JP2007281820A - Solid-state imaging element and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging element and an imaging method which can arrange photoelectric conversion efficiency over a wide wavelength region, and can preferably raise whole photoelectric conversion efficiency. <P>SOLUTION: A photodiode 5 which converts light to electric charge, is formed on a surface of a silicon semiconductor substrate 4. A light conversion filter 2 and a micro lens 1 are formed on the silicon semiconductor substrate 4 through a flattening layer 3. The micro lens 1 effectively focuses input light to the photo-diode 5. The light conversion filter 2 absorbs a specified wavelength component of the input light and makes a light of different wavelength from the absorbed wavelength generate. One unit is composed of four photoconversion filters arranged in vertically and horizontally (rectangular form), and the units are further arranged in vertically and horizontally. The one unit includes the light conversion filter which passes through a light of R component, a light conversion filter which absorbs the light of G component, and emits the light of R component, and a light conversion filter which absorbs the light of B component, and emits the light of R component. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device and an imaging method suitable for an imaging apparatus such as a digital camera.

  2. Description of the Related Art Conventionally, CCD transfer type solid-state image sensors and XY address type CMOS image sensors are known as image sensors used in image pickup apparatuses such as digital cameras. In these solid-state imaging devices, light is incident on a photodiode formed on a semiconductor substrate, and a video signal is obtained by signal charges generated and accumulated by the photodiode.

  In addition, as a configuration for obtaining a color video signal, a color filter that separates light incident on the photodiode into, for example, three primary color components of RGB is provided, and a video signal is obtained from signal charges generated by the light of each color component. The configuration is known.

  FIG. 9 is a diagram illustrating an example of a filter array used in a conventional color solid-state imaging device. In this arrangement, four pixels are configured as one unit. This color filter array is generally called a Bayer array.

  FIG. 10 is a diagram illustrating an example of the spectral transmittance of the color filter. The spectral transmittance of the color filter is controlled by changing the coloring matter such as a dye or pigment and the concentration thereof.

  FIG. 11 is a cross-sectional view showing the structure of the light receiving portion of the color solid-state imaging device. As shown in FIG. 11, a photodiode (PD) 105 that converts light into electric charge is formed on the surface of a silicon semiconductor substrate 104. On the silicon semiconductor substrate 104, a color filter 103 and a microlens 101 are formed via a planarization layer 103. The microlens 101 effectively collects incident light on the photodiode 105. The color filter 102 transmits only a specific wavelength component of incident light. The flattening layer 103 is flattened on the base in order to accurately form the microlens 101 and the color filter 102. The signal charge generated by the photodiode 105 is output to the outside of the image sensor by a transfer unit (not shown) connected to the light receiving unit.

  However, in the above-described conventional color solid-state imaging device, the light transmitted through each color filter 103 is incident on the photodiode 105, but the place where the charge generated in the photodiode 105 is generated differs depending on the color of the color filter 103. . That is, the depth at which charges are generated is different. This is because the light absorption coefficient of silicon varies depending on the wavelength of light. The absorption coefficient of silicon increases as the wavelength of light decreases, and decreases as the wavelength increases. For this reason, the light transmitted through the blue (B) color filter 103 is absorbed by the surface of the photodiode 105 and generates charges, whereas the light transmitted through the red (R) color filter 103 is transmitted through the photodiode 105. It penetrates to the deep part of the surface and generates charges there. For this reason, photoelectric conversion efficiency is different among the three colors, and processing such as white balance cannot be performed appropriately, and noise may occur.

  Therefore, in order to effectively convert light into electric charges in a solid-state imaging device using a color filter, there is a technique for optimizing the depth of the photodiode according to each color of the color filter using the above-described properties. It is known (see Patent Document 1).

Japanese Patent Laid-Open No. 61-234072 JP-A-4-206571

  However, in the technique described in Patent Document 1, since the depth of the photodiode is adjusted according to each color, for this purpose, the structure of the photodiode is stably extended to a deeper portion of silicon. Need to form. Therefore, it is very difficult to actually manufacture.

  Further, as described in Patent Document 2, as a method for making light incident on the silicon semiconductor substrate more efficiently in order to increase the efficiency of charge generation, the reflection of the silicon semiconductor substrate on the surface of the silicon semiconductor substrate is reduced. A structure with an antireflection film for the purpose is also considered. However, even if it is possible to reduce the reflectance with respect to light in a specific wavelength range, it is extremely difficult to effectively function with respect to all the light transmitted through the RGB color filters.

  An object of the present invention is to provide a solid-state imaging device and an imaging method capable of aligning photoelectric conversion efficiency over a wide wavelength range, and preferably improving the overall photoelectric conversion efficiency.

  As a result of intensive studies to solve the above problems, the present inventor has come up with various aspects of the invention described below.

  The solid-state imaging device according to the present invention includes a plurality of photoelectric conversion units that convert light into electric charges, each of which is disposed on a light incident side of the plurality of photoelectric conversion units, and absorbs and absorbs light in different specific wavelength ranges. A plurality of light conversion filters that emit light in a wavelength region different from the wavelength of the light, and the wavelength regions of the light emitted by the plurality of light conversion filters are substantially the same as each other .

  The imaging method according to the present invention includes a light conversion step of causing a plurality of light conversion filters to absorb light in a specific wavelength range different from each other and emitting light in a wavelength range different from the absorbed wavelength, and the plurality of light conversion filters. And a photoelectric conversion step for converting the light emitted by the light into charges, and in the light conversion step, the wavelength ranges of the light emitted to the plurality of light conversion filters are substantially the same as each other. It is characterized by.

  According to the present invention, since the light incident on the photoelectric conversion means is limited to a specific wavelength region by the plurality of light conversion filters, photoelectric conversion is performed with the same efficiency in the plurality of photoelectric conversion means. Therefore, the quality of the video output signal is improved and noise is reduced. Also, the photoelectric conversion means can be easily designed. Furthermore, even when an antireflection film is provided in order to efficiently capture light of each color, the design and the like can be easily performed.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

(First embodiment)
First, a first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing a structure of a light receiving portion of a solid-state imaging device according to the first embodiment of the present invention.

  In the present embodiment, as shown in FIG. 1, a photodiode (PD) 5 that converts light into electric charges is formed on the surface of the silicon semiconductor substrate 4. On the silicon semiconductor substrate 4, the light conversion filter 2 and the microlens 1 are formed via the planarization layer 3. The microlens 1 effectively collects incident light on the photodiode 5. The light conversion filter 2 absorbs a specific wavelength component of incident light and generates light having a wavelength different from the absorbed wavelength. The flattening layer 3 is flattened in order to accurately form the microlens 1 and the light conversion filter 2. For the light conversion filter 2, for example, a fluorescent compound such as coumarin, dicyanomethylenepyran (DCM), rhodamine or zinc tetraphenylporphyrin (ZnTPP) is used.

  Although not shown, the solid-state imaging device is provided with a transfer unit connected to the light receiving unit, and the signal charge generated by the photodiode 5 is output to the outside of the solid-state imaging device by the transfer unit.

  Next, the arrangement of the light conversion filters 2 in this embodiment will be described. FIG. 2 is a diagram illustrating the arrangement of the light conversion filters 2 in the solid-state imaging device according to the first embodiment. In this embodiment, one unit is composed of four light conversion filters arranged vertically and horizontally (rectangular shape), and these units are further arranged vertically and horizontally. Within one unit, a light conversion filter (R) that transmits R component light, a light conversion filter (GR) that absorbs G component light and emits R component light, and B component light. A light conversion filter (BR) that absorbs R and emits R component light is included. Within one unit, the two light conversion filters (GR) are located on one diagonal line, and the light conversion filter (R) and the light conversion filter (BR) are located on the other diagonal line. .

  FIG. 3 is a diagram illustrating the characteristics of each light conversion filter 2 in the first embodiment. 3 (a) shows the characteristics of the light conversion filter (R), FIG. 3 (b) shows the characteristics of the light conversion filter (GR), and FIG. 3 (c) shows the light conversion filter (BR). The characteristics are shown.

  In the present embodiment, for example, a conventional R color filter can be used as the light conversion filter (R). For example, rhodamine can be used as the light conversion filter (GR). For example, DCM can be used as the light conversion filter (BR).

  In such a first embodiment, the light incident on the photodiode 5 is only the R component below any light conversion filter 2. For this reason, the depth at which charges are generated in the photodiodes 5 is almost uniform among all the photodiodes 5. Therefore, only the R component light needs to be considered in the design of the photodiode 5. Furthermore, even when an antireflection film is provided to improve the charge generation efficiency, only the R component light needs to be considered. The antireflection film is formed on the surface of the silicon semiconductor substrate 4 on which the photodiode 5 is formed.

  Here, the imaging apparatus using the solid-state imaging device according to the first embodiment will be described. FIG. 4 is a block diagram illustrating an imaging apparatus using the solid-state imaging device according to the first embodiment.

  The imaging apparatus includes an optical system 201 including a lens and a diaphragm, a mechanical shutter (illustrated as a mechanical shutter) 202, and a solid-state imaging device 203 according to the first embodiment. In addition, a CDS circuit 204 that performs analog signal processing, an A / D converter 205 that converts an analog signal into a digital signal, and a timing signal that generates a signal for operating the image sensor 203, the CDS circuit 204, and the A / D converter 205. A generation circuit 206 is provided. Further, a driving circuit 207 for driving the optical system 201, the mechanical shutter 202, and the image sensor 203, a signal processing circuit 208 for performing signal processing necessary for captured image data, and an image memory 209 for storing the signal processed image data. Is provided. Further, the recording circuit 211 that records the signal processed image data on the removable image recording medium 210, the image display device 212 that displays the signal processed image data, and the display circuit 213 that displays the image on the image display device 211. Is provided. Furthermore, a system control unit 214 that controls the entire imaging apparatus and a nonvolatile memory (ROM) 215 that stores programs executed by the system control unit 214 are provided. The nonvolatile memory 215 also stores control data such as parameters and tables used when executing this program, and correction data such as a scratch address. Further, a volatile memory (RAM) 216 that stores a program, control data, and correction data transferred from the nonvolatile memory 215 and is used as a work area when the system control unit 214 controls the imaging apparatus is also provided. It has been.

  Next, a photographing operation using the mechanical shutter 202 of the imaging apparatus configured as described above will be described.

  When the operation is started by turning on the power or the like prior to the photographing operation, the system control unit 214 reads a predetermined program, control data, and correction data from the nonvolatile memory 215 and transfers them to the volatile memory 216 for storage. These programs and data are used when the system control unit 214 controls the imaging apparatus. Further, the system control unit 214 transfers additional programs and data from the nonvolatile memory 215 to the volatile memory 216 as necessary, or the system control unit 214 directly reads and uses the data in the nonvolatile memory 215. To do.

  First, the optical system 201 drives a diaphragm and a lens according to a control signal from the system control unit 214 to form an object image set to an appropriate brightness on the solid-state image sensor 203. Next, the mechanical shutter 202 shields the solid-state image sensor 203 in accordance with the operation of the solid-state image sensor 203 so that the required exposure time is reached by a control signal from the system control unit 214. At this time, when the solid-state imaging device 203 has an electronic shutter function, it may be used together with the mechanical shutter 202 to secure a necessary exposure time.

  The solid-state image sensor 203 is driven by a drive pulse based on an operation pulse generated by the timing signal generation circuit 206 controlled by the system control unit 214, and converts the subject image into an electrical signal by photoelectric conversion to generate an analog image signal. Output as. Next, the CDS circuit 204 removes clock synchronization noise from the analog image signal output from the image sensor 203 by an operation pulse generated by the timing signal generation circuit 206 controlled by the system control unit 214. Then, the A / D converter 205 converts the analog signal image into a digital image signal.

  Next, the signal processing circuit 208 is controlled by the system control unit 214 to perform image processing such as color conversion, white balance and gamma correction, resolution conversion processing, image compression processing, and the like on the digital image signal. At this time, the image memory 209 is used to temporarily store a digital image signal being subjected to signal processing or to store image data which is a digital image signal subjected to signal processing. The image data subjected to signal processing by the signal processing circuit 208 is converted into data suitable for the image recording medium 210 (for example, file system data having a hierarchical structure) by the recording circuit 211 and recorded on the image recording medium 210, for example. . In addition, after the resolution conversion process is performed by the signal processing circuit 208, the display circuit 213 converts the signal into a signal suitable for the image display device 211 (for example, an NTSC analog signal) and displays it on the image display device 211. There is also. Similarly, the image data stored in the image memory 209 is recorded on the image recording medium 210 or displayed on the image display device 211.

  Note that the signal processing circuit 208 outputs information on digital image signals and image data generated in the signal processing process to the system control unit 214 when requested by the system control unit 214. Examples of such information include information such as the spatial frequency of the image, the average value of the designated area, the data amount of the compressed image, and information extracted from them. Furthermore, the recording circuit 211 outputs information such as the type and free capacity of the image recording medium 210 to the system control unit 214 when requested by the system control unit 214.

  The signal processing circuit 208 may output the digital image signal as it is to the image memory 209 or the recording circuit 211 without performing signal processing by the control signal from the system control unit 214.

  Next, the reproduction operation when image data is recorded on the image recording medium 210 of the imaging apparatus will be described.

  First, the recording circuit 211 reads image data from the image recording medium 210 in accordance with a control signal from the system control unit 214. If the image data read by the recording circuit 211 is a compressed image, the signal processing circuit 208 performs an image expansion process in accordance with a control signal from the system control unit 214 and stores it in the image memory 209. The image data stored in the image memory 209 is subjected to resolution conversion processing by the signal processing circuit 208, converted to a signal suitable for the image display device 211 by the display circuit 213, and displayed on the image display device 211. .

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the second embodiment, the arrangement of the light conversion filters 2 is different from that of the first embodiment. Other points are the same as in the first embodiment. FIG. 5 is a diagram illustrating the arrangement of the light conversion filters 2 in the solid-state imaging device according to the second embodiment. Also in this embodiment, one unit is constituted by four light conversion filters arranged vertically and horizontally (rectangular), and this unit is further arranged vertically and horizontally.

  Within one unit, a light conversion filter (R.Ir) that absorbs R component light and emits near infrared light Ir, and a light conversion filter (G. G) that absorbs G component light and emits near infrared light Ir (G). . Ir) and a light conversion filter (B.Ir) that absorbs B component light and emits near-infrared light Ir. Within one unit, the two light conversion filters (G.Ir) are located on one diagonal line, and the light conversion filter (R.Ir) and the light conversion filter (B.Ir) are on the other diagonal line. To position.

  FIG. 6 is a diagram illustrating the characteristics of each light conversion filter 2 in the second embodiment. 6A shows the characteristics of the light conversion filter (R.Ir), FIG. 6B shows the characteristics of the light conversion filter (G.Ir), and FIG. The characteristics of Ir) are shown.

  In the present embodiment, for example, porphyrin can be used as the light conversion filter (R.Ir). As the light conversion filter (G.Ir), for example, rhodamine or porphyrin can be used. As the light conversion filter (B.Ir), for example, ZnTPP can be used.

  In such a second embodiment, the light incident on the photodiode 5 is only near-infrared light Ir below any light conversion filter 2. For this reason, as in the first embodiment, the depth at which charges are generated in the photodiodes 5 is almost uniform among all the photodiodes 5. Therefore, only the near-infrared light Ir needs to be considered in the design of the photodiode 5. Furthermore, even when an antireflection film is provided to improve the charge generation efficiency, only the near infrared light Ir needs to be considered. In particular, the present embodiment is more effective when a semiconductor substrate that can efficiently absorb near-infrared light or infrared light, for example, a silicon germanium semiconductor substrate, is used instead of the silicon semiconductor substrate 4.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the third embodiment, the arrangement of the light conversion filters 2 is different from that of the first embodiment. Other points are the same as in the first embodiment. FIG. 7 is a diagram illustrating an arrangement of the light conversion filters 2 in the solid-state imaging device according to the third embodiment. Also in this embodiment, one unit is constituted by four light conversion filters arranged vertically and horizontally (rectangular), and this unit is further arranged vertically and horizontally.

  Within one unit, a light conversion filter (R.G ′) that absorbs R component light and emits G ′ component light, a light conversion filter (R) that transmits G component light, and B component light. And a light conversion filter (BG ′) that emits G ′ component light. Here, the light of the G ′ component is light that approximates the light of the G component that is transmitted through the light conversion filter (G). For example, the center wavelength is shifted to the longer wavelength side with respect to G. Within one unit, the two light conversion filters (G) are positioned on one diagonal line, and the light conversion filter (R.G ′) and the light conversion filter (B.G ′) are on the other diagonal line. To position.

  FIG. 8 is a diagram illustrating characteristics of each light conversion filter 2 in the third embodiment. 8A shows the characteristics of the light conversion filter (RG ′), FIG. 8B shows the characteristics of the light conversion filter (G), and FIG. 8C shows the light conversion filter (BG). ′) Is shown.

  In such a third embodiment, the light incident on the photodiode 5 is only G component light or light in the vicinity of the G component below any of the light conversion filters 2. For this reason, as in the first embodiment, the depth at which charges are generated in the photodiodes 5 is almost uniform among all the photodiodes 5. Therefore, in designing the photodiode 5, only the G component light and the light in the vicinity of the G component (light in a specific wavelength region) need be considered. Furthermore, even when an antireflection film is provided to improve the charge generation efficiency, only the G component light and the light in the vicinity of the G component (light in a specific wavelength region) need only be considered. The degree of “near” is preferably within a range of about ± 50 nm from the center wavelength.

  The present invention is not limited to these embodiments, and can be applied to, for example, both a CCD transfer image sensor and a CMOS image sensor. Further, the combination of the light conversion filter and the color filter is not limited to the above-described embodiment. In particular, the material of the light conversion filter described in the description of the above-described embodiment is merely an example, and the material is not limited as long as desired absorption characteristics and emission (light emission) characteristics can be obtained. Further, for example, if the wavelength range of light incident on the photodiode is narrower than the conventional one by combining two types of color filters and one type of light conversion filter, variations in photoelectric conversion efficiency are suppressed.

It is sectional drawing which shows the structure of the light-receiving part of the solid-state image sensor concerning the 1st Embodiment of this invention. It is a figure which shows the arrangement | sequence of the light conversion filter 2 in the solid-state image sensor which concerns on the 1st Embodiment of this invention. It is a figure which shows the characteristic of each light conversion filter 2 in the 1st Embodiment of this invention. 1 is a block diagram illustrating an imaging apparatus using a solid-state imaging element according to a first embodiment of the present invention. It is a figure which shows the arrangement | sequence of the light conversion filter 2 in the solid-state image sensor which concerns on the 2nd Embodiment of this invention. It is a figure which shows the characteristic of each light conversion filter 2 in the 2nd Embodiment of this invention. It is a figure which shows the arrangement | sequence of the light conversion filter 2 in the solid-state image sensor which concerns on the 3rd Embodiment of this invention. It is a figure which shows the characteristic of each light conversion filter 2 in the 3rd Embodiment of this invention. It is a figure which shows the example of the filter arrangement | sequence used for the conventional color solid-state image sensor. It is a figure which shows the example of the spectral transmittance of a color filter. It is sectional drawing which shows the structure of the light-receiving part of a color solid-state image sensor.

Explanation of symbols

1: Micro lens 2: Optical exchange filter 3: Planarization layer 4: Semiconductor substrate 5: Photodiode (PD)
201: Optical system 202: Mechanical shutter 203: Image sensor 204: CDS circuit 205: A / D converter 206: Timing signal generation circuit 207: Drive circuit 208: Signal processing circuit 209: Image memory 210: Image recording medium 211: Recording Circuit 212: Image display device 213: Display circuit 214: System control unit 215: Non-volatile memory (ROM)
216: Volatile memory (RAM)

Claims (7)

A plurality of photoelectric conversion means for converting light into electric charge;
A plurality of light conversion filters, each of which is disposed on the light incident side of the plurality of photoelectric conversion means, absorbs light in a specific wavelength range different from each other, and emits light in a wavelength range different from the absorbed wavelength;
Have
The solid-state imaging device, wherein wavelength ranges of light emitted from the plurality of light conversion filters are substantially the same.   All of the plurality of light conversion filters are disposed on the light incident side of the photoelectric conversion means that is not disposed on the light incident side, and have a color filter that transmits light in the wavelength region emitted by the plurality of light conversion filters. The solid-state imaging device according to claim 1.   2. The solid-state imaging device according to claim 1, wherein the plurality of light conversion filters include at least three types of light conversion filters having different specific wavelength ranges of light to be absorbed.   4. The solid-state imaging device according to claim 1, further comprising an antireflection film disposed on a light emission side of the plurality of light conversion filters. 5. A light conversion step of causing a plurality of light conversion filters to absorb light in different specific wavelength ranges and emitting light in a wavelength range different from the absorbed wavelengths;
A photoelectric conversion step of converting light emitted by the plurality of light conversion filters into electric charge;
Have
In the light conversion step, a wavelength region of light emitted to the plurality of light conversion filters is made substantially the same as each other. In the light conversion step, the color filter transmits light in a wavelength range emitted by the plurality of light conversion filters,
6. The imaging method according to claim 5, wherein, in the photoelectric conversion step, light transmitted through the color filter is also converted into electric charges.   6. The imaging method according to claim 5, wherein at least three types of light conversion filters having different specific wavelength ranges of light to be absorbed are used as the plurality of light conversion filters.

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