JP5742403B2 - Method and apparatus for forming transparent conductive film for solar cell - Google Patents

Description

  The present invention relates to a method for forming a transparent conductive film used for a solar cell and a forming apparatus therefor.

  In recent years, as a solar cell for performing photovoltaic power generation, a crystalline semiconductor solar cell, a thin film Si solar cell, a compound semiconductor solar cell using a CIGS (Cu-In-Ga-Se quaternary alloy) film, etc. And organic solar cells using organic thin films. Among them, thin-film Si-based solar cells are rapidly expanding the range of use because they are inexpensive and have relatively high photoelectric conversion efficiency.

This thin-film Si-based solar cell includes a substrate (such as glass), a metal electrode layer, a p-type Si layer, an n-type Si layer, and a transparent electrode layer as basic components. Each layer is formed mainly by a vacuum film forming method such as CVD or sputtering. Among these, as the transparent electrode layer, SnO ₂ type (FTO: F added SnO ₂ etc.), In ₂ O ₃ type (ITO: SnO ₂ added In ₂ O ₃ etc.), ZnO type (AZO: Al ₂ O ₃ added) A transparent conductive film such as ZnO is used.
In order to increase the photoelectric conversion efficiency, the transmittance of the transparent conductive film is increased so that a large amount of light reaches the Si p / n junction that is the power generation layer, and at the same time, the generated charges (electrons or holes) are not lost. In order to collect current, it is necessary to reduce the resistance of the transparent conductive film. In addition, it is also required to form irregularities on the surface of the transparent conductive film in order to confine incident light without escaping and efficiently use it for power generation.

  As such a film having high transmittance, low resistance, and appropriate surface irregularities, transparent conductive films as shown in Patent Documents 1 to 5 have been known so far.

Patent Document 1 describes a light detector in which a SnO ₂ film doped with halogen (Cl or the like) having a predetermined textured surface is used as a translucent electrical contact to improve photoelectric conversion efficiency. .

In Patent Document 2, an FTO film (a SnO ₂ film doped with F) having a plurality of micro convex portions continuously provided on the surface of a plurality of peaks and a plurality of flat portions is provided on a substrate, and photoelectric conversion efficiency is obtained. The photoelectric conversion element which improved is described.

  In Patent Document 3, a ZnO transparent electrode having a surface uneven structure is formed on a substrate by MOCVD (organometallic vapor phase method) at 200 ° C. or lower to improve the efficiency of a silicon-based thin film photoelectric conversion device. A method is described.

In order to reduce the resistance of the transparent conductive film, a ZnO-based or In ₂ O ₃ -based transparent conductive film may be formed by a sputtering method. Usually, the sputtering method is performed at a low temperature process of 300 ° C. or lower. Therefore, there is a problem that the crystal growth in the transparent conductive film is not sufficient, and the surface unevenness does not increase. In order to solve the problem, various methods have been used to increase the surface roughness.

  For example, Patent Document 4 describes a method of forming irregularities on the surface of a transparent electrode by forming a transparent conductive film made of zinc oxide by sputtering and then etching with an acid or alkali solution. Patent Document 5 describes a method in which after forming 0.1 to 1 μm insulating fine particles on the surface of a glass substrate, a transparent conductive film is formed thereon to obtain an uneven transparent electrode.

Japanese Patent Publication No. 6-12840 International Publication No. 2003/036657 JP 2000-252501 A JP-A-11-233800 JP 2003-243676 A

However, the SnO ₂ -based transparent conductive film described in Patent Document 1 has a higher resistivity (a value obtained by multiplying the sheet resistance and the film thickness) than a ZnO-based or In ₂ O ₃ -based transparent conductive film. For this reason, in order to obtain a sheet resistance equivalent to that of a transparent conductive film such as a ZnO-based film, the film must be thickened, resulting in increased light absorption and reduced transmittance. On the other hand, if the film thickness is about the same as that of a transparent conductive film such as a ZnO-based film, preferable light absorptivity and transmittance can be obtained, but sheet resistance increases.

The FTO film described in Patent Document 2 also has a higher resistivity than the ZnO-based and In ₂ O ₃ -based transparent conductive films, and has the same problem as the SnO ₂ -based transparent conductive film.
Furthermore, both Patent Documents 1 and 2 use the CVD method for forming the transparent conductive film. However, since the CVD method is usually performed at a temperature of about 500 ° C., compared with a sputtering method performed at a lower temperature than that. , Heating / cooling takes time and production cost is high. In addition, in the CVD method, in addition to the film forming chamber and the vacuum apparatus, additional equipment is necessary for processing the film forming gas and the like, so that the entire equipment cost is higher than that of the sputtering method or the like. Furthermore, the CVD method cannot obtain a film having a sufficiently low resistance.

  In the invention disclosed in Patent Document 3, since the MOCVD method is used, a film can be formed at a low temperature of 200 ° C. or lower. However, since the MOCVD method is a kind of CVD method, Patent Document 1 2 had the same drawbacks.

  If the methods disclosed in Patent Documents 4 and 5 are used, a transparent conductive film with low resistance and large surface irregularities can be obtained. However, since a process for forming chemical etching and insulating fine particles is added before and after sputtering, the production cost is low. high.

As described above, according to the conventional technology, it has been impossible to obtain a transparent conductive film having low resistance, high transmittance, and appropriate surface irregularities by a process with a low number of steps at a low temperature.

The present invention has been made in view of the above-mentioned problems, and is a transparent conductive film for solar cells obtained by a low-resistance, high transmittance, and a transparent conductive film having appropriate surface irregularities at a low temperature and with fewer processes. A forming method, a transparent conductive film formed thereby, and a forming apparatus for forming the transparent conductive film are provided.

The method for forming a transparent conductive film of the present invention is a method of forming a transparent conductive film on the surface of a substrate by sputtering in one vacuum chamber, and irradiates the surface of the substrate with laser light through a diffusion plate. and will it have a laser-assisted deposition step of depositing while, causing the ablation to the membrane by irradiation of the laser light to form a crater-like depressions, in addition to the fine unevenness corresponding to the film surface upon crystal size , Large irregularities corresponding to the crater-like depressions are formed .

In this method of forming a transparent conductive film, when sputtered particles come by sputtering and a thin film is formed, the thin film grows while the surface is continuously irradiated with laser light. Thus, even if the substrate is not heated, crystallization of the particles forming the thin film is promoted, and crystal grains having good crystallinity and large size are formed. When the crystallinity is improved, the absorption of light is reduced and the transmittance is increased. At the same time, the electron mobility is improved and the resistivity is lowered. In addition, as the crystal size increases, the unevenness on the surface also increases, and it is possible to form an unevenness whose maximum height difference is about half of the film thickness (for example, a height difference of about 0.5 μm with a film thickness of 1 μm). Irregularities).
In addition, when laser light is irradiated onto a thin film, film ablation (evaporation) occurs depending on the intensity of the laser light. Therefore, when the laser light that has passed through the diffusion plate is irradiated onto the film being formed, the intensity distribution is reflected to reflect the diameter. Crater-shaped depressions of about 1 to 100 μm are uniformly formed, and a film having an uneven structure corresponding to their distribution is formed. Thereby, in addition to the fine unevenness corresponding to the crystal size, a double surface uneven structure in which large unevenness corresponding to the crater-like depression is formed can be configured. For example, if the thickness of the film to be formed is about 0.5 μm to 3 μm, 0.05 μm to 0.5 μm is formed on the uneven surface corresponding to the crater-shaped depression having a height difference of about 0.5 μm to 3 μm. A film in which irregularities corresponding to fine crystal grains of a certain degree are continuously distributed is formed. In this way, by forming a transparent conductive film having a double-surface concavo-convex structure whose surface is formed by large and small unevenness, the light scattering effect on the uneven surface can be increased, and light that can be confined The wavelength can be expanded to several tens of nanometers to several tens of micrometers.
As described above, since a transparent conductive film having low resistance, high transmittance, and appropriate surface irregularities can be formed without heating the substrate, the photovoltaic cell of the solar cell formed using this transparent conductive film can be formed. Conversion efficiency can also be improved.

In addition, the method for forming a transparent conductive film of the present invention includes a film forming step of forming a thin film on the surface of a substrate by sputtering in one vacuum chamber, and irradiating the surface of the thin film with laser light through a diffusion plate. will be have a deposition laser assisted deposition process, causing the ablation to the membrane by irradiation of the laser light to form a crater-like depressions, in addition to the fine unevenness corresponding to the film surface in crystal size, the Large irregularities corresponding to crater-shaped depressions are formed .
Further, the transparent conductive film is formed by repeating the film forming step and the laser assist film forming step.

In this method of forming a transparent conductive film, there is a portion that is formed without being irradiated with laser light. However, the temperature of the portion is increased immediately by the laser light that is irradiated simultaneously with the formation of the film. A transparent conductive film having crystal grains with favorable crystallinity and large crystal size can be formed. Therefore, a transparent conductive film having a low resistivity and a high transmittance is obtained, as in the case where laser light irradiation is performed simultaneously with film formation.
Moreover, moderate film ablation occurs by irradiation of the laser light through the diffusion plate, and a crater-like depression is formed. This makes it possible to construct a double-surface concavo-convex structure in which large irregularities corresponding to crater-like depressions are formed on the film surface in addition to fine irregularities corresponding to the crystal size. The wavelength range of can be expanded.

The transparent conductive film forming method of the present invention includes a film forming process for forming a thin film on the surface of a substrate by sputtering in one vacuum chamber, and a laser assist process for irradiating the thin film with laser light through a diffusion plate. it was closed the door, causing the ablation layer to form a crater-like depressions by irradiation of the laser beam, in addition to the fine unevenness corresponding to the film surface upon crystal size, corresponding to the crater-like recesses It is characterized by forming large irregularities .
The film forming step and the laser assist step are repeated.

  In this method of forming a transparent conductive film, laser light is irradiated after the transparent conductive film is formed on the surface of the substrate by sputtering, but the temperature of the film can be raised by laser light irradiation. A transparent conductive film made of crystal grains having good crystallinity and large size can be formed. Therefore, a transparent conductive film having a low resistivity and a high transmittance is obtained as in the case where laser light irradiation is performed simultaneously with film formation. Moreover, moderate film ablation occurs by irradiation of the laser light through the diffusion plate, and a crater-like depression is formed. As a result, the surface of the transparent conductive film can be confined in a double surface uneven structure in which large unevenness corresponding to the crater-like depression is formed in addition to fine unevenness corresponding to the crystal size. The wavelength range of light can be expanded.

Moreover, in the formation method of the transparent conductive film of this invention, you may have a pause process which does not perform both sputtering film-forming and laser beam irradiation.
The temperature rise of the film due to laser light irradiation occurs instantaneously, and effects such as crystal grain growth and film ablation can be obtained in that moment, so even if a pause process is added, the resistivity is low and the transmittance is high Simultaneously with the formation of the transparent conductive film, the surface can have a double surface uneven structure.
By this forming method, a large number of substrates can be put into a vacuum chamber and the process can be repeated while moving the substrate, and a substrate with a transparent conductive film having low resistance, high transmittance, and appropriate surface irregularities can be shortened. Can be manufactured in large quantities in time.

The transparent conductive film of the present invention is a transparent conductive film produced by the method for forming a transparent conductive film, wherein a crater-shaped depression having a diameter of 1 μm or more and 100 μm or less is uniformly formed on the surface, and the surface thereof is formed. A small unevenness with a height difference of 0.05 μm or more and less than 1 μm is formed along with a resistivity of 1 × 10 ⁻³ Ω · cm or less.
By forming the transparent conductive film having such a surface shape, the wavelength region of light to be confined can be widened. Further, by forming the resistivity to 1 × 10 ⁻³ Ω · cm or less, a transparent conductive film having a lower resistance and a higher transmittance can be obtained.

The film thickness of the transparent conductive film of the present invention is preferably formed to 500 nm or more.
When the film thickness is 500 nm or less, the resistance becomes high and the surface unevenness cannot be made sufficiently large. By setting the film thickness to 500 nm or more, a transparent conductive film with low resistance and large surface irregularities can be formed.

The transparent conductive film forming apparatus of the present invention is an apparatus for carrying out the transparent conductive film forming method of the present invention, and is a substrate for moving a vacuum chamber and a substrate through a sputtering region in the vacuum chamber. It is provided with a moving mechanism and a laser beam irradiation mechanism provided so as to be able to irradiate a laser beam through a diffusion plate on the moving region of the substrate other than the sputtering region or the sputtering region.

  According to the present invention, a transparent conductive film having a double-surface concavo-convex structure, which is composed of crystal grains having good crystallinity and a large particle size, and has fine concavo-convex shapes formed along a relatively large concavo-convex surface. Can be formed without heating the substrate, so that the resistivity of the transparent conductive film can be reduced to increase the transmittance, and the wavelength range of the confined light can be widened. In addition, since film formation can be performed by a low-temperature process that does not require heating, it is suitable for mass production, and the manufacturing cost of a substrate on which such a transparent conductive film is formed and a solar cell using the substrate can be reduced. it can.

It is a schematic block diagram which shows the cross section of the formation apparatus for enforcing the formation method of the transparent conductive film which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the longitudinal cross-section of the formation apparatus of FIG. It is a schematic block diagram which shows the cross section of the formation apparatus of the transparent conductive film of a form different from FIG. It is a schematic block diagram which shows the longitudinal cross-section of the formation apparatus of FIG. It is a figure explaining the transparent conductive film formed, (a) is a top view, (b) is sectional drawing.

The formation method of the transparent conductive film of one Embodiment of this invention is as follows.
As shown in FIGS. 1 to 4, the forming apparatus 100 of the present embodiment is configured to perform sputter film formation and laser light irradiation on the substrate 7 at the same time.
The part of the forming apparatus 100 for performing the sputter film formation includes a film formation vacuum chamber 1, a vacuum pump 2, a power source 4, a substrate holder 5, a target 6, and the like. 2 and 4, the forming apparatus 100 includes a substrate moving mechanism such as a rotation mechanism and an inter-back mechanism, and a window 15 of the vacuum chamber 1 so that the substrate 7 can be arranged in four steps. And a laser beam irradiation mechanism for irradiating the substrate 7 with the laser beam L through the diffusion plate 16.
As shown in FIGS. 2 and 4, the process P <b> 1 is a process in which the substrate 7 is disposed in the sputtering region on the target 6, but only the sputtering film formation is performed without being irradiated with the laser beam L (film formation process). ). Moreover, the process P2 is a process (laser assist process) which performs only the irradiation of the laser beam L to the board | substrate 7, as shown in FIG. The process P3 is a combination of the process P1 and the process P2, and is a process (laser assist film forming process) in which the sputtering film formation on the substrate 7 and the irradiation with the laser beam L are performed simultaneously. The process P4 is a process in which only the movement of the substrate 7 having a pause process in which neither sputtering film formation nor laser beam L irradiation is performed is performed.
The substrate moving mechanism is configured to horizontally rotate the substrate 7 on a circumference passing directly above the target 6, and the substrate 7 attached to the substrate holder 5 is rotationally moved by the rotation shaft 11.

The laser light irradiation mechanism includes a laser device 12 and an optical system. The usable wavelength range of the laser beam L is from the near infrared region to the ultraviolet region, and as the type of the laser device 12, an excimer laser, an Nd-YAG laser, a semiconductor laser, or the like can be used. Preferably, an excimer laser, an Nd-YAG laser, or the like that can emit ultraviolet light with large absorption in many transparent conductive films is used.
The optical system is configured so that the laser beam L is applied to the substrate 7 immediately above the target 6 shown in FIGS. 1 and 2 or the substrate 7 immediately after the sputtered particles shown in FIGS. It is configured using the reflection mirror 14 or the like, and is provided on the movement locus of the substrate 7 so as to be able to irradiate laser light. The reflection mirror 14 can be adjusted in the horizontal and vertical directions at the same time as it moves back and forth, right and left, and up and down. Switching and adjustment of the irradiation position of the laser beam L are performed by moving the reflecting mirror 14.
Further, the optical system is provided with a beam expander 13 so that the irradiation area of the laser beam L can be adjusted.

  As shown in FIGS. 1 and 2, the window 15 for taking in the laser light L is formed so that the laser light L is irradiated onto the substrate 7 when the substrate 7 comes over the target 6 used for film formation. As shown in FIGS. 3 and 4, the substrate 7 is attached to the lower portion of the vacuum chamber 1 or the like so as to be able to perform only the process of irradiating the substrate 7 with the laser light L. If the sputtering apparatus has a plurality of targets 6, one of them may be removed and a window 15 may be attached to that part. The material of the window 15 is preferably made of quartz or the like so that light from the infrared region to the ultraviolet region can be transmitted.

As shown in FIGS. 1 to 4, the diffusion plate 16 is attached to the outside of the vacuum chamber 1, for example, in front of the window 15. The type of the diffusion plate 16 includes a frost type diffusion plate in which one side of the substrate glass is treated with ground glass (sand surface), a corrosion type diffusion plate in which the surface of the ground glass surface is corroded and smoothed with hydrogen fluoride, and the surface of the substrate glass. An opal diffusion plate provided with a milky white film can be used. Preferably, a frost-type diffusion plate or a corrosion-type diffusion plate using silica glass that can obtain a sufficient diffusion effect even with short-wavelength ultraviolet light or the like is used.
In the figure, 8 is a cathode, and 9 is a gas inlet.

Using the forming apparatus 100 configured as described above, a transparent conductive film is formed.
The sputtering target 6 includes an AZO sintered target obtained by adding Al ₂ O ₃ to ZnO, a GZO sintered target obtained by adding Ga ₂ O ₃ to ZnO, an ITO sintered target obtained by adding SnO ₂ to In ₂ O ₃ , and SnO. _{2 Sb} 2 _{O 3} the ATO sintered target in which, ZnAl alloy target in which Al to Zn, ZnGa alloy target in which Ga to Zn, and the like InSn alloy target in which Sn to in is used. Preferably, a ZnO-based sintered target such as an AZO sintered target or a GZO sintered target is used. In that case, the concentration of Al ₂ O ₃ is preferably 0.2 to 3.0% by weight, and the concentration of Ga ₂ O ₃ is preferably 0.5 to 6.0% by weight.

As the sputtering method, a DC sputtering method, an RF sputtering method, or a DC + RF sputtering method combining these can be used.
As the sputtering gas, an inert gas such as Ar is used. If necessary, an oxidizing gas or a reducing gas may be introduced.
The temperature during film formation is as low as possible. Preferably, film formation is performed without heating.
The distance between the target 6 and the substrate 7 is about 50 to 300 mm at which discharge is stable and the substrate 7 can be irradiated even while the laser beam L is sputtered. Preferably, it is 50-100 mm in which resistance falls.
As the substrate 7, glass, resin, or the like is used, and the four processes P <b> 1 to P <b> 4 described above can be performed separately by performing sputter film formation while moving, such as attaching to the substrate holder 5 and rotating.
The total thickness of the thin film to be formed is preferably 500 nm or more because if the thickness is 500 nm or less, the growth of crystal grains does not proceed sufficiently and surface irregularities are lowered.

The laser light irradiation conditions are such that the oscillation temperature of the laser device 12 and the beam expander are adjusted using a diffusion plate 16 so that the film temperature rises, crystallization is promoted, and the laser power is such that moderate ablation occurs. 13 is set by adjusting the enlargement ratio.
The energy density per unit time and unit area of the laser light applied to the film is preferably 10 mJ / (s · cm ² ) or more and 100 J / (s · cm ² ) or less.
The enlargement ratio of the beam expander 13 is adjusted so as to obtain a target laser irradiation area in consideration of the roughness of the diffusion plate 16 and the diffusion angle.

In the case where the sputter film formation is performed only in the process P3 of performing the sputter film formation while irradiating the laser light L, for example, as shown in FIGS. After adjusting the reflection mirror 14 to irradiate, sputter film formation and laser irradiation are performed simultaneously with the substrate 7 fixed.
In the method of forming the transparent conductive film only in this process P3, as described in the means for solving the problems, the film temperature rise and moderate ablation occur due to the irradiation of the laser beam L. From the film temperature rise, A transparent conductive film having a low resistivity and a high transmittance can be obtained due to the effect of improving the crystallinity and the enlargement of crystal grains, and fine irregularities 21 corresponding to the crystal size can be formed on the surface of the film by appropriate ablation of the film. In addition, a double surface uneven structure in which large unevenness 20 corresponding to the crater-like depression is formed can be configured.

When the sputter film formation is performed by combining the process P1 of only the sputter film formation and the process P3 of performing the sputter film formation while irradiating the laser beam L, for example, as shown in FIG. 1 and FIG. After adjusting the reflection mirror 14 so that the laser beam L is irradiated to the substrate 7 at the top, the substrate 7 smaller than the area of the target 6 is used to adjust the irradiation area of the laser beam L to be the same as the substrate area. In order to prevent the sputtered particles from flying onto the substrate 7, the laser beam L of the laser beam L is reciprocated while reciprocating the substrate 7 within a range of about ¼ circumference of the substrate holder 5 around the center of the target 6. Irradiation and sputter deposition are repeated.
In this case, a portion that is formed without being irradiated with the laser beam L is generated, but since the laser beam is irradiated at the same time as the formation of the film immediately after that, the temperature of the entire film rises and moderate ablation Happens. As a result, a transparent conductive film having a low resistivity and a high transmittance can be obtained in the same manner as in the method using only the step P3. At the same time, in addition to the fine irregularities 21 corresponding to the crystal size on the surface of the film, the crater It is possible to form a double surface concavo-convex structure in which large concavo-convex portions 20 corresponding to the dents are formed.

In the case of performing the combination of the process P1 only for the sputter film formation and the process P2 only for the irradiation with the laser beam L, for example, as shown in FIGS. After adjusting the reflection mirror 14 so that the substrate 7 is irradiated with the laser beam L, the irradiation position of the laser beam L and an appropriate position on the target 6 (the position where the sputtered particles come, for example, the center of the target 6) ), The irradiation of the laser beam L and the sputtering film formation are repeatedly performed while the substrate 7 is reciprocated a plurality of times. Whether or not the sputtered particles are present is determined by fixing the substrate 7 at each position and performing sputter film formation and confirming whether or not the film is attached using a film thickness meter.
In this case, laser light is irradiated after the film is formed. However, since the temperature of the film is increased and appropriate ablation occurs, the resistivity is low and the transmittance is low as in the method using only the step P3. In addition to the fine unevenness 21 corresponding to the crystal size on the surface of the transparent conductive film having a high thickness, a double surface uneven structure in which large unevenness 20 corresponding to the crater-like depression is formed can be configured.

  A process P1 for only sputtering film formation, a process P3 for performing sputtering film formation while irradiating the laser beam L, and a process P4 for performing only the movement of the substrate 7 without performing any of the sputtering film formation and the irradiation with the laser beam L. 1 and 2, for example, as shown in FIGS. 1 and 2, after adjusting the reflection mirror 14, the substrate holder 5 is continuously rotated while laser beam L irradiation and sputtering are performed. Repeat with membrane. When the substrate 7 is at the position of the substrate holder 5 that is about 3/4 of the circumference of the substrate holder 5 from the target 6 on which the sputtering is being performed, film deposition does not occur and the substrate 7 is only rotating.

Since the temperature rise and moderate ablation of the thin film due to the irradiation of the laser beam L occur instantaneously, even if the process P1 only for the sputter film formation and the process P4 for the pause are added, the resistivity is the same as the method using only the process P3. A double surface concavo-convex structure in which large irregularities 20 corresponding to crater-like depressions are formed on the surface of a transparent conductive film with low transmittance and high transmittance in addition to fine irregularities 21 corresponding to crystal size Can do.
In this method, a large number of substrates 7 can be attached to the substrate holder 5 and the process can be repeated while continuously rotating. Therefore, a substrate having a transparent conductive film with low resistance, high transmittance, and appropriate surface irregularities. Can be manufactured in large quantities in a short time.

Sputtering is performed by combining a process P1 only for sputtering film formation, a process P2 only for laser beam L irradiation, and a process P4 for performing only the movement of the substrate 7 without performing any of the sputtering film formation and laser beam L irradiation. A film can also be formed. For example, as shown in FIGS. 3 and 4, after adjusting the reflection mirror 14, the sputter deposition process P <b> 1, the pause process P <b> 4, and the laser beam L irradiation process while the substrate holder 5 is continuously rotated. P2 and the pause process P4 are successively performed.
Also in this case, since the temperature rise of the thin film and moderate ablation occur due to the irradiation of the laser beam L, the crystal size is formed on the surface of the transparent conductive film having a low resistivity and a high transmittance as in the method using only the step P3. In addition to the fine unevenness 21 corresponding to, a double surface uneven structure in which large unevenness 20 corresponding to a crater-like depression is formed can be formed.

  As described above, according to the method for forming a transparent conductive film of the present invention, a transparent conductive film having good crystallinity, a large crystal size, and a double surface uneven structure is formed without heating the substrate. it can. Thereby, the resistance of the transparent conductive film is reduced, the transmittance is increased, and the light confinement effect by the transparent conductive film is improved. Therefore, when such a transparent conductive film is used for a solar cell, photoelectric conversion efficiency can be improved. Moreover, since it can implement by the low-temperature process which does not require a heating in formation of a film | membrane, it is suitable for mass production, and the manufacturing cost of such a board | substrate with a film | membrane and a solar cell using the same can be reduced.

Next, Examples 1 to 5 and Comparative Examples 1 to 3 according to the transparent conductive film forming apparatus of the present invention will be described.
(Example 1-1 and Example 1-2)
1 and FIG. 2, a method according to step P3 in which the substrate 7 is fixed to the center around the center of the target 6 and laser light irradiation and sputtering film formation are simultaneously performed. An AZO transparent conductive film was formed. The sputtering film forming conditions and laser light irradiation conditions are as shown below.

(Sputtering film formation conditions)
Sputtering device: DC magnetron sputtering device (ULVAC CS-200)
Target: AZO (ZnO + 2 wt% Al ₂ O ₃ ) sintered target, sintered density 98.5%
Substrate used: 50 mm x 50 mm x 1 mmt, alkali-free glass target-substrate distance: 60 mm
Magnetic field intensity: 1000 Gauss (directly above the target, vertical component)
Ultimate vacuum: <5 × 10 ⁻⁵ Pa
Sputtering gas: Ar, gas flow rate 100 sccm
Introduced gas: O ₂ , gas flow rate 0-3 sccm
Sputtering pressure: 0.5 Pa
DC power: 200W
Substrate heating: None Film thickness: 500 nm (Example 1-1), 1000 nm (Example 1-2) Film formation time: Determining the film formation rate and setting it to the above film thickness

(Laser irradiation conditions)
Laser: Nd-YAG pulse laser (Spectrophysics QR PRO-290)
Wavelength: 266 nm (4th harmonic)
Oscillation frequency: 10Hz
Expander magnification: 200%
Diffusion plate: Frost type diffusion plate (LSD 0.5U3-φ50 manufactured by Lumine), diffusion angle 0.5 °, diameter 50 mm
Oscillation energy density (unit time, per unit area): 2.0 J / (s · cm ² )
Energy density on substrate (unit time, per unit area): 0.5 J / (s · cm ² )
The energy density of the laser beam on the substrate was obtained by dividing the value of energy measured by installing a power meter for measuring the intensity at that portion by the irradiation area.

  About the obtained sample, the shape observation of the surface and the cross section was performed by SEM (SU8000 made by Hitachi High-Technologies) and a laser microscope (VK-9710 made by Keyence). It was confirmed by a laser microscope that crater-shaped depressions having a diameter of 1 to 100 μm were uniformly distributed, and that the unevenness of the depressions was 0.3 μm to 0.5 μm. In addition, SEM confirmed that fine irregularities having a height difference of 0.05 μm to 0.25 μm corresponding to the crystal grain size were continuously distributed on the irregular surface as seen with a laser microscope. It was. That is, crater-like depressions having a diameter of 1 μm to 100 μm are uniformly formed on the surface, and fine irregularities having a height difference of 0.05 μm to 1 μm are formed along the surface, as shown in FIG. It can be considered that it is such a film.

Further, the resistivity, the maximum height difference PV (Peak-Valley), the arithmetic average surface roughness Ra, and the transmittance of the obtained thin film were measured.
The resistivity was obtained by measuring the film thickness (using a film thickness meter manufactured by ULVAC, DEKTAK) and measuring the sheet resistance by a four-probe method (using a resistance measuring instrument manufactured by Mitsubishi Chemical, RORESTER). The maximum height difference PV and the arithmetic average surface roughness Ra were evaluated by AFM measurement (atomic force microscope manufactured by Seiko Instruments Inc., using SPI4000). The transmittance (average value in the wavelength range of 400 to 1000 nm) was determined by a spectrophotometer (using a spectrophotometer manufactured by Hitachi High-Technologies Corporation, U4100).

  Moreover, the transparent conductive film board | substrate similar to these samples was produced, the thin film Si solar cell was produced simply using this board | substrate, and the photoelectric conversion efficiency was calculated | required. The thin-film Si solar cell is formed by sequentially forming amorphous p-type Si (boron (B) doped) and n-type Si (phosphorus (P) doped) on a transparent conductive film using a CVD apparatus. It was performed by forming ITO and Ag in this order as a back electrode on the top by sputtering. Photoelectric conversion efficiency was measured using a solar simulator and an IV tracer (using a solar cell performance evaluation system manufactured by Eihiro Seiki Co., Ltd.).

(Example 2-1 and Example 2-2)
1 and 2, the substrate 7 is reciprocated within the range of about ¼ circle of the substrate holder 5 around the center of the target 6, and only the sputtering film formation is performed. An AZO transparent conductive film was produced by a method including two steps of step P1, step P3 of simultaneously performing laser light irradiation and sputtering film formation.
The sputtering film forming conditions, the laser light irradiation conditions, and the evaluation method are the same as those in Example 1. Moreover, the thin film Si solar cell was simply produced using the formed transparent conductive film substrate, and the photoelectric conversion efficiency was calculated | required. The production method and the evaluation method are the same as those in Example 1.

(Example 3-1 and Example 3-2)
Using the forming apparatus 100 having the configuration shown in FIG. 3 and FIG. 4, the process P <b> 1 of only the sputter film formation is performed while reciprocating the substrate between the position immediately after the sputtered particles no longer fly and the immediately above the center of the target. The AZO transparent conductive film was prepared by a method including the process P2 and the process P2 of only laser light irradiation.
The sputtering film forming conditions, the laser light irradiation conditions, and the evaluation method are the same as those in Example 1. Moreover, the thin film Si solar cell was simply produced using the formed transparent conductive film substrate, and the photoelectric conversion efficiency was calculated | required. The production method and the evaluation method are the same as those in Example 1.

(Example 4-1 and Example 4-2)
Using the forming apparatus 100 having the configuration shown in FIGS. 1 and 2, while rotating the substrate, the step P1 of only sputtering film formation, the step P3 of simultaneously performing laser beam irradiation and sputtering film formation, and film deposition and laser light An AZO transparent conductive film was produced and evaluated by a method including three steps of rotation P4 that does not include any step of irradiation and only rotation. The sputtering film forming conditions, the laser light irradiation conditions, and the evaluation method are the same as those in Example 1.
Moreover, the thin film Si solar cell was simply produced using the formed transparent conductive film substrate, and the photoelectric conversion efficiency was calculated | required. The production method and the evaluation method are the same as those in Example 1.

(Example 5-1 and Example 5-2)
3 and 4, a method including three steps: a process P1 only for sputter film formation, a process P2 only for laser light irradiation, and a process P4 only for rotation while rotating the substrate using the forming apparatus 100 having the configuration shown in FIGS. Thus, an AZO transparent conductive film was prepared, and the film was evaluated. The sputtering film forming conditions, the laser light irradiation conditions, and the evaluation method are the same as those in Example 1.
Moreover, the thin film Si solar cell was simply produced using the formed transparent conductive film substrate, and the photoelectric conversion efficiency was calculated | required. The production method and the evaluation method are the same as those in Example 1.

(Comparative Example 1-1 and Comparative Example 1-2)
Using only the sputtering part of the apparatus shown in FIGS. 1 and 2, the substrate is fixed by a normal sputtering method without performing laser light irradiation, and an AZO transparent conductive film is formed, and the characteristics of the film are evaluated. did. The sputtering film forming conditions and the evaluation method are the same as those in Example 1.
Moreover, the thin film Si solar cell was simply produced using the formed transparent conductive film substrate, and the photoelectric conversion efficiency was calculated | required. The production method and the evaluation method are the same as those in Example 1.

(Comparative Example 2-1 and Comparative Example 2-2)
1 and 2 is used to remove the diffusion plate 16 and form an AZO transparent conductive film while irradiating the laser beam without passing through the diffusion plate 16 to evaluate the characteristics of the film. did. The sputtering film forming conditions, the laser light irradiation conditions, and the evaluation method are the same as in Example 1 except that there is no diffusion plate.
Moreover, the thin film Si solar cell was simply produced using the formed transparent conductive film substrate, and the photoelectric conversion efficiency was calculated | required. The production method and the evaluation method are the same as those in Example 1.

(Comparative Example 3)
Using a CVD apparatus, the substrate is heated to 500 ° C. on a 50 mm × 50 mm × 1 mmt non-alkali glass substrate, stannic chloride, water, methanol and hydrogen fluoride are introduced, and a 1 μm-thick FTO film is formed. A transparent conductive film was produced. The obtained film was evaluated in the same manner as in Example 1.
Moreover, the thin film Si solar cell was simply produced using the formed transparent conductive film substrate, and the photoelectric conversion efficiency was calculated | required. The production method and the evaluation method are the same as those in Example 1.
These evaluation results are shown in Table 1.

As shown in Table 1, the photoelectric conversion efficiency of the solar cells produced using the transparent conductive films of Examples 1 to 5 can be larger than that produced using the transparent conductive films of Comparative Examples 1 to 3. It could be confirmed. In particular, in Example 1 in which the AZO transparent conductive film was formed by the method according to Step P3 in which laser beam irradiation and sputtering film formation were performed simultaneously, the resistivity was the lowest among Examples 1 to 5, and the maximum height difference PV And the value of arithmetic average roughness Ra was large, and the photoelectric conversion rate became the highest.
Further, in Examples 1 to 5 and Comparative Examples 1 and 2 in which two types of samples having different film thicknesses were formed, the resistance was lower when the film thickness was 1000 nm than when the film thickness was 500 nm. It was confirmed that a transparent conductive film having a large maximum height difference PV (large surface irregularities) can be formed.

In Comparative Example 1 formed without performing laser light irradiation, the resistivity is higher and the transmittance is lower than in Examples 1 to 5, and the PV value and arithmetic average roughness Ra are small. The photoelectric conversion efficiency was also low.
Further, in the comparative example 2 in which the laser light is directly irradiated without passing through the diffusion plate, the transmittance is increased with a low resistance compared to the case of the comparative example 1 in which the laser light is not irradiated. Although some improvement in photoelectric conversion efficiency could be confirmed, the PV value was lower and the photoelectric conversion efficiency was lower than in Examples 1 to 5.
Moreover, in Comparative Example 3 in which the FTO film was formed, the resistivity was higher and the transmittance was lower than in Examples 1 to 5 in which the AZO transparent conductive film was formed with the same film thickness of 1000 nm, and the photoelectric conversion efficiency was high. Was also low.

  As described above, in the method of the present invention, it is possible to form a transparent conductive film having appropriate surface irregularities with low resistivity and high transmittance. When such a transparent conductive film is used in a solar cell, Conversion efficiency can be improved.

In addition, this invention is not limited to the thing of the structure of the said embodiment, In a detailed structure, it is possible to add a various change in the range which does not deviate from the meaning of this invention.
For example, in the above-described embodiment, an AZO transparent conductive film is formed using an AZO sintered target as a target. However, in addition to AZO, ITO or FTO sintered targets are formed by sputtering according to the method of the present invention. Thus, a transparent conductive film having good crystallinity, a large crystal size, and a double surface uneven structure can be formed without heating the substrate.

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Vacuum pump 4 DC, RF power supply 5 Substrate holder 6 Target 7 Substrate 8 Cathode 9 Gas inlet 11 Substrate holder rotating shaft 12 Laser apparatus 13 Beam expander 14 Reflection mirror 15 Quartz window 16 Diffuser plate L Laser light

Claims (9)

A method of forming a transparent conductive film on the surface of a substrate by sputtering in one vacuum chamber, wherein a laser assisted film forming step is performed on the surface of the substrate while irradiating a laser beam through a diffusion plate. Yes and will be, causing the ablation to the membrane by irradiation of the laser light to form a crater-like depressions, in addition to the fine unevenness corresponding to the film surface upon crystal size, large irregularities corresponding to the crater-like recesses Forming a transparent conductive film. One in a vacuum chamber, a film forming step of forming a thin film on the surface of the substrate by a sputtering method, and have a and laser-assisted film deposition process which forms while irradiating a laser beam through the diffuser to the surface of the thin film The film is ablated by irradiation with the laser beam to form a crater-shaped depression, and in addition to the fine irregularities corresponding to the crystal size on the film surface, large irregularities corresponding to the crater-shaped depression are formed . A method for forming a transparent conductive film.   The method for forming a transparent conductive film according to claim 2, wherein the film forming step and the laser assisted film forming step are repeated. One in a vacuum chamber, a film forming step of forming a thin film on the surface of the substrate by a sputtering method, will be closed and the laser-assisted step of irradiating laser light through the diffusing plate to the thin film, by irradiation of the laser beam A transparent conductive film characterized in that a film is ablated to form a crater-shaped depression, and the film surface is formed with large irregularities corresponding to the crater-shaped depression in addition to fine irregularities corresponding to the crystal size. Forming method.   The method for forming a transparent conductive film according to claim 4, wherein the film forming step and the laser assist step are repeated.   6. The method for forming a transparent conductive film according to claim 2, further comprising a pause step in which neither sputtering film formation nor laser beam irradiation is performed. A transparent conductive film produced by the method for forming a transparent conductive film according to claim 1, wherein a crater-shaped depression having a diameter of 1 μm to 100 μm is uniformly formed on the surface. A transparent conductive film characterized in that fine irregularities having a height difference of 0.05 μm or more and less than 1 μm are formed along the surface, and the resistivity is 1 × 10 ⁻³ Ω · cm or less. .   The transparent conductive film according to claim 7, wherein the film thickness is 500 nm or more. An apparatus for carrying out the method for forming a transparent conductive film according to any one of claims 1 to 6, wherein the substrate moves to move the vacuum chamber and the substrate through the sputtering region in the vacuum chamber. An apparatus for forming a transparent conductive film, comprising: a mechanism; and a laser light irradiation mechanism provided so as to be capable of irradiating a laser beam through a diffusion plate on the movement region of the substrate other than the sputtering region or the sputtering region.

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