JP4599417B2 - Back-illuminated solid-state image sensor - Google Patents

Description

  The present invention relates to a back-illuminated solid-state imaging device having a structure in which the resolution of a captured image is high and color mixing between adjacent pixels can be suppressed.

  Solid-state imaging devices such as a CMOS image sensor and a CCD image sensor include a front side illumination type and a back side illumination type. One side of a semiconductor substrate on which a signal readout circuit (a transistor circuit and wiring layer for a CMOS image sensor, a charge transfer path including wiring for a CCD image sensor), which is a main electronic element of an image sensor, is formed (this surface is The surface irradiation type is the same plane as “front side” and has a structure for receiving incident light from a subject.

  On the other hand, the back-illuminated type has a structure in which incident light from a subject is received on the surface opposite to the surface side of the semiconductor substrate on which the signal readout circuit is formed, as shown in FIG. 6, for example. Say.

  A back-illuminated solid-state imaging device 1 illustrated in FIG. 6 is a CCD type provided with a charge transfer path as a signal readout circuit, and an n region 3 constituting a photodiode and a charge transfer path on the surface side of the silicon substrate 2. An n region 4 constituting a buried channel is provided. A p region 5 is provided on the side and lower side (back side) of the n region 4.

  A gate insulating film 6 is formed on the surface of the silicon substrate 2, a transfer electrode (polysilicon electrode) 7 is formed on the n region 4 via the gate insulating film 6, and an insulating layer 8 is formed thereon. A light shielding film 9 is laminated. A p-layer 10 for suppressing dark current is provided on the surface of the n region 3.

  A planarizing film 11 is laminated on the light shielding film 9, and a support substrate 12 is provided thereon. A p layer 13 is formed on the rear surface of the semiconductor substrate 2, a color filter layer 14 is laminated thereon, and a microlens 15 is laminated thereon.

  In the backside illumination solid-state imaging device 1 having such a configuration, light enters from the backside of the semiconductor substrate 2. This incident light is condensed by the on-chip microlens 15 in the direction of the electron capture region 3a of the n region 3, and only the wavelength that passes through the color filter 14 is incident on the photosensitive portion of the n region 3. The incident light is photoelectrically converted into electrons at a depth corresponding to the wavelength of the incident light and the absorption coefficient of the silicon substrate 2.

  The photoelectrically converted electrons move due to the potential gradient shown in FIG. 7 (potential gradient in the section taken along line VII-VII ′ in FIG. 6) in the photosensitive portion, and accumulate in the electron capture region 3a. Incident light with a longer wavelength penetrates into deeper sites and undergoes photoelectric conversion.

  Incident light is incident with a spread of the upper and lower ray angles in addition to the chief ray angle depending on the pupil position and brightness (FF value) of the photographing lens of the camera (not shown). As a result, for example, a part of the light transmitted through the red color filter reaches a pixel having an adjacent green color filter, and then is photoelectrically converted into electrons and captured in the electron capture region 3a of the green pixel. As a result, a captured image signal is obtained.

  In this way, when incident light enters adjacent pixels, this becomes a factor that degrades the resolution of the captured image. Further, when some of the electrons generated as the red pixel signal move in the horizontal direction in the substrate 2 by thermal diffusion and are captured by the electron capture region of the adjacent green pixel, this becomes a color mixture signal, and the color It becomes a factor which degrades reproducibility and color SN.

  As described above, since the signal separation becomes difficult with the structure shown in FIG. 6, as shown in Patent Documents 1, 2, 3, 4, and 5, proposals for improving these conventional defects have been made. .

  In the back-illuminated solid-state imaging devices of Patent Documents 1 and 2, in order to achieve good separation between pixels, multiple different concentration layers are provided in a semiconductor substrate to be subjected to photoelectric conversion, so that the gradient is steeper than the potential gradient shown in FIG. In which the electrons (signal charges) generated by the light incident on the pixel position are guided to the capture region of the pixel. However, this configuration cannot prevent incident light from leaking into adjacent pixels.

  In the back-illuminated solid-state imaging device of Patent Document 3, a p-type impurity different from the photoelectric conversion unit is provided between the pixels in order to prevent diffusion of lateral (horizontal) electrons (signal charges) generated in the structure of FIG. A potential barrier is provided by region.

  However, in this configuration, signal charges can be prevented from diffusing in the horizontal direction as compared with Patent Documents 1 and 2, but leakage of incident light to adjacent pixels cannot be prevented. In addition, since ion implantation and thermal diffusion are performed to form the potential barrier deeply, p-type impurities different from the photoelectric conversion portion are diffused in the lateral direction, and the effective charge trapping region of the photodiode is reduced. The problem also arises.

  The back-illuminated solid-state imaging device of Patent Document 4 has a structure that suppresses direct leakage of incident light to adjacent pixels by providing a film that reflects light in adjacent portions of the pixels. However, when incident light is incident at a predetermined angle, leakage into adjacent pixels can be effectively suppressed. However, since the light path is only bent by reflecting off the reflection film, There is a problem that it is difficult to control the behavior.

  The back-illuminated solid-state imaging device of Patent Document 5 applies a predetermined potential different from that during signal charge accumulation operation to a transparent electrode disposed on a light incident surface, thereby changing the potential on the transparent electrode side to a photoelectric conversion unit. The signal charge accumulated in the photoelectric conversion unit is extracted to the transparent electrode side.

  This structure is suitable for extracting the signal charges of the entire screen at the same time. However, in order to obtain a structure in which the charge is extracted separately for each pixel, for each row, for each column, for each block of a predetermined size, shape, etc. There is a problem that is accompanied by difficulties.

JP 2006-66710 A JP 2006-134915 A JP 2005-294705 A JP 2006-80457 A JP 2001-257337 A

  An object of the present invention is to provide a back-illuminated solid-state imaging device capable of capturing a subject image with high resolution and low color mixing while suppressing both signal charge diffusion between adjacent pixels and direct leakage of incident light. There is to do.

(1) A plurality of photodiodes are formed in a two-dimensional array on the first surface (hereinafter referred to as the front surface) side of the semiconductor substrate, and light incident from the second surface (hereinafter referred to as the back surface) side of the semiconductor substrate. In the back-illuminated solid-state imaging device in which each of the photodiodes detects the signal charge generated by the device, an element isolation region having a trench structure groove that separates each of the photodiodes from the adjacent photodiode is provided on the back surface side. Formed, the groove is filled with a metal that blocks light, a wiring for applying a predetermined voltage from the outside is connected to the metal, and when the predetermined voltage is applied at the time of an electronic shutter, the accumulated charge of the photodiode is A back-illuminated solid-state imaging device, which is discarded through the metal in the front element isolation region .
(2) The back-illuminated solid-state imaging device according to (1), wherein the predetermined voltage is a voltage that stabilizes an inner peripheral surface potential of the groove and suppresses dark current generation.

  According to the present invention, since the diffusion of the signal charge in the direction of the adjacent pixel is suppressed by the trench groove, and the leakage of the incident light in the direction of the adjacent pixel is also suppressed, a subject image with high resolution and less color mixing can be obtained. Imaging can be performed.

  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 backside illumination type solid-state imaging device according to the first embodiment of the present invention. The CCD back-illuminated solid-state image pickup device will be described below, but the present invention is also applicable to a MOS-type solid-state image pickup device in which a signal readout circuit is constituted by a transistor.

  In FIG. 1, an n region 3 that constitutes a photodiode and an n region 4 that constitutes a buried channel of a charge transfer path are provided on the surface side of the silicon substrate 2 on which the back-illuminated solid-state imaging device 30 is manufactured. . A p region 5 is provided on the side and lower side (back side) of the n region 4.

  A gate insulating film 6 is formed on the surface of the silicon substrate 2, a transfer electrode (polysilicon electrode) 7 is formed on the n region 4 via the gate insulating film 6, and an insulating layer 8 is formed thereon. A light shielding film 9 is laminated. A p-layer 10 for suppressing dark current is provided on the surface of the n region 3.

  A planarizing film 11 is laminated on the light shielding film 9, and a support substrate 12 is provided thereon. A p layer 13 is formed on the rear surface of the semiconductor substrate 2, a color filter layer 14 is laminated thereon, and a microlens 15 is laminated thereon. The p-layer 13 on the back side is connected to the ground via the wiring 16.

  The back-illuminated solid-state imaging device 30 of the present embodiment is further provided so that an element isolation region 31 having a trench structure that separates adjacent pixels extends from the back side to the vicinity of the n region 4.

  The element isolation region 31 includes a thin p region 31a having a side wall (inner peripheral surface) portion and a central cavity 31b. In the case of manufacturing, although details will be described later, first, a trench having a trench structure of about 0.4 μm width and a depth of about 6 μm is formed from the back side of the semiconductor substrate 2 by a lithography technique, and is formed on the side wall of the trench. A thin p region 31a is formed by diffusing impurities of a conductivity type (p type in this example) different from that of the photoelectric conversion portion (n region 3), and then the color filter layer 14 and the microlens layer 15 are laminated. .

  When a trench groove is formed in the semiconductor substrate 2, dark current is generated due to the interface state of the side wall. By diffusing impurities of the opposite conductivity type into this side wall portion, the interface state is shielded by the p region 31a and dark. Generation of current is suppressed.

  In the illustrated embodiment, since the bottom surface of the trench groove reaches the p region 5, the bottom surface is shielded by the p region 5. If the bottom surface of the trench groove is separated from the p region 5, a p layer is also formed on the bottom surface when the p region 31 a is formed (diffusion of p-type impurities). Occurrence is suppressed.

  In the back-illuminated solid-state imaging device 30 having such a structure, when light from a subject enters through the microlens 15 and the color filter layer 14, the incident light enters the semiconductor substrate 2 while being condensed in the direction of the n region 3. Then, photoelectric conversion is performed to generate signal charges (electrons).

  This signal charge is suppressed in the lateral direction (adjacent pixel direction) by the cavity 31b of the element isolation region 31, is captured by the signal charge capture region 3a, and is read out to the n region 4 of the vertical charge transfer path. The image is output to the outside as a captured image signal. On the other hand, holes generated by photoelectric conversion are captured by the p layer 13 and discarded to the ground.

  Some of the incident light tends to leak directly into the adjacent pixel direction in the semiconductor substrate 2, but this light is the inner peripheral surface (perpendicular to the back surface) of the cavity 31 b in the center of the element isolation region 31. And the leakage to the adjacent pixels is suppressed.

  As described above, in the backside illumination type solid-state imaging device 30 according to the present embodiment, the diffusion of signal charges to adjacent pixels and the leakage of incident light are both suppressed, so that a captured image signal having a high resolution and a high color SN can be obtained. Can be obtained.

  FIG. 2 is a schematic cross-sectional view of an essential part of a backside illumination type solid-state imaging device 40 according to the second embodiment of the present invention. The structure of the backside illumination type solid-state imaging device 40 of this embodiment is basically the same as that of the first embodiment. The difference is that in the first embodiment, the cavity 31b is left in the element isolation region 31, but in this embodiment, the element isolation region 41 is divided into a p region 41a having a thin sidewall and a cavity (the cavity 31b portion in FIG. 1). This is a point constituted by the buried conductive material 41b.

  The conductive material 41b is preferably a light-shielding and conductive metal, and for example, aluminum, tungsten, cobalt, nickel, molybdenum or the like used as a wiring or a light-shielding film is preferable.

  According to the present embodiment, since the cavity of the element isolation region 41 is filled with a light-shielding metal, it is possible to further prevent light from directly entering the adjacent pixel direction as compared with the first embodiment. It becomes possible. Further, if an arbitrary electric field is applied to the conductive material 41b from the outside through a wiring or the like not shown, this electric field is applied to the deep part of the substrate 2 and the potential near the trench interface can be modulated. As a result, the dark current in the p region 41a at the interface of the trench groove can be more effectively suppressed.

  FIG. 3A is a cross-sectional view of a main part and a wiring diagram of a backside illumination type solid-state imaging device 40 according to the third embodiment of the present invention. FIG. 3B is a potential diagram at the cross-sectional position along the line ABC in FIG.

  The structure of the backside illumination type solid-state imaging device 40 of the present embodiment is the same as that of the second embodiment. The difference is that a switch 45 is provided to switch the voltage applied through the conductive material 41b through the wiring 44 and the p layer 13 to the deep part of the substrate 2 between a low voltage and a high voltage.

  The connection between the wiring 44 and each conductive material 41 b may be performed by vapor deposition or the like on the back surface of the substrate 2, or may be performed through the p layer 13. Furthermore, the wiring 44 and each conductive material 41b may be connected in all pixels, or the wiring 44 and the switch 45 may be provided separately for each column, row, and partial region pixel.

  In the back-illuminated solid-state imaging device 40 having such a wiring connection, by applying a predetermined high voltage to the conductive material 41b at a predetermined timing, the charge in the electron capture region 3a can be discharged to the outside of the substrate via the wiring 44. An electronic shutter function can be realized. For example, if the charge of the electron capture region 3a of the pixel for each row is discharged, a rolling shutter is realized, and if the charge of all the pixels is discharged at once, an operation suitable for still image shooting can be performed.

  When the electrode for drawing the wiring 44 is provided in the solid-state imaging device chip, the electronic shutter wiring can be efficiently manufactured by providing it in the area of the invalid pixel provided around the light receiving surface of the solid-state imaging device.

  FIG. 4 is a schematic cross-sectional view of an essential part of a backside illumination type solid-state imaging device 50 according to the fourth embodiment of the present invention. The structure of the backside illumination type solid-state imaging device 50 of this embodiment is basically the same as that of the first embodiment. The difference is that in the first embodiment, the cavity 31b is left in the center of the element isolation region 31, but in this embodiment, the element isolation region 51 is divided into a p region 51a having a thin sidewall and a cavity (the cavity of FIG. 1). 31b portion) and a light absorbing member 51b embedded therein.

  For example, a color filter material is used for the light absorbing member 51b. That is, the light absorbing member used in the element isolation region 51 provided between the red pixel and the green pixel uses a material obtained by mixing a red color filter material and a blue color filter material. As a result, light leakage between the red pixel and the green pixel can be suppressed.

  Although the second, third, and fourth embodiments described above have been described separately, a back-illuminated solid-state imaging device that combines a plurality of these embodiments can also be provided.

  FIG. 5 is a main manufacturing process diagram when manufacturing the back-illuminated solid-state imaging device according to the above-described embodiment. First, as shown in FIG. 5A, a semiconductor substrate (wafer) 2 is prepared, and trench grooves 55 are formed in a grid shape by lithography using laser light (FIG. 5B). At this time, a potential gradient as described in Patent Documents 1 and 2 may be formed in the thickness direction of the substrate 2.

  5C, p-type impurities are thermally diffused to form p regions (31a, 41a, and 51a in the first, second, third, and fourth embodiments) on the inner peripheral surface in the trench groove 55. In FIG. Form. Then, as shown in FIG. 5D, the support substrate 56 such as another semiconductor wafer is bonded to the surface where the trench groove 55 is formed.

  In the next FIG. 5 (e), the surface of the substrate 2 (surface opposite to the support substrate 56) is polished so that the thickness of the substrate 2 is about 5 μm to 10 μm. In FIG. On the front surface side, the n regions 3, 4, the electrode film 7, etc. described in the embodiment are formed, and the front surface structure of the backside illumination type solid-state imaging device is formed. Next, in FIG. 5G, the support substrate 56 is all removed, and the back-illuminated solid-state imaging device is taken out as shown in FIG.

  In the description of FIG. 5, the potential gradient in the substrate thickness direction is manufactured in the process of FIG. 5B, but it can also be manufactured in the process after FIG. Also, the diffusion of the p-type impurity can be performed not by FIG. 5C but by the process of FIG. 5H.

  As described above, according to the embodiments of the present invention, the light receiving area can be widened compared to the front-illuminated type, and the back-illuminated solid-state imaging has the advantages of high quantum efficiency and high sensitivity. Since the diffusion of signal charges and light leakage generated between adjacent pixels in the element can be effectively suppressed by the trench groove, it is possible to capture a high-quality subject image with high resolution and little color mixing.

  The backside illumination type solid-state imaging device according to the present invention is useful as a solid-state imaging device mounted on a digital camera or the like because it can capture a high-resolution subject image with little color mixing.

It is a principal part cross-sectional schematic diagram of the backside illumination type solid-state image sensor which concerns on 1st Embodiment of this invention. It is a principal part cross-sectional schematic diagram of the backside illumination type solid-state image sensor which concerns on 2nd Embodiment of this invention. It is a principal part cross-sectional schematic diagram of the backside illumination type solid-state image sensor which concerns on 3rd Embodiment of this invention. It is a principal part cross-sectional schematic diagram of the backside illumination type solid-state image sensor which concerns on 4th Embodiment of this invention. It is a principal part manufacturing-process figure of the back irradiation type solid-state image sensor which concerns on embodiment of this invention. It is a principal part cross-sectional view of the conventional back irradiation type solid-state image sensor. FIG. 7 is a potential diagram along a section VII-VII in FIG. 6.

Explanation of symbols

2 Semiconductor substrate 3 n region (electron capture region)
4 n region (Built-in channel of charge transfer path)
14 Color filter 15 Microlens 30, 40, 50 Back-illuminated solid-state imaging device 31, 41, 51 Element isolation region 31a, 41a, 51ap region 31b Cavity (groove) portion 41b Conductive material 51b Light absorbing material

Claims (2)

A plurality of photodiodes are formed in a two-dimensional array on the first surface (hereinafter referred to as the front surface) side of the semiconductor substrate, and generated by light incident from the second surface (hereinafter referred to as the back surface) side of the semiconductor substrate. In the back-illuminated solid-state imaging device in which each of the photodiodes detects a signal charge, an element isolation region having a trench structure groove that separates each of the photodiodes from the adjacent photodiode is formed on the back surface side, The groove is filled with a metal that blocks light, and a wiring for applying a predetermined voltage from the outside is connected to the metal, and when the predetermined voltage is applied at the time of an electronic shutter, the accumulated charge of the photodiode is separated from the previous element. A back-illuminated solid-state imaging device, which is disposed through the metal in a region .   The backside illuminated solid-state imaging device according to claim 1, wherein the predetermined voltage is a voltage that stabilizes an inner peripheral surface potential of the groove and suppresses dark current generation.

Images