Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2000-12-19
2003-04-08
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S223000
Reexamination Certificate
active
06545301
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state image sensor such as CCD (Charge Coupled Device memory) having high detection sensitivity, and to a manufacturing method therefor.
FIG. 4A
is a plan view showing main part of a CCD according to the prior art. In the figure, reference numeral
41
denotes a horizontal transfer section,
42
denotes a horizontal power output gate,
43
denotes a reset gate,
44
denotes a reset drain,
45
denotes a detector MOSFET (MOS Field Effect Transistor),
46
denotes a floating diffusion layer (hereinafter, referred to as FD),
47
and
57
denote contact holes,
48
denotes an aluminum line, and
50
denotes a gate electrode of the detector MOSFET
45
. This detector MOSFET
45
is a part of a detector circuit for detecting potential changes of the FD
46
. The FD
46
is formed of an N
+
layer, and the N
+
layer is made by exposing part where the FD
46
is to be formed with photoresist by patterning, and performing ion implantation to the exposed part.
FIG. 4B
is a sectional view taken along the line B—B of
FIG. 4A
, where reference numeral
51
denotes a P-type semiconductor substrate and
52
denotes field oxide. As shown in
FIG. 4B
, a contact hole
47
is formed above the FD
46
, and a contact hole
57
is also formed above an FD
46
side end portion of the gate electrode
50
. The aluminum line
48
is formed at the contact holes
47
,
57
, by which the FD
46
and the gate electrode
50
are connected to each other by the aluminum line
48
.
In the CCD of this constitution, a reset pulse voltage applied to a reset gate
43
is made high level to reset the FD
46
, and the reset pulse voltage is made low level to transfer signal charges from the horizontal transfer section
41
to the FD
46
. In this case, assuming that the entire capacitance containing the gate electrode
50
of the detector MOSFET
45
connected to the FD
46
is Ct and that the amount of transferred signal charges is Q, then there arises a potential change of &Dgr;Vfd=Q/Ct in the FD
46
and the potential change is detected by the detector MOSFET
45
. Also, when the gain of the detector circuit having the detector MOSFET
45
is assumed to be G, the detection sensitivity of the detector circuit becomes &Dgr;Vout=G·Q/Ct, where a voltage change proportional to the signal charge Q is outputted to the detector circuit.
In this case, capacitances composing the Ct principally includes an FD—reset gate junction capacitance Cfr, an FD—horizontal output gate junction capacitance Cog, a gate capacitance Cg of the detector MOSFET, an FD—semiconductor substrate junction capacitance Cfd, an aluminum wiring capacitance Cmr and the like. That is, the entire capacitance Ct containing the gate electrode
50
of the detector MOSFET
45
connected to the FD
46
is Ct=Cfr+Cog+Cg+Cfd+Cmr. Therefore, if the gain G of the detector circuit is constant, then the detection sensitivity can be made higher more and more with Cfd smaller. Since the capacitance Cfd of the FD
46
can be considered proportional to the area of the FD
46
, the area of the FD
46
needs to be reduced as much as possible in order to achieve a high detection sensitivity.
FIG. 5A
is a plan view showing main part of another CCD according to the prior art, and
FIG. 5B
is a sectional view taken along the line
5
B—
5
B of FIG.
5
A.
FIGS. 5A and 5B
are different from the prior art example of
FIGS. 4A and 4B
in that a gate electrode
150
of a detector MOSFET
145
is formed so as to extend to above an FD
146
, and that aluminum line
148
formed at one contact hole
147
interconnects the FD
146
and the gate electrode
150
. Therefore, in
FIGS. 5A and 5B
, the same component parts as those of
FIGS. 4A and 4B
are designated by the same reference numerals and omitted in description.
For manufacturing methods of the prior art CCDs, because it is difficult to further reduce the area of the FD
46
,
146
, the detection sensitivity of the charge detector circuit cannot be enhanced. That is, there is a problem that signal charges transferred from the horizontal transfer section
41
to the FD
46
cannot be detected at high sensitivity. In more detail, since the FD
46
,
146
and the contact hole
47
,
147
are formed by patterning with photoresist, there has been a need for ensuring alignment margins d
1
, d
2
for the FD
46
,
146
and the contact hole
47
,
147
. The alignment margin d should be 0.2-0.4 &mgr;m or so, taking into consideration variations in line widths of the aluminum lines
48
,
148
and the FD
46
,
146
as well as in alignment. However, because the FD
46
,
146
is sized about 1-2 &mgr;m□, the alignment margins d
1
, d
2
are as large as 10-25% of the FD
46
,
146
, making it impossible to reduce the area of the FD
46
,
146
.
Therefore, an object of the present invention is to provide a CCD, as well as its manufacturing method, which makes it possible to reduce the area of the FD and to detect signal charges of the FD at high sensitivity.
In order to achieve the above object, there is provided a solid-state image sensor comprising: a first-conductive-type semiconductor substrate; a charge transfer section formed on the first-conductive-type semiconductor substrate; a second-conductive-type floating diffusion layer for receiving signal charges from the charge transfer section; and a detector transistor for detecting a potential change of the second-conductive-type floating diffusion layer, wherein
an opening is formed in a gate electrode of the detector transistor;
the gate electrode of the detector transistor extends toward the second-conductive-type floating diffusion layer
26
and the opening
30
a
is positioned above the second-conductive-type floating diffusion layer
26
.
In this solid-state image sensor according to the invention, since the opening formed in the gate electrode of the detector transistor is positioned above the floating diffusion layer of the second-conductive-type floating diffusion layer, forming a metal line above the opening of the gate electrode allows self alignment to be achieved, by which the second-conductive-type floating diffusion layer and the metal line are connected to each other. Therefore, the alignment margin between the second-conductive-type floating diffusion layer and the contact hole can be eliminated, so that the area of the second-conductive-type floating diffusion layer can be reduced. As a result, the junction capacitance between the second-conductive-type floating diffusion layer and the semiconductor substrate is decreased so that signal charges of the second-conductive-type floating diffusion layer can be detected at high sensitivity.
Also, there is provided a solid-state image sensor comprising: a first-conductive-type semiconductor substrate; a charge transfer section formed on the first-conductive-type semiconductor substrate; a second-conductive-type floating diffusion layer for receiving signal charges from the charge transfer section; and a detector transistor for detecting a potential change of the second-conductive-type floating diffusion layer, wherein
the detector transistor has discontinuous first and second gate electrodes;
an opening is formed in the first gate electrode; and
the opening is positioned above the second-conductive-type floating diffusion layer.
In this solid-state image sensor according to one embodiment of the invention, since the detector transistor has discontinuous first and second gate electrodes and the opening of the first gate electrode is positioned above the second-conductive-type floating diffusion layer, forming a metal line above the opening of the first gate electrode allows self alignment to be achieved, by which the second-conductive-type floating diffusion layer and the metal line are connected to each other. Therefore, the alignment margin between the second-conductive-type floating diffusion layer and the contact hole can be eliminated, so that the area of the second-conductive-type flo
Conlin David G.
Edwards & Angell LLP
Jensen Steven M.
Meier Stephen D.
Sharp Kabushiki Kaisha
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