JP2011119445A - Backside illuminated solid-state imaging device - Google Patents

Abstract

A back-illuminated solid-state imaging device capable of reducing the occurrence of color mixing due to light leakage to adjacent pixels and suppressing the decrease in the amount of light taken in by a photoelectric conversion element.
A back-illuminated solid-state imaging device that irradiates light to a back surface 11 side of a semiconductor substrate 1 and captures a subject image, and is provided on the semiconductor substrate 1 and photoelectric conversion that converts incident light into signal charges. The light-shielding part 9 provided on the back surface 11 side of the element and the semiconductor substrate 1 and having an opening 12 corresponding to each of the photoelectric conversion elements, and the flat surface 13 provided on the semiconductor substrate 1 and the light-shielding part 9 The opening 12 of the light shielding portion 9 has a shape that is narrowed from the flat surface 13 side toward the semiconductor substrate 1 side.
[Selection] Figure 1

Description

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

  A back-illuminated solid-state imaging device that picks up a subject image by making light incident from the back side opposite to the side on which the wiring layer is formed in the semiconductor substrate is equivalent to the fact that no wiring member is provided on the incident side. There is an advantage that the whole can be used as a photoelectric conversion region. On the other hand, in the case of a back-illuminated solid-state imaging device, there is a problem of generation of optical color mixture due to light incident on a certain unit pixel region leaking out to a photoelectric conversion element in the adjacent unit pixel region. Color mixing is a phenomenon that occurs when charges that pass through a color filter in a certain unit pixel region and are to be taken in by that pixel are taken into another adjacent pixel for color light, and can cause a decrease in color reproducibility. Therefore, conventionally, for the purpose of reducing optical color mixing in the back-illuminated solid-state imaging device, a technique for providing a light shielding film for shielding light that becomes a color mixing component has been proposed. For example, Patent Document 1 discloses a configuration in which a light shielding layer is provided between color filters.

  When a light-shielding layer is provided between the color filters, the aperture ratio corresponding to the amount of the light-shielding layer provided is lowered when the color filter passes. The light receiving sensitivity of the backside illumination type solid-state imaging device is reduced as the amount of light taken into the photoelectric conversion element is reduced. In particular, the finer the unit pixel region, the more significant the decrease in sensitivity due to the smaller opening area.

JP-A-7-99297

  An object of the present invention is to provide a back-illuminated solid-state imaging device that can reduce the occurrence of color mixing due to light leakage to adjacent pixels and can suppress a decrease in the amount of light captured by a photoelectric conversion element.

  According to one aspect of the present invention, there is provided a back-illuminated solid-state imaging device that irradiates light on the back side of a semiconductor substrate and picks up a subject image, and is provided on the semiconductor substrate and converts incident light into signal charges. A photoelectric conversion element to be provided; a light shielding portion provided on the back surface side of the semiconductor substrate and having an opening corresponding to each of the photoelectric conversion elements; and a flat surface provided on the semiconductor substrate and the light shielding portion. There is provided a back-illuminated solid-state imaging device, characterized in that the opening of the light shielding portion has a shape narrowed from the flat surface side toward the semiconductor substrate side. The

  According to the present invention, it is possible to reduce the occurrence of color mixing due to light leakage to adjacent pixels and to suppress the decrease in the amount of light captured by the photoelectric conversion element.

The principal part cross-sectional schematic diagram of the back surface irradiation type solid-state imaging device which concerns on 1st Embodiment. The figure explaining the progress of the light which injected into the back irradiation type solid-state imaging device. The figure explaining the progress of the light which injected into the back irradiation type solid-state imaging device. The cross-sectional schematic diagram explaining the procedure which forms a light-shielding part. Sectional schematic diagram explaining the other procedure which forms a light-shielding part. The principal part cross-sectional schematic diagram of the backside illumination type solid-state imaging device which concerns on 2nd Embodiment.

  Hereinafter, a back-illuminated solid-state imaging device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a schematic cross-sectional view of an essential part of a backside illumination type solid-state imaging device according to the first embodiment of the present invention. The back-illuminated solid-state imaging device irradiates light on the back surface 11 side of the semiconductor substrate 1 and captures a subject image. The back surface 11 is a main surface of the semiconductor substrate 1 opposite to the side on which the wiring part 2 is provided. A large number of photoelectric conversion elements (photodiodes) made of, for example, an N-type semiconductor are formed on the semiconductor substrate 1. The photoelectric conversion element converts incident light into signal charges. The photoelectric conversion elements are respectively formed in the unit pixel areas A delimited by element isolation areas made of, for example, a P-type semiconductor. The cross section shown in the figure is a cut surface that crosses the vicinity of the center position of the unit pixel region A. Note that the detailed configuration of the semiconductor substrate 1 is not shown.

  The wiring unit 2 includes a wiring layer 8 for transferring signal charges generated by photoelectric conversion in the photoelectric conversion element, and an insulating member 7 for insulating the wiring layers 8 from each other. The light shielding portion 9 is provided on the back surface 11 of the semiconductor substrate 1. The light shielding unit 9 includes openings 12 corresponding to the respective photoelectric conversion elements, and is provided in a lattice that borders the openings 12. The light shielding portion 9 has a triangular shape in the illustrated cross section. The opening 12 has a tapered shape composed of a surface corresponding to the hypotenuse of such a triangle. The tapered shape formed by the opening 12 is a shape narrowed from the flat surface 13 side toward the semiconductor substrate 1 side. In addition, the light-shielding part 9 should just be comprised so that the opening 12 may make a taper shape, and the shape suitably deform | transformed on the basis of the shape whose cross section is a triangle may be sufficient. For example, the light-shielding part 9 may have a shape with a curved surface or a shape in which a part on the flat surface 13 side is rounded or flat.

  The first planarization layer 3 is provided on the back surface 11 and the light shielding portion 9 of the semiconductor substrate 1. The first planarization layer 3 constitutes a flat surface 13 on the side opposite to the semiconductor substrate 1 and the light shielding part 9 side. The 1st planarization layer 3 is comprised using resin materials, such as an acrylic resin.

  The color separation layer 4 is provided on the flat surface 13 of the first flattening layer 3. The color separation layer 4 includes a number of color filters 14 provided in an array. The color separation layer 4 includes a color filter 14 that selectively transmits red (R) light, a color filter 14 that selectively transmits green (G) light, and a color filter that selectively transmits blue (B) light. 14 is provided. The color filter 14 is provided so as to correspond to each of the photoelectric conversion elements. By providing the first planarizing layer 3, the configuration on the side of the semiconductor substrate 1 that is uneven by the light-shielding portion 9 and the color separation layer 4 are firmly fixed.

  The second planarization layer 5 is provided on the color separation layer 4. The second planarizing layer 5 constitutes a planar surface 15 on the side opposite to the first planarizing layer side. In the color separation layer 4, the gap between the color filters 14 is provided with a gap layer 10 configured to be filled with the same material as that of the second planarization layer 5. The 2nd planarization layer 5 is comprised using resin materials, such as an acrylic resin. The microlens array 6 is provided on the flat surface 15 of the second flattening layer 5. The microlens array 6 includes a number of microlens elements 16 provided in an array. The microlens element 16 is provided so as to correspond to each of the photoelectric conversion elements. By providing the second planarization layer 5, the color separation layer 4 and the microlens array 6 are firmly fixed.

  In the present embodiment, by providing the light shielding portion 9 on the semiconductor substrate 1 side of the first planarization layer 3, from the incident side surface of the backside illumination type solid-state imaging device to the first planarization layer 3 through the light separation layer 4. Until it reaches, it can be maintained without decreasing the opening area. Therefore, it is possible to efficiently advance light toward the semiconductor substrate 1 as compared with the case where a light shielding layer is provided on the incident-side surface of the back-illuminated solid-state imaging device or the color separation layer 4.

  2 and 3 are diagrams for explaining the progress of light incident on the back-illuminated solid-state imaging device. FIG. 2 shows an example in which the principal ray is parallel to the optical axis of the microlens element 16. The light traveling parallel to the optical axis is collected by the microlens element 16, passes through the opening 12 of the light shielding unit 9, and enters the photoelectric conversion element. The light shielding unit 9 is disposed so as not to block the light collected by the microlens element 16 by installing the opening 12 in the vicinity of the boundary between the unit pixel regions A with a tapered shape. Thereby, the light blocked by the light shielding unit 9 can be suppressed as much as possible, and the light can be efficiently advanced to the photoelectric conversion element. By making it possible to secure a large amount of light captured by the photoelectric conversion element, it is possible to obtain high light receiving sensitivity.

  FIG. 3 shows an example of light traveling in a direction greatly inclined with respect to the optical axis. By making the refractive index different between the gap layer 10 and the color filter 14, the gap layer 10 forms a so-called waveguide structure in which light is advanced by total reflection at the interface with the color filter 14. Light that enters the vicinity of the outer edge of the microlens element 16 in a certain unit pixel region A and travels toward the adjacent unit pixel region A is blocked by a light shielding portion below the gap layer 10 due to the waveguide effect in the gap layer 10. Proceed to 9. In this way, it is possible to suppress light leakage to adjacent pixels as indicated by broken line arrows in the drawing and reduce the occurrence of optical color mixing.

  Each color filter 14 is patterned so that a gap corresponding to the gap layer 10 is formed. When the second planarization layer 5 is formed, the gap layer 10 that can function as a waveguide structure can be formed by embedding the material of the second planarization layer 5 in the gap between the color filters 14. By performing patterning so that a gap is formed at the stage of forming the color filter 14, a separate process for forming a gap corresponding to the gap layer 10 becomes unnecessary.

  FIG. 4 is a schematic cross-sectional view illustrating a procedure for forming the light-shielding portion 9 in the manufacturing process of the solid-state imaging device according to the present embodiment. In the step shown in (a), a black photosensitive resin 17 is applied to the entire back surface 11 of the semiconductor substrate 1 stacked on the wiring portion 2. In the step shown in (b), the black photosensitive resin 17 is exposed through the photomask 18. In the step shown in (c), the light-shielding portion 9 having a desired shape is obtained by developing the black photosensitive resin 17. Furthermore, the structure shown in FIG. 1 is obtained by sequentially forming the first planarization layer 3, the color separation layer 4, the second planarization layer 5, and the microlens array 6.

  FIG. 5 is a schematic cross-sectional view illustrating another procedure for forming the light shielding portion 9. In the step shown in FIG. 5A, a black resin 20 is applied to the entire back surface 11, and a photosensitive resist (positive photoresist) 19 is applied thereon. As the black resin 20, for example, a black photosensitive resin is used. In the step shown in (b), the photosensitive resist 19 is exposed through the photomask 18. In the step shown in (c), the photosensitive resist 19 is patterned by a development process. In the step shown in (d), the shape of the patterned photosensitive resist 19 is transferred to the black resin 20 by etching to obtain the light-shielding portion 9 having a desired shape. The light shielding portion 9 may be formed by a method other than that described in this embodiment as long as it can be formed in a desired shape.

  The light shielding portion 9 is not limited to the one provided on the back surface 11 of the semiconductor substrate 1, and is on the back surface 11 side of the semiconductor substrate 1 and below the color separation layer 4. 3 is sufficient if it is provided so as to be covered with 3. For example, another layer such as an antireflection film may be provided between the back surface 11 and the light shielding portion 9.

(Second Embodiment)
FIG. 6 is a schematic cross-sectional view of an essential part of a backside illumination type solid-state imaging device according to the second embodiment of the present invention. The present embodiment is characterized in that a microlens array 30 is formed on the color separation layer 4. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The microlens array 30 includes a large number of microlens elements 16 provided in an array. In the color separation layer 4, the gap between the color filters 14 is provided with a gap layer 10 that is filled with the same material as the microlens array 30. When the microlens array 30 is formed, the gap layer 10 that can function as a waveguide structure can be formed by embedding the material of the microlens array 30 in the gap between the color filters 14.

  In the present embodiment, similarly to the first embodiment, the occurrence of color mixture due to light leakage to adjacent pixels can be reduced, and the decrease in the amount of light captured by the photoelectric conversion element can be suppressed. In addition, the configuration of the present embodiment can be manufactured with fewer manufacturing steps because the second planarization layer 5 (see FIG. 1) in the first embodiment is unnecessary.

  DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 3 1st planarization layer, 4 color separation layer, 5 2nd planarization layer, 6, 30 micro lens array, 9 light-shielding part, 10 gap layer, 11 back surface, 12 opening, 13, 15 flat surface, 14 color filters, 16 microlens elements.

Claims (5)

A back-illuminated solid-state imaging device that irradiates light on the back side of a semiconductor substrate and captures a subject image,
A photoelectric conversion element provided on the semiconductor substrate for converting incident light into a signal charge;
A light-shielding portion provided on the back side of the semiconductor substrate and provided with an opening corresponding to each of the photoelectric conversion elements;
A flattening layer provided on the semiconductor substrate and the light-shielding portion and constituting a flat surface;
The back irradiation type solid-state imaging device, wherein the opening of the light-shielding portion has a shape narrowed from the flat surface side toward the semiconductor substrate side. A color separation layer provided on the flat surface and provided with a color filter corresponding to each of the photoelectric conversion elements;
The back-illuminated solid-state imaging device according to claim 1, wherein the color separation layer includes a gap layer provided in a gap between the color filters. A first planarization layer that is the planarization layer provided on the semiconductor substrate and the light shielding portion;
A second planarization layer provided on the color separation layer and constituting a flat surface;
The back-illuminated solid-state imaging device according to claim 2, wherein the gap layer is made of the same material as the second planarization layer. A microlens array that is provided on the color separation layer and includes a microlens element corresponding to each of the photoelectric conversion elements;
The backside illumination type solid-state imaging device according to claim 2, wherein the gap layer is made of the same material as the microlens array.   The back-illuminated solid-state imaging device according to any one of claims 1 to 4, wherein the light shielding portion has a substantially triangular cross-sectional shape.

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