JP2016086092A - Method for forming impurity-diffusion layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an impurity-diffusion layer which does not need the use of a concentrated nitric acid solution in hydrophilization of a semiconductor substrate surface.SOLUTION: A method for forming an impurity-diffusion layer according to the invention comprises: a texture structure-forming step where a texture structure is formed on at least one primary surface of a semiconductor substrate; a primary surface treatment step where the primary surface with the texture structure formed thereon is processed with a liquid solution containing a surfactant; a coating step where the primary surface processed with the liquid solution is coated with a diffusing agent composition containing an impurity-diffusion component and a solvent; and a diffusion step where the impurity-diffusion component in the diffusing agent composition applied to the primary surface is diffused into the semiconductor substrate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for forming an impurity diffusion layer.

  Conventionally, in the manufacture of solar cells, for example, when an n-type impurity diffusion layer is formed in a semiconductor substrate, a diffusing agent containing an n-type impurity diffusing component is applied to the n-type from the diffusing agent applied to the surface of the semiconductor substrate. The impurity diffusion component was diffused to form an n-type impurity diffusion layer. Specifically, first, a thermal oxide film is formed on the surface of the semiconductor substrate, and then a resist having a predetermined pattern is laminated on the thermal oxide film by a photolithography method, and the resist is used as a mask with an acid or an alkali. The portion of the thermal oxide film that is not masked is etched, and the resist is removed to form a mask of the thermal oxide film. Then, a diffusing agent composition containing an n-type impurity diffusing component is applied, and a film of the diffusing agent composition is formed in a portion where the mask is open. By heating the portion to a high temperature, the impurity diffusion component is diffused to form an n-type impurity diffusion layer (Patent Documents 1 to 3).

JP 2001-071489 A JP 2002-075892 A Special table 2008-543097 gazette

  The conventional impurity diffusion layer forming methods described in Patent Documents 1 to 3 have the following problems. Before applying the diffusing agent composition on the semiconductor substrate, the surface of the semiconductor substrate is hydrophilized. Conventionally, the surface hydrophilization is performed by immersing a semiconductor substrate in concentrated nitric acid (for example, a commercially available 67 mass% nitric acid stock solution). Therefore, since the conventional impurity diffusion layer forming method uses concentrated nitric acid, it is difficult to reduce costs and save resources and to ensure safety.

  The present invention has been made in view of the above problems, and an object thereof is to provide a method for forming an impurity diffusion layer that does not require the use of concentrated nitric acid when the surface of a semiconductor substrate is hydrophilized.

  The present inventors have found that the above problem can be solved by using a solution containing a surfactant instead of concentrated nitric acid, and have completed the present invention.

  Aspects of the present invention include a texture structure forming step of forming a texture structure on at least one main surface of a semiconductor substrate, and a main surface in which the main surface on which the texture structure is formed is treated with a solution containing a surfactant. A treatment step, a coating step of applying a diffusing agent composition containing an impurity diffusing component and a solvent to the main surface treated with the solution, and the impurity diffusion in the diffusing agent composition applied to the main surface. And a diffusion step of diffusing components into the semiconductor substrate.

  According to the present invention, it is possible to provide a method for forming an impurity diffusion layer that does not require the use of concentrated nitric acid when the surface of a semiconductor substrate is hydrophilized.

FIGS. 1A to 1E are views showing cross sections of a substrate in each step relating to a method for manufacturing a solar cell including a method for forming an impurity diffusion layer. FIGS. 2A to 2D are views showing cross sections of the substrate in each step related to a method for manufacturing a solar cell including a method for forming an impurity diffusion layer.

<< Method for forming impurity diffusion layer and method for producing solar cell >>
A method for forming an impurity diffusion layer according to the present invention includes a texture structure forming step of forming a texture structure on at least one main surface of a semiconductor substrate, and the main surface on which the texture structure is formed, containing a surfactant. A main surface treatment step treated with a solution; an application step of applying a diffusing agent composition containing an impurity diffusing component and a solvent to the main surface treated with the solution; and the diffusing agent composition applied to the main surface. A diffusion step of diffusing the impurity diffusion component in the object into the semiconductor substrate. In the method for forming an impurity diffusion layer according to the present invention, at least one main surface of a semiconductor substrate on which a texture structure is formed can be hydrophilized without using concentrated nitric acid. Further, in the method for forming an impurity diffusion layer according to the present invention, the impurity diffusion component can be uniformly diffused in the substrate in the same manner as or more than the conventional method using concentrated nitric acid in the main surface treatment step.

  Hereinafter, referring to FIG. 1A to FIG. 1D and FIG. 2A to FIG. 2D, an impurity diffusion layer forming method according to the present invention and an impurity diffusion layer formed thereby. A method for manufacturing a solar cell provided with the semiconductor substrate will be described.

  1 (a) to 1 (d) and FIGS. 2 (a) to 2 (d) are cross-sectional views of a semiconductor substrate at each step in a method for manufacturing a solar cell including a method for forming an impurity diffusion layer. FIG.

  First, as shown in FIG. 1A, a semiconductor substrate 1 such as a p-type silicon substrate is prepared. And as shown in FIG.1 (b), the texture structure 1a which has a fine unevenness | corrugation is formed in one main surface of the semiconductor substrate 1 using a well-known wet etching method (texture structure formation process). By this texture structure 1a, reflection of light on the surface of the semiconductor substrate 1 is prevented. 1B shows the case where the texture structure 1a is formed on one main surface of the semiconductor substrate 1, the texture structure 1a may be formed on both main surfaces of the semiconductor substrate 1. FIG.

  Then, as shown in FIG.1 (c), the main surface by the side of the texture structure 1a of the semiconductor substrate 1 is processed with the solution 10 containing surfactant (main surface treatment process). Thereby, even if concentrated nitric acid is not used, the main surface of the semiconductor substrate 1 on the texture structure 1a side is hydrophilized, and the diffusing agent composition 2 applied in the next step is the main surface of the semiconductor substrate 1 on the texture structure 1a side. It becomes easy to be suppressed from being played above. Further, even if concentrated nitric acid is not used, the impurity diffusion component can be uniformly diffused in the substrate in the diffusion step in the same or more than the conventional method using concentrated nitric acid.

  The method for treating the main surface of the semiconductor substrate 1 on the texture structure 1a side with the solution 10 containing a surfactant is not particularly limited. For example, the semiconductor substrate 1 is immersed in the solution 10 containing a surfactant. A method is mentioned.

  As the surfactant, any known surfactant can be used without particular limitation as long as it exhibits an effect of hydrophilizing the substrate. Examples include, but are not limited to, silicone surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, and fluorosurfactants. Of these, silicone surfactants are preferred.

  It does not specifically limit as content of surfactant in the solution 10 containing surfactant, It is 0.1-5 mass% with respect to the total mass of the solution 10 containing surfactant. Preferably, it is 0.3-2 mass%. When the content of the surfactant is within the above range, the main surface on the texture structure 1a side of the semiconductor substrate 1 is more easily hydrophilized, and the amount of the surfactant remaining on the main plane is more effective. Can be reduced.

  Examples of the solvent in the solution 10 containing the surfactant include an organic solvent, water, and a combination thereof, and water is preferable. As an organic solvent, what was illustrated in the below-mentioned description regarding the solvent contained in the diffusing agent composition 2 is mentioned.

  After the main surface treatment step, the semiconductor substrate 1 may be washed with water, and further, the semiconductor substrate 1 may be dried by a known method such as air blow.

  Subsequently, as shown in FIG. 1 (d), a diffusing agent composition 2 containing an impurity diffusing component (A) and a solvent (S) is applied to the main surface treated with the solution 10 containing a surfactant. Apply (application process). After forming the impurity diffusing agent layer in this way, the diffusing agent composition 2 applied using a known means such as an oven is dried. The method for applying the diffusing agent composition 2 to the main surface is not particularly limited. For example, spray coating method; spin coating method; ink jet printing method, roll coat printing method, screen printing method, letterpress printing method, intaglio printing. And a printing method such as an offset printing method, and the spray coating method is preferable from the viewpoint of cost reduction, the necessity of introducing an apparatus such as a coater, and the ease of application to a large area. Hereinafter, the method of apply | coating the diffusing agent composition 2 to the said main surface by the spray application method is demonstrated in detail.

  Spray coating of the diffusing agent composition 2 can be performed, for example, by spraying the diffusing agent composition 2 in the form of droplets from a sprayer (not shown) installed above the semiconductor substrate 1. Spraying of the diffusing agent composition 2 may be performed at room temperature or under heating. When spraying of the diffusing agent composition 2 is performed under heating, examples of the heating temperature include 60 to 120 ° C.

  The droplet size of the diffusing agent composition 2 at the time of spraying is preferably 5 μm or less. In this case, the sprayed diffusing agent composition 2 tends to be more effectively prevented from being repelled on the surface of the semiconductor substrate 1. Here, the droplet size of the diffusing agent composition 2 at the time of spraying means the droplet size of the diffusing agent composition 2 immediately after spraying, and is an arbitrary one existing on the outer surface of the droplet of the diffusing agent composition 2. The length of the longest straight line connecting the two points is defined as the droplet size.

  In order to effectively prevent the sprayed diffusing agent composition 2 from being repelled on the surface of the semiconductor substrate 1, the number of droplets of the diffusing agent composition 2 having a droplet size of 5 μm or less is set to It is preferable to occupy 50% or more of the total number of droplets of the diffusing agent composition 2 to be formed.

  The shortest distance between the sprayer and the surface of the semiconductor substrate 1 is about 180 mm in order to bring about an evaporation effect of the solvent constituting the diffusing agent composition 2 and to effectively spray the diffusing agent composition 2. preferable.

<Impurity diffusion component (A)>
The impurity diffusion component (A) is not particularly limited as long as it has the desired properties as the impurity diffusion component, and may be either an n-type impurity diffusion component or a p-type impurity diffusion component, and is a low molecular compound. Or a polymer compound. The impurity diffusion component (A) may be used alone or in combination of two or more. Examples of the n-type impurity diffusion component include phosphorus-containing compounds, arsenic-containing compounds, antimony-containing compounds, and the like. Examples of the p-type impurity diffusion component include boron-containing compounds, aluminum-containing compounds, gallium-containing compounds, and indium-containing compounds. In the present invention, the impurity diffusion component (A) is applied to the main surface of the semiconductor substrate that has been hydrophilized by treatment with a solution containing a surfactant. Therefore, it is desired that the impurity diffusion component (A) is excellent in hydrophilicity. Since the phosphorus-containing compound is easily soluble in water and tends to be excellent in hydrophilicity, the impurity diffusion component (A) is preferably a phosphorus-containing compound. Hereinafter, the phosphorus-containing compound will be described in detail.

Preferable examples of the phosphorus-containing compound include phosphoric acid, P ₂ O ₅ , phosphate ester and the like. Preferred examples of the phosphate ester include monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, diethyl phosphate, triethyl phosphate, monopropyl phosphate, dipropyl phosphate, monobutyl phosphate, dibutyl phosphate, phosphoric acid. Examples include tributyl.

  Moreover, as a phosphorus containing compound, the phosphoric acid monoalkyl ester and phosphoric acid dialkyl ester containing a C5-C20 alkyl group are also preferable. Deposition containing a large amount of phosphorus compound in the furnace when the semiconductor substrate 1 coated with the diffusing agent composition 2 is dried in a drying furnace by using phosphate esters containing an alkyl group having 5 to 20 carbon atoms. Things are difficult to produce.

  Specific examples of the monoalkyl phosphate and dialkyl phosphate containing an alkyl group having 5 to 20 carbon atoms include monopentyl phosphate, dipentyl phosphate, monohexyl phosphate, dihexyl phosphate, monohexyl phosphate, and phosphoric acid. Examples include dihexyl, monooctyl phosphate, dioctyl phosphate, monoethylhexyl phosphate, diethylhexyl phosphate, tridecyl phosphate, and isotridecyl phosphate.

  What is necessary is just to change suitably content of the impurity diffusion component (A) in the diffusing agent composition 2 according to the application | coating method of the diffusing agent composition 2, and it is 0.5 with respect to the total mass of the diffusing agent composition 2. It is preferable that it is -50 mass%, and it is more preferable that it is 1-30 mass%.

<Solvent (S)>
The diffusing agent composition 2 contains a solvent (S). Examples of the solvent (S) include organic solvents, water, and combinations thereof. As the organic solvent, a polar organic solvent is preferable. The polar organic solvent is not particularly limited as long as it is generally recognized as a polar organic solvent by those skilled in the chemical field. As the solvent (S), a combination of a polar organic solvent and water is preferable.

  Specific examples of the organic solvent include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, propylene glycol monomethyl ether, Propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monopropyl ether, diethylene glycol Mono- or dialkyl ether glycols such as monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono Propyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, 2-methoxybutyl acetate, 3-methoxybutyl acetate, 4-methoxybutyl acetate, 2-methyl-3-methoxybutyl acetate, Ether ethers such as ethoxybutyl acetate, 4-ethoxybutyl acetate, and 4-propoxybutyl acetate; ketones such as diethyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone, and cyclohexanone; propyl propionate, isopropyl propionate, Methyl-3-methoxypropionate, ethyl-3-methoxypropionate, ethyl-3-ethoxypropionate, ethyl-3-propoxypropionate, propyl-3-methoxypropionate, and isopropyl-3- Propionate esters such as methoxypropionate; Esters such as butyl acetate, isoamyl acetate, methyl acetoacetate, methyl lactate, and ethyl lactate; benzyl methyl ether, benzyl ethyl ether, benzene, Aromatics such as toluene, xylene, benzyl alcohol, and 2-phenoxyethanol; methanol, ethanol, propanol, isopropanol, butanol, isobutanol, 2-methoxyethanol, 2-ethoxyethanol, 3-methyl-3-methoxybutanol, hexanol And alcohols such as cyclohexanol; cyclic esters such as gamma-butyrolactone; polar organic solvents such as glycols such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol. Among these, the organic solvent is preferably an alcohol, and more preferably ethanol. An organic solvent may be used independently and may be used in combination of 2 or more type.

  What is necessary is just to change suitably content of the solvent (S) in the diffusing agent composition 2 according to the coating method of the diffusing agent composition 2, and 50-99.5 with respect to the total mass of the diffusing agent composition 2. It is preferable that it is mass%, and 70-99 mass% is more preferable. When the solvent (S) is a combination of an organic solvent and water, the mixing ratio (mass ratio) of the organic solvent and water is preferably 99.9: 0.1 to 50:50. 7: 0.3 to 70:30 is more preferable.

<Other ingredients>
The diffusing agent composition 2 may further include a surfactant; an organic binder resin; a SiO ₂ fine particle; a metal compound such as a titanium compound and a zirconium compound; a siloxane polymer and the like as other components other than the above-described components. A conventionally well-known thing can be used as a surfactant component, A silicone type surfactant is preferable. By adding a surfactant to the diffusing agent composition 2, it is easy to improve the coating property, flattening property, and developability of the diffusing agent composition 2, and uneven coating of the diffusing agent composition layer formed after coating can be prevented. It can be made difficult to occur. However, the silicone-based surfactant in the diffusing agent composition 2 is easily deteriorated by the impurity diffusing component, particularly when the impurity diffusing component in the diffusing agent composition 2 is a phosphorus-containing compound. The effect of using is likely to deteriorate over time. Further, the surfactant other than the silicone surfactant in the diffusing agent composition 2 tends to remain on the semiconductor substrate 1 as a residue.

  Next, as shown in FIG.1 (e), the semiconductor substrate 1 with which the diffusing agent composition 2 was apply | coated is mounted in an electric furnace, and is baked. After firing, the impurity diffusion component in the diffusing agent composition 2 is diffused (thermally diffused) into the semiconductor substrate 1 from the surface of the semiconductor substrate 1 in an electric furnace (diffusion process). The diffusion temperature in the diffusion step is, for example, in the range of 800 to 1000 ° C. Instead of the electric furnace, the semiconductor substrate 1 may be heated by a commonly used method such as laser irradiation. In this way, the impurity diffusion component is diffused into the semiconductor substrate 1 to form the impurity diffusion layer 3. For example, when the impurity diffusion component is an n-type impurity diffusion component, the impurity diffusion layer 3 is an n-type impurity diffusion layer.

  Next, as shown in FIG. 2A, an unnecessary oxide film is removed by a known etching method. Then, as shown in FIG. 2B, a silicon nitride film (SiN) is formed on the main surface of the semiconductor substrate 1 on the texture structure 1a side by using a well-known chemical vapor deposition method (CVD method), for example, a plasma CVD method. A passivation film 4 made of a film is formed. This passivation film 4 also functions as an antireflection film.

  Next, as shown in FIG. 2C, the surface electrode 5 is patterned on the main surface of the semiconductor substrate 1 on the side of the passivation film 4 by, for example, screen printing of silver (Ag) paste. The surface electrode 5 is patterned to increase the efficiency of the solar cell. Further, the back electrode 6 is formed on the other main surface of the semiconductor substrate 1 by, for example, screen printing an aluminum (Al) paste.

  Next, as shown in FIG. 2 (d), the semiconductor substrate 1 on which the back electrode 6 is formed is placed in an electric furnace and baked, and then the aluminum on which the back electrode 6 is formed is transferred into the semiconductor substrate 1. To diffuse. Thereby, the electrical resistance on the back electrode 6 side can be reduced. The solar cell 10 can be manufactured through the above steps.

  The present invention is not limited to the embodiments described above, and various modifications such as design changes can be added based on the knowledge of those skilled in the art, and embodiments to which such modifications are added are also possible. It is included in the scope of the present invention. A new embodiment generated by the combination of the above-described embodiment and the following modified example has the effects of the combined embodiment and modified example.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

[Example 1]
(Si substrate surface treatment)
A p-type Si substrate is immersed in a 0.5 mass% aqueous solution of a silicone-based surfactant (trade name: Polyflow KL-401, manufactured by Kyoeisha Chemical Co., Ltd.) for 30 seconds, then washed with water for 1 minute, and then dried by air blowing. I let you.

(Preparation of diffusing agent composition)
Phosphoric acid, ethanol, and water were mixed to obtain a diffusing agent composition containing 3.0% by mass of phosphoric acid, 96.5% by mass of ethanol, and 0.5% by mass of water.

(Measuring method of sheet resistance)
After spin-coating the diffusing agent composition on the p-type Si substrate at a rotation speed of 1000 rpm and a rotation time of 20 seconds using a spin coater (Opticoat MS-A150, manufactured by Mikasa Co., Ltd.), 200 ° C. The diffusing agent composition was dried for 3 minutes.
Next, a baking treatment for removing organic components was performed at 600 ° C. for 30 minutes in an oxygen atmosphere. Baking treatment and diffusion treatment of impurity diffusion components were performed at 900 ° C. for 30 minutes in a nitrogen / oxygen mixed gas atmosphere (volume ratio: nitrogen / oxygen = 8/2).
After the diffusion treatment, the p-type Si substrate was immersed in an aqueous hydrofluoric acid solution having a concentration of 5% by mass at room temperature for 15 minutes to peel off the film derived from the diffusing agent composition formed on the substrate surface.
After the film is peeled off, the sheet resistance value of the surface subjected to the diffusion treatment of the impurity diffusion component of the p-type Si substrate by the four-probe method using a sheet resistance measuring device (VR-70: manufactured by Kokusai Electric Co., Ltd.) (Minimum value, maximum value, average value) and uniformity of sheet resistance value defined by the following formula. Table 1 shows the average sheet resistance value and the uniformity of the sheet resistance value.

      Uniformity of sheet resistance value (%) = (maximum value of sheet resistance value−minimum value of sheet resistance value) / (maximum value of sheet resistance value + minimum value of sheet resistance value) × 100

[Comparative Example 1]
(Si substrate surface treatment)
The p-type Si substrate was immersed in 67% by mass of concentrated nitric acid for 1 minute, washed with water for 1 minute, and then dried by air blowing.

(Preparation of diffusing agent composition)
Phosphoric acid, ethanol and water were mixed to obtain a diffusing agent composition containing 3.0% by mass of phosphoric acid, 48.5% by mass of ethanol and 48.5% by mass of water.

(Measuring method of sheet resistance)
In the same manner as in Example 1, the diffusing agent composition was spin-coated on the p-type Si substrate.
Next, in the same manner as in Example 1, the diffusion treatment of the impurity diffusion component and the peeling of the film derived from the diffusing agent composition formed on the substrate surface are performed, and the average value of the sheet resistance value and the uniform sheet resistance value are obtained. Sought sex. Table 1 shows the average sheet resistance value and the uniformity of the sheet resistance value.

  In Example 1, the Si substrate was surface-treated with an aqueous solution of a silicone-based surfactant, whereas in Comparative Example 1, the Si substrate was surface-treated with concentrated nitric acid. As shown in Table 1, the average value of the sheet resistance value and the uniformity of the sheet resistance value were the same between Example 1 and Comparative Example 1. In other words, it was confirmed that the impurity diffusion layer forming method according to the present invention can diffuse the impurity diffusion component uniformly in the substrate as in the conventional method using concentrated nitric acid in the main surface treatment step.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 1a Texture structure 2 Diffusing agent composition 3 Impurity diffusion layer 4 Passivation film 5 Front surface electrode 6 Back surface electrode 10 Solution containing surfactant 100 Solar cell

Claims (3)

A texture structure forming step of forming a texture structure on at least one main surface of the semiconductor substrate;
A main surface treatment step of treating the main surface on which the texture structure is formed with a solution containing a surfactant;
An application step of applying a diffusing agent composition containing an impurity diffusing component and a solvent to the main surface treated with the solution;
A diffusion step of diffusing the impurity diffusion component in the diffusing agent composition applied to the main surface into the semiconductor substrate.   The method for forming an impurity diffusion layer according to claim 1, wherein the semiconductor substrate is used in a solar cell.   The method for forming an impurity diffusion layer according to claim 1, wherein the impurity diffusion component is a phosphorus-containing compound.

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