WO2006103966A1 - METHOD FOR FORMING In-Ga-Zn-O FILM AND SOLAR CELL - Google Patents

Abstract

Disclosed is a method for rapidly and stably forming an In-Ga-Zn-O film. A first target composed of an In-Ga oxide and a second target composed of a Zn oxide are arranged in a cover (26), and a substrate (1) is arranged above these targets. After creating a vacuum in the cover (26), a mixed gas obtained by adding oxygen in an inert gas is introduced into the cover (26). Pulse-packet voltages are alternately applied to the target (21a) and the target (21b). The emission wavelengths and luminous intensities of the discharges of In, Ga and Zn during sputtering of the targets (21a, 21b) are sensed by PEM (31a, 31b). The sputtering speeds of the targets (21a, 21b) are calculated; and the pulse power, pulse amount and pulse width applied to the targets (21a, 21b), the amount of oxygen supplied into the cover (26) and the pressure within the cover are controlled based on the results of the calculation.

Description

 Specification

 In-Ga-Zn- ○ film formation method and solar cell

 Field of Invention

 The present invention relates to a method for forming an In—Ga—Zn_O film at high speed and stably. The present invention relates to a solar cell, and more particularly to a pn junction solar cell.

 Background of the Invention

[0002] <Film formation method>

 Oxide semiconductors are indispensable materials for realizing electronic and optical devices with new physical properties. For example, TiO is an n-type oxide semiconductor whose thin films and particles are photocatalysts and

 2

 It is used as an optical film with high refractive index. In recent years, dye-sensitized solar cell power using titanium dioxide has been attracting attention as an inexpensive and clean solar cell (for example, Japanese Patent Application Laid-Open No. 2003-123853).

 [0003] In addition, a transparent oxide semiconductor composed of In—Ga—Zn—O is also an indispensable material for an electronic optical device. Recently, it has been shown that the oxide of In—Ga—Zn—O has a large field effect mobility even in an amorphous state, and succeeded in producing a field effect transistor (FET) on PET (Nature 2004 432).ペ ー ジ page 488).

 [0004] When forming this In—Ga—Zn—O film, a ceramic target is used, and the sputtering is performed in an oxygen-containing atmosphere using an RF sputtering method in which film formation is performed using an RF power source or a metal target. The reactive sputtering method is used. In addition, the film can be deposited by pulsed laser deposition.

 [0005] The conventional method has a low film formation rate and poor productivity. Further, stable composition control is difficult and it is difficult to maintain the characteristics.

[0006] For example, the reactive sputtering method in which sputter film formation is performed in an oxygen-containing atmosphere using a metal target has a low film formation speed and poor productivity because the target is coated with an oxide. Further, when a large voltage is applied to the target coated with an oxide, an arc is generated and a stable discharge cannot be obtained. On the other hand, when an alloy target is used, the sputtering rate differs for each metal element, so that the composition of the target and the composition of the resulting film are shifted. Powerful composition control is difficult. It is also difficult to control the amount of oxygen in the film. In addition, when RF sputtering using a ceramic target is performed, the deposition rate is slow and productivity is poor.

[0007] <Solar cell>

 I. Conventional materials used for solar cells include silicon (monocrystalline Si, polycrystalline Si and amorphous Si), GaAs, CuInSe and CdTe. Of these, silicon solar cells and GaAS solar cells have high conversion efficiency but are expensive. On the other hand, CuInSe-based and CdTe-based solar cells are relatively inexpensive, but materials such as selenium and cadmium are toxic, causing environmental problems when mass-produced and widely used.

 II. Dye-sensitized solar cells using titanium dioxide have attracted attention as inexpensive and clean solar cells, and various proposals have been made (for example, JP-A-2003-123853). Titanium dioxide is a material that shows almost no response to visible light and has a response only to ultraviolet light because its band gap is about 3.2 eV. Therefore, in dye-sensitized solar cells, visible light response is improved by adsorbing organic dyes that absorb visible light to the surface of titanium dioxide, and high conversion efficiencies of up to about 10% are achieved. However, the fundamental problem with dye-sensitized solar cells is that conversion efficiency varies greatly depending on the amount of dye adsorbed, and it is necessary to use an electrolyte solution, which makes packaging difficult. , Etc.

 [0009] III. Transparent pn-junction solar cell with a combination of CuAlO / Zn〇 and compatible with ultraviolet light

 2

 Has been proposed. We also offer a pn junction solar cell consisting of a combination of Cu 2 O / ZnO.

 2

 It has been proposed. CuAlO or CuO functions as a p-layer and a light-absorbing layer.

 twenty two

 Function. During light irradiation, solar cell characteristics are developed by generating electrons and holes at the pn interface by photoexcitation.

 Patent Document 1: Japanese Unexamined Patent Publication No. 2003-123853

 Non-Patent Document 1: Nature 2004 432 卷 488 pages

 Patent Document 2: Japanese Patent Laid-Open No. 2003-123853

 Summary of the Invention

[0010] The present invention solves the above problems and forms an In—Ga—Zn—O film stably at high speed. The primary purpose is to provide a method.

In the first aspect of the present invention, the In—Ga—Zn—O film is formed by sputtering using a target in an atmosphere containing oxygen gas. In the method of forming a film, a plurality of the targets are provided, and each target is a metal, alloy, or oxide composed of at least one of In, Ga, and Zn, and includes In, Ga, and Zn. Each is contained in at least one of the targets, and at least one of the targets has a composition different from that of the other targets, and sputtering is performed by alternately applying an intermittent voltage to each target. It is characterized by.

[0012] A second object of the present invention is to provide a solar cell with high conversion efficiency.

[0013] The solar cell of the second aspect is a pn junction solar cell in which a p layer and an n layer are stacked, wherein the p layer is made of Cu 2 O, and the n layer is made of In_Ga_Zn_O in an amorphous state.

 2

 Features.

 Brief Description of Drawings

 FIG. 1 is a schematic diagram for explaining a dual force sword type magnetron sputtering method.

 FIG. 2 is a diagram for explaining an example of a voltage applied to the target electrode in FIG.

 FIG. 3 is a schematic cross-sectional view of a solar cell according to an embodiment.

 FIG. 4 is a schematic cross-sectional view of solar cells according to different embodiments.

 Detailed description

 [0015] The film formation method of the first aspect is a method of forming an In-Ga-Zn-O film by sputtering using a target in an atmosphere containing oxygen gas. Several targets are provided, and each target is a metal, alloy or oxide composed of at least one of In, Ga and Zn, and each of In, Ga and Zn is contained in at least one of the targets. At least one of the targets has a composition different from that of the other targets, and sputtering is performed by alternately applying an intermittent voltage to each target.

[0016] ₁ 1 1-0 & — 2 ₁ 1—O in the first aspect, there are a plurality of targets, and intermittent voltage is alternately applied to each target. Target large current to apply In this way, stable high-speed film formation can be performed.

 [0017] Further, since abnormal discharge can be significantly suppressed by using this method, stable long-time discharge is possible, and a high-quality film with little damage can be produced.

 [0018] When the In_Ga_Zn_O film is formed by the reactive sputtering method using a single composition target, the target composition and the composition of the resulting film are usually different because the sputtering rate differs for each metal element. And fine composition control is difficult.

 [0019] In the method of the present invention, sputtering is performed using a plurality of targets having different compositions. Therefore, by adjusting the sputtering amount of the target of each composition and controlling the sputtering ratio of the metal element, the In_Ga_Zn_ of the desired composition is obtained. -A film can be easily formed.

 [0020] Each of the targets may be a metal or oxide made of any one of In, Ga, and Zn, and the amount of sputtering of each metal can be increased or decreased independently. Therefore, an In_Ga_Zn_O film with a controlled composition can be formed more easily.

 [0021] It should be noted that the film may be formed using a plurality of targets containing In, Ga and Zn and having different compositions, and a target made of an alloy of In and Ga or ceramics. The film may be formed using a metal or oxide target made of Zn.

 [0022] A pulse packet composed of a plurality of pulse voltages may be alternately and intermittently applied to each target, thereby allowing a larger current to flow than when applying a single pulse to each target. And stable high-speed film formation is possible.

 Even if a positive voltage is intermittently applied to the target to prevent charging of the target, a large current can be passed through each target, and stable high-speed film formation is possible.

 [0024] The emission wavelength and emission intensity of the discharge of In, Ga, and Zn during sputtering may be monitored, whereby the amount of sputtering of In, Ga, and Zn can always be accurately recognized. Therefore, the In—Ga—Zn—O film can be formed accurately and stably by controlling the film formation conditions based on the monitoring result.

[0025] The emission wavelength and emission intensity of the discharge of In, Ga, and Zn may be monitored for each target using a monitor. This makes it possible to individually recognize the discharge status of each target. wear.

 [0026] Based on the monitoring, at least one of the pulse power, the pulse amount, the pulse width, the pressure during film formation, and the oxygen supply amount applied to each target may be changed. And crystallinity can be precisely controlled.

 [0027] In particular, when the supply amount of oxygen becomes excessive, the surface of the target is completely oxidized, and the film formation rate becomes very slow. On the other hand, if the amount of oxygen introduced is too small, the target surface is not oxidized and film formation is performed. As a result, the amount of oxygen during film formation is insufficient. However, as described above, since the oxygen supply amount is controlled based on the monitoring, an appropriate amount of oxygen can be introduced based on the densities of In, Ga, and Zn in the plasma. This enables sputtering in the “transition region”, which is an intermediate region between the two oxygen supply amount regions. As a result, a film containing an appropriate amount of oxygen can be formed at high speed.

 [0028] By adjusting the temperature of the substrate during sputtering, the crystallinity of the deposited film may be controlled, whereby the crystallinity of the In-Ga-Zn-O film can be controlled.

 [0029] The substrate temperature during sputtering may be adjusted to 77K to 300K. This reduces the agglomeration energy of sputtered particles that have reached the surface of the In—Ga—Zn—〇 film, resulting in film uniformity. And the surface flatness of the film can be improved.

 Hereinafter, embodiments of the first aspect of the present invention will be described in detail with reference to the drawings.

 [0031] FIG. 1 is a schematic diagram for explaining a method of forming an In—Ga—Zn—O film according to the embodiment of the first aspect by a dual force sword magnetron sputtering method, and FIG. It is a figure explaining an example of the voltage applied to the target electrode of.

As shown in FIG. 1, a first sputtering unit is composed of a target electrode 20A in which a first target 21a is provided on a support 20a, and a magnet 22a disposed below the target electrode 20A. In addition, a second sputtering unit is constituted by a target electrode 20B in which a second target 21b is provided on a support 20b and a magnet 22b disposed below the target electrode 20B. The first sputtering unit and the second sputtering unit are installed adjacent to each other, and an AC power supply 25 is connected to these sputtering units via a switching unit 24. In the present embodiment, the first target 21a is made of an oxide of Ιη—Ga, and the second target 21a. b is made of ZnO. In addition, since each target is not completely oxidized, conductivity is sufficiently ensured.

[0033] These target electrodes 20A, 20B are covered with a cover 26. The cover 26 is connected to a pump (not shown) via an exhaust port 28, and connected to a gas supply source (not shown) via a gas inlet 27.

[0034] Collimators 30a and 30b are provided in the cover 26, and these collimators 30a and 30b are respectively connected to a plasma emission monitor via a not-shown filter, a filter, and an optical amplifier tube.

(Hereinafter referred to as PEM.) Connected to 31a and 31b. These collimators 30a,

The first monitor and the second monitor are composed of 30b, a fineletter, a photomultiplier tube, and PEMs 31a and 31b.

 The PEM is an apparatus that monitors an electrical signal obtained by condensing plasma emission with a collimator and photoelectrically converting it with a photomultiplier tube (PM). PEM is set to a certain sensitivity and monitors the emission intensity of the plasma.

 [0036] As the filter for the target 21a, a filter that can selectively pass at least wavelengths of 23.06 nm and 209. lnm of emission spectra of In and Ga is used. As the filter for the target 21b, a filter that can selectively pass at least wavelengths of 202.5 nm, 213 nm, and 334 nm of the emission spectrum of Zn is used.

 [0037] When forming an In—Ga—Zn—O film using the above apparatus, first, the substrate 1 is placed above the targets 21a, 21b in the cover 26, and the inside of the cover 26 is evacuated by a pump. After that, a mixed gas containing oxygen in an inert gas such as argon is introduced into the cover 26, and the inside of the cover 26 is brought to a predetermined pressure.

 [0038] As the substrate 1, for example, glass such as alkali silicate glass, non-alkali glass, or quartz glass can be used. Also, various plastic substrates such as acrylic can be used. A polymer film substrate such as PET can also be used. The thickness of the substrate is generally 0.1 to 10mm, preferably 0.3 to 5mm. The glass plate is preferably chemically or thermally reinforced.

Next, as shown in FIG. 2, for example, a voltage in the form of a pulse packet is alternately applied to the target electrodes 20A and 20B to form a glow discharge. As a result, the grains from the targets 21a and 21b The child is sputtered and the particles adhere to the substrate 1 above the targets 21a and 21b. At this time, the targets 21a and 21b or the sputtered particles are oxidized by oxygen gas.

 [0040] The emission wavelength and emission intensity of the In, Ga, and Zn discharges during sputtering of the targets 21a and 21b become electrical signals via the collimators 30a and 30b, the filter, and the optical amplification tube, and are detected by the PE M31a and 31b Is done. From these electric signals, the sputtering speed of the first target 21a and the sputtering speed of the second target 21b are calculated. Based on the calculation result, the pulse power applied to each target 21a, 21b, the pulse amount and the pulse width, the oxygen amount introduced into the cover 26, and the pressure in the cover are controlled.

 [0041] The pulse power, the pulse amount, and the pulse width vary depending on the target volume, the volume in the cover 26, the required film formation speed, etc. For example, the no power is lkW to 20kW, and the pulse amount is 5%. ~ 50%, pulse width is controlled within the range of 0.:!~500msec. If the panoramic power is 50 kW or more, abnormal discharge occurs and an N-doped ZnO film with a precisely controlled composition cannot be stably formed, while the pulse power is 500 W or less. The deposition speed is slow. If the no-reel amount is 90% or more, continuous discharge occurs. On the other hand, if the amount is 1% or less, the film formation rate becomes slow.

 [0042] The oxygen supply amount is, for example, about:! To 50 sccm. If the amount of oxygen introduced is excessive, the surfaces of the targets 21a and 21b are completely oxidized, and the film formation rate becomes very slow. Such a region where the amount of introduced oxygen is excessive is referred to as a “reactive sputtering region”. On the other hand, if the amount of oxygen introduced is too small, the target surface is not oxidized and film formation is performed. As a result, the amount of oxygen in the film is insufficient. Such a region is referred to as a “metallic sputter region”. In the present embodiment, an appropriate amount of oxygen is introduced based on the density of In, Ga, and Zn in the plasma by the above control.

 [0043] The pressure in the cover 26 during the film formation is preferably controlled within a range of 0.01 to 30 Pa, particularly 0.1 to 10 Pa.

 [0044] After the In_Ga_Zn_ ○ film formed on the substrate 1 reaches a predetermined thickness, the sputtering is finished.

Then, the inside of the cover 20 is set to atmospheric pressure, and the substrate 1 on which the In_Ga_Zn_ ○ film is laminated is taken out.

[0045] As the film thickness of the In_Ga_Zn_O film, for example, a film having a thickness of about 5 mm to 5 μm can be formed. In the In—Ga—Zn—O film forming method according to the present embodiment, an intermittent voltage is alternately applied to the targets 21a and 21b, so that a large current flows through the targets, Stable high-speed film formation can be performed. As described above, by performing such high-speed film formation, new metal particles can fly and cover the surface before the oxidation reaction takes place preferentially on the sample surface. Oxygen can be taken into the film, and the In-Ga-Zn_O film can be formed at high speed and reliably. Also, by using this method, abnormal discharge can be greatly suppressed, so that stable long-time discharge is possible and a high-quality film with less damage can be produced.

 [0047] Further, as shown in FIG. 2, by applying a pulse packet to each target 21a, 21b, a single pulse is applied to each target 21a, 21b. Larger current can be applied compared to when a single pulse is applied to 21b, and stable high-speed film formation is possible.

 [0048] In the present embodiment, by monitoring the emission wavelength and emission intensity of the discharge of In, Ga, and Zn during sputtering, the amount of sputtering of In, Ga, and Zn is always accurately recognized. can do. Therefore, by controlling the film formation conditions based on the results of this monitoring, an In—Ga—Zn—O film with a controlled composition can be formed accurately and stably.

 When the ratio of In to Ga in the obtained film is different from the desired ratio, the composition was controlled by using an appropriate InGa content ratio as the first target. In Ga—Zn—O film can be formed accurately and stably.

 [0049] In the present embodiment, the same number (two) of monitors as the targets 21a and 21b are provided, and the emission wavelengths and the emission intensities of the In, Ga, and Zn discharges in the targets 21a and 21b correspond to each other. Since monitoring is performed using a monitor, the discharge status of each target 21a, 21b can be recognized individually.

 [0050] In the present embodiment, a composition to be formed by changing the pulse power, the pulse amount, the pulse width, and the pressure during film formation applied to each target 21a, 21b based on monitoring. And crystallinity can be precisely controlled.

[0051] In the present embodiment, the oxygen supply amount is controlled based on monitoring. Thus, the oxygen supply amount can be precisely controlled. Therefore, it is possible to stably supply an In—Ga—Zn—O film whose oxidation number is precisely controlled. Further, by supplying an appropriate amount of oxygen, sputtering in the “transition region” becomes possible. As a result, a film containing an appropriate amount of oxygen can be formed at a high speed.

 [0052] In addition, when the In_Ga_Zn_O film is formed by controlling the oxygen supply amount using a conventional flow meter, it is difficult to stably control the oxidation number of the In_Ga_Zn_O film. This is because, for example, the film formation rate changes as the target is consumed, and the sputtering conditions such as the oxygen flow rate during film formation change. In this embodiment, the emission wavelengths and amounts of In, Ga, and Zn in the first and second targets 21a, 21b are monitored during film formation, and the inside of the chamber is determined from the density of In, Ga, and Zn in the plasma. Since Plasma Emission Monitor Control (PEM control) is used to control the amount of oxygen introduced into the substrate, it is possible to stably form an In_Ga_Zn_0 film in which the number of oxygen atoms is controlled.

 The above embodiment is an example of the present invention, and the present invention is not limited to the above embodiment. For example, a force that applies a negative voltage to a normal target may be intermittently applied with a positive voltage to prevent the target from being charged. In this case, since the charge accumulated in the target due to the negative voltage is eliminated by the positive voltage, formation of an insulating film such as an oxide on the edge of the target during sputtering can be suppressed. As a result, a large current can flow through each target, and stable high-speed film formation is possible.

 [0054] The crystallinity of the In-Ga-Zn-O film may be controlled by adjusting the temperature of the substrate during sputtering.

 In particular, the substrate temperature during sputtering may be adjusted to 77K to 300K. In this case, the agglomeration energy of the sputtered particles reaching the surface of the In—Ga—Zn—O film is reduced, and the uniformity of the film is reduced. The surface flatness of the film can be improved.

 [0055] In the above embodiment, a force using the bipolar dual magnetron sputtering method in which the common switching unit 24 is installed in the two sputtering units. The unipolar dual magnetron in which the switching unit is individually installed in each sputtering unit. A sputtering method may be used.

[0056] In the above embodiment, the first target made of In-Ga oxide and the first target made of Zn oxide. For example, a first target made of In, a second target made of Ga, and a third target made of Zn may be used. ,. In this case, the spatter amount of each metal can be individually adjusted by changing any of the pulse power, pulse amount, and pulse width of each target, so the composition of the In_Ga_Zn_〇 film can be easily controlled. It is.

 [0057] Alternatively, a plurality of In_Ga_Zn oxides having different compositions may be used as a target. For example, an alloy having a larger In content ratio than the content ratio of In, Ga and Zn in the desired In_Ga_Zn_〇 film as the first target is used, and the desired In_Ga_Zn_〇 as the second target. Use an alloy with a large Ga content ratio compared to the In, Ga, and Zn content ratio in the film, and use Zn as the third target in comparison with the In, Ga, and Zn content ratio in the desired In_Ga_Zn_ film. An alloy with a large content ratio may be used. In this case as well, the spatter amount of each metal can be adjusted by changing any of the pulse power, pulse amount, and pulse width of each target, so the composition of the In-Ga-Zn-O film can be controlled. Is easy.

 [0058] Hereinafter, the ability to explain Examples:! To 3 and Comparative Examples 1 and 2 The first aspect of the present invention is not limited to Examples 1 to 3.

 <Example 1>

 Film formation was performed using the apparatus shown in FIG. The first target is an In—Ga oxide target (100 mm φ X thickness 5 mm) consisting of In50 atm% and Ga 50 at m%, and the second target is a Zn oxide target (100 mm φ X thickness 5 mm). Was used. Corning 7059 alkali-free glass (length 80 mm x width 25 mm x thickness 1 · 1 mm) was used for the substrate.

[0060] First, the substrate is put inside the cover, introduced after the inside of the cover below the vacuum 5 · 0 X 10- ⁴ Pa by the pump, argon 80 sccm, the mixed gas composed of oxygen 20sccm in the cover 26 did. Then, 111_0 & _211_0 films were fabricated by alternately applying a pulsed voltage to each target electrode.

 [0061] Pulse frequency is 50 Hz, applied power is about lkW X 2 target, pulse duty ratio is Zn

 : InGa = 50: 50. The pressure during film formation was 0.7 Pa.

[0062] The thickness of the obtained film was measured using Dektak 6M manufactured by Veeco, and the film formation rate at the time of film formation was calculated to be 62.6 nmZmin. In addition, the XRD crystal structure of the obtained film As a result of structural analysis, it was confirmed to be in an amorphous state.

 As a result of composition analysis by EDX, the obtained film composition was 111: 0 &: 211 = 1.1: 1.0: 0.9.

 The surface roughness of the film obtained using Dektak 6M was measured and found to be 6.2 nm.

<Example 2>

Based on the results of Example 1, except that the pulse duty ratio was changed to Zn: InGa = 53:47, an In-Ga-Zn-O film was prepared in the same manner as in Example 1, and the composition analysis was performed by EDX. It was. As a result, the obtained film composition was 111: 0 &: 2 ₁ 1 = 1.1: 1.0: 1.0.

<Comparative Example 1>

 Only one In-Ga-Zn alloy target (composition ratio: In: Ga: Zn = 1: 1: 1 (atm%)) was used, and Example 1 was applied except that DC 200 W was applied to the target. Samples were prepared in the same manner, and the film thickness was measured in the same manner as in Example 1 to calculate the film formation rate. As a result, the deposition rate was 8.7 nm / min, which was extremely slow.

<Comparative Example 2>

 A sample was prepared in the same manner as in Comparative Example 1 except that DC 300 W or more was applied to the target. The state of discharge during film formation became extremely unstable.

<Example 3>

 A sample was prepared in the same manner as in Example 1 except that the substrate temperature during film formation was adjusted to 223 k (−50 ° C.). The film thickness was measured in the same manner as in Example 1, and the film formation rate was calculated to be 65. InmZ mm.

 [0068] Further, when an XRD crystal structure analysis was performed on the obtained film, it was confirmed to be in an amorphous state.

As a result of composition analysis by EDX, the obtained film composition was 1 ₁ 1: 0 &: 2 ₁ 1 = 1.1: 1.0: 0.9.

 The surface roughness of the film obtained by Dektak 6M was measured and found to be 5.9 nm.

[0070] The solar cell of the second aspect is a pn junction solar cell in which a p layer and an n layer are stacked. The p layer is made of Cu 2 O, and the ₁₁ layer is in the amorphous state 111-0 & -211

2

 Features.

 [0071] In the solar cell of the second aspect, since In-Ga-Zn_0 in an amorphous state is used as the n layer, discontinuities, such as voids, are generated at the junction interface between the n layer and the p layer. This is prevented and a good bonding interface is formed, whereby a large conversion efficiency can be obtained.

 [0072] Since In_Ga_Zn_O has a large electron mobility even in an amorphous state, a large conversion efficiency can be obtained also from this point that electric power can be easily extracted.

 [0073] Furthermore, since it is only necessary to form In-Ga-Zn-O in an amorphous state, In-Ga_Zn_O can be formed on the p-layer at a low temperature. For this reason, there is no significant modification such as grain growth in the Cu layer of the p layer due to heating when forming the n layer.

 2

 It is possible to prevent the bonding interface from deteriorating, thereby obtaining a large conversion efficiency.

[0074] The solar cell of the present invention includes a first electrode made of an indium tin oxide substrate, the p layer made of CuO formed on the indium tin oxide substrate, and the p layer. Been formed

 2

 You may have the said n layer which consists of In-Ga-Zn-0, and the 2nd electrode formed on this n layer.

 [0075] Further, the solar cell of the present invention is formed on a first electrode made of a Cu plate, the p layer made of CuO formed by oxidizing the surface of the Cu plate, and the p layer. In—Ga—Zn—O

 2

 And an electrode film made of indium tin oxide formed on the n layer, and a second electrode formed on the electrode film. Thus, by oxidizing the Cu plate, the first electrode and the p layer made of CuO can be easily formed. N

 2

 By forming an electrode film made of indium tin oxide between the layer and the second electrode, the series resistance component can be greatly reduced, and as a result, the conversion efficiency can be improved.

 [0076] Since In_Ga_Zn_O is in an amorphous state and can be formed on the p layer at a low temperature, the p layer or the n layer may be formed on an inexpensive polymer substrate. ). In this case, the low cost of the solar cell can be achieved.

[0077] The p layer and n layer of this solar cell are formed by sputtering, reactive sputtering, CVD, or vapor deposition. It can be easily formed by the method.

 [0078] The composition of the n layer is 8 to 67 atm% for In, 8 to 67 atm% for Ga, and 8 to 67 atm% for Zn, where the total of In, Ga and Zn in the n layer is 100 atm%. Thus, an amorphous state with a high electron mobility can be easily obtained. In addition, it has sufficient visible light transmission, which prevents light from entering the CuO layer, which is a light absorption layer.

 2

 [0079] This solar cell preferably has a conversion efficiency of 0.67% or more.

 [0080] When the average particle size of the p layer is 10 nm to 10 µm, the hole mobility is further increased, and the interfacial bonding property between the p layer and the n layer is improved.

Hereinafter, an embodiment of the second aspect of the present invention will be described with reference to the drawings.

FIG. 3 is a schematic cross-sectional view of a solar cell according to an embodiment of the second aspect. The solar cell 30 includes a transparent conductive substrate 31, a P layer 32 and an n layer 33 formed on the transparent conductive substrate 31 by sputtering, and a metal electrode 34 provided on the n layer 33. It consists of.

 A conductive wire 36 is bonded to the surfaces of the transparent conductive substrate 31 and the electrode 34.

As the transparent conductive substrate 31, a substrate made of a conductive material such as a conductive metal oxide thin film or metal is used. As a preferred example of the conductive metal oxide, In 2 O 3: Sn (lTO)

 twenty three

SnO: Sb, SnO: F, ZnO: Al, ZnO: F, CdSnO.

 2 2 4

 [0085] The thickness of the transparent conductive substrate 31 is generally 0.1 to 10 mm, preferably 0.3 to 5 mm.

 [0086] Instead of the transparent conductive substrate 31, a substrate obtained by forming the transparent conductive substrate 1 on a transparent substrate may be used. In this case, for example, glass such as alkali silicate glass, non-alkali glass, or quartz glass can be used as the transparent substrate. A polymer film substrate such as Atalya PET can also be used. When these polymer substrates are used, the cost can be reduced. The thickness of the substrate is generally from 0.1 to 10 mm, preferably from 0.3 to 5 mm. The glass plate is preferably chemically or thermally strengthened.

 [0087] The p layer 32 is Cu 2 O. This Cu ○ functions as a p-layer as well as a light-absorbing layer.

 twenty two

 It also has the ability.

[0088] The average particle diameter of the deposited Cu 2 O is preferably lOnm lO zm. From 10nm If it is small, Cu O cannot sufficiently grow and crystallinity deteriorates.

2

 The hole mobility is reduced. On the other hand, if it is larger than 10 μΐη, the surface of the p layer becomes too rough and the bonding property between the ρ layer and the η layer deteriorates, and the conversion efficiency decreases. Also, the leakage current component increases significantly.

The thickness of the ρ layer is, for example, 100 nm to 3 μm, preferably 300 nm to 1 μm. The electron mobility of the p-layer is preferably from 0.01 to 100 cm ² / V 'sec, particularly from! to 100 cm ² ZV' sec.

The n layer 33 is In_Ga_Zn_O in an amorphous state. In this amorphous state

— Since Ga—Zn—O is uniform without forming grain boundaries, the crystalline Cu 2 O surface

 As a result, discontinuities and voids are prevented from occurring at the junction interface between the n layer and the p layer, and a good junction interface is formed. As a result, a large conversion efficiency can be obtained.

 In addition, since In—Ga—ZnO has a large electron mobility even in an amorphous state, it is possible to obtain a large conversion efficiency from this point of easily taking out electric power.

[0092] Further, since In-Ga-Zn-O in an amorphous state may be formed, In-Ga

— Zn ○ can be formed on the p-layer at low temperature. For this reason, there is no significant modification such as grain growth in the Cu layer of the p layer due to heating when forming the n layer.

 2

 It is possible to prevent the bonding interface from deteriorating, thereby obtaining a large conversion efficiency.

[0093] When the total of In, Ga and Zn in the n layer is 100 atm%, In is preferably 8 to 67 atm%, Ga is 1 to 50 atm%, and Zn is 8 to 67 atm%. In—Ga—Zn O with such a composition satisfies all of the sufficient mobility of electrons, the transmittance of visible light, and the bonding property with the CuO layer.

 2

 I can help.

 [0094] The thickness of the n layer is, for example, 100 nm to 5 μm, preferably 300 nm to 1 μm.

[0095] The n layer is preferably formed under the condition that the temperature of the film formation surface is in the range of room temperature to 200 ° C. In this case, the bondability between the n layer and the p layer is improved, and the Cu O in the p layer has a grain growth or the like.

 2

 It can suppress that modification | denaturation arises. In addition, a polymer substrate can be used as the substrate.

[0096] As the metal electrode 34, platinum, Al, Cu, Ti, Ni, or the like can be used. In the present embodiment, a transparent conductive substrate 1 is placed in a mixed gas atmosphere of oxygen and argon using a DC power source, and a voltage is applied to a Cu target for sputtering. The sputtered Cu is oxidized on the surface of the transparent conductive substrate 1 and the Cu O layer is formed on the transparent conductive substrate 1.

 2 Made. Next, sputtering is performed by applying a voltage to a target made of In—Ga—Zn. Sputtered In, Ga, and Zn are oxidized on the surface of the CuO layer, etc.

 twenty two

 n_ ○ layer is formed.

 [0098] Instead of using one type of target composed of In_Ga_Zn, the In_Ga_Zn_O layer may be formed using a plurality of types of targets having different compositions composed of at least one of In, Ga, and Zn. Yo!

 Next, a solar cell 10 is obtained by forming an electrode on the n layer made of In_Ga_Zn_O.

 [0100] The solar cell 10 thus obtained preferably has a high functionality with a conversion efficiency of 0.67% or more.

[0101] In this embodiment, the force Cu is applied to form the p-layer and n-layer by reactive sputtering.

 2

The ρ layer and the n layer may be formed by sputtering using an O target and an In—Ga—Zn—O target. Further, the p layer and the n layer may be formed by CVD, vapor deposition or the like.

 [0102] FIG. 4 is a schematic cross-sectional view of a solar cell according to an embodiment having a different second aspect. The solar cell 40 includes a Cu plate 41, a p-layer 42 made of CuO formed by oxidizing the surface of the Cu plate 41, and an In-Ga formed on the p-layer 42 by sputtering.

 2

 — Consists of an n layer 43 and an ITO (indium tin oxide) layer 45 made of Zn—O, and a metal electrode 44 provided on the plating layer 45. The p-layer 42 made of Cu 2 O has the Cu plate 41 in the atmosphere.

 2

 It is formed by heat treatment. A conductive wire 46 is connected to the Cu plate 41 and the electrode 44. This solar cell 40 also has a high conversion efficiency.

Hereinafter, Examples 4 and 5 and Comparative Example 3 will be described, but the second aspect is not limited to Examples 4 and 5.

<Example 4>

A p-layer made of CuO and In_Ga_Zn on an ITO glass substrate using reactive sputtering An n layer made of O was formed in this order. The film forming conditions were as follows.

 [P layer]

Target: Cu, ultimate vacuum: 5 · 0 X 10— ⁴ Pa, pressure during film formation: 0 · 7 Pa

 Gas flow rate during deposition: Ar / O = 95 / 5sccm, applied power: DC50W,

 2

 Deposition time: 30 minutes, film thickness: 350 nm

 [n layers]

 Target: InGaZnO (In: Ga: Zn = 1: 1: 1),

Ultimate vacuum: 5.0 X 10— ⁴ Pa, film-forming pressure: 0.7 Pa,

 Gas flow rate during deposition: Ar / O = 80 / 20sccm

 2,

 Applied power: DC50W, deposition time: 30 minutes, film thickness: 300nm

[0105] Al (thickness lOOnm) was formed on this n layer to form an electrode.

 About the obtained solar cell, the conducting wire was joined to the ITO glass substrate and the A1 electrode, and the conversion efficiency was measured using a solar simulator. The measurement was performed under the conditions of AMI.5 and 30 ° C in the atmosphere. The element size is 10mm x 10mm.

 As a result, the conversion efficiency 77 was 1.9%.

<Example 5>

 A Cu plate with a thickness of 0.3 mm is heat-treated in air at 450 ° C for 6 hours, and Cu O is applied to the Cu plate surface.

 A P layer (thickness 350 nm) consisting of 2 was formed. Next, on this p layer of Cu 2 O, the reactivity

 2

 An n layer composed of In—Ga—Zn—O and an ITO layer were formed in this order using a sputtering method, and an electrode of A beam was formed on the ITO layer. The n layer and the A1 electrode were formed in the same manner as in Example 4. The ITO layer was formed by reactive sputtering under the following conditions.

 [Midori]

 Target: Indium tin alloy (In: Sn = 97: 3atm%),

Ultimate vacuum: 5.0 X 10— ⁴ Pa, film-forming pressure: 0.7 Pa,

 Gas flow rate during deposition: Ar / O = 95 / 5sccm, applied power: DC50W,

 2

 Deposition time: 30 minutes, film thickness: lOOnm

[0107] About the obtained solar cell, a conductor was joined to the Cu plate and the A1 electrode, and as in Example 4, Conversion efficiency was measured using a solar simulator.

 As a result, the conversion efficiency 77 was 2.1%.

<Comparative Example 3>

 A solar cell was obtained in the same manner as in Example 4 except that the n layer was ZnO. ZnO was formed by reactive sputtering under the following conditions.

 [n layer (ZnO)

Target: Zn, ultimate vacuum: 5.0 X 10— ⁴ Pa, film-forming pressure: 0.7 Pa,

 Gas flow rate during deposition: Ar / O = 80 / 20sccm, applied power: DC50W,

 2

 Deposition time: 30 minutes, film thickness: 280nm

[0109] The conversion efficiency of the obtained solar cell was measured using a solar simulator in the same manner as in Example 4.

 As a result, the conversion efficiency η was 0.2%.

[0110] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.

 This application consists of a Japanese patent application filed on March 25, 2005 (Japanese Patent Application 2005-0 89078) and a Japanese patent application filed June 1, 2005 (Japanese Patent Application 2005-161582). Which is incorporated by reference in its entirety.

Claims

The scope of the claims  [1] In a method of forming an In-Ga-Zn_O film by sputtering using a target in an atmosphere containing oxygen gas,  A plurality of the targets are provided,  Each target is a metal or alloy or oxide composed of at least one of In, Ga and Zn, and each of In, Ga and Zn is contained in at least one of the targets,  At least one of the targets has a composition different from that of other targets, and sputtering is performed by alternately applying intermittent voltage to each target. A method for forming a Ga—Zn—O film. [2] The method for forming an In—Ga—Zn—O film according to claim 1, wherein each of the targets is a metal or an oxide of any one of In, Ga, and Zn. [3] The method for forming an In—Ga—Zn—O film according to claim 1, wherein the target is an alloy containing In, Ga, and Zn and having different compositions. [4] The In—Ga of claim 1, wherein at least one of the targets is an alloy or oxide made of In and Ga, and the remainder of the target is a metal or oxide made of Zn. —Zn—O film formation method. [5] The method of forming an In_Ga_Zn_0 film according to claim 1, wherein a pulse packet including a plurality of pulse voltages is alternately and intermittently applied to each target. 6. The method of forming an In_Ga_Zn_O film according to claim 1, wherein charging of the target is prevented by intermittently applying a positive voltage to each target. [7] The method for forming an In-Ga-Zn-0 film according to claim 1, wherein the emission wavelength and emission intensity of discharge of In, Ga, and Zn during sputtering are monitored. [8] The method for forming an In—Ga—Zn—O film according to claim 7, wherein the emission wavelength and emission intensity of discharge of In, Ga, and Zn during sputtering are monitored for each target. [9] In Claim 7, based on the monitoring, at least one of a no-load power, a pulse amount, a pulse width, a pressure during film formation, and an oxygen supply amount applied to each target is changed. To control the composition and crystallinity of the film to be formed. 10. The method for forming an In—Ga—Zn—O film according to claim 1, wherein the crystallinity of the film to be formed is controlled by adjusting the temperature of the substrate during sputtering. [11] The method for forming an In—Ga—Zn—coating film according to claim 10, wherein the temperature of the substrate is adjusted to 77K to 300K during sputtering. [12] In a pn junction solar cell in which a p layer and an n layer are stacked,  The p layer is made of Cu 2 O,  2  The solar cell, wherein the n layer is composed of In_Ga_Zn_O in an amorphous state. [13] The indium tin oxide substrate according to claim 12,  The p-layer formed on the indium tin oxide substrate;  The n layer formed on the p layer;  A solar cell comprising an electrode formed on the n layer. [14] In claim 12, a Cu plate;  The p layer formed by oxidizing the surface of the Cu plate;  The n layer formed on the p layer;  An electrode film made of indium tin oxide formed on the n layer;  A solar cell comprising an electrode formed on the electrode film. 15. The solar cell according to claim 12, wherein the p layer or the n layer is formed on a polymer substrate. 16. The solar cell according to claim 12, wherein the p layer and the n layer are formed by a sputtering method, a reactive sputtering method, a CVD method, or an evaporation method. [17] The sum of In, Ga and Zn in the n layer is 100atm in claim 12. / _o  In is 8 ~ 67atm%,  Ga:! ~ 50atm%,  Zn 8 ~ 67atm%  A solar cell characterized by being 18. The conversion efficiency of the solar cell according to claim 12, wherein the conversion efficiency of the solar cell is 0.67. / ₀ or more Solar cell.  13. The solar cell according to claim 12, wherein an average particle size of the p layer is lOnm˜: 10 μΐη.