Photoelectric transducer and method of manufacturing same

The present invention relates to a method for manufacturing a photoelectric conversion device and a photoelectric conversion device, and particularly relates to a photoelectric conversion device such as a photosensor or a solar cell using a compound semiconductor thin film having a pyrite 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), p on the Mo electrode layer 200 by composition control.^-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 such as 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> CIS-based thin films and CIGS-based thin films are mainly used as solar cells.</p><p> On the other hand, the present inventors 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. , Security cameras (cameras that sense visible light during the day and near-infrared light at night), personal authentication cameras (cameras for personal authentication with near-infrared light that is not affected by external light), or , We examined the use as an image sensor for in-vehicle cameras (cameras mounted on cars to assist visuals at night and 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 A and B parts 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 has reached the side wall of 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 method for manufacturing a photoelectric conversion device 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 calcopyrite structure functioning as a light absorption layer, and a translucent electrode layer are laminated on a substrate. The step of patterning the compound semiconductor thin film having the calcopyrite structure by photolithography is included.</p><p> According to this configuration, instead of mechanical scribing, a compound semiconductor thin film having a calcopyrite structure is patterned by etching by photolithography. Along with this, each of the lower electrode layer and the translucent electrode layer will also be patterned by etching using photolithography. 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.</p><p> Further, in the method for manufacturing the photoelectric conversion device of the present invention, the step of patterning the compound semiconductor thin film having the calcopyrite structure is a first step of patterning by dry etching and a wet etching residue generated in this first step. Includes a second step of removing by etching.</p><p> When patterning a compound semiconductor thin film having a pyrite structure that functions as a light absorption layer, two-stage etching that combines dry etching and wet etching is performed, thereby realizing highly accurate pattern formation without residue. A p-type compound semiconductor thin film having a calcopyrite structure that functions as a light absorption layer can be etched by dry etching, but in this case, complete etching cannot be performed, and a large number of columnar residues remain. Further, in wet etching, undercut occurs due to side etching (a phenomenon in which etching proceeds in the lateral direction for a portion immediately below the resist pattern), and the pattern cannot be formed accurately. Therefore, the compound semiconductor thin film is patterned by dry etching without side etching, and then only the dry etching residue is removed by a short-time wet etching process, whereby the residue is not generated and the precision is high. It becomes possible to form a pattern. As a result, damage and defects do not occur in the crystal of the compound semiconductor as in the case of adopting mechanical etching, and the dark current can be significantly reduced.</p><p> Further, in the method for manufacturing a photoelectric conversion device of the present invention, in the first step, dry etching is performed using chlorine-based gas as an etchant, and in the second step, the compound semiconductor thin film having a chalcopyrite structure is formed. Includes those treated with a mixed solution of bromine and methanol or a mixed solution of water and ammonia, and then treated with a mixed solution of hydrochloric acid and nitric acid.</p><p> By using a chlorine-based gas as an etchant for dry etching, the compound semiconductor thin film constituting the light absorption layer can be etched at a high rate. Also, in wet etching, the residue can be removed efficiently and completely.</p><p> Further, in the method for manufacturing 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> To reduce dark current, CIS thin film (CuInSe)₂) Is effective in widening the bandgap, and therefore, a CIGS-based thin film in which a part of In (indium) is replaced with gallium is used. By increasing the bandwidth, the carrier recombination process can be reduced and the dark current can be reduced. In addition, CuAlS is another compound semiconductor thin film with a calcopyrite structure.₂, CuAlSe₂, CuAlTe₂, CuGaS₂, CuGaSe₂, CuGaTe₂, CuInS₂, CuInSe₂, CuInTe₂, AgAlS₂, AgAlSe₂, AgAlTe₂, AgGaS_2,AgGaSe₂, AgGaTe₂, AgInS₂, AgInSe₂, AgInTe₂Other compound semiconductor thin films can also be applied.</p><p> Further, 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 steps of forming the translucent electrode layer including the step of forming a thin film include 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. To n⁺Includes those involving the step of forming a type ZnO film.</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. Here, the PVD method refers to a method of depositing raw materials evaporated in a vacuum to form a film.</p><p> Further, the photoelectric conversion device of the present invention is a photoelectric conversion device manufactured by the method for manufacturing the photoelectric conversion device of the present invention.</p><p> The photoelectric conversion device of the present invention is accurately patterned without leaving a residue by using photolithography, and does not cause damage or defects in the crystal of the compound semiconductor as in the case of adopting mechanical scribing. Unnecessary energy levels are not generated at the interface of the PN junction, and dark current can be dramatically reduced. That is, the dark current can be improved on the order of 103 by changing the manufacturing process and optimizing the device structure of the light absorption layer and the translucent electrode layer. Also, Cu (In)_x, Ga_(1-x)) Se₂Bandgap control at the can reduce dark currents on the order of 102.</p><p> Further, one aspect of the photoelectric conversion device of the present invention is a photosensor having sensitivity in the near infrared light region.</p><p> The sensor of the present invention, obtained by forming a photosensor (image sensor) using a compound semiconductor thin film with significantly reduced dark current, has high sensitivity to near-infrared light, and thus has security. Cameras (cameras that sense visible light during the day and near-infrared light at night), personal authentication cameras (cameras for personal authentication with near-infrared light that is not affected by external light), or in-vehicle It can be fully used as a camera (a camera mounted on a car for visual assistance at night and for securing a distant field of view).</p><p> Further, the photoelectric conversion device of the present invention is a solar cell.</p><p> 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 solar cell with high photoelectric conversion efficiency is realized. can do.</p>

<p> According to the present invention, by adopting a method of patterning a compound semiconductor thin film having a calcopyrite structure that functions as a lower electrode layer and a light absorption layer by etching by photolithography, damage as in the case of mechanical scribing is performed. Etching and defects do not occur in the compound semiconductor thin film, and dark current can be significantly reduced.</p><p> In addition, the light absorption layer is highly accurate by performing two-stage etching that combines dry etching and wet etching without causing damage or defects to the crystals of the compound semiconductor thin film and without leaving any residue. Patterning can be realized.</p><p> Further, by using a chlorine-based gas as an etchant for dry etching, the compound semiconductor thin film constituting the light absorption layer can be etched at a high rate and with high accuracy. Also, in wet etching, the residue can be removed efficiently and completely.</p><p> In addition, as a compound semiconductor thin film that serves as a light absorption layer, a CIGS-based thin film in which a part of In (indium) is replaced with gallium is used, and by widening the bandwidth, the carrier recombination process can be reduced, resulting in darkness. The current can be reduced (reduced to 1/5).</p><p> Further, the photoelectric conversion device of the present invention is scribed with high accuracy without leaving a residue by using photolithography, and the crystal of the compound semiconductor is not damaged or defective as in the case of adopting mechanical scribing. Therefore, unnecessary energy levels are not generated at the interface of the PN junction, and the dark current can be significantly reduced. That is, the dark current can be improved on the order of 103 by modifying the manufacturing process to optimize the device structure of the light absorbing layer as well as the translucent electrode layer. Also, Cu (In)_x, Ga_(1-x)) Se₂Bandgap control at the can reduce dark currents on the order of 102.</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 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.</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 method for manufacturing a photoelectric conversion device according to the present invention.

In this manufacturing process, the lower electrode layer that is laminated and formed, the p-type compound semiconductor thin film with a calcopyrite structure that functions as a light absorption layer (hereinafter referred to as CIGS thin film), and the translucent electrode layer (non-doped portion and impurities are present. Doped n⁺Each of the mold-indicating parts) was 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 photolithography (step). S1). This forms an electrically separated Mo island region.

Next, a CIGS thin film is formed and patterning is performed using photolithography (step S2). This step S2 is the most important feature of the manufacturing method of the present invention.

That is, composition-controlled p^-A type CIGS thin film (Cu (Inx, Ga (1-x)) Se2 (0 x 1)) is formed by, for example, an ion beam sputtering method (step S2a). 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 S2b). 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 S3).

Next, by the sputtering method, a non-doped ZnO film (i-ZnO) and an impurity-doped low-resistance ZnO (n)⁺) A film is continuously formed (step S4). 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 S5). In this step S5, 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 as appropriate. 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 1.7 μm thick by the ion beam sputtering method using a sputtering target having a composition of Cu: In: Ga: Se = 1: 0.5: 0.5: 2. Formed with.

As shown in FIG. 2 (c), 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 as an etchant. 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.

In this way, by using a chlorine-based gas as an etchant for dry etching, 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. The 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 sputtering 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, although 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 as an etching mask, the ZnO film (i-ZnO and ZnO (n +)) 30 is wet-etched.

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 the 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 lead-out electrodes 90 and 95 made of aluminum or the like are formed. This completes the photoelectric conversion device.

This photoelectric conversion device can also be applied 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 in the figure, 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 MOS transistor or the like is formed to form a composite image sensor.

FIG. 6 is a schematic cross-sectional view of a normal CMOS image sensor formed on a silicon substrate. Further, FIG. 7 is a 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-based CMOS circuit.

As shown in Fig. 6, a normal CMOS image sensor has a 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.^-The n + diffusion layers 702, 704, 706, 708 constituting the MOS transistor are formed in the type silicon substrate 700, 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. Also, by patterning the ZnO film, 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 dramatically reduced by about 5 orders of magnitude compared to conventional devices. Has been done.

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 (In)._x, Ga_(1-x)) Se₂Is used, but the present invention is not limited to this.

As a CIGS thin film, Cu (In_x, Ga_(1-x)) (Se_y, 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, a method of patterning each of a lower electrode layer, a compound semiconductor thin film having a calcopylite structure that functions as a light absorption layer, and a translucent electrode layer by etching by photolithography is adopted. As a result, damage and defects do not occur in the compound semiconductor thin film as in the case of mechanical scribing, and dark current can be significantly reduced.

Further, for the light absorption layer, by performing two-stage etching that combines dry etching and wet etching, high-precision patterning is performed without causing damage or defects to the crystal of the compound semiconductor and without leaving a residue. Can be realized.

Further, by using a chlorine-based gas as an etchant for dry etching, the compound semiconductor thin film constituting the light absorption layer can be etched at a high rate. Also, in wet etching, the residue can be removed efficiently and completely.

In addition, a CIGS-based compound semiconductor thin film in which a part of In (indium) is replaced with gallium is used as the compound semiconductor thin film to be the light absorption layer, and the carrier recombination process can be reduced by widening the bandwidth. And the dark current can be reduced.

Further, the photoelectric conversion device of the present invention is scribed with high accuracy without leaving a residue by using photolithography, and the crystal of the compound semiconductor is not damaged or defective as in the case of adopting mechanical etching. Therefore, unnecessary energy levels are not generated at the interface of the PN junction, and the dark current can be significantly reduced.

That is, the dark current can be improved on the order of 103 by modifying the manufacturing process and optimizing the device structure. Also, Cu (In)_x, Ga_(1-x)) Se₂Bandgap control at the can reduce dark currents on the order of 102.

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.

Since the present invention can significantly reduce the dark current of a photoelectric conversion element using a compound semiconductor thin film, it is possible to manufacture a photosensor, a solid-state image sensor, a solar cell, and these photoelectric conversion elements suitable for security cameras, personal authentication cameras, and the like. It is effective as a method.

<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 a photoelectric conversion device (photosensor) made of a compound semiconductor thin film.</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