JP2008251985A - Solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently collect light to a light receiving element, without interfering an incident light by a light shielding film. <P>SOLUTION: CCD 10 includes: a semiconductor substrate 15 on which a photo diode 11 and a charge transfer part 14 are formed; an insulating film 16; a transfer electrode 17 constituting a vertical transfer path 13 together with a charge transfer part 14; a light shielding film 18 positioned in the upper part of the transfer electrode 17 and the semiconductor substrate 15; a color filter 24; and a micro lens 25. An opening part 20 adjusted to the photo diode 11 is formed on the light shielding film 18. The opening part 20 is formed in a tapered shape of gradually decreasing an area toward the photo diode 11 from the micro lens 25, and the lights incident from the micro lens 25 is collected to the photo diode 11 without being interrupted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device.

  In recent years, digital cameras that convert a captured image captured using a solid-state imaging device such as a CCD into digital image data and record it on a recording medium such as a built-in memory or a memory card have become widespread. In a solid-state imaging device as provided in this digital camera, for example, as described in Patent Documents 1 and 2, the upper surface of a semiconductor substrate on which light receiving elements (photodiodes) arranged in a matrix are formed. In addition, a light-shielding film having an opening corresponding to the position of each light-receiving element is formed, and a microlens positioned above the light-receiving element is formed, and incident light from the photographing lens optical system is condensed by this microlens. Then, the light is received by each light receiving element through the opening.

Moreover, in the solid-state imaging device described in Patent Document 1, two or more light shielding layers (light shielding films) are provided between the light receiving element and the microlens, and the light shielding layers are formed from the substrate side. A step is formed so that the area gradually decreases toward the microlens side to eliminate flare light caused by obliquely incident light and internally reflected light, thereby preventing generation of false signals. Furthermore, in Patent Document 2, a transparent film (waveguide) is further formed from the inside of the opening of the light shielding layer to the flattening layer above the light shielding layer, and light is guided to the light receiving element through this waveguide.
JP-A-6-45569 JP 2003-46074 A

  On the other hand, recently, solid-state imaging devices have been increasingly reduced in size and increased in pixel count, and as a result, it is necessary to reduce the opening area of the light-shielding film formed in accordance with the light receiving element. Of the incident light that has passed through, the incident light that is substantially parallel to the optical axis reaches the light receiving element through the opening, but the oblique incident light is blocked by the periphery of the opening of the light shielding film. The light collection efficiency is becoming insufficient.

  Furthermore, in the configuration described in Patent Document 1, although prevention of flare light and false signals is considered, improvement of light collection efficiency to the light receiving element is not considered. Further, in the configuration of Patent Document 2, light incident on the waveguide from the microlens is guided to the light receiving element, but light collection efficiency is improved for light incident from the periphery of the waveguide. Is not taken into account. Furthermore, Patent Documents 1 and 2 are limited to a case where there are a large number of light shielding films, and cannot be applied to a configuration having only one light shielding film.

  The present invention has been made in view of the above circumstances, and improves the sensitivity by efficiently collecting light to the light receiving element and guiding it to the light receiving surface without hindering the incident light by the light shielding film. An object of the present invention is to provide a solid-state imaging device capable of satisfying the requirements.

  The solid-state imaging device according to the present invention includes a semiconductor substrate on which a plurality of light receiving units are formed, a condensing lens positioned above the light receiving unit, and covers and shields at least part of the semiconductor substrate, and the light receiving unit The shape of the opening formed in accordance with the position of D is the outer dimension of the condensing lens is D, the opening interval of the opening close to the condensing lens is W1, and the opening is close to the light receiving portion. A light-shielding film having a relationship of 0.5 ≦ (W1−W2) / (D−W2) ≦ 0.9 is provided, where W2 is a position opening interval. The opening of the light shielding film is preferably formed in a tapered shape that gradually narrows from the condenser lens side toward the light receiving unit side.

  The condensing lens is a microlens positioned above the light receiving unit, or includes a microlens positioned above the light receiving unit, and the condensing lens includes the microlens and the semiconductor substrate. It is effective to be an inner lens formed between the two. The opening of the light shielding film preferably has a reflective film formed on the surface thereof.

  In the solid-state imaging device of the present invention, the shape of the opening is D, the outer dimension of the condensing lens is W, the opening interval of the opening close to the condensing lens is W1, and the opening is close to the light receiving unit. Assuming that the opening interval of the position is W2, a light shielding film having a relationship of 0.5 ≦ (W1−W2) / (D−W2) ≦ 0.9 is provided. Since the light can be efficiently collected to the light receiving element and guided to the light receiving surface, the sensitivity can be improved.

  Furthermore, since the opening of the light shielding film is formed in a tapered shape that gradually narrows from the condenser lens side toward the light receiving portion side, the incident light is not obstructed and the light is collected to the light receiving element. Can be lighted.

  A structure of a CCD, which is an example of a solid-state imaging device to which the present invention is applied, will be described below with reference to the drawings. The present invention is not limited to the CCD, but can be applied to other image sensors such as a CMOS. 1 is a plan view, and FIG. 2 is a cross-sectional view taken along line XX (parallel to the horizontal transfer direction H) in FIG. In FIG. 1, a part of the upper surface structure such as a light shielding film is omitted. The CCD 10 has a plurality of photodiodes (light receiving portions) 11 arranged in a two-dimensional matrix in the imaging region, and a vertical transfer path 13 is provided along each column of the photodiodes 11, that is, along the vertical transfer direction V. Configured.

As shown in FIG. 2, the cross-sectional structure of the CCD 10 includes a photodiode (light receiving portion) 11 and a semiconductor substrate 15 in which a charge transfer portion 14 constituting a vertical transfer path 13 is formed in a portion excluding the photodiode 11. A transfer electrode 17 is formed on the charge transfer portion 14 via an insulating film 16. The charge transfer unit 14 and the transfer electrode 17 constitute a vertical transfer path 13 and vertically transfer the charges accumulated in the photodiode 11. Note that the transfer electrode 17 is made of, for example, first polysilicon by a dry etching method or the like. Further, a light shielding film 18 is formed above the transfer electrode 17 and the semiconductor substrate 15. The light shielding film 18 covers the transfer electrode 17 and shields it from light. Further, an opening 20 is formed in the light shielding film 18 in accordance with the position of the photodiode 11. The details of the shape of the light shielding film 18 and the opening 20 will be described later. The insulating film 16 is formed of SiO ₂ by, for example, a thermal oxidation method or a CVD (Chemical Vapor Deposition) method.

  Further, a waveguide 22 is formed above the photodiode 11 and inside the opening 20, and a planarization layer (intermediate layer) 23 is formed so as to surround the waveguide 22. The planarization layer 23 is formed so that the upper surface thereof is planarized, and a color filter 24 and a microlens 25 are formed on the upper surface. The planarizing layer 23 is made of, for example, BPSG (boron phosphorus silicate glass; refractive index n1 = 1.4 to 1.5), and the waveguide 22 is made of, for example, SiN (silicon nitride; refractive index n2 = 1.9). 2.0). The color filter 24 is made of a resist material or the like containing pigments corresponding to three colors (R, G, B) or four colors (R, G, B + intermediate colors). Note that the materials of the waveguide 22 and the planarization layer 23 are not limited to these.

  The waveguide 22 is formed in a rectangular shape or a substantially circular shape whose cut surface cut in parallel with the semiconductor substrate 15 is slightly smaller than the opening 20, from a position close to the microlens 25 to a position close to the photodiode 11. It is formed in a quadrangular prism shape or a substantially cylindrical shape extending straight along a direction perpendicular to the semiconductor substrate 15. In addition, the waveguide 22 is formed at a constant interval with respect to the inner wall surface of the opening 20.

  The shape of the light shielding film 18 and the opening 20 is shown in detail in FIG. In this embodiment, the height Hm from the upper surface of the semiconductor substrate 15 to the lower surface of the microlens 25 is 1 μm, and the height Hf from the semiconductor substrate 15 to the upper surface of the light shielding film 18 is 0.6 to 0.8 μm. The space for forming the light shielding film 18 is very limited. The opening 20 of the light shielding film 18 has a large interval on the side close to the micro lens 25 and a small interval on the side close to the photodiode 11, and gradually from the micro lens 25 side toward the photodiode 11 side. It is formed in a taper shape whose area decreases. As described above, as a method of manufacturing the opening 20 of the light shielding film 18 in a tapered shape, in this embodiment, the peripheral portion 17a of the transfer electrode 17 under the light shielding film 18 is formed on the semiconductor substrate by a known dry etching technique. 15 by forming a light shielding film 18 on the upper surface of the transfer electrode 17 by a photoetching method or the like, thereby forming an inclined surface along the peripheral edge portion 17a of the transfer electrode 17, The opening 20 can be formed in a tapered shape. In addition, the inclined surface formed in the peripheral part of such an electrode is formed by the well-known method described in Unexamined-Japanese-Patent No. 2003-332555, Unexamined-Japanese-Patent No. 2005-340287, etc., for example. In addition, the manufacturing method for forming the opening 20 is not limited to this. For example, when the light shielding film 18 is formed, a plurality of layers of photoetching are formed, and a taper is provided by adding a minute step to each adjacent layer. Can be formed. Further, the light shielding film 18 is preferably formed from tungsten (W), which is a refractory metal, but is not limited thereto, and aluminum (Al), silver (Ag), gold (Au), copper (Cu). Etc. may be used.

In the present embodiment, since the distance on the microlens 25 side is wider than the distance on the photodiode 11 side of the opening 20, it is possible to improve the light collection efficiency on the photodiode 11. Yes. Therefore, the value at which the ratio of the spread dimension is optimized will be described below. First, the outer dimension of the microlens 25 (in this embodiment, since the outer dimension of the microlens 25 is equal to the arrangement pitch, hereinafter referred to as pitch) is D, and the distance between the openings 20 on the microlens 25 side (hereinafter referred to as inlet). that side spacing.) the W _1, photodiode 11 side of the spacing of the opening 20 side (hereinafter, when referred to.) outlet spacing and W _2, spread size of the opening 20 (the inlet side and the outlet side of the gap Difference) is W ₁ −W ₂ . Further, if when the inlet-side distance W ₁ of the opening 20 is substantially equal to the pitch D, opening 20 is most extended state. Therefore, when the ratio of the actual spread with respect to the most spread state is defined as a spread ratio η, the spread ratio is η = (W ₁ −W ₂ ) / (D−W ₂ ).

Further, the optimum value of the spread ratio η is obtained as follows. First, since the light near the optical axis of the microlens 25 naturally enters the photodiode 11, a condition in which light incident from near the outer shape of the microlens 25 enters the inside of the opening 20 is considered. Of light incident from the vicinity of the outer shape of the microlens 25, light incident perpendicularly to the lens surface of the microlens 25 and light incident obliquely are considered. Here, as shown in FIG. 3, the light L ₁ perpendicularly incident on the lens surface of the microlens 25 and the normal line angle of the microlens 25 are θ ₁ , and the light L perpendicularly incident on the obliquely incident light L _2. An angle with ₁ (so-called incident angle) is θ ₂ . Further, the effective refractive index from the microlens 25 to the waveguide 22 is n, the numerical aperture is NA = n sin θ, the focal length is f, the refraction angle of the light L ₁ incident on the microlens 25 is θ _s1 , and the microlens 25 is incident. The refraction angle of the light L2 thus obtained is defined as θ _s2 . Then, if the distance obtained by removing the entrance-side interval W ₁ from the pitch D of the CCD 10 is X = D−W ₁ , the following equation is established.

  And when X is calculated from these equations,

Also, when sin θ ₃ is obtained,

Further, when sin θ ₁ is obtained,

  From the above formulas 1 to 4, the spread ratio η is as follows.

In order to actually improve the light collection efficiency, it is preferable that obliquely incident light with an incident angle θ ₂ = 15 ° is also guided to the waveguide 22, and the effective refractive index is set to n = 1.4 to 1. 9. When the numerical aperture NA = 0.3 to 0.4 and the ratio α (= (W ₂ /D))=0.25 to 0.5 of the outlet side interval W _{2 with} respect to the pitch D is applied to the above equation 5. The spread ratio η is as shown in Table 1 below.

  From Table 1 above, the spreading ratio η is preferably 0.5 or more and 0.9 or less, and more preferably 0.75 or more and 0.9 or less.

  Further, the waveguide 22 is formed in a rectangular shape or a substantially circular shape whose cut surface cut in parallel with the semiconductor substrate 15 is slightly smaller than the opening 20, and from the microlens 25 side to the photodiode 11 side. It is formed in a quadrangular prism shape or a substantially cylindrical shape extending straight along a vertical direction. As a result, light that has passed through the microlens 25 and entered the waveguide 22 is guided to the photodiode 11.

The operation of the above configuration will be described below. As described above, in the CCD 10 of this embodiment, the opening 20 of the light shielding film 18 satisfies the relationship of the above formula (4), and the area gradually decreases from the microlens 25 side toward the photodiode 11 side. Therefore, not only the incident light from the vicinity of the optical axis L of the microlens 25 but also the incident light from the vicinity of the peripheral edge of the microlens 25 and the oblique incident light having the incident angle θ ₂ are shielded. Without being obstructed by the light, the light enters the inside of the opening 20. In the present embodiment, as described above, the oblique incident light up to the incident angle θ ₂ = 15 ° enters without being blocked by the light shielding film 18. Thereby, the light collection efficiency to the photodiode 11 is increased, and the sensitivity of the CCD 10 is improved. On the other hand, in the configuration of the conventional solid-state imaging device, the opening of the light shielding film is formed to extend vertically from the photodiode side to the microlens side, and the vicinity of the upper end of the opening blocks the incident light and collects it. Although the light efficiency has been reduced, this is not the case in this embodiment.

  In the above-described embodiment, the shape of the opening 20 of the light shielding film 18 will be described by taking as an example the case where the opening is formed in a tapered shape whose area gradually decreases from the microlens 25 side to the photodiode 11 side. However, the shape of the opening 20 is not limited to this, and it may be formed in the shape shown in FIGS. 4 to 7 described below.

  In FIG. 4, a rounded curved opening 30 is formed from the upper surface of the light shielding film 18 (the surface on the side close to the microlens 25) to the inner peripheral surface. Since the interval on the 25 side is wide and the interval on the photodiode 11 side is narrow, the light incident from the microlens 25 is condensed to the photodiode 11 without being obstructed, and the same effect as in the above embodiment is obtained. be able to.

  In FIG. 5, an opening 35 is formed which includes a curved surface 36 that is rounded from the upper surface to the inner peripheral surface of the light shielding film 28, and a curved surface 37 that continues from the lower end portion of the curved surface 36 and protrudes inward. Also in this shape, since the interval on the microlens 25 side is wide and the interval on the photodiode 11 side is narrow, the light incident from the microlens 25 is collected on the photodiode 11 without being obstructed. .

  In FIG. 6, a tapered shape 41 whose area gradually decreases from the side close to the microlens 25 toward the photodiode 11 side, and a substantially columnar shape 42 extending straight from the lower end of the tapered shape 41 to the photodiode 11 side. The opening part 40 which consists of is formed.

  In FIG. 7, a reflective film 50 made of a metal having a high reflectance is formed on the upper surface of the light shielding film 18 and the inner surface of the opening 20 formed in the same shape as the above embodiment. The reflective film 50 is formed at a position as close to the color filter 24 as possible. As a result, it is possible to prevent light from entering the transfer electrode 17 and to prevent light from leaking to the outside of the opening 20, thereby improving light collection efficiency and preventing smear. .

  In the above embodiment, the waveguide 22 is formed inside the opening 20, but the planarization layer 23 may be continuous to the inside of the opening 20 without providing the waveguide 22.

  In the above-described embodiment, the condensing lens that collects light to the photodiode 11 has a configuration in which only the uppermost microlens 25 is formed, but is not limited thereto, and as shown in FIG. An inner lens 55 may be formed between the diode 11 and the diode 11. Although FIG. 8 shows an example in which the inner lens 55 and the waveguide 22 are integrally formed, the configuration of the inner lens is not limited to this. In the case where the inner lens 55 is provided, the opening 60 is manufactured by the same manufacturing method as in the above-described embodiment. Form narrow. The shape of the opening 60 may be not only a tapered shape shown in the drawing but also a curved surface.

  In the above-described embodiment, the microlens whose lens surface is convex upward is described as an example, but the present invention is not limited to this, and a microlens whose lens surface is convex downward may be used. Alternatively, a microlens whose upper and lower surfaces are convex may be formed.

  The solid-state imaging device of the present invention is applied not only to various imaging devices such as a digital camera and a camera unit for a mobile phone, but also to medical equipment such as an electronic endoscope.

It is a top view which shows an example of the solid-state imaging device which implemented 1st Embodiment. It is principal part sectional drawing in the XX of FIG. It is principal part sectional drawing to which the opening part vicinity of the light shielding film was expanded. It is principal part sectional drawing which shows the 1st modification of 1st Embodiment. It is principal part sectional drawing which shows the 2nd modification of 1st Embodiment. It is principal part sectional drawing which shows the 3rd modification of 1st Embodiment. It is principal part sectional drawing which shows the 4th modification of 1st Embodiment. It is principal part sectional drawing which shows the 5th modification of 1st Embodiment.

Explanation of symbols

10 CCD (solid-state imaging device)
11 Photodiode (light receiving part)
15 Semiconductor substrate 17 Transfer electrode 18 Light shielding film 20, 30, 35, 40 Opening 25 Micro lens

Claims (5)

  A semiconductor substrate on which a plurality of light receiving parts are formed, a condenser lens located above the light receiving part, and at least part of the semiconductor substrate is shielded from light and formed in accordance with the position of the light receiving part When the shape of the opening is D, the outer dimension of the condensing lens is D, the opening interval of the opening close to the condensing lens is W1, and the opening interval of the opening close to the light receiving portion is W2. , 0.5 ≦ (W1−W2) / (D−W2) ≦ 0.9, a solid-state imaging device.   The solid-state imaging device according to claim 1, wherein the opening of the light shielding film is formed in a tapered shape that gradually becomes narrower from the condenser lens side toward the light receiving unit side.   The solid-state imaging device according to claim 1, wherein the condenser lens is a microlens located above the light receiving unit.   The microlens located above the light receiving part is provided, and the condenser lens is an inner lens formed between the microlens and the semiconductor substrate. Solid-state imaging device.   The solid-state imaging device according to claim 1, wherein a reflection film is formed on a surface of the opening of the light shielding film.

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