JP2008010879A - Solid state imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high resolution solid state imaging apparatus which can properly use functions each according to the purpose. <P>SOLUTION: This solid state imaging apparatus comprises a semiconductor substrate having a light receiving region, multiple pixels formed in matrix in the light receiving region of the semiconductor substrate while each pixel including a main photosensitive part having a relatively wide area and a sub-photosensitive part having a relatively narrow area, a shading film having one aperture above one pixel including the main photosensitive part and the sub-photosensitive part, and a charge readout mechanism which allows the main photosensitive part or the sub-photosensitive part to selectively take out an image signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device, and more particularly to a solid-state imaging device having a large number of pixels.

  Known solid-state imaging devices include CCD solid-state imaging devices that transfer signal charges using a charge-coupled device (CCD), MOS-type solid-state imaging devices that amplify an image signal from a photosensitive element, and output the amplified signal. . As the photosensitive element, a photodiode is mainly used, and a large number of pixels are arranged in a matrix in the light receiving region. The photosensitive elements are arranged in a square matrix at a constant pitch in the row direction and the column direction, or every other position in the row direction and the column direction (for example, shifted by 1/2 pitch). There is a honeycomb arrangement.

  In the case of a solid-state imaging device including an on-chip color filter, a color filter layer is formed on a semiconductor chip on which a photosensitive element and a signal transfer unit are formed. In many cases, an on-chip microlens is further disposed on the color filter layer so that incident light is efficiently incident on the photosensitive element.

  In order to obtain an image signal with high resolution, it is desired to increase the number of pixels. Each pixel is generally formed in the same shape, but the image signals obtained from each pixel do not necessarily have the same function and importance. For example, in order to obtain a luminance signal that dominates the resolution, a light amount signal for the entire visible region or a light amount signal for the green region is required. When a luminance signal is obtained from a green signal, it is desirable that the number of green pixels is large in order to obtain a high-resolution image signal.

  An object of the present invention is to provide a high-resolution solid-state imaging device.

  Another object of the present invention is to provide a solid-state imaging device capable of properly using functions according to the purpose.

  Still another object of the present invention is to provide a solid-state imaging device having an auxiliary function and minimizing the extent to which the main function is reduced by the auxiliary function.

  Another object of the present invention is to provide a solid-state imaging device capable of increasing the resolution and suppressing the decrease in sensitivity without increasing the occupied area.

  According to one aspect of the present invention, a main substrate having a light receiving region and a plurality of pixels formed in a matrix in the light receiving region of the semiconductor substrate, each pixel having a relatively large area. A plurality of pixels including a secondary photosensitive portion having a relatively small area, a light shielding film having an opening above one pixel including the primary photosensitive portion and the secondary photosensitive portion, the primary photosensitive portion, and the secondary photosensitive portion. There is provided a solid-state imaging device having a charge reading mechanism capable of selectively extracting an image signal from any of the photosensitive portions.

  According to the present invention, a high-resolution image signal can be read out.

  It becomes possible to reproduce high-quality images.

  Embodiments of the present invention will be described below with reference to the drawings.

  1A to 1C and 2A to 2C are a plan view, a cross-sectional view, and a block diagram for explaining a solid-state imaging device according to an embodiment of the present invention. In FIG. 1A, two pixels PIX are shown side by side. Each pixel PIX includes two photodiode regions 21 and 22. The photodiode region 21 has a relatively large area and constitutes a main photosensitive portion. The photodiode 22 has a relatively small area and constitutes a secondary photosensitive portion. A vertical charge transfer path (VCCD) 6 is arranged on the right side of the pixel PIX.

  The illustrated configuration is a honeycomb-structured pixel array, and the upper and lower pixels of the two illustrated pixels are arranged at positions shifted by a half pitch in the horizontal direction. The VCCD 6 shown on the left side of each pixel PIX is for reading and transferring charges from the upper and lower pixels PIX.

  As indicated by dotted lines, polysilicon electrodes 14, 15, 18, and 19 (collectively indicated by EL) for driving four layers are arranged above the VCCD 6. For example, when the transfer electrode is formed of two-layer polysilicon, the transfer electrodes 14 and 18 are formed of, for example, a first polysilicon layer, and the transfer electrodes 15 and 19 are formed of a second polysilicon layer. The transfer electrode 14 also controls charge reading from the subordinate photosensitive unit 22 to the VCCD 6. The transfer electrode 15 also controls charge reading from the main photosensitive portion 21 to the VCCD 6.

1B and 1C show one-dot broken lines IB-IB and IC-I shown in FIG.
It is sectional drawing which follows C. A p-type well 17 is formed on one surface of the n-type semiconductor substrate 16. Two n-type regions 21 and 22 are formed in the surface region of the p-type well 17 to constitute a main photodiode portion and a sub-photodiode portion. The p ⁺ type region 27 is a channel stop region for performing electrical separation of pixels, VCCDs, and the like.

  As shown in FIG. 1C, an n-type region 6 constituting a VCCD is arranged in the vicinity of an n-type region 21 constituting a photodiode. The p-type well 17 between the n-type regions 21 and 6 constitutes a read transistor.

  An insulating layer such as a silicon oxide film is formed on the surface of the semiconductor substrate, and a transfer electrode EL made of polysilicon is formed thereon. The transfer electrode EL is disposed so as to cover the upper part of the VCCD 6. An insulating layer such as silicon oxide is further formed on the transfer electrode EL, covers a component such as a VCCD thereon, and has a light shielding film 12 having one opening above one pixel including the main photodiode portion and the sub-photodiode. Is formed of tungsten or the like. An interlayer insulating film 13 made of phosphosilicate glass or the like is formed so as to cover the light shielding film 12, and the surface thereof is flattened.

  A color filter layer 10 is formed on the interlayer insulating film 13. The color filter layer 10 includes three or more color regions such as a red region 25 and a green region 26, for example. On the color filter layer 10, microlenses 11 are formed of a resist material or the like corresponding to each pixel.

  As shown in FIG. 1B, one microlens 11 is formed on each pixel, and two types of color filters 25 and 26 are disposed below the microlens 11. The color filter 25 is formed so as to cover the top of the main photosensitive portion 21 and is disposed so that light incident on the photosensitive portion 21 from at least the vertical direction is transmitted. The light transmitted through the color filter 26 is disposed so as to be incident on the main photosensitive portion 22. The microlens 11 has a function of condensing light incident from above into an opening defined by the light shielding film 12. Two microlenses may be provided in accordance with the photosensitive portions 21 and 22.

  FIG. 2A shows the arrangement of the pixels PIX and VCCD 6 in the light receiving region PS. The pixels PIX are arranged at every other column in each row and at every other row in each column to constitute a so-called honeycomb structure. Each pixel PIX includes a main photosensitive portion and a secondary photosensitive portion as described above. The VCCD 6 is arranged in a meandering manner close to each column.

  A VCCD driving circuit 2 for driving the vertical transfer electrode EL is arranged on the right side of the light receiving region PS. A horizontal charge transfer path (HCCD) 3 that receives charges from the VCCD 6 and transfers them in the horizontal direction is disposed below the light receiving region PS. An output amplifier 4 is disposed on the left side of the HCCD 3.

  FIG. 2B shows a system configuration of the solid-state imaging device. The solid-state image sensor 51 is formed of a semiconductor chip and includes a light receiving region PS and a peripheral circuit region. The drive circuit 52 supplies a drive signal for driving the solid-state imaging device. A signal for reading out the accumulated charge of the main photosensitive portion and a signal for reading out the accumulated charge of the subordinate photosensitive portion are supplied.

  Two types of output signals from the solid-state imaging device 51 are processed by the processing circuit 53. The storage device 54 has two areas for receiving and storing image signals from the processing circuit 53. One area stores an image signal based on the main photosensitive part, and the other area stores an image signal based on the subordinate photosensitive part. The image signal processed by the processing circuit 53 is supplied to the display device 55, the interface 56, the television TV 57, and the like.

  In the configuration as shown in FIGS. 1B and 1C, the light transmitted through the two types of color filters is not necessarily completely separated and incident on the two photosensitive portions 21 and 22. That is, color mixing may occur in the photosensitive part. However, the light transmitted through the microlens 11 always passes through one of the two types of color filters 25 and 26. That is, the color mixture that can occur in the photosensitive portions 21 and 22 is limited to two types of color mixture.

  In advance, the proportion of light transmitted through one color filter is incident on the two photosensitive portions, and the proportion of light transmitted through the other color filter is incident on the two photosensitive portions in advance. By setting how the light reception signals of the two photosensitive portions are converted to derive each color signal component, the light incident on the two photosensitive portions can be organized by the processing of the processing circuit 53.

    For example, before shipment, the entire light receiving area is irradiated with red light, green light, and blue light having a constant illuminance, and output signals from the respective photosensitive units are obtained. From the signals of the two photosensitive portions of the same pixel, it can be seen how the light passing through one filter is distributed to the two photosensitive portions. When the light that has passed through the two filters enters two photosensitive portions, each photosensitive portion receives a certain proportion of incident light of two colors. Since this ratio is a fixed value, the light quantity of the target color can be calculated by conversion. The processing circuit 53 stores these numerical values in advance.

    It should be noted that the color mixing at the main photosensitive portion may be suppressed to a negligible level, and processing for eliminating the color mixing may be performed only for the signal of the subordinate photosensitive portion.

  Note that a green filter 26 is disposed above the photosensitive portion 22 according to the above-described embodiment. Therefore, a green signal (luminance signal) at all pixel positions can be obtained using the detection signal of the subsequent photosensitive portion. By obtaining luminance signals at all pixel positions, it is possible to perform further interpolation as necessary to reproduce a high-resolution image.

  The image signal of the main photosensitive portion 21 can be handled in the same manner as the image signal of a normal CCD type solid-state imaging device. If necessary, an image can be reproduced only with a signal from the main photosensitive portion.

  FIG. 2C shows a method of obtaining an interpolation signal by interpolating the signal obtained from the subordinate photosensitive portion. Pixels P1, P2, P3, and P4 are all green subordinate photosensitive portions. Since the number of pixels serving as the basis for calculating the luminance signal is increasing, the resolution can be improved. In a normal Bayer array, only the top and bottom or left and right are green pixels. Even when the green signal of the interpolation pixel IP is created, the average value of the two signals can only be obtained.

  If there are four upper, lower, left and right green pixels, the signal value of the interpolation pixel can be created using the four signal values. For example, if three pixel signals are substantially the same and only one has a different value, it may be a boundary of the subject. In this case, only one different signal is ignored, and an average value can be obtained from the remaining three signals. In this way, a high resolution image signal can be obtained. The high-resolution information obtained can be used when processing the signal from the main photosensitive part.

3A and 3B show the configuration of a solid-state imaging device according to another embodiment of the present invention. A p ⁺ type separation region 29 is formed between the main photosensitive portion 21 and the secondary photosensitive portion 22. Further, a light shielding film 28 is formed at a position corresponding to the separation region 29 above it. By using the light shielding film 28 and the separation region 29, the incident light is efficiently separated and the charges once accumulated in the photosensitive portions 21 and 22 are prevented from being mixed thereafter. Other configurations are the same as those of the embodiment shown in FIGS.

  4A and 4B show other modified examples.

  FIG. 4A shows a configuration in which two photosensitive portions 21 and 22 are separated in an oblique direction. The separation shape of the main photosensitive portion 21 and the secondary photosensitive portion 22 is not particularly limited as long as the accumulated charge can be read out to the VCCD. However, the area of the subordinate photosensitive part is set to a smaller value than the area of the main photosensitive part. Suppresses the area reduction of the main photosensitive area and minimizes the decrease in sensitivity.

  FIG. 4B shows a configuration in which the microlens 11 is formed only on the color filter corresponding to the main photosensitive portion. No microlens is disposed on the color filter 26 corresponding to the subordinate photosensitive portion. For this reason, the amount of light per area incident on the secondary photosensitive portion 22 is reduced. On the contrary, even if intense light is incident, the subordinate photosensitive portion 22 is hardly saturated and a wide dynamic range can be realized. The color filter corresponding to the subordinate photosensitive portion can be omitted to make a transparent region.

  As described above, the solid-state imaging device having the honeycomb structure has been described as an example. However, the pixel arrangement of the solid-state imaging device is not limited to the honeycomb configuration.

  FIG. 4C shows an example in which all pixels PIX are arranged in a square matrix of (n x m). Each pixel PIX includes a main photosensitive portion 21 and a secondary photosensitive portion 22. The charge can be selectively transferred from these two types of photosensitive portions to the adjacent VCCD.

  Furthermore, the present invention can be applied to a solid-state imaging device other than a CCD solid-state imaging device.

  FIG. 4D shows a configuration example of a MOS type solid-state imaging device. Each pixel image includes a plurality of regions of photodiodes 21 and 22. A MOS transistor is connected to each of the main photosensitive unit 21 and the secondary photosensitive unit 22 so that the accumulated charge of each photosensitive unit can be selectively read out.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

It is the top view and sectional drawing which show the structure of the solid-state imaging device by the Example of this invention. It is the top view and block diagram which show the whole structure of the solid-state imaging device shown in FIG. It is the top view and sectional drawing which show the structure of the solid-state imaging device by the other Example of this invention. It is the top view and sectional drawing which show the modification of the Example of this invention.

Explanation of symbols

2 VCCD drive circuit 3 HCCD
4 Output amplifier 6 VCCD
16 Semiconductor substrate (n-type region)
17 p-type well 21 n-type region (main photosensitive area)
22 n-type region (subordinate photosensitive part)
EL transfer electrode 14, 15, 18, 19 Polysilicon electrode 10 Color filter layer 11 Micro lens 12 Light-shielding film 13 Interlayer insulating film 25, 26 Color filter

Claims (4)

A semiconductor substrate having a light receiving region;
A large number of pixels formed in a matrix in the light receiving region of the semiconductor substrate, each pixel including a main photosensitive portion having a relatively large area and a secondary photosensitive portion having a relatively small area When,
A light-shielding film having one opening above one pixel including the main photosensitive portion and the secondary photosensitive portion;
A charge readout mechanism capable of selectively extracting an image signal from either the main photosensitive portion or the secondary photosensitive portion;
A solid-state imaging device. The charge readout mechanism is:
Vertical charge transfer paths formed in the semiconductor substrate along each column of the pixels;
A group of vertical transfer electrodes formed above the semiconductor substrate in a shape that controls charge transfer in the vertical charge transfer path and can read out charges from the main photosensitive portion and the secondary photosensitive portion to the vertical charge transfer path. When,
A horizontal charge transfer path formed on the semiconductor substrate adjacent to one end of the vertical charge transfer path, receiving charges from the vertical charge transfer path, and transferring a charge signal for each row;
A horizontal transfer electrode group formed above the semiconductor substrate and controlling charge transfer of the horizontal charge transfer path;
The solid-state imaging device according to claim 1, comprising: further,
Two types of color filters arranged on the primary photosensitive portion and the secondary photosensitive portion of one pixel;
A processing circuit for processing image signals from the main photosensitive portion and the secondary photosensitive portion and organizing light incident on each photosensitive portion;
The solid-state imaging device according to claim 1, comprising:   The solid-state imaging device according to any one of claims 1 to 3, wherein the plurality of pixels are arranged in a honeycomb shape in which the positions are shifted every other in the row direction and the column direction.

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