JP2009117503A - Method of roughening substrate and method of manufacturing photoelectromotive force device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of roughening a substrate, capable of stably forming an etching mask of a single-layer particle layer without causing the agglomeration of particles and executing etching using the mask. <P>SOLUTION: The method includes: a first step (a) of forming a first adhesive layer 2 on the substrate 1; a second step (b) of attaching etching-resistant particles 3 onto the first adhesive layer 2 by a dry method; a third step (c) of pressurizing the particles 3 on the first adhesive layer 2 using a compaction roller 4; a fourth step (d) of removing the particles 3 leaving the single-layer particle layer 3a of the lowest layer; a fifth step (e) of etching the substrate 1 with the particle layer 3a of the lowest layer as a mask; and a sixth step (f) of removing the first adhesive layer 2 from the substrate 1 and also removing the particle layer 3a of the lowest layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for roughening a substrate and a method for manufacturing a photovoltaic device using the method.

  As is well known, in order to improve the performance of a photoelectric conversion device such as a solar cell, it is important to efficiently incorporate sunlight into the substrate constituting the solar cell. For this reason, a method is adopted in which the surface of the substrate on the light incident side is roughened, and light reflected once on the surface is incident again on the surface, so that more sunlight is taken into the substrate. Here, the roughening means that fine irregularities having a size of several tens [nm] to several tens [μm], that is, a so-called texture structure is intentionally formed on the substrate surface.

  As a conventional method of roughening the substrate for solar cells, when the substrate is a single crystal substrate, anisotropic etching treatment with an aqueous alkali solution such as sodium hydroxide or potassium hydroxide having a crystal orientation dependency on the etching rate. Is widely used. For example, when anisotropic etching is performed on the surface of a (100) substrate, a pyramidal texture structure with an exposed (111) plane is formed.

  However, according to the anisotropic etching method using the above alkaline aqueous solution, when a polycrystalline substrate is used, various crystal plane orientations are mixed on the substrate surface. Can only be made. Therefore, there has been a problem that there is a limit in achieving the purpose of reducing the reflectance.

  Therefore, as a conventional method for roughening the entire surface regardless of the crystal plane orientation, a method is adopted in which an etching mask is formed on the substrate surface by using lithography or the like, and recesses and depressions are formed by reactive ion etching (RIE). Has been. In this case, the problem is the mask formation method. That is, in lithography used in the semiconductor field, when there is a step corresponding to the crystal plane orientation like a polycrystalline solar cell substrate, it is difficult to obtain a good mask pattern on the entire surface of the substrate.

In order to solve the above-mentioned mask formation problem, a method using a single particle layer of fine particles as a mask has been proposed (for example, see Patent Document 1).
In the method described in Patent Document 1, a particle dispersion in which particles are dispersed in a liquid dispersion medium is prepared, a trapping layer containing a polymer is formed on a substrate, and the particle dispersion is applied to the trapping layer. , Heating above the glass transition temperature of the trapping layer to embed only the bottom layer of particles into the trapping layer and removing particles not embedded in the trapping layer to form a single layer particle mask, and then RIE A texture structure is formed on the substrate using a method or the like.

JP 2005-230947 A

In the conventional substrate roughening method, in the case of Patent Document 1, since the particles are applied as a liquid dispersion by a wet method, a stable particle dispersion can be prepared when the particle size exceeds 1 [μm]. There was a problem of difficulty.
In addition, in the case of wet coating, there is a problem that the dispersion medium is partially dried (that is, in the form of islands) and the dispersed particles are aggregated during drying.
Furthermore, when the trapping layer elutes in the dispersion medium when coated on the trapping layer, particles are aggregated with the trapping layer components when applied to the trapping layer to obtain a single particle layer. There was a problem that it was not possible.

  The present invention has been made to solve the above-described problems. A single-layer particle layer etching mask is stably formed without causing particle aggregation, and etching is performed using this mask. The object is to obtain a roughening method of the substrate that can be carried out.

  The substrate roughening method according to the present invention includes a first step of forming a first adhesive layer on the substrate, and a second step of depositing etching-resistant particles on the first adhesive layer by a dry method. A third step of pressing the particles onto the first adhesive layer using a rolling roller, a fourth step of removing the particles leaving the lowermost single layer particle layer, and a single layer particle layer A fifth step of etching the substrate as a mask and a sixth step of removing the first adhesive layer from the substrate and removing the single-layer particle layer are provided.

  According to the method for roughening a substrate according to the present invention, the particles are not agglomerated by depositing the particles dry, so that a uniform single-layer particle layer is formed and a uniform texture is obtained by etching. A structure can be obtained.

Embodiment 1 FIG.
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIG.
FIG. 1 is a side view showing a method for roughening a substrate according to Embodiment 1 of the present invention. First to sixth steps (a) in the case where the method is applied to a manufacturing process of a polycrystalline silicon solar cell. -(F) is shown.

  In FIG. 1, a substrate 1 is a polycrystalline silicon substrate that is most often used for consumer solar cells. After being sliced from a polycrystalline silicon ingot with a multi-wire saw, wet etching using an acid or alkali solution is performed. It removes damage when slicing. The substrate 1 after removing the damage has, for example, a thickness of 250 [μm] and a dimension of 156 [mm] × 156 [mm].

  First, in the first step (a), a first adhesive thin film (hereinafter referred to as “adhesive layer”) 2 is formed on a substrate 1. Here, the first adhesive layer 2 is formed by diluting an acrylic adhesive with toluene and spin coating, and the film thickness after drying is set to 0.8 [μm], for example. .

  If the film thickness of the first adhesive layer 2 is equal to or greater than the radius of the etching-resistant fine particles (hereinafter simply referred to as “particles”) deposited on the first adhesive layer 2 in a later step. When embedding particles in the first adhesive layer 2 in a later step, the components of the first adhesive layer 2 pushed away by the particles overflow from the gaps between the particles and stick to the second layer of particles. Therefore, a single particle layer cannot be obtained.

  On the contrary, when the film thickness of the first adhesive layer 2 is too thin, the adhesive strength is weakened below the required amount. Therefore, in the post-process for removing the particles of the second and higher layers excluding the lowermost layer, Lower layer particles are also dropped off, and a homogeneous single layer particle layer cannot be obtained.

Therefore, in order to obtain a uniform single-layer particle layer in a later step, the thickness of the first adhesive layer 2 is set to 0.8 [μm] here.
In addition, although the acrylic material was used here as an adhesive material which forms the 1st adhesion layer 2, you may use a silicon system, a rubber system, etc. In FIG. 1, the surface of the substrate 1 is expressed as being flat, but may be uneven.

Subsequently, in the second step (b), the dry and etching resistant particles 3 are deposited on the first adhesive layer 2 to form a particle layer.
At this time, as a method for depositing the particles 3, first, a sufficient amount of the particles 3 is placed on the first adhesive layer 2, and then a knife with the gap with respect to the surface of the substrate 1 set to 0.5 [mm]. A method of moving the edge in parallel along the surface of the substrate 1 is applied. Thereby, the excess particles 3 can be scraped off while spreading the arranged particles 3 over the entire surface of the substrate 1.

Here, for example, spherical silica particles having a diameter of 3 [μm] are used as the etching-resistant particles 3.
Needless to say, the material of the particles 3 may be inorganic particles other than silica, resin particles such as PMMA and polystyrene, or metal particles, and may be selected according to the purpose. Moreover, the diameter of the particle | grains 3 can also be selected according to the objective.

Further, the method for depositing the particles 3 on the first adhesive layer 2 is not limited to the method using the knife edge, and the particles 3 are ejected from the nozzle together with the gas flow, and deposited on the first adhesive layer 2. You may apply the method.
As another method, the particles 3 are placed in a container (not shown), and then the first adhesive layer 2 is pressed to deposit the particles 3, or the particles 3 are placed in the container. A method may be applied in which the substrate 1 on which the first adhesive layer 2 is formed is passed through and deposited.

  At the time when the particles 3 are deposited as in the second step (b), the lowermost particles 3 a are not densely arranged with respect to the first adhesive layer 2. This is because, due to the nature of the first adhesive layer 2, when the particles 3 reach the first adhesive layer 2, the particles 3 are fixed at the position at the time of arrival and are not rearranged so as to have a close-packed arrangement.

  Therefore, in the subsequent third step (c), the substrate 1 is placed on a flat fixed plate (not shown), and the rolling roller 4 is pressed from above the particles 3 that are deposited in multiple layers. By rolling the roller 4 while moving it in the direction of the arrow, the particles 3a in the lowermost layer are rearranged so as to be in the most dense arrangement.

Here, a mechanism for rearranging the particles 3 to the close-packed arrangement by rolling by the rolling roller 4 will be described.
First, in the particles 3 in which the lowermost layer is not in the close-packed arrangement, the lowermost layer 3a that forms the lowermost layer on the first adhesive layer 2 and the second layer that forms the second layer immediately above the lowermost layer Focusing on the particles 3b, the case where a force directed to the lowermost particle 3a is applied to the second particle 3b is considered.

At this time, by applying a force toward the surface of the substrate 1 to the second layer of particles 3b, a force is applied to the lowermost layer of particles 3a from the contact point with the second layer of particles 3b. Although applied, this stress direction is opposite to the direction toward the center point of the second layer of particles 3b.
However, in the vertical direction of the surface of the substrate 1, the lowermost particle 3 a can only move in the in-plane direction of the substrate 1 because it cannot be moved by being obstructed by the first adhesive layer 2.

The lowermost particle 3a is fixed to the first adhesive layer 2, but due to the nature of the first adhesive layer 2, even if it is an adherend that has been fixed once, it receives a certain level of force. It is possible to detach from the first adhesive layer 2 or move on the first adhesive layer 2.
Therefore, the rearmost particles 3a are rearranged by the force in the in-plane direction from the contact point with the second layer particles 3b.

If the straight line connecting the bottom layer particle 3a and the center of the second layer particle 3b is parallel to the stress direction, the in-plane force of the substrate 1 is not applied, and the bottom layer particle 3a No placement occurs.
However, in the case of rolling with the rolling roller 4 as in the third step (c), the direction of the force applied to the second-layer particles 3b and the third-layer or more particles 3 is not limited to one direction. Since the change is made sequentially by the movement of the rolling roller 4 (see arrow), the rearmost particles 3a may be rearranged.

Next, in the fourth step (d), the particles 3b in the second layer and the particles 3 in the third and higher layers are removed by ultrasonic cleaning in deionized water, leaving only the lowest layer particles 3a.
At this time, since the lowermost particles 3a are fixed to the substrate surface by adhesion, they are not detached, and as a result, only the lowermost particles 3a arranged in the most dense form are left as a particle layer. Can do.
As a method for removing the second layer of particles 3b and the third or higher layer of particles 3, a method of blowing high-pressure air can be employed.

Subsequently, in the fifth step (e), the substrate 1 is etched by the RIE method (reactive ion etching method) to form a texture structure.
For example, as the etching gas for RIE, a mixed gas of SF 6 and O 2 can be used, and the reaction chamber pressure can be set to 50 [Pa] and the RF output can be set to 2000 [W].

  Furthermore, in the sixth step (f), only oxygen is introduced and etching is performed at a pressure of 100 [Pa], whereby the first adhesive layer 2 below the lowermost particle 3 a is removed from the substrate 1. The substrate 1 is wet-etched with an HF aqueous solution to remove the lowermost particle 3a (particle layer).

  As a result, a texture structure is formed in which the portion immediately below where the lowermost particles 3a existed has a mountain shape, and the portion located between the lowermost particles 3a has a valley shape, and is uniform on the surface of the substrate 1. A stable rough surface 1s is formed.

  In order to confirm the reflection reduction effect, the reflectance of the substrate 1 textured by the method shown in FIG. 1 was evaluated and compared with the reflectance of the texture formed by the above-described conventional method (alkaline solution). Thus, it was confirmed that the reflection reduction effect of 12 pt was obtained over a wide wavelength range.

In addition, a solar battery cell was prototyped using the substrate 1 subjected to the roughening step of FIG. 1, and the effect of the roughening on the solar battery performance was also investigated.
Hereinafter, the manufacturing process of the solar battery cell to which the roughening method of FIG. 1 is applied will be described with reference to FIG.

FIG. 2 is a side view showing a method for manufacturing a solar battery cell using the method of Embodiment 1 (FIG. 1) of the present invention, and shows first to fourth steps (a) to (d). .
In FIG. 2, a p-type silicon substrate (hereinafter simply referred to as “silicon substrate”) 10 has a rough surface 10s formed on the surface by applying the same method as in FIG.
First, in the first step (a), a silicon substrate 10 having a roughened surface is prepared.

Subsequently, in the second step (b), phosphorus diffusion is performed on the silicon substrate 10 to form an n layer 11, and a pn junction is formed on the surface of the roughened silicon substrate 10.
Further, in the third step (c), a SiN film 12 is formed by plasma CVD as an antireflection film on the surface of the n layer 11 on the roughened silicon substrate 10.

Finally, in the fourth step (d), an Ag electrode 13 and an Al electrode 14 are formed as collector electrodes on the front surface of the SiN film 12 and the back surface of the silicon substrate 10 by screen printing technology, respectively.
That is, a comb-shaped Ag electrode 13 is formed on the surface of the SiN film 12, a solid Al electrode 14 is formed on the back surface of the silicon substrate 10, and each collector electrode is sintered by heat treatment, whereby a solar cell is obtained. The cell is complete.

The solar cell completed through steps (a) to (d) in FIG. 2 was evaluated for current-voltage characteristics under a solar simulator. Compared to a conventional substrate using an alkali texture, the short-circuit current It was possible to confirm an improvement of 1.6 [mA / cm ² ] and an improvement of 0.9 [pt] in conversion efficiency.

  As described above, the substrate roughening method (FIG. 1) according to the first embodiment of the present invention includes the first step (a) for forming the first adhesive layer 2 on the substrate 1, the first step A second step (b) of depositing the etching resistant particles 3 on the adhesive layer 2 by a dry method, and a third step of pressing the particles 3 onto the first adhesive layer 2 using a rolling roller 4. A step (c), a fourth step (d) for removing the particles 3 while leaving the lowermost monolayer particle layer, and a fifth step for etching the substrate 1 using the particle layer composed of the lowermost particles 3a as a mask. A step (e) and a sixth step (f) for removing the first adhesive layer 2 from the substrate 1 and removing the lowermost particle layer are provided.

In this way, by applying dry and etching-resistant particles 3 on the first adhesive layer 2, a uniform single-layer particle layer (lowermost particle 3 a) without aggregation is formed on the substrate 1. Therefore, the substrate 1 can be uniformly roughened.
In addition, since the film thickness of the first adhesive layer 2 is set to a value (0.8 [μm]) smaller than the radius of the particle 3 as described above, in the fourth step (d), A homogeneous single-layer particle layer (particles 3a) can be reliably formed.

In the photovoltaic device manufacturing method (FIG. 2) according to the first embodiment of the present invention, the rough surface 10s is formed on the surface of the silicon substrate 10 by applying the method of FIG. A first step (a), a second step (b) for forming a PN junction (n layer 11) on the surface of the roughened silicon substrate 10, and a surface of the PN junction (n layer 11). Third step (c) for forming the antireflection film (SiN layer 12), and forming collector electrodes (Ag electrode 13 and Al electrode 14) on the surface of the antireflection film (SiN layer 12) and the back surface of the silicon substrate 10. And a fourth step (d).
Thereby, as above-mentioned, a highly efficient photovoltaic cell can be comprised using the silicon substrate 10 roughened uniformly.

Embodiment 2. FIG.
In the first embodiment, after a large amount of particles 3 are deposited on the first adhesive layer 2 on the substrate 1, unnecessary particles 3 are removed to form only the lowermost particles 3a as a particle layer. However, as shown in FIG. 3, a required amount of particles 3 a corresponding to the lowermost layer may be attached to the first adhesive layer 2 on the substrate 1 using the application roller 5.

Hereinafter, the substrate roughening method according to the second embodiment of the present invention will be described with reference to the side view of FIG. 3, taking as an example the case where it is applied to the manufacturing process of a polycrystalline silicon solar cell, as described above. To do.
FIG. 3 shows the first to fourth steps (a) to (d) according to the second embodiment of the present invention.

In FIG. 3, the same components as those described above (see FIG. 1) are denoted by the same reference numerals as those described above, and detailed description thereof is omitted.
In addition, the 1st process (a) in FIG. 3 is the same as the 1st process (a) of the above-mentioned (refer FIG. 1). The fifth and sixth steps according to the second embodiment of the present invention are not shown, but are the same as the fifth and sixth steps (e) and (f) described above (see FIG. 1). It is.

First, similarly to the above, in the first step (a), the first adhesive layer 2 is formed on the surface of the substrate 1.
Subsequently, in the second step (b), the second adhesive layer 6 having a lower adhesive strength than the first adhesive layer 2 is formed on the surface of the wearing roller 5.
Specifically, as shown in the figure, the toluene diluted solution 7 of acrylic adhesive is stored on an adhesive bat 8 having a flat bottom surface, and the wearing roller 5 is rolled on the bottom surface of the bat in the direction of the arrow. The second adhesive layer 6 having a uniform film thickness is adhered to the surface of the roller 5 to be worn. Moreover, the stable 2nd adhesion layer 6 is obtained by passing through a drying process for 120 [degreeC] and 10 minutes after that.

Next, in the third step (c), the etching-resistant particles 3 are deposited on the second adhesive layer 6 on the surface of the wearing roller 5 by a dry method.
Specifically, as shown in the figure, the particles 3 are stored in the particle bat 9, and the wear roller 5 is rolled on the particles 3 in the direction of the arrow, so that the second adhesion on the wear roller 5 is achieved. The particles 3 are deposited on the layer 6.

  At this time, since the particles 3 are deposited in multiple layers on the second adhesive layer 6, the wearing roller 5 is ultrasonically cleaned in deionized water, leaving only the lowermost particle 3 a 2. Unnecessary particles 3 beyond the first layer are removed to form a single particle layer.

Subsequently, in the fourth step, the particles 3a (single-layer particle layer) deposited on the second adhesive layer 6 on the wearing roller 5 are placed on the first adhesive layer 2 formed on the substrate 1. Transcript.
At this time, since the particles 3a adhere to the first adhesive layer 2 by rolling the wearing roller 5 in the direction of the arrow from the end of the substrate 1, a single particle layer can be formed.

In order to reliably transfer the particles 3 a on the second adhesive layer 6 onto the first adhesive layer 2, the adhesive force of the second adhesive layer 6 is the first adhesive layer 2 as described above. Must be less than the adhesive strength.
Therefore, when forming the second adhesive layer 6 in the second step (b), by adjusting the film thickness of the second adhesive layer 6 to be thinner than the first adhesive layer 2, Adjustments are made to reduce the adhesive strength.

  Further, since the particle 3a cannot be deposited on the entire surface of the substrate 1 unless the width and circumferential size of the wear roller 5 are equal to or larger than the size (width and length) of the substrate 1, the size is sufficiently large. Is set.

Hereinafter, although illustration and description are omitted, the fifth and sixth steps (e) and (f) similar to those described above (FIG. 1) are performed.
Further, by applying the method shown in FIG. 3, a highly efficient photovoltaic device (aspect battery cell) can be configured by the same method as described above (see FIG. 2).
belongs to.

  As described above, the substrate roughening method (FIG. 3) according to the second embodiment of the present invention includes the first step (a) for forming the first adhesive layer 2 on the substrate 1, and the first step. The second step (b) of preparing the wearing roller 5 on which the second adhesive layer 6 having weaker adhesive strength than the adhesive layer 2 is prepared, and the second adhesive layer 6 on the wearing roller 5 A third step of depositing the etching particles 3 by a dry method and removing the particles 3 while leaving the lowermost single-layer particle layer 3a among the particles 3 transferred onto the second adhesive layer 6 ( c), a fourth step (d) for transferring the lowermost particle layer (particles 3a) deposited on the second adhesive layer 6 onto the first adhesive layer 2, and a mask for the lowermost particle layer As the fifth step ((e) in FIG. 1) for etching the substrate 1, the first adhesive layer 2 is removed from the substrate 1, and the lowermost particle layer (3a) is removed. Sixth step of removed by and a ((f) in FIG. 1).

In this way, by depositing the etching resistant particles 3 on the first adhesive layer 2 in a dry manner, a uniform single layer particle layer without aggregation can be formed, and the substrate 1 can be uniformly roughened. The surface 1s can be formed.
Further, in the fourth step ((d) in FIG. 3), it is possible to avoid contamination of the substrate 1 with excess particles 3 by directly forming a single particle layer on the substrate 1. Furthermore, a more uniform and stable rough surface 1s can be formed.

It is a side view which simplifies and shows a part of each process of the roughening method of the board | substrate which concerns on Embodiment 1 of this invention. It is a side view which simplifies and shows a part of each process of the manufacturing method of the photovoltaic device concerning Embodiment 1 and 2 of this invention. It is a side view which simplifies and shows a part of each process of the roughening method of the board | substrate which concerns on Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Substrate, 2 1st adhesion layer, 3 particles, 3a Bottom layer particle (single layer particle layer), 3b 2nd layer particle, 4 Rolling roller, 5 Wear roller, 6 2nd adhesion layer, 10 Silicon substrate (p-type silicon substrate), 11 n layer (PN junction), 12 SiN film (antireflection film), 13 Ag electrode (collector electrode), 14 Al electrode (collector electrode).

Claims (4)

A first step of forming a first adhesive layer on the substrate;
A second step of dryly depositing etching resistant particles on the first adhesive layer;
A third step of pressing the particles onto the first adhesive layer using a rolling roller;
A fourth step of removing the particles leaving the lowest monolayer particle layer;
A fifth step of etching the substrate using the monolayer particle layer as a mask;
And a sixth step of removing the first adhesive layer from the substrate and removing the monolayer particle layer. A first step of forming a first adhesive layer on the substrate;
A second step of preparing a wearing roller on which a second adhesive layer having a lower adhesive strength than the first adhesive layer is formed;
Etch-resistant particles are dry-deposited on the second adhesive layer on the wearing roller, and the single-layer particle layer of the lowermost layer among the particles transferred onto the second adhesive layer A third step of leaving and removing the particles;
A fourth step of transferring the single-layer particle layer deposited on the second adhesive layer onto the first adhesive layer;
A fifth step of etching the substrate using the monolayer particle layer as a mask;
And a sixth step of removing the first adhesive layer from the substrate and removing the monolayer particle layer.   3. The substrate roughening method according to claim 1, wherein the thickness of the first adhesive layer is set to a value smaller than the radius of the particles. A method for manufacturing a photovoltaic device using the method according to any one of claims 1 to 3,
Applying the method to a silicon substrate to form a rough surface on the surface of the silicon substrate;
A second step of forming a PN junction on the roughened surface of the silicon substrate;
A third step of forming an antireflection film on the surface of the PN junction;
And a fourth step of forming a collector electrode on the front surface of the antireflection film and the back surface of the silicon substrate.

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