Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Charge transfer device
Reexamination Certificate
1999-02-03
2002-10-29
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Charge transfer device
C438S060000, C438S075000, C438S145000
Reexamination Certificate
active
06472255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid-state imaging device and a method of its production, and more particularly to a solid-state imaging device and a method of its production, wherein the device comprises: an electric charge transfer portion provided with a gate insulation film constructed of a plurality of films which are different in thickness from each other; and, an output amplifier portion.
2. Description of the Related Art
Heretofore, a CCD (i.e., Charge Coupled Device) typical of the solid-state imaging devices has been known. Formed on a common substrate of this CCD are: a photodetector for performing photoelectric conversion from incident light to an electric charge; an electric charge transfer portion for transferring the electric charge thus converted in the photodetector; and, an output amplifier portion for detecting the electric charge to issue a signal. In this case, each of the photodetector, electric charge transfer portion and the output amplifier portion has a gate insulation film formed on the semiconductor substrate as one of its constituent elements, and serves its own function as described above.
FIG. 14
is a schematic diagram of a conventional solid-state imaging device (hereinafter referred to as a first prior art) used in the interline transfer system, for example. As is clear from this diagram, a photodetector
51
is constructed of a matrix of a plurality of photodiodes, which are formed in a light receiving region of a semiconductor substrate. Formed in this photodetector
51
are vertical charge transfer portions (i.e., vertical shift registers)
52
arranged in a vertical series, wherein an electric charge issued from the photodetector
51
is vertically transferred through these vertical shift registers
52
. Formed under these vertical charge transfer portions
52
are horizontal charge transfer portions (i.e., horizontal shift registers)
53
arranged in a horizontal series, wherein the electric charge having been vertically transferred is then transferred horizontally through these horizontal shift registers
53
. Formed adjacent to these horizontal shift registers
53
is an output amplifier portion
54
.
FIG. 15
shows in cross section both the horizontal charge transfer portion
53
and the output amplifier portion
54
. The horizontal charge transfer portion
53
comprises: a first layer charge transfer electrode
58
constructed of a polysilicon film and the like, the polysilicon film and the like being formed on an n-type semiconductor layer
56
which forms an electric charge transfer channel formed in a p-type semiconductor substrate
55
; and, a second layer charge transfer electrode
60
constructed of a polysilicon film and the like, the polysilicon and the like being formed on the n-type semiconductor layer
56
through the first layer charge transfer electrode
58
, oxide film
59
and the gate insulation film
57
. The gate insulation film
57
is constructed of a multilayer film comprising a nitride film (Si
3
N
4
)
61
sandwiched between a pair of oxide films (SiO
2
)
62
,
64
. Incidentally, though the photodetector is formed in the other portion of the p-type semiconductor substrate
55
, it is omitted in the drawings.
On the other hand, the output amplifier portion
54
comprises in construction: a source region
65
and a drain region
66
each of which is constructed of an n-type semiconductor region formed in the other portion of the p-type semiconductor substrate
55
; and, a MOS (Metal Oxide Semiconductor) transistor provided with a gate electrode
68
which is constructed of a polysilicon film and the like formed through a gate insulation film
67
constructed of an oxide film. Here, the MOS transistor is often used in a source follower grounded circuit which is excellent in impedance transformation properties. Incidentally, the vertical charge transfer portion
52
has substantially the same construction as that of the horizontal charge transfer portion
53
.
FIGS. 16
to
20
show a conventional method of producing the solid-state imaging device of the first prior art, illustrating the producing steps of the method in the order of these steps. Hereinbelow, the conventional method will be described in the order of its steps.
First of all, as shown in
FIG. 16
, by using the p-type semiconductor substrate
55
on which the n-type semiconductor substrate
56
is formed, sequentially formed on the n-type semiconductor substrate
56
in the regions in which both the horizontal and the vertical charge transfer portion are formed in the following order are: the oxide film
62
, nitride film
61
and the oxide film
63
, of which films a multilayer film is constructed, As a result, the gate oxide films
57
and
67
are formed in the regions in which the horizontal charge transfer portion
53
and the output amplifier portion
54
are formed, respectively. Next, as shown in
FIG. 17
, only in the region in which the horizontal charge transfer portion
53
is formed, the first layer charge transfer electrode
58
constructed of a polysilicon film is formed through the gate oxidation film
57
. Then, as shown in
FIG. 18
, all the oxide film
63
other than one directly under the first layer charge transfer electrode
58
is removed. After that, a CVD oxidation film
64
is newly formed through a high-temperature CVD (Chemical Vapor Deposition) process. Subsequent to this process, as shown in
FIG. 19
, the polysilicon film forming the first layer charge transfer electrode
58
is subjected to an oxidation process to develop an oxide film on both its upper and side surface portions. Due to this, the oxide film
64
of both the upper and side surface portions of the first layer charge transfer electrode
58
is increased in film thickness. The reason why the above film thickness is increased is that it is necessary to have the first layer charge transfer electrode
58
sufficiently insulated from a second layer charge transfer electrode
60
which is formed later. Subsequent to this step, now, as shown in
FIG. 20
, after a polysilicon film is formed on the entire surface of the CVD oxidation film
64
, the thus formed polysilicon film is patterned using a photolithography processing such that both the second layer charge transfer electrode
60
and the gate electrode
68
are formed. After that, by self alignment using the gate electrode
68
as a mask, an n-type impurity is ion-implanted in the semiconductor substrate
55
to form an n-type source electrode
65
and an n-type drain electrode
68
, so that a MOS transistor
69
is produced. Through the above process steps, the solid-state imaging device of the first prior art type (shown in
FIG. 15
) is produced.
FIG. 21
shows a second prior art in cross section. The main difference between this second prior art and the first prior art is that the second prior art discloses a horizontal charge transfer portion constructed of a single layer. In other words, as shown in the drawings, in the horizontal charge transfer portion
53
, an electric charge transfer electrode
70
constructed of a polysilicon film and the like is formed on the n-type semiconductor substrate
56
through the gate insulation film
57
. Incidentally, other than the above difference, there is substantially no difference between the first and the second prior art. Though like reference numerals apply to similar parts through
FIGS. 16
to
20
in construction, this is also true in FIG.
21
. Consequently, to avoid redundancy in description of the reference numerals, such description is omitted.
FIGS. 22 and 23
show process steps for producing the solid-state imaging device of the second prior art. First, as shown in
FIG. 22
, the p-type semiconductor substrate
55
on which the n-type semiconductor layer
56
is previously formed is used to produce an oxide film by using a thermal oxidation process in a region where both the horizontal charge transfer portion and the output amplifier portion are to be formed, so that the gate insulation films
Hatano Keisuke
Nakashiba Yasutaka
Malsawma Lex H.
Smith Matthew
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