Co., Ltd.) (hereinafter referred to as polyvinyl alcohol (49)), 3.9 g of "Aerosil (registered trademark)" VPNKC130 which is fine particle silicon oxide (manufactured by Nippon Aerosil Co., Ltd.), 24.6 g of GBL, 35.1 g of terpineol (manufactured by Tokyo Chemical Industry Co., Ltd.), and 10.0 g of water were mixed and sufficiently stirred to be uniform to obtain a p-type impurity diffusion composition A.

[0107] (Production Example 2) <Synthesis of Solution of Polymer of Silane Compound> 183.2 g of KBM-13, 266.7 g of KBM-103, and 403.3 g of GBL were charged, and while stirring at 40 °C, an aqueous formic acid solution in which 0.5 g of formic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 145.2 g of water was added over 30 minutes. After the dropping was completed, it was stirred at 40 °C for 1 hour, then heated to 70 °C and stirred for 30 minutes. Thereafter, the oil bath was heated to 115 °C. One hour after the start of heating, the internal temperature of the solution reached 100 °C, and it was heated and stirred for 1 hour from there (the internal temperature was 100 to 110 °C). The obtained solution was cooled in an ice bath to obtain a solution of the polymer of the silane compound represented by the aforementioned general formula (2) (concentration 40%). In the general formula (2), R 3 ~R 6 were a phenyl group, a hydroxyl group, a methyl group, and a hydroxyl group respectively, and n:m was 50:50.

[0108] <Preparation of p-Type Impurity Diffusion Composition> 13.4 g of the solution of the polymer of the silane compound synthesized above, 1.3 g of boric acid, 11.6 g of polyvinyl alcohol (49), 3.9 g of "Aerosil" VPNKC130, 24.6 g of GBL, 35.1 g of terpineol, and 10.0 g of water were mixed and stirred well until homogeneous to obtain a p-type impurity diffusion composition B.

[0109] (Production Example 3) <Synthesis of Particles Containing Group 13 Elements> B 2 O 3 , SiO 2 , Al 2 O 3 and CaO were weighed so that the compositional molar ratios were 40 mol%, 45 mol%, 5 mol%, and 10 mol%, respectively, for B 2 O 3 , SiO 2 , Al 2 O 3 and CaSO 4 . After mixing in an agate mortar, it was put into a platinum crucible and held at 1500 °C for 2 hours in a glass melting furnace. Then, it was rapidly cooled to obtain a glass mass. This was pulverized in an agate mortar and then pulverized in a planetary ball mill to obtain glass particles having a spherical particle shape, an average particle diameter of 0.35 μm, and a softening point of about 800 °C.

[0110] <Preparation of p-Type Impurity Diffusion Composition> 10 g of the above glass particles, 6 g of ethyl cellulose, and 84 g of terpineol were mixed and made into a paste to obtain a p-type impurity diffusion composition C.

[0111] (Production Example 4) <Preparation of p-Type Impurity Diffusion Composition> 10 g of the glass particles obtained in Production Example 3, 1.3 g of boric acid, 11.6 g of polyvinyl alcohol (49), 24.6 g of GBL, 35.1 g of terpineol, and 10.0 g of water were mixed and stirred well until homogeneous to obtain a p-type impurity diffusion composition D.

[0112] (Production Example 5) <Preparation of p-Type Impurity Diffusion Composition> 13.4 g of a GBL solution of tetramethoxysilane with a concentration of 40%, 1.3 g of boric acid, 11.6 g of polyvinyl alcohol (49), 3.9 g of "Aerosil (registered trademark)" VPNKC130, 24.6 g of GBL, 35.1 g of terpineol, and 10.0 g of water were mixed and stirred well until homogeneous to obtain a p-type impurity diffusion composition E.

[0113] (Example 1) (1-1) As a substrate, a semiconductor substrate made of n-type single crystal silicon with a side length of 156 mm was prepared, and alignment marks for alignment were laser processed. Then, in order to remove slice damage and natural oxide, both surfaces were alkali etched. At this time, innumerable uneven textures with a typical width of 40 to 100 μm and a depth of about 3 to 4 μm were formed on both surfaces of the semiconductor substrate, and this was used as the coating substrate.

[0114] (1-2) Here, the p-type impurity diffusion composition A obtained in Production Example 1 was screen printed using a screen printing machine (Microtech Co., Ltd. TM-750 type) and a screen mask (manufactured by SUS Co., Ltd., 400 mesh, wire diameter 23 μm). Alignment was performed using alignment marks so that the printing pattern would be arranged as shown in FIGS. 2 to 3. In the screen printing pattern shown in FIG. 2, in the semiconductor substrate 1, there are 5 vertical and 121 horizontal in-plane patterns 6 of impurity diffusion layers and an outermost peripheral pattern 5 of the impurity diffusion layer, and an enlarged view of the in-plane pattern portion (G) of the substrate is shown in FIG. 3. In the enlarged view shown in FIG. 3, among the in-plane patterns 6 of the impurity diffusion layers of the substrate, the width (H) of the horizontal impurity diffusion layer pattern is 0.08 mm, the interval (J) is 1.2844 mm, the width (H) of the vertical impurity diffusion layer pattern is 0.766 mm, and the interval (J) is 31.19 mm.

[0115] After screen printing the p-type impurity diffusion composition A, the semiconductor substrate was heated on a hot plate at 140°C for 5 minutes and then in an oven at 230°C for 30 minutes in air to form a pattern of an impurity diffusion composition film with a thickness of about 2.5 μm.

[0116] (1-3) Next, the semiconductor substrate with the pattern of the impurity diffusion composition film was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.) at room temperature in an atmosphere of 19 L / min of nitrogen and 0.6 L / min of oxygen (oxygen concentration 3%), heated at 10 °C / min to 980 °C, and maintained at 980 °C for 30 minutes to form an impurity diffusion layer.

[0117] After cooling to room temperature, the semiconductor substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch and remove the pattern of the impurity diffusion composition A film and the layer containing silicon oxide formed on the surface of the semiconductor substrate, followed by washing with water and drying.

[0118] This semiconductor substrate was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.), and the inside of the furnace was made into an atmosphere containing impurity diffusion components by bubbling and flowing boron tribromide (BBr 3 ) at 0.06 L / min in nitrogen at 0.06 L / min, and impurity diffusion was performed on the entire surface of the semiconductor substrate at 920 °C for 30 minutes.

[0119] After the diffusion was completed, the semiconductor substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch and remove the layer containing borosilicate glass, followed by washing with water and drying.

[0120] (1-4) Next, in order to form an n-type impurity diffusion layer on the back surface, the surface of this semiconductor substrate was placed in a plasma CVD apparatus, with substrate temperature: 400 °C, RF power: 180 W, gas flow rate: SiH 4 = 35 scc, N 2 O = 1500 scc, and a silicon oxide layer with a thickness of 500 nm was formed on the p-type impurity diffusion layer at a pressure of 2.5 Torr.

[0121] Next, this semiconductor substrate was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.), and nitrogen 19 L / min, oxygen 0.6 L / min, phosphorus oxychloride (POCl 3By bubbling and flowing (0) at 0.06 L / min of nitrogen, the inside of the furnace was made into an atmosphere containing an n-type impurity diffusion component, and it was maintained at 850 °C for 20 minutes to perform n-type impurity diffusion on the surface opposite to the p-type impurity diffusion surface. After the diffusion was completed, the substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes, and after etching and removing the silicon oxide-containing layers on both sides of the semiconductor substrate, it was washed with water and dried.

[0122] (1-5) Next, this semiconductor substrate was placed in a plasma CVD apparatus, with a substrate temperature of 400 °C, an RF power of 180 W, and a gas flow rate: N 2 = 750 scc, SiH 4 = 35 scc, NH 3 = 90 scc, and a passivation film made of silicon nitride with a thickness of 80 nm was formed on both sides at a pressure of 2.0 Torr.

[0123] (1-6) Next, a commercially available Ag electrode paste was screen-printed on both sides of this semiconductor substrate using a screen printing machine (Microtech Co., Ltd. TM-750 type) and a screen mask (manufactured by SUS Co., Ltd., 400 mesh, wire diameter 23 μm). Alignment was performed using an alignment mark so that the printed pattern of the electrode overlapped the pattern of the p-type impurity diffusion composition A film.

[0124] Next, this substrate with the electrode pattern was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.), and in an atmosphere of 16 L / min of nitrogen and 4 L / min of oxygen, it was processed at 750 °C for 3 minutes to conduct the electrode and the p-type impurity diffusion layer, and a solar cell J was formed.

[0125] (Example 2) A solar cell K was fabricated in the same manner as in Example 1, except that the p-type impurity diffusion composition B obtained in Production Example 2 was used instead of the p-type impurity diffusion composition A obtained in Production Example 1.

[0126] (Example 3) A solar cell L was fabricated in the same manner as in Example 2, except that the step of (1-3) was changed to the step of (3-3) below.

[0127] (3-3) Next, the semiconductor substrate with the pattern of the impurity diffusion composition film was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.) at 800 °C in an atmosphere of 16 L / min of nitrogen and 4 L / min of oxygen (oxygen concentration 20%) and processed for 30 minutes. Then, it was switched to 19 L / min of nitrogen and 0.06 L / min of oxygen (oxygen concentration 3%), and the temperature was raised to 980 °C at a rate of 10 °C / min and maintained at 980 °C for 30 minutes to form an impurity diffusion layer.

[0128] After cooling to room temperature, the semiconductor substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch and remove the pattern of the impurity diffusion composition film and the layer containing silicon oxide formed on the surface of the semiconductor substrate, followed by washing with water and drying.

[0129] This semiconductor substrate was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.), and boron tribromide (BBr 3 ) was bubbled and flowed at 0.06 L / min in nitrogen to make the atmosphere in the furnace contain impurity diffusion components, and impurity diffusion was performed on the entire surface of the semiconductor substrate at 920 °C for 30 minutes.

[0130] After the diffusion was completed, the semiconductor substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch and remove the layer containing borosilicate glass, followed by washing with water and drying.

[0131] (Example 4) A solar cell M was fabricated in the same manner as in Example 2 except that the steps of (1-3) were changed to the steps of (4-3) below.

[0132] (4-3) Next, laser irradiation was performed on the semiconductor substrate with the pattern of the impurity diffusion composition film using an alignment mark so as to have the arrangement shown in FIGS. 2 to 3 to form an impurity diffusion layer. The second harmonic (532 nm) of a Nd:YAG laser was used for the irradiation, and the irradiation was performed under the conditions of a pulse width of 100 nsec, an oscillation frequency of 10 kHz, an output of 5 W, and a beam diameter of 40 μmφ, and the time was appropriately adjusted so that the temperature of the irradiated portion became 950 °C.

[0133] The substrate after laser irradiation was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch away the pattern of the impurity diffusion composition film and the layer containing silicon oxide formed on the surface of the semiconductor substrate, followed by washing with water and drying.

[0134] This semiconductor substrate was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.), and nitrogen at 19 L / min, oxygen at 0.06 L / min, and boron tribromide (BBr 3 ) was bubbled and flowed through nitrogen at 0.06 L / min to make the atmosphere in the furnace an atmosphere containing impurity diffusion components, and impurity diffusion was performed on the entire surface of the semiconductor substrate at 920 °C for 30 minutes.

[0135] After the diffusion was completed, the semiconductor substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch away the layer containing borosilicate glass, followed by washing with water and drying.

[0136] (Example 5) A solar cell O was fabricated in the same manner as in Example 1, except that the p-type impurity diffusion composition C obtained in Production Example 3 was used instead of the p-type impurity diffusion composition A obtained in Production Example 1.

[0137] (Example 6) A solar cell P was fabricated in the same manner as in Example 1, except that the p-type impurity diffusion composition D obtained in Production Example 4 was used instead of the p-type impurity diffusion composition A obtained in Production Example 1.

[0138] (Example 7) A solar cell Q was fabricated in the same manner as in Example 1, except that the p-type impurity diffusion composition E obtained in Production Example 5 was used instead of the p-type impurity diffusion composition A obtained in Production Example 1.

[0139] (Example 8) A solar cell R was fabricated in the same manner as in Example 2, except that the steps of (1-3) were changed to the steps of (8-3) below.

[0140] (8-3) Next, the semiconductor substrate on which the pattern of the impurity diffusion composition film was formed was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.) at room temperature in an atmosphere of 19 L / min of nitrogen and 0.6 L / min of oxygen (oxygen concentration 3%), heated at 10 °C / min to 980 °C, and maintained at 980 °C for 30 minutes to form an impurity diffusion layer.

[0141] After cooling to room temperature, the semiconductor substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch and remove the pattern of the impurity diffusion composition film and the layer containing silicon oxide formed on the surface of the semiconductor substrate, followed by washing with water and drying.

[0142] This semiconductor substrate was placed in a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.), and the inside of the furnace was made into an atmosphere containing impurity diffusion components by flowing nitrogen at 19 L / min, oxygen at 0.06 L / min, and boron tribromide (BBr3) bubbling through nitrogen at 0.06 L / min, and impurity diffusion was performed on the entire surface of the semiconductor substrate at 920 °C for 30 minutes.

[0143] Next, alignment was performed using an alignment mark, and laser irradiation was performed so as to overlap the pattern of the p-type impurity diffusion composition film to advance the impurity diffusion. For the irradiation, the second harmonic (532 nm) of a Nd:YAG laser was used, and the irradiation was performed by appropriately adjusting the time so that the temperature of the irradiated portion became 950 °C under the conditions of a pulse width: 100 nsec, an oscillation frequency: 10 kHz, an output: 5 W, and a beam diameter: 40 μmφ.

[0144] After the diffusion was completed, the semiconductor substrate was immersed in a 5% hydrofluoric acid solution for 10 minutes to etch and remove the layer containing borosilicate glass, followed by washing with water and drying.

[0145] (Example 9) A solar cell S was fabricated in the same manner as in Example 6, except that the steps (1-3) were changed to the steps (8-3) described in Example 8.

[0146] (Example 10) A solar cell T was fabricated in the same manner as in Example 7, except that the steps (1-3) were changed to the steps (8-3) described in Example 8.

[0147] (Comparative Example 1) A solar cell N was fabricated in the same manner as in Example 1, except that the steps (1-3) were changed to the following steps (9-3).

[0148] (9-3) Next, the semiconductor substrate on which the pattern of the impurity diffusion composition film was formed was put into a diffusion furnace (manufactured by Koyo Thermo Systems Co., Ltd.) at room temperature in an atmosphere of 19 L / min of nitrogen and 0.6 L / min of oxygen, heated to 980°C at a rate of 10°C / min, and maintained at 980°C for 30 minutes to form an impurity diffusion layer. Then, the temperature in the furnace was lowered to 920°C, and the inside of the furnace was made into an atmosphere containing a p-type impurity diffusion component by flowing nitrogen at 19 L / min, oxygen at 0.06 L / min, and boron tribromide (BBr3) bubbled with nitrogen at 0.06 L / min, and impurity diffusion of the unpatterned portion was performed.

[0149] After the diffusion was completed, the substrate was immersed in a 5% hydrofluoric acid solution for 5 minutes to remove the pattern of the impurity diffusion composition film and the layer containing silicon oxide formed on the surface of the semiconductor substrate, followed by washing with water and drying.

[0150] The evaluation results of Examples 1 to 10 and Comparative Example 1 are shown in Table 1.

[0151] [Table 1]

Explanation of Signs

[0152] 1 Semiconductor substrate 2 Pattern of impurity diffusion composition film (B) 3 Laser irradiation 4 Impurity diffusion component-containing gas 5 Outermost peripheral pattern of impurity diffusion layer 6 In-plane pattern of impurity diffusion layer (5 vertical, 121 horizontal) (C), (D) Impurity diffusion layer (E) Layer containing silicon oxide (F) Layer containing borosilicate glass or phosphosilicate glass (G) In-plane pattern portion of substrate (H) Width of the impurity diffusion layer pattern (J) Spacing between the impurity diffusion layer patterns

Claims

1. A method for manufacturing a solar cell having an impurity diffusion layer having two or more different levels of impurity concentration on a semiconductor substrate, the method comprising the following steps (a) to (d) in this order: (a) applying an impurity-diffusing composition (A) to a semiconductor substrate to partially form an impurity-diffusing composition film (B); (b) a step of diffusing impurities in the impurity diffusion composition film (B) into a semiconductor substrate to form an impurity diffusion layer (C); (c) removing the impurity diffusion composition film (B) by etching; (d) A process of heating the semiconductor substrate in a gas atmosphere containing boron or phosphorus to diffuse the boron or phosphorus into the semiconductor substrate, thereby forming an impurity diffusion layer (D) in a portion of the semiconductor substrate where the impurity diffusion composition film (B) was not formed, and at the same time, further promoting diffusion of the impurity diffusion layer (C).

2. 2. The method for producing a solar cell according to claim 1, further comprising, after the step (d), a step (e) of removing the layer containing boron silicate glass or phosphorus silicate glass on the semiconductor substrate by etching.

3. 3. The method for producing a solar cell according to claim 1, further comprising the step of: (f) irradiating a portion of the impurity diffusion layer (C) with a laser to further promote diffusion of the impurity diffusion layer (C) after the step (c).

4. 4. The method for producing a solar cell according to claim 1, wherein the impurity-diffusing composition (A) comprises (A-1) a hydroxyl group-containing polymer and (A-2) an impurity-diffusing component.

5. 5. The method for producing a solar cell according to claim 1, wherein the impurity-diffusing composition (A) contains (A-3) a polymer of a silane compound represented by the following general formula (1): 【Chemistry 1】 (In general formula (1), R １ and R ２ represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms; １ and R ２ may be the same or different. l represents an integer of 1 to 10,000.

6. 6. The method for producing a solar cell according to claim 5, wherein the polymer of the silane compound represented by the general formula (1) is represented by the following general formula (2): 【Chemistry 2】 (In general formula (2), R ３ represents an aryl group having 6 to 15 carbon atoms, ３ may be the same or different. ４ represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms; ４ may be the same or different. ５ and R ６ represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an acyl group having 2 to 6 carbon atoms; ５ and R ６ may be the same or different. n and m represent integers of 1 to 9,999, n+m=2 to 10,000, and n:m=95:5 to 25:

75.

7. 7. The method for producing a solar cell according to claim 1, wherein the impurity-diffusing composition (A) contains (A-4) a silane compound represented by the following general formula (3): 【Chemistry 3】 (In general formula (3), R ７ ~R １０ represents any one of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an acyl group having 2 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms.

8. 8. The method for producing a solar cell according to claim 1, wherein the impurity-diffusing composition (A) contains (A-5) particles containing a Group 13 element or a Group 15 element.

9. 9. The method for producing a solar cell according to claim 1, wherein in the step (b), the impurity diffusion layer (C) is formed by heating in a heating furnace or by irradiating with a laser.

10. 10. The method for producing a solar cell according to claim 9, wherein the semiconductor substrate is placed in the heating furnace at 700° C. to 850° C. and with an oxygen concentration of 10 to 50%.

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