JP2009259934A - Solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging device preventing incidence of an infrared ray from a wiring layer-side on a photoelectric conversion device. <P>SOLUTION: The solid-state imaging device includes: a semiconductor substrate having a light receiving face on one face; a wiring layer arranged on the other face of the semiconductor substrate; an imaging pixel part disposed between the light receiving face and the wiring layer; and a peripheral circuit part installed on the other face-side of the semiconductor substrate, which is at a periphery of the imaging pixel part. The imaging pixel part includes: a plurality of photoelectric conversion devices arranged in a two-dimensional array shape; a device separating layer dividing the photoelectric conversion device at every pixel; and an infrared ray cut filter film or a shielding film which is partially installed between the photoelectric conversion device and the wiring layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solid-state image sensor, and more particularly to a back-illuminated solid-state image sensor.

  As solid-state imaging devices, CCD (Charge Coupled Device) type and CMOS (Complementary Metal-Oxide-Semiconductor) type are known, but in recent years, digital still cameras and camera-equipped mobile phones have been reduced in size and power consumption. Along with this, CMOS type solid-state imaging devices are often used.

  Also, a thinned semiconductor substrate is used, and a light receiving unit side element including a photodiode is provided on one surface (light receiving surface) side, and an electric signal is transmitted to the outside on the other surface side on the opposite side. A backside illumination type CMOS image sensor having a structure in which a wiring layer for input / output is provided has been proposed and developed (for example, Patent Document 1).

However, the back-illuminated solid-state imaging device needs to reduce the thickness of the semiconductor substrate because the signal charge needs to be read and processed from the light receiving surface side to the signal processing circuit formed on the opposite surface side. When long-wavelength light such as infrared light is incident, there is a possibility that light that is easily transmitted to the wiring layer side and reflected by the wiring layer enters the photodiode of the adjacent pixel and causes color mixing. is there.
JP 2005-217439 A

  The present invention provides a solid-state imaging device that prevents the incidence of infrared light from the wiring layer side to the photoelectric conversion device.

  According to one aspect of the present invention, a semiconductor substrate having a light receiving surface on one surface, a wiring layer provided on the other surface of the semiconductor substrate, and provided between the light receiving surface and the wiring layer. An imaging pixel unit, and a peripheral circuit unit provided around the imaging pixel unit and on the other surface side of the semiconductor substrate, and the imaging pixel unit is arranged in a two-dimensional array A plurality of photoelectric conversion elements, an element isolation layer that divides the photoelectric conversion elements for each pixel, and at least an infrared cut filter film or a light shielding film provided partially between the photoelectric conversion elements and the wiring layer, A solid-state imaging device is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the solid-state image sensor which prevented incidence | injection of the infrared light from the wiring layer side with respect to a photoelectric conversion element is provided.

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

  The solid-state imaging device according to the embodiment of the present invention has a structure in which a photodiode, various transistors, and the like are formed on a thin semiconductor substrate having a thickness of, for example, 10 μm or less, and a multilayer wiring structure portion is provided thereon. This is a so-called back-illuminated solid-state imaging device in which light incident from the back surface (surface opposite to the surface provided with the multilayer wiring structure portion) of the semiconductor substrate is received by a photodiode. In the present embodiment, a CMOS image sensor will be described as an example of the solid-state imaging device.

  FIG. 1 is a schematic diagram illustrating a planar layout of an imaging pixel unit (sensor unit) 11 and peripheral circuit units 12 to 18 in a solid-state imaging device according to an embodiment of the present invention.

  An imaging pixel unit 11 and peripheral circuit units 12 to 18 are provided on one semiconductor chip (semiconductor substrate) 10.

  The imaging pixel unit 11 includes, for example, photodiodes as a large number of photoelectric conversion elements arranged in a two-dimensional array. One photoelectric conversion element corresponds to one pixel.

  The peripheral circuit unit includes a signal processing circuit that processes an electrical signal (pixel signal) output from the imaging pixel unit 11, and a drive control circuit that drives each pixel of the imaging pixel unit 11 to control the output of the pixel signal. Have.

  Each pixel is sequentially selected in units of horizontal lines (rows) in the vertical direction by the vertical selection means 12, and the transistors of each pixel are controlled by various pulse signals from the timing generator 13, so that the signals of each pixel are correlated. Read out to the double sampling circuit 14.

  The correlated double sampling circuit 14 performs signal processing such as correlated double sampling on the pixel signal. The horizontal selection means 15 outputs the output signal of the correlated double sampling circuit 14 to the gain control circuit 18, and the gain control circuit 18 performs predetermined gain control on the output signal. The A / D conversion circuit 17 converts the output signal of the gain control circuit 18 from analog to digital. The digital amplifier 16 performs amplification and buffering on the digital signal output of the A / D conversion circuit 17.

  FIG. 2 is a schematic diagram illustrating a cross-sectional structure of a main part of the solid-state imaging device according to the embodiment of the present invention.

In a P-type semiconductor substrate (for example, a silicon substrate) 10, a region corresponding to the imaging pixel unit 11 is divided (separated) for each pixel by a P ⁺ -type element isolation layer 22 and is in a two-dimensional array shape. A plurality of N-type diffusion layers 23 arranged in the same manner are formed.

A P ⁺ -type surface layer 24 is formed on one surface side of the N-type diffusion layer 23 and the element isolation layer 22. The N type diffusion layer 23 and the P ⁺ type surface layer 24 are PN-junctioned, and these constitute a photodiode 30 as a photoelectric conversion element.

Further, in the semiconductor substrate 10, one surface side on which the P ⁺ type surface layer 24 is formed functions as a light receiving surface 50, and color filters R, G, B, a micro lens 29, and the like are provided on the light receiving surface 50 side. It has been.

  An insulating film 25 such as a silicon oxide film is formed on the light receiving surface 50, and a light shielding film 28 such as aluminum is formed on the insulating film 25. The light shielding film 28 exists over one side (light receiving surface 50) side of the semiconductor substrate 10 but does not shield the entire surface, and faces a portion facing the N-type diffusion layer 23 and an alignment mark 31 described later. The part to be opened is opened.

  A passivation film 26 such as a silicon nitride film is formed on the insulating film 25 so as to cover the light shielding film 28. On the passivation film 26, red, green, and blue color filters R, G, and B are formed corresponding to the position of the N-type diffusion layer 23, and are flat so as to cover the color filters R, G, and B. An organic layer (for example, an organic film) 27 is formed. The planarizing layer 27 is provided with microlenses 29 at positions corresponding to the color filters R, G, and B.

  In the semiconductor substrate 10, the P-type semiconductor layer 20, the multilayer wiring structure portion, and the support substrate 41 are provided on the other surface opposite to the light receiving surface 50.

  In the P-type semiconductor layer 20, an FD (Floating Diffusion) portion 36 is selectively formed in a region corresponding to the imaging pixel portion 11, in which the charge photoelectrically converted by the photodiode 30 is transferred and accumulated. The FD portion 36 is formed at a position slightly shifted laterally with respect to the N-type diffusion layer 23. A transfer gate 37 is provided above the FD portion 36 at a position shifted to the N-type diffusion layer 23 side through a gate insulating film.

  An infrared cut filter film (or a light shielding film) 21 is selectively provided between the N-type diffusion layer 23 and the P-type semiconductor layer 20. The infrared cut filter film (or light-shielding film) 21 is provided at a position where the N-type diffusion layer 23 is shielded when viewed from the P-type semiconductor layer 20 side, but does not shield all of the N-type diffusion layer 23. In the N-type diffusion layer 23, a part on the FD portion 36 side is in contact with the P-type semiconductor layer 20. Through this portion, charges generated in the N-type diffusion layer 23 by photoelectric conversion can be transferred to the FD portion 36.

The infrared cut filter film (or light-shielding film) 21 has characteristics that do not transmit infrared light having a wavelength of at least about 700 nm or more, and also has electrical insulation.
FIG. 3 shows a specific configuration example of the infrared cut filter film 21.

The infrared cut filter film 21 has a structure in which two types of dielectric films having different refractive indexes (there is a difference in refractive index) are alternately and repeatedly stacked. On the first layer on the semiconductor substrate 10 side, a high refractive index film 51 is formed with a thickness of λ / 2 (λ is the wavelength of infrared light). A low refractive index film 52 having a thickness of λ / 4 is formed on the second layer thereon, and a high refractive index film 51 having a thickness of λ / 4 is formed on the third layer thereon. Thereafter, a laminated structure in which the second layer and the third layer are alternately repeated is formed, and the high refractive index film 51 is formed on the uppermost layer with a thickness of λ / 2. Examples of the material of the high refractive index film 51 include TiO ₂ (refractive index n = 2.4 to 2.5) and ZrO (refractive index n = 2.4). Examples of the material for the low refractive index film 52 include SiO ₂ (refractive index n = 1.46).
Further, a light shielding film 21 having a light shielding property against visible light as well as infrared light may be used. As this light shielding film, for example, a material containing at least one of titanium nitride, chromium oxide, silica, and alumina can be used.

  Referring to FIG. 2 again, in the P-type semiconductor layer 20, N-type diffusion regions 32 and 33 functioning as sources and drains of various transistors 35 are formed in regions corresponding to the peripheral circuit portion outside the imaging pixel portion region. Has been. A gate electrode 34 is provided between the N-type diffusion regions 32 and 33 via a gate insulating film.

  An infrared cut filter film (or a light shielding film) 21 is provided between the portion where the transistor 35 is formed and the semiconductor substrate 10. The infrared cut filter film (or light shielding film) 21 shields the peripheral circuit portion where the transistor 35 is formed when viewed from the back surface (light receiving surface 50) side of the semiconductor substrate 10.

  In the P-type semiconductor layer 20, an alignment mark 31 made of a metal film such as aluminum is formed on the outer side of the peripheral circuit portion. As shown in FIG. 1, the alignment mark 31 is formed in a line shape, for example.

  On the P-type semiconductor layer 20, a multilayer wiring structure having a plurality of wiring layers 38 and an interlayer insulating film 39 is provided. A support substrate 41 is provided on the multilayer wiring structure. An electrode pad 40 connected to the wiring layer 38 is formed on the surface side of the interlayer insulating film 39. Electrode terminals 45 are formed at positions facing the electrode pads 40 on the surface of the support substrate 41. The electrode pad 40 and the electrode terminal 45 are connected via a conductive material 43 provided through the support substrate 41.

  The solid-state imaging device according to this embodiment configured as described above is a backside illumination type, and light enters from the backside (light receiving surface 50) side of the semiconductor substrate 10. The incident light is collected by the micro lens 29, passes through the color filters R, G, and B, and enters the photodiode 30.

  Light incident on the photodiode 30 is photoelectrically converted, and charges generated thereby are transferred and accumulated in the FD unit 36 by the transfer transistor, and the potential fluctuation of the FD unit 36 is detected by the amplification transistor and output to the peripheral circuit unit. Is done.

  Here, FIG. 10 shows a solid-state imaging device of a comparative example. The solid-state image sensor of this comparative example is different from the solid-state image sensor according to this embodiment described above in that it does not have the infrared cut filter film (or light-shielding film) 21.

  In the back-illuminated solid-state imaging device, the thickness of the semiconductor substrate is generally required to be as thin as 10 μm or less because it is necessary to read and process signal charges from the light receiving surface side to the signal processing circuit formed on the opposite surface side. When long wavelength light such as infrared light is incident, it is easily transmitted to the wiring layer 38 side as shown by the one-dot chain line in the comparative example of FIG. The reflected light may enter the photodiode 30 of the adjacent pixel and cause color mixing.

  On the other hand, in this embodiment, since the infrared cut filter film (or light shielding film) 21 is provided between the photodiode 30 and the wiring layer 38, the wiring is transmitted from the light receiving surface 50 through the element isolation layer 22. Even if the long-wavelength light (infrared light) reaching the layer 38 is reflected by the wiring layer 38, the reflected light is prevented from being incident on the photodiode 30 by the infrared cut filter film (or light shielding film) 21; Will not cause.

  Next, an example of a method for manufacturing the solid-state imaging device according to the present embodiment will be described with reference to FIGS.

  First, as shown in FIG. 4A, an infrared cut filter film (or a light shielding film) 21 is selectively formed on a P-type silicon semiconductor substrate 10. The infrared cut filter film (or light shielding film) 21 has a structure as described above with reference to FIG. 3, for example. The infrared cut filter film (or light shielding film) 21 is first formed on the entire surface of the semiconductor substrate 10, and then a desired portion is opened by selective etching.

  Next, using the surface portion of the semiconductor substrate 10 exposed at the opening of the infrared cut filter film (or light shielding film) 21 as a crystal growth seed, the P-type semiconductor layer 20 is selected as shown in FIG. Epitaxial lateral growth (ELO) is performed. The infrared cut filter film (or light shielding film) 21 needs to be made of a material that can withstand the temperature in this epitaxial growth process.

  The P-type semiconductor layer 20 also grows on the infrared cut filter film (or light shielding film) 21, and crystals grown from the opening side are bonded near the center on the infrared cut filter film (or light shielding film) 21. Since this coupling portion 20a is a portion where the crystallinity is poor and defects are concentrated, the FD portion formed in the P-type semiconductor layer 20 in the later process, the N-type diffusion region serving as the source and drain, etc. Form on the avoidance part.

After the surface of the P-type semiconductor layer 20 is polished flat by, for example, a CMP (Chemical Mechanical Polishing) method, the N-type diffusion layer 23, the P ⁺ -type element isolation layer 22, the FD portion 36, and transfer are performed for the imaging pixel region. A gate 37, a signal amplification transistor and the like are formed, and a signal processing transistor and the like are formed for the peripheral circuit portion. The N-type diffusion layer 23, the element isolation layer 22, the FD portion 36, and the N-type diffusion regions 32 and 33 can be formed by ion implantation of various impurities from the P-type semiconductor layer 20 side.

  In addition to the formation of these elements, the alignment mark 31 is formed as a metal pattern such as aluminum on the surface layer portion of the P-type semiconductor layer 20 outside the peripheral circuit portion. The alignment mark 31 is used for alignment with an element formed on the front surface side when forming an element on the back surface (light receiving surface) side of the semiconductor substrate 10 in a later process.

  Next, as shown in FIG. 5A, a multilayer wiring structure having a multilayer wiring layer 38 and an interlayer insulating film (for example, silicon oxide layer) 39 is formed on the P-type semiconductor layer 20. Furthermore, an electrode pad 40 connected to the wiring layer 38 is also formed on the surface of the interlayer insulating film 39.

  After the surface of the multilayer wiring structure is flattened, a support substrate 41 is pasted thereon as shown in FIG. The support substrate 41 functions as a support when the back surface side is polished to reduce the thickness of the semiconductor substrate 10.

Next, the back surface side of the semiconductor substrate 10 is polished until the N-type diffusion layer 23 is exposed to reduce the thickness of the semiconductor substrate 10, and then the alignment mark 31 is irradiated with infrared rays from the back surface side to detect the alignment mark 31. while performing alignment with, as shown in FIG. 6 (a), on the back side of the isolation layer 22 and the N-type diffusion layer 23 in the image pickup pixel region, for example, boron is ion-implanted P ⁺ -type surface layer 24 Form. Since the infrared cut filter film (or light-shielding film) 21 is not formed on the portion facing the alignment mark 31, the alignment mark 31 can be detected by infrared irradiation from the back side of the semiconductor substrate 10.

  Next, after covering the back surface of the semiconductor substrate 10 with a protective film, as shown in FIG. 6B, a through via 42 reaching the electrode pad 40 is formed on the support substrate 41, and thereafter, FIG. As shown, the conductive material 43 is embedded in the through via 42, and the electrode terminal 45 is formed on the conductive material 43 on the surface of the support substrate 41.

  Next, the protective film formed on the back surface side of the semiconductor substrate 10 is removed, and the surface of the support substrate 41 is covered with a protective film, and then, as shown in FIG. A film (for example, a silicon oxide film) 25, a light shielding film (for example, a metal film such as aluminum) 28, and a passivation film (for example, a silicon nitride film) 26 are formed.

  Thereafter, the color filters R, G, and B, the planarizing layer 27, the microlens 29, and the like shown in FIG. 2 are formed on the light receiving surface side, and further divided into chips for each chip from the wafer state. An image sensor (CMOS image sensor chip) is obtained.

  FIG. 8 is a schematic diagram showing a cross-sectional structure of a main part of a solid-state imaging device according to another embodiment of the present invention. The same elements as those of the above-described solid-state imaging device shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the solid-state imaging device shown in FIG. 8, an infrared cut filter film (or light shielding film) 21 is also provided between the element isolation layer 22 and the P-type semiconductor layer 20. In the imaging pixel portion region, the infrared cut filter film (or light shielding film) 21 is formed over the entire surface excluding a part 23 a of the N-type diffusion layer 23. This part 23 a is a path for transferring charges generated in the N-type diffusion layer 23 by photoelectric conversion to the FD 36 by the operation of the transfer gate 37.

  According to the structure shown in FIG. 8, since there is an infrared cut filter film (or light shielding film) 21 between the element isolation layer 22 and the wiring layer 38, the element isolation layer 22 is incident from the light receiving surface 50 side. Incident long wavelength light (infrared light) can be prevented from entering the wiring layer 38 side. That is, the infrared light incident from the light receiving surface 50 side does not reach the wiring layer 38, and therefore, no color mixing occurs due to the reflected light from the wiring layer 38 entering the photodiode 30.

  Next, FIG. 9 shows a schematic diagram of a camera module using the solid-state imaging device (indicated by reference numeral 60 in FIG. 9) according to the embodiment of the present invention described above with reference to FIG. 2 and FIG.

  Conductive bumps 67 are provided between the electrode terminals 45 of the solid-state image sensor 60 and the circuit board 70, and the solid-state image sensor 60 is electrically connected to the circuit board 70 and mounted via the bumps 67. Has been. Resin spacers 65 are provided at the joint between the solid-state imaging device 60 and the circuit board 70.

  The light receiving surface of the solid-state imaging device 60 faces the optical lens 61 with a space therebetween. The optical lens 61 is held by, for example, a cylindrical lens holder 62. A resin spacer 64 is provided between the lens holder 62 and the solid-state imaging device 60. Further, in this camera module, a metal shield 63 is formed on the outer surface of the other elements excluding the optical lens 61.

  2. Description of the Related Art In recent years, camera-type mobile phones have been made thinner, and low-profile camera modules having a WLCM (Wafer Level Camera Module) structure have been developed. However, in the case of this structure, there is a problem that infrared light is incident from the gap on the back side of the camera module, and the wiring layer pattern formed on the surface of the semiconductor substrate 10 opposite to the light receiving surface is imaged. .

  However, according to the present embodiment, as described above with reference to FIG. 2 or FIG. 8, even if infrared light leaks and enters from the opposite side of the light receiving surface, the infrared cut filter film (or light shielding film) 21 prevents the infrared light from entering the photodiode 30 and the wiring layer 38 is not imaged.

  Further, since the infrared cut filter film (or the light shielding film) 21 is also provided in the peripheral circuit portion, the infrared light leaked from the back surface (surface opposite to the light receiving surface) side of the peripheral circuit portion is directly The light enters the transistor in the peripheral circuit section, or reaches the light shielding film 28 that is a metal film and reflects, and the reflected light reaches the photodiode 30 and the wiring layer 38 in the adjacent transistor, the imaging pixel region, and enters. Can be prevented.

  Here, FIG. 11 shows a camera module of a comparative example. In addition, the same code | symbol is attached | subjected to the element corresponding to FIG. When using the solid-state image sensor 80 not provided with the infrared cut filter film (or light-shielding film) 21 as in this embodiment, as shown in FIG. 11, the light-receiving surface of the solid-state image sensor 80 and the optical lens 61 It is conceivable to incorporate a film-like infrared cut filter 71 between them.

  However, in this case, since the infrared cut filter 71 is incorporated as a part of the camera module, the height of the entire module is increased and the height is reduced compared to the embodiment of the present invention in which the infrared cut filter film 21 is formed as a thin film on the semiconductor substrate. This is disadvantageous to the increase in the number of parts in the assembly process. In addition, in the structure of FIG. 11, it is impossible to prevent the wiring pattern from being captured by infrared light that leaks from the opposite side of the light receiving surface.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to them, and various modifications can be made based on the technical idea of the present invention.

  In forming the N-type diffusion layer 23 and the element isolation layer 22, the semiconductor substrate 10 is attached to the support substrate 41, and then the light receiving surface side of the semiconductor substrate 10 is polished and thinned. The N-type diffusion layer 23 and the element isolation layer 22 may be formed by ion implantation.

The schematic diagram which shows the planar layout of the imaging pixel part and peripheral circuit part in the solid-state image sensor which concerns on embodiment of this invention. The schematic diagram which shows the principal part cross-section of the solid-state image sensor concerning embodiment of this invention. The schematic diagram which shows the specific structural example of the infrared cut filter film | membrane in the solid-state image sensor which concerns on embodiment of this invention. The schematic diagram which shows an example of the manufacturing method of the solid-state image sensor which concerns on embodiment of this invention. The schematic diagram which shows the process of following FIG. FIG. 6 is a schematic diagram illustrating a process following FIG. 5. FIG. 7 is a schematic diagram illustrating a process following FIG. 6. The schematic diagram which shows the principal part cross-section of the solid-state image sensor which concerns on other embodiment of this invention. The schematic diagram of the camera module incorporating the solid-state image sensor which concerns on embodiment of this invention. The schematic diagram which shows the principal part cross-section of the solid-state image sensor which concerns on a comparative example. The schematic diagram of the camera module which concerns on a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate, 11 ... Imaging pixel part, 20 ... P type semiconductor layer, 21 ... Infrared cut filter film (or light shielding film), 22 ... Element isolation layer, 23 ... N type diffused layer, 24 ... P ⁺ type surface layer , 30 ... Photoelectric conversion element (photodiode), 31 ... Alignment mark, 36 ... FD (Floating Diffusion) part, 37 ... Transfer gate, 38 ... Wiring layer, 41 ... Support substrate, 50 ... Light receiving surface

Claims (5)

A semiconductor substrate having a light receiving surface on one side;
A wiring layer provided on the other surface of the semiconductor substrate;
An imaging pixel portion provided between the light receiving surface and the wiring layer;
A peripheral circuit portion provided around the imaging pixel portion and on the other surface side of the semiconductor substrate;
With
The imaging pixel unit includes:
A plurality of photoelectric conversion elements arranged in a two-dimensional array;
An element isolation layer that divides the photoelectric conversion element for each pixel;
At least an infrared cut filter film or a light shielding film partially provided between the photoelectric conversion element and the wiring layer;
A solid-state imaging device comprising:   The solid-state imaging device according to claim 1, wherein the infrared cut filter film or the light shielding film is further provided between the element isolation layer and the wiring layer.   3. The solid-state imaging device according to claim 1, wherein the infrared cut filter film or the light shielding film is further provided between the light receiving surface and the peripheral circuit unit. An alignment mark is formed outside the peripheral circuit portion,
The infrared cut filter film or the light shielding film is not provided between the light receiving surface and the alignment mark, and the alignment mark can be read from the light receiving surface side using infrared rays. Item 4. The solid-state imaging device according to any one of Items 1 to 3.   The infrared cut filter film or the light shielding film includes at least one of titanium oxide, silicon oxide, zirconium oxide, titanium nitride, chromium oxide, silica, and alumina. The solid-state imaging device described.

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