Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2003-05-06
2004-04-13
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S246000, C257S248000, C257S249000, C257S250000
Reexamination Certificate
active
06720593
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a charge-coupled device (CCD) having a reduced width for barrier sections in a transfer channel and thus suited to a finer structure of the CCD.
(b) Description of the Related Art
In a recent solid-state imaging device including a CCD, the dimensions of the pixels are more and more reduced to have a finer structure, whereby the CCD therein is also requested to have a smaller width. The width of the CCD is an important factor which determines the amount of electrons (or electric charge) to be transferred in the solid-state imaging device, and a larger width of the CCD allows the CCD to transfer a lager amount of electrons therein and to afford an improved image quality for the solid-state imaging device.
FIG. 14
shows the structure of transfer electrodes in a conventional CCD in a top plan view. The CCD includes a plurality of first-level transfer electrodes
11
and a plurality of second-level transfer electrodes
12
, which are alternately arranged along a transfer channel
17
to transfer electric charge within the transfer channel
17
. The transfer channel
17
includes therein an n-well
20
heavily doped with n-type impurities and underlying the electrodes
11
and
12
. A first group of pairs each including one of the first-level transfer electrodes
11
and an adjacent one of the second-level transfer electrodes
12
and a second group of pairs each including another of the first-level transfer electrodes
11
and adjacent another of the second-level transfer electrodes
12
are alternately arranged along the transfer channel
17
. The first group of pairs are connected to a first interconnect line, whereas the second group of pairs are connected to a second interconnect line.
FIG. 15
shows the underlying transfer channel
17
in a top plan view. The transfer channel
17
is encircled by a p-well, and includes an n-well
20
heavily doped with impurities and a plurality of stripe n
−
-wells
21
lightly doped with impurities and arranged along the transfer channel
17
. The n
−
-wells
21
are formed on the surface regions of the n-well
20
. The portions of the n-well
20
exposed from the n
−
-wells
21
underlie the first-level transfer electrodes
11
, whereas the n
−
-wells
20
underlie the second-level transfer electrodes
12
. The electric charge is transferred along the transfer channel
17
in the direction of the arrows depicted.
FIG. 16
shows a flowchart of the process for manufacturing the CCD shown in FIG.
14
. The n-well
20
of the transfer channel
17
is first formed within a p-well formed in a semiconductor substrate (step S1), followed by implantation of boron ions into the peripheral area of the transfer channel
17
to form the p
+
-diffused region (step S2). Thereafter, an oxide film is formed over the entire surface of the substrate (step S3), followed by depositing a first polysilicon film and patterning thereof to thereby form the first-level transfer electrodes
11
(step S4). Subsequently, boron ions are implanted into surface regions of the n-well
20
in a self-alignment technique using the first-level transfer electrodes
11
as a mask, thereby selectively changing the surface regions of the n-well
21
to the n
−
-wells
21
(step S5). Thereafter, an oxide film and an inter-level dielectric film are formed (step S6), followed by depositing a second polysilicon film and patterning thereof to form the second-level transfer electrodes
12
(step S7).
As shown in
FIG. 14
, it is assumed that P, S
1
, S
2
, A
1
, A
2
, A
3
, A
4
and A
5
are pitch of the combination transfer electrodes
11
and
12
, space between adjacent two first-level transfer electrodes
11
, space between adjacent two second-level transfer electrodes
12
, distance between the contact plug
13
and the edge of the corresponding first-level transfer electrode
11
, distance between the contact plug
13
and the edge of the corresponding second-level transfer electrode
12
, width of the first-level transfer electrodes
11
, dimension of the overlapped portion between the first-level transfer electrode
11
and the corresponding second-level transfer electrode
12
and width of the contact plugs
13
, respectively.
In the design of the CCD shown in
FIG. 14
, the above pitch P, spaces S
1
and S
2
, distances A
1
and A
2
, width A
3
, dimension A
4
and width A
5
are determined in consideration of the design margin so that the pitch P satisfies the following relationship:
P≧S
1
+
S
2
+
A
1
+
A
2
+
A
4
+
A
5
.
This relationship, if satisfied, allows the CCD to have the overall configuration shown in FIG.
14
. However, due to the recent development of smaller dimensions for the pixels of CCD, it is desired that the pitch P of the combination transfer electrodes be equal to or below 2 &mgr;m, which fact renders the employment of configuration shown in
FIG. 14
to be difficult.
It may be considered that such a small-dimension CCD should have the configuration shown in FIG.
17
and
FIG. 18
, which show the structure of the CCD similarly to
FIGS. 14 and 15
, respectively. In the depicted structure, the contact plugs
13
connecting the first interconnect line
41
and the corresponding transfer electrodes
11
and
12
in the first group are disposed in the vicinity of one edge of the transfer channel
17
opposite to the edge, in the vicinity of which the contact plugs
13
connecting the second interconnect line
42
and the corresponding transfer electrodes
11
and
12
in the second group are disposed. In other words, the contact plugs
13
are arranged in a staggered configuration with respect to the center of the transfer channel
17
. This structure may allow the design margin in the patterning for the contact plugs
13
to be reduced to reduce the pitch P of the combination transfer electrodes. However, this structure has a disadvantage in that the width (W2) of the transfer channel
17
is reduced, as shown in
FIGS. 18 and 19
, whereby the maximum electric charge to be transferred by the transfer channel
17
is also reduced.
In order to assure a sufficient width for the transfer channel
17
, another structure such as shown in
FIG. 19
may be considered. However, this structure requires a sufficient space between adjacent two second-level transfer electrodes
12
for assuring an equal width for the second-level transfer electrode
12
and the barrier section or n
−
-well. This results in a larger pitch P for the transfer channel, and thus is not suitable.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a CCD having a reduced pitch P for the combination transfer electrodes and a width sufficient for transferring an adequate amount of electric charge, irrespective of the CCD being designed in a design rule similar to the conventional design rule and manufactured by a process similar to the conventional process.
The present invention provides a charge-coupled device (CCD) including: a semiconductor substrate having therein a transfer channel on a surface region of the semiconductor substrate; a plurality of first transfer electrodes and a plurality of second transfer electrodes overlying the semiconductor substrate and alternately arranged along the transfer channel; and first and second interconnect lines for supplying two-phase driving signals to the first and second transfer electrodes to transfer electric charge along the transfer channel, wherein: the transfer channel includes a plurality of first diffused regions each underlying a corresponding one of the first transfer electrodes and a plurality second diffused regions each underlying a corresponding one of the second transfer electrodes, the first diffused regions constituting charge storage sections and the second diffused regions constituting barrier sections during transferring the electric charge; and each of the charge storage sections has a width larger than a width of each of the barri
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