JP2012234968A - Solid state image pickup device, manufacturing method of the same and electronic information apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state image pickup device 100 which enables a multiple interference effect increasing light incidence efficiency, and in addition, enables mitigation of tensile stress of a silicon in the first place and inhibition of metal contamination to a silicon substrate in the second place.SOLUTION: A solid state image pickup device 100 comprises a light transmission film 123 formed on a second surface of a silicon substrate 101. The light transmission film 123 has a structure in which a silicon oxide film (first transparent insulation film) 102 formed on the second surface of the silicon substrate 101 and a silicon nitride film (second transparent insulation film) 103 formed on the silicon oxide film 102 and having a refraction factor higher than that of the silicon oxide film are laminated in such a manner that a reflection factor of incident light at the second surface of the silicon substrate periodically becomes local minimum with an increase in thickness of the silicon nitride film. The thickness of the silicon nitride film 103 is set within a range including only a second period local minimum value as the local minimum value of the reflection factor.

Description

  The present invention relates to a solid-state imaging device, a method for manufacturing the same, and an electronic information device, and in particular, a solid-state imaging device such as a CMOS image sensor or a CCD image sensor with reduced dark current and white spot defects, and such dark current. The present invention also relates to a method for manufacturing a solid-state imaging device with few white spot defects, and an electronic information device equipped with such a solid-state imaging device.

  In recent years, a back-illuminated solid-state imaging device has been developed as a high-sensitivity solid-state imaging device. This back-illuminated solid-state imaging device is configured such that a circuit element, a wiring layer, or the like is formed on the surface side of a silicon substrate, and light is incident from the back side of the silicon substrate to perform imaging.

  In the solid-state imaging device having such a configuration, it is possible to increase the aperture ratio for light reception and to suppress the absorption or reflection of incident light reaching the photoelectric conversion element.

  For example, in Patent Document 1, in a back-illuminated solid-state imaging device, a method of improving light transmittance in a transparent insulating film on a light incident surface side of a substrate and achieving a dark current suppression function and a prevention of quantum efficiency loss For example, a structure in which silicon oxide and silicon nitride are stacked on the back surface of a semiconductor substrate on which a light receiving portion is formed has been proposed.

  FIG. 9 is a diagram for explaining the solid-state imaging device disclosed in Patent Document 1 and shows a cross-sectional structure of the main part of the light receiving unit.

  In the solid-state imaging device 50, a semiconductor substrate 1 made of, for example, p-type silicon is used. The thickness of the semiconductor substrate 1 is 4 to 6 μm in the solid-state imaging device for visible light, and 6 to 10 μm in the solid-state imaging device for near infrared rays.

  In the surface region of the semiconductor substrate 1, an n-type semiconductor region 2 and a p-type semiconductor region 3 constituting the light receiving unit 4 are formed for each pixel. The n-type semiconductor region 2 is a region that substantially accumulates signal charges photoelectrically converted in the semiconductor substrate 1.

  The p-type semiconductor region 3 is formed on the surface side of the n-type semiconductor region 2 and is a region having a higher concentration of p-type impurities than the semiconductor substrate 1. In this p-type semiconductor region 3, a depletion layer generated between the n-type semiconductor region 2 and the surrounding p-type region is prevented from reaching the surface of the semiconductor substrate 1, and generation of dark current is suppressed. It works to improve quantum efficiency.

  On the surface of the semiconductor substrate 1, an electrode 6 constituting a pixel circuit is formed via an insulating layer 5 made of, for example, silicon oxide. On the insulating layer 5, an interlayer insulating film 7 made of, for example, silicon oxide is formed so as to cover the electrode 6.

  By the way, the solid-state imaging device includes a CCD solid-state imaging device and a CMOS solid-state imaging device. In the CCD solid-state imaging device, the pixel circuit includes a CCD vertical transfer register. In this case, the electrode 6 corresponds to, for example, a transfer electrode of a CCD vertical transfer register, and a transfer channel composed of an n-type region is formed on the semiconductor substrate 1 immediately below the electrode 6.

  On the other hand, in the CMOS type solid-state imaging device, the pixel circuit includes various transistors such as a read transistor, an amplification transistor, a reset transistor, and an address transistor. In this case, the electrode 6 corresponds to, for example, gate electrodes of various transistors, and the source / drain regions of various transistors and floating diffusions are formed on the semiconductor substrate 1.

  Since the semiconductor substrate 1 is thinned to about 4 to 10 μm, a support substrate is formed on the interlayer insulating film 7 as necessary, although not shown. As this support substrate, it is preferable to use the same silicon substrate as the semiconductor substrate 1.

  A transparent first insulating film and a transparent second insulating film having a refractive index higher than that of the first insulating film are formed on the back surface side of the semiconductor substrate 1. Here, a silicon oxide film 8 is formed as the first insulating film, and a silicon nitride film 9 is formed as the second insulating film.

  The thicknesses of the silicon oxide film 8 and the silicon nitride film 9 are higher than those using only the silicon oxide film 8 so that a high transmittance can be obtained for incident light due to the multiple interference effect of light. The thickness is adjusted.

  The thickness of the silicon oxide film 8 is in the range of 15 nm to 40 nm, and the thickness of the silicon nitride film 9 is in the range of 20 nm to 50 nm. In this range, by optimizing the thickness of each other, a higher transmittance can be obtained for incident light than when the silicon oxide film 8 is used alone.

  In this prior art, charges having the same polarity as the signal charges, in this case electrons, are injected into the silicon nitride film 9 at the interface with the silicon oxide film 8 or in the film of the silicon nitride film 9. The reason for adopting the silicon nitride film 9 is that it has good charge retention characteristics as employed in a nonvolatile memory. Second, since the refractive index is higher than that of the silicon oxide film 8, the transmittance is higher with respect to incident light than the case of the silicon oxide film 8 alone due to the multiple interference effect by adjusting the film thickness. .

  In addition, since electrons are accumulated in the silicon nitride film 9, a hole accumulation layer 10 composed of many holes h is induced in the semiconductor substrate 1 near the interface between the semiconductor substrate 1 and the silicon oxide film 8. The As will be described later, the hole accumulation layer 10 prevents generation of dark current and loss of quantum efficiency.

  A protective film 11 is formed on the silicon nitride film 9 to prevent electrons accumulated in the silicon nitride film 9 from escaping to the outside and disappearing. The protective film 11 is preferably made of a material having a low refractive index and little light absorption in the vicinity of visible light. Many of transparent resin films generally used in semiconductor elements can be used, and a silicon oxide film generated by a low temperature plasma CVD method or a silicon oxynitride film formed in the same manner may be used.

  Next, a method for manufacturing the solid-state imaging device will be described.

  FIG. 10 is a diagram for explaining a method for manufacturing the solid-state imaging device, and shows a cross-sectional structure in a main process.

  Here, an example in which a solid-state imaging device is manufactured using an SOI substrate will be described.

  First, as shown in FIG. 10A, an SOI substrate is prepared in which a p-type silicon layer (SOI layer) 1 is formed on a silicon substrate 12 via a silicon oxide film 8. Here, the film thickness of the silicon oxide film 8 is 15 nm to 40 nm.

  Next, a light receiving portion and a pixel circuit are formed on the surface side of the SOI layer 1.

  That is, the n-type semiconductor region 2, the p-type semiconductor region 3, and other various semiconductor regions (not shown) are formed in the SOI layer 1 by ion implantation.

  Subsequently, an insulating layer 5 made of a silicon oxide film is formed, and an electrode 6 is further formed. The electrode 6 is made of, for example, tungsten or aluminum. After the formation of the electrode 6, silicon oxide is deposited to form an interlayer insulating film 7.

  Thereafter, after attaching a support substrate (not shown) on the interlayer insulating film 7, the silicon oxide film 8 is exposed by grinding and etching the silicon substrate 12 using the silicon oxide film 8 as an etching stopper.

  Next, as shown in FIG. 10B, the front and back of the SOI layer 1 are reversed, and a silicon nitride film 9 is formed on the silicon oxide film 8 by, for example, plasma CVD. The film thickness of the silicon nitride film 9 is selected in the range of 20 to 50 nm. If an SOI substrate is not used, the silicon oxide film 8 and the silicon nitride film 9 may be sequentially deposited after the silicon substrate is thinned.

  Next, for example, UV light is irradiated from the back surface side of the SOI layer 1 in a state where the positively charged electrode is opposed to the back surface side of the SOI layer 1. The electrons e near the back surface of the SOI layer 1 are excited by the UV light, and the excited electrons e jump over the silicon oxide film 8 and in the interface between the silicon oxide film 8 and the silicon nitride film 9 or in the film of the silicon nitride film 9. To be captured. Note that it is possible to inject electrons into the interface between the silicon oxide film 8 and the silicon nitride film 9 or into the silicon nitride film 9 only by applying UV light or applying an electric field to the silicon oxide film 8.

  As shown in FIG. 10C, as a result of electrons being accumulated in the interface between the silicon oxide film 8 and the silicon nitride film 9 and in the silicon nitride film 9, in the p-type silicon layer (SOI layer) 1, Holes h gather near the interface with the silicon oxide film 8 to induce the hole accumulation layer 10.

  Next, as shown in FIG. 10D, a protective film 11 is formed on the silicon nitride film 9. As described above, in forming the protective film 11, for example, a transparent resin film is applied, a silicon oxide film is deposited by a low temperature plasma CVD method, or a silicon oxynitride film is deposited by a low temperature plasma CVD method.

  Although not shown, in the subsequent steps, a color filter is formed on the protective film 11 as necessary, and an on-chip lens is formed. Thereby, a solid-state imaging device is manufactured.

  As described above, in this prior art, the thickness of silicon oxide is 15 nm to 40 nm, and the thickness of silicon nitride is 20 nm to 50 nm. As an effect thereof, as shown in FIG. 11, the transmittance for incident light is improved as compared with the case where silicon oxide is used alone due to the multiple interference effect of light using a laminated film of silicon oxide and silicon nitride.

  However, in a back-illuminated solid-state imaging device, since the silicon thickness is usually processed to 10 microns or less, a strong tensile stress is generated on the silicon substrate after the processing. There is a problem in that this tensile stress causes distortion in the silicon substrate and dark current is generated. It is generally known that mechanical stress causes a change in the silicon band gap and increases the leakage current, as described in Non-Patent Document 1, and this is caused by the tensile stress in the back-illuminated solid-state imaging device. Generation of dark current becomes a problem. Furthermore, there is a problem that white point defective pixels are generated due to metal contamination on the silicon substrate. The back-illuminated solid-state imaging device has a drawback that white point defects are likely to occur due to metal contamination because the distance between the silicon substrate, the light-shielding metal film, and the color filter film is shorter than that of the front-illuminated solid-state imaging device.

JP 2010-87530 A

Journal of Applied Physics 103, 026103 (2008)

  As described above, the conventional back-illuminated solid-state imaging device can improve the light transmittance and suppress the dark current, but the back-illuminated solid-state imaging device usually has a thickness of 10 silicon substrate. Since it is processed to a micron or less, a strong tensile stress is generated in the silicon substrate after processing. There is a problem in that this tensile stress generates strain in the silicon substrate and dark current is generated. In addition, suppression of metal contamination on the silicon substrate is insufficient with the above film thickness, and there is a problem that white point defect pixels increase.

  The present invention has been made to solve the above-described problems, and is caused by dark current resulting from back stress of a thinly processed semiconductor substrate and contamination from a metal film formed on the back side of the semiconductor substrate. It is an object of the present invention to obtain a solid-state imaging device capable of suppressing white spot defects caused by the above, a manufacturing method thereof, and an electronic information device equipped with such a solid-state imaging device.

  A solid-state imaging device according to the present invention is a solid-state imaging device including a pixel circuit formed on a first surface side of a semiconductor substrate and configured to photoelectrically convert light incident from the second surface side of the semiconductor substrate. A light receiving portion for generating a signal charge according to the amount of incident light incident on the second surface of the semiconductor substrate and storing the signal charge; and a light transmission formed on the second surface of the semiconductor substrate. A first transparent insulating film formed on the second surface of the semiconductor substrate; and the first transparent insulating film formed on the first transparent insulating film. The second transparent insulating film having a higher refractive index than the refractive index of the film, and the reflectance of incident light on the second surface of the semiconductor substrate is periodic with the increase in the thickness of the second transparent insulating film. The thickness of the second transparent insulating film is set to the minimum value of the reflectance and the second period Is obtained by setting the range including only a small value, the object is achieved.

  A solid-state imaging device according to the present invention is a solid-state imaging device including a pixel circuit formed on a first surface side of a silicon substrate and configured to photoelectrically convert light incident from the second surface side of the silicon substrate. A light receiving portion for generating a signal charge according to the amount of incident light incident on the second surface of the silicon substrate and storing the signal charge, and a light transmission formed on the second surface of the silicon substrate. A light-transmitting film is formed on the second surface of the silicon substrate, and the first transparent insulating film is formed on the first transparent insulating film. A second transparent insulating film having a refractive index higher than the refractive index of the film, wherein the first transparent insulating film is a silicon oxide film having a thickness of 5 nm to 15 nm. The transparent insulating film is a silicon nitride film or a silicon nitride oxide film having a thickness of 100 nm. Are those having a film thickness of the upper 300nm or less, the object can be achieved.

  In the solid-state imaging device according to the aspect of the invention, it is preferable that the silicon nitride film or the silicon nitride oxide film has a thickness of 180 nm to 250 nm.

  The present invention has the light-shielding film formed on the light transmission film in the solid-state imaging device, and the light-shielding film is arranged with effective pixels that perform photoelectric conversion of incident light on the second surface of the semiconductor substrate. It is preferable to have an opening corresponding to the effective pixel region.

  According to the present invention, in the solid-state imaging device, the silicon substrate is a first conductivity type silicon substrate, and the first conductivity type silicon substrate constitutes the light receiving unit and includes a plurality of second conductivity arranged in a matrix. A second conductivity type semiconductor region including the type semiconductor region and constituting the light receiving section is electrically isolated by a high concentration first conductivity type isolation region formed in the first conductivity type silicon substrate. preferable.

  In the solid-state imaging device according to the present invention, the solid-state imaging device includes a light-shielding film formed on the light transmission film, and the light-shielding film performs photoelectric conversion of incident light on the second surface of the first conductivity type silicon substrate. In an effective pixel region where effective pixels are arranged, an optical black located on the high-concentration first conductivity type isolation region and located around the effective pixel region on the second surface of the first conductivity type silicon substrate. The region is preferably formed so as to cover the entire surface of the optical black region.

  According to the present invention, in the solid-state imaging device, a color filter of a predetermined color corresponding to each pixel is formed on the light transmission film, and a microlens is provided on the color filter at a position corresponding to each pixel. Preferably it is formed.

  A solid-state imaging device manufacturing method according to the present invention includes a pixel circuit formed on a first surface side of a semiconductor substrate, and is configured to photoelectrically convert light incident from the second surface side of the semiconductor substrate. A method of manufacturing an apparatus, comprising: forming a light receiving portion that generates a signal charge according to an incident light amount of incident light and accumulates the signal charge on a first surface side of the semiconductor substrate; and Forming the pixel circuit on the first surface of the substrate; forming a planarizing film on the first surface of the semiconductor substrate so as to cover the pixel circuit; and then supporting the first surface side of the semiconductor substrate on the support substrate. A step of affixing to the semiconductor substrate, a step of grinding the second surface opposite to the first surface of the semiconductor substrate to a depth at which the light receiving portion is formed, and a step of thinning the semiconductor substrate, Forming a light transmission film on the second surface side of the substrate. Forming the light transmissive film includes forming a first transparent insulating film on the second surface of the semiconductor substrate; and forming the first transparent insulating film on the first transparent insulating film. The second transparent insulating film having a refractive index higher than the refractive index of the second transparent insulating film is periodically reflected by the second surface of the semiconductor substrate as the thickness of the second transparent insulating film increases. And the thickness of the second transparent insulating film is set to a range including only the minimum value of the second period as the minimum value of the reflectance, thereby The objective is achieved.

  A solid-state imaging device manufacturing method according to the present invention includes a pixel circuit formed on a first surface side of a silicon substrate, and is configured to photoelectrically convert light incident from the second surface side of the silicon substrate. A method of manufacturing an apparatus, comprising: forming a light receiving portion that generates a signal charge according to an incident light amount of incident light and accumulates the signal charge on a first surface side of the silicon substrate; Forming the pixel circuit on the first surface of the substrate; forming a planarizing film on the first surface of the silicon substrate so as to cover the pixel circuit; and then supporting the first surface side of the silicon substrate on the supporting substrate. A step of affixing to the silicon substrate, a step of grinding the second surface opposite to the first surface of the silicon substrate to a depth where the light receiving portion is formed, and thinning the silicon substrate, and the thinned silicon substrate A light-transmitting film is formed on the second surface side The step of forming the light transmissive film includes grinding and thinning the second surface opposite to the first surface of the silicon substrate to a depth at which the light receiving portion is formed. Forming a silicon oxide film as a first transparent insulating film to a thickness of 5 nm or more and 15 nm or less on the second surface of the silicon oxide film, and forming a silicon nitride film as the second transparent insulating film on the silicon oxide film Or a step of forming silicon nitride oxide with a thickness of 100 nm to 300 nm, whereby the above object is achieved.

  An electronic information device according to the present invention is an electronic information device including an imaging unit that captures an image of a subject, and the imaging unit includes the above-described solid-state imaging device according to the present invention. The objective is achieved.

  Next, the operation will be described.

  In the present invention, in the solid-state imaging device, a light transmission film is formed on the second surface of the semiconductor substrate opposite to the first surface on which the pixel circuit is formed, and the light transmission film is formed on the semiconductor substrate. A first transparent insulating film formed on the second surface, and a second transparent insulating film formed on the first transparent insulating film and having a refractive index higher than that of the first transparent insulating film Are stacked so that the reflectance of incident light on the second surface of the semiconductor substrate periodically becomes minimum as the thickness of the second transparent insulating film increases, and the second transparent Since the thickness of the insulating film is set to a range including only the minimum value of the second period as the minimum value of the reflectance, in addition to the multiple interference effect, the thickness of the second transparent insulating film is increased first. This can relieve the tensile stress of silicon and, second, suppress metal contamination of the silicon substrate. It can be.

  As a result, a solid-state imaging device such as a CMOS image sensor with less dark current and white spot defects can be manufactured.

  In the present invention, in the solid-state imaging device, a light transmission film is formed on a second surface of the semiconductor substrate opposite to the first surface on which the pixel circuit is formed, and the light transmission film is formed on the semiconductor substrate. A first transparent insulating film formed on the second surface of the second transparent insulating film, and a second transparent insulating film formed on the first transparent insulating film and having a refractive index higher than that of the first transparent insulating film. An insulating film, a silicon oxide film having a thickness of 5 nm to 15 nm as the first transparent insulating film, and a thickness of 100 nm to 300 nm as the second transparent insulating film. Since a silicon nitride film or a silicon nitride oxide film is used, a laminated structure in which the reflectance of incident light on the second surface of the semiconductor substrate periodically becomes minimum as the thickness of the second transparent insulating film increases. The thickness of the second transparent insulating film is determined by the reflectance. In addition to the multiple interference effect, the thickness of the second transparent insulating film can be increased, and firstly, the tensile stress of silicon can be relaxed. Second, Further, metal contamination to the silicon substrate can be suppressed.

  In the present invention, the light-shielding film is formed on the light-transmitting film, and the light-shielding film has an effective pixel that performs photoelectric conversion of incident light on the second surface of the first conductivity type silicon substrate. The arranged effective pixel region is located on the first conductivity type isolation region, and the optical black region located around the effective pixel region on the second surface of the first conductivity type silicon substrate is the optical pixel region. Since it is formed so as to cover the entire black region, the light shielding film has a negative effect on the dark current and white point defects due to the stress and diffusion of the metal atoms themselves into the silicon substrate. Setting the thickness to 100 nm or more and 300 nm or less has the effect of suppressing contamination in the solid-state imaging device not only in the optical black region but also in the effective pixel region. It is.

  As described above, according to the present invention, the dark current caused by the stress of the semiconductor substrate processed thinly and the white spot caused by the contamination from the metal film formed on the second surface side (back surface side) of the semiconductor substrate. A solid-state imaging device capable of suppressing defects, a manufacturing method thereof, and an electronic information device equipped with such a solid-state imaging device can be obtained.

FIG. 1 is a diagram for explaining a solid-state imaging device according to Embodiment 1 of the present invention. A cross-sectional structure of a main part of the solid-state imaging device (FIG. 1A) and a configuration of a pixel array (FIG. 1B). ). FIG. 2 is a diagram for explaining the solid-state imaging device according to Embodiment 1 of the present invention. A silicon oxide film and a silicon nitride film are formed on the second surface of the semiconductor substrate, and the thickness of the silicon nitride film is increased. In the structure where the reflectance of the incident light on the second surface of the semiconductor substrate is periodically minimized, the change in the reflectance of the incident light when the thickness of the silicon nitride film is changed is shown. FIG. 3 is a diagram for explaining a method of manufacturing the solid-state imaging device according to Embodiment 1 of the present invention, in which a light receiving portion and a pixel circuit are formed on the first surface side (front surface side) of the silicon substrate (FIG. 3A). ) To FIG. 3 (c)). FIG. 4 is a diagram for explaining the method of manufacturing the solid-state imaging device according to Embodiment 1 of the present invention, and shows a state where the first surface side (front surface side) of the silicon substrate is attached to the support substrate. FIG. 5 is a diagram for explaining a method of manufacturing the solid-state imaging device according to Embodiment 1 of the present invention. After polishing the second surface side (back surface side) of the silicon substrate attached to the support substrate, the silicon oxide film and silicon A state in which a nitride film is formed is shown. FIG. 6 is a diagram for explaining the method of manufacturing the solid-state imaging device according to Embodiment 1 of the present invention, in which a color filter is formed after a silicon oxide film and a silicon nitride film are formed on the second surface side (back surface side) of the silicon substrate. And the state which formed the micro lens is shown. FIG. 7 is a diagram for explaining a solid-state imaging device according to Embodiment 2 of the present invention. A cross-sectional structure of a main part of the solid-state imaging device (FIG. 7A) and a configuration of a pixel array (FIG. 7B). ). FIG. 8 is a block diagram showing a schematic configuration example of an electronic information device using the solid-state imaging device of Embodiment 1 or 2 as an imaging unit as Embodiment 3 of the present invention. FIG. 9 is a diagram for explaining the solid-state imaging device disclosed in Patent Document 1, and shows a cross-sectional structure of the main part of the light receiving unit. FIG. 10 is a diagram for explaining a method of manufacturing the solid-state imaging device disclosed in Patent Document 1, and shows a cross-sectional structure in main steps (FIGS. 10A to 10D). FIG. 11 is a diagram for explaining the solid-state imaging device disclosed in Patent Document 1, and transmits blue light and green light with respect to the thickness of the silicon oxide film and the silicon nitride film formed on the second surface side (back surface side). Shows the rate.

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

(Embodiment 1)
FIG. 1 is a diagram for explaining a solid-state imaging device according to Embodiment 1 of the present invention. A cross-sectional structure of a main part of the solid-state imaging device (FIG. 1A) and a configuration of a pixel array (FIG. 1B). In FIG. 1B, a part of the pixel array is enlarged.

  In the layout shown in FIG. 1B, the portion shown in the A part is different from the layout shown in the part other than the A part in the position in the thickness direction of the semiconductor substrate. The layout of the film 121 is shown, and the portion A shows the layout of the high-concentration N-type region 101b and the high-concentration P-type region 101a located further below the light transmission film 123 below the light-shielding film 121. .

  The solid-state imaging device 100 according to the first embodiment includes a pixel circuit formed on the first surface side of the semiconductor substrate 101, and is configured to photoelectrically convert light incident from the second surface side of the semiconductor substrate 101. It is. Here, the first surface of the semiconductor substrate 101 is a lower surface of the semiconductor substrate 101 in FIG. In addition, the second surface of the semiconductor substrate 101 is an upper surface of the semiconductor substrate 101 in FIG. In FIG. 1A, the multilayer wiring and the like forming the pixel circuit formed on the first surface side of the semiconductor substrate 101 are not shown.

  The solid-state imaging device 100 includes a light receiving unit PD that generates a signal charge according to the amount of incident light incident on the second surface of the semiconductor substrate 101 and stores the signal charge, and the second of the semiconductor substrate 101. And a light transmission film 123 formed on the surface.

  Here, the light transmission film 123 is formed on the first transparent insulating film 102 formed on the second surface of the semiconductor substrate 101 and the first transparent insulating film 102, and the first transparent insulating film 102 is formed on the first transparent insulating film 102. Incidence of the second transparent insulating film 103 having a refractive index higher than the refractive index of the transparent insulating film 102 on the second surface of the semiconductor substrate 101 as the thickness of the second transparent insulating film 103 increases. It has a laminated structure so that the light reflectance is periodically minimized. The thickness of the second transparent insulating film 102 is set in a range including only the second period regarding the minimum value of the reflectance.

  Specifically, the semiconductor substrate 101 is a low-concentration P-type silicon substrate, the first transparent insulating film 102 is a silicon oxide film (hereinafter also referred to as a silicon oxide film), and the second. The transparent insulating film 103 is a silicon nitride film (hereinafter also referred to as a silicon nitride film). Note that a silicon nitride oxide film can be used as the transparent insulating film 103 instead of the silicon nitride film.

  The silicon oxide film 102 has a thickness of 5 nm to 15 nm, and the silicon nitride film 103 has a thickness of 100 nm to 300 nm. The silicon oxide film 102 necessary for obtaining the multiple interference effect is improved in light incident efficiency as the film thickness is reduced. However, the film thickness should be 5 nm or more and 15 nm or less from the film formation limit for obtaining a stable film thickness. desirable. Note that in the case where a silicon nitride oxide film is used as the second transparent insulating film 103 instead of the silicon nitride film, the thickness of the silicon nitride oxide film is preferably 100 nm to 300 nm.

  In particular, the silicon nitride film or the silicon nitride oxide film preferably has a thickness of 180 nm to 250 nm.

  2 shows a structure in which a light transmission film 123 composed of a silicon oxide film (first transparent insulating film) 102 and a silicon nitride film (second transparent insulating film) 103 is formed on a P-type silicon substrate 101. The result of simulating the change in the reflectance of the incident light when the thickness of the film 102 is fixed to 10 nm and the thickness of the silicon nitride film 103 is changed in the range of 0 to 300 nm using the wavelength of the incident light as a parameter. Show.

  That is, in FIG. 2, the vertical axis represents the reflectance (%), and the horizontal axis represents the thickness (nm) of the silicon nitride film. Here, a change in reflectance when the wavelength of the input light is 610 nm is indicated by a graph L1 connecting points indicated by ♦, and a change in reflectance when the wavelength of the input light is 540 nm is indicated by a ■ mark. This is indicated by a graph L2 connecting dots, and a graph L3 connecting dots indicated by ▲ indicates the change in reflectance when the wavelength of the input light is 450 nm.

  Thus, it can be seen that the reflectance of light of each wavelength periodically changes as the thickness of the silicon nitride film increases. In the solid-state imaging device of the first embodiment, the second transparent insulating film 102 It can be seen that the thickness of the silicon nitride film (thickness of 100 nm or more and 300 nm or less) is set to a range in which the reflectance at each wavelength includes only the second period regarding the minimum value.

  Further, a pixel array 110a is formed on the back side of the P-type silicon substrate 101 constituting the solid-state imaging device 100 of the first embodiment, and left and right side end portions L0B and R0B of the pixel array 110a and upper and lower The side end portions U0B and D0B are optical black portions, respectively. An area other than the optical black portion in the pixel array 110a is an effective pixel area R.

  That is, incident light incident on the effective pixel region R is photoelectrically converted and output as signal charges, and pixel signals from the pixels of the optical black portions L0B, R0B, U0B, and D0B are used as reference values for the output level of the solid-state imaging device. Used.

  The optical black portions L0B, R0B, U0B and D0B are shielded from light by the light shielding film 121 formed on the light transmission film 123, as shown in FIG. That is, the light shielding film 121 has an opening corresponding to the effective pixel region R. As shown in an enlarged view of a part of the effective pixel region R in part A of FIG. Then, neither the light-shielding film 121 is formed on the high-concentration N-type region 101b constituting the light-receiving unit nor on the high-concentration P-type region 101a that separates the adjacent high-concentration P-type region 101b.

  In the pixel array 110a, pixels having a light receiving portion are arranged in a matrix, and the light receiving portion includes a high concentration N type region 101b formed in the P type silicon substrate 101 and the high concentration N type region. And a high-concentration P-type surface layer 101c formed on the lower surface of 101b. Further, the high-concentration N-type region 101b that constitutes the light receiving unit PD is electrically separated from the adjacent high-concentration N-type region 101b by the high-concentration P-type region 101a.

  A gate electrode G is formed on the surface side of the semiconductor substrate 101 with a gate insulating film 108 interposed therebetween. Further, on the back side of the semiconductor substrate 101, a light shielding film 121 is formed on the light transmission film 123, and a predetermined insulating layer 122 corresponding to each pixel is provided thereon via an interlayer insulating film 122 as a planarizing film. A color filter 104 of color is formed, and a microlens 105 is formed on the color filter 104 at a position corresponding to each pixel. In the Ia-Ia cross section of FIG. 1B, the green filter 104b and the red filter 104a are alternately arranged in the horizontal direction.

  Next, a method for manufacturing the solid-state imaging device will be described.

  First, a P-type silicon wafer is prepared as the P-type silicon substrate 101 (FIG. 3A), and a high-concentration N-type region 101b constituting a light receiving portion is formed on the first surface (front surface) of the P-type silicon substrate 101. A high concentration P-type region 101a that electrically separates these high-concentration N-type regions 101b is formed, and a high-concentration N-type photodiode is formed so that the photodiode as the light receiving portion becomes a surface-embedded photodiode. A high-concentration P-type surface layer 101c constituting the light receiving portion is formed on the surface of the mold region 101b. Thereafter, the gate electrode G is formed through the gate insulating film 108 (FIG. 3B). Here, the photodiode generates signal charges in accordance with the amount of incident light incident on the second surface of the silicon substrate and accumulates the signal charges.

  Next, multilayer wirings 111 and 112 are formed on a P-type silicon wafer (P-type silicon substrate) 101 via an interlayer insulating film 110. At this time, the upper interlayer insulating film is formed as a planarizing film so as to cover the pixel circuit. Thereafter, a passivation film 113 is formed on the outermost surface (FIG. 3C). At this time, a gate electrode and a metal wiring (not shown in FIG. 1) are formed as a pixel circuit.

  Thereafter, the surface side of the P-type silicon substrate 101, that is, the surface of the passivation film 113 is bonded to another P-type silicon wafer 201 as a support substrate by a conventional technique (FIG. 4).

  Subsequently, the back side of the P-type silicon substrate 101 is ground by a chemical mechanical polishing method (CMP method) until the P-type silicon substrate 101 has a thickness of about 2 to 3 μm, that is, a light receiving portion is formed. It is thinned to such an extent that the high concentration N-type region 101b is exposed.

  Next, a high-concentration P-type region 106 is formed on the back surface of the thinned P-type silicon substrate 101 by ion implantation and annealing, and then the film thickness is 5 nm or more and 15 nm on the back surface of the thinned P-type silicon substrate 101. The following silicon oxide film 102 is deposited by a low temperature CVD method at 450 ° C. or lower, and a silicon nitride film 103 having a film thickness of 100 nm to 300 nm is formed on the silicon oxide film 102 by a similar low temperature CVD method ( FIG. 5). Here, the refractive index of silicon oxide is 1.4 to 1.5, and the refractive index of silicon nitride is 1.8 to 2.0.

  The film thickness of the silicon nitride film 103 is preferably 150 nm or more and 250 nm or less, and more preferably 180 nm or more and 250 nm or less.

  Thereafter, a light shielding film 121 is formed on the silicon nitride film 103, an interlayer insulating film 122 as a planarizing film is formed thereon, and then a color filter 104 is formed on the interlayer insulating film 122, A lens 105 is formed (FIG. 6). Here, in this color filter 104, for example, green filters 104b and red filters 104a are alternately arranged in the odd-numbered pixel columns, and blue filters (not shown) are arranged in the even-numbered pixel columns. Green filters (not shown) are alternately arranged. The microlens 105 is disposed on the color filter 104 so as to correspond to each pixel.

The silicon nitride film 103 formed by low-temperature CVD has a compressive stress of 1E9 (dyne / cm ² ) to 1E10 (dyne / cm ² ). Further, the color filter 104 is formed on the silicon nitride film 103 directly or via an adhesion organic material. A microlens 105 is formed on the color filter 104 directly or via a planarizing organic material.

  Next, the function and effect will be described.

  In the solid-state imaging device 100 according to the first embodiment, the light transmission film 123 is formed on the second surface (back surface) of the P-type silicon substrate 101, and the light transmission film 123 is formed on the second surface of the P-type silicon substrate 101. The silicon oxide film 102 formed on the surface and the silicon nitride film 103 formed on the silicon oxide film 102 and having a refractive index higher than the refractive index of the silicon oxide film 102 are changed to the thickness of the silicon nitride film 103. As the thickness of the silicon nitride film 103 is increased, the reflectance of the incident light on the second surface of the P-type silicon substrate 101 is periodically minimized. Since the value is set in a range including only the second period, the tensile stress of silicon is relaxed in addition to the multiple interference effect obtained by stacking the silicon nitride film 103 on the silicon oxide film 102. DOO can be effectively (first effect) effect (second effect) is obtained that can be further suppressed metal contamination of the silicon substrate.

  First, the multiple interference effect will be specifically described with reference to FIG.

  FIG. 2 shows the relationship between the film thickness and reflectance of a silicon nitride film laminated on the silicon oxide film when a 10 nm silicon oxide film, for example, is formed on the second surface (back surface) side of the P-type silicon substrate. The relationship is shown for each incident light wavelength.

  The silicon nitride film thickness that minimizes the reflectance of incident light varies depending on the wavelength of incident light, but silicon that has the smallest reflectance at a wavelength of 540 nm (green), which is important for color reproduction close to human vision. When the film thickness of the nitride film is examined, it can be seen from FIG. 2 that an appropriate film thickness is 50 nm to 80 nm or 200 nm to 250 nm.

  Further, the thickness of the silicon nitride film necessary for obtaining the first and second effects is often as thin as about 50 nm, and there are many dark currents and white spot defects, which are reduced by increasing the film thickness. Therefore, it is 100 nm or more. Therefore, in order to obtain all the two effects, the thickness of the silicon nitride film must be 200 nm to 250 nm.

  This assumes that the wavelength of incident light is focused on 540 nm (green), but when focused on 450 nm (blue), the thickness of the silicon nitride film is optimally 150 nm to 200 nm, and 610 nm (red). When attention is paid to the above, the optimum film thickness of silicon nitride is 225 nm to 275 nm.

  Further, since the reflectivity shown in FIG. 2 varies depending on the thickness of the underlying silicon oxide film, the optimum silicon nitride film thickness corresponding to a silicon oxide film of 5 nm to 15 nm is in the range of 100 nm to 300 nm. Limited.

  Further, as shown in FIG. 2, the film thickness of the silicon nitride film that minimizes the reflectance of light varies depending on the wavelength of incident light. Therefore, from the viewpoint of color balance, the optimum silicon nitride film in the range of 100 nm to 300 nm. The film thickness can be set.

  By setting the film thickness of the silicon nitride film to such a film thickness, the silicon substrate has a tensile stress while the silicon nitride film has a strong compressive stress. It is relaxed and the dark current is reduced. Further, the silicon nitride film has a film thickness sufficient to suppress metal contamination.

As a result, in the solid-state imaging device, not only the light transmittance in the transparent insulating film on the light incident surface side of the substrate is improved, but also the dark current defect caused by stress (stress) and the white spot defect caused by metal contamination. Can be suppressed.
(Embodiment 2)
FIG. 7 is a diagram for explaining a solid-state imaging device according to Embodiment 2 of the present invention. A cross-sectional structure of the main part of the solid-state imaging device (FIG. 7A) and a light-shielding pattern in a pixel array (FIG. 7 ( b)), and part B of the pixel array is shown enlarged in part B of FIG. 7B.

  Here, the first surface (front surface) of the semiconductor substrate 101 is the lower surface of the semiconductor substrate 101 in FIG. 7A, and the second surface (back surface) of the semiconductor substrate 101 is in FIG. 7A. This is the upper surface of the semiconductor substrate 101. The semiconductor substrate 101 is specifically a low-concentration P-type silicon substrate. In FIG. 7A, as in FIG. 1A, the multilayer wiring and the like that form the pixel circuit formed on the first surface side of the semiconductor substrate 101 are not shown.

  7B, the layout shown in the B part is different from the layout shown in the part other than the B part in the position in the thickness direction of the semiconductor substrate. Specifically, the part other than the B part is shielded from light. The layout of the film 221 is shown, and the portion B shows the layout of the high-concentration N-type region 101b and the high-concentration P-type region 101a located further below the light transmission film 123 below the light-shielding film 221. .

  The solid-state imaging device 100a according to the second embodiment is an effective pixel that performs photoelectric conversion of incident light on the second surface (back surface) of the P-type silicon substrate 101 instead of the light shielding film 121 in the solid-state imaging device 100 according to the first embodiment. Are arranged on the high-concentration P-type region 101a, and optical black regions U0B, D0B, which are located around the effective pixel region R on the second surface of the P-type silicon substrate 101. In L0B and R0B, a light shielding film 221 formed so as to cover the entire surface of the optical black region is provided.

  That is, in the solid-state imaging device 100a of the second embodiment, the pixel circuit is formed on the first surface (front surface) side of the silicon substrate 101 and the second surface of the P-type silicon substrate 101 is the same as the solid-state imaging device of the first embodiment. It is a solid-state imaging device in which light is incident from (back surface).

  A laminated structure of a silicon oxide film 102 having a thickness of 5 nm to 15 nm and a silicon nitride film 103 having a thickness of 100 nm to 300 nm is formed on the second surface (back surface) side of the P-type silicon substrate 101. On the laminated structure, a light shielding film 221 is formed via an interlayer insulating film 122 as a planarizing film.

  The difference between the solid-state imaging device 100a according to the second embodiment and the solid-state imaging device 100 according to the first embodiment is that, in the solid-state imaging device 100 according to the first embodiment, the light shielding film 221 includes the optical black portion U0B of the pixel array 110. , D0B, L0B, and R0B are formed only on the solid-state imaging device 100a according to the second embodiment, the light shielding film 221 includes the optical black portions U0B, D0B, L0B, and R0B of the pixel array 110a. The entire surface of the pixel array 110a is covered as in the first embodiment. However, in the effective pixel region R of the pixel array 110a, a part of the effective pixel region R is enlarged and shown in a portion B of FIG. It is formed only on the high-concentration P-type region 101a so as to have a planar pattern, and is opposed to the high-concentration N-type region 101b of the photodiode PD which is a light receiving portion. The portion that is that has an opening 221a (FIG. 7 (a)).

  Here, the material of the light shielding film 221 is, for example, aluminum or tungsten.

  Generally, the light shielding film is arranged in the effective pixel region for the purpose of suppressing color mixing, but the stress of the light shielding film and the diffusion of the metal atoms themselves into the silicon substrate adversely affect the dark current and white spot defects. By setting the silicon nitride film 103 to 100 nm or more and 300 nm or less, an effect of suppressing contamination can be obtained.

  Needless to say, the solid-state imaging device of the first and second embodiments may be a CCD image sensor or a CMOS image sensor.

Furthermore, although not specifically described in the first and second embodiments, a digital camera such as a digital video camera or a digital still camera using at least one of the solid-state imaging devices of the first and second embodiments as an imaging unit. An electronic information device having an image input device, such as an image input camera, a scanner, a facsimile machine, or a camera-equipped mobile phone, will be briefly described below.
(Embodiment 3)
FIG. 8 is a block diagram showing a schematic configuration example of an electronic information device using the solid-state imaging device of Embodiment 1 or 2 as an imaging unit as Embodiment 3 of the present invention.

  An electronic information device 90 according to Embodiment 3 of the present invention shown in FIG. 8 includes at least one of the solid-state imaging devices 100 and 100a according to Embodiments 1 and 2 of the present invention as an imaging unit 91 that captures a subject. And a memory unit 92 such as a recording medium for recording data after high-quality image data obtained by photographing by such an imaging unit is subjected to predetermined signal processing for recording, and the image data is predetermined for display. A display unit 93 such as a liquid crystal display device that displays the signal on a display screen such as a liquid crystal display screen after the signal processing, and a communication unit 94 such as a transmission / reception device that performs communication processing after processing this image data for predetermined signal processing. And an image output unit 95 for printing (printing) and outputting (printing out) the image data.

  As mentioned above, although this invention has been illustrated using preferable embodiment of this invention, this invention should not be limited and limited to this embodiment. 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 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, a method of manufacturing the same, and a device in which dark current and white point defects are reduced in a solid-state imaging device such as a CMOS image sensor, and such dark current and white point defects. Manufacturing method of a solid-state imaging device with a small amount and an electronic information device equipped with such a solid-state imaging device can be obtained.

DESCRIPTION OF SYMBOLS 90 Electronic information apparatus 91 Imaging part 92 Memory part 93 Display means 94 Communication means 95 Image output means 100, 100a Solid-state imaging device 101 Semiconductor substrate (P-type silicon substrate)
101a High-concentration P-type region 101b High-concentration N-type region 101c High-concentration P-type surface layer 102 Silicon oxide film (first transparent insulating film)
103 Silicon nitride film (second transparent insulating film)
104 Color filter 104b Green filter 104a Red filter 105 Micro lens 106 High-concentration P-type region 108 Gate insulating film 110 Interlayer insulating film 110a Pixel array 111, 112 Multi-layer wiring 113 Passivation film 123 Light transmission film 201 Support substrate (P-type silicon wafer)
L0B, R0B, U0B, D0B Optical black area PD Light-receiving area R Effective pixel area

Claims (10)

A solid-state imaging device including a pixel circuit formed on a first surface side of a semiconductor substrate and configured to photoelectrically convert light incident from the second surface side of the semiconductor substrate,
A light receiving unit that generates a signal charge according to an incident light amount of light incident on the second surface of the semiconductor substrate and accumulates the signal charge;
A light transmissive film formed on the second surface of the semiconductor substrate,
The light transmission film is formed on the first transparent insulating film formed on the second surface of the semiconductor substrate and on the first transparent insulating film, and the refractive index of the first transparent insulating film With the second transparent insulating film having a high refractive index, the reflectance of incident light on the second surface of the semiconductor substrate periodically becomes minimum as the thickness of the second transparent insulating film increases. With a laminated structure
A solid-state imaging device, wherein the thickness of the second transparent insulating film is set to a range including only the minimum value of the second period as the minimum value of the reflectance. A solid-state imaging device including a pixel circuit formed on a first surface side of a silicon substrate and configured to photoelectrically convert light incident from the second surface side of the silicon substrate,
A light receiving unit that generates a signal charge according to an incident light amount of light incident on the second surface of the silicon substrate and accumulates the signal charge;
A light transmissive film formed on the second surface of the silicon substrate,
The light transmission film is formed on the first transparent insulating film formed on the second surface of the silicon substrate and on the first transparent insulating film, and the refractive index of the first transparent insulating film is A second transparent insulating film having a high refractive index,
The first transparent insulating film is a silicon oxide film, and has a film thickness of 5 nm or more and 15 nm or less,
The second transparent insulating film is a silicon nitride film or a silicon nitride oxide film, and has a thickness of 100 nm to 300 nm. The solid-state imaging device according to claim 2,
The solid-state imaging device, wherein the silicon nitride film or the silicon nitride oxide film has a thickness of 180 nm to 250 nm. The solid-state imaging device according to claim 1 or 2,
A light-shielding film formed on the light-transmitting film;
The solid-state imaging device, wherein the light-shielding film has an opening corresponding to an effective pixel region in which effective pixels that perform photoelectric conversion of incident light are arranged on the second surface of the semiconductor substrate. The solid-state imaging device according to claim 2 or 3,
The silicon substrate is a first conductivity type silicon substrate;
The first conductivity type silicon substrate includes a plurality of second conductivity type semiconductor regions arranged in a matrix, constituting the light receiving unit,
The solid-state imaging device, wherein the second conductivity type semiconductor region constituting the light receiving unit is electrically separated by a high concentration first conductivity type isolation region formed in the first conductivity type silicon substrate. The solid-state imaging device according to claim 5,
A light-shielding film formed on the light-transmitting film;
The light shielding film is
In the effective pixel region in which effective pixels for photoelectric conversion of incident light are arranged on the second surface of the first conductivity type silicon substrate, the first conductivity type is located on the high concentration first conductivity type separation region. A solid-state imaging device formed so as to cover the entire surface of the optical black region in the optical black region positioned around the effective pixel region on the second surface of the silicon substrate. In the solid-state imaging device according to any one of claims 1 to 6,
A solid-state imaging device, wherein a color filter of a predetermined color corresponding to each pixel is formed on the light transmission film, and a microlens is formed on the color filter at a position corresponding to each pixel. A method of manufacturing a solid-state imaging device including a pixel circuit formed on a first surface side of a semiconductor substrate and configured to photoelectrically convert light incident from the second surface side of the semiconductor substrate,
Forming a light receiving portion on the first surface side of the semiconductor substrate for generating a signal charge according to the amount of incident light and storing the signal charge;
Forming the pixel circuit on a first surface of the semiconductor substrate;
Forming a planarization film on the first surface of the semiconductor substrate so as to cover the pixel circuit, and then attaching the first surface side of the semiconductor substrate to a support substrate;
Grinding the second surface opposite to the first surface of the semiconductor substrate to a depth at which the light receiving portion is formed to thin the semiconductor substrate;
Forming a light transmission film on the second surface side of the thinned semiconductor substrate,
The step of forming the light transmissive film includes:
Forming a first transparent insulating film on the second surface of the semiconductor substrate;
A second transparent insulating film having a refractive index higher than the refractive index of the first transparent insulating film is formed on the first transparent insulating film as the thickness of the second transparent insulating film increases. Laminating so that the reflectance of incident light on the second surface of the semiconductor substrate is periodically minimized,
The method for manufacturing a solid-state imaging device, wherein the thickness of the second transparent insulating film is set in a range including only the minimum value of the second period as the minimum value of the reflectance. A method of manufacturing a solid-state imaging device including a pixel circuit formed on a first surface side of a silicon substrate and configured to photoelectrically convert light incident from the second surface side of the silicon substrate,
Forming a light receiving portion on the first surface side of the silicon substrate for generating a signal charge according to an incident light quantity of incident light and storing the signal charge;
Forming the pixel circuit on a first surface of the silicon substrate;
Forming a planarizing film on the first surface of the silicon substrate so as to cover the pixel circuit, and then attaching the first surface side of the silicon substrate to a support substrate;
Grinding the second surface opposite to the first surface of the silicon substrate to a depth at which the light receiving portion is formed to thin the silicon substrate;
Forming a light transmission film on the second surface side of the thinned silicon substrate,
The step of forming the light transmissive film includes:
Silicon as the first transparent insulating film is formed on the second surface of the silicon substrate which is thinned by grinding the second surface opposite to the first surface of the silicon substrate to the depth where the light receiving portion is formed. Forming an oxide film in a thickness of 5 nm to 15 nm;
Forming a silicon nitride film or a silicon nitride oxide film with a thickness of 100 nm to 300 nm as the second transparent insulating film on the silicon oxide film. An electronic information device having an imaging unit for imaging a subject,
The electronic imaging device includes the solid-state imaging device according to any one of claims 1 to 7.

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