Solid-state pickup element and method for producing the same

Details Solid-state pickup element and method for producing the same Solid-state pickup element and method for producing the same

2001-04-04

2003-07-29

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

C438S506000, C438S916000

Reexamination Certificate

active

06599772

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a solid-state pickup element employing a vertical type overflow drain structure in, for example, a CCD solid-state pickup element, etc., and a method for producing the solid-state pickup element.
BACKGROUND OF THE INVENTION
A solid-state pickup element of a so-called vertical type overflow drain structure, in which surplus charge is discharged to the substrate side at a light receptive sensor part, has been publicly known as a solid-state pickup element.
A solid-state pickup element has been proposed which has sensitivity in a near-infrared ray area by deeply forming a charge collecting area of a light receptive sensor part in a solid-state pickup element of a vertical type overflow drain system like this.
A general configurational view (cross-sectional view) of such a CCD solid-state pickup element having sensitivity in a near-infrared ray area is shown in FIG.
11
.
The CCD solid-state pickup element
51
is such that the first semiconductor well area
53
of the second conductive type, that is, a p-type, which becomes an overflow barrier area, is formed on a semiconductor substrate
52
made of the first conductive type, that is, an n-type silicon, and a high resistance area
54
having high specific resistance such as, for example, p
−
area, non-doped area, n
−
area, etc., is formed on the semiconductor substrate
52
on which the first p-type semiconductor well area
53
is formed.
An n
+
semiconductor area
56
that constitutes respective matrix-arrayed light receptive sensor parts
55
is formed on the surface of the high resistance area
54
, and a p+ positive charge accumulating area
57
is also formed thereabove. The p
+
positive charge accumulating area
57
prevents a dark current from occurring due to a phase boundary level. The n
+
semiconductor area
56
becomes a so-called charge accumulating area. An n
−
semiconductor area
70
having a denser concentration than that of the high resistance area, which will become a charge collecting area reaching the first p-type semiconductor well area, which is so-called overflow barrier area
53
, from the n
+
semiconductor area
56
, is formed on the high resistance area
54
below the n
+
semiconductor area
56
. An area where photo-electric conversion of the light receptive sensor part
55
is carried out includes the n
+
semiconductor area
56
and the n
−
semiconductor area
70
before the overflow barrier area
53
of a depletion layer extending from the n
+
semiconductor area
56
downward of the substrate.
An n-type embedded transfer channel area
60
of a vertical transfer register
59
is formed at the position corresponding to one side of the respective light receptive sensor part row of the high resistance area
54
so that a reading gate part
58
is placed between the same and the p+ positive charge accumulating area
57
. Also, the second p-type semiconductor well area
61
is formed so as to surround the embedded transfer channel area
60
. Further, a p-type channel stop area
62
is formed, which sections respective pixels including the light receptive sensor part
55
.
A transfer electrode
65
made of, for example, polycrystalline silicon is formed on the embedded transfer channel area
60
, channel stop area
62
, and reading gate part
58
via a gate insulation film
64
. The vertical transfer register
59
of a CCD structure is constructed of the embedded transfer channel area
60
, gate insulation film
64
, and transfer electrode
65
.
A light shielding film
67
made of, for example, Al is formed on the entire surface excluding an opening of the light receptive sensor part
55
via an interlayered insulation film
66
that shields the transfer electrode
65
. Light is made incident into the light receptive sensor part
55
via the opening of the light shielding film
67
, and the light can be prevented from incidence into parts other than the light receptive sensor part
55
by the light shielding film
67
.
Further, although not illustrated, a flattening film, a color film, on-chip lens, etc., are formed, thereby constituting a CCD solid-state pickup element
51
.
And, in the above-described structure, as a method for improving the sensitivity with respect to a longer wavelength, as disclosed in, for example, Japanese Patent Laid-Open No. 331058/1997, a method has been proposed which deeply widens the charge collecting area
70
by causing a silicon epitaxial film of a low impurity concentration to thickly grow on the upper layer of the first p-type well area
53
as the high resistance area
54
of
FIG. 11
in order to form an overflow barrier area at a deeper position.
Herein, in order to introduce electrons, which are photo-electrically converted at a deeper position from the surface, to the surface of the light receptive sensor part
55
, it is necessary that the potential is inclined toward the surface side in a depletion layer between an n+ semiconductor area
56
that constitutes a photo diode of the light receptive sensor part
55
and a p-type semiconductor well area
53
that constitutes an overflow barrier.
Conventionally, the sensitivity with respect to a longer wavelength has been achieved by making the charge collecting area
70
into a low concentration area (n
−
).
Further, since, at the semiconductor area
54
B downward of the second p
+
semiconductor well area
61
that constitutes the vertical transfer register
59
, inclination that is inverse of the light receptive sensor part
55
is formed to be potentially continuous with the first p
+
type semiconductor well area
53
, which is positioned further downward thereof, such a profile is provided, in which electrons flow in the direction of the substrate
52
.
Therefore, as the pixel size becomes small, the low concentration area, that is, the charge collecting area
70
is subjected to three-dimensional potential modulation from the above-described semiconductor area
54
B, whereby the overflow barrier will move to the surface side.
Resultantly, such a situation occurs, where no sensitivity is provided with respect to the longer wavelength side.
To suppress the situation, it is necessary to form the n
+
semiconductor area
56
of the light receptive sensor part
55
further closer to the first p-type semiconductor well area
53
.
Therefore, ion injection of high energy will be required.
However, in the present situation, there exists no equipment that can inject electrons with energy that is more than 3.2 Mev.
SUMMARY OF THE INVENTION
Therefore, where P (phosphor) is injected with energy of 3.2 MeV at maximum, the projection range Rp becomes Rp=2.6 &mgr;m+&Dgr;Rp=0.3 &mgr;m, wherein the n
+
semiconductor area
56
can be formed at only a depth of 3 &mgr;m in total.
Accordingly, the pixel size cannot be reduced further.
In order to solve the above-described problem, it is therefore an object of the invention to provide a solid-state pickup element that is capable of achieving improvement of the sensitivity and reducing the size thereof, and a method for producing the same.
A solid-state pickup element according to the invention is constructed so that an overflow barrier area is formed in a semiconductor substrate, an epitaxial layer is formed on the semiconductor substrate, a first conductive type semiconductor area, which widens a charge collecting area upward of the overflow barrier area, is formed so as to include at least the inside of the semiconductor substrate, and a charge accumulating area of a light receptive sensor part is formed at the position corresponding to the first conductive type semiconductor area of the epitaxial layer.
A method for producing the solid-state pickup element according to the invention includes the steps of forming an overflow barrier area in a semiconductor substrate, forming the first conductive type semiconductor area on the surface of the semiconductor substrate, forming an epitaxial layer on the semicon

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