JP2021114554A - Solid-state imaging element and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image sensor capable of suppressing an increase in dark current due to addition of impurities while enabling carrier multiplication at a low voltage.
A crystallized gallium oxide film 10 is used in a solid-state image sensor 100 including a gallium oxide film 10 containing impurities and a crystalline selenium film 20. Further, a signal readout circuit board 60, a first electrode 40, a bonding film 30, a crystalline selenium film 20, a gallium oxide film, a second electrode, and a transparent substrate 70 are provided in this order.
[Selection diagram] Fig. 1

Description

The present invention relates to a solid-state image sensor and a method for manufacturing the same, and more particularly to a junction-type solid-state image sensor in which the photoelectric conversion unit is a PN junction of crystalline selenium and gallium oxide and a method for manufacturing the same.

In recent years, the number of pixels of a solid-state image sensor has increased, and the pixel area has been reduced accordingly, so that the sensitivity of the solid-state image sensor has become a problem. Therefore, as shown in FIG. 9, a laminated image sensor that uses crystalline selenium or the like having a high absorption coefficient in visible light instead of conventional silicon as a photoelectric conversion material has been studied. By using a material with a high absorption coefficient in a stacked image pickup device, sufficient light absorption is possible even with a thin film, and carrier multiplication is possible by applying a voltage, so high sensitivity is expected (for example, non-patented). See Document 1 and Non-Patent Document 2). On the other hand, in the laminated image sensor, there is a concern that the sensitivity may be insufficient due to the fact that the traveling carrier is an electron and the incident light is absorbed in the selenium film before reaching the depletion layer.

Therefore, a junction type image pickup device including a signal readout circuit board, a pixel electrode, a crystalline selenium film, a gallium oxide film, a transparent electrode, and a transparent substrate in this order has been proposed (see, for example, Patent Document 1). In the above-mentioned stacked image sensor, since the photoelectric conversion unit is directly laminated on the signal readout circuit board, the photoelectric conversion unit cannot be heated above the heat resistant temperature (approximately 350 degrees) of the signal readout circuit board. On the other hand, as shown in FIG. 10, in each of the junction type imaging devices, after the first amorphous selenium film is formed on the signal readout circuit board and the gallium oxide film and the second amorphous selenium film are formed on the transparent substrate. Since the amorphous selenium film is bonded, the photoelectric conversion portion on the transparent substrate side can be heated above the heat resistant temperature of the signal readout circuit board. As a result, the characteristics of the photoelectric conversion unit are expected to be improved by crystallization and the like, so that the sensitivity of the junction type image sensor is expected to be further increased.

JP-A-2017-208376

S. Imura, K. Kikuchi, K. Miyakawa, H. Ohtake, M. Kubota, T. Okino, Y. Hi-rose, Y. Kato, N. Teranishi, IEEE Trans. Electron Devices 63, 86 (2016) S. Imura et al., "Low-voltage-operation avalanche photodiode based on n-gallium oxide / p-crystalline selenium heterojunction", Applied Physics Letters, Vol. 104, No. 24, pp. 242101-242101-4 (2014) )

However, when a high voltage is applied to the conventional junction type image sensor in order to increase the sensitivity by multiplying the carrier, the signal readout circuit may be destroyed. Therefore, it has been studied to realize carrier multiplication at a low voltage by adding an impurity to the photoelectric conversion unit, but there is a concern that the dark current will increase due to the addition of the impurity.

An object of the present invention made in view of such circumstances is to provide a solid-state image sensor capable of suppressing an increase in dark current due to the addition of impurities while enabling carrier multiplication at a low voltage, and a method for manufacturing the same. ..

In order to solve the above-mentioned problems, the present inventors have diligently studied and conceived to crystallize a gallium oxide film to which impurities are added by high-temperature heat treatment in a junction-type image sensor. Then, the present inventors have experimentally confirmed that this junction-type image sensor can suppress the increase in dark current due to the addition of impurities while being able to multiply carriers at a low voltage. The present invention has been completed based on the above findings, and its gist structure is as follows.

The solid-state imaging device according to one embodiment is characterized by including a gallium oxide film containing impurities and crystallized, and a crystalline selenium film.

Further, in the solid-state image sensor according to the embodiment, the signal readout circuit board, the first electrode, the bonding film, the crystal selenium film, the gallium oxide film, the second electrode, and the transparent substrate are used. It is characterized by preparing in order.

The method for manufacturing a solid-state imaging device according to one embodiment includes a step of forming a first amorphous selenium film on a signal readout circuit substrate, a step of forming a gallium oxide film to which impurities are added on a transparent substrate, and the oxidation. A step of subjecting a gallium film to a first heat treatment to crystallize the gallium oxide film, a step of forming a second amorphous selenium film on the crystallized gallium oxide film, and the first amorphous selenium film and the first amorphous selenium film. 2. It is characterized by including a step of joining the amorphous selenium film and a step of subjecting the bonded amorphous selenium film to a second heat treatment to crystallize the amorphous selenium film.

Further, in the method for manufacturing a solid-state image sensor according to one embodiment, the step of crystallizing the gallium oxide film is 700 degrees or more and 1200 degrees or less and 10 minutes or more in an atmosphere containing oxygen in the gallium oxide film. It is a step of performing the first heat treatment for less than an hour.

According to the present invention, it is possible to provide a solid-state image sensor capable of suppressing an increase in dark current due to the addition of impurities while enabling carrier multiplication at a low voltage, and a method for manufacturing the same.

It is a schematic cross-sectional view which shows an example of the structure of the solid-state image sensor which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the reverse bias voltage and dark current density which concerns on one Embodiment of this invention. It is a schematic cross-sectional view which shows an example of the manufacturing method of the solid-state image sensor which concerns on one Embodiment of this invention. It is a schematic cross-sectional view which shows an example of the manufacturing method of the solid-state image sensor which concerns on one Embodiment of this invention. It is a schematic cross-sectional view which shows an example of the manufacturing method of the solid-state image sensor which concerns on one Embodiment of this invention. It is a schematic cross-sectional view which shows an example of the manufacturing method of the solid-state image sensor which concerns on one Embodiment of this invention. It is a schematic cross-sectional view which shows an example of the manufacturing method of the solid-state image sensor which concerns on one Embodiment of this invention. It is a schematic cross-sectional view which shows an example of the manufacturing method of the solid-state image sensor which concerns on one Embodiment of this invention. It is a flowchart which shows an example of the manufacturing method of the solid-state image sensor which concerns on one Embodiment of this invention. It is a schematic cross-sectional view of the sample 1 which concerns on Example. It is a schematic cross-sectional view of the sample 2 which concerns on Example. It is a schematic cross-sectional view of the sample 3 which concerns on Example. It is a figure which shows an example of the voltage-current characteristic in a sample 1, a sample 2, and a sample 3 which concerns on Experimental Example 1. It is a figure which shows an example of the surface of the crystalline selenium film in the sample 1, the sample 2, and the sample 3 obtained by the AFM measurement which concerns on Experimental Example 2. FIG. It is a figure which shows an example of the relationship between the diffraction angle and the intensity in Sample 1, Sample 2, and Sample 3 obtained by the XRD measurement which concerns on Experimental Example 3. FIG. FIG. 5 is an enlarged view showing an example of the relationship between the diffraction angle and the intensity in Sample 1, Sample 2, and Sample 3 obtained by the XRD measurement according to Experimental Example 3. It is a schematic cross-sectional view which shows an example of the structure of the conventional laminated type image sensor. It is a schematic cross-sectional view which shows an example of the structure of the conventional junction type image sensor.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In principle, the same components are given the same reference number, and duplicate explanations are omitted. In each figure, for convenience of explanation, the aspect ratio of each configuration is exaggerated from the actual ratio.

<Solid image sensor>
An example of the configuration of the solid-state image sensor 100 according to the present embodiment will be described with reference to FIGS. 1 and 2.

The solid-state image sensor 100 includes a signal readout circuit board 60, a first electrode 40, a bonding film 30, a crystalline selenium film 20, a gallium oxide film 10 crystallized containing impurities, a second electrode 50, and a transparent substrate. 70 and 70 are provided in this order. The gallium oxide film 10, the crystalline selenium film 20, and the bonding film 30 crystallized containing impurities function as the photoelectric conversion unit 200. The negative electrode of the power supply is connected to the first electrode 40, and the positive electrode of the power supply is connected to the second electrode 50.

Hereinafter, the case where tin is used as an impurity added to the gallium oxide film will be described as an example, but the impurity added to the gallium oxide film is not limited to tin. As the impurities added to the gallium oxide film, for example, silicon, germanium or the like may be used.

[Gallium oxide film]
The gallium oxide film 10 crystallized containing tin is a photoelectric conversion unit 200 in the solid-state imaging device 100 and functions as an n-type semiconductor. The tin-containing crystallized gallium oxide film 10 is formed by subjecting a tin-added gallium oxide film to high-temperature heat treatment and crystallizing it. Here, the crystallization of the tin-added gallium oxide film is due to the fact that diffraction peaks are observed at diffraction angles of 38.4 °, 59.2 °, and 82.4 ° in the XRD pattern, for example. It can be confirmed (see FIG. 8A).

The atomic percentage of tin added to the gallium oxide film is preferably 6.0 atom% or more and 9.0 atom% or less. The atomic percentage of tin added to the gallium oxide film was measured by, for example, Rutherford Backscattering Analysis (RBS), and in the examples described later, the value measured by the Rutherford Backscattering Analysis was adopted.

The conditions for the heat treatment applied to the tin-added gallium oxide film are preferably 700 ° C. or higher and 1200 ° C. or lower, 10 minutes or longer and 3 hours or shorter in an oxygen-containing atmosphere. The heat treatment conditions applied to the tin-added gallium oxide film are more preferably 700 ° C. or higher and 1100 ° C. or lower, and 45 minutes or longer and 2 hours or shorter in an oxygen-containing atmosphere. The heat treatment conditions applied to the tin-added gallium oxide film are more preferably 800 ° C. or higher and 1000 ° C. or lower, 1 hour or longer and 2 hours or lower in an oxygen-containing atmosphere, and an oxygen-containing atmosphere. Of these, 800 degrees and 1 hour are most preferable.

The reason why it is preferable to set the atomic percentage of tin added to the gallium oxide film in the above range will be described.

The present inventors have experimentally confirmed that when tin is added to the gallium oxide film, the energy in the conduction band is reduced and the band gap is reduced while maintaining the energy in the valence band. Therefore, by optimizing the amount of tin added, the band offset of the conduction band can be reduced between gallium oxide and crystalline selenium. Therefore, when the atomic percentage of tin added to the gallium oxide film is 6.0 atom% or more, the operating voltage of the solid-state image sensor 100 can be reduced. Further, when the atomic percentage of tin added to the gallium oxide film is 9.0 atom% or less, excessive carrier generation due to the addition of tin can be suppressed, and an increase in dark current of the solid-state image sensor 100 can be suppressed. Therefore, the atomic percentage of tin added to the gallium oxide film is preferably 6.0 atom% or more and 9.0 atom% or less.

The reason why it is preferable to set the heat treatment conditions applied to the tin-added gallium oxide film to the above conditions will be described.

By adding tin to the gallium oxide film, carrier multiplication at low voltage becomes possible, while the surface of the crystalline selenium film becomes rough and the crystallinity of the photoelectric conversion part deteriorates, and the solid-state image sensor We have experimentally confirmed that the dark current increases. On the other hand, by heat-treating the gallium oxide film to which tin is added at a high temperature and crystallizing it, the crystallinity of the photoelectric conversion part deteriorated by the addition of tin can be improved, and the dark current of the solid-state image sensor increased by the addition of tin. In addition, the present inventors have experimentally confirmed that the treatment does not adversely affect carrier multiplication at low voltage. Therefore, by optimizing the heat treatment conditions, it is considered possible to realize a solid-state image sensor capable of suppressing the increase in dark current due to the addition of tin while enabling carrier multiplication at a low voltage.

FIG. 2 is a diagram showing an example of the relationship between the reverse bias voltage of the solid-state image sensor 100 and the dark current density when the heat treatment conditions are changed. The horizontal axis is the reverse bias voltage [V]. The vertical axis is the dark current density [nA / cm ² ].

FIG. 201 shows voltage-current characteristics when a tin-added gallium oxide film is heat-treated at 400 degrees for 1 hour in an oxygen-containing atmosphere. FIG. 202 shows voltage-current characteristics when a tin-added gallium oxide film is heat-treated at 600 degrees for 1 hour in an oxygen-containing atmosphere. FIG. 203 shows the voltage-current characteristics when the gallium oxide film to which tin is added is heat-treated at 800 ° C. for 10 minutes in an atmosphere containing oxygen. FIG. 204 shows voltage-current characteristics when a tin-added gallium oxide film is heat-treated at 800 ° C. for 30 minutes in an oxygen-containing atmosphere. FIG. 205 shows the voltage-current characteristics when the tin-added gallium oxide film is heat-treated at 800 degrees for 1 hour in an oxygen-containing atmosphere.

Comparing Graph 201, Graph 202, and Graph 205, it can be seen that Graph 205 has the smallest dark current density. That is, when the heat treatment time is constant, it can be seen that when the heat treatment temperature is 800 degrees, the dark current reduction effect is large, and when the heat treatment temperature is 600 degrees, the dark current reduction effect is small. Therefore, it is suggested that the temperature of the heat treatment is preferably 700 ° C. or higher, and more preferably 800 ° C. or higher.

Comparing Graph 203, Graph 204, and Graph 205, it can be seen that Graph 205 has the smallest dark current density. That is, when the heat treatment temperature is constant, it can be seen that when the heat treatment time is 1 hour, the dark current reduction effect is large, and when the heat treatment time is 30 minutes, the dark current reduction effect is small. Therefore, it is suggested that the temperature of the heat treatment is preferably 45 minutes or more, and more preferably 1 hour or more.

Therefore, the heat treatment conditions applied to the tin-added gallium oxide film are preferably 700 ° C. or higher and 1200 ° C. or lower, 10 minutes or longer and 3 hours or shorter in an oxygen-containing atmosphere. The heat treatment conditions applied to the tin-added gallium oxide film are more preferably 700 ° C. or higher and 1100 ° C. or lower, and 45 minutes or longer and 2 hours or shorter in an oxygen-containing atmosphere. The heat treatment conditions applied to the tin-added gallium oxide film are more preferably 800 ° C. or higher and 1000 ° C. or lower, 1 hour or longer and 2 hours or lower in an oxygen-containing atmosphere, and an oxygen-containing atmosphere. Of these, 800 degrees and 1 hour are most preferable.

The film thickness of the gallium oxide film 10 crystallized containing tin is not particularly limited, but is preferably 1 nm or more and 100 nm or less. When the film thickness of the gallium oxide film 10 crystallized containing tin is 1 nm or more, the hole injection charge from the electrode can be efficiently blocked. Further, when the film thickness of the gallium oxide film 10 crystallized containing tin is 100 nm or less, more preferably 50 nm or less, the externally applied voltage is efficiently applied to the crystal selenium film 20 side.

[Crystal selenium film]
The crystalline selenium film 20 is a photoelectric conversion unit 200 in the solid-state imaging device 100, and functions as a p-type semiconductor. The surface roughness of the crystalline selenium film 20 obtained by measurement with an atomic force microscope (AFM) is 10 nm or more and 50 nm or less when the film thickness of the crystalline selenium film 20 is 0.3 μm. It is preferably 10 nm or more and 20 nm or less, more preferably. The surface roughness of the crystalline selenium film 20 is one index for determining the crystallinity of the photoelectric conversion unit 200, and is applied to the amount of tin added to the gallium oxide film and the tin-added gallium oxide film. It changes depending on the heat treatment conditions. This is because the crystals of the crystalline selenium film 20 grow depending on the condition of the crystals of the gallium oxide film 10 crystallized containing tin formed on the lower side (see FIG. 3D described later). .. Therefore, by optimizing the amount of tin added to the gallium oxide film and the conditions of the heat treatment applied to the gallium oxide film to which tin is added as described above, the surface roughness of the crystalline selenium film 20 can be adjusted within the range. Can be. As a result, the surface of the crystalline selenium film 20 can be smoothed, and the deterioration of the crystallinity of the photoelectric conversion unit 200 due to the addition of tin can be improved. Further, it is considered that the increase in dark current of the solid-state image sensor 100 due to the addition of tin can be suppressed.

In the crystalline selenium film 20, the peak intensity of the diffraction peak on the Se (100) plane in the XRD pattern obtained by X-ray diffraction (XRD) measurement has a thickness of the crystalline selenium film 20 of 0.3 μm. Occasionally, it is preferably 5000 counts or more and 10000 counts or less, and more preferably 8000 counts or more and 10000 counts or less. The peak intensity of the diffraction peak on the Se (100) plane in the XRD pattern is one index for determining the crystallinity of the photoelectric conversion unit 200, and the amount of tin added to the gallium oxide film and tin added. It changes depending on the conditions of the heat treatment applied to the gallium oxide film. Therefore, by optimizing the amount of tin added to the gallium oxide film and the conditions of the heat treatment applied to the gallium oxide film to which tin is added as described above, the diffraction peak of the Se (100) plane in the XRD pattern The peak intensity of can be within the range. As a result, the peak intensity of the diffraction peak on the Se (100) plane in the XRD pattern can be increased, and the deterioration of the crystallinity of the photoelectric conversion unit 200 due to the addition of tin can be improved. Further, it is considered that the increase of the dark current of the solid-state image sensor 100 due to the addition of tin can be suppressed.

The film thickness of the crystalline selenium film 20 is not particularly limited, but is preferably 0.1 μm or more. When the film thickness of the crystalline selenium film 20 is 0.1 μm or more, preferably 0.5 μm or more, the film thickness is sufficient, so that the solid-state image sensor 100 can obtain sufficient sensitivity in the entire visible light range. The upper limit of the film thickness of the crystalline selenium film 20 is not particularly limited, but when it is 5 μm or less, preferably 2 μm or less, the crystalline selenium film 20 can be efficiently formed, which is preferable from the viewpoint of productivity.

[Joint membrane]
The bonding film 30 is a photoelectric conversion unit 200 in the solid-state imaging device 100, and bonds the signal readout circuit board 60 provided with the first electrode 40 and the crystal selenium film 20. The material of the bonding film 30 is not particularly limited as long as the signal readout circuit board 60 and the crystalline selenium film 20 can be bonded, but the bonding film 30 is selected from a group consisting of tellurium (Te), bismuth (Bi), and antimony (Sb). It is more preferable to use tellurium in order to reliably bond the signal readout circuit board 60 and the crystalline selenium film 20.

The film thickness of the bonding film 30 is not particularly limited, but can be 0.1 nm or more and 10 nm or less. When the film thickness of the bonding film 30 is 0.1 nm or more, the adhesive force between the signal readout circuit board 60 and the crystalline selenium film 20 can be effectively increased, which is preferable. Further, when the film thickness of the bonding film 30 is 10 nm or less, more preferably 3 nm or less, the bonding film 30 can prevent the formation of defects in the crystal selenium film 20, so that an increase in dark current can be suppressed, which is preferable. (See, for example, Non-Patent Document 1).

The bonding film 30 may be continuously formed over the entire area between the signal readout circuit board 60 and the crystal selenium film 20. Alternatively, the bonding film 30 may be provided with a hole in a part in the in-plane direction and may be formed in a part region between the signal readout circuit board 60 and the crystal selenium film 20. In any case, the bonding between the signal readout circuit board 60 and the crystal selenium film 20 may be ensured.

[First electrode]
The first electrode 40 is provided on the surface of the signal readout circuit board 60 corresponding to each pixel, and is provided between the photoelectric conversion unit 200 and the signal readout circuit board 60. The negative electrode of the power supply is connected to the first electrode 40. As the first electrode 40, for example, a metal film such as gold (Au), copper (Cu), aluminum (Al), tungsten (W), or molybdenum (Mo) can be used. In FIG. 1, a part of the signal readout circuit board 60 is shown in the same layer as the first electrode 40 with a hatch different from that of the first electrode 40.

[Second electrode]
The second electrode 50 is on the incident side of light, is provided on the side opposite to the first electrode 40 via the photoelectric conversion unit 200, and is provided between the photoelectric conversion unit 200 and the transparent substrate 70. A positive electrode of a power source is connected to the second electrode 50. The second electrode 50 is preferably made of a translucent material. As the second electrode 50, for example, a transparent oxide conductive film such as ITO (indium tin oxide), IZO (zinc oxide tin), and AZO (aluminum-added participating zinc) can be used. The second electrode 50 may be formed of the same material as the first electrode 40, or may be formed of a material different from that of the first electrode 40. The film thickness of the second electrode 50 is not particularly limited, but is preferably 5 nm or more and 30 nm or less.

[First substrate]
The signal readout circuit board 60 is, for example, a substrate in which a CMOS (Complementary Metal Oxide Semiconductor) structure is formed on a silicon substrate. The signal readout circuit board 60 is provided with a first electrode 40 on the surface thereof. The signal readout circuit board 60 is bonded to the crystal selenium film 20 in the photoelectric conversion unit 200 via the bonding film 30.

[Second board]
The transparent substrate 70 is on the incident side of light, and is provided on the opposite side of the signal readout circuit board 60 via the photoelectric conversion unit 200. The transparent substrate 70 is preferably made of a translucent material. As the transparent substrate 70, for example, a glass substrate, a sapphire substrate, a silicon substrate, or the like can be used. The material of the transparent substrate 70 is preferably selected as appropriate according to the material of the second electrode 50.

In the solid-state image sensor 100 according to the present embodiment, the photoelectric conversion unit 200 includes at least a gallium oxide film 10 that contains impurities and is crystallized, and a crystal selenium film 20. That is, it includes a photoelectric conversion unit 200 having good crystallinity and physical characteristics not found in the prior art. This makes it possible to realize a solid-state image sensor 100 capable of suppressing an increase in dark current due to the addition of impurities while enabling carrier multiplication at a low voltage.

<Manufacturing method of solid-state image sensor>
An example of a method for manufacturing the solid-state image sensor 100 according to the present embodiment will be described with reference to FIGS. 3A to 3F and FIG.

The method for manufacturing the solid-state imaging device 100 includes a step of forming the first amorphous selenium film 20A on the signal readout circuit substrate 60 (S101) and a step of forming a gallium oxide film 10A to which tin is added on the transparent substrate 70 (S101). S102) and the step (S103) of subjecting the tin-added gallium oxide film 10A to the first heat treatment to crystallize the tin-added gallium oxide film 10A, and the tin-containing crystallized gallium oxide film 10 A step of forming the second amorphous selenium film 20B on the top (S104), a step of joining the first amorphous selenium film 20A and the second amorphous selenium film 20B (S105), and a step of joining the bonded amorphous selenium films 20A and 20B. 2. The step (S106) of crystallizing the bonded amorphous selenium films 20A and 20B by performing heat treatment is included.

Hereinafter, details of each step will be described in sequence. The same components are given the same reference numbers, and the description of the material, film thickness, etc. of each component is as described above, and duplicate description will be omitted. Further, steps S101 and steps S102 to S104 may be performed in parallel or in order.

[Forming Step of First Amorphous Selenium Film 20A: Step S101]
First, as shown in FIG. 3A, the bonding film 30 is formed on the signal readout circuit board 60 provided with the first electrode 40 by, for example, a vacuum vapor deposition method, a sputtering method, or the like. By forming the bonding film 30 on the signal reading circuit board 60, the adhesive force between the signal reading circuit board 60 and the crystalline selenium film 20 can be improved in the second heat treatment step described later. This makes it possible to prevent the crystalline selenium film 20 from peeling off.

Next, a first amorphous selenium film 20A having a film thickness of 10 nm or more and 500 nm or less is formed on the bonding film 30 by, for example, a vacuum vapor deposition method or a sputtering method. The film thickness of the first amorphous selenium film 20A is preferably half the film thickness of the crystalline selenium film 20 or less than half the film thickness of the crystalline selenium film 20.

[Step of forming gallium oxide film 10A to which tin is added: step S102]
Next, as shown in FIG. 3B, the second electrode 50 is formed on the transparent substrate 70 by, for example, a vacuum vapor deposition method, a sputtering method, or the like.

Next, a gallium oxide film 10A to which tin is added is formed on the second electrode 50 by, for example, a sputtering method, a pulse laser vapor deposition method, a vacuum vapor deposition method, or the like. For example, a single target made of metallic tin or tin oxide-containing gallium oxide is subjected to a sputtering device so that the atomic percentage of tin added to the gallium oxide film is 6.0 atom% or more and 9.0 atom% or less. Sputtering is performed using this method to form a tin-added gallium oxide film 10A on the second electrode 50. For example, a tin metal target or a tin oxide sintered body target and gallium oxide are used by a sputtering device so that the atomic percentage of tin added to the gallium oxide film is 6.0 atom% or more and 9.0 atom% or less. Co-sputtering is performed using a target made of tin, and a tin-added gallium oxide film 10A is formed on the second electrode 50.

The tin content in the tin-added gallium oxide film 10A is roughly proportional to the tin content in the target, but is not linear. Therefore, the tin content in the gallium oxide film 10A to which tin is added after film formation is determined according to the output conditions (RF power, etc.), atmospheric gas conditions (oxygen partial pressure, etc.), and the tin content of the target.

[First heat treatment step: step S103]
Next, as shown in FIG. 3C, the tin-added gallium oxide film 10A is subjected to the first heat treatment to crystallize the tin-added gallium oxide film 10A.

The condition of the first heat treatment is preferably 700 ° C. or higher and 1200 ° C. or lower, 10 minutes or longer and 3 hours or shorter in an atmosphere containing oxygen. Further, the conditions of the first heat treatment are more preferably 700 ° C. or higher and 1100 ° C. or lower, 45 minutes or longer and 2 hours or shorter in an atmosphere containing oxygen. Further, the condition of the first heat treatment is more preferably 800 degrees or more and 1000 degrees or less, 1 hour or more and 2 hours or less in an atmosphere containing oxygen. By optimizing the conditions of the first heat treatment, the crystallinity of the photoelectric conversion unit 200 formed later can be improved. Further, by optimizing the conditions of the first heat treatment, it is possible to suppress an increase in the dark current of the solid-state image sensor 100 formed later. The above-mentioned first heat treatment condition is an example, and is not particularly limited to this condition.

[Step of Forming Second Amorphous Selenium Film 20B: Step S104]
Next, as shown in FIG. 3D, a second amorphous selenium film 20B having a film thickness of 10 nm or more and 500 nm or less is formed on the tin-containing crystallized gallium oxide film 10 by, for example, a vacuum vapor deposition method or a sputtering method. do. The film thickness of the second amorphous selenium film 20B is preferably half the film thickness of the crystalline selenium film 20 or half or more of the film thickness of the crystalline selenium film 20.

[Joining step: Step S105]
Next, as shown in FIG. 3E, the first amorphous selenium film 20A formed on the signal readout circuit board 60 and the second amorphous selenium film 20B formed on the transparent substrate 70 are joined to face each other.

For example, the first amorphous selenium film 20A and the second amorphous selenium film 20B are brought into contact with each other and pressed at a pressure of 0.01 MPa to 100 MPa to join the first amorphous selenium film 20A and the second amorphous selenium film 20B. .. At this time, in order to soften the first amorphous selenium film 20A and the second amorphous selenium film 20B, the first amorphous selenium film 20A and the second amorphous selenium film 20B may be heat-treated in advance. However, the temperature in the heat treatment is preferably 50 degrees or less.

[Second heat treatment step: step S106]
Next, as shown in FIG. 3F, the bonded first amorphous selenium film 20A and the second amorphous selenium film 20B are subjected to a second heat treatment, and the bonded first amorphous selenium film 20A and the second amorphous selenium film 20B are subjected to a second heat treatment. To crystallize. As a result, the photoelectric conversion unit 200 is formed.

The conditions for the second heat treatment are preferably 100 degrees or more and 220 degrees or less, and 30 seconds or more and 1 hour or less. The condition of the second heat treatment is an example, and is not particularly limited to this condition.

The solid-state image sensor 100 according to the present embodiment can be manufactured by going through each step including the above optional steps. In the solid-state image sensor 100 according to the present embodiment, the photoelectric conversion unit 200 includes at least a gallium oxide film 10 that contains impurities and is crystallized, and a crystal selenium film 20. That is, it includes a photoelectric conversion unit 200 having good crystallinity and physical characteristics not found in the prior art. This makes it possible to realize a solid-state image sensor 100 capable of suppressing an increase in dark current due to the addition of impurities while enabling carrier multiplication at a low voltage.

<Example>
Hereinafter, the present invention will be described in more detail with reference to FIGS. 5A to 8B with reference to Examples, but the present invention is not limited to the following Examples. For convenience of explanation, the reference numerals of FIGS. 5A to 5C refer to the components used in FIGS. 1 and 3A to 3F.

[Preparation of sample]
Sample 1 according to Comparative Example, Sample 2 according to Comparative Example, and Sample 3 according to Example were prepared as evaluation samples by the methods shown below. Sample 1, Sample 2, and Sample 3 imitate an element (see FIG. 3D) formed on the transparent substrate side before bonding in a bonded image sensor. Therefore, it can be considered that the evaluation results obtained by using Sample 1, Sample 2, and Sample 3 are substantially the same as the evaluation results obtained by using an actual solid-state image sensor (junction type image sensor).

<< Sample 1 >>
As shown in FIG. 5A, a first transparent electrode 202 made of an ITO film having a film thickness of 10 nm was formed on the sapphire substrate 201 by a sputtering method. Next, a gallium oxide film 10B having a film thickness of 20 nm was formed on the first transparent electrode 202 by a sputtering method. As a target, a target made of gallium oxide to which tin was not added was used. Next, a bonding film 30 made of a tellurium film having a film thickness of 1 nm was formed on the gallium oxide film 10B by a vacuum vapor deposition method. Next, an amorphous selenium film having a film thickness of 0.5 μm was formed on the bonding film 30 by a vacuum vapor deposition method. Next, the first transparent electrode 202, the gallium oxide film 10B, the bonding film 30, and the sapphire substrate 201 on which the amorphous selenium film was formed were heat-treated at 200 ° C. for 1 minute to obtain a thickness of 0.5 μm. A crystalline selenium film 20 was formed. Finally, a second transparent electrode 203 made of an ITO film having a film thickness of 30 nm was formed on the crystalline selenium film 20 by a sputtering method to obtain Sample 1.

<< Sample 2 >>
As shown in FIG. 5B, a first transparent electrode 202 made of an ITO film having a film thickness of 10 nm was formed on the sapphire substrate 201 by a sputtering method. Next, a gallium oxide film 10A to which tin having a film thickness of 20 nm was added was formed on the first transparent electrode 202 by a sputtering method. As a target, a target made of tin-added gallium oxide to which 6.0 atom% of tin was added was used. Next, a bonding film 30 made of a tellurium film having a film thickness of 1 nm was formed on the gallium oxide film 10A to which tin was added by a vacuum vapor deposition method. Next, an amorphous selenium film having a film thickness of 0.5 μm was formed on the bonding film 30 by a vacuum vapor deposition method. Next, the first transparent electrode 202, the tin-added gallium oxide film 10A, the bonding film 30, and the selenium substrate 201 on which the amorphous selenium film is formed are heat-treated at 200 ° C. for 1 minute to form a film. A crystalline selenium film 20 having a thickness of 0.5 μm was formed. Finally, a second transparent electrode 203 made of an ITO film having a film thickness of 30 nm was formed on the crystalline selenium film 20 by a sputtering method to obtain Sample 2.

<< Sample 3 >>
As shown in FIG. 5C, a first transparent electrode 202 made of an ITO film having a film thickness of 10 nm was formed on the sapphire substrate 201 by a sputtering method. Next, a gallium oxide film 10A to which tin having a film thickness of 20 nm was added was formed on the first transparent electrode 202 by a sputtering method. As a target, a target made of tin-added gallium oxide to which 6.0 atom% of tin was added was used. Next, the first transparent electrode 202 and the sapphire substrate 201 on which the gallium oxide film 10A to which tin was added were heat-treated at 800 ° C. for 1 hour in an atmosphere containing oxygen to have a film thickness of 20 nm. A crystallized gallium oxide film 10 containing tin was formed. Next, on the gallium oxide film 10 crystallized containing tin, a bonding film 30 made of a tellurium film having a thickness of 1 nm was formed by a vacuum vapor deposition method. Next, an amorphous selenium film having a film thickness of 0.5 μm was formed on the bonding film 30 by a vacuum vapor deposition method. Next, the first transparent electrode 202, the gallium oxide film 10 crystallized containing tin, the bonding film 30, and the selenium substrate 201 on which the amorphous selenium film is formed are heat-treated at 200 ° C. for 1 minute. A crystalline selenium film 20 having a thickness of 0.5 μm was formed. Finally, a second transparent electrode 203 made of an ITO film having a film thickness of 30 nm was formed on the crystalline selenium film 20 by a sputtering method to obtain Sample 3. At the time of the first heat treatment, the tin-added gallium oxide film was not completely crystallized.

In the above-mentioned Samples 2 and 3, the atomic percentage of tin added to the gallium oxide film was a value measured by the Rutherford backscatter analysis method and was 6.0 atom%.

[Experimental Example 1]
Using the samples 1, sample 2, and sample 3 shown in FIGS. 5A to 5C, the voltage at the time of light irradiation when a voltage is applied so that the first transparent electrode 202 is the positive electrode and the second transparent electrode 203 is the negative electrode. -The photocurrent characteristics were measured. Further, in the dark when a voltage is applied so that the first transparent electrode 202 becomes a positive electrode and the second transparent electrode 203 becomes a negative electrode using the samples 1, sample 2, and sample 3 shown in FIGS. 5A to 5C. The voltage-dark current characteristics were measured. In measuring the voltage-photocurrent characteristics, a light ^{source with a light intensity of 2.5 μW / cm 2} and a wavelength of 550 nm was used.

[Evaluation in Experimental Example 1]
FIG. 6 is a diagram showing an example of a voltage-photocurrent characteristic at the time of light irradiation and a voltage-dark current characteristic at the time of darkness. The solid line shows the voltage-photocurrent characteristics at the time of light irradiation. The dotted line shows the voltage-dark current characteristic in dark. The horizontal axis shows the voltage [V]. The vertical axis shows the current density [pA / cm ² ].

From the solid line graph of FIG. 6, it can be seen that the photocurrent of Sample 2 and Sample 3 rises near the voltage of 15 V, whereas the photocurrent of Sample 1 does not rise near the voltage of 15 V. That is, the sample 1 has a slow rise of photocurrent and requires a very high voltage for carrier multiplication, whereas the samples 2 and 3 have a fast rise of photocurrent for carrier multiplication. It can be seen that the voltage can be reduced.

This is because the carrier concentration of non-doped gallium oxide is lower than that of crystalline selenium and the depletion layer does not spread efficiently on the crystalline selenium side, whereas the addition of tin increases the carrier concentration of gallium oxide, which is efficient. It is considered that the depletion layer spreads on the crystal selenium side. Therefore, it is suggested that the carrier multiplication at a low voltage is possible by adding tin to the gallium oxide film.

Further, from the solid line graph of FIG. 6, it can be seen that the photocurrents of the sample 2 and the sample 3 are substantially the same. Therefore, even if the gallium oxide film to which tin is added is heat-treated, it does not affect the photocurrent so much, suggesting that the effect of carrier multiplication at a low voltage is not lost.

From the dotted line graph of FIG. 6, it can be seen that among the sample 1, the sample 2, and the sample 3, the dark current of the sample 1 is the smallest as a whole. Further, it can be seen that among the sample 1, the sample 2, and the sample 3, the sample 2 has the largest dark current as a whole. Therefore, the dark current increases by adding tin to the gallium oxide film, but the increase in dark current due to the addition of tin can be suppressed by further heat-treating the gallium oxide film to which tin has been added. It is suggested that there is.

From Experimental Example 1, by optimizing the amount of tin added to the gallium oxide film and the conditions of the heat treatment applied to the tin-added gallium oxide film, carrier multiplication at a low voltage is possible. It is suggested that the solid-state image sensor 100 capable of suppressing an increase in dark current due to the addition of tin can be realized.

[Experimental Example 2]
Using Sample 1, Sample 2, and Sample 3 shown in FIGS. 5A to 5C, the surface roughness Ra of the crystalline selenium film 20 was measured by an atomic force microscope.

[Evaluation in Experimental Example 2]
FIG. 7 is a diagram showing an example of the surface of the crystalline selenium film in Sample 1, Sample 2, and Sample 3 obtained by AFM measurement.

The surface roughness of the crystalline selenium film 20 in Sample 1 was 20.8 [nm]. The surface roughness of the crystalline selenium film 20 in Sample 2 was 41.1 [nm]. The surface roughness of the crystalline selenium film 20 in Sample 3 was 17.7 [nm].

From FIG. 7, it can be seen that the surfaces of the crystalline selenium film 20 in Samples 1 and 3 have few irregularities and are smooth to some extent. On the other hand, it can be seen that the surface of the crystalline selenium film 20 in Sample 2 has many irregularities and is rough.

In this way, the difference appears on the surface of the crystalline selenium film 20 because the crystals of the crystalline selenium film 20 grow depending on the condition of the crystals of the gallium oxide film formed on the lower side. .. It can be evaluated that the coarser the surface of the crystalline selenium film 20 is, the worse the crystallinity of the entire photoelectric conversion unit is, and it is considered that the dark current in the evaluation sample becomes larger. On the other hand, the smoother the surface of the crystalline selenium film 20, the better the crystallinity of the entire photoelectric conversion unit can be evaluated, and it is considered that the dark current in the evaluation sample becomes smaller.

That is, since the surface of the crystalline selenium film 20 in sample 1 is smooth, the crystallinity of the crystalline selenium film 20 formed on the gallium oxide film 10B to which tin is not added is good, and the photoelectric conversion unit has good crystallinity. It can be evaluated that the crystallinity is good. Further, since the surface of the crystalline selenium film 20 in Sample 2 is rough, the crystallinity of the crystalline selenium film 20 formed on the gallium oxide film 10A to which tin is added is not good, and the crystallinity of the photoelectric conversion part is poor. It can be evaluated as bad. Further, since the surface of the crystalline selenium film 20 in the sample 3 is smooth, the crystallinity of the crystalline selenium film 20 formed on the gallium oxide film 10 crystallized containing tin is good, and the photoelectric conversion unit has good crystallinity. It can be evaluated that the crystallinity is good.

Therefore, by adding tin to the gallium oxide film, the surface of the crystalline selenium film becomes rough and the crystallinity of the photoelectric conversion part deteriorates. , The surface of the crystalline selenium film becomes smooth, and it is suggested that the deterioration of the crystallinity of the photoelectric conversion part due to the addition of tin can be improved.

From Experimental Example 2, by optimizing the amount of tin added to the gallium oxide film and the conditions of the heat treatment applied to the tin-added gallium oxide film, the crystallinity of the photoelectric conversion part is improved and the photoelectric conversion is performed. It is suggested that the characteristics of the part can be improved. This suggests that the solid-state image sensor 100 capable of suppressing an increase in dark current due to the addition of tin can be realized.

[Experimental Example 3]
X-ray diffraction measurements were performed using Sample 1, Sample 2, and Sample 3 shown in FIGS. 5A to 5C. Out-of-Plane measurements were applied to evaluate the lattice planes parallel to the surfaces of Sample 1, Sample 2, and Sample 3.

The measurement conditions are shown below.
X-ray source: Cu-Kα ray Output setting: 45kV, 200mA
Angle measurement range: 2θ = 10 ° to 90 °
Scan speed: 2 ° (2θ / min), continuous scan divergence slit: 5 °
Scattering slit: 5 °
Light receiving slit: 1 mm

[Evaluation in Experimental Example 3]
8A and 8B are diagrams showing an example of the relationship between the diffraction angle and the intensity in Sample 1, Sample 2, and Sample 3 obtained by XRD measurement. FIG. 8B is an enlarged view of FIG. 8A. The horizontal axis is the diffraction angle 2θ [deg. ] Is shown. The vertical axis is the intensity [a. u. ] Is shown.

The peak intensity of the diffraction peak on the Se (100) plane in the XRD pattern in Sample 1 was 7975 counts. The half width of the diffraction peak was 0.2433 deg. The peak intensity of the diffraction peak on the Se (100) plane in the XRD pattern in Sample 2 was 4971 counts. The half width of the diffraction peak was 0.2499 deg. The peak intensity of the diffraction peak on the Se (100) plane in the XRD pattern in Sample 3 was 6060 counts. The half width of the diffraction peak was 0.2546 deg.

From FIG. 8A, it can be seen that sample 3 has a plurality of prominent peaks in the XRD pattern. Further, from FIG. 8B, it can be seen that the peak intensity in sample 1 is the largest, the peak intensity in sample 2 is the smallest, and the peak intensity in sample 3 is between the peak intensity in sample 1 and the peak intensity in sample 2.

Therefore, by adding tin to the gallium oxide film, the crystallinity of the photoelectric conversion part deteriorates, but by further heat-treating the gallium oxide film to which tin is added, the photoelectric conversion part due to the addition of tin It is suggested that the deterioration of crystallinity can be improved.

From Experimental Example 3, the crystallinity of the photoelectric conversion part is improved by optimizing the amount of tin added to the gallium oxide film and the conditions of the heat treatment applied to the tin-added gallium oxide film, and the photoelectric conversion is performed. It is suggested that the characteristics of the part can be improved. This suggests that the solid-state image sensor 100 capable of suppressing an increase in dark current due to the addition of tin can be realized.

From the above-mentioned examples, it is suggested that the deterioration of the crystallinity of the photoelectric conversion part due to the addition of tin can be improved by subjecting the gallium oxide film to which tin is added to high temperature heat treatment and crystallizing it. This suggests that it is possible to realize a solid-state image sensor 100 capable of suppressing an increase in dark current due to the addition of tin while enabling carrier multiplication at a low voltage.

In the above-described embodiment, the case where tin is used as the impurity added to the gallium oxide film has been described as an example, but for example, silicon, germanium or the like is selected as the impurity added to the gallium oxide film. Of course, the same effect can be obtained even if it is used.

Although the above embodiments have been described as representative examples, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and modifications can be made without departing from the scope of claims. For example, the order of each process described in the flowchart of the embodiment is not limited to the above and can be changed as appropriate. Further, it is possible to combine a plurality of processes into one or to divide one process.

1 Sample 2 Sample 3 Sample 10 Gallium oxide film crystallized with tin 10A Gallium oxide film with tin added 10B Gallium oxide film 20 Crystalline selenium film 20A 1st amorphous selenium film 20B 2nd amorphous selenium film 30 Bonded film 40th 1 electrode 50 2nd electrode 60 Signal readout circuit board 70 Transparent board 100 Solid-state imaging element 200 Photoelectric conversion unit 201 Sapphire board 202 1st transparent electrode 203 2nd transparent electrode

Claims (4)

A gallium oxide film that contains impurities and is crystallized,
Crystalline selenium film and
A solid-state image sensor, characterized in that it comprises. A signal readout circuit board, a first electrode, a bonding film, a crystalline selenium film, a gallium oxide film, a second electrode, and a transparent substrate are provided in this order.
The solid-state image sensor according to claim 1. The process of forming the first amorphous selenium film on the signal readout circuit board and
The process of forming a gallium oxide film with impurities added on a transparent substrate,
A step of subjecting the gallium oxide film to the first heat treatment to crystallize the gallium oxide film, and
A step of forming a second amorphous selenium film on the crystallized gallium oxide film, and
The step of joining the first amorphous selenium film and the second amorphous selenium film, and
A step of subjecting the bonded amorphous selenium film to a second heat treatment to crystallize the amorphous selenium film, and
A method for manufacturing a solid-state image sensor, which comprises. The step of crystallizing the gallium oxide film is
This is a step of subjecting the gallium oxide film to the first heat treatment at 700 ° C. or higher and 1200 ° C. or lower for 10 minutes or longer and 3 hours or shorter in an atmosphere containing oxygen.
The method for manufacturing a solid-state image sensor according to claim 3.

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