JP2009182047A - Solid-state imaging device and electronic information apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide image data of high image quality without the decline of a signal charge storage amount and the sensitivity degradation of blue light, for which noise is suppressed more. <P>SOLUTION: Since a second surface high concentration diffusion layer (N+)5 of the same polarity (first conductivity type) as an embedded photodiode (N-)3 is formed between the first surface high concentration diffusion layer (P+)4 of a polarity (second conductivity type) opposite to the embedded photodiode (N-)3 as a photoelectric conversion part and the surface of a silicon substrate 1, a leakage current (dark current) generated on the boundary surface of the surface of the silicon substrate 1 and the surface oxide film 7 is swept away to the inner side of the second surface high concentration diffusion layer (N+)5 of the same polarity (first conductivity type) as the embedded photodiode (N-)3, the leakage current does not intervene the side of the embedded photodiode (N-)3, and then low noise is realized and high image quality is obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor constituted by a semiconductor element that photoelectrically converts image light from a subject by a photoelectric conversion unit and images the same, and this solid-state imaging device as an image input device. For example, digital cameras such as digital video cameras and digital still cameras used as imaging units, image input cameras such as surveillance cameras, in-vehicle cameras, industrial cameras, and medical cameras, scanners, facsimiles, and camera-equipped mobile phones The present invention relates to electronic information equipment such as devices.

  In recent years, there has been an increasing demand for higher definition of camera images and the like, and the number of pixels in a solid-state imaging device such as a CCD image sensor or a CMOS image sensor mounted on a digital camera or a mobile phone device with a camera is increased. Is progressing rapidly.

  The market where solid-state image sensors such as CCD image sensors and CMOS image sensors are used includes the above-described digital cameras and camera-equipped mobile phone devices, as well as surveillance cameras, in-vehicle cameras, industrial cameras, and medical cameras. It is expanding rapidly in various ways. In this solid-state imaging device, a plurality of photoelectric conversion units that convert light into electrical signals are two-dimensionally arranged as light receiving units, and each of the photoelectric conversion units is embedded in a silicon substrate. As a result, low noise and high image quality contributed greatly. An example of this embedded photodiode is shown in FIG.

  FIG. 9 is a longitudinal sectional view schematically showing an example of the configuration of the main part of a conventional CMOS solid-state imaging device (imager).

  As shown in FIG. 9, a conventional CMOS solid-state imaging device 100 has a buried photodiode (N−) 103 formed in a P-well 102 of a P-type silicon substrate 101, and a surface high-concentration diffusion layer (on the surface side) P +) 104 and a P well 102 are embedded. It becomes a signal charge transfer region (transistor region) between the embedded photodiode (N−) 103 and the surface high-concentration diffusion layer (P +) 104 and the charge detection unit 105 (N +) that converts the signal charge into a voltage. A transfer gate 107 of a charge transfer transistor is provided on the P well 102 via a surface oxide film 106. Further, a reset gate 109 of the reset transistor is formed on the P well 102 serving as a transistor region between the charge detection unit 105 (N +) and the drain region 108 connected to the output terminal of the power supply potential via the surface oxide film 106. Is provided. The P-type silicon substrate 101 is connected to the output terminal of the GND potential.

  With the above configuration, incident light is photoelectrically converted by the embedded photodiode (N−) 103, and the accumulated signal charge is applied to the transfer gate 107 of the charge transfer transistor, whereby the embedded photodiode (N -) Charge is transferred from 103 to the charge detection unit 105. Next, in the charge detection unit 105, the signal charge transferred is converted into a signal voltage, amplified by an amplification transistor (not shown) according to the signal voltage, and output as an imaging signal to the signal line. Thereafter, a reset signal is applied to the reset gate 109 of the reset transistor, and the charge detection unit 105 is reset to the power supply potential. In this manner, the signal charge transferred to the charge detection unit 105 is discharged to the drain region 109 side connected to the output terminal of the power supply potential.

  In general, near the surface of a silicon substrate as a semiconductor substrate, there is a lattice defect due to a difference in atomic structure at the interface between the surface silicon oxide film and the silicon surface, and this lattice defect causes a leak current having temperature characteristics. To do. In FIG. 9, the interface that is the source of the leakage current is covered with the surface high-concentration diffusion layer (P +) 104, and unnecessary leak current (charge in this case) that causes noise is regenerated by the surface high-concentration diffusion layer (P +) 104. By combining them, unnecessary leakage current is removed, the influence of this leakage current (noise) is eliminated, and high image quality is maintained.

  Thus, in order to suppress the dark current, the surface high concentration diffusion layer (P +) 104 is provided to form the embedded photodiode (N−) 103. As described above, examples in which the surface P + layer is formed on the surface of the photodiode (N−) as a buried type are disclosed in detail in, for example, Patent Documents 1 to 3 and the like.

On the other hand, although the surface N + layer is disclosed in Patent Document 4, this is an example in which the polarity is reverse to that of Patent Documents 1 to 3, and the incident light is received as an embedded type. A surface N + layer is formed on the surface side of a P-type well layer as a light receiving portion. The signal in this case is not a charge but a hole as in Patent Documents 1 to 3. Even if the polarity of the conductivity type (P-type and N-type) is reversed as in Patent Document 4, it operates in substantially the same manner as in Patent Documents 1 to 3.
JP 2000-150847 A JP 2002-217397 A JP 2003-188367 A JP 2005-294554 A

However, each of the conventional configurations has the following problems. Here, the signal is described as an electric charge.
That is, the charge of the leak current is minority carriers in the surface high-concentration diffusion layer (P +) 104 and becomes noise if it reaches the embedded photodiode (N−) 103 by diffusion. In order to prevent this, the concentration of the surface high concentration diffusion layer (P +) 104 may be further increased. However, if the concentration of the surface high concentration diffusion layer (P +) 104 is further increased, the surface high concentration diffusion layer (P +) is increased. ) 104 and the embedded photodiode (N−) 103 increase in electric field strength, and another noise due to the junction leakage current occurs. Conversely, when the concentration of the embedded photodiode (N−) 103 is lowered, the electric field strength of the embedded photodiode (N−) 103 decreases, but as a side effect, the amount of signal charge that can be accumulated by the embedded photodiode (N−) 103. Will also go down.

  As another method for preventing the occurrence of this noise, the formation thickness of the surface high-concentration diffusion layer (P +) 104 is made sufficiently wide (thick) in the substrate depth direction, and the leakage current charge is buried by diffusion. Although it is conceivable to recombine before reaching (N−) 103, in this case, the formation position of the embedded photodiode (N−) 103 becomes deep in the substrate, and in particular, photoelectric conversion near the surface. However, the sensitivity deterioration of short-wavelength light (blue, etc.) becomes significant.

  The present invention solves the above-described conventional problems, and there is no reduction in the amount of accumulated signal charges and no deterioration in the sensitivity of blue light, and a solid-state imaging device capable of obtaining high-quality image data in which noise is further suppressed, and An object of the present invention is to provide an electronic information device such as a mobile phone device with a camera using the solid-state imaging device as an image input device in an imaging unit.

  The solid-state imaging device according to the present invention is a solid-state imaging device in which a plurality of first conductive photoelectric conversion units that photoelectrically convert incident light to generate signal charges are two-dimensionally provided as unit pixels. A first conductivity type second surface diffusion layer is provided between the second conductivity type first surface diffusion layer provided on the surface side of the type photoelectric conversion portion and the silicon surface or surface oxide film; This achieves the above object.

  The solid-state imaging device according to the present invention includes a plurality of first conductivity type photoelectric conversion units that photoelectrically convert incident light to generate a signal charge in a two-dimensional manner as each unit pixel. The one-conductivity-type photoelectric conversion unit is provided on the semiconductor substrate or the semiconductor layer for each unit pixel, and the second-conductivity-type first surface diffusion layer is provided on the surface side of the first-conductivity-type photoelectric conversion unit. The first conductivity type second surface diffusion layer is provided on the surface side of the two conductivity type first surface diffusion layer, and thereby the above object is achieved.

  More preferably, the first conductivity type second surface diffusion layer in the solid-state imaging device of the present invention is provided on a part of the surface side of the second conductivity type first surface diffusion layer.

  Further, preferably, the first conductivity type second surface diffusion layer in the solid-state imaging device of the present invention is not formed up to a reading region for reading the signal charge photoelectrically converted by the first conductivity type photoelectric conversion unit. A predetermined interval is provided between the first conductivity type second surface diffusion layer and the readout region.

  Further preferably, a predetermined interval between the first conductivity type second surface diffusion layer in the solid-state imaging device of the present invention and a readout region for reading out signal charges photoelectrically converted by the first conductivity type photoelectric conversion unit. Is provided with the second conductivity type first surface diffusion layer interposed therebetween.

  Further preferably, the predetermined interval in the solid-state imaging device of the present invention is an interval that can prevent diffusion of the charge of the first conductivity type second surface diffusion layer into the readout region when the signal charge is read out.

  Further preferably, the first conductivity type second surface diffusion layer in the solid-state imaging device of the present invention is provided in contact with the side surface and the bottom surface from the side surface to the bottom surface side of the element isolation region around the photoelectric conversion unit. ing.

  Further preferably, in the solid-state imaging device of the present invention, the second conductivity type first surface diffusion layer is a second conductivity type first surface high concentration diffusion layer having a higher concentration than the semiconductor substrate or the semiconductor layer, and the first conductivity type. The type second surface diffusion layer is a first conductivity type second surface high concentration diffusion layer having a higher concentration than that of the first conductivity type photoelectric conversion unit.

  Further preferably, the second conductivity type first surface diffusion layer in the solid-state imaging device of the present invention is a second conductivity type first surface low concentration diffusion layer having a lower concentration or equivalent to the semiconductor substrate or the semiconductor layer, The first conductivity type second surface diffusion layer is a first conductivity type second surface high concentration diffusion layer having a higher concentration than the first conductivity type photoelectric conversion portion.

  Further preferably, the first conductivity type second surface high concentration diffusion layer in the solid-state imaging device of the present invention has the same potential as the second conductivity type first surface low concentration diffusion layer.

  Furthermore, preferably, the first conductivity type second surface high-concentration diffusion layer in the solid-state imaging device of the present invention is connected to the output terminal of the ground potential.

  Further preferably, the first conductivity type second surface high-concentration diffusion layer in the solid-state imaging device of the present invention has a higher potential than the second conductivity type first surface low-concentration diffusion layer, and the second conductivity type first The surface low concentration diffusion layer is depleted.

  Further preferably, the first conductivity type second surface high-concentration diffusion layer in the solid-state imaging device of the present invention is connected to the output terminal of the direct current potential.

  Further preferably, the concentration of the first conductivity type photoelectric conversion unit in the solid-state imaging device of the present invention is higher than the concentration of the first conductivity type photoelectric conversion unit.

  Still preferably, in a solid-state imaging device of the present invention, the first conductivity type photoelectric conversion unit is a CMOS type in which the second conductivity type first surface diffusion layer and the first conductivity type second surface diffusion layer are embedded. It is a solid-state image sensor or a CCD solid-state image sensor.

  The solid-state imaging device of the present invention uses the solid-state imaging device of the present invention as an image input device in an imaging unit, thereby achieving the above object.

  With the above configuration, the operation of the present invention will be described below.

  In the present invention, the second surface diffusion layer having the same polarity (first conductivity type) as that of the photoelectric conversion portion is interposed between the photoelectric conversion portion, the first surface diffusion layer having the opposite polarity (second conductivity type), and the silicon substrate surface. Form. As a result, leakage current (dark current) generated at the interface between the semiconductor surface and the surface oxide film is swept out to the inside of the second surface diffusion layer having the same polarity (first conductivity type) as the photoelectric conversion unit, Leakage current does not intervene on the photoelectric conversion unit side, and noise reduction is realized. In this case, since the second surface diffusion layer having the same polarity as that of the photoelectric conversion unit is not formed to the full extent of the reading region for reading the signal charge generated in the photoelectric conversion unit, the second surface is read when the signal charge is read from the photoelectric conversion unit. The charge from the diffusion layer is not read out together with the signal charge.

  Further, the concentration is decreased as the first surface low-concentration diffusion layer having the opposite polarity (second conductivity type), and the concentration of the photoelectric conversion unit is increased or decreased. This also realizes low noise. In addition, by fixing the potential of the second surface high-concentration diffusion layer having the same polarity (first conductivity type) as that of the photoelectric conversion unit, the leakage current is completely swept to the fixed potential side, thereby further reducing noise. The Further, by increasing the density of the photoelectric conversion unit, the charge storage capacity is increased and a high dynamic range of the signal amount is realized.

  Furthermore, the second surface high-concentration diffusion layer is formed not only on the surface side of the first surface high-concentration diffusion layer but also on the side surface to the bottom surface side of the element isolation region around the photoelectric conversion unit. As a result, the leakage current (dark current) generated from the side surface of the element isolation region to the boundary surface between the bottom surface and the semiconductor surface is also swept out to the inside of the second surface high-concentration diffusion layer having the same polarity as the photoelectric conversion unit. The reduction of noise is realized.

  As described above, according to the present invention, the same polarity as the photoelectric conversion unit (the same polarity as the photoelectric conversion unit) is provided between the photoelectric conversion unit, the first surface diffusion layer having the opposite polarity (second conductivity type), and the silicon surface (or surface oxide film). In order to form the second surface high concentration diffusion layer of the first conductivity type, it is possible to prevent leakage current (dark current) generated at the interface between the semiconductor surface and the surface oxide film from flowing into the photoelectric conversion unit side. Thus, low noise can be realized and high-quality image data can be obtained. Further, the noise can be reduced by decreasing the concentration as the first surface low-concentration diffusion layer having the opposite polarity (second conductivity type) and increasing or decreasing the concentration of the photoelectric conversion unit. In addition, if the potential of the second surface high-concentration diffusion layer having the same polarity (first conductivity type) as that of the photoelectric conversion portion is fixed to a DC potential, the leakage current can be completely swept out to the fixed potential side, and further High-quality image data can be obtained by reducing noise. Further, if the concentration is lowered and the concentration of the photoelectric conversion unit is increased as the first surface low concentration diffusion layer having the opposite polarity (second conductivity type) to the photoelectric conversion unit, a high dynamic range of the signal amount can be realized. Furthermore, if the second surface high-concentration diffusion layer is formed also from the side surface to the bottom surface side of the element isolation region around the photoelectric conversion portion, a leakage current generated from the side surface of the element isolation region to the boundary surface between the bottom surface and the semiconductor surface. (Dark current) can also be swept out to the inside of the second surface high-concentration diffusion layer having the same polarity as that of the photoelectric conversion unit, and high-quality image data can be obtained by further reducing noise.

  Therefore, the solid-state imaging device of the present invention is extremely useful for forming a high-performance image sensor that obtains image data with high image quality and high dynamic range.

  Hereinafter, a case where the present invention is applied to a CMOS type solid-state image sensor will be described as Embodiments 1 to 3 of the solid-state image sensor of the present invention. Further, an electronic information device using the solid-state imaging device of any one of the first to fourth embodiments as an image input device in an imaging unit will be described in detail as a fifth embodiment with reference to the drawings. .

(Embodiment 1)
FIG. 1 is a longitudinal sectional view schematically showing an example of the configuration of the main part of a CMOS solid-state imaging device according to Embodiment 1 of the present invention.
In FIG. 1, a CMOS type solid-state imaging device 20 according to the first embodiment has a signal charge obtained by photoelectrically converting incident light into a P type well 2 of a P type silicon substrate 1 (or N type silicon substrate) as a semiconductor substrate. A plurality of embedded photodiodes (N−) 3 as a plurality of first-conductivity-type photoelectric conversion units (a plurality of light-receiving units) that generate a pixel are formed in a matrix in the matrix direction as unit pixels. A second conductivity type first surface high-concentration diffusion layer (P +) 4 is provided on the surface side of the embedded photodiode (N−) 3, and the surface side of the first surface high-concentration diffusion layer (P +) 4 is further provided. A first conductivity type second surface high-concentration diffusion layer (N +) 5 is provided in part of the first conductive type. That is, the second surface high concentration diffusion layer (N +) 5 is provided between the second conductivity type first surface high concentration diffusion layer (P +) 4 and the silicon surface (surface oxide film 7) of the P type silicon substrate 1. ing. The embedded photodiode (N−) 3 is sandwiched between the first surface high-concentration diffusion layer (P +) 4 on the surface side, the second surface high-concentration diffusion layer (N +) 5 thereon, and the P well 2. It has an embedded structure.
The difference between the case of FIG. 9 of the conventional example and the case of the first embodiment is that the second surface high concentration diffusion between the conventional surface high concentration diffusion layer (P +) 4 and the surface oxide film 7 (silicon surface). The layer (N +) 5 is further formed.

  In this case, the second surface high-concentration diffusion layer (N +) 5 is not formed up to the end face on the photodiode side of the transfer gate 8 of the charge transfer transistor, but a predetermined interval (for example, 0.3 μm ± 0.1 μm; high surface concentration) The diffusion layer (N +) 5 does not escape charges). This is because when the signal charge photoelectrically converted from the embedded photodiode (N−) 3 is transferred (read out), the charge from the surface high concentration diffusion layer (N +) 5 is charged. This is to prevent sweeping out of the transfer transistor under the transfer gate 8 to the charge detection unit 6 side.

  In short, the second surface high-concentration diffusion layer (N +) 5 is formed on the surface side of the first surface high-concentration diffusion layer (P +) 4 for embedding the embedded photodiode (N−) 3. The transistor (P well 2) for reading the signal charge photoelectrically converted by receiving incident light by the diode (N−) 3 is not formed up to the transistor region (P well 2) for reading to the charge detection unit 6 side which is the floating diffusion FD. A first surface high concentration diffusion layer (P +) 4 is interposed between the two surface high concentration diffusion layer (N +) 5 and the transistor region (P well 2).

A surface oxide film is formed on the P well 2 serving as a signal charge transfer region (transistor region) between the buried photodiode (N−) 3 and the first surface high-concentration diffusion layer (P +) 4 and the charge detection unit 6. A transfer gate 8 of the charge transfer transistor is provided through 7. Further, a reset transistor reset gate 9 is provided on the P well 2 serving as a transistor region between the charge detection unit 6 and the drain region 10 connected to the output terminal of the power supply potential via the surface oxide film 7. Yes. The P-type silicon substrate 1 is connected to the output terminal of the GND potential.
The potential of the second surface high-concentration diffusion layer (N +) 5 is shown in FIG. 2 as a potential diagram in the substrate depth direction. In order to avoid a junction leakage current, the first surface high-concentration diffusion layer (P +) 4, The potential of the second surface high concentration diffusion layer (N +) 5 is substantially the same as that of the P well 2 and the P silicon substrate 1, but the potential of the second surface high concentration diffusion layer (N +) 5 is higher than the potential of the first surface high concentration diffusion layer (P +) 4. Of the leakage current generated near the silicon surface, the unnecessary charge is lower than the built-in potential difference and exceeds the GND potential of the first surface high concentration diffusion layer (P +) 4 from the surface of the second surface high concentration diffusion layer (N +) 5. Thus, it does not diffuse toward the embedded photodiode (N−) 3 side. The unnecessary charges are swept out from the second surface high concentration diffusion layer (N +) 5 to the GND potential side.

  The connection between the second surface high-concentration diffusion layers (N +) 5 does not need to be performed within the unit pixel. This is because, as shown in the pixel pattern diagram of FIG. 3, element isolation from each transistor is isolated by an element isolation oxide film in a unit pixel, but an element between embedded photodiodes (N−) 3. Isolation (vertical direction in FIG. 3) is performed by ion implantation (first surface high-concentration diffusion layer (P +) 4 or P well 2), so that the second surface high-concentration diffusion layer (N +) 5 (second The surface high concentration diffusion layer (N +) pattern) is also connected to each pixel in the vertical direction. Therefore, it is not necessary to connect to the GND potential in each pixel, and connection to the GND potential outside the pixel array is possible.

  With the above configuration, incident light is photoelectrically converted by the embedded photodiode (N−) 3, and the stored signal charge is applied to the transfer gate 8 of the charge transfer transistor by applying a transfer signal to the embedded photodiode (N−) 3. Then, the charge is transferred to the charge detector 6. In the charge detector 6, the signal charge transferred is converted into a signal voltage, amplified by an amplification transistor (not shown) in accordance with the signal voltage, and output as an imaging signal to the signal line. Thereafter, a reset signal is applied to the reset gate 9 of the reset transistor, and the charge detection unit 6 is reset to the power supply potential. As described above, the signal charge transferred to the charge detection unit 6 is discharged to the drain region 10 connected to the output terminal of the power supply potential.

  In this case, out of the leakage current generated near the silicon surface, the charge is completely swept from the second surface high-concentration diffusion layer (N +) 5 to the GND potential side, and the leakage current component generated on the silicon surface is completely It does not diffuse toward the embedded photodiode (N−) 3 side, and extremely high image quality is obtained.

  As described above, according to the first embodiment, the embedded photodiode (N−) 3 as the photoelectric conversion unit, the first surface high-concentration diffusion layer (P +) 4 having the opposite polarity (second conductivity type), and the silicon substrate 1 In order to form a second surface high-concentration diffusion layer (N +) 5 having the same polarity (first conductivity type) as the embedded photodiode (N−) 3 between the surface and the surface, the surface of the silicon substrate 1 and its surface oxide film The leakage current (dark current) generated at the boundary surface between the second surface high-concentration diffusion layer (N +) 5 having the same polarity (first conductivity type) as that of the embedded photodiode (N−) 3 is brought to the GND potential side. As a result, the leakage current does not intervene on the side of the embedded photodiode (N−) 3 and the noise can be reduced, and high image quality can be obtained. In this case, the second surface high-concentration diffusion layer (N +) 5 having the same polarity as that of the embedded photodiode (N−) 3 is formed to fill the readout region for reading the signal charge generated in the embedded photodiode (N−) 3. Therefore, it is possible to prevent the charge from the second surface high-concentration diffusion layer (N +) 5 from being read together with the signal charge when the signal charge is read from the embedded photodiode (N−) 3.

(Embodiment 2)
In the first embodiment, the embedded photodiode (N) is interposed between the first surface high-concentration diffusion layer (P +) 4 having the opposite polarity (P type) to the embedded photodiode (N−) 3 and the semiconductor surface of the silicon substrate 1. -) The case where the second surface high-concentration diffusion layer (N +) 5 having the same polarity (N type) as 3 is formed to reduce the noise of the image pickup signal and to improve the image quality has been described. In the second mode, the density is reduced as the first surface low-concentration diffusion layer (P−) of the opposite polarity (P type), and the density is increased or decreased as in the case of the embedded photodiode (N or N−). A case of realizing low noise will be described.

  FIG. 4 is a longitudinal sectional view schematically showing an example of the configuration of the main part of a CMOS solid-state imaging device according to Embodiment 2 of the present invention. In addition, the same code | symbol is attached | subjected and demonstrated to the member which show | plays the effect similar to the said FIG.

  In FIG. 4, the CMOS type solid-state imaging device 20A of the second embodiment has a plurality of signals that generate signal charges by photoelectrically converting incident light in a P well 2 of a P type silicon substrate 1 as a second conductive semiconductor substrate. A plurality of embedded photodiodes (N or N−) 3 as first conductive photoelectric conversion portions (a plurality of light receiving portions) are formed in a matrix in the matrix direction as unit pixels. A second conductivity type first surface low-concentration diffusion layer (P−) 4A is provided on the surface side of the embedded photodiode (N or N−) 3, and further, the first surface low-concentration diffusion layer (P−) is provided. ) A first conductivity type second surface high-concentration diffusion layer (N +) 5 connected to the output terminal of the DC potential VD is provided on a part of the surface side of 4A. That is, the second surface high concentration diffusion layer (N +) 5 is provided between the second conductivity type first surface low concentration diffusion layer (P−) 4A and the silicon surface (surface oxide film 7) of the P type silicon substrate 1. It has been. The buried photodiode (N or N−) 3 includes a first surface low concentration diffusion layer (P−) 4A on the surface side, a second surface high concentration diffusion layer (N +) 5 thereon, and a P well 2. It has an embedded structure sandwiched between.

  Here, the difference from the case of the first embodiment is that the first surface diffusion layer is not the high concentration (P +) as in the first embodiment but the first surface low concentration diffusion layer (P−) layer 4A. The point is that the concentration is increased and the potential of the second surface high-concentration diffusion layer (N +) 5 is fixed by applying the DC potential VD instead of the GND potential as in the first embodiment.

  In the conventional example, in order to recombine the charge of the leakage current generated on the silicon surface (semiconductor surface), it is desirable that the first surface high-concentration diffusion layer has a high concentration, and for this reason, the (P +) layer was used. In the second embodiment, since the second surface high concentration diffusion layer (N +) 5 exists, the first surface high concentration diffusion layer includes the second surface high concentration diffusion layer (N +) 5 and the embedded photodiode (N−). 3 and only a low concentration.

By reducing the concentration of the first surface diffusion layer, the electric field strength between the first surface low concentration diffusion layer (P−) 4A and the embedded photodiode (N or N−) 3 is weakened, and the embedded photodiode (N) 3 Thus, even if the concentration is increased, junction leakage current does not occur, and as a result, the signal charge capacity that can be stored in the embedded photodiode (N) 3 increases, and the dynamic range of the signal amount to be handled can be increased. .
Further, on the surface side, a potential diagram in the substrate depth direction as shown in FIG. 5 is obtained, and the first surface low concentration diffusion layer (P−) 4A is thinned and depleted, but the second surface high concentration diffusion layer. By fixing the potential of (N +) 5 not to the GND potential but to the constant potential VD of the DC high potential, from the second surface high concentration diffusion layer (N +) 5 to the embedded photodiode (N or N−) 3, A punch-through current flowing beyond the depletion layer can be prevented.

  As described above, according to the second embodiment, the concentration is lowered as the first surface low concentration diffusion layer (P−) layer 4A having the opposite polarity (second conductivity type) to the embedded photodiode (N or N−) 3 and embedded. Even if the concentration of the photodiode (N−) 3 is left as it is or is increased, the leakage current (dark current) generated at the boundary surface between the semiconductor surface of the silicon substrate 1 and the surface oxide film 7 can be reduced. (N or N−) 3 is swept out to the inside of the second surface high-concentration diffusion layer (N +) 5 having the same polarity (first conductivity type) as that of the (N or N−) 3, and a leak current is generated on the embedded photodiode (N or N−) 3 side. Without intervention, low noise can be realized and high image quality can be obtained. Moreover, by fixing the potential of the second surface high-concentration diffusion layer (N +) 5 having the same polarity (first conductivity type) as the embedded photodiode (N or N−) 3 to a predetermined DC potential, Leakage current can be completely swept away to achieve further noise reduction and high image quality. Further, by increasing the concentration as in the case of the embedded photodiode (N) 3, the charge storage capacity is increased, and a high dynamic range of the signal amount can be realized.

(Embodiment 3)
In the first embodiment, the embedded photodiode (N) is interposed between the first surface high-concentration diffusion layer (P +) 4 having the opposite polarity (P type) to the embedded photodiode (N−) 3 and the semiconductor surface of the silicon substrate 1. -) The case where low noise is realized by forming the second surface high concentration diffusion layer (N +) 5 having the same polarity (N type) as 3 has been described. The diffusion layer (N +) 5 is also formed between the side surface and the bottom surface of the element isolation region 11 around the buried photodiode (N−) 3 and the semiconductor surface, so that the bottom surface and the semiconductor of the element isolation region 11 are formed. A case will be described in which a leak current (dark current) generated at the interface with the surface is also swept out to the second surface high-concentration diffusion layer (N +) 5 side to further reduce noise.

  FIG. 6 is a longitudinal sectional view schematically showing an example of the configuration of the main part of a CMOS solid-state imaging device according to Embodiment 3 of the present invention. In addition, the same code | symbol is attached | subjected and demonstrated to the member which show | plays the effect similar to the said FIG.

  In FIG. 6, the CMOS type solid-state imaging device 20 </ b> B of the third embodiment generates a signal charge by photoelectrically converting incident light in a P well 2 of a P type silicon substrate 1 as a second conductivity type semiconductor substrate. A plurality of embedded photodiodes (N−) 3 as first conductive photoelectric conversion units (a plurality of light receiving units) are formed in a matrix in the matrix direction as unit pixels. A second conductivity type first surface high-concentration diffusion layer (P +) 4 is provided on the surface side of the embedded photodiode (N−) 3, and the surface of the first surface high-concentration diffusion layer (P +) 4 is further provided. A first conductivity type second surface high-concentration diffusion layer (N +) 5 connected to the output terminal of the GND potential is provided on a part of the side. Further, a diffusion layer similar to the first conductivity type second surface high-concentration diffusion layer (N +) 5 is formed on the side surface and the bottom surface of the element isolation oxide film 11 around the buried photodiode (N−) 3 and the semiconductor surface in contact therewith. The first conductive type third high-concentration diffusion layer (N +) 5B is provided so as to extend between the two. Thus, the embedded photodiode (N−) 3 includes the first surface high concentration diffusion layer (P +) 4, the second surface high concentration diffusion layer (N +) 5, and the second surface high concentration. The buried structure is surrounded by the third high-concentration diffusion layer (N +) 5B extending from the diffusion layer (N +) 5 and the P well 2. The third high concentration diffusion layer (N +) 5B is made of the same material as the second surface high concentration diffusion layer (N +) 5. The arrangement range of the first conductivity type third high-concentration diffusion layer (N +) 5B may be only around the pixel that causes noise, and the side surface of the element isolation oxide film 11 around the embedded photodiode (N−) 3 and Just below the bottom.

  Here, the difference from the case of the first embodiment is that the second surface high-concentration diffusion layer (N +) 5 is extended to the side surface and below the bottom surface of the element isolation oxide film 11 around the embedded photodiode (N−) 3. The third surface high-concentration diffusion layer (N +) 5B is formed in succession to the second surface high-concentration diffusion layer (N +) 5 by widening and injecting high energy.

  As described above, according to the third embodiment, the second surface high concentration diffusion layer (N +) 5 is not only the surface side of the first surface high concentration diffusion layer, but also an element around the embedded photodiode (N−) 3. Since the third surface high-concentration diffusion layer (N +) 5B is provided from the side surface to the bottom surface of the isolation oxide film 11, a leakage current component generated at the interface between the side surface and the bottom surface of the element isolation oxide film 11 and the P-type silicon substrate 1 Can be swept to the GND potential side via the second surface high concentration diffusion layer (N +) 5 and the third surface high concentration diffusion layer (N +) 5B, and further noise reduction can be realized. Further, high image quality can be realized.

  In the first to third embodiments, the CMOS solid-state image pickup devices 20, 20A, and 20B have been described. However, the present invention is not limited to this, and the solid-state image pickup device of the present invention can also be applied to a CCD solid-state image pickup device. This case is shown in the following fourth embodiment.

  Here, the signal readout circuits of the CMOS type solid-state imaging devices 20, 20A and 20B will be further described.

  Each of the CMOS type solid-state imaging devices 20, 20A and 20B reads the signal charge from each embedded photodiode 3, and for each pixel unit, the embedded photodiode 3 as a light receiving unit for receiving subject light, and the embedded photodiode It is necessary to provide a charge detector 6 for converting the signal charge from 3 into a signal voltage and a plurality of transistors constituting a signal readout circuit. Specifically, for example, generally, as a plurality of transistors, a charge transfer transistor that transfers signal charges from the embedded photodiode 3 to the charge detection unit 6, and signal charges accumulated in the charge detection unit 6 Is reset before the charge transfer, an amplification transistor that amplifies and reads out the signal charge accumulated in the charge detection unit 6 as a signal, and a signal amplified by the amplification transistor by selecting the readout pixel unit As a selection transistor that outputs a signal to a signal line, a photodiode 3 and a charge detection unit 6 and four transistors (sometimes omitting the selection transistor to form three transistors) are required for each pixel unit. Yes.

  CMOS type solid-state imaging devices 20, 20A and 20B have begun to be widely used alongside CCD (Charge Coupled Device) type solid-state imaging devices described later. The reason is that the CMOS solid-state imaging devices 20, 20 A and 20 B can be manufactured by using conventional IC (integrated circuit) manufacturing technology, and an image in which signal charges are read from the embedded photodiode 3 and amplified. For example, it is possible to reduce the size and speed by mounting the sensor on the same chip as the peripheral circuit that drives the sensor. Further, the CMOS solid-state imaging devices 20, 20A, and 20B have an advantage that the structure itself is simple and does not require a high driving voltage, as compared with the CCD solid-state imaging device 40 described later.

(Embodiment 4)
FIG. 7 is a longitudinal sectional view schematically showing an example of the configuration of the main part of a CCD solid-state imaging device according to Embodiment 4 of the present invention.
In FIG. 7, the CCD type solid-state imaging device 40 of Embodiment 4 includes a plurality of signals that generate signal charges by photoelectrically converting incident light into a P-well 32 of an N-type silicon substrate 31 as a first conductive semiconductor substrate. A plurality of embedded photodiodes (N−) 33 as first conductive photoelectric conversion units (a plurality of light receiving units) are formed in a matrix in the matrix direction as unit pixels. A second conductivity type first surface high-concentration diffusion layer (P +) 34 is provided on the surface side of the embedded photodiode (N−) 33, and the surface side of the first surface high-concentration diffusion layer (P +) 34 is provided. A first conductivity type second surface high-concentration diffusion layer (N +) 35 is provided in part of the first conductive type. That is, the second surface high concentration diffusion layer (N +) 35 is provided between the second conductivity type first surface high concentration diffusion layer (P +) 34 and the silicon surface (surface oxide film 36) of the P type silicon substrate 1. ing. As described above, the embedded photodiode (N−) 33 is surrounded by the first surface high concentration diffusion layer (P +) 34 and the second surface high concentration diffusion layer (N +) 35 and the P well 32 on the surface side. It has an embedded structure.

  In this case, the second surface high-concentration diffusion layer (N +) 35 is not formed up to the photodiode side end face 37a of the charge transfer gate 37 of the vertical charge transfer portion. This is because when the signal charge is read from the embedded photodiode (N−) 33 to the charge transfer region 38 through the charge reading portion (P well 32), the charge of the second surface high concentration diffusion layer (N +) 35 is transferred to the charge transfer region 38. This is to prevent the gate 37 from sweeping out to the charge transfer region 38 side through the charge reading portion.

  In short, the second surface high-concentration diffusion layer (N +) 35 is formed on the surface side of the first surface high-concentration diffusion layer (P +) 34 for embedding the embedded photodiode (N−) 33, but the embedded photo The diode (N−) 33 is not formed up to the transistor region (P well 32) for reading the signal charge photoelectrically converted by receiving incident light by the diode (N−) 33, and the second surface high concentration diffusion. A first surface high-concentration diffusion layer (P +) 34 is provided between the layer (N +) 35 and its transistor region (P well 2).

  The embedded photodiode (N−) 33 and the first surface high-concentration diffusion layer (P +) 34, the charge readout portion 37 and the charge transfer region 38 adjacent thereto, and the stopper for the element isolation diffusion layer adjacent thereto A charge transfer gate 37 is provided on the portion 39, the charge readout portion (P well 32), the charge transfer region 38, and the stopper portion 39 via a surface oxide film 36. The N-type silicon substrate 1 is connected to an output terminal having a positive potential suitable for operation.

  As described above, according to the fourth embodiment, the first surface high-concentration diffusion layer (P +) 34 and the N-type silicon substrate having the opposite polarity (second conductivity type) to the embedded photodiode (N−) 33 as the photoelectric conversion unit. In order to form a second surface high-concentration diffusion layer (N +) 35 having the same polarity (first conductivity type) as that of the embedded photodiode (N−) 33 between the semiconductor surface 31 and the surface of the semiconductor 31, the surface of the N-type silicon substrate 31 is formed. The second surface high-concentration diffusion layer (N +) 35 having the same polarity (first conductivity type) as the buried photodiode (N−) 33 is leaked (dark current) generated at the interface between the surface oxide film 36 and the surface oxide film 36. It is swept inward and no leakage current intervenes on the embedded photodiode (N−) 33 side, so that noise can be reduced and high image quality can be obtained. In this case, the second surface high-concentration diffusion layer (N +) 35 having the same polarity as the embedded photodiode (N−) 33 reads out the signal charge generated in the embedded photodiode (N−) 33 (P-type well). 32) Since it is not formed to the full extent, it prevents the charge from the second surface high-concentration diffusion layer (N +) 35 from being read together with the signal charge when reading the signal charge from the embedded photodiode (N−) 33. can do.

  In the fourth embodiment, the CCD solid-state imaging device 40 has been described. However, this corresponds to the first embodiment, and the CCD solid-state imaging device can correspond to the second or third embodiment. .

(Embodiment 5)
FIG. 8 is a block diagram schematically showing a configuration example of a main part of an electronic information device in which the solid-state imaging device of the present invention is used as an image input camera in an imaging unit as Embodiment 5 of the present invention.

  In FIG. 8, an electronic information device 90 according to the fifth embodiment uses a solid-state imaging device 20 or 20A, 20B, or 40 described in any one of the first to fourth embodiments as an analog signal process and a digital signal. A solid-state imaging device 91 that obtains image data by processing, a memory unit 92 such as a recording medium that records data after high-quality image data from the solid-state imaging device 91 is subjected to predetermined signal processing for recording, and the image data A display means 93 such as a liquid crystal display device that performs predetermined signal processing for display on a display screen such as a liquid crystal display screen, and a transmission / reception device that performs communication processing after performing predetermined signal processing of the image data for communication And a communication means 94 such as an image output device 95 for printing (printing) and outputting (printing out) the image data. The electronic information device 90 according to the fifth embodiment includes at least one of a memory unit 92, a display unit 93, a communication unit 94, and an image output device 95 in addition to the solid-state imaging device 91. May be.

  As the electronic information device 90 according to the fifth embodiment, for example, a digital camera such as a digital video camera and a digital still camera, an image input such as a surveillance camera, a door phone camera, an in-vehicle camera, a television phone camera, and a mobile phone camera are input. A camera, a scanner, a facsimile, a mobile phone device with a camera, a form terminal device (PDA), and the like can be considered.

  As described above, conventionally, in order to suppress dark current caused by lattice defects at the interface between the silicon surface and the surface oxide film, it has been common to use a photodiode as a buried type and cover the silicon surface with a surface P + layer. However, the dark current is a minority carrier in the surface P + layer (the first surface high-concentration diffusion layer 4 or the first surface low-concentration diffusion layer 4A), and the minority carriers reach the photodiode (N−) layer by diffusion. Then, it becomes a dark current component. To prevent this, if the concentration of the surface P + layer is increased, recombination is accelerated and it is good for unwanted charges. However, in this case, the electric field strength between the surface P + layer and the photodiode (N−) layer increases. A dark current is generated due to the junction leakage current. When the concentration of the photodiode (N−) layer is lowered, the electric field strength is lowered, but as a side effect, the saturation signal (signal charge storage capacity) is lowered. Therefore, according to the first to fourth embodiments, it is only necessary to accumulate signal charges in the photodiode (N−) layer and prevent the charges generated in the surface P + layer from diffusing to the photodiode (N−) layer side. Further, a surface N + layer (second surface high concentration diffusion layer 5) is further provided on the surface of the surface P + layer (first surface high concentration diffusion layer 4 or first surface low concentration diffusion layer 4A) as a drain for the dark current component (charge). It is newly provided and charges are trapped. Thereby, high-quality image data in which noise is further suppressed can be obtained. In particular, in the case of a solid-state imaging device used under a high temperature condition such as an in-vehicle camera or a space camera, surface noise increases. Therefore, the present invention can be applied to a high temperature such as daytime or a long time when noise is easily affected. Strongly useful for exposure.

  Although not particularly described in the first to fourth embodiments, a plurality of first conductivity type photoelectric conversion units that photoelectrically convert incident light to generate signal charges are provided two-dimensionally as each unit pixel. In the solid-state imaging device, when the first conductivity type second surface diffusion layer is provided between the second conductivity type first surface diffusion layer provided on the surface side of the photoelectric conversion unit and the silicon surface, or photoelectric The conversion unit is provided for each unit pixel on the second conductivity type semiconductor substrate or the second conductivity type semiconductor layer, and the second conductivity type first surface diffusion layer is provided on the surface side of the first conductivity type photoelectric conversion unit, If any of the cases where the first conductivity type second surface diffusion layer is provided on the surface side of the second conductivity type first surface diffusion layer, there is no reduction in the amount of accumulated signal charge and deterioration in sensitivity of blue light, It is possible to obtain high-quality image data with reduced noise. It is possible to achieve the objective.

  As mentioned above, although this invention has been illustrated using preferable Embodiment 1-5 of this invention, this invention should not be limited and limited to this Embodiment 1-5. It is understood that the scope of the present invention should be construed only by the claims. It is understood that those skilled in the art can implement an equivalent range based on the description of the present invention and the common general technical knowledge from the description of specific preferred embodiments 1 to 5 of the present invention. Patents, patent applications, and documents cited herein should be incorporated by reference in their entirety, as if the contents themselves were specifically described herein. Understood.

  The present invention relates to a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor constituted by a semiconductor element that photoelectrically converts image light from a subject by a photoelectric conversion unit and images the same, and this solid-state imaging device as an image input device. For example, digital cameras such as digital video cameras and digital still cameras used as imaging units, image input cameras such as surveillance cameras, in-vehicle cameras, industrial cameras, and medical cameras, scanners, facsimiles, and camera-equipped mobile phones In the field of electronic information equipment such as devices, the same polarity (first conductivity type) as the photoelectric conversion portion between the photoelectric conversion portion and the first surface high-concentration diffusion layer having the opposite polarity (second conductivity type) and the silicon substrate surface. ) Of the second surface high-concentration diffusion layer, a leakage current (dark current) generated at the interface between the semiconductor surface and the surface oxide film. The can be prevented to flow into the photoelectric conversion portion side, to be able to realize a low noise can be obtained high-quality image data. Further, if the concentration is lowered as the first surface low-concentration diffusion layer having the opposite polarity (second conductivity type) and the concentration of the photoelectric conversion unit is increased, a high dynamic range of the signal amount can be realized. In addition, if the potential of the second surface high-concentration diffusion layer having the same polarity (first conductivity type) as that of the photoelectric conversion portion is fixed to a DC potential, the leakage current can be completely swept out to the fixed potential side, and further High-quality image data can be obtained by reducing noise. Furthermore, if the second surface high-concentration diffusion layer is formed also from the side surface to the bottom surface side of the element isolation region around the photoelectric conversion portion, a leakage current generated from the side surface of the element isolation region to the boundary surface between the bottom surface and the semiconductor surface. (Dark current) can also be swept out to the inside of the second surface high-concentration diffusion layer having the same polarity as that of the photoelectric conversion unit, and high-quality image data can be obtained by further reducing noise.

  Therefore, the solid-state imaging device of the present invention is extremely useful for forming a high-performance image sensor that obtains image data with high image quality and high dynamic range.

It is a longitudinal cross-sectional view which shows typically the principal part structural example of the CMOS type solid-state image sensor which concerns on Embodiment 1 of this invention. FIG. 2 is a potential diagram in a substrate depth direction in the solid-state imaging device of FIG. 1. It is a top view which shows typically the pixel pattern in the solid-state image sensor of FIG. It is a longitudinal cross-sectional view which shows typically the example of a principal part structure of the CMOS type solid-state image sensor concerning Embodiment 2 of this invention. FIG. 5 is a potential diagram in the substrate depth direction in the solid-state imaging device of FIG. 4. It is a longitudinal cross-sectional view which shows typically the example of a principal part structure of the CMOS type solid-state image sensor concerning Embodiment 3 of this invention. It is a longitudinal cross-sectional view which shows typically the example of a principal part structure of the CCD type solid-state image sensor concerning Embodiment 4 of this invention. It is a block diagram which shows typically the example of a principal part structure of the electronic information equipment which used the solid-state image sensor of this invention as an image input camera for the imaging part as Embodiment 5 of this invention. It is a longitudinal cross-sectional view which shows typically the example of a principal part structure of the conventional CMOS type image sensor (imager).

Explanation of symbols

1 P-type silicon substrate 2, 32 P-type well 3, 33 Embedded photodiode (N or N-)
4, 34 First surface high concentration diffusion layer (P +)
4A First surface low concentration diffusion layer (P-)
5, 35 Second surface high-concentration diffusion layer (N +)
5B Third high concentration diffusion layer (N +)
6 Charge detection unit 7, 36 Surface oxide film 8, 37 Transfer gate 9 of charge transfer transistor Reset gate 10 of reset transistor Drain region 11 Element isolation oxide film 20, 20A, 20B CMOS type solid-state imaging device 31 N type silicon substrate 37a photo Diode side end surface 38 Charge transfer region 39 Stopper unit 40 CCD type solid-state imaging device 90 Electronic information equipment 91 Solid-state imaging device 92 Memory unit 93 Display unit 94 Communication unit 95 Image output device

Claims (16)

  In a solid-state imaging device in which a plurality of first conductivity type photoelectric conversion units that photoelectrically convert incident light to generate signal charges are two-dimensionally provided as unit pixels, on the surface side of the first conductivity type photoelectric conversion unit A solid-state imaging device in which a first conductivity type second surface diffusion layer is provided between the provided second conductivity type first surface diffusion layer and a silicon surface or a surface oxide film.   In a solid-state imaging device in which a plurality of first conductive photoelectric conversion units that photoelectrically convert incident light to generate signal charges are two-dimensionally provided as unit pixels, the first conductive photoelectric conversion unit includes the unit Each pixel is provided on a semiconductor substrate or a semiconductor layer, a second conductivity type first surface diffusion layer is provided on the surface side of the first conductivity type photoelectric conversion unit, and the surface of the second conductivity type first surface diffusion layer A solid-state imaging device provided with a first conductivity type second surface diffusion layer on the side.   3. The solid-state imaging device according to claim 1, wherein the first conductivity type second surface diffusion layer is provided on a part of a surface side of the second conductivity type first surface diffusion layer.   The first conductivity type second surface diffusion layer is not formed up to a reading region for reading signal charges photoelectrically converted by the first conductivity type photoelectric conversion unit, and the first conductivity type second surface diffusion layer is not formed. The solid-state imaging device according to claim 3, wherein a predetermined interval is provided between the readout area and the readout area.   The second conductivity type first surface diffusion is provided at a predetermined interval between the first conductivity type second surface diffusion layer and a readout region for reading the signal charge photoelectrically converted by the first conductivity type photoelectric conversion unit. The solid-state image sensor according to any one of claims 1 to 3, wherein a layer is interposed.   6. The solid-state imaging device according to claim 4, wherein the predetermined interval is an interval capable of preventing diffusion of the charge of the first conductivity type second surface diffusion layer into the reading region during reading of the signal charge.  The said 1st conductivity type 2nd surface diffusion layer is provided in contact with this side surface and this bottom face also from the side surface to the bottom face side of the element isolation region around the said photoelectric conversion part. The solid-state imaging device described.   The second conductivity type first surface diffusion layer is a semiconductor substrate or a second conductivity type first surface high concentration diffusion layer having a higher concentration than the semiconductor layer, and the first conductivity type second surface diffusion layer is the first conductivity type. 3. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is a first conductivity type second surface high-concentration diffusion layer having a higher concentration than the type photoelectric conversion unit.   The second conductivity type first surface diffusion layer is a second conductivity type first surface low concentration diffusion layer having a lower concentration or equivalent to a semiconductor substrate or semiconductor layer, and the first conductivity type second surface diffusion layer is 3. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is a first conductivity type second surface high concentration diffusion layer having a higher concentration than the first conductivity type photoelectric conversion unit.   The solid-state imaging device according to claim 8, wherein the first conductivity type second surface high-concentration diffusion layer has the same potential as the second conductivity type first surface low-concentration diffusion layer.   The solid-state imaging device according to claim 10, wherein the first conductivity type second surface high-concentration diffusion layer is connected to an output terminal of a ground potential.   The first conductivity type second surface high concentration diffusion layer has a higher potential than the second conductivity type first surface low concentration diffusion layer, and the second conductivity type first surface low concentration diffusion layer is depleted. The solid-state imaging device according to claim 9.   The solid-state imaging device according to claim 12, wherein the first conductivity type second surface high concentration diffusion layer is connected to an output terminal of a direct current potential.   The solid-state imaging device according to claim 9, wherein the concentration of the first conductivity type photoelectric conversion unit is higher than the concentration of the first conductivity type photoelectric conversion unit.   The CMOS-type solid-state imaging device or the CCD-type solid-state imaging device, wherein the first-conductivity-type photoelectric conversion unit is embedded by the second-conductivity-type first surface diffusion layer and the first-conductivity-type second surface diffusion layer. The solid-state imaging device according to 1 or 2.   An electronic information device using the solid-state imaging device according to claim 1 as an image input device in an imaging unit.

Images