JP2008227250A - Compound type solid-state image pickup element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact, light compound-type solid-state image pickup element capable of simultaneously capturing two images in the same object. <P>SOLUTION: A first solid-state image pickup element 1 for receiving and photoelectrically converting incident light and a second solid-state image pickup element 2 for receiving and photoelectrically converting light through the first solid-state image pickup element 1 are overlapped. At least one of the first and second solid-state image pickup elements 1, 2 is preferably a back irradiation type solid-state image pickup element. Further, the pixel pitch of the second solid-state image pickup element 2 is allowed to be equal to or an integer multiple of that of the first solid-state image pickup element 1 for arrangement and overlapping. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite solid-state imaging device capable of simultaneously capturing two images of the same subject.

  For example, Patent Document 1 below discloses a camera that can simultaneously capture two images of the same subject. This conventional camera has two solid-state image sensors inside, and divides the incident light into two by an optical path dividing element such as a half mirror, and receives one divided incident light that has traveled straight through the half mirror with the first solid-state image sensor. Then, a moving image of the subject is picked up, and the other split incident light reflected in the right-angle direction by the half mirror is received by the second solid-state image pickup device to pick up a still image of the subject.

JP 2006-86967 A

  When capturing two images of the same subject at the same time, conventionally, an optical path dividing element such as a half mirror is interposed between two solid-state imaging elements so that incident light is divided into two. There is a problem of becoming.

  An object of the present invention is to provide a compact and lightweight composite solid-state imaging device capable of simultaneously capturing two images of the same subject.

  The composite solid-state imaging device according to the present invention includes a first solid-state imaging device that receives incident light and performs photoelectric conversion, and a second solid-state imaging device that receives and photoelectrically converts light transmitted through the first solid-state imaging device. It is characterized by being configured.

  The composite solid-state imaging device of the present invention is characterized in that at least one of the first solid-state imaging device and the second solid-state imaging device is a back-illuminated solid-state imaging device.

  The composite solid-state imaging device of the present invention is characterized in that the pixel pitch of the second solid-state imaging device is aligned and overlapped with the pixel pitch of the first solid-state imaging device at an equal pitch or an integral multiple.

  The composite solid-state imaging device according to the present invention is configured such that when the focal position of the center wavelength of light photoelectrically converted by the first solid-state imaging device is matched with the photoelectric conversion region of the first solid-state imaging device, the second solid-state imaging device. A focal length adjustment spacer for aligning the focal position of the center wavelength of the light to be photoelectrically converted with the photoelectric conversion region of the second solid-state image sensor is interposed between the first solid-state image sensor and the second solid-state image sensor. It is characterized by.

  The composite solid-state imaging device according to the present invention is characterized in that the focal length adjusting spacer also serves as an optical filter.

  The composite solid-state imaging device of the present invention is characterized in that the second solid-state imaging device is a MOS type back-illuminated solid-state imaging device.

  The composite solid-state imaging device of the present invention is characterized in that the MOS-type back-illuminated solid-state imaging device is used for moving image capturing or monitoring.

  The composite solid-state imaging device of the present invention is characterized in that the first solid-state imaging device is a CCD type back-illuminated solid-state imaging device.

  The composite solid-state image pickup device of the present invention is characterized in that the CCD type back-illuminated solid-state image pickup device is used for still image pickup.

  The composite solid-state imaging device of the present invention is characterized in that the first solid-state imaging device is for ultraviolet light imaging.

  The composite solid-state imaging device of the present invention is characterized in that the second solid-state imaging device is for near-infrared light imaging.

  The composite solid-state imaging device of the present invention is characterized in that the first solid-state imaging device is for ultraviolet light and visible light imaging, and the second solid-state imaging device is for visible light and near-infrared light imaging. .

  According to the present invention, since the first solid-state imaging device and the second solid-state imaging device are arranged in series on the same optical axis of the incident light and overlapped, a beam splitter or the like is not required, and a reduction in size and weight can be achieved. It is possible to simultaneously capture two images of the same subject. In addition, since the light transmitted through the first solid-state imaging device is converted by the second solid-state imaging device, the light use efficiency is increased.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of an essential part of a composite solid-state imaging device according to an embodiment of the present invention. A composite type solid-state imaging device 100 of the illustrated embodiment includes a CCD-type back-illuminated solid-state imaging device 1 shown in FIG. 2 and a CMOS-type back-illuminated solid-state imaging device 2 shown in FIG. It is comprised by bonding through the spacer 3. In practice, a semiconductor wafer on which a large number of solid-state image sensors 1 are manufactured and a semiconductor wafer on which a large number of solid-state image sensors 2 are manufactured are bonded together via spacers 3 and each composite solid-state image sensor 100 is diced. It is manufactured by dividing it into individual pieces.

  As a technique for bonding two semiconductor wafers through a spacer, for example, Mitsubishi Heavy Industries Technical Report VOL. 43 No. 1: 2006, page 51 “Wafer Room Temperature Bonding Equipment Contributing to High-Efficiency and Low-Cost Production of MEMS Devices”, and the technology described in Takayuki Goto et al.

  In the embodiment shown in FIG. 1, the CCD type and the CMOS type are bonded together, but both may be a CCD type or both may be a CMOS type. Alternatively, another type of solid-state imaging device may be bonded. The CCD type includes an interline transfer type, a frame transfer type, a full frame type, and the like.

  2 is an interline type CCD, and a vertical charge transfer path (VCCD) 21 and a photodiode (photoelectric conversion element) 22 are provided on the surface side of a p-type semiconductor substrate 20. The color filter (red (R), green (G), blue (B)) layer 23 and the microlens 24 are laminated on the back side.

  A high-concentration p-layer 25 is formed on the rear surface side surface portion of the semiconductor substrate 20, and this p-layer 25 is grounded. An insulating layer 26 such as silicon oxide or silicon nitride that is transparent to incident light is laminated on the high-concentration p layer 25, and transparent to incident light such as silicon nitride or diamond structure carbon film. A high refractive index layer 27 is stacked as an antireflection layer, and a color filter layer 23 and a microlens (top lens) layer 24 are sequentially stacked thereon. Each microlens 24 is formed so as to be focused on the center of a corresponding photodiode (photoelectric conversion element) 22 provided at an opposing position.

  The color filter layer 23 is partitioned in units of pixels (photodiodes), and a light shielding member 28 for preventing color mixture between the pixels is provided between adjacent partitions of the color filter layer 23 on the semiconductor substrate 20 side. The light shielding member 28 also prevents the object light incident from the back surface from entering the vertical charge transfer path 21 from the back surface side.

  A vertical charge transfer path (VCCD) 21 formed on the surface side of the semiconductor substrate 20 includes a buried channel 31 of a high concentration n layer and a silicon oxide film or ONO (oxide film) formed on the outermost surface side of the semiconductor substrate 20. (Transfer electrode film 33) laminated with a gate insulating layer 32 made of an insulating film of (nitride film-oxide film) structure.

  The vertical charge transfer path 21 is formed so as to extend in a direction perpendicular to a direction in which a horizontal charge transfer path (HCCD) (not shown) extends, and a plurality of vertical charge transfer paths 21 are formed. A plurality of n regions (photodiodes) 22 are formed at a predetermined pitch in the direction along the vertical charge transfer path 21 between the adjacent vertical charge transfer paths 21.

A thin p-type high-concentration surface layer 38 for suppressing dark current is formed on the surface portion of the photodiode 22 serving as a signal charge accumulation region, and an n ⁺ layer as a contact portion is formed on the central surface portion of the surface layer 38. 39 is formed.

A p layer 41 having a p concentration higher than that of the substrate 20 is formed under the buried channel (n ⁺ layer) 31 of the vertical charge transfer path 21. The n layer 31 and the p layer 41 are adjacent to the right side in the illustrated example. A p ⁺ region 43 as an element isolation band is formed between the photodiode 22 and the photodiode 22.

The p layer 41 formed below the buried channel 31 of the vertical charge transfer path 21 extends to the upper surface end portion of the n region 22 on the left side in the illustrated example, and the p ⁺ surface layer 38 at this end portion is The position is set backward from the position of the right end surface of the n region 22. The left end surface of the transfer electrode film 33 extends so as to overlap with the left end surface of the p layer 41, and the n region 22 and the surface end portions of the transfer electrode film 33 and the p layer 41 slightly overlap. It has become.

  Such an overlap configuration is possible because the back-illuminated type has an area margin on the front surface side of the semiconductor substrate 20. In a front-illuminated image sensor in which incident light from a subject enters from the front side of the substrate 20, there is no area margin to secure an opening, and it is easy to extend the end of the transfer electrode film above the photodiode. However, the backside illumination type is easy.

  If the p layer 41 is interposed between the transfer electrode film 33 and the n region 22 as in this embodiment, the read voltage applied to the transfer electrode film (also used as the read electrode) 33 can be reduced. Thus, it is possible to reduce the power consumption of the CCD solid-state imaging device.

A transfer electrode film 33 made of, for example, a polysilicon film is formed on the insulating layer 32 formed on the outermost surface of the semiconductor substrate 20, and an insulating layer 45 such as silicon dioxide is stacked thereon. Then, openings are formed in the insulating layers 32 and 45 on the n ⁺ layer 39, and the openings 46 are filled with a metal material such as tungsten, whereby the wiring 46 connected to the contact portion 39 is formed. Each wiring 46 is drawn out of the solid-state imaging device 1 and functions as an overflow drain of the back-illuminated solid-state imaging device 1.

  When a subject image is picked up by the backside illumination type solid-state imaging device 1 having such a configuration, incident light from the object scene enters from the backside of the semiconductor substrate 20. The incident light is collected by the microlens 24, passes through the color filter layer 23, and enters the semiconductor substrate 20.

  When the light condensed by the microlens 24 enters the semiconductor substrate 1, the incident light travels while condensing in the direction of the photodiode 22 corresponding to the microlens 24 and the color filter 23, and enters the semiconductor substrate 20. It is absorbed and photoelectrically converted to generate hole electron pairs. The generated holes are discarded to the ground through the p layer 25.

  Electrons generated in the photoelectric conversion region (region from the p layer 25 to the n region 22) of each pixel are accumulated in the n region 22 in the pixel, and when a read voltage is applied to the transfer electrode film 33 serving as a read electrode. , N region 22 is read out to buried channel 31 on the right in the illustrated example. Thereafter, the signal is transferred along the vertical charge transfer path 21 to the horizontal charge transfer path (not shown), transferred along the horizontal charge transfer path to the amplifier, and the amplifier outputs a voltage value signal corresponding to the signal charge amount to the captured image signal. Output as.

  A CMOS type solid-state imaging device 2 shown in FIG. 3 is manufactured on a p-type semiconductor substrate 50. A high-concentration p-type impurity layer 51 connected to the ground is formed on the back side of the p-type semiconductor substrate 50, and an insulating layer 52 such as silicon dioxide is formed on the back side surface.

  An n region 53 constituting a photodiode is formed on the surface side of the p-type semiconductor substrate 50, and a high-concentration p-type surface layer 54 for suppressing dark current is formed on the surface. In the illustrated example, a p region 55 having an impurity concentration higher than that of the substrate 50 is formed on the left side of the n region 53 and the surface layer 54 and functions as an element isolation region.

An n region 57 serving as a drain is formed at a position slightly adjacent to the right of the n region 53, and a p region 58 having an impurity concentration higher than that of the substrate 50 is formed below the n region 57. In the illustrated example, the p region 58 extends to above the surface end portion of the n region 53 adjacent to the left, and the p ⁺ surface layer 54 at the end portion is located at a position recessed from the right end surface position of the n region 53. Yes. The n region 53 and the p region 58 slightly overlap each other. This overlap configuration is intended to reduce the read voltage similarly to the overlap configuration of the p region 41 in FIG.

  A high-concentration n region 59 as a contact portion is formed at the center of the surface of the n region 57, and a p region 55 that performs element isolation with the right n region 53 (not shown) is adjacent to the right side of the n region 57 and the p region 58. Is provided.

  A gate insulating film 61 such as silicon dioxide is formed on the outermost surface of the p-type semiconductor substrate 50. On the insulating film 61 from the left end of the n region 57 to the left end of the overlapped p region 58, A gate electrode film 62 made of polysilicon is formed.

  An insulating layer 63 is formed on the gate electrode film 62 and the insulating film 61, and a three-layer wiring 64 used in a CMOS image sensor or the like is embedded therein. Further, the three-layer wiring 64, the contact portion 59, and the gate electrode film 62 are connected by wirings 65 and 66, respectively.

  When the field light is incident on the CMOS back-illuminated solid-state imaging device 2 from the back side, the incident light is absorbed by the substrate 50 to generate hole electron pairs. Holes are discarded from the high-concentration p-type layer 51 to the ground, and electrons are accumulated in the n region 53.

  The accumulated charge in the n region 53 is read out to the corresponding drain 57 when a read voltage is applied to the gate electrode film 62, and a captured image signal corresponding to this charge amount is read out of the element 2 by the three-layer wiring 64. It is.

  As shown in FIG. 1, the composite solid-state imaging device 100 of the present embodiment has a CMOS-type backside illumination on the CCD-type backside-illuminated solid-state imaging device 1 (on the front side) via a spacer 3. This is configured by attaching the solid-state solid-state imaging device 2 together.

  In the illustrated example, the pixel (n region 53) pitch of the solid-state image sensor 2 is doubled with respect to the pixel (n region 22) pitch of the solid-state image sensor 1, and the element separation region 55 of the solid-state image sensor 2 is solid-state imaged. Although arranged in alignment with the light-shielding member 28 of the element 1, the pixel pitch of both the solid-state imaging elements 1 and 2 may be equal pitch, or may be an integer multiple of 3 times or more.

  Incident light from the subject ranges from ultraviolet light to visible light, near infrared light, and infrared light. A semiconductor substrate such as silicon has a wavelength dependency of a light absorption coefficient. Light with a short wavelength is absorbed in a portion with a shallow penetration distance to generate a hole electron pair, and light with a long wavelength is a portion with a deep penetration distance. The hole electron pair is generated due to the large absorption at.

  Accordingly, if the thickness of the solid-state image sensor 1 constituting the composite solid-state image sensor 100 shown in FIG. 1 (thickness of the semiconductor portion functioning as a photoelectric conversion element) is reduced, the solid-state image sensor 1 becomes visible light. However, the remaining half of the visible light passes through the solid-state image sensor 1 and leaks into the solid-state image sensor 2, and the solid-state image sensor 2 is visible. A light subject image can be captured.

  If the thickness of the solid-state image sensor 2 (thickness of the semiconductor portion functioning as a photoelectric conversion element) is thin, near-infrared light and infrared light will also be transmitted through the solid-state image sensor 2. If the thickness of the element 2 is increased, the solid-state imaging element 2 can capture a subject image using near infrared light or infrared light.

  For this reason, the thickness (same as above) of each of the solid-state imaging device 1 and the solid-state imaging device 2 is designed depending on what wavelength range the subject image is captured. For example, by making the thickness (same as above) of the solid-state imaging device 1 less than 1 μm or less than 0.5 μm (by making optical characteristics of the cover glass, microlens, filter, etc. suitable for the wavelength band), light incidence The solid-state imaging device 1 disposed on the side can capture a subject image of near-ultraviolet light or ultraviolet light, and can increase the amount of visible light transmitted through the solid-state imaging device 2.

  In the composite solid-state imaging device 100 of the embodiment shown in FIG. 1, the solid-state imaging device 1 captures a visible light image of a subject as a still image, and the solid-state imaging device 2 captures a near-infrared light image or an infrared light image of the subject. Is taken as a moving image.

  Therefore, the thickness of the solid-state imaging device 1 (distance from the p layer 25 to the n region 22) is set to 3 to 5 μm, and the thickness of the solid-state imaging device 2 is set to 5 μm or more or 10 μm or more (for example, 20 to 30 μm).

  For example, when a still image is captured by a digital camera, AE (automatic exposure) processing or AF (automatic) is performed using captured image data output in a moving image state from the solid-state image sensor before capturing the still image from the solid-state image sensor. It is usual to perform focus processing. Therefore, in the composite solid-state imaging device 100 of the present embodiment, AE processing and AF processing are performed using the output signal of the CMOS type back-illuminated solid-state imaging device 2, and the CCD-type back-illuminated solid-state imaging device 1 is stationary. Take an image.

  The problem at this time is that the imaging position (focal position) of the incident light has wavelength dependency. The focal position of the short wavelength light is in front, and the focal position of the long wavelength is in the back. That is, even if the subject incident light (visible light) is focused on the photoelectric conversion region of the solid-state image sensor 1 shown in FIG. If the focus position of (external light) does not match, even if AF processing is performed using the output of the solid-state imaging device 2, the solid-state imaging device 1 can only capture a defocused still image of the subject.

  Therefore, in the composite solid-state imaging device 100 of the present embodiment, when the focal position at the center wavelength of the photoelectric conversion target wavelength region of the solid-state imaging device 1 is matched with the photoelectric conversion region of the solid-state imaging device 1, the photoelectric of the solid-state imaging device 2 is detected. A transparent spacer 3 for focus adjustment is inserted so that the focal position at the center wavelength of the conversion target wavelength region matches the photoelectric conversion region of the solid-state imaging device 2. The spacer 3 can also have an optical filter function.

  When the composite solid-state imaging device 100 shown in FIG. 1 is designed to have a thickness that allows the solid-state imaging devices 1 and 2 to capture a visible light image, the individual pixels 22 of the solid-state imaging device 1 that captures a still image have different colors. Since the color filter 23 is provided, a color still image can be taken.

  However, since each pixel 53 of the solid-state imaging device 2 is mixed with light that has passed through the color filters of different colors of the four pixels 22, a color moving image cannot be captured, and a monochrome moving image cannot be captured. I can only take images. Of course, there is no problem if only AE processing and AF processing are performed, but when a color moving image is to be captured, a color filter for selecting one of the color filters of the four pixels 22 is provided in the spacer 3, A color moving image can be captured.

  As described above, in the above-described embodiment, since a composite solid-state image sensor is manufactured by bonding two solid-state image sensors, it is possible to simultaneously capture two images of the same subject. In addition, since a half mirror that divides the optical path of incident light is not used, it is possible to reduce the size and weight when mounted on a camera. In addition, since much of the incident light is absorbed by the semiconductor substrate and subjected to photoelectric conversion, light utilization efficiency is high and a bright image can be taken.

  In the above-described embodiment, since the solid-state imaging device 1 arranged on the light incident side is a CCD type, a high S / N still image can be taken and incident light transmitted through the solid-state imaging device 1 is received. Since the solid-state imaging device 2 is a random access CMOS type, AE processing and AF processing can be performed at high speed.

  In the above-described embodiment, the solid-state imaging devices 1 and 2 are both back-illuminated, but the present invention is not limited to this. The surface irradiation type in which a photodiode is provided on the light incident surface side of the semiconductor substrate can use only incident light in a short wavelength region because the photoelectric conversion region becomes shallow, and the light utilization efficiency is low. For this reason, if the solid-state imaging devices 1 and 2 are both of the surface irradiation type, the degree of freedom in designing the thickness of the solid-state imaging devices 1 and 2 described above is lost.

  On the other hand, the back-illuminated type can take a deep photoelectric conversion region of light incident on the semiconductor substrate, so that the light use efficiency is high, and the above-described thickness design flexibility is widened. For this reason, it is preferable that at least one of the solid-state imaging devices 1 and 2 is a back-illuminated type.

  Further, in the CMOS type solid-state imaging device, since the wiring layer is a three-layer wiring, it is preferable to prevent the three-layer wiring from entering the optical path of the incident light, and as in the embodiment shown in FIG. The element 2 is preferably a CMOS type and a back-illuminated type.

  In the composite solid-state imaging device 100 shown in FIG. 1, since most of the constituent members provided between the microlens 24 and the insulating film 61 are made of a semiconductor or an oxide film, they have light transmittance. However, since the light shielding member 28 and the overflow drain electrode 46 are made of metal, they do not transmit light. In particular, since the electrode 46 existing in the optical path to the second solid-state imaging device 2 scatters light when it hits, in the illustrated example, the electrode 46 is provided directly under the n region 53. Needless to say, it should be provided at a position avoiding the optical path to the n region 53 as much as possible.

  The composite solid-state imaging device according to the present invention is useful when mounted on a digital camera or the like because it can simultaneously capture two images of a subject with a small and lightweight solid-state imaging device.

1 is a schematic cross-sectional view of a composite solid-state imaging device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a CCD-type back-illuminated solid-state image sensor constituting the composite solid-state image sensor shown in FIG. 1. FIG. 2 is a schematic cross-sectional view of a CMOS-type back-illuminated solid-state image sensor constituting the composite solid-state image sensor shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 CCD type back-illuminated solid-state image sensor 2 CMOS type back-illuminated solid-state image sensor 3 Focal length adjustment spacers 20 and 50 p-type semiconductor substrate 21 Vertical charge transfer path (VCCD)
22, 53 n region 23 constituting photodiode 23 color filter 24 micro lens 25, 51 high concentration p-type impurity layer 57 drain (n region)
64 Three-layer wiring 100 Composite type solid-state imaging device

Claims (12)

  A composite type comprising a first solid-state imaging device that receives incident light and performs photoelectric conversion and a second solid-state imaging device that receives and photoelectrically converts light transmitted through the first solid-state imaging device. Solid-state image sensor.   2. The composite solid-state image sensor according to claim 1, wherein at least one of the first solid-state image sensor and the second solid-state image sensor is a back-illuminated solid-state image sensor.   3. The composite type according to claim 1, wherein a pixel pitch of the second solid-state image sensor is aligned and overlapped with a pixel pitch of the first solid-state image sensor at an equal pitch or an integer multiple. Solid-state image sensor.   The focal position of the center wavelength of light photoelectrically converted by the second solid-state image sensor when the focal position of the center wavelength of light photoelectrically converted by the first solid-state image sensor is matched with the photoelectric conversion region of the first solid-state image sensor 2. A focal length adjustment spacer for aligning with a photoelectric conversion region of the second solid-state imaging device is interposed between the first solid-state imaging device and the second solid-state imaging device. 4. The composite solid-state imaging device according to any one of 3 above.   The composite solid-state imaging device according to claim 4, wherein the focal length adjustment spacer also serves as an optical filter.   6. The composite solid-state image pickup device according to claim 1, wherein the second solid-state image pickup device is a MOS type back-illuminated solid-state image pickup device.   7. The composite solid-state image pickup device according to claim 6, wherein the MOS type back-illuminated solid-state image pickup device is for moving image pickup or monitoring.   8. The composite solid-state image sensor according to claim 1, wherein the first solid-state image sensor is a CCD type back-illuminated solid-state image sensor. 9. The composite solid-state image pickup device according to claim 8, wherein the CCD type back-illuminated solid-state image pickup device is used for still image pickup.   The composite solid-state imaging device according to claim 1, wherein the first solid-state imaging device is for ultraviolet light imaging.   The composite solid-state imaging device according to claim 1, wherein the second solid-state imaging device is for near-infrared light imaging.   The first solid-state imaging device is for ultraviolet light and visible light imaging, and the second solid-state imaging device is for visible light and near-infrared light imaging. A composite type solid-state imaging device described in 1.

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