Solid-state imaging device having aspheric lenses

Details Solid-state imaging device having aspheric lenses Solid-state imaging device having aspheric lenses

2000-10-02

2002-07-02

Nelms, David (Department: 2818)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S291000, C438S048000

Reexamination Certificate

active

06414343

ABSTRACT:

This application is based on Japanese Patent Application HEI 11-287336, filed on Oct. 7, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to a shape and a structure of an on-chip micro-lens formed in a solid-state imaging device in order to input light efficiently.
b) Description of the Related Art
In a solid-state imaging device having a multiplicity of photoelectric conversion units formed on a semi-conductor substrate in a matrix shape, a light shielding film is formed on the substrate. The light shielding film has openings, each of which corresponds to each of the photoelectric conversion units formed on the substrate. A micro-lens is formed just above each opening of the light shielding film to increase the efficiency of the light concentration.
FIG. 6
are enlarged cross sectional views of a part of the solid-state imaging device according to the prior art.
Photoelectric conversion units
2
and transfer channels
3
are formed on a semi-conductor substrate
1
made of silicon. A partition region
4
is formed next to each transfer channel
3
. After that, an upper surface of the semi-conductor substrate
1
having the photoelectric conversion units
2
, the transfer channels
3
and the partition regions
4
are oxidized to form an insulating film
5
made of silicon oxide or the like.
Next, a transfer electrode is formed above each transfer channel
3
, and an insulating film
5
a
is formed on the substrate
1
covering the transfer electrodes
5
a
. A light shielding film
7
having openings is formed on the insulating film
5
a
to shade the transfer electrodes
5
a
. Each opening of the light shielding film
7
is formed just above each photoelectric conversion unit
2
.
On the light shielding film
7
, a focus adjusting layer
8
including a passivation layer, and then a color filter layer
9
is formed thereon.
A planarizing layer
10
is formed on the color filter layer
9
, and thereon a lens layer
11
made of transparent resin is formed by the spin-coat. The lens layer
11
is patterned by the photolithography to make a shape shown in FIG.
6
A.
Then, to make the patterned lens layers
11
into micro-lenses
11
, each having a shape shown in
FIG. 6B
, by flowing with heating process at a temperature beyond a softening temperature of the transparent resin used for forming the lens layers
11
.
A commonly used imaging sensor for camcorders and digital still cameras has over one million pixels. In this kind of multi-pixel imaging sensor, a size of an on-chip micro lens is less than about five micrometers around, and is getting nearly three micrometers around. The size of that kind of imaging sensor is less than a quarter of a size of an old imaging sensor.
As a pixel gets smaller, an on-chip micro lens gets smaller, too. Shrinking of the on-chip micro lens makes a radius of curvature short. Therefore, it will make a focal length short. Also, the small on-chip micro lens faces a problem of focal length that a focal length near the edges of the on-chip micro lens is shorter than that of the axis of the on-chip micro lens.
For example, a lens for a conventional camera is made into an aspheric lens so as to solve the problem of focal length. Therefore, it is preferable to make an on-chip micro lens used for a solid-state imaging device into an aspheric lens. However, it is very difficult to form an aspheric lens as an on-chip micro lens according to a prior manufacturing method.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a solid-state imaging device, wherein a micro lens can gather light onto a photoelectric conversion unit, manufactured without a complex step such as forming an inner lens.
It is another object of the present invention to provide a solid-state imaging device that can effectively lead incident light onto a pixel.
According to one aspect of the present invention, there is provided a solid-state imaging device comprising: a semiconductor substrate which demarcates a two-dimensional surface; a multiplicity of photoelectric conversion units configured in a multiplicity of rows and columns on the surface of said semiconductor substrate; a light shielding film having openings formed above said semiconductor substrate, each of the openings is formed on each of said photoelectric conversion unit; a planarizing insulating film formed on said light shielding film; micro lenses formed on said planarizing insulating film, each micro lens is formed just above each of said opening; and a modifying film having one layer or a plurality of layers formed directly on said micro lenses and having a top surface with different curvature from that of a top surface of the micro lenses.
According to another aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device comprising the steps of: (a) forming a multiplicity of photoelectric conversion units configured in a multiplicity of rows and columns on a surface of a semiconductor substrate which demarcates a two-dimensional surface; (b) forming a light shielding film having openings, each of which is formed on each of said photoelectric conversion unit, above said semiconductor substrate; (c) forming a planarizing insulating film on said light shielding film; (d) forming micro lenses, each of which is formed just above each of said opening, on said planarizing insulating film; (e) forming a modifying film having one layer or a plurality of layers on said micro lenses; and (f) curing said film having one layer or a plurality of layers formed at said step (e) by heating.
According to another aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device comprising the steps of: (a) forming a multiplicity of photoelectric conversion units configured in a multiplicity of rows and columns on a surface of a semiconductor substrate which demarcates a two-dimensional surface; (b) forming a light shielding film having openings, each of which is formed on each of said photoelectric conversion unit, above said semiconductor substrate; (c) forming a planarizing insulating film on said light shielding film; (d) forming color filters in a plurality of colors on said planarizing insulating layer; (e) forming micro lenses, each of which is formed just above each of said openings, on said color filters; (f) forming a modifying film having one layer or a plurality of layers on said micro lenses; (g) removing part of said modifying film according to colors of said color filters by patterning; and (h) curing said modifying film formed at said steps (f) and (g) by heating.


REFERENCES:
patent: 5451766 (1995-09-01), Van Berkel
patent: 6060732 (2000-05-01), Murakami et al.
patent: 6069350 (2000-05-01), Ohtsuka et al.
patent: 6274516 (2001-08-01), Kamei et al.
patent: 6295107 (2001-09-01), Watanabe et al.
patent: 6297911 (2001-10-01), Nishikawa et al.

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