JP2013084786A - Solid-state imaging element and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state imaging element capable of suppressing optical interference.SOLUTION: A solid-state imaging element 30 is configured to have a semiconductor base substance 31, and a first semiconductor layer 32 formed on a first principal surface of the semiconductor base substance 31 and containing Ge. The solid-state imaging element 30 also has a transfer transistor Tr1 formed on a second principal surface of the semiconductor base substance 31, and a photodiode 33 formed in a region including the first semiconductor layer 32.

Description

  The present technology relates to a solid-state imaging device and an electronic device. In particular, the present invention relates to a solid-state imaging device including a Ge-containing semiconductor layer and an electronic device.

  An image sensor using Si as a substrate, particularly a back-illuminated image sensor, has a structure in which the wiring layer of the circuit part is not provided on the light-receiving part side, and therefore, the sensitivity is improved compared to the front-illuminated type. In such a back-illuminated solid-state imaging device, there is a demand for a reduction in color mixture due to interference between adjacent pixels, in particular, light entering the adjacent pixels. As a method of suppressing color mixing, a method of forming a light shielding layer between pixels has been proposed (see, for example, Patent Document 1).

JP 2010-186818 A

  In the above-described solid-state imaging device, there is a demand for interference between adjacent pixels, in particular, optical interference in which incident light enters the adjacent pixels, for example, reduction in optical color mixing.

  The present technology provides a solid-state imaging device and an electronic device that can suppress optical interference.

The solid-state imaging device according to the present technology includes a semiconductor substrate and a first semiconductor layer containing Ge formed on the first main surface of the semiconductor substrate. A transfer transistor formed on the second main surface of the semiconductor substrate and a photodiode formed in a region including the first semiconductor layer are provided.
Moreover, the electronic device of this technique has the said solid-state image sensor and the signal processing circuit which processes the output signal of a solid-state image sensor.

  According to the above-described solid-state imaging device, by including the first semiconductor layer containing Ge, absorption of incident light in the first semiconductor layer is increased. For this reason, the amount of light that passes through the first semiconductor layer and re-enters the adjacent pixel can be reduced. As a result, optical interference of the solid-state image sensor can be suppressed. And by using this solid-state image sensor, it is possible to configure an electric device having excellent optical characteristics.

  According to the present technology, it is possible to provide a solid-state imaging device and an electronic apparatus that can suppress optical interference.

It is a top view which shows the structure of the solid-state image sensor of 1st Embodiment. It is sectional drawing which shows the structure of the pixel part of the solid-state image sensor of 1st Embodiment. It is a graph which shows the light absorption ratio in Si substrate. Is a graph showing the light absorption rate in the Si _0.9 Ge _0.1 semiconductor layer. Is a graph showing the light absorption rate in the Si _0.8 Ge _0.2 semiconductor layer. Is a graph showing the light absorption rate in the Si _0.7 Ge _0.3 semiconductor layer. Is a graph showing the light absorption rate in the Si _0.6 Ge _0.4 semiconductor layer. Si _. Is a graph showing the light absorption rate in the ₀₅ Ge _0.5 semiconductor layer. It is a graph which shows the relationship between the light absorption coefficient of the semiconductor layer of each composition, and incident light wavelength. It is a figure which shows the dimension of each structure of the pixel part of the solid-state image sensor used in the Example. It is a graph which shows the incident light depth and incident light intensity of each wavelength. It is sectional drawing which shows the structure of the pixel part of the solid-state image sensor of 2nd Embodiment. It is a figure which shows the structure of an electronic device.

Hereinafter, examples of the best mode for carrying out the present technology will be described, but the present technology is not limited to the following examples.
The description will be given in the following order.
1. 1. First embodiment of solid-state imaging device 2. Second embodiment of solid-state imaging device Electronics

<1. First Embodiment of Solid-State Image Sensor>
[Configuration example of solid-state imaging device: schematic configuration diagram]
Hereinafter, specific embodiments of the solid-state imaging device of the present embodiment will be described.
FIG. 1 shows a schematic configuration diagram of a three-dimensional MOS (Metal Oxide Semiconductor) type solid-state image pickup device as an example of a back-illuminated solid-state image pickup device. A solid-state imaging device 10 illustrated in FIG. 1 includes a sensor substrate 11 on which photoelectric conversion units are arranged and a circuit substrate 21 that is bonded to the sensor substrate 11 in a stacked state.

  The sensor substrate 11 includes a pixel region 14 in which one surface is a light receiving surface A and a plurality of pixels 13 including a photoelectric conversion unit are two-dimensionally arranged with respect to the light receiving surface A. In the pixel region 14, a plurality of pixel drive lines 15 are wired in the row direction, a plurality of vertical signal lines 16 are wired in the column direction, and one pixel 13 includes one pixel drive line 15 and one pixel drive line 15. They are arranged in a state of being connected to the vertical signal line 16. Each of these pixels 13 is provided with a photoelectric conversion unit, a charge storage unit, and a pixel circuit composed of a plurality of transistors (so-called MOS transistors) and a capacitor element. A part of the pixel circuit is provided on the surface side opposite to the light receiving surface A. A part of the pixel circuit may be shared by a plurality of pixels.

  The sensor substrate 11 includes a peripheral region 17 outside the pixel region 14. In the peripheral region 17, a wiring 18 including an electrode pad is provided. The wiring 18 is connected to the pixel drive line 15 and the vertical signal line 16 provided on the sensor substrate 11 and the pixel circuit, and further to the drive circuit provided on the circuit board 21 as necessary.

  The circuit board 21 has a vertical drive circuit 22, a column signal processing circuit 23, a horizontal drive circuit 24, and a system control circuit for driving each pixel 13 provided on the sensor board 11 on one side facing the sensor board 11 side. 25 etc. are provided. These drive circuits are connected to the wiring 18 on the sensor substrate 11 side. Note that the pixel circuit provided on the front surface side of the sensor substrate 11 is also a part of the drive circuit.

[Configuration Example of Solid-State Image Sensor: Pixel Unit]
Next, FIG. 2 shows a cross-sectional view of a main part constituting one pixel of the solid-state imaging device of the present embodiment.
A solid-state imaging device 30 shown in FIG. 2 includes a semiconductor substrate 31 and a first semiconductor layer 32 formed on the semiconductor substrate 31. The first semiconductor layer 32 is formed on the first main surface (light receiving surface of the solid-state imaging device 30) side of the semiconductor substrate 31.
The surface of the first semiconductor layer 32 opposite to the semiconductor substrate 31 is a light incident surface of the solid-state imaging device 30. In the following description, the light incident surface is the first main surface of the first semiconductor layer 32, and the surface in contact with the semiconductor substrate 31 is the second main surface of the first semiconductor layer 32. The light incident surface is the back surface of the solid-state image sensor 30, and the second main surface side of the semiconductor substrate 31 is the surface of the solid-state image sensor 30.

As the semiconductor substrate 31, for example, a silicon substrate or the like that is generally used for manufacturing a solid-state imaging device is used.
The first semiconductor layer 32 is a semiconductor layer containing Ge. As the semiconductor layer containing Ge, a SiGe mixed crystal formed by epitaxial growth or a Ge single semiconductor layer is used. In the case of using a SiGe mixed crystal, a composition in which the composition ratio x of the composition formula Si _(1-x) Ge _(x) is other than 0, particularly a composition in which x is 0.05 or more and less than 1.0 is used.

  A photodiode (PD) 33 is formed from the surface of the first main surface of the first semiconductor layer 32 to the second main surface side of the semiconductor substrate 31. The PD 33 has a first conductivity type (p-type) semiconductor region on the surface of the first main surface of the first semiconductor layer 32 and the surface on the second main surface side of the semiconductor substrate 31. Between the p-type semiconductor regions, there is a second conductivity type (n-type) semiconductor region formed continuously from the first semiconductor layer 32 to the semiconductor substrate 31. In addition, a pixel separation unit including a first conductivity type (p-type) semiconductor region is provided between the PD 33 and the PD 33A of the adjacent pixel.

  A gate electrode 34 is formed on the second main surface of the semiconductor substrate 31 via a gate insulating film. A floating diffusion (FD) 35 is formed on the surface side of the semiconductor substrate 31 at a position where it is paired with the PD 33 via the gate electrode 34. As a result, the gate electrode 34 and the transfer transistor Tr1 using the PD 33 and the FD 35 as the source / drain are formed.

  On the second main surface of the semiconductor substrate 31, a multilayer wiring layer 36 of the solid-state imaging device 30 is formed. The multilayer wiring layer 36 includes a plurality of laminated interlayer insulating layers and conductor layers. On the first main surface of the first semiconductor layer 32, a light shielding film 37 for shielding light between pixels is provided. Light enters the PD 33 from the opening of the light shielding film 37. Various optical components such as a color filter 38 and a micro lens 39 are mounted on the light shielding film 37.

In the solid-state imaging device 30 having the above-described configuration, a Ge-containing semiconductor layer is formed on the light-receiving surface side of the solid-state imaging device 30. A circuit portion including the transistor Tr1 and the like is formed on the second main surface of the semiconductor substrate 31.
Ge has a band gap of 0.66 eV. In general, the band gap of Si constituting the light receiving unit of the solid-state imaging device is 1.11 eV. That is, the band gap of Ge is smaller than Si. For this reason, the PD 33 formed in the first semiconductor layer 32 containing Ge has a larger light absorption coefficient in the entire wavelength region than that formed in the Si substrate.

The light absorption coefficient of the semiconductor layer containing Ge will be described.
FIGS. 3 to 8 are graphs showing the state of absorption of incident light with respect to the Si single substrate and the semiconductor layer having a composition in which the composition ratio x of the composition formula Si _(1-x) Ge _(x) is changed.
FIG. 3 shows a graph of the light absorption ratio with respect to the depth of the substrate made of Si alone. 4 to 8 show the light of the semiconductor layer in which the Ge ratio x is increased by 0.1 from 0.1 to 0.5 in the semiconductor layer having the composition of Si _(1-x) Ge _(x). The graph of an absorption rate is shown.
FIG. 4 is a graph of the light absorption ratio in a semiconductor layer having a composition of Si _0.9 Ge _0.1 . 5 shows Si _0.8 Ge _0.2 , FIG. 6 shows Si _0.7 Ge _0.3 , FIG. 7 shows Si _0.6 Ge _0.4 , and FIG _. It is a graph of the light absorption ratio in the semiconductor layer of the composition of ₀₅ Ge _0.5 .
Further, FIG. 9 shows the Si substrate and the above-mentioned Si _0.9 Ge _0.1 , Si _0.8 Ge _0.2 , Si _0.7 Ge _0.3 , and Si _0.6 Ge _0.4 . The relationship between the light absorption coefficient (cm ^<-1> ) and incident light wavelength in the semiconductor layer of a composition is shown.

  In the graphs shown in FIGS. 3 to 8, the wavelength of incident light is shown in increments of 50 nm from 400 nm to 950 nm, the horizontal axis indicates the depth of the substrate on which light is incident, and the vertical axis indicates the light absorption ratio. The light absorption ratio represents the attenuation from the light intensity at the time of incidence in the range of 0-1. That is, the light absorption ratio at the time of incidence is set to 0, and the light absorption ratio at the time when the intensity of the incident light gradually decreases and becomes 0 is shown as 1.

As shown in FIGS. 3 to 8, as the Ge composition ratio increases, the light absorption ratio in the shallow region increases in the entire wavelength region from visible light to infrared light. For example, a semiconductor layer having a composition of Si ₄ Ge (Si _0.8 Ge _0.2 ) has a thickness of about 1.5 μm and a photoelectric conversion efficiency equivalent to that of a Si substrate having a thickness of 3 μm. Further, it can be seen from the graph shown in FIG. 9 that the Si _(1-x) Ge _(x) semiconductor layer has a light absorption coefficient larger than that of Si over the entire wavelength region.
Therefore, when the light receiving part of the solid-state imaging device 30 is formed in the first semiconductor layer 32 containing Ge, the light absorption coefficient of the light receiving part becomes higher than Si in the entire wavelength region. Thus, the photoelectric conversion efficiency in PD33 becomes large because the light absorption coefficient by the side of a light-receiving part increases.

Further, according to the relationship between the incident depth and the light absorption ratio and the relationship between the wavelength and the light absorption coefficient, the semiconductor layer containing Ge has a light absorption coefficient continuously due to a change in the composition ratio of Ge. Change. That is, the band gap of the semiconductor layer can be continuously changed by changing the Ge addition ratio.
The compatibility of Ge with Si is 100% solid solution. For this reason, the Ge-containing semiconductor layer can freely and continuously change the Ge composition ratio.
Therefore, by adjusting the Ge content ratio of the first semiconductor layer 32, the light absorption coefficient of the light receiving portion of the solid-state imaging device 30 can be designed to a desired value.

  Further, the thickness of the first semiconductor layer 32 is preferably 0.01 to 5 μm for practical use of the solid-state imaging device from the above-described relationships. Since the absorption coefficient can be increased by increasing the composition ratio of Ge, it is possible to express a difference in light absorption from the Si substrate with a thickness of at least about 0.01 μm. Further, if the thickness is about 5 μm, a sufficient difference can be expressed.

As described above, the solid-state imaging device 30 according to the present embodiment includes the first semiconductor layer 32 having high photoelectric conversion efficiency on the light receiving surface side of the PD 33. With this configuration, incident light is largely photoelectrically converted on the light receiving surface side. Since the photoelectric conversion amount of incident light on the surface of the PD 33 is increased, the light that penetrates to the deep part of the base body is attenuated. For this reason, the proportion of light that reaches the adjacent pixel directly without being subjected to photoelectric conversion in the desired pixel is reduced. In addition, the ratio of light that once passes through the photoelectric conversion region, is reflected by the wiring layer, is re-entered, and reaches the adjacent pixel is reduced.
As described above, the optical color mixing of the solid-state imaging device 30 can be suppressed by reducing the ratio of light entering the adjacent pixels. Furthermore, it is possible to improve image quality degradation due to false signals in the optical black region.

  For example, as shown in FIG. 2, consider a case where incident light 41 incident obliquely on the PD 33 passes through the first incident PD 33 and enters the PD 33A of an adjacent pixel. In this case, the incident light 41 first passes through the first semiconductor layer 32. Since the first semiconductor layer 32 contains Ge as described above, the photoelectric conversion efficiency is higher than that of the Si substrate. Therefore, the incident light 41 is photoelectrically converted in the first semiconductor layer 32 and absorbed on the way to the adjacent pixel. Accordingly, the amount of incident light 41 is greatly reduced before reaching the adjacent pixel 33A.

  Further, the incident light 41 incident obliquely on the PD 33 has a longer distance to pass through the first semiconductor layer 32 than the incident light 42 incident on the PD 33 at an angle close to perpendicular. For this reason, the incident light 41 incident obliquely has a large amount of absorption in the first semiconductor layer 32. Therefore, by providing the first semiconductor layer 32 having a high photoelectric conversion rate on the light receiving surface side, the amount of light reaching the adjacent pixel 33A can be reduced.

Thus, by providing the first semiconductor layer 32, the amount of light can be greatly reduced before reaching the adjacent pixel with respect to the oblique light entering the adjacent pixel. And in PD33A of an adjacent pixel, the ratio of the false signal resulting from the optical interference photoelectrically converted by the oblique light from PD33 can be reduced.
Further, since the light absorption coefficient on the light receiving surface of the solid-state imaging device 30 is increased, the proportion of incident light that passes through the light receiving portion and reaches the wiring layer is also reduced. For this reason, optical interference (color mixing) to adjacent pixels due to reflection from the wiring layer can be suppressed.

A conventional solid-state image sensor composed of only a substrate made of Si, particularly a back-illuminated solid-state image sensor, photoelectrically converts a part of incident light due to insufficient condensing by an inner lens. Optical color mixing that reaches the adjacent pixel before becomes a problem. In addition, the phenomenon that incident light reaches the circuit part side without photoelectric conversion, is reflected by the wiring layer etc. on the circuit part side, and this reflected light re-enters the adjacent pixel is also a false signal in the backside illuminated image sensor. It becomes a factor of.
In the surface type solid-state imaging device, the above optical color mixture is reduced by arranging the wiring layer of the circuit portion on the light receiving surface side between the pixels. In a back-illuminated solid-state imaging device, since no wiring layer is formed on the light receiving surface side, optical color mixing cannot be prevented by a method of forming a wiring layer of a circuit portion between pixels.

  In the solid-state imaging device according to the above-described embodiment, a semiconductor layer containing Ge is formed by epitaxial growth on the light receiving portion side of the back-illuminated image sensor, and the circuit portion side is formed in a semiconductor substrate such as Si. With the solid-state imaging device having such a configuration, it is possible to suppress interference between adjacent pixels, particularly optical interference in which incident light enters the adjacent pixels, for example, optical color mixing.

In the above-described embodiment, the light receiving portion is formed across the first semiconductor layer and the semiconductor substrate. However, the PD is formed only in the first semiconductor layer by forming the semiconductor substrate thin and the first semiconductor layer thick. It is good also as a structure formed in. In particular, since long wavelength components such as infrared rays are highly transmissive on the Si substrate, the light receiving portion is formed deep in the substrate. On the other hand, in the semiconductor layer containing Ge, the photoelectric conversion efficiency is higher than that of Si in the entire wavelength region including the infrared region. For this reason, by using a semiconductor layer containing Ge, a long wavelength component such as infrared rays can be sufficiently converted even if the light receiving portion is formed shallow.
Furthermore, in the above-described embodiment, the case where the Ge-containing semiconductor layer is applied to the back-illuminated solid-state image sensor has been described.
Also in the above-described case, since it is preferable that there is no crystal defect in the charge transfer path or the like, it is preferable to form the circuit portion under the gate electrode or the FD in the semiconductor substrate.

[Example]
Next, in the solid-state imaging device of the above-described embodiment, the state of attenuation of incident light to adjacent pixels will be described using examples. The solid-state imaging device used in the embodiment has the same configuration as the solid-state imaging device 30 shown in FIG. The dimension of each structure of the pixel part of the solid-state image sensor 30 used in an Example is shown in FIG.
As shown in FIG. 10, the thickness of the semiconductor substrate 31 was 1.5 μm, and the first semiconductor layer 32 was formed on the semiconductor substrate 31 to a thickness of 1.5 μm. The semiconductor substrate 31 is a simple substance of Si. The composition of the first semiconductor layer 32 is Si _0.8 Ge _0.2 . With this configuration, a back-illuminated solid-state imaging device having a photoelectric conversion region with a thickness of 3 μm from the sensor light-receiving portion side was obtained.
In addition, regarding the incident light 41 incident on the PD 33A of the adjacent pixel through the PD 33, the position where the incident light 41 passes through the pixel boundary 43 between the PD 33 and the PD 33A is set to 1.5 μm from the light receiving surface side.

  FIG. 11 shows how the incident light 41 is attenuated in the solid-state imaging device 30 having the above-described configuration. In the graph shown in FIG. 11, the vertical axis indicates the incident light intensity of the incident light 41, and the horizontal axis indicates the depth from the light receiving surface of the substrate. With respect to the incident light intensity, the intensity of the incident light 41 on the outermost surface of the light receiving surface of the solid-state imaging device 30 is set to 1. As the incident light 41, 650 nm (Red) light, 550 nm (Green) light, and 450 nm (Blue) light are shown.

A solid line A indicates the relationship between the substrate depth of 650 nm (Red) light and the incident light intensity under the above-described conditions. Similarly, the relationship between the substrate depth of 550 nm (Green) light and the incident light intensity is indicated by a solid line B, and the relationship between the substrate depth of 450 nm (Blue) light and the incident light intensity is indicated by a solid line C.
As a comparative example, the relationship between the substrate depth of 650 nm (Red) light and the incident light intensity with respect to the Si single substrate is indicated by a broken line D. Similarly, the relationship between the substrate depth of 550 nm (Green) light and the incident light intensity with respect to the Si single substrate is indicated by a broken line E, and the relationship between the substrate depth of 450 nm (Blue) light and the incident light intensity is indicated by a broken line F.
As shown in FIG. 11, the light passing through the first semiconductor layer 32 (Si _0.8 Ge _0.2 ) has a lower incident light intensity than the light passing through the Si substrate. This decrease occurs at the same time as the first semiconductor layer 32 enters.

Further, from the results shown in FIG. 11, the reduction rate of the optical color mixture of the example was obtained. The decrease rate was obtained from the ratio of incident high intensity between the example and the comparative example at each wavelength when the incident light 41 passes through the pixel boundary 43, that is, at a depth of 1.5 μm from the light receiving surface.
The decrease rate of the optical color mixture of the Si _0.8 Ge _0.2 semiconductor layer (Example) with respect to the Si single substrate (Comparative Example) at 450 nm light was 99.6%.
The reduction rate of the optical color mixture of the Si _0.8 Ge _0.2 semiconductor layer (Example) with respect to the Si single substrate (Comparative Example) at 550 nm was 87.1%.
The decrease rate of the optical color mixture of the Si _0.8 Ge _0.2 semiconductor layer (Example) with respect to the Si single substrate (Comparative Example) at 650 nm light was 52.9%.

  As shown by the reduction rate of the optical color mixture, the incident light 41 can be attenuated by the first semiconductor layer 32 by providing the first semiconductor layer 32 containing Ge on the light receiving surface side of the solid-state imaging device 30. For this reason, it is possible to reduce the amount of light that passes through a pixel once incident and reaches an adjacent pixel, thereby suppressing the occurrence of optical color mixing.

<2. Second Embodiment of Solid-State Image Sensor>
Next, a second embodiment of the solid-state image sensor will be described. FIG. 12 is a cross-sectional view of a main part constituting one pixel of the solid-state imaging device of the second embodiment.
A solid-state imaging device 50 illustrated in FIG. 12 includes a semiconductor substrate 51, a first semiconductor layer 52, and a second semiconductor layer 53.
Note that the solid-state imaging device 50 of the second embodiment shown in FIG. 12 has the same configuration as the solid-state imaging device 30 of the first embodiment shown in FIG. Will not be described in detail.

The solid-state imaging device 50 is formed on the first main surface side of the semiconductor substrate 51.
A first semiconductor layer 52 is formed on the first main surface of the semiconductor substrate 51 (light receiving surface of the solid-state imaging device 50). Further, a second semiconductor layer 53 is formed on the first main surface side (light receiving surface) of the first semiconductor layer 52.
For this reason, the solid-state imaging device 50 includes three layers of the second semiconductor layer 53, the first semiconductor layer 52, and the semiconductor substrate 51 in order from the light receiving surface side.

A photodiode (PD) 54 including the first semiconductor layer 52 is formed from the surface of the second semiconductor layer 53 to the second main surface side of the semiconductor substrate 31. The PD 54 has a first conductivity type (p-type) semiconductor region on the light receiving surface side surface of the second semiconductor layer 53 and the surface of the second main surface of the semiconductor substrate 51. Between the p-type semiconductor regions, a second conductive type (n-type) semiconductor region formed continuously in three layers of the two semiconductor layers 53, the first semiconductor layer 52, and the semiconductor substrate 51 is provided. In addition, a pixel separation unit made of a first conductivity type (p-type) semiconductor region is provided between the PD 54 and the PD 54A of an adjacent pixel.
A transistor Tr1 is formed on the second main surface of the semiconductor substrate 51 from a gate electrode 55 and a PD 54 formed via a gate insulating film and a floating diffusion (FD) 56 formed on the surface of the semiconductor substrate 51. Is formed.

  In addition, a multilayer wiring layer 57 of the solid-state imaging device 50 is formed on the surface of the semiconductor substrate 51. The multilayer wiring layer 57 includes a plurality of laminated interlayer insulating layers and conductor layers. On the light receiving surface of the second semiconductor layer 53, a light shielding film 58 for shielding light between pixels is provided. Various optical components such as a color filter 59 and a microlens 60 are mounted on the light shielding film 58.

  For example, a silicon substrate is used as the semiconductor substrate 51, which is generally used for manufacturing a solid-state imaging device. The first semiconductor layer 52 is a semiconductor layer containing Ge, as in the first embodiment described above.

The second semiconductor layer 53 is formed of a semiconductor layer that does not contain Ge. The second semiconductor layer 53 is particularly preferably formed from a simple substance of Si. The second semiconductor layer 53 is formed by bonding, for example, an Si epitaxial growth layer or an Si thin film.
The thickness of the second semiconductor layer 53 is preferably at least as thick as the first conductivity type semiconductor region formed on the light receiving surface side surface of the PD 54. The thickness of the first conductivity type semiconductor region is preferably at least 0.01 μm or more in order to suppress dark current from the substrate surface. For this reason, the thickness of the second semiconductor layer 53 is also preferably 0.01 μm or more.
Further, the second semiconductor layer 53 formed on the light receiving surface side of the first semiconductor layer 52 containing Ge is preferably thin. Since the photoelectric conversion efficiency is better when the semiconductor layer containing Ge is formed near the light receiving surface, the arrival of oblique light to adjacent pixels can be reduced. For this reason, it is necessary to form the second semiconductor layer 53 with a thickness that does not lower the suppression of optical interference. For example, the maximum value of the thickness of the second semiconductor layer 53 is preferably 5 μm or less.

When Ge is included in the light receiving surface, that is, when the composition ratio x of Si _(1-x) Ge _(x) is other than 0 at the light receiving portion interface, the band gap of the semiconductor layer becomes smaller than Si. For this reason, the generation rate of the electron-hole pair from the interface state on the surface of the light receiving portion formed by the terminal portion of the crystal continuity increases. For this reason, there is a concern about an increase in dark current on the surface of the light receiving unit. For this reason, in the solid-state imaging device 50 of the second embodiment described above, a configuration in which Ge is not included in the light receiving unit interface, for example, a configuration in which the Si _(1-x) Ge _(x) composition ratio x = 0 is obtained. By providing the second semiconductor layer 53 made of, for example, Si alone on the first semiconductor layer 52 containing Ge, the state of the light receiving unit interface becomes equivalent to that of conventional Si. In this configuration, the generation rate of electron-hole pairs from the interface state can be kept equal to that of a solid-state imaging device using a conventional Si substrate.
Therefore, in the solid-state imaging device of the second embodiment, optical interference can be suppressed and dark current from the light receiving interface can be suppressed as in the solid-state imaging device of the first embodiment. As a result, the image quality of the solid-state image sensor can be improved.

<3. Electronics>
Next, an embodiment of an electronic device including the above-described solid-state imaging device will be described.
The above-described solid-state imaging device can be applied to electronic devices such as a camera system such as a digital camera or a video camera, a mobile phone having an imaging function, or another device having an imaging function. FIG. 13 illustrates a schematic configuration when a solid-state imaging device is applied to a camera capable of capturing a still image or a moving image as an example of an electronic device.

  The camera 70 of this example includes a solid-state image sensor 71, an optical system 72 that guides incident light to the light receiving sensor portion of the solid-state image sensor 71, a shutter device 73 provided between the solid-state image sensor 71 and the optical system 72, And a drive circuit 74 for driving the image sensor 71. Further, the camera 70 includes a signal processing circuit 75 that processes an output signal of the solid-state image sensor 71.

  As the solid-state image sensor 71, the solid-state image sensor of the first embodiment and the second embodiment described above can be applied. The optical system (optical lens) 72 forms image light (incident light) from a subject on an imaging surface (not shown) of the solid-state imaging device 71. Thereby, signal charges are accumulated in the solid-state imaging device 71 for a certain period. The optical system 72 may be composed of an optical lens group including a plurality of optical lenses. The shutter device 73 controls the light irradiation period and the light shielding period of the incident light to the solid-state image sensor 71.

  The drive circuit 74 supplies drive signals to the solid-state image sensor 71 and the shutter device 73. The drive circuit 74 controls the signal output operation to the signal processing circuit 75 of the solid-state image sensor 71 and the shutter operation of the shutter device 73 by the supplied drive signal. That is, in this example, a signal transfer operation from the solid-state imaging device 71 to the signal processing circuit 75 is performed by a drive signal (timing signal) supplied from the drive circuit 74.

  The signal processing circuit 75 performs various types of signal processing on the signal transferred from the solid-state image sensor 71. The signal (video signal) that has been subjected to various signal processing is stored in a storage medium (not shown) such as a memory, or is output to a monitor (not shown).

  In the solid-state imaging device according to each of the above-described embodiments, an example is described in which the solid-state imaging device is applied to an image sensor in which unit pixels that detect signal charges corresponding to the amount of visible light as physical quantities are arranged in a matrix. did. However, the above-described solid-state imaging device is not limited to application to an image sensor, and can be applied to all column-type solid-state imaging devices in which column circuits are arranged for each pixel column of the pixel array unit. .

In addition, the solid-state imaging device described above is not limited to application to a solid-state imaging device that senses the distribution of the amount of incident light of visible light and captures it as an image. The present invention can be applied to a solid-state imaging device for imaging. In a broad sense, the present invention can be applied to all solid-state imaging devices (physical quantity distribution detection devices) such as a fingerprint detection sensor that senses other physical quantity distributions such as pressure and capacitance and captures images as images.
Furthermore, the above-described solid-state imaging device is not limited to a solid-state imaging device that sequentially scans each unit pixel of the pixel array unit in units of rows and reads a pixel signal from each unit pixel. For example, the present invention can also be applied to an XY address type solid-state imaging device that selects an arbitrary pixel in pixel units and reads signals from the selected pixels in pixel units.
Even when a solid-state image sensor is applied to each of the above embodiments, optical interference can be suppressed as in the solid-state image sensor of the above-described embodiment.
The solid-state imaging device may be formed as a single chip, or may be in a module-like form having an imaging function in which an imaging unit and a signal processing unit or an optical system are packaged together. Good.

  Further, in the solid-state imaging device of each of the embodiments described above, the solid-state imaging device using electrons as signal charges has been described, but the present invention can also be applied to a solid-state imaging device using holes as signal charges. In this case, in the above example, the first conductivity type is p-type and the second conductivity type is n-type, and the first conductivity type is n-type and the second conductivity type is p-type.

In addition, this indication can also take the following structures.
(1) A semiconductor substrate, a first semiconductor layer containing Ge formed on the first main surface of the semiconductor substrate, a transfer transistor formed on the second main surface of the semiconductor substrate, and the first semiconductor And a photodiode formed in a region including the layer.
(2) The solid-state imaging device according to (1), wherein the first semiconductor layer is represented by Ge alone or a composition formula Si _(1-x) Ge _x , and x is 0.05 or more and less than 1.0. .
(3) The solid-state imaging device according to (1) or (2), wherein a second semiconductor layer not containing Ge is provided on the first semiconductor layer.
(4) The solid-state imaging device according to (3), wherein the second semiconductor layer is formed to have a thickness equal to or greater than a thickness of a first conductivity type semiconductor region formed on a light receiving surface side of the photodiode.
(5) The solid-state imaging device according to any one of (1) to (4), wherein a thickness of the first semiconductor layer is 0.01 μm or more and 5 μm or less.
(6) An electronic apparatus comprising: the solid-state imaging device according to any one of (1) to (5); and a signal processing circuit that processes an output signal of the solid-state imaging device.

  10, 30, 50, 71 Solid-state imaging device, 11 sensor substrate, 13 pixels, 14 pixel region, 15 pixel drive line, 16 vertical signal line, 17 peripheral region, 18 wiring, 21 circuit substrate, 22 vertical drive circuit, 23 column Signal processing circuit, 24 horizontal drive circuit, 25 system control circuit, 31, 51 semiconductor substrate, 32, 52 first semiconductor layer, 33, 54 photodiode, 33A adjacent pixel, 34, 55 gate electrode, 35, 56 floating diffusion, 36, 57 Multilayer wiring layer, 37, 58 Light shielding film, 38, 59 Color filter, 39, 60 Micro lens, 41, 42 Incident light, 43 Pixel boundary, 53 Second semiconductor layer, 70 Camera, 72 Optical system, 73 Shutter Device, 74 drive circuit, 75 signal processing circuit, Tr1 transistor

Claims (6)

A semiconductor substrate;
A first semiconductor layer containing Ge formed on the first main surface of the semiconductor substrate;
A transfer transistor formed on the second main surface of the semiconductor substrate;
A photodiode formed in a region including the first semiconductor layer;
A solid-state imaging device. The solid-state imaging device according to claim 1, wherein the first semiconductor layer is represented by Ge alone or a composition formula Si _(1-x) Ge _x , and x is 0.05 or more and less than 1.0.   The solid-state imaging device according to claim 1, further comprising a second semiconductor layer not containing Ge on the first semiconductor layer.   The photodiode includes a first conductive type semiconductor region and a second conductive type semiconductor region from the light receiving surface side, and the second semiconductor layer is formed on the light receiving surface side of the photodiode. The solid-state imaging device according to claim 3, wherein the solid-state imaging device is formed to have a thickness equal to or greater than a thickness of the conductive semiconductor region.   The solid-state imaging device according to claim 1, wherein a thickness of the first semiconductor layer is 0.01 μm or more and 5 μm or less. A semiconductor substrate; a first semiconductor layer containing Ge formed on the first main surface of the semiconductor substrate; a transfer transistor formed on the second main surface of the semiconductor substrate; and the first semiconductor layer. A solid-state imaging device comprising a photodiode formed in the region;
And a signal processing circuit for processing an output signal of the solid-state imaging device.

Images