JP6890004B2 - Solid-state image sensor and its manufacturing method - Google Patents

Description

The present invention relates to a solid-state image sensor such as a CMOS image sensor formed by electrically connecting a photoelectric conversion film and a signal reading circuit manufactured by semiconductor technology, and a method for manufacturing the same. It relates to a solid-state image sensor used and a method for manufacturing the same.

In recent years, the pixel size of image sensors (image sensors) used in television cameras and digital cameras has been rapidly decreasing, and the efficiency of light utilization per pixel is significantly reduced, resulting in insufficient sensitivity. It has become to.

Solid-state image sensors (silicon photodiodes) that use Si substrates are the mainstream for such image sensors, but it is said that some such silicon photodiodes are approaching their performance limits in performing photoelectric conversion. I can say.

On the other hand, it is possible to form a photoelectric conversion film in which selenium is formed on a substrate in an amorphous state and then polycrystallized by heating to improve the light absorption rate and widen the spectral sensitivity band of visible light. Is known (see Non-Patent Document 1 below).
Further, an attempt has been made to improve the sensitivity by laminating a photoelectric conversion film on a CMOS image sensor instead of the conventional silicon photodiode (see Non-Patent Document 2 below).

High-Sensitivity Image Sensors Overlaid With Thin-Film Gallium Oxide / Crystalline Selenium Heterojunction Photodiodes: Shigeyuki Imura et al .: IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 63, NO. 1, JANUARY 2016 Stacked Image Sensor Using Chlorine-doped Crystalline Selenium Photoconversion Layer Composed of Size-controlled Polycrystalline Particles: S. Imura et al .: IEEE 2015 (IEDM15-798)

As shown in FIG. 3A, in order to form the crystallized selenium film (polycrystalline film) 105 on the circuit board 130, a method of forming selenium once in an amorphous state and then crystallizing it by heating. However, fine irregularities occur on the surface of the film when it is crystallized (the surface opposite to the surface in contact with the substrate).
On the other hand, when used as a photoelectric conversion film, it is required to reduce the electric charge (dark current) generated in a state where light is not incident, so that an n-type material is placed on the crystalline selenium film (p-type) 105. It is necessary to form a p / n joint surface by laminating a film (n-type layer 103) (depositing / forming a film by using a sputtering method, a vacuum deposition method, or the like).

However, the n-type layer 103 is placed on the crystal selenium film 105 having irregularities on the crystallized surface.
When these are laminated, the p / n junction becomes insufficient and the dark current cannot be reduced.

On the contrary, as shown in FIG. 3B, if an amorphous selenium film is formed and crystallized on a flat film in which an n-type material film (n-type layer 203) is formed on the circuit substrate 230, Although a flat p / n joint surface can be produced, the surface of the transparent electrode film 202 formed by applying an electric field into the film has an uneven shape that follows the unevenness of the surface of the crystalline selenium film 205. This causes a disconnection state.

If the uneven surface itself of the crystalline selenium film 305 (see FIG. 3C) is polished, cracks and defects of the film itself are likely to occur, and the characteristics may deteriorate. Further, a method is also conceivable in which a metal electrode for connection (connection electrode 320) for each pixel is provided on the uneven surface, and the connection electrode 320 is joined to the pixel electrode 334 of the circuit board 330 of the signal reading circuit. As shown in 3 (c), the surface of the connecting electrode 320 laminated on the uneven surface of the crystalline selenium film 305 has irregularities following the uneven surface of the crystalline selenium film 305, which causes the pixel electrode 334. The contact area with the connection electrode 320 changes each time, and it is difficult to uniformly join the connection electrode 320 with the pixel electrode 334 over the entire light receiving region. This causes variations in the contact resistance of each pixel and causes deterioration of the in-plane uniformity of the output image.

A method of forming the connecting electrode 320 thickly and then polishing and flattening it is conceivable, but there is a problem in the adhesion between the connecting electrode 320 and the crystalline selenium film 305, so that the film peels off during polishing. There is a risk that it will end up.

The present invention has been made in view of such circumstances, and when the selenium constituting the photoelectric conversion film is crystallized, it is possible to form a selenium having good characteristics even if the surface of the selenium film is uneven. It is an object of the present invention to provide a solid-state image sensor and a method for manufacturing the same, which can improve the sensitivity while suppressing the occurrence of cracks and the like even when the photoelectric conversion film is combined with a signal reading circuit manufactured by semiconductor processing technology. Is.

In order to achieve the above object, the solid-state image sensor of the present invention and the manufacturing method thereof have the following configurations.
That is, the solid-state image sensor of the present invention is
In a solid-state image sensor in which a photoelectric conversion unit and a signal reading circuit unit using semiconductor technology are integrated.
In the photoelectric conversion unit, a transparent electrode film, an n-type layer, a p-type layer made of crystalline selenium, and connection electrodes located so as to correspond to each pixel are arranged in this order on a translucent substrate. The photoelectric conversion film composed of the n-type layer and the p-type layer is formed during polishing of the photoelectric conversion film, except for the joint portion with the connection electrode and the surface facing the transparent electrode film. The connection electrode embedded in an opening formed in the insulator so as to be abutted and surrounded by an insulator functioning as a protective film, and corresponding to each pixel. However, one end side is bonded to the photoelectric conversion film, and the other end side is such that the tip surface flattened by the polishing treatment protrudes from the opening by a minute amount, or around the opening. It is arranged so that it is flush with the surface of the insulator by polishing.
The signal reading circuit unit includes a signal reading circuit arranged on the substrate and a circuit board having pixel electrodes provided for each circuit corresponding to each pixel of the signal reading circuit.
And said photoelectric conversion portion and the signal reading circuit section, characterized and each of the connection electrodes, that picture element electrode that corresponds to the connection electrodes of the each formed by integrally by joining together It is a thing.

Further, the insulator is preferably made of SiOxNy (0 ≦ x, 0 ≦ y).
Further, the connection electrode is preferably made of Au.

Further, the method for manufacturing the solid-state image sensor of the present invention is
In a method for manufacturing a solid-state image sensor that integrates a photoelectric conversion unit and a signal reading circuit unit using semiconductor technology.
The photoelectric conversion unit is formed by laminating a transparent electrode film, an n-type layer, and a p-type layer made of crystalline selenium on a translucent substrate in this order, and then the n-type layer and the n-type layer. The photoelectric conversion film composed of the p-type layer is covered with an insulator that functions as a protective film that prevents the photoelectric conversion film from peeling off during polishing , and then at a position corresponding to each pixel of the insulator. An opening reaching the photoelectric conversion film is formed from the surface facing the signal reading circuit portion, and the opening and the facing surface side facing the signal reading circuit portion are embedded and covered with a predetermined metal. Next, the predetermined metal is polished so that the predetermined metal protrudes from the opening by a small amount or is flush with the surface of the insulator around the opening.
After that, each of the connection electrodes made of the predetermined metal is joined to the corresponding pixel electrode of the signal reading circuit unit to integrate the photoelectric conversion unit and the signal reading circuit unit. Is to be.

Further, it is preferable that the electroplating method is a process of embedding and covering the opening and the side of the photoelectric conversion unit facing the signal reading circuit unit with a predetermined metal.
Further, the treatment for polishing the predetermined metal is preferably CMP polishing.

In the solid-state image sensor of the present invention, the photoelectric conversion unit is connected to a transparent electrode film, an n-type layer, and a p-type layer made of crystalline selenium on a translucent substrate so as to correspond to each pixel. For electrodes and
Are arranged in this order, and the photoelectric conversion film is arranged so as to be surrounded by an insulator except for the joint portion with the connection electrode. Further, the connection electrode extends inside the insulator and is joined to each pixel electrode of the signal reading circuit section.
Further, in the method for manufacturing a solid-state image sensor of the present invention, the photoelectric conversion unit is laminated on a translucent substrate in this order with a transparent electrode film, an n-type layer, and a p-type layer made of crystalline selenium. Then, the photoelectric conversion film composed of the n-type layer and the p-type layer is coated with an insulator, and then
An opening that reaches the photoelectric conversion film from the side facing the signal reading circuit section is formed at a position corresponding to each pixel of the insulator, and the opening and the facing surface of the signal reading circuit section are formed. The side surface is embedded and coated with a predetermined metal so that the predetermined metal protrudes from the opening by a small amount or is flush with the surface of the insulator around the opening. Is polishing the metal.

As described above, according to the solid-state image sensor of the present invention and the method for manufacturing the same, the connection electrode bonded to the pixel electrode passes through the insulator having a predetermined length and is further laminated on the insulator. Therefore, it is possible to polish the unevenness of the surface of the connecting electrode formed by imitating the unevenness of the surface of the photoelectric conversion film, and the unevenness formed on the other surface does not cause any inconvenience.
Thereby, depending on the solid-state image sensor of the present invention and the manufacturing method thereof, the above-mentioned problems of the prior art can be solved. That is, the p / n bonding of the photoelectric conversion film is incomplete (
(See FIG. 3 (a)), the transparent electrode does not become non-uniform (see FIG. 3 (b)), and the connection between the connection electrode on the photoelectric conversion unit side and the pixel electrode is non-uniform (see FIG. 3 (b)). (See FIG. 3C), and a highly sensitive solid-state image sensor can be obtained while suppressing the occurrence of cracks and the like.

It is the schematic sectional drawing which shows the solid-state image sensor which concerns on embodiment of this invention. It is a schematic diagram (FIGS. 2A to 2G) which shows a part of the process of the manufacturing method of the solid-state image sensor which concerns on embodiment of this invention. It is a figure (the problem (a) of the prior art 1, the problem (b) of the prior art 2, and the problem (c) of the prior art 3) for explaining the problem which concerns on the prior art.

Hereinafter, the solid-state image sensor and the manufacturing method thereof according to the embodiment of the present invention will be described with reference to the drawings.
First, the solid-state image sensor according to the present embodiment will be described with reference to FIG.

The solid-state image sensor 50 is formed by joining a photoelectric conversion unit 60 and a signal reading circuit unit 70.
In the photoelectric conversion unit 60, a transparent electrode film 2, an n-type layer 3, a crystalline selenium film (p-type layer) 5, and a connection electrode (Au8) 20 are arranged in this order on a translucent substrate 1. A photoelectric conversion film (n-type layer 3 and a crystalline selenium film (p-type layer)) other than the joint portion with the connecting electrode 20 and the surface facing the transparent electrode film 2 together with the (photoelectric conversion unit laminate). 10 (consisting of 5) is arranged so as to be in contact with and surrounded by the insulating film 6.

The translucent substrate 1 is made of glass or transparent plastic, and the transparent electrode film 2 is ITO.
The n-type layer 3 is composed of gallium oxide (Ga ₂ O ₃ ) or the like, and the crystalline selenium film 5 is composed of polycrystalline selenium.

Further, the transparent electrode film 2 and the photoelectric conversion film 10 of the photoelectric conversion unit laminate are covered with the insulating film 6, and the surface side of the insulating film 6 which is the signal reading circuit facing surface at the position corresponding to each pixel. A connection electrode 20 (Au8) is provided in the opening (see FIG. 2E) extending from the metal to the surface of the crystalline selenium film 5.
In FIG. 1, the connection electrode 20 is formed so as to protrude slightly outward from the surface of the insulating film 6 (lower surface in FIG. 1).

The insulating film 6 is formed from _{an oxide of Si such as SiO 2} , SiON and SiN, a nitride and an oxynitride. Therefore, the general formula is SiOxNy (0 ≦ x, 0 ≦ y).
It is represented by.
Further, the connection electrode 20 is made of Au. However, a Ti layer may be provided between Au in order to improve the adhesion between Au and crystalline selenium.

On the other hand, the signal reading circuit unit 70 is composed of a circuit board 30 provided with the signal reading circuit 32, and pixel electrodes 34 are provided corresponding to each pixel circuit of the signal reading circuit 32.
The signal reading circuit unit 70 and the photoelectric conversion unit 60 described above configured in this way are integrated by joining the pixel electrode 34 and the connection electrode 20 respectively.
As described above, in the present embodiment, the connection electrode 20 slightly protrudes (for example, on the submicron order) from the lower surface of the insulating film 6 shown in FIG. There is a slight gap between the read circuit units 70.

Since the solid-state imaging device 50 of the present embodiment has the above-described configuration, when the crystalline selenium film 5 used as the p-type layer of the photoelectric conversion film 10 is heated from the amorphous selenium film 4 to be formed. Even if the surface of the crystalline selenium film 5 is uneven, the uneven shape is not reflected on the other surface, and is generated by the uneven shape being reflected on the other surface in the prior art. It is possible to solve various problems (FIGS. 3A, 3B, and 3C).

Next, a method of manufacturing the solid-state image sensor according to the present embodiment, particularly the manufacturing method of the photoelectric conversion unit 60 will be described with reference to FIG.
First, as shown in FIG. 2A, the transparent electrode film 2 is sputtered on the translucent substrate 1 with a material such as ITO and ZnO, and the n-type layer 3 is sputtered with a material such as _{Ga 2} O _{3 respectively.} It is formed flat to a desired thickness by using a method, a vacuum deposition method, or the like.

Next, as shown in FIG. 2B, the amorphous selenium film 4 is formed flat on the n-type layer 3 to a desired thickness by using a sputtering method, a vacuum vapor deposition method, or the like.
Next, as shown in FIG. 2C, the amorphous selenium film 4 formed to a desired thickness is heated to undergo polycrystallization. At that time, the surface of the crystalline selenium film 5 in contact with the n-type layer 3 becomes flat, and a good p / n joint surface is formed. However, the surface of the crystal selenium film 5 (the surface opposite to the n-type layer 3) has irregularities (steps) due to the crystal grains.
As described above, the step of forming the photoelectric conversion unit laminate is completed.

Next, as shown in FIG. 2D, the photoelectric conversion film (n-type layer 3 and the crystalline selenium film 5) 10 (see FIG. 1) is entirely covered with the insulating film 6. The insulating film 6 includes SiO ₂ , SiON, SiN.
It is formed by a CVD method, a sputtering method, a vacuum vapor deposition method, or the like using an insulating material such as. The insulating film 6 functions as a protective film for preventing the photoelectric conversion film 10 from peeling off during polishing, which will be described later.

Subsequently, as shown in FIG. 2 (e), an opening 7 is formed in the insulating film 6 for each region corresponding to the pixel by using a photolithography method, and the surface of the crystalline selenium film 5 is the opening. It is formed so as to be exposed through 7.

Next, as shown in FIG. 2 (f), a metal for electrically connecting to the crystalline selenium film 5 (Au8 in the present embodiment: the same applies hereinafter) is embedded in the opening 7 of the insulating film 6, and this metal is formed. Also covers the surface of the insulating film 6 with. The coating thickness of the surface of the insulating film 6 is, for example, 1 μm. After that, this metal portion on the opening 7 and the insulating film 6 is polished.
As a result, the metal portion provided on the insulating film 6 is removed, and the uneven portion on the surface of the metal portion on the opening 7 that reflects the uneven shape of the crystalline selenium film 5 is also removed.

Hereinafter, a case where the manufacturing process using FIG. 2 (f) is performed by a damascene process using Au8 as the metal will be specifically described.
First, in order to embed Au 8 in the opening 7 of the insulating film 6, the entire upper surface of the insulating film 6 is electroplated with Au. The thickness of the electroplating layer is such that the opening 7 of the insulating film 6 is completely filled with Au8 and the thickness required for the subsequent flattening treatment by polishing is satisfied. Further, in order to improve the adhesion between Au and crystalline selenium and to serve as the core of the growth of the plating film, a Ti layer may be provided by sputtering or the like before electroplating Au.

At this stage, as shown in FIG. 2 (f), the surface of the electroplating layer directly above the opening 7 reflects the uneven shape of the surface of polycrystalline selenium. After electroplating, the electroplating layer is polished and flattened using a chemical / mechanical polishing (CMP) method. At this time, the insulating film 6 that covers the entire surface of the photoelectric conversion film 10 functions as a protective film, and peeling of the photoelectric conversion film 10 can be prevented.

Further, as shown in FIG. 2 (g), polishing is completed in a state where all unnecessary Au directly above the insulating film 6 is removed and the surface of Au 8 embedded in the opening 7 is flattened. At this time, the embedded Au 8 is prevented from being lower than the insulating film 6. That is, the embedded Au 8 is formed so as to be slightly protruding from the insulating film 6 or in a flush state (in this case, there is no gap between the photoelectric conversion unit 60 and the signal reading circuit unit 70).

In the method for manufacturing the solid-state image sensor of the present embodiment, since the electroplated Au8 is polished by CMP polishing, the uneven shape generated on the surface of the crystal selenium film 5 is reflected on other surfaces. It is possible to solve the conventional problem such as being done.

The solid-state image sensor and the method for manufacturing the solid-state image sensor of the present invention are not limited to those of the above-described embodiment, and various other aspects can be changed. For example, in the above embodiment, specific materials for forming the translucent substrate 1, the transparent electrode film 2, and the n-type layer 3 are described, but the present invention is not limited thereto. The film thickness can also be appropriately selected.

Further, the method for crystallizing amorphous selenium is not limited to the heating method.
The material for forming the insulating film 6 and the pixel electrode 34 is not limited to that of the above embodiment. As the material for forming the insulating film 6, a resin may be used as long as it has a property that can be deposited around the photoelectric conversion film 10.
As a material for forming the connecting electrode 20, another metal or resin-based conductive material may be used as long as it can be embedded in the opening 7. However, when gold is plated, the seed layer, which is the core for electroplating, is generally formed of titanium, so that there is an advantage that it is easy to obtain an ohmic. Further, when the connection electrode 20 is made of gold, if the pixel electrode 34 of the signal readout circuit side 70 is also made of gold, diffusion bonding can be used for the connection, and better conduction characteristics and strong bonding can be obtained. Be done.

Further, the method of embedding the forming material of the connecting electrode 20 in the opening 7 is not limited to electroplating, and a metal material may be formed by using another film forming method such as a sputtering method or a vacuum vapor deposition method. good. However, if the electroplating method is used, the production is easy.

Further, the connection electrode 20 may be formed by filling the opening 7 with a resin-based conductive material by a coating method, forming a metal film on the opening, and patterning the metal. In this case, the reflection of the uneven shape on the surface of the crystalline selenium film 5 can be reduced by the treatment of filling the opening 7 with the resin-based conductive material.
Further, the polishing method of the connecting electrode 20 is not limited to CMP polishing, and other polishing methods may be used.

1,301 Translucent substrate 2, 102, 202, 302 Transparent electrode film 3, 103, 203, 303 n-type layer 4 Amorphous selenium film 5, 105, 205, 305 Crystalline selenium film 6 Insulation film 7 Opening 8 Au
10 Photoelectric conversion film 20, 320 Connection electrode 30, 130, 230, 330 Circuit board 32 Signal read circuit 34, 334 Pixel electrode 50 Solid-state image sensor 60 Photoelectric conversion unit 70 Signal read circuit unit

Claims (6)

In a solid-state image sensor in which a photoelectric conversion unit and a signal reading circuit unit using semiconductor technology are integrated.
In the photoelectric conversion unit, a transparent electrode film, an n-type layer, a p-type layer made of crystalline selenium, and connection electrodes located so as to correspond to each pixel are arranged in this order on a translucent substrate. The photoelectric conversion film composed of the n-type layer and the p-type layer is formed during polishing of the photoelectric conversion film, except for the joint portion with the connection electrode and the surface facing the transparent electrode film. The connection electrode embedded in an opening formed in the insulator so as to be abutted and surrounded by an insulator functioning as a protective film, and corresponding to each pixel. However, one end side is bonded to the photoelectric conversion film, and the other end side is such that the tip surface flattened by the polishing treatment protrudes from the opening by a minute amount, or around the opening. It is arranged so that it is flush with the surface of the insulator by polishing.
The signal reading circuit unit includes a signal reading circuit arranged on the substrate and a circuit board having pixel electrodes provided for each circuit corresponding to each pixel of the signal reading circuit.
And said photoelectric conversion portion and the signal reading circuit section, characterized and each of the connection electrodes, that picture element electrode that corresponds to the connection electrodes of the each formed by integrally by joining together Solid-state image sensor. The solid-state image sensor according to claim 1, wherein the insulator is made of SiOxNy (0 ≦ x, 0 ≦ y). The solid-state image sensor according to claim 1 or 2, wherein the connection electrode is made of Au. In a method for manufacturing a solid-state image sensor that integrates a photoelectric conversion unit and a signal reading circuit unit using semiconductor technology.
The photoelectric conversion unit is formed by laminating a transparent electrode film, an n-type layer, and a p-type layer made of crystalline selenium on a translucent substrate in this order, and then the n-type layer and the n-type layer. The photoelectric conversion film composed of the p-type layer is covered with an insulator that functions as a protective film that prevents the photoelectric conversion film from peeling off during polishing , and then at a position corresponding to each pixel of the insulator. An opening reaching the photoelectric conversion film is formed from the surface facing the signal reading circuit portion, and the opening and the facing surface side facing the signal reading circuit portion are embedded and covered with a predetermined metal. Next, the predetermined metal is polished so that the predetermined metal protrudes from the opening by a small amount or is flush with the surface of the insulator around the opening.
After that, each of the connection electrodes made of the predetermined metal is joined to the corresponding pixel electrode of the signal reading circuit unit to integrate the photoelectric conversion unit and the signal reading circuit unit. A method for manufacturing a solid-state image sensor. The solid-state image sensor according to claim 4, wherein a process of embedding the opening and the side of the photoelectric conversion unit facing the signal reading circuit unit with the predetermined metal and covering the openings is an electroplating method. Production method. The method for manufacturing a solid-state image sensor according to claim 4 or 5, wherein the process for polishing the predetermined metal is a CMP polishing method.

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