JP2004103964A - Solid-state imaging element and imaging device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging element enabling visible and infrared ray imaging at low costs, and to contrive miniaturization. <P>SOLUTION: An infrared ray receiving layer 13 is formed on the back of a silicon substrate 10 formed with a PN junction photodiode on a surface, and carriers are produced by the infrared ray passing inside the substrate 10. In a visible ray imaging mode, the surface of the substrate 10 near an N-type area 11 is short-circuited to a lower surface of the infrared ray receiving layer 13, and the entrance of the carriers into a cavity layer 12 is restricted. In an infrared ray imaging mode, the cavity layer 12 is enlarged by applying a negative voltage to a lower surface of the infrared ray receiving layer 13, and the carriers generated in the infrared ray receiving layer 13 are promoted to enter the cavity layer 12. The carriers (electrons) entered the cavity layer 12 are promptly moved to the N-type area 11 by an electric field and are excluded to the outside. Thus, it is possible to manufacture an infrared charge-coupled device by a production process at the substantially same degree as a conventional Si charge-coupled device, and to curtail the costs fairly with a small device size. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid-state imaging device (generally referred to as an image sensor) and an imaging device using the same, and more particularly, to a visible / infrared light compatible having sensitivity not only in a visible light region but also in an infrared light region. And an imaging device using the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, solid-state imaging devices have been used in various electronic devices such as digital cameras, camera-integrated VTRs, facsimile machines, and mobile phones with camera functions, and there has been remarkable progress in their performance. The most common silicon (Si) solid-state imaging device has a configuration in which a large number of pixels are two-dimensionally arranged, and each pixel mainly includes a light receiving element (photoelectric conversion unit) and a charge reading circuit. It is configured. At present, the mainstream structure of the light receiving element is a PN junction photodiode or a photogate structure, both of which detect a carrier (photocarrier) which is an electron-hole pair generated by incident light to perform an imaging function. Has been realized.
[0003]
FIG. 9 shows an example of a conventionally known element structure, in which (A) is a schematic longitudinal sectional view of a PN junction photodiode structure, and (B) is a schematic sectional view of a MOS photogate structure (for example, see Non-Patent Document). 1 etc.).
[0004]
In the example of FIG. 9A, when light enters the photoelectric conversion portion, carriers are generated mainly in the depletion layer 52 formed near the junction boundary of the source region 51 which is an N-type region. Of the generated carriers, holes are discharged through the substrate 50, while electrons are accumulated inside the depletion layer 52. Thereafter, when a predetermined voltage is applied to the gate electrode 53, a channel 54 is formed immediately below the gate electrode 53, electrons flow through the channel 54 to the drain region 55, which is an N-type region, and the signal line 56 connected to the drain region 55 Is extracted as a signal.
[0005]
In the example of FIG. 9B, when light enters the photoelectric conversion unit, carriers are generated mainly in the MOS capacitor region 62 formed immediately below the photogate electrode 61 to which a DC voltage is applied. Of the generated carriers, holes are ejected through the substrate 60, while electrons are accumulated inside the MOS capacitor region 62. Thereafter, when a predetermined voltage is applied to the gate electrode 63, the potential barrier drops in the transfer region 64 immediately below the gate electrode 63, the electrons flow over the potential barrier to the N-type region 65, and the signal connected to the N-type region 65 The signal is extracted from the line 66 as a signal.
[0006]
In an imaging device using such a solid-state imaging device, as described above, a signal corresponding to the amount of electrons stored in the photoelectric conversion unit is detected for each pixel, and the pixel signal is processed by an image processing circuit. A two-dimensional image can be constructed.
[0007]
[Non-patent document 1]
Takao Ando, Hirohito Komobuchi, "Basics of solid-state image sensors-The mechanism of electronics", The Institute of Image Information and Television Engineers, 1999
[0008]
[Problems to be solved by the invention]
In a surveillance camera, a night vision camera, a surveillance management system, and the like, which are one of the application fields of such a solid-state imaging device, there is a strong demand for imaging with infrared light or near-infrared light. In the Si solid-state imaging device, since the forbidden band of Si is about 1.11 [eV], regardless of the above-described structure, infrared light having a wavelength of about 1.1 [μm] or more is generally used regardless of the structure described above. It has almost no sensitivity. Therefore, for imaging using light having a wavelength of 1.1 [μm] or more, an InGaAs solid-state imaging device, an infrared vidicon tube, or the like is generally used.
[0009]
However, since the InGaAs solid-state imaging device is much more expensive than the Si solid-state imaging device, it is a major factor preventing cost reduction of the imaging device. In addition, the infrared vidicon tube has a larger device and consumes more power than a solid-state imaging device, and is often expensive in terms of cost.
[0010]
The present invention has been made in view of such a problem, and a main object of the present invention is to provide a solid-state imaging device capable of performing imaging using infrared light at a lower cost than before and to reduce the size thereof. That is. Another object of the present invention is to add an infrared light imaging function while having an imaging function using visible light, and if necessary, image both visible light and infrared light or only one of them. It is an object of the present invention to provide a solid-state image pickup device and an image pickup apparatus capable of performing selective image pickup.
[0011]
[Means for Solving the Problems and Effects]
The solid-state imaging device according to the present invention made in order to solve the above problems,
a) a visible light receiving means formed on a light irradiation surface on a silicon substrate and having a carrier collection region for generating carriers by receiving light in at least a visible band or for accumulating after generating carriers;
b) an infrared light receiving means which is provided on the surface on the back side of the visible light receiving means or on the same surface as the visible light receiving means with the substrate interposed therebetween, and which generates carriers by receiving light in an infrared band;
c) a carrier inside the substrate so as to promote the movement of the carrier generated by the infrared receiving means to the carrier collection area, or to suppress the carrier from reaching the carrier collection area. Carrier movement control means for controlling the movement of
It is characterized by having.
[0012]
Here, the “infrared band” is a wavelength band including near-infrared light and is longer than 0.76 to 0.83 [μm], which is the long wavelength end of visible light. Indicates a wavelength of 1.1 [μm] or more. As the infrared light receiving means having sensitivity to light in such a wavelength band, for example, a thin film layer of a semiconductor material whose forbidden band width is smaller than Si, such as Ge, InAs or InGaAs, which is a III-V compound semiconductor, is a P-type, Although it can be provided with any of N-type, P-type / N-type, or N-type / P-type structure, other materials such as an organic material can also be considered.
[0013]
In the solid-state imaging device according to the present invention, when it is desired to obtain a detection signal for visible light, the carrier movement control unit moves the carrier such that the carrier generated by the infrared light receiving unit does not reach the carrier collection area as much as possible. Control. Therefore, even if the incident light contains light in the infrared band and the infrared light generates carriers in the infrared light receiving means, the carriers hardly or almost do not enter the carrier collection area, and serve as detection signals. Is not used. On the other hand, since carriers are generated in the carrier collection region by light in the visible band included in the incident light, by extracting a signal current or a signal voltage corresponding to the carrier generated in the carrier collection region or accumulated after the generation. Thus, an image signal based on visible light, which is not affected by infrared light, can be obtained.
[0014]
When it is desired to obtain a detection signal for infrared light, the carrier movement control means controls the movement of the carrier such that the carrier generated by the infrared light receiving means moves to the carrier collection area. As a result, the carriers generated by the infrared receiving means due to the infrared light move to the carrier collection area and are handled as if they were generated inside the area. If the incident light contains light in the visible band, the carriers generated in the carrier collection region by the visible light and the carriers that have moved from the infrared receiving means are mixed, so that the carrier collection region By extracting a signal current or a signal voltage corresponding to the existing carrier, an image signal using both infrared light and visible light can be obtained. Further, when the incident light does not include light in the visible band, since only carriers that have moved from the infrared light receiving means are present in the carrier collection area, it is possible to obtain an image signal using infrared light. it can.
[0015]
Furthermore, if the carrier movement control means can control the amount of the carrier generated by the infrared light receiving means which moves to the carrier collection area (or the ratio of the movement to the carrier collection area), the light reception for visible light can be achieved. The sensitivity and the light receiving sensitivity to infrared light can be appropriately adjusted, and the signal intensity due to infrared light can be relatively increased or reduced.
[0016]
The visible light receiving means can be in various forms known in the art, and specifically, for example, can be a PN junction photodiode or a MOS photogate. In the case of a PN junction photodiode, the carrier collection region is a depletion layer (sometimes called a depletion region) formed near the junction boundary. In the case of a MOS photogate, the carrier collection region is a MOS capacitor region. is there. Carriers for visible light are not necessarily generated only in the carrier collection area, but most of them are generated in the carrier collection area. Can be.
[0017]
As described above, according to the solid-state imaging device according to the present invention, the structure of a conventional solid-state Si solid-state imaging device using a silicon substrate is basically provided, and an infrared light receiving unit and a carrier movement control unit are provided. Thereby, imaging up to an infrared band of 1.1 [μm] or more can be performed. A standard silicon substrate can be used as the substrate, and the manufacturing process may be slightly added to the conventional Si solid-state imaging device manufacturing process. Significant cost reduction can be achieved as compared with the imaging device. Also, not only can the size be significantly reduced compared to the vidicon tube, but also the MOS type enables extremely miniaturization other than the photoelectric conversion section, and the peripheral circuits can be mounted on the same substrate. Easy. Thereby, not only the element itself can be miniaturized, but also the imaging device using the element can be miniaturized.
[0018]
In particular, light in the infrared band of 1.4 [μm] or more is called eye-safe light and is known to have a large permissible exposure to human eyes. The solid-state imaging device according to the present invention can easily use such light in the infrared band, so that an active night-vision system using strong light can be constructed. In addition, sunlight contains a lot of components of 1.1 [μm] or more. However, by using a bright light source of 1.4 [μm] or more that is safe for eyes, active imaging that is less affected by sunlight can be performed. It is also possible to construct a dynamic imaging system. Such an imaging technique cannot be realized by a conventional Si solid-state imaging device.
[0019]
Furthermore, according to the solid-state imaging device according to the present invention, not only infrared imaging can be performed, but also imaging using only visible light without using infrared light or infrared light and visible light can be performed as necessary. And imaging using only infrared light without using visible light can be selectively performed by one element. Therefore, it is possible to realize an imaging apparatus that switches between various kinds of imaging at low cost and to reduce the size of the imaging apparatus.
[0020]
In a preferred embodiment of the solid-state imaging device according to the present invention, the infrared light receiving means may be provided on a back surface of the substrate and receive infrared light passing through the inside of the substrate to generate carriers. .
[0021]
As described above, as a method of providing the infrared light receiving layer as the infrared light receiving means on the back surface of the substrate, bonding or vapor deposition is generally performed, but when a liquid such as an organic material can be used, a thin film is formed by coating or the like. A layer may be formed.
[0022]
According to the configuration of this preferred embodiment, since the infrared light receiving means is provided on the back surface of the substrate, it is possible to secure a large area for forming the visible light receiving means on the surface of the substrate, and to improve performance such as definition. Is advantageous. Further, since the infrared light receiving means can be formed without affecting the visible light receiving means and other circuits (for example, a signal readout circuit), a simple process can be added to the conventional Si solid-state imaging device manufacturing process. It suffices to be advantageous in terms of cost. Furthermore, since the visible light receiving means and the infrared light receiving means are paired on the front and back of the substrate, any of the light receiving means can use the light irradiated to the substantially same area. When switching between the two, the correspondence between the two images is improved, and when both infrared light and visible light are used, blurring and blurring of the image can be reduced.
[0023]
When the infrared light receiving means is provided on the back surface of the substrate, the infrared light receiving means may be formed after the substrate is thinned by polishing or the like. This reduces the distance from the infrared light receiving means to the carrier collection area, and suppresses the spread of light when the light incident from the front light irradiation surface reaches the infrared light receiving means. As a result, carriers generated by the infrared receiving means can be more efficiently collected in the carrier collection area. Accordingly, it is possible to improve the light receiving sensitivity of infrared light and reduce leakage of adjacent pixels into the carrier collection region, which is also effective in reducing image bleeding and blurring.
[0024]
In the solid-state imaging device according to the present invention, as one mode of the carrier movement control means, the carrier collection from the infrared light receiving means is performed by giving a potential difference between the infrared light receiving means and the carrier collection area or increasing the potential difference. A configuration that promotes the movement of carriers to the region can be adopted.
[0025]
Specifically, for example, when the visible light receiving means is a PN junction photodiode, by giving a predetermined potential difference between the infrared light receiving means and the carrier collection area or by increasing the potential difference even when there is already a potential difference, The depletion layer, which is a carrier collection region, can be enlarged, and an appropriate electric field can be formed in the depletion layer. As the depletion layer spreads to the vicinity of the infrared light receiving means, the carriers generated by the infrared light receiving means are easily captured by the depletion layer, and the mobility of the carriers in the depletion layer is extremely high. Generated carriers can be efficiently collected.
[0026]
In the configuration in which the infrared light receiving means is provided on the back surface of the substrate, the carrier collection area is relatively located on the front surface side of the substrate. As a method for "increase the potential difference", a potential difference may be provided between the substrate surface and the infrared receiving means or the potential difference may be increased. Note that the polarity of the potential difference at that time depends on whether electrons or holes are used as carriers.
[0027]
Further, in the solid-state imaging device according to the present invention, as one mode of the carrier movement control means, the carrier reaches the carrier collection area by forming a virtual carrier passage path that is easy to pass through the carrier outside the carrier collection area. It can be configured.
[0028]
Specifically, an electrode that comes into contact with the substrate may be provided outside the carrier collection area so that the carriers generated by the infrared receiving means move toward the electrode instead of the carrier collection area. In the configuration in which the infrared light receiving means is provided on the back surface of the substrate, for example, if the electrode provided on the surface of the substrate and the infrared light receiving means are short-circuited or substantially in the same state as substantially short-circuited, a virtual A carrier passage path is formed inside the substrate.
[0029]
Further, in the solid-state imaging device according to the present invention, the carrier movement control unit includes a P-type and / or N-type diffusion region formed around the visible light receiving unit, and a voltage application unit that applies a predetermined voltage to the diffusion region. And a configuration including:
[0030]
In this configuration, by adjusting the voltage applied to the diffusion region, the potential distribution of the electric field formed inside the substrate or on the surface of the substrate is appropriately determined, whereby the carriers generated by the infrared light receiving means are effectively reduced. It is possible to move the carrier to the collection area or to extract a carrier having a high possibility of obstructing or interfering with an adjacent pixel from carriers generated by the infrared receiving unit. Therefore, blurring or blurring of an image can be improved, and image quality can be improved.
[0031]
In addition, an imaging device using the solid-state imaging device according to the present invention includes the solid-state imaging device according to the present invention, an optical filter that blocks light in a visible band, and an optical filter that covers the light irradiation surface of the solid-state imaging device. Filter driving means to be inserted in front or to be removed from the front of the light irradiation surface, and in a state where the optical filter is inserted in front of the light irradiation surface of the solid-state imaging device, the carrier movement control means, infrared receiving means By promoting the movement of the carrier generated in step (1) to the carrier collection region, an image signal is obtained by removing light in the visible band and using light in the infrared band.
[0032]
That is, according to this imaging apparatus, by combining the solid-state imaging device and the optical filter as described above, it is possible to realize infrared imaging that is not affected by visible light with relatively simple control, This is advantageous for construction of various systems using infrared imaging as described above.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the solid-state imaging device according to the present invention will be described with reference to the drawings with specific examples.
[0034]
FIG. 1 is a schematic diagram showing a vertical cross-sectional structure of a photoelectric conversion unit of one pixel in a solid-state imaging device according to a first embodiment which is an embodiment of the present invention. In the first embodiment, a PN junction photodiode similar to that shown in FIG. 9A is used as the visible light receiving means. In FIG. 1 (and FIGS. 2 to 7 used in the following description), only the photoelectric conversion unit is described because the photoelectric conversion unit has a characteristic feature of the present invention.
[0035]
That is, in general, a solid-state imaging device includes a voltage / current conversion unit, a signal readout unit, and the like at a stage subsequent to the photoelectric conversion unit, depending on the structure, but these components may be of any type. For example, signal reading may be of a CMOS type or a CCD type. In many cases, carriers are accumulated in the carrier collection region of the photoelectric conversion unit. However, such accumulation of carriers is not essential, and the present invention can be applied to a case where generated carriers are immediately read.
[0036]
Referring to FIG. 1, a PN junction photodiode is formed on the surface of a P-type silicon substrate (hereinafter, simply referred to as “substrate”) 10 by providing an N-type region 11 as in the related art. The carriers mainly generate visible light in the depletion layer 12 formed near the junction boundary. On the back surface of the substrate 10, an infrared light receiving layer 13 made of a thin film layer of a group III-V compound semiconductor such as InGaAs or InAs is formed as infrared light receiving means. The infrared light receiving layer 13 has a function of receiving light that has passed through the inside of the substrate 10 among the light irradiated on the surface of the substrate 10 and generating carriers.
[0037]
However, the material of the infrared light-receiving layer 13 is not limited to this, and any other material having sufficient sensitivity to infrared light (here, a wavelength band of 1.1 [μm] or more) may be used. Good. Further, the method of forming the infrared light receiving layer 13 is not particularly limited. For example, a method of attaching a previously formed infrared light receiving layer to the back surface of the substrate 10, a method of vapor deposition such as sputtering, and the like can be used. When the material is a liquid, a coating method or a spraying method can be used.
[0038]
Usually, the thickness of the substrate 10 is often several hundred [μm]. However, in order to enhance the carrier collection efficiency by enlarging the depletion layer 12 as described later, the substrate 10 is polished to 30 to 100 [μm]. [μm]. At this time, the thickness of the infrared light receiving layer 13 can be set to several hundred [nm] to several [μm].
[0039]
A first electrode 14 for ensuring contact with the substrate 10 is provided at a position appropriately separated from the N-type region 11, while a contact with the infrared light receiving layer 13 is ensured on the lower surface of the infrared light receiving layer 13. A second electrode 15 is provided. A switch 16 that is switched by a control signal (not shown) is provided between the first electrode 14 and the second electrode 15, and a DC power supply 17 is connected to the other terminal of the switch 16. The switch 16 has a function of switching the imaging mode of the solid-state imaging device, as described later. Although the switch 16 is illustrated separately from the substrate 10 in FIG. 1, it is obvious that the function can be formed on the substrate 10.
[0040]
FIG. 3 is a conceptual diagram for explaining the light receiving operation of the solid-state imaging device according to the first embodiment. Here, the light receiving mode inherent in the conventional Si solid-state imaging device is called a visible light (normal) imaging mode, and the infrared light imaging state unique to the present device is called an infrared light imaging mode.
[0041]
1. Visible light imaging mode (see FIG. 3A)
By tilting the switch 16 to the left, the first electrode 14 on the surface of the substrate 10 and the second electrode 15 on the lower surface of the infrared light receiving layer 13 are short-circuited (or may be connected via a very small load). Carriers are generated and accumulated in the depletion layer 12 by the visible light of the light emitted to the photoelectric conversion unit from above. On the other hand, since a PN junction photodiode has little sensitivity to infrared light, the infrared light penetrates deeply into the substrate 10 without losing energy on the way, penetrates the substrate 10 and receives infrared light on the back surface. It reaches the layer 13. Since the infrared receiving layer 13 has high sensitivity to infrared light, carriers are generated in the infrared receiving layer 13. However, since the first electrode 14 and the second electrode 15 are short-circuited as described above, carriers (here, electrons) easily pass between the first electrode 14 and the second electrode inside the substrate 10. ing. Therefore, the carriers generated in the infrared light receiving layer 13 are quickly dissipated through the above-mentioned path, and hardly enter the depletion layer 12. Therefore, since the carriers generated in the infrared light receiving layer 13 are not used, it can be considered that the carrier operates in the same manner as the conventional Si solid-state imaging device.
[0042]
2. Infrared light imaging mode (see FIG. 3B)
By tilting the switch 16 to the right, a negative voltage is applied to the second electrode 15 that contacts the infrared light receiving layer 13. As a result, as shown in the figure, the depletion layer 12 at the PN junction boundary expands to the vicinity of the infrared light receiving layer 13, and the mobility of carriers is greatly improved by the electric field formed inside the depletion layer 12. In such a state, when carriers are generated in the infrared light receiving layer 13, electrons of the carriers easily enter the depletion layer 12, and the inside of the depletion layer 12 is brought close to the N-type region 11 by the action of the electric field. Accumulate while moving quickly. When visible light is included in the incident light, carriers are generated in the depletion layer 12 by the visible light. Therefore, the carrier due to visible light and the carrier due to infrared light are mixed in the depletion layer 12, and a detection output for both visible light and infrared light is obtained.
[0043]
When it is desired to switch between imaging using only infrared light and imaging using only visible light using the solid-state imaging device, an imaging device configuration as shown in FIG. 8 can be employed, for example.
[0044]
That is, an optical filter 104 having a wavelength characteristic that allows only desired infrared light to pass therethrough is installed between the solid-state imaging device 100 and the condenser lens system 106 so as to be freely inserted and removed. When performing infrared imaging, the control unit 103 causes the filter driving unit 105 to insert the optical filter 104 between the condenser lens system 106 and the solid-state imaging device 100. When the projection light from the imaging target 107 passes through the optical filter 104, light in the visible band is removed, and only infrared light enters the solid-state imaging device 100. The solid-state imaging device 100 is controlled by the control unit 103 to operate in the infrared light imaging mode. As a result, a detection signal based on only the carrier generated in the infrared light receiving layer 13 is extracted from the solid-state imaging device 100 as described above, and an infrared image is displayed on the image monitor 102 via the image processing unit 101. It is.
[0045]
Further, as described above, by applying a negative voltage to the second electrode 15, the depletion layer 12 can be enlarged in the back direction, and the degree of expansion of the depletion layer 12 causes carriers generated in the infrared light receiving layer 13. The degree of entering the depletion layer 12 changes. Therefore, by appropriately controlling the voltage applied to the second electrode 15 (strictly, the voltage difference between the voltage on the surface of the substrate 10 and the voltage of the infrared light receiving layer 13), and controlling the spread of the depletion layer 12, The light receiving sensitivity to light can be adjusted. Thereby, in an image finally reproduced, various images can be obtained by adjusting the relative dependence on infrared light.
[0046]
Next, as a second embodiment of the present invention, an example in which a MOS photogate is used as a visible light receiving unit will be described. FIG. 2 is a schematic diagram illustrating a vertical cross-sectional structure of a photoelectric conversion unit of one pixel of the solid-state imaging device according to the second embodiment.
[0047]
A photogate electrode 21 is provided on the surface of the substrate 20 with an oxide film 28 interposed therebetween, and mainly generates carriers for visible light in a MOS capacitor region 22 formed immediately below the photogate electrode 21. Further, similarly to the first embodiment, an infrared receiving layer 23 is formed on the back surface of the substrate 10. A first electrode 24 for ensuring contact with the substrate 20 is provided near the photogate electrode 21, while a first electrode 24 for securing contact with the infrared light-receiving layer 23 is provided on the lower surface of the infrared light-receiving layer 23. Two electrodes 25 are provided. A switch 26 that is switched by a control signal is provided between the first electrode 24 and the second electrode 25, and a DC power supply 27 is connected to the other terminal of the switch 26.
[0048]
FIG. 4 is a conceptual diagram for explaining the light receiving operation of the solid-state imaging device according to the second embodiment. The basic operations in the visible light imaging mode (see FIG. 4A) and the infrared light imaging mode (see FIG. 4B) differ only in the carrier accumulation operation using visible light. Since this is the same as the first embodiment, a brief description will be given.
[0049]
1. Visible light imaging mode (see FIG. 4A)
By tilting the switch 26 to the left, the first electrode 24 and the second electrode 25 on the lower surface of the infrared light receiving layer 23 are short-circuited. Carriers are generated and accumulated in the MOS capacitor region 22 by the visible light of the light emitted to the photoelectric conversion unit from above. On the other hand, the infrared light penetrates deeply into the substrate 20 without losing energy on the way, passes through the substrate 20, and reaches the infrared light receiving layer 23 on the back surface. Since the infrared light receiving layer 23 has high sensitivity to infrared light, carriers are generated in the infrared light receiving layer 23 but are quickly dissipated and hardly enter the MOS capacitor region 22. The infrared light receiving layer 23 does not substantially contribute to imaging, and operates similarly to a conventional photogate type solid-state imaging device.
[0050]
2. Infrared light imaging mode (see FIG. 4B)
By tilting the switch 26 to the right, a negative voltage is applied to the second electrode 25 that contacts the infrared light receiving layer 23. As a result, as shown in the figure, the MOS capacitor region 22 expands to the vicinity of the infrared light receiving layer 23, and the mobility of carriers is greatly improved by the electric field formed in the MOS capacitor region 22 with the expansion. When carriers are generated in the infrared light receiving layer 23 in such a state, the electrons easily enter the MOS capacitor region 22 and quickly move to the upper part of the region 22 by the action of the electric field to be accumulated. . Since carriers generated by visible light also exist in the MOS capacitor region 22, for example, when a transfer gate (not shown) is opened, carriers by infrared light and carriers by visible light are simultaneously sent in the horizontal direction.
[0051]
In this manner, the solid-state imaging device of the second embodiment can switch between the visible light imaging mode and the infrared light imaging mode and execute the same as in the first embodiment. If it is desired to do so, the same method as in the first embodiment may be used.
[0052]
In the above description of the first and second embodiments, the configuration and operation of one pixel have been described. However, in an actual solid-state imaging device, many pixels are arranged close to each other. Therefore, in order to ensure operation stability and improve performance, for example, in the visible light imaging mode, the carrier generated in the infrared light receiving layer of a certain pixel leaks into the depletion layer of an adjacent pixel. It is preferable to adopt a configuration in which prevention of interference or interference between them is considered.
[0053]
Next, the structure and operation of the solid-state imaging device in consideration of such points will be described. FIG. 5 shows an example of a longitudinal sectional structure in which the visible light receiving means is a PN junction photodiode, and FIG. 6 shows an example of a longitudinal sectional structure in which the visible light receiving means is a photogate. The same components as those in FIGS. The same reference numerals are given. Except for the visible light receiving means, the basic structures are the same, so only FIG. 5 will be described.
[0054]
A first diffusion region 30 having conductivity opposite to that of the substrate 10 (N-type in this example) is formed between the N-type regions 11 of adjacent pixels, and the first diffusion region 30 and the N-type region 11 of each pixel are formed. A second diffusion region 31 having the same conductivity as that of the substrate 10 (P type in this example) is formed between them. Appropriate voltages DC1 and DC2 are applied to the first diffusion region 30 and the second diffusion region 31, respectively.
[0055]
By applying an appropriate voltage to the first diffusion region 30, the uniformity of the potential distribution inside the substrate 10 can be improved, so that the carriers generated in the infrared light receiving layer 13 immediately below the depletion layer 12 can be reduced. It can be led to the depletion layer 12 stably. In addition, by extracting carriers generated in the infrared light receiving layer 13 in the middle of the adjacent pixel, leakage of the other pixel to the depletion layer 12 is prevented, thereby improving image quality deterioration such as image blurring and blurring. You can also.
[0056]
On the other hand, by applying an appropriate voltage to the second diffusion region 31, the uniformity of the potential distribution in the vicinity of the surface of the substrate 10 can be improved, thereby further stabilizing the behavior of carriers in the substrate 10. it can. Further, it is possible to assist the extraction of the carrier by the first diffusion region 30 as described above, and it is possible to further improve image quality deterioration such as blurring or blurring of an image.
[0057]
In addition, since the influence of the adjacent pixels can be reduced by adopting the above-described configuration, the infrared light receiving layers 13 and 23 formed on the back surfaces of the substrates 10 and 20 are common to a large number of pixels (that is, separated for each pixel). The infrared light receiving layers 13 and 23 may be separated for each pixel or for each pixel group in which a plurality of pixels are grouped. With such a configuration, although the manufacturing process of the element is slightly complicated, the influence of the adjacent pixels is further reduced, and the image quality can be further improved.
[0058]
In each of the above embodiments, the infrared light receiving layers 13 and 23 are formed on the back surfaces of the substrates 10 and 20, however, for example, as shown in FIG. May be formed. In this case, when a negative voltage is applied to the infrared light receiving layer 13, the depletion layer 12 expands in the lateral direction, and carriers generated in the infrared light receiving layer 13 easily reach the depletion layer 12.
[0059]
Furthermore, it is not necessary to provide an infrared light receiving layer (infrared light receiving means) corresponding to the visible light receiving means of all the pixels included in the solid-state imaging device. An infrared light receiving layer may be provided only in the pixel. Also. When there are pixels provided with an infrared light receiving layer and pixels not provided with an infrared light receiving layer (pixels provided only with visible light receiving means) (particularly arranged close to each other), for example, a difference between the two signals is obtained. Thereby, only the signal for the infrared light can be extracted. By utilizing such a function, an infrared image can be created, and various types of imaging that cannot be realized by a conventional Si solid-state imaging device can be performed.
[0060]
It is to be noted that each of the above embodiments is merely an example, and it is apparent that any changes or modifications within the spirit of the present invention are included in the scope of the claims of the present application.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a vertical cross-sectional structure of a photoelectric conversion unit of one pixel in a solid-state imaging device according to a first embodiment.
FIG. 2 is a schematic diagram illustrating a vertical cross-sectional structure of a photoelectric conversion unit of one pixel in a solid-state imaging device according to a second embodiment.
FIG. 3 is an operation explanatory diagram of the solid-state imaging device according to the first embodiment.
FIG. 4 is an operation explanatory diagram of a solid-state imaging device according to a second embodiment.
FIG. 5 is a schematic diagram showing a longitudinal sectional structure of a main part of a solid-state imaging device according to another embodiment.
FIG. 6 is a schematic diagram showing a longitudinal sectional structure of a main part of a solid-state imaging device according to another embodiment.
FIG. 7 is a schematic diagram showing a longitudinal sectional structure of a main part of a solid-state imaging device according to another embodiment.
FIG. 8 is a configuration diagram of an imaging device using the solid-state imaging device of the first embodiment.
FIG. 9 is a schematic longitudinal sectional view showing an element structure of a conventional Si solid-state imaging element.
[Explanation of symbols]
10, 20 ... substrate
11 ... N-type region
12 ... depletion layer
13, 23 ... infrared receiving layer
14, 24 ... first electrode
15, 25 ... second electrode
16, 26 ... Switch
17, 27… DC power supply
21 ... Photogate electrode
22 ... MOS capacitor area
28 ... Oxide film
30... First diffusion region
31 second diffusion region
100 ... Solid-state image sensor
101 ... Image processing unit
103 ... Control unit
104 ... Optical filter
105 ... Filter drive unit
106: Condensing lens system

Claims (6)

a) a visible light receiving means formed on a light irradiation surface on a silicon substrate and having a carrier collection region for generating carriers by receiving light in at least a visible band or for accumulating after generating carriers;
b) an infrared light receiving means which is provided on the surface on the back side of the visible light receiving means or on the same surface as the visible light receiving means with the substrate interposed therebetween, and which generates carriers by receiving light in an infrared band;
c) a carrier inside the substrate so as to promote the movement of the carrier generated by the infrared receiving means to the carrier collection area, or to suppress the carrier from reaching the carrier collection area. Carrier movement control means for controlling the movement of
A solid-state imaging device comprising: 2. The solid-state imaging device according to claim 1, wherein the infrared light receiving unit is provided on a back surface of the substrate, and generates a carrier by receiving infrared light passing through the inside of the substrate. 3. The carrier movement control means promotes the movement of carriers from the infrared light receiving means to the carrier collection area by giving a potential difference between the infrared light receiving means and the carrier collection area or increasing the potential difference. The solid-state imaging device according to claim 1, wherein: The carrier movement control means suppresses the carrier from reaching the carrier collection area by forming a virtual carrier passage path outside the carrier collection area where the carrier easily passes. The solid-state imaging device according to any one of claims 1 to 3. The carrier movement control unit includes a P-type and / or N-type diffusion region formed around the visible light receiving unit, and a voltage application unit that applies a predetermined voltage to the diffusion region. The solid-state imaging device according to claim 1. The solid-state imaging device according to claim 1, an optical filter that blocks light in a visible band, and the optical filter is inserted in front of a light irradiation surface of the solid-state imaging device or the light irradiation surface. Filter driving means for removing from the near side, and in a state where the optical filter is inserted just before the light irradiation surface of the solid-state imaging device, the carrier generated by the infrared receiving means by the carrier movement control means, the carrier collection area An imaging apparatus characterized by acquiring an image signal by light in an infrared band by removing light in a visible band by facilitating the movement of the image signal.

Images