Method for manufacturing semiconductor equipment and method for manufacturing solar cells

Abstract

To provide a semiconductor device manufacturing method capable of suppressing reduction in efficiency due to adherence of foreign matter.SOLUTION: The semiconductor device manufacturing method includes the steps of immersing a semiconductor substrate in an alkaline solution, immersing the semiconductor substrate in an acidic oxidizing solution containing an oxidizing agent and having a pH of less than 4, immersing the semiconductor substrate in a neutral oxidizing solution containing an oxidizing agent and having a pH of greater than or equal to 6 and less than or equal to 8, and immersing the semiconductor substrate in an oxide film removal solution, in this order.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In the process of manufacturing a semiconductor device such as a solar cell using a semiconductor substrate, a process of immersing the semiconductor substrate in an alkaline solution is performed, such as anisotropic etching that forms pyramid-shaped irregularities on the entire surface of the semiconductor substrate in order to improve the light incidence rate into the semiconductor substrate. After such an alkali treatment, it is common to clean the surface of the semiconductor substrate by immersing it in an oxidizing solution containing an oxidizing agent to oxidize the surface of the semiconductor substrate and then removing the oxide film with an oxide film removing solution (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When immersing a semiconductor substrate in an oxidizing solution, it is known that by using an acidic oxidizing solution with a low pH, metal elements can be ionized and the metal on the surface of the semiconductor substrate can be removed. Also, by using an acidic oxidizing solution, it is said that the alkali solution remaining on the surface of the semiconductor substrate can be neutralized, and the effect of preventing poor formation of the oxide film due to the alkali solution can be obtained. However, it has been confirmed that when using an acidic oxidizing solution, foreign particles may adhere to the surface of the semiconductor substrate, reducing the efficiency of the solar cell.

[0005] Therefore, an object of the present invention is to provide a method for manufacturing a semiconductor device and a method for manufacturing a solar cell that can suppress a decrease in efficiency due to the adhesion of foreign substances.

Means for Solving the Problems

[0006] A semiconductor device manufacturing method according to one aspect of the present invention comprises, in this order, the steps of: immersing a semiconductor substrate in an alkaline solution; immersing the semiconductor substrate in an acidic oxidizing solution containing an oxidizing agent and having a pH of less than 4; immersing the semiconductor substrate in a neutral oxidizing solution containing an oxidizing agent and having a pH of 6 or more and 8 or less; and immersing the semiconductor substrate in an oxide film removal solution.

[0007] In the semiconductor device manufacturing method described above, the acidic oxidizing solution may be hydrochloric acid ozonated water, sulfuric acid ozonated water, hydrochloric acid hydrogen peroxide solution, sulfuric acid hydrogen peroxide solution, or nitric acid.

[0008] In the semiconductor device manufacturing method described above, the acidic oxidizing solution may contain ozone in a concentration of 10 ppm to 120 ppm.

[0009] In the semiconductor device manufacturing method described above, the neutral oxidizing solution may be either ozonated water or hydrogen peroxide.

[0010] In the semiconductor device manufacturing method described above, the neutral oxidizing solution may contain ozone in a concentration of 10 ppm to 120 ppm.

[0011] In the semiconductor device manufacturing method described above, the alkaline solution may be an inorganic alkaline aqueous solution.

[0012] In the semiconductor device manufacturing method described above, the oxide film removal solution may be hydrofluoric acid, ammonium fluoride, or a mixture thereof.

[0013] In the semiconductor device manufacturing method described above, the oxide film removal solution may be hydrofluoric acid with a concentration of 0.5% to 10%.

[0014] A solar cell manufacturing method according to one aspect of the present invention comprises the steps of forming a lamid-shaped uneven texture on a semiconductor substrate using the semiconductor device manufacturing method described above, and forming a photoelectric conversion structure on the semiconductor substrate. [Effects of the Invention]

[0015] According to one aspect of the present invention, a semiconductor device manufacturing method and a solar cell manufacturing method can suppress the reduction in efficiency due to the adhesion of foreign matter. [Brief explanation of the drawing]

[0016] [Figure 1] This flowchart shows the procedure for a semiconductor device manufacturing method according to one embodiment of the present invention. [Figure 2] Figure 1 is a flowchart detailing the steps involved in the texture formation process. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below. Figure 1 is a flowchart showing the procedure for a semiconductor device manufacturing method according to one embodiment of the present invention. The semiconductor device manufacturing method according to this embodiment is a solar cell manufacturing method for manufacturing a solar cell in which a photoelectric conversion structure is formed on a semiconductor substrate.

[0018] The solar cell manufacturing method of this embodiment comprises the steps of forming a pyramidal texture on the surface of a semiconductor substrate (step S1: texture formation step), forming a photoelectric conversion structure on the semiconductor substrate (step S2: photoelectric conversion structure formation step), and forming electrodes for extracting power from the photoelectric conversion structure (step S3: electrode structure formation step).

[0019] The anisotropic etching process in step S1 of Figure 1 comprises, in this order, an alkaline solution immersion step (step S11), an acidic oxidizing solution immersion step (step S12), a neutral oxidizing solution immersion step (step S13), and an oxide film removal solution immersion step (step S14), as shown in Figure 2.

[0020] In the alkali solution immersion step of step S11, the semiconductor substrate is immersed in an alkali solution to anisotropically etch the semiconductor substrate, thereby forming a large number of pyramid-shaped irregularities on the entire surface of the semiconductor substrate. As the alkali solution, it is preferable to use an inorganic alkali aqueous solution that is difficult to remain on the semiconductor substrate, such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution. The pH of the alkali solution can be selected based on common technical knowledge according to the purpose of the treatment, the properties of the semiconductor substrate, etc.

[0021] In the acidic oxidizing solution immersion step of step S12, the semiconductor substrate is immersed in an acidic oxidizing solution containing an oxidizing agent and having a pH less than 4, thereby forming an oxide film on the surface of the semiconductor substrate. Since the acidic oxidizing solution is acidic, it can neutralize the alkali solution remaining on the semiconductor substrate, thereby preventing the inhibition of oxide film formation by the alkali solution and preventing the deposited gold electrode formed by ionizing metal elements from adhering to the semiconductor substrate.

[0022] As the acidic oxidizing solution, hydrochloric acid ozone water, sulfuric acid ozone water, hydrochloric acid hydrogen peroxide water, sulfuric acid hydrogen peroxide water, and nitric acid are preferable, and among them, hydrochloric acid ozone water is particularly preferable. Further, the acidic oxidizing solution preferably contains ozone of 10 ppm or more and 120 ppm or less. By using such an acidic oxidizing solution, the surface of the semiconductor substrate can be appropriately oxidized, and the adhesion of foreign substances to the semiconductor substrate can be effectively suppressed.

[0023] In the neutral oxidizing solution immersion step of step S13, the semiconductor substrate is immersed in a neutral oxidizing solution containing an oxidizing agent and having a pH of 6 or more and 8 or less, thereby removing deposits such as fine particles of resin having a potential capable of adhering to the oxide film having a positive potential formed by the acidic oxidizing solution. Since the pH of the neutral oxidizing solution is 6 or more, the potential of the oxide film can be reduced to a negative value. Further, since the pH of the neutral oxidizing solution is 8 or less, the potential of the oxide film can be adjusted without etching the semiconductor substrate.

[0024] As the neutral oxidizing solution, ozonated water and hydrogen peroxide are preferred, with ozonated water being particularly preferred. Furthermore, the neutral oxidizing solution preferably contains 10 ppm to 120 ppm of ozone. By using such a neutral oxidizing solution, foreign matter on the surface of the semiconductor substrate can be reduced.

[0025] In step S14, the oxide film removal solution immersion step, the semiconductor substrate is immersed in an oxide film removal solution to remove the oxide film from the surface of the semiconductor substrate. This results in a clean semiconductor substrate free of oxide film on its surface. Hydrofluoric acid, ammonium fluoride, or a mixture thereof are preferably used as the oxide film removal solution.

[0026] The concentration of hydrofluoric acid is preferably 0.5% to 10%, and more preferably 2% to 8%. By using hydrofluoric acid at such a concentration as an oxide film removal solution, the oxide film can be reliably removed without eroding the semiconductor substrate.

[0027] Thus, in the texture formation process, an oxide film is formed on the semiconductor substrate using an acidic oxidizing solution that can suppress metal contamination after anisotropic etching with an alkaline solution, and then resin and other deposits are removed from the semiconductor substrate using a neutral oxidizing solution. This forms a texture substrate with less foreign matter adhesion, and suppresses the reduction in solar cell efficiency due to foreign matter adhesion.

[0028] In the photoelectric conversion structure formation step S2, a photoelectric conversion structure is formed by stacking semiconductor layers with different conductivity types on a semiconductor substrate. In this photoelectric conversion structure formation step, if the semiconductor substrate is immersed in an alkaline solution for purposes such as removing a resist pattern, the semiconductor substrate may be immersed in an alkaline solution, followed by sequential immersion in an acidic oxidizing solution, a neutral oxidizing solution, and an oxide film removal solution, similar to the anisotropic etching step S1.

[0029] In step S3, the electrode structure formation process, electrodes are formed to extract power from the photoelectric conversion structure. The electrodes can be formed by printing conductive paste, or by laminating metal over the entire main surface and patterning the metal by etching. In this electrode structure formation process as well, the semiconductor substrate may be sequentially immersed in an alkaline solution, an acidic oxidizing solution, a neutral oxidizing solution, and an oxide film removal solution.

[0030] As described above, in the solar cell manufacturing method of this embodiment, by sequentially immersing the semiconductor substrate in an alkaline solution, an acidic oxidizing solution, a neutral oxidizing solution, and an oxide film removal solution, the adhesion of foreign substances is suppressed, and a solar cell (semiconductor device) with high photoelectric conversion efficiency can be manufactured.

[0031] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible. The semiconductor device manufacturing method according to the present invention only needs to include a step of sequentially immersing a semiconductor substrate in an alkaline solution, an acidic oxidizing solution, a neutral oxidizing solution, and an oxide film removal solution. Immersion in the alkaline solution may be performed for purposes other than anisotropic etching, and the method may be applied to the manufacture of semiconductor devices other than solar cells. Furthermore, in the semiconductor device manufacturing method according to the present invention, a step of washing the semiconductor substrate with pure water may be included between immersions in the alkaline solution, acidic oxidizing solution, neutral oxidizing solution, and oxide film removal solution. [Examples]

[0032] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples.

[0033] A comparative example of a heterojunction back-contact solar cell manufactured by immersing a silicon semiconductor substrate in an alkaline solution, an acidic oxidizing solution, and an oxide film removal solution in that order to form a texture, and an example of a solar cell manufactured under the same conditions except that immersion in a neutral oxidizing solution was added between immersion in the acidic oxidizing solution and immersion in the oxide film removal solution, were measured for photoelectric conversion efficiency, short-circuit current, open-circuit voltage, shape factor, series resistance, parallel resistance, and pH. An A&D AP-20 pH meter was used to measure pH. In the alkaline solution immersion step, the substrate was immersed in a 1% potassium hydroxide aqueous solution at 30°C for 100 seconds. In the acidic oxidizing solution immersion step, the substrate was immersed in hydrochloric acid ozonated water with an ozone concentration of 50 ppm, pH 2.6, and temperature 22°C for 600 seconds. In the neutral oxidizing solution immersion step, the substrate was immersed in ozonated water with an ozone concentration of 20 ppm, pH 7.0, and temperature 21°C for 600 seconds. In the oxide film removal immersion process, the sample was immersed in 2% hydrofluoric acid at 23°C for 24 seconds.

[0034] The average values ​​of each measurement in the comparative example (sample size 802) were: photoelectric conversion efficiency (Eff) 19.37%, short-circuit current (Isc) 3.62A, open-circuit voltage (Voc) 0.71V, form factor (FF) 0.73, series resistance (Rs) 11.79mΩ, and parallel resistance (Rsh) 38.89Ω. On the other hand, the average values ​​of each measurement in the example (sample size 399) were: photoelectric conversion efficiency 20.80%, short-circuit current 3.78A, open-circuit voltage 0.72V, form factor 0.74, series resistance 11.88mΩ, and parallel resistance 61.74Ω.

[0035] Based on the above, it was confirmed that the photoelectric conversion efficiency can be improved by adding a neutral oxidizing solution immersion step between the acidic oxidizing solution immersion step and the oxide film removal solution immersion step.

[0036] Furthermore, as shown in Table 1 below, solar cells were manufactured under conditions 1 to 9, in which only the pH of the acidic and neutral oxidizing solutions was changed from the above examples, and the effect on the performance of the resulting solar cells was confirmed. Note that even if the pH deviates from the acidic and neutral ranges, it is noted in the acidic and neutral oxidizing solution columns for convenience.

[0037] [Table 1]

[0038] These results confirm that by using an acidic oxidizing solution with a pH of less than 4 and a neutral oxidizing solution with a pH between 6 and 8, it is possible to suppress the reduction in efficiency due to the adhesion of foreign substances to the semiconductor substrate and manufacture solar cells with superior photoelectric conversion efficiency. [Explanation of symbols]

[0039] S1 Texture formation process S2 Photoelectric conversion structure formation process S3 Electrode structure formation process S11 Alkaline solution immersion process S12 Acidic oxidizing solution immersion process S13 Neutral oxidizing solution immersion process S14 Oxide film removal solution immersion process

Claims

1. The process involves immersing the semiconductor substrate in an alkaline solution, The semiconductor substrate is immersed in an acidic oxidizing solution containing an oxidizing agent and having a pH of less than 4. The steps include immersing the semiconductor substrate in a neutral oxidizing solution containing an oxidizing agent and having a pH of 6 or more and 8 or less, The steps include immersing the semiconductor substrate in an oxide film removal solution, Prepare them in this order, A method for manufacturing a semiconductor device, wherein the acidic oxidizing solution contains ozone at a concentration of 10 ppm to 120 ppm.

2. The semiconductor device manufacturing method according to claim 1, wherein the neutral oxidizing solution is either ozonated water or hydrogen peroxide.

3. The semiconductor device manufacturing method according to claim 1 or 2, wherein the neutral oxidizing solution contains ozone at a concentration of 10 ppm to 120 ppm.

4. The semiconductor device manufacturing method according to claim 1 or 2, wherein the alkaline solution is an inorganic alkaline aqueous solution.

5. The semiconductor device manufacturing method according to claim 1 or 2, wherein the oxide film removal solution is hydrofluoric acid, ammonium fluoride, or a mixture thereof.

6. The semiconductor device manufacturing method according to claim 1 or 2, wherein the oxide film removal solution is hydrofluoric acid with a concentration of 0.5% or more and 10% or less.

7. A step of forming a pyramidal texture on a semiconductor substrate using the semiconductor manufacturing method described in claim 1 or 2, A method for manufacturing a solar cell, comprising the step of forming a photoelectric conversion structure on the semiconductor substrate.

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