Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1998-08-13
2001-07-10
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S216000, C257S432000, C216S024000
Reexamination Certificate
active
06259083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a solid state imaging device having, for example, a concave lens structure formed therein and its manufacturing method.
2. Description if the Related Art
Recently, in a color solid state imaging device, as the device is down-sized, a so-called on-chip structure, in which a color filter is formed within the device and further a microlens is formed on the color filter, is employed, whereby an incident light is converted by the microlens to improve the sensitivity at a sensor or light receiving portion.
Further, there is proposed such a solid state imaging device in which a second lens structure having a light converging characteristic is provided in the solid state imaging device having the above-mentioned on-chip structure between the microlens on its surface and the light receiving portion.
As the second lens structure, there is proposed a concave lens structure in which the boundary face between two layers having different refractive indexes, for example, is a concave face on which a concave lens is formed, and so on.
FIG. 1
is a schematic diagram showing an example of a solid state imaging device
50
in which a concave lens structure is formed between a surface layer and a light receiving portion.
In the solid state imaging device
50
, a sensor (light receiving portion)
52
is formed in the semiconductor substrate
51
and a transfer electrode
54
is formed on the semiconductor substrate
51
except for the light receiving portion
52
through a gate insulating film
53
. A light shielding film
56
is formed on the transfer electrode
54
through an intra-layer insulating film
55
. The light shielding film
56
prevents a light from being incident on the transfer electrode
54
. An opening is formed through the light shielding film
56
at its portion on the light receiving portion
52
so that the light is incident on the light receiving portion
52
through the opening.
For example, a BPSG film
57
is formed to cover the light shielding film
56
. This BPSG film
57
has on its surface a concave and a convex corresponding to a step formed by the light shielding film
56
or the surface portion of the BPSG film
57
just on the light receiving portion
52
becomes a concave portion.
On the BPSG film
57
, there is formed a high refractive index layer
58
which is made of, for example, a SiN film (refractive index n=1.9~2.0) or the like to form a concave lens structure (so-called intra-layer lens) therein. The upper surface of the high refractive index layer
58
is flattened and a color filter
60
is formed on the flattened surface through a passivation film
59
. On the color filter
60
, a microlens is formed
61
.
In this case, in order that a light incident on the concave lens surface, namely on the boundary surface between the two layer or BPSG film
57
and the high refractive layer
58
is converged on the light receiving portion
52
, it is necessary to adjust the relation between the refractive indexes of the BPSG film
57
and the high refractive index layer
58
.
In general, in consideration of the concave lens, in order to converge the incident light on the light on the light receiving portion
52
, such an adjustment is carried out that the refractive index of the high refractive index layer
58
, which is an upper layer than the BPSG film
57
with the lens surface as the boundary, is made higher than the refractive index of the BPSG film
57
.
When a light is incident on the concave lens surface in an inclined direction, however, dependent on the incident angle of light, there is such a case that the light will be incident on the concave lens surface at a large angle which will not occur in a structure having formed no concave lens structure.
Therefore, it will be predicted that a total reflection of light occurs on the concave lens surface dependent on the incident angle and hence there may be such a fear that the improvement of sensitivity becomes insufficient.
SUMMARY OF THE INVENTION
In view of the above-mentioned point, it is an object of the present invention to provide a solid state imaging device with high sensitivity in which an incident light is introduced to a light receiving portion widely. According to an aspect of the present invention, there is provided a solid state imaging device in which provided is a layer having a concave lens structure in a portion from an opening of a sensor to an uppermost surface layer and a well-shaped dug structure is formed at a bottom portion of the concave lens structure.
According to the solid state imaging device with the above arrangement of the present invention, since the well-shaped dug structure is provided at the bottom portion of the concave lens structure, a light incident on the bottom portion of the concave lens structure at a large incident angle does not cause a total reflection, but is introduced to the sensor opening by the well-shaped dug structure, to thereby increase a light receiving amount in the sensor.
REFERENCES:
patent: 4694185 (1987-09-01), Weiss
patent: 5306926 (1994-04-01), Yonemoto
patent: 5323052 (1994-06-01), Koyama
patent: 5371397 (1994-12-01), Maegawa et al.
patent: 5593913 (1997-01-01), Aoki
patent: 5633527 (1997-05-01), Lear
patent: 5844290 (1998-12-01), Furumiya
Le Que T.
Luu Thanh X.
Sonnenschein Nath & Rosenthal
Sony Corporation
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