Photoelectric conversion device and its manufacturing method

The present invention relates to a photoelectric conversion device and a method for manufacturing the same, and particularly relates to a photoelectric conversion device using a semiconductor thin film having a calcopyrite structure.

CuInSe, a semiconductor thin film with a calcopyrite structure, consisting of Group Ib elements, Group IIIb elements, and Group VIb elements.₂(CIS thin film) or Cu (In, Ga) Se with Ga dissolved in it₂A thin-film solar cell using (CIGS-based thin film) as a light absorption layer has the advantages of exhibiting high energy conversion efficiency and little deterioration of efficiency due to light irradiation or the like.

8 (a) to 8 (d) are cross-sectional views of a device for explaining a conventional method for manufacturing a cell of a CIGS-based thin-film solar cell.

As shown in FIG. 8A, first, a Mo (molybdenum) electrode layer 200 serving as a lower electrode on the plus side is formed on the SLG (soda lime glass) substrate 100.

Next, as shown in FIG. 8 (b), the composition is controlled on the Mo electrode layer 200.^-A light absorption layer 3 made of a CIGS-based thin film showing a mold is formed.

Next, as shown in FIG. 8 (c), a buffer layer 400 made of CdS is formed on the light absorption layer 3, and impurities are doped on the buffer layer 400.⁺A translucent electrode layer 500 made of ZnO (zinc oxide), which serves as an upper electrode on the minus side and indicates a mold, is formed.

Next, as shown in FIG. 8 (d), the translucent electrode layer 500 to the Mo electrode layer 200 made of ZnO are collectively scribed by the mechanical scribe device. As a result, each cell of the thin-film solar cell is electrically separated (that is, each cell is individualized).

This scribing step can also utilize laser scribing (a scribe technique for partially removing a thin film by irradiating a laser beam).

However, in this case, since the laser beam is intensively irradiated, high heat is locally generated, which causes a disadvantage that the characteristics of the cell are deteriorated.

Therefore, the cells of the solar cell are generally electrically separated by a mechanical scribing device.

In the mechanical scribe device described in Patent Document 1, a blade that is tapered at a predetermined taper angle and has a flat tip is pressed vertically against a scribing portion of the work surface with a predetermined pressure, and the blade is pressed against the work surface. The scribe processing is performed by moving along the line.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-115356</text></patcit>

<p> Currently, CIS-based thin films and CIGS-based thin films are mainly used as solar cells.</p><p> On the other hand, the inventors of the present invention have focused on the high light absorption coefficient of this compound semiconductor thin film material and the characteristic of having high sensitivity over a wide wavelength range from visible light to near-infrared light, and have focused on this compound semiconductor thin film. Materials are security cameras (cameras that sense visible light during the day and near-infrared light at night) and personal authentication cameras (cameras for personal authentication with near-infrared light that is not affected by external light). Alternatively, we considered using it as an image sensor for an in-vehicle camera (a camera mounted on a car to assist vision at night or secure a distant field of view).</p><p> As a result, CIS thin films (CuInSe)₂), It was found that the dark current (current flowing through the PN junction at the time of reverse bias) is unexpectedly large.</p><p> That is, for example, at the reverse bias of -0.8V, 1 × 10^-3A / cm²A degree of dark current flows, and this value is 6 orders of magnitude higher than that of silicon-based materials. If nothing is done, weak light of 1000 Lux or less will be buried in noise and cannot be detected.</p><p> Therefore, it became necessary to significantly reduce the dark current. The inventor of the present invention has investigated in detail the factors that increase the dark current in the compound semiconductor thin film, and as a result, the crystals of the compound semiconductor material are damaged or defective during mechanical scribing, which causes the interface of the PN junction to be affected. It was found that multiple energy levels were generated, which contributed to a large dark current.</p><p> That is, in FIG. 8 (d), the end portion (circled parts A and B in the figure) of the interface of the PN junction (boundary of the depletion layer: indicated by the dotted line) is mechanically scribed and exposed. It reaches the side wall of CIGS thin film 300. The mechanical scribing surface has a large amount of crystal damage and has an unnecessary interfacial order. Therefore, the leakage current of the PN junction increases at this portion.</p><p> The present invention has been made based on such consideration, and an object of the present invention is to significantly reduce the dark current of a photoelectric conversion element using a compound semiconductor thin film.</p>

<p> The present invention is a photoelectric conversion device in which a lower electrode layer, a compound semiconductor thin film having a calcopyrite structure functioning as a light absorption layer, and a translucent electrode layer are sequentially laminated on a substrate, and has the calcopyrite structure. The pattern of the translucent electrode layer is formed so that the end portion of the compound semiconductor thin film is located outside the end portion of the translucent electrode layer.</p><p> Dangling bonds (junctions) and the like may be present on the end face of the pattern of the compound semiconductor thin film to form unnecessary energy levels. According to this configuration, the compound semiconductor thin film and the translucent electrode are used. Since the translucent electrode is removed so that the end of the PN junction interface formed at the interface does not function as an element region, it is possible to reduce the dark current caused by the leak current.</p><p> The photoelectric conversion device of the present invention includes a device in which a plurality of photoelectric conversion element cells are integrated.</p><p> With this configuration, it is possible to reduce the dark current even in the photoelectric conversion device having an integrated structure.</p><p> The photoelectric conversion device of the present invention includes a plurality of photoelectric conversion element cells integrated, and the compound semiconductor thin film having the calcopyrite structure integrally formed on the substrate surface.</p><p> With this configuration, it is possible to form a photoelectric conversion device having good workability and low dark current only by patterning the translucent electrodes.</p><p> In the photoelectric conversion device of the present invention, a plurality of photoelectric conversion element cells are integrated so that the compound semiconductor thin film having the calcopyrite structure has the pattern edge located outside the pattern edge of the translucent electrode. Including those formed.</p><p> With this configuration, it is possible to reduce the dark current even in the photoelectric conversion device having an integrated structure.</p><p> The photoelectric conversion device of the present invention includes the compound semiconductor thin film arranged so that the pattern width is larger than the pattern of the translucent electrode.</p><p> With this configuration, a matrix type photoelectric conversion device having a low dark current can be easily formed. In the case of forming by one-time photolithography, by adjusting the etching conditions, the pattern edge of the compound semiconductor thin film having the calcopyrite structure is located outside the pattern edge of the translucent electrode. Can be formed.</p><p> In the photoelectric conversion device of the present invention, the compound semiconductor thin film having the calcopyrite structure is Cu (In)._x, Ga_(1-x)) Se₂Includes those for which (0 x 1).</p><p> According to this configuration, by using a CIGS-based thin film in which a part of In (indium) is replaced with gallium, a CIS-based thin film (CuInSe) is used.₂), The widening of the bandgap is effective, and by widening the bandwidth, the carrier recombination process can be reduced and the dark current can be reduced.</p><p> In the photoelectric conversion device of the present invention, the translucent electrode layer is provided on a non-doped ZnO film provided at an interface with the compound semiconductor thin film and on the non-doped ZnO film.⁺Includes those composed of type ZnO films.</p><p> According to this configuration, by providing a non-doped ZnO film (i-ZnO) as a translucent electrode layer, voids and pinholes generated in the underlying CIGS thin film are embedded in a semi-insulating layer, and the CIGS thin film and ip bond are formed. Formed and conductive ZnO film (n)⁺) Can be prevented from leaking due to the tunnel current that occurs when it is in direct contact with the CIGS thin film. Therefore, by thickening the non-doped ZnO film (i-ZnO), the dark current at the PN junction interface can be reduced.</p><p> The photoelectric conversion device of the present invention includes a photoelectric conversion device that is a photosensor having sensitivity also in the near infrared light region.</p><p> Since the sensor of the present invention has high sensitivity to near-infrared light, it can be used as a security camera (a camera that senses visible light during the day and near-infrared light at night) or a personal authentication camera (effect of external light). It can be sufficiently used as a camera for personal authentication with near-infrared light that does not receive light) or as an in-vehicle camera (camera mounted on a car for visual assistance at night or for securing a distant field of view).</p><p> The photoelectric conversion device of the present invention includes a photoelectric conversion device that is a solar cell.</p><p> In the photoelectric conversion device of the present invention, the photoelectric conversion loss at the interface of the PN junction is sufficiently reduced as compared with the conventional case, so that the solar cell has a high collection efficiency of electric charges generated by light and a high photoelectric conversion efficiency. It can be realized.</p><p> The method of the present invention is a method for manufacturing a photoelectric conversion device in which a lower electrode layer, a compound semiconductor thin film having a calcopylite structure functioning as a light absorption layer, and a translucent electrode layer are laminated on a substrate. The step of selectively removing the translucent electrode from the compound semiconductor thin film having a calcopyrite structure and patterning the compound semiconductor thin film having a calcopyrite structure is included so that a part of the compound semiconductor thin film having a calcopyrite structure is exposed.</p><p> In the method for manufacturing a photoelectric conversion device of the present invention, the step of patterning the translucent electrode layer is such that the end of the PN junction interface formed by the contact between the translucent electrode layer and the compound semiconductor thin film is the compound. The step includes a step of patterning so that the position of the end portion of the translucent electrode layer is inside the side surface of the compound semiconductor thin film so as not to reach the side surface of the semiconductor thin film.</p><p> In the method for manufacturing the photoelectric conversion device of the present invention, the step of forming the compound semiconductor thin film having the calcopyrite structure is Cu (In) by the PVD method._x, Ga_(1-x)) Se₂(0 x 1) The step of forming the translucent electrode layer including the step of forming a thin film includes a step of forming a non-doped ZnO film on the compound semiconductor thin film and a step of forming the non-doped ZnO film on the non-doped ZnO film. Including the step of forming an n + type ZnO film.</p><p> Instead of mechanical scribing, it is desirable to pattern the translucent electrode layer using etching by photolithography. Along with this, the compound semiconductor thin film having a calcopyrite structure that functions as the lower electrode layer and the light absorption layer is also patterned by etching by photolithography as well as after the film formation by the PVD method. As a result, damage and defects do not occur in the compound semiconductor thin film as in the case of mechanical scribing, and the dark current can be significantly reduced. Here, the PVD method refers to a method of depositing raw materials evaporated in a vacuum to form a film.</p><p> In addition, by patterning using photolithography, damage and defects do not occur in the crystal of the compound semiconductor as in the case of adopting mechanical scribing, and therefore unnecessary energy levels do not occur at the interface of the PN junction. It is possible to reduce dark current. Further, by devising the pattern of the ZnO film and adopting a structure in which the PN junction interface is embedded, it is possible to prevent a leakage current from the end of the PN junction interface. That is, by changing the manufacturing process and optimizing the device structure of the light absorption layer and the translucent electrode layer, the dark current is reduced to 10.³Can be improved on the order of. Also, Cu (Inx, Ga (1-x)) Se₂Bandgap control at 10 dark current²It can be reduced on the order of.</p>

<p> According to the present invention, the position of the end portion of the translucent electrode layer is patterned so as to be inside the side surface of the compound semiconductor thin film, and the end portion of the PN junction interface is on the side surface of the patterned compound semiconductor thin film. Leakage current from the end of the PN junction interface can be further reduced by preventing it from reaching (that is, the structure is such that the PN junction interface is embedded inside the compound semiconductor thin film).</p><p> Further, by widening the bandwidth by using a CIGS-based thin film in which a part of In (indium) is replaced with gallium, the carrier recombination process can be reduced, and the dark current can be further reduced.</p><p> Also, Cu (Inx, Ga (1-x)) Se₂Bandgap control at 10 dark current²It can be reduced on the order of.</p><p> Since the sensor of the present invention has high sensitivity to near-infrared light, it can be used as a security camera (a camera that senses visible light during the day and near-infrared light at night) or a personal authentication camera (effect of external light). It can be sufficiently used as a camera for personal authentication with near-infrared light that does not receive light) or as an in-vehicle camera (camera mounted on a car for visual assistance at night or for securing a distant field of view).</p><p> Further, in the photoelectric conversion device of the present invention, the photoelectric conversion loss at the interface of the PN junction is sufficiently reduced as compared with the conventional case, so that the collection efficiency of the electric charge generated by light is high and the photoelectric conversion efficiency is high. A battery can be realized.</p>

Next, an embodiment of the present invention will be described with reference to the drawings. (Embodiment 1)

FIG. 1 is a flow chart showing an outline of a main process of a method for manufacturing a photoelectric conversion device according to the present invention. FIG. 2 is a cross-sectional view of the process. As shown in FIG. 2 (j), the photoelectric conversion device of the present invention is a p-type compound semiconductor having a calcopyrite structure that functions as a lower electrode layer 20 made of a Mo thin film and a light absorption (photoelectric conversion) layer on a substrate 10. Thin film (Cu (In)_x, Ga_(1-x)) Se₂(0 x 1)) 30, the translucent electrode layers are sequentially laminated, and the end portion of the compound semiconductor thin film having the calcopyrite structure is located outside the end portion of the translucent electrode layer. As a result, the pattern of the translucent electrode layer is formed, and the translucent electrode layer is provided on the non-doped ZnO film 50 provided at the interface with the compound semiconductor thin film and the non-doped ZnO film. n⁺It is characterized by being composed of a type ZnO film 60.

According to this configuration, by providing a non-doped ZnO film (i-ZnO) as a translucent electrode layer, voids and pinholes generated in the underlying CIGS thin film are embedded in a semi-insulating layer, and the CIGS thin film and ip bond are formed. Formed and conductive ZnO film (n)⁺) Can be prevented from leaking due to the tunnel current that occurs when it is in direct contact with the CIGS thin film. Therefore, by thickening the non-doped ZnO film (i-ZnO), the dark current at the PN junction interface can be reduced.

In the manufacturing process of the photoelectric conversion device of the present invention, a lower electrode layer formed in layers, a p-type compound semiconductor thin film having a calcopyrite structure (hereinafter referred to as CIGS thin film) that functions as a light absorption layer, and a translucent electrode layer (non-doped). And the part is doped with impurities n⁺Each of the mold-indicating parts) is patterned using photolithography technology to minimize damage to the crystals of the CIGS thin film.

That is, in the method for manufacturing the photoelectric conversion device of the present invention, a Mo (molybdenum) layer to be a lower electrode is formed on a glass substrate by a sputtering method (about 0.6 μm), and then patterned using a photolithography technique (about 0.6 μm). Process S1).

Next, a CIGS thin film is formed and patterning is performed using photolithography. That is, composition-controlled p^-Mold CIGS thin film (Cu (Inx, Ga (1-x)) Se₂(0 &lt;x &lt;1)) is formed into a film by, for example, an ion beam sputtering method (step S2). Its thickness is about 1.7 μm.

Next, the CIGS thin film (p)^-) Is patterned by two-stage etching using both dry etching and wet etching (step S3). As a result, the electrically separated CIGS thin film (p)^-) Is obtained.

Next, a thin CdS film (about 50 nm) as a buffer layer (window layer) is formed by a solution growth method (step S4).

Next, a ZnO film as a translucent electrode layer is formed (step S5). This step is the most important feature of the present invention.

That is, a non-doped ZnO film (i-ZnO) and a low-resistance ZnO (n) doped with impurities by the sputtering method.⁺) A film is continuously formed (step S5a). Here, i-ZnO is as thin as about 60 nm, while ZnO (n) with low resistance is used.⁺) Has a sufficient thickness of about 1 μm.

The non-doped ZnO film (i-ZnO) embeds voids and pinholes generated in the underlying CIGS thin film with a semi-insulating layer, and forms an ip bond with the CIGS thin film to form a low-resistance ZnO film (n).⁺) Plays a role in preventing leakage due to tunnel current that occurs when it is in direct contact with the CIGS thin film.

Therefore, by thickening the non-doped ZnO film (i-ZnO), the dark current at the PN junction interface can be reduced (the effect of reducing it to about 1/5 was confirmed). However, even if the film is thickened, its thickness is sufficiently thin (for example, 60 nm), so that it has a low resistance of ZnO (n) that functions as a translucent electrode layer.⁺) Membrane and CIGS thin film (p)^-) Is considered to form a substantial pn junction.

Next, ZnO films (i-ZnO and ZnO (n)⁺)) Is patterned (step S5b). In this step S5b, the position of the edge of the ZnO film is patterned CIGS thin film (p.^-Patterning so that it is inside the side of (ie) CIGS thin film (p)^-) On top of this CIGS thin film (p^-A ZnO film with a width narrower than that of) is formed, and a parent turtle and a turtle structure are formed).

This results in ZnO (n)⁺) And CIGS thin film (p^-) And the edge of the PN junction interface (the boundary of the depletion layer) is patterned CIGS thin film (p)^-) Does not reach the side wall (the surface exposed by etching), which realizes the embedded structure of the PN junction interface.

CIGS thin film patterned by photolithography (p^-On the side of), there are sufficiently fewer crystal defects and damage than in the case of mechanical scribing, but even so, there is no dangling bond (bonding hand) etc. and unnecessary energy levels are not formed. I can't say. Therefore, the end of the PN junction interface is this patterned CIGS thin film (p.^-The leakage current from the end of the interface of the PN junction can be further reduced by not reaching the side surface (the surface exposed by etching).

Finally, a lead-out electrode is formed (step S6). This completes the photoelectric conversion device.

Next, a method for manufacturing the photoelectric conversion device of the present invention will be specifically described with reference to FIG.

2 (a) to 2 (j) are cross-sectional views of the device for each of the main steps for specifically explaining the manufacturing method of the photoelectric conversion device of the present invention.

In the following description, FIGS. 3 (a) and 3 (b) and FIG. 4 will be referred to. Here, FIG. 3 is a diagram schematically showing a 10,000-fold magnified photograph of a device for explaining a patterning method of a CIGS thin film by an SEM (scanning microscope), and FIG. 3A is a diagram showing dry etching of the CIGS thin film. It is a figure which shows the state immediately after, and (b) is the figure which shows the state after further performing wet etching.

Further, FIG. 4 is a schematic diagram showing a cross-sectional photograph (20,000 times magnified photograph) of the SEM (scanning microscope) of the device after patterning the translucent electrode layer (ZnO film).

First, as shown in FIG. 2A, a Mo (molybdenum) film is formed on a soda lime glass substrate (SLG) 10 by a sputtering method to a thickness of 0.6 μm.

As shown in FIG. 2 (b), for example, the CIGS thin film 30 is formed with a thickness of 1.7 μm by the composition of Cu: In: Ga: Se = 1: 0.5: 0.5: 2.

In FIG. 2C, the CIGS thin film 30 is dry-etched using the resist pattern 40. That is, the CIGS thin film 30 is vertically etched and patterned using chlorine-based gas and bromine-based gas as etchants. In this case, etching with almost no side etching is possible at a high rate, but a large number of residues 35 remain (as can be seen from FIG. 3 (a), a large number of columnar residues remain on a large number of Mo films. ing).

Therefore, as shown in FIG. 2 (d), after treating with a mixed solution of bromine and methanol or a mixed solution of water and ammonia, the mixture is treated with a mixed solution of hydrochloric acid and nitric acid to completely remove the residue 35. .. As shown in FIG. 3 (b), the residue 35 is completely removed.

As described above, by using the chlorine-based gas and the bromine-based gas as the dry etching etchant, the CIGS thin film 30 constituting the light absorption layer can be etched at a high rate and with high accuracy without causing undercut. After that, wet etching is performed for a short time to completely remove the columnar residue 35. This enables highly accurate patterning of CIGS thin films without producing residues. In this case, the crystals of the CIGS thin film 30 do not suffer damage or defects as in the case of adopting mechanical etching, and the dark current can be significantly reduced.

Next, the resist pattern 40 is removed. A cross section of the device in this state is shown in FIG. 2 (e).

As shown in FIG. 2 (f), a thin CdS film 50 (about 50 nm) as a buffer layer (window layer) is formed by a solution growth method, and then a ZnO film 60 is formed by a sputtering method. ..

The ZnO film 60 consists of a non-doped ZnO film (i-ZnO) and a low-resistance ZnO (n) doped with n-type impurities.⁺) A film (denoted as n-ZnO in the figure) is formed by continuously forming a film. Here, the thickness of i-ZnO is about 60 nm, while the resistance of ZnO (n) is reduced.⁺) Is about 1 μm.

The non-doped ZnO film (i-ZnO) embeds voids and pinholes generated in the underlying CIGS thin film with a semi-insulating layer, and forms an ip bond with the CIGS thin film 30 to prevent leakage due to tunneling current.

Therefore, by thickening the non-doped ZnO film (i-ZnO), the dark current at the PN junction interface can be reduced. However, even if the film is thickened, its thickness is sufficiently thin (for example, 60 nm), so that it has a low resistance of ZnO (n) that functions as a translucent electrode layer.⁺) Membrane and CIGS thin film (p)^-) Is considered to form a substantial pn junction.

Next, as shown in FIG. 2 (g), after forming the resist pattern 70, ZnO films (i-ZnO and ZnO (n)⁺)) Wet etch 30.

That is, for example, wet etching is performed using a dilute acid of hydrochloric acid: water = 1:10. At this time, the etching time is adjusted to intentionally cause side etching and undercut under the resist pattern 70. This is because the position of the edge of the patterned ZnO film 60 is patterned CIGS (p.^-) This is so that it is inside the side surface of the thin film 60.

Next, dry etching is performed using the resist pattern 70 to remove the CdS film 50 on the side wall of the CIGS thin film 30. The cross-sectional structure of the device in this state is shown in FIG. 2 (h).

Next, as shown in FIG. 2 (i), the resist pattern 70 is removed. As shown, the width W2 of ZnO film 60 is CIGS (p.^-) It is narrower than the width W1 of the thin film 30, which forms the parent turtle child turtle structure. As is clear from FIG. 4, the position P2 at the end of the ZnO film 60 is located inside the position P1 at the side wall of the CIGS thin film 30.

As a result, ZnO (n) (n), as shown in Fig. 2 (i).⁺) Membrane 60 and CIGS (p^-) The edge of the PN junction interface 80 (depletion layer boundary: shown by the dotted line in the figure) formed by the thin film 30 is patterned CIGS (p).^-) The side wall of the thin film 30 (the surface exposed by etching) is not reached, which realizes the embedded structure of the PN junction interface.

CIGS (p) patterned by photolithography^-) The side wall of the thin film (the surface exposed by etching) has sufficiently few crystal defects and damage compared to the case of mechanical scribing, but there are still dangling bonds (bonding hands) and unnecessary energy levels. It cannot be said that it will not be formed.

Therefore, the end of the PN junction interface 80 is this patterned CIGS (p.^-) The leakage current from the end of the interface of the PN junction can be further reduced by not reaching the side wall of the thin film 30.

Finally, as shown in FIG. 2 (j), the extraction electrodes 90 and 95 made of aluminum or the like are formed. This completes the photoelectric conversion device.

This photoelectric conversion device can be used as it is as a high-efficiency solar cell. (Embodiment 2)

In the present embodiment, an example in which the photoelectric conversion device of the present invention is used as a photosensor having high sensitivity even in the near infrared light region will be described.

FIG. 5 is a diagram showing the absorption coefficient of the CIS thin film (the same applies to the CIGS thin film) with respect to the wavelength of light. As shown, it can be seen that the CIS film (CIGS thin film) has high sensitivity over a wide range from visible light to near-infrared light.

Focusing on this point, in the present embodiment, the photoelectric conversion device made of the compound semiconductor thin film of the present invention is laminated on a silicon substrate on which a CMOS circuit is formed to form a composite image sensor.

FIG. 6 is a schematic cross-sectional view of a CMOS image sensor formed on a conventional silicon substrate. Further, FIG. 7 shows a schematic cross section of the composite image sensor of the present invention, which is formed by laminating a photoelectric conversion device (photosensor) made of a compound semiconductor thin film on a silicon substrate on which a CMOS circuit according to an embodiment of the present invention is formed. It is a figure.

As shown in Figure 6, a typical CMOS image sensor is P.^-A photodiode 610 (for example, having a pin structure) and a MOS transistor are formed in a silicon substrate 600.⁺Diffusion layers 616, 618, 620 are formed and also P^-A gate layer 612,614 of a MOS transistor, a wiring layer 622, and a protective film (including an interlayer insulating film) 624 are formed on the type silicon substrate 600.

On the other hand, the composite image sensor of the present invention has P.^-N forming a MOS transistor in a silicon substrate 700⁺Diffusion layers 702, 704, 706, 708 are formed and P^-A gate layer 703,705 of a MOS transistor, a wiring layer 712,714, and an interlayer insulating film 710 are formed on a silicon substrate 700.

A photoelectric conversion device (photosensor) made of a compound semiconductor thin film is laminated and formed on the interlayer insulating film 710.

This photoelectric conversion device (photosensor) is composed of a lower wiring layer 716, a CIGS thin film (PD) 718 (the electrode layer is omitted in the figure) that functions as a light absorption layer, and an upper wiring layer 720. Has been done.

As described in the above-described embodiment, the CIGS thin film of the present invention is patterned with high accuracy without residue by two-stage etching of dry and wet using photolithography, and damage to crystals and crystal defects are reduced. In addition, by patterning the ZnO film by photolithography, the edge of the PN junction interface is embedded so that it does not reach the etched side wall of the CIGS thin film, and the dark current is about 5 orders of magnitude higher than that of the conventional device. Has been reduced.

Since the sensor of the present invention has high sensitivity to near-infrared light, it can be used as a security camera (a camera that senses visible light during the day and near-infrared light at night) or a personal authentication camera (effect of external light). It can be sufficiently used as a camera for personal authentication with near-infrared light that does not receive light) or as an in-vehicle camera (camera mounted on a car for visual assistance at night or for securing a distant field of view).

In the above embodiment, the compound semiconductor thin film (CIGS thin film) having a calcopyrite structure is Cu (Inx, Ga (1-x)) Se.₂Is used, but the present invention is not limited to this.

As a CIGS thin film, Cu (Inx, Ga (1-x)) (Sey, S (1-y))₂ Those having a composition of x = 0 to 1, y = 0 to 1 are also known, and CIGS thin films having such a composition can also be used.

This CIGS thin film can be formed on a substrate by a vacuum deposition method or a sputtering method. When the vacuum vapor deposition method is used, each component (Cu, In, Ga, Se, S) of the compound is separately vapor-deposited on the substrate as an evaporation source. In the sputtering method, a calcopyrite compound is used as a target, or each component thereof is used as a target separately. When a chalcopyrite compound semiconductor thin film is formed on a metal substrate or a glass substrate, the substrate is heated to a high temperature, so that reevaporation occurs due to heating of the chalcogenite element (Se, S). For this reason, compositional deviation may occur due to the departure of the chalcogenite element. In this case, it is desirable to replenish Se or S by performing heat treatment at a temperature of 400 to 600 ° C for about 1 to several hours in a vapor atmosphere of Se or S after film formation (selenium treatment or selenium treatment or). Sulfurization treatment).

As described above, according to the present invention, instead of mechanical scribing, etching by photolithography is used to pattern a translucent electrode layer, and accordingly, a calco that functions as a lower electrode layer and a light absorption layer. Similarly, the compound semiconductor thin film having a pyrite structure is also patterned by etching by photolithography, which makes it possible to significantly reduce dark current without causing damage or defects to the compound semiconductor thin film as in the case of mechanical scribing. Become.

Further, the position of the end portion of the translucent electrode layer is patterned so as to be inside the side surface of the compound semiconductor thin film so that the end portion of the PN junction interface does not reach the side surface of the patterned compound semiconductor thin film. (That is, the structure is such that the PN junction interface is embedded inside the compound semiconductor thin film), so that the leakage current from the end of the PN junction interface can be further reduced.

Further, by widening the bandwidth by using a CIGS-based thin film in which a part of In (indium) is replaced with gallium, the carrier recombination process can be reduced, and the dark current can be further reduced.

In addition, by providing a non-doped ZnO film (i-ZnO) as a translucent electrode layer, voids and pinholes generated in the underlying CIGS thin film are embedded in a semi-insulating layer, and an ip bond is formed with the CIGS thin film to form a conductive film. Sexual ZnO membrane (n)⁺) Can be prevented from leaking due to the tunnel current that occurs when it is in direct contact with the CIGS thin film. Therefore, by thickening the non-doped ZnO film (i-ZnO), the dark current at the PN junction interface can be further reduced (it can be reduced to about 1/5).

Further, the photoelectric conversion device of the present invention is patterned by using photolithography, and damage or defects do not occur in the crystal of the compound semiconductor as in the case of adopting mechanical scribing, and therefore, it is useless at the interface of the PN junction. No energy level is generated, and dark current can be reduced.

Further, by devising the pattern of the ZnO film and adopting a structure in which the PN junction interface is embedded, it is possible to prevent a leakage current from the end of the PN junction interface. That is, by changing the manufacturing process and optimizing the device structure of the light absorption layer and the translucent electrode layer, the dark current is reduced to 10.³Can be improved on the order of.

Also, Cu (Inx, Ga (1-x)) Se₂Bandgap control at 10 dark current²It can be reduced on the order of.

Since the sensor of the present invention has high sensitivity to near-infrared light, it can be used as a security camera (a camera that senses visible light during the day and near-infrared light at night) or a personal authentication camera (effect of external light). It can be sufficiently used as a camera for personal authentication with near-infrared light that does not receive light) or as an in-vehicle camera (camera mounted on a car for visual assistance at night or for securing a distant field of view).

Further, in the photoelectric conversion of the present invention, the photoelectric conversion loss at the interface of the PN junction is sufficiently reduced as compared with the conventional case, so that the collection efficiency of the electric charge generated by light is high and the photoelectric conversion efficiency is high. Can be realized.

The present invention has the effect of significantly reducing the dark current of a photoelectric conversion element using a compound semiconductor thin film, and therefore, a photosensor, a solid-state image sensor, and a solar cell suitable for security cameras, personal authentication cameras, and the like. It is effective as a method for manufacturing a photoelectric conversion device.

<figref num="1">The flow chart which shows the outline of the main process of the manufacturing method of the photoelectric conversion apparatus which concerns on this invention.</figref><figref num="2">(a) to (j) are cross-sectional views of the device for each of the main steps for specifically explaining the method for manufacturing the photoelectric conversion device of the present invention.</figref><figref num="3">It is a figure which shows typically the SEM (scanning electron microscope) photograph of the device for demonstrating the patterning method of a CIGS thin film, (a) is a figure which shows the state immediately after dry etching of a CIGS thin film, and (b) is further The figure which shows the state after performing wet etching</figref><figref num="4">The figure which shows typically the cross-sectional photograph of SEM (scanning microscope) of the device after patterning of a translucent electrode layer (ZnO film).</figref><figref num="5">The figure which shows the absorption coefficient with respect to the wavelength of light of a CIS thin film (CIGS thin film)</figref><figref num="6">Schematic cross-sectional view of a CMOS image sensor formed on a silicon substrate</figref><figref num="7">Schematic cross-sectional view of the composite image sensor of the present invention, in which a photoelectric conversion device (photosensor) made of a compound semiconductor thin film is laminated on a silicon substrate provided with a CMOS circuit.</figref><figref num="8">(a) to (d) are cross-sectional views of a device for explaining a conventional method for manufacturing a cell of a CIGS-based thin-film solar cell.</figref>

Code description

10 Soda lime glass (SLG) 20 Mo (molybdenum) film 30 CIGS thin film as a light absorbing layer 35 Residue after dry etching 40 Resist pattern for CIGS thin film etching 50 CdS film as a buffer layer 60 ZnO film (i-ZnO, n-ZnO) 70 ZnO film etching mask (resist pattern) 80 PN bonding interface (boundary of depleted layer) 85,90 Drawer electrode of photoelectric conversion device