JP2003282520A - Cleaning method of vessel and method for manufacturing solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device wherein the sufficient cleaning effect of a semiconductor is obtained and stable high characteristics are obtained. <P>SOLUTION: By using the mixture of a solution of NaOH and a surfactant, a vessel is cleaned in which vessel anisotropic etching and cleaning which are used for forming unevenness on a silicon substrate for a solar battery are performed repeatedly. The mixture solution of NaOH and the surfactant which has been used in preceding treatment is discharged (S1), and the vessel is cleaned once by using pure water (S2). After that, the vessel is filled with pure water in a state with pH set as at most 7 (S3), an ozone gas is injected, and an ozone concentration is maintained at almost 5 ppm, and the vessel is left as it is for about three hours (S4). Due to cleaning by ozone water, a cleaning inhibitor stuck on the wall surface of the vessel is oxidized, decomposed and removed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device such as a solar cell, and more particularly to a method for cleaning a container for cleaning a semiconductor using a surfactant.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device such as a solar cell, when a semiconductor is cleaned in a container using a surfactant, a cleaning inhibitor generated by cleaning adheres to the wall surface of the container. . The cleaning inhibitor attached to the wall surface of the container needs to be removed because the cleaning inhibitor reduces the cleaning ability and adversely affects the processing such as the etching process during manufacturing of the semiconductor device.

Therefore, conventionally, the cleaning inhibitor is removed by cleaning the container with a cleaning liquid having the same composition as that used in the semiconductor cleaning process, a high-concentration alkaline solution, or water.

[0004]

However, in the conventional container cleaning method described above, when the semiconductor cleaning process is continued for a long period of time, the cleaning inhibitor adhered to the wall surface of the container is sufficiently removed. However, there is a problem in that a sufficient cleaning effect on the semiconductor cannot be obtained, and a semiconductor device having characteristic deterioration due to insufficient cleaning is manufactured.

The present invention has been made in view of such circumstances, and by cleaning the container using ozone,
To provide a method for cleaning a container capable of sufficiently removing a cleaning inhibitor, obtaining a stable cleaning effect, and manufacturing a semiconductor device without deterioration in characteristics, and a method for manufacturing a solar cell to which the cleaning method is applied. With the goal.

[0006]

According to a first aspect of the present invention, there is provided a method for cleaning a container, which is characterized in that the container is cleaned using a surfactant, and the container is cleaned using ozone. To do.

In the first aspect of the present invention, the wall surface of the container is washed with ozone, specifically with ozone water or ozone gas, so that the cleaning inhibitor attached to the wall surface of the container is oxidized with ozone. It is oxidized and decomposed by force and removed. As a result, the cleaning inhibitor is sufficiently removed, and the cleaning effect of the semiconductor performed in the container is stabilized, and as a result, characteristic deterioration due to insufficient cleaning does not occur in the manufactured semiconductor device.

A method of manufacturing a solar cell according to a second aspect of the present invention comprises performing an etching treatment for forming an uneven shape on a silicon substrate for a solar cell in a container to which the cleaning method according to claim 1 is applied. Characterize.

In the second aspect of the invention, ozone is used in the first aspect of the invention for a container that is subjected to an etching treatment for forming an uneven shape (texture structure) on the surface of a silicon substrate in order to obtain a light confining effect. Implement container cleaning method.
As a result, the etching process is stabilized, an ideal pyramid-like texture structure having almost no mirror surface can be formed on the surface of the silicon substrate, and the photoelectric conversion characteristics of the manufactured solar cell are improved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings showing the embodiments thereof. In the following description, HIT (Heterojunction with Intrinsic Thin
An example in which the present invention is applied to a container that is subjected to an etching treatment for forming an uneven shape (texture structure) on the surface of a silicon substrate in a -layer) type solar cell will be described.

FIG. 1 is a sectional view showing the structure of a HIT type solar cell. In FIG. 1, reference numeral 1 is an n-type silicon substrate made of a crystalline semiconductor such as single crystal silicon or polycrystalline silicon. The surface (one main surface) of the silicon substrate 1 is processed to have a uniform uneven shape (texture structure) in order to obtain a light confinement effect in order to improve photoelectric conversion efficiency. This uneven shape (texture structure) is formed by anisotropic etching as described later.

On the surface of the silicon substrate 1, a laminate 2 of i-type amorphous silicon layer / p-type amorphous silicon layer and a transparent conductive film 3 made of, for example, ITO (Indium Tin Oxide).
And are stacked. Thus, the heterojunction between the n-type silicon substrate and the amorphous silicon layer is formed on the front surface side. A comb-shaped collector electrode 4 made of, for example, Ag paste is formed on the transparent conductive film 3. Also,
On the back surface (the other main surface) of the silicon substrate 1, for example, Al
A back surface electrode 5 made of a film is formed.

Next, a manufacturing process of the solar cell having such a structure will be described. First, the n-type silicon substrate 1 sliced along the (100) plane is heated at a temperature of 85 ° C.
Immerse in 2.5 mol / liter NaOH aqueous solution. By this immersion, the deposits and processing strains on the surface of the silicon substrate 1 are removed by etching.

Then, the silicon substrate 1 after the above treatment is
For example, 10 mol / l of a surfactant made of caprylic acid is added to 0.5 mol / l of NaOH aqueous solution and immersed in a container containing an etching solution having a temperature of 85 ° C. for 40 minutes. Although caprylic acid is used as the surfactant, other organic acids such as alkyl sulfonic acid may be used. In anisotropic etching using an aqueous NaOH solution, the etching rate of the (111) plane is extremely slow compared to the etching rates of other crystal orientations,
By anisotropic etching with this NaOH on the silicon substrate 1 sliced on the (100) plane, (111)
A pyramidal concavo-convex shape having a V-shaped cross section, which is composed of four walls oriented in the plane, is formed on the surface of the silicon substrate 1. In this example, the added surfactant is N
It has a function of cleaning the silicon substrate 1 by removing the residue of etching by aOH, and performs the anisotropic etching process and the cleaning process on the silicon substrate 1 at the same time.

Next, the silicon substrate 1 after the above treatment is washed with pure water at room temperature and then immersed in a 2 mol / l HF aqueous solution at room temperature to remove the oxide film on the surface of the silicon substrate 1, and thereafter. Wash again with pure water at room temperature. Next, H
The silicon substrate 1 is dipped in a solution in which F and HNO ₃ are mixed at a ratio of 1:10 at room temperature for 30 seconds to have a rounded pyramid shape, and then washed with pure water at room temperature.

Next, the silicon substrate 1 is immersed in ozone water having a concentration of 15 ppm at room temperature for 5 minutes to decompose and remove the surfactant, and then washed with pure water at room temperature. Next, the silicon substrate 1 is immersed in a 2 mol / liter HF aqueous solution at room temperature to remove the surface oxide film formed by ozone, and then washed with pure water at room temperature. The processing on the silicon substrate 1 is completed at this point, and the silicon substrate 1 is finally dried.

The silicon substrate 1 which has been subjected to the above-mentioned processing
Plasma CVD (Chemical Vapor Depositio)
By the method n), a laminate 2 of i-type / p-type amorphous silicon layers is formed. Next, I is formed on the laminate 2 by a sputtering method.
A transparent conductive film 3 made of TO is formed. Next, the comb-shaped collector electrode 4 is formed on the translucent conductive film 3 by a screen printing method of Ag paste. Finally, the silicon substrate 1
A back electrode 5 is formed by evaporating Al on the back surface of.

NaO in the manufacturing process as described above
Anisotropic etching using mixed solution of H / surfactant /
In the cleaning process, good etching /
A cleaning process can be performed. However, if this treatment is continued for a long time without cleaning the container, the amount of the cleaning inhibitor adhering to the wall surface of the container increases and mixes into the mixed solution, and the effect of the cleaning inhibitor appears. come.
As a result, the interaction between the surfactant and silicon is weakened, the cleaning effect by the surfactant becomes unstable, and a desired random texture structure is formed on the silicon substrate 1 without performing good anisotropic etching. become unable.

That is, as shown in FIG. 2, an ideal pyramid-shaped concave-convex shape that does not have a flat portion and is fine and dense must be originally formed on the surface of the silicon substrate 1.
As shown in FIG. 3, the flat portion 1a is formed between the adjacent pyramids. This flat portion serves as a light reflection portion, and the uneven shape as shown in FIG. 3 has a smaller light confining effect than the uneven shape shown in FIG. 2, and the silicon substrate 1 having the uneven shape as shown in FIG. 3 is used. In the solar cell manufactured as described above, the short-circuit current value decreases and the output characteristics deteriorate.

Whether or not this uneven shape has been successfully formed can be monitored by the light reflectance of the silicon substrate 1 after the uneven formation, and when the uneven shape is good (FIG. 2).
(See FIG. 3) shows a stable low value of the light reflectance, and when the concave and convex shape is defective (see FIG. 3), the light reflectance shows a high unstable value. FIG. 4 is a graph showing the relationship (rough value) between the number of anisotropic etching / cleaning treatments and the light reflectance of the silicon substrate 1. In the initial stage, the silicon substrate 1 can be stably washed,
Although the ideal uneven shape can be formed, the light reflectance becomes high after the number of times of processing reaches a predetermined number a,
It can be seen that the stable cleaning process and the good anisotropic etching based on the cleaning process cannot be performed.

Since the destabilization of the anisotropic etching / cleaning process is caused by the cleaning inhibitor attached to the wall surface of the container as described above, the anisotropic etching / cleaning process is performed in the present invention. Prior to destabilizing, ozone is used to clean the container to remove its cleaning inhibitors.

FIG. 5 is a diagram showing a procedure for cleaning the container according to the present invention. First of all, use the NaOH /
The mixed solution of the surfactant is discharged (S1). Next, the container is washed once with pure water and the washing water is discharged (S
2). Next, the container is filled with deionized water while keeping the pH at 7 or less (S3). Ozone gas is injected into the pure water in the container, the ozone concentration in the water is maintained at about 5 ppm, and it is left for about 3 hours (S4). By this cleaning with ozone water, the cleaning inhibitor attached to the wall surface of the container is oxidized and decomposed and removed. The ozone concentration in the water at this time is 2
10 ppm is preferable.

Next, after discharging the ozone water (S5), the container is washed again with pure water and the cleaning water is discharged (S5).
6). Finally, the container is washed with a NaOH / surfactant solution having the same composition ratio as the mixed solution used in the anisotropic etching / washing process, and the washing solution is discharged (S7), and then the anisotropic Prepare for etching / cleaning process.

It should be noted that instead of injecting ozone gas into the pure water in the container as described above, ozone water is allowed to overflow into the container to maintain a constant ozone concentration in water and the container is washed (cleaning inhibitor is removed. Of course, the same effect can be obtained.

FIG. 6 is a graph showing the relationship (measured value) between the number of anisotropic etching / cleaning treatments and the light reflectance of the silicon substrate 1 showing the effect of the present invention. In FIG. 6, (A) shows a high value where the light reflectance is unstable, and favorable anisotropic etching cannot be performed due to the influence of the cleaning inhibitor attached to the wall surface of the container. Therefore, before the B-th treatment in FIG. 6, the container was washed as described above. As a result, in each of the B-th and subsequent treatments ((C) of FIG. 6), the light reflectance was kept at a low value and the ideal concavo-convex shape as shown in FIG. 2 could be formed. It can be seen that the stable cleaning process of No. 1 and the excellent anisotropic etching process can be realized.

The case of applying to the etching process for forming the uneven shape of the silicon substrate for the solar cell has been described, but this is an example, and the cleaning inhibitor adhered to the container is the semiconductor device manufactured. Needless to say, the above-described container cleaning method is effective in all cases where the characteristics of (1) are adversely affected.

[0027]

As described above, according to the present invention, the container is cleaned using ozone, and the cleaning inhibitor adhering to the wall surface of the container is removed by oxidation / decomposition, so that the cleaning effect of the semiconductor is stabilized. Therefore, a semiconductor device having high and stable characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a HIT type solar cell.

[Fig. 2] Ideal surface shape (irregular shape) of a silicon substrate
FIG.

FIG. 3 is a diagram showing a defective surface shape (uneven shape) of a silicon substrate.

FIG. 4 is a graph showing the relationship (rough value) between the number of anisotropic etching / cleaning treatments and the light reflectance of a silicon substrate.

FIG. 5 is a diagram showing a procedure of container cleaning in the present invention.

FIG. 6 is a graph showing the relationship (measured value) between the number of times of anisotropic etching / cleaning treatment and the light reflectance of a silicon substrate, which shows the effect of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Laminated body of i-type amorphous silicon layer / p-type amorphous silicon layer 3 Translucent conductive film 4 Collection electrode 5 Backside electrode

Claims (2)

[Claims] 1. A method of cleaning a container for cleaning a semiconductor using a surfactant, which comprises cleaning the container with ozone. 2. A method of manufacturing a solar cell, wherein an etching treatment for forming an uneven shape on a silicon substrate for a solar cell is performed in a container to which the cleaning method according to claim 1 is applied.