JP2004243245A - Washing equipment for solar cell substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tray which makes good operation possible in washing the surface of a substrate used for a solar cell in liquid by using a horn type ultrasonic sonic washing equipment. <P>SOLUTION: This washing equipment for the solar cell substrate for washing the substrate 18 placed on the tray 17 by putting the substrate into a water tank and applying ultrasonic waves thereto is provided with a groove 28 on a substrate installation surface 27 for the tray 17 and the peripheral edge of the surface 27 is provide with a projecting part 19 for preventing the substrate 18 from shifting in a horizontal direction. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for cleaning a solar cell substrate, and more particularly to an apparatus for cleaning a solar cell substrate having a tray on which the substrate is placed.
[0002]
2. Description of the Related Art
A solar cell converts incident light energy into electric energy. Major solar cells are classified into crystalline, amorphous, and compound solar cells according to the type of materials used. Most of these are crystalline silicon solar cells currently on the market. The crystalline silicon solar cells are further classified into a single crystal type and a polycrystalline type. Single-crystal silicon solar cells have the advantage that the efficiency of the substrate can be easily increased due to the good quality of the substrate, but have the disadvantage that the cost of manufacturing the substrate is high. On the other hand, a polycrystalline silicon solar cell has a disadvantage that it is difficult to increase the efficiency due to poor substrate quality, but has an advantage that it can be manufactured at low cost. Recently, a conversion efficiency of about 18% has been achieved at the research level due to the improvement in the quality of polycrystalline silicon substrates and advances in cell technology.
[0003]
On the other hand, polycrystalline silicon solar cells at the mass production level have been distributed on the market because of their low cost, but demand has been increasing in recent years as environmental issues have been addressed. Was required.
[0004]
In the solar cell, various attempts have been made in the past to improve the conversion efficiency into electric energy. One of the techniques is a technique for reducing the reflection of light incident on the substrate. By reducing the reflection of light on the surface, the conversion efficiency to electric energy can be increased.
[0005]
When a solar cell element is formed using a silicon substrate, when the surface of the substrate is etched with an aqueous alkali solution such as sodium hydroxide, fine irregularities are formed on the surface of the substrate, and reflection can be reduced to some extent. When a single crystal silicon substrate having a (100) plane orientation is used, a pyramid structure called a texture structure can be uniformly formed on the surface of the substrate by such a method. Since the orientation depends on the orientation, when a solar cell element is formed from a polycrystalline silicon substrate, the pyramid structure cannot be formed uniformly, and therefore, there is a problem that the overall reflectance cannot be reduced effectively.
[0006]
In order to solve such a problem, it has been proposed that when a solar cell element is formed of polycrystalline silicon, fine irregularities are formed on the surface thereof by a reactive ion etching method (Reactive Ion Etching) ( For example, see Patent Document 1). In other words, it is intended to form fine irregularities uniformly without being affected by the plane orientation of irregular crystals in polycrystalline silicon, and to reduce the reflectance more effectively even in a solar cell element using polycrystalline silicon. It is.
[0007]
However, when fine irregularities are formed on the surface of the solar cell by this method, an etching residue is generated on the surface of the etched substrate. If the surface of the substrate needs to be clean in the next step, it is necessary to remove this etching residue. As a method of removing this residue, there is a method of removing the residue by ultrasonic cleaning in water in a water tank.
[0008]
In this method, a tray is placed on which a substrate is placed in water stored in a water tank, and ultrasonic waves are applied to the surface of the substrate with an ultrasonic horn to remove residues. Further, in order to continuously perform the residue removing operation, for example, as described in Japanese Patent Application No. 2002-73057, a belt or a chain including a plurality of trays for mounting a solar cell substrate is provided. By rotating the belt or chain, ultrasonic waves are applied when the substrates on the plurality of trays continuously pass through the ultrasonic horn.
[0009]
However, in this method, when the tray on which the substrate is placed enters the water, the substrate sometimes floats due to the surface tension of the water surface. In addition, when the substrate floats, the substrate sometimes shifts in the horizontal direction with respect to the tray and protrudes from the tray.
[0010]
In addition, in order to continuously perform the residue removal operation, an automatic substrate supply / recovery device corresponding to the operation is required. In general, in order to supply a plate-like material such as a substrate in a single sheet, the substrate is sucked by a suction pad attached to a transport arm and transported onto a tray fixed to a belt of a residue removing device and supplied. I do. Thereafter, the substrate from which the residue has been removed in water is sucked again from the tray by the suction arm to collect the substrate.At this time, the tray and the substrate are sucked more than necessary due to the interposition of water, and the suction pad is used to collect the substrate. Sometimes it became difficult.
[0011]
The present invention has been made in view of such problems of the related art, and enables a good operation when cleaning the surface of a substrate used for a solar cell in a liquid using a horn-type ultrasonic cleaning device. Provide a tray.
[0012]
[Patent Document 1]
JP-A-9-102625
[Means for Solving the Problems]
In order to achieve the above object, in the solar cell substrate cleaning apparatus according to claim 1, in a solar cell substrate cleaning apparatus in which a substrate placed on a tray is placed in a water tank and cleaned by applying ultrasonic waves, A groove is provided on the substrate mounting surface, and a protrusion for preventing the substrate from shifting in the horizontal direction is provided on a peripheral portion of the substrate mounting surface.
[0014]
Preferably, the substrate is a crystalline substrate having a thickness of 200 to 600 μm, and an area of the tray on the substrate mounting surface which is in contact with the substrate is 3% or more of the area of the substrate.
[0015]
Preferably, the substrate is a crystalline substrate having a thickness of 200 to 600 μm, and the area of the region where the groove is formed is 10% or more of the area of the substrate.
[0016]
Further, it is desirable that the groove has a depth of 0.2 mm or more with respect to the substrate mounting surface.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a structure of a solar cell element formed by a substrate etching method and an etching apparatus according to the present invention. In FIG. 1, 1 is a silicon substrate, 2 is uneven, 3 is an impurity diffusion layer on the light receiving surface side, 4 is an impurity diffusion layer (BSF) on the back surface, 5 is an antireflection film, 6 is a front electrode, and 7 is a back electrode. Is shown.
[0018]
The silicon substrate 1 is a monocrystalline or polycrystalline silicon substrate. This substrate may be either p-type or n-type. In the case of single crystal silicon, it is formed by a pulling method or the like, and in the case of polycrystalline silicon, it is formed by a casting method or the like. Polycrystalline silicon can be mass-produced and is extremely advantageous over monocrystalline silicon in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is sliced into a thickness of about 300 μm, and cut into a size of about 15 cm × 15 cm to obtain a silicon substrate.
[0019]
On the surface side of the silicon substrate 1, irregularities 2 are formed in order to effectively capture incident light without reflecting it. In this method, plasma is generated by introducing a gas into a evacuated chamber, maintaining the pressure at a constant pressure, and applying RF power to an electrode provided in the chamber, thereby generating ions, radicals, etc., which are active species generated. Is used to etch the surface of the substrate. This method, called the reactive ion etching (RIE) method, is shown in FIG.
[0020]
In FIG. 2, 1 is a silicon substrate, 8 is a mass flow controller, 9 is an RF electrode, 10 is a pressure regulator, 11 is a vacuum pump, 12 is an RF power source, 13 is a ground, and 14 is a chamber. Introducing an etching gas from the mass flow controller 8 into the apparatus and supplying RF power from the RF electrode 9 to generate plasma to excite and activate ions and radicals, and to install the silicon substrate on the RF electrode 9. 1 to act on the surface.
[0021]
Among the generated active species, a method in which the effect of the ions acting on the etching is increased is generally called a reactive ion etching method. There is a similar method such as plasma etching, but the principle of plasma generation is basically the same, and the distribution of active species acting on the substrate is changed to a different distribution depending on the chamber structure, electrode structure, generation frequency, etc. It is just that. Therefore, the present invention is effective not only for the reactive ion etching method but also for the whole plasma etching method.
[0022]
In the present invention, for example, while flowing chlorine (Cl ₂ ), oxygen (O ₂ ), and sulfur hexafluoride (SF ₆ ) at a ratio of 1: 5: 5, a reaction pressure of 7 Pa and an RF power of 1 kW for generating plasma are used. Etch for about a minute. Thereby, irregularities are formed on the surface of the silicon substrate 1. Silicon is basically vaporized when etched, but a part thereof cannot be completely vaporized and molecules are adsorbed and remain as residues on the surface of the substrate. That is, when the surface of the silicon substrate 1 is roughened by a reactive ion etching method or a similar dry etching method, the rate at which the etching residue containing the etched silicon as a main component is reattached to the surface of the silicon substrate 1 is increased. The surface of the silicon substrate 1 is made uneven by using this as a micromask for etching. Note that this etching residue is finally removed.
[0023]
Further, when the gas conditions, reaction pressure, RF power, and the like are set to such conditions that an etching residue of silicon remains on the surface of the silicon substrate 1, irregularities can be surely formed. However, the aspect ratio of the unevenness needs to be optimized. Conversely, it is difficult to form irregularities under the condition that no etching residue remains on the surface of the silicon substrate 1.
[0024]
After the formation of the concavities and convexities, the residue on the surface is removed before performing the processing in the subsequent step. As a method of removing the residue, for example, there is a method of removing the residue in water using a horn type ultrasonic cleaning device as described in Japanese Patent Application No. 2002-73057.
[0025]
FIG. 3 shows an example of this ultrasonic cleaning device. 3, 15 is an ultrasonic transducer unit, 16 is an ultrasonic horn, 17 is a tray, 18 is a solar cell substrate, 19 is a water tank, 20 is water, 21 is an ultrasonic oscillator, and 22 is a chain. The tray 17 is fixed to the rotary chain 22, the substrate 18 is placed on the tray 17, the chain 22 is rotated, and the tray 17 is moved in the water in the water tank 20 by the ultrasonic oscillator 21 and the ultrasonic transducer 21. When passing through the lower part of the ultrasonic horn 16 to be driven, the ultrasonic waves of the horn 16 remove the residue. However, this is only an example, and the substance serving as an ultrasonic medium is not limited to water, and a dedicated cleaning solution can be used, and an organic solvent can be used. In addition, although removal of a residue in forming irregularities is described as an example, it can be used for other cleaning.
[0026]
4 and 5 show an example of the tray according to the present invention. 4 and 5, reference numeral 16 denotes a horn, 17 denotes a tray, 18 denotes a substrate, 24 denotes a water surface, 27 denotes a substrate mounting surface, 28 denotes a groove, and 29 denotes a protrusion. FIG. 5 shows the tray of FIG. 4 viewed from above.
[0027]
In the present invention, a substrate mounting surface 27 is provided on the surface of the tray 17 so that the substrate 18 can easily adhere. The flatter and smoother the substrate mounting surface 27, the better the adhesion to the substrate 18. The adhesion varies depending on the medium of the ultrasonic wave used for removing the residue. Generally, the higher the viscosity of the medium and the smoother the roughness of the contact surface on the substrate 18 side, the better the adhesion. The required adhesion varies depending on the roughness of the surface of the substrate 18 on the horn 16 side and the weight of the substrate 18.
[0028]
It is also necessary to optimize the contact area of the tray 17 with the substrate 18 on the substrate mounting surface 27. When the substrate 18 is a crystal substrate having a thickness of 200 to 600 μm, the contact area of the substrate 17 on the substrate mounting surface 27 of the tray 17 is preferably 3% or more of the area of the substrate 18 to be mounted. Thereby, the minimum suction that the substrate 18 does not shift when the substrate 18 on the tray 17 is transferred into the ultrasonic medium can be secured.
[0029]
In order to continuously perform the residue removal operation, an automatic supply and recovery device for the substrate 18 corresponding to the operation is required. Generally, in order to supply a plate-like material such as the substrate 18 as a single wafer, the substrate is sucked by a suction pad (not shown) attached to the transfer arm, and is sucked on a tray 17 fixed to a belt of a residue removing device. To be supplied to Thereafter, the substrate 18 whose residue has been removed in water is sucked again from the tray 17 by the suction arm and the substrate 18 is collected. At this time, the tray 17 and the substrate 18 are unnecessarily adsorbed due to the water. Recovery with a suction pad becomes difficult.
[0030]
In order to solve this, in the present invention, a groove 28 is provided on the substrate mounting surface 27 of the tray 17 in addition to the contact portion of the tray 17 with the substrate 18. Further, a protruding portion 29 for preventing the substrate 18 from being displaced in the horizontal direction on the tray 17 mounting surface is provided. Due to the groove 28, the force of the substrate 18 adsorbed on the tray 17 by the liquid of the ultrasonic medium is weakened, and the collection by the suction pad is facilitated. Therefore, a smooth horn-type ultrasonic cleaning apparatus in which the substrate 18 is appropriately attracted to the tray 17 and no displacement occurs.
[0031]
Although the groove 28 depends on the suction force of the suction pad, when the substrate 18 is a crystalline substrate 18 having a thickness of 200 to 600 μm, the groove 28 preferably has an area of 10% or more of the area of the substrate 18. Preferably, the groove 28 has a depth of 0.2 mm or more with respect to the mounting surface of the substrate 18. With such a configuration, the suction of the substrate 18 and the tray 17 is weakened by the ultrasonic liquid medium leaking through the groove 28, and the suction of the tray 17 by the transfer arm of the automatic supply and recovery device is reduced. The degree of separation of the substrate 18 becomes suitable.
[0032]
When the degree of separation of the substrate 18 becomes better, the substrate 18 becomes easier to float. However, since the substrate 18 and the tray 17 are in close contact with each other by ultrasonic waves, it is possible to prevent the substrate 18 from floating only when the tray 17 enters the water. However, since the substrate 18 is in close contact with the tray 17 and shifts horizontally in the tray 17, a protruding portion 29 is provided around the periphery of the tray 17.
[0033]
【The invention's effect】
As described above, according to the apparatus for cleaning a solar cell substrate according to the present invention, a groove is formed on a substrate mounting surface of a tray on which a substrate is placed, placed in a water tank, and cleaned by applying ultrasonic waves. Protrusions are provided at the periphery of the mounting surface to prevent the substrate from shifting in the horizontal direction, so there is no problem when supplying and recovering the substrate by an automatic machine, and the ultrasonic An apparatus in which the substrate does not shift even in the medium can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a solar cell element prepared using a cleaning device according to the present invention.
FIG. 2 is a view showing an apparatus for performing etching before being cleaned by the cleaning apparatus according to the present invention.
FIG. 3 is a diagram showing an example of an ultrasonic cleaning device according to the present invention.
FIG. 4 is a sectional view showing an example of a tray of the ultrasonic cleaning apparatus according to the present invention.
FIG. 5 is a plan view showing an example of a tray of the ultrasonic cleaning apparatus according to the present invention.
[Explanation of symbols]
17; tray, 18; solar cell substrate, 27; substrate mounting surface, 28; groove, 29;

Claims (4)

In a solar cell substrate cleaning apparatus for cleaning a substrate mounted on a tray by placing the substrate in a water tank and applying ultrasonic waves thereto, a groove is provided on a substrate mounting surface of the tray, and the substrate is provided on a peripheral portion of the substrate mounting surface. A cleaning device for a solar cell substrate, comprising: a projection for preventing horizontal deviation of the substrate. 2. The substrate according to claim 1, wherein the substrate is a crystalline substrate having a thickness of 200 to 600 [mu] m, and a contact area of the tray on the substrate mounting surface with the substrate is 3% or more of an area of the substrate. 3. The cleaning device for a solar cell substrate according to claim 1. 2. The solar cell substrate according to claim 1, wherein the substrate is a crystalline substrate having a thickness of 200 to 600 μm, and an area of a region where the groove is formed is 10% or more of an area of the substrate. Cleaning equipment. The apparatus for cleaning a solar cell substrate according to claim 1, wherein the groove has a depth of 0.2 mm or more with respect to the substrate mounting surface.

Images