JP2876838B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device of the present invention, and more particularly to a method for improving the sensitivity of a solid-state imaging device.

[0002]

2. Description of the Related Art Various characteristics of solid-state imaging devices have been improved due to recent advances in technology, and due to improvements in resolution, they have been adopted in cameras for broadcast and business use as well as for consumer use. However, since the area of the unit cell is reduced due to the reduction of the chip area for the purpose of improving the chip yield, the sensitivity is reduced. As a countermeasure against this, when performing charge detection using a floating diffusion layer, a method such as reducing the capacitance of the floating diffusion layer is generally adopted.

FIG. 4A is a cross-sectional view of a horizontal cell of an interline solid-state imaging device equipped with an on-chip microlens. A photodiode 2 composed of an n-type diffusion layer diffused in a p-type substrate 1 is formed with a channel stop 4 and a vertical transfer register 3 interposed therebetween. Further, since the opening of the photodiode 2 is defined by the blocking film 6 laminated on the transfer electrode 5 of the vertical transfer register 3 via an insulating film, the aperture ratio in the horizontal direction is usually about 40%. Therefore, the optical axis of the lens 8 is aligned with the center of the opening of the photodiode 2 through the base layer 7 to improve the apparent aperture ratio, and the focal length of the lens 8 substantially matches the thickness d of the base layer 7. It is formed so that.

FIG. 4B is a plan view showing the configuration of a lens when the distance a between adjacent photodiodes 2 is common in the vertical and horizontal directions. Even if the lens 8 is formed in a circular shape and the incident light 9 is condensed on the photodiode 2 without aberration, the non-photosensitive area 10 exists as shown by oblique lines.

Generally, the distance between the photodiodes 2 is different in the vertical and horizontal directions, so that the lens has an elliptical shape as shown in FIG. Accordingly, FIG.
Even if the incident light 9 is condensed on the photodiode 2 as shown in FIG. 5A, the lens 11 becomes an aspherical surface as shown in FIG.
Will not collect light. For this reason, as shown in FIG. 5B, the non-photosensitive area 12 may be further enlarged.

[0006]

As described above, the conventional laminated lens of the solid-state imaging device cannot always say that the incident light is condensed efficiently, and has a drawback that the non-photosensitive region exists at about 25 to 30%. was there.

[0007]

According to the present invention, there is provided a solid-state image pickup device comprising a transfer register, a photoelectric conversion device arranged two-dimensionally in a vertical direction and a horizontal direction, and a stacked type having a focus near a surface of the photoelectric conversion device. A first one-dimensional microlens and the first
Is formed in a direction perpendicular to the direction in which the one-dimensional microlens is formed, has a focal point near the surface of the photoelectric conversion element, and is further laminated on the first one-dimensional microlens. It has a second one-dimensional microlens provided on the filter.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a partial configuration diagram of one embodiment of the present invention. A chip 15 on which a photodiode and a transfer register are formed has a first one-dimensional lens stacked in a horizontal direction (x direction), while a second one is formed. The one-dimensional lens is formed on the lower surface of the filter 14 in the vertical direction (y direction), and the chip 15 and the filter 14 are bonded together such that each lens is focused on the center of the opening of each photodiode. Note that parts other than the lens, such as the photodiode and the transfer register, are the same as those in the related art, and a description thereof will be omitted.

FIG. 2A is a sectional view of a bit in a horizontal direction,
FIG. 2B is a sectional view of the bit in the vertical direction. FIG.
3A, the incident light 19 is vertically incident on the filter base 16 and the second one-dimensional lens 17 in the horizontal direction, and thus does not exhibit a light condensing action. The light is condensed on the surface of the photodiode 2 with a focal length dx determined by the difference in the refractive index of the gap between the filter chip and the filter chip. In addition, as shown in FIG. 2B, the incident light 19 includes the first one-dimensional lens 18 and the second light source provided on the filter base 16 including the curvature of the gap between the filter and the chip in the vertical direction. Dimensional lens 1
7, the light is collected with a different focal length dy.

Accordingly, since the incident light 19 can be condensed with the focal lengths dx and dy independently of each other in the x and y directions, an ideal lens shape can be obtained, and the collection of light nearly 100% with respect to each cell area. A light effect is obtained, and the sensitivity can be improved by about 30% as compared with the related art.

The photodiode 2 generally has a lower aperture ratio in the x direction than in the y direction. In this case, when the F value of the lens to be imaged is small, that is, when the incident angle of the incident light is wide, vignetting occurs. In order to reduce the vignetting, it is necessary to shorten the focal length (= dx) of the lens. However, the two-dimensional lens has a drawback that the aberration increases. By stacking the one-dimensional lens, dx and dy are reduced. Since they can be set separately, there is an advantage that the design margin is widened.

FIG. 3 is an oblique sectional view of a bit according to another embodiment of the present invention. The first one-dimensional lens 18 and the second one-dimensional lens 21 are respectively formed in the horizontal and vertical directions with respect to the arrangement direction of the photodiodes 2 as in the front row. However, in contrast to the previous example, the second one-dimensional lens 21 is formed by forming a first one-dimensional lens 18 and then stacking a base layer 20 for flattening and providing the base layer 20 thereon. In this example, since light is condensed due to the difference in the refractive index between the base layer 20 and the first one-dimensional lens 18, there is a disadvantage that a general material (eg, resin) is not large because it is about 1.4 to 1.6. Despite this, it is possible to form a two-layer lens by process matching, which is expected to improve the accuracy. Also, compared to the case of attaching a filter, the absorption due to the thickness of the base layer and the number of reflective surfaces are small, and the sensitivity is high. There is an advantage that the rate of decrease is small.

[0013]

As described above, according to the present invention, the solid-state image pickup device has two laminated lenses or two layers including a lens on a bonding filter, each of which is made orthogonal by a one-dimensional lens. By doing so, since the focal length can be set independently for each direction, the light condensing power per cell area can be improved and the sensitivity can be improved.

[Brief description of the drawings]

FIG. 1 is a partial configuration diagram of an embodiment of the present invention.

FIG. 2 is a sectional view of a bit in horizontal and vertical directions.

FIG. 3 is a cross-sectional view of a bit according to another embodiment of the present invention.

FIG. 4A is a cross-sectional view of a conventional cell in the horizontal direction, and FIG.
2 is a plan view showing the configuration when the cell pitch is the same.

5A is a cross-sectional view taken along the line BB ′ of FIG. 5B, FIG.
2 is a plan view of a conventional example in which the cell pitch is different between vertical and horizontal.

[Explanation of symbols]

 Reference Signs List 1 P-type substrate 2 Photodiode 3 Vertical transfer register 4 Channel stop 5 Transfer electrode 6 Light-shielding film 7, 20 Base layer 8, 11 Lens 9, 13, 19, 22 Incident light 10, 12 Light-insensitive area 14 Filter 15 Chip 16 Filter Base 17, 21 Second one-dimensional lens 18 First one-dimensional lens

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/335 H01L 27/14

Claims (2)

(57) [Claims] A photoelectric conversion element arranged two-dimensionally in a vertical and horizontal direction; a transfer register; a first stacked one-dimensional microlens having a focal point near a surface of the photoelectric conversion element; A second one-dimensional array formed in a direction perpendicular to the direction in which the one one-dimensional microlens is formed, also having a focal point near the surface of the photoelectric conversion element and further laminated on the first one-dimensional microlens; A solid-state image sensor comprising a micro lens. 2. The solid-state imaging device according to claim 1, wherein
A solid-state imaging device, wherein the second one-dimensional microlens is provided on a bonding filter.