Method of manufacturing semiconductor memory device

Details Method of manufacturing semiconductor memory device Method of manufacturing semiconductor memory device

2000-09-08

2002-01-29

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

On insulating substrate or layer

C438S285000, C438S306000, C438S129000

Reexamination Certificate

active

06342408

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device in which a MOS transistor is formed on a semiconductor film on an insulating film and, more particularly, to a semiconductor device in which a MOS transistor constituting a sensor amplifier or a boosting circuit of a DRAM is improved.
2. Description of the Related Art
High performance of a recent semiconductor integrated circuit in, especially, a silicon MOS transistor technique is considerably developed. In this silicon MOS transistor technique, it is known that a micropatterned, high-speed, and high-performance element can be realized by forming a MOS transistor on an SOI (Silicon-On-Insulator) film (to be referred to as an SOI·MOSFET hereinafter).
FIG. 1
is a plan view showing a layout pattern of a conventional sense amplifier using such an SOI·MOSFET, and
FIGS. 2A and 2B
are sectional views showing the conventional sense amplifiers along lines
2
A—
2
A and
2
B—
2
B in
FIG. 1
, respectively.
FIG. 1
shows a sense amplifier SA, a bit line BL, a control line
1
for connecting a common source terminal of the sense amplifier SA, a source-contact portion
2
, a drain-contact portion
3
, and a gate-contact portion
4
.
FIGS. 2A and 2B
show a p-type monocrystal silicon film
7
as an SOI film. A silicon oxide film (SiO
2
film)
6
is formed on the bottom and side surfaces of the p-type monocrystal silicon film
7
. The silicon oxide film
6
on the bottom surface is an insulating film of an SOI substrate, and the silicon oxide film
6
on each side surface is an element isolation insulation film.
An n-type source region
8
and an n-type drain region
9
are selectively formed in the p-type monocrystal silicon film
7
. A gate electrode
11
is arranged on the p-type monocrystal silicon film
7
in a channel region between the n-type source region
8
and the n-type drain region
9
through a gate oxide film
10
.
In the SOI·MOSFET, due to a so-called substrate floating effect, problems such as a low drain breakdown voltage or an unstable drain current in a switching operation are posed.
In particular, in a flip-flop type sense amplifier used in a DRAM or the like or a current mirror type differential amplifier, when an n-type SOI·MOSFET is used in a potential difference detection unit, holes are stored in an SOI·MOSFET channel portion, and the threshold value of the SOI·MOSFET decreases. Since the decrease in threshold value depends on the number of stored holes, the decrease in threshold value depends on a transistor. For this reason, the threshold value is unbalanced, and detection sensitivity to a potential difference. When the decrease in threshold value is considerably large, an erroneous operation may be caused.
In a pump circuit constituting a boosting circuit or a lowering circuit, when a capacitor constituting a pump has first and second electrodes, and an SOI·MOSFET is used as a switching means for connecting the first electrode of the capacitor to an output, a decrease in drain breakdown voltage is caused by the substrate floating effect of the SOI·MOSFET.
For example, in the lowering circuit, when the first potential is boosted at a timing at which the potential of the second electrode is charged by a capacitor driver circuit, the SOI·MOSFET must be turned off. When an n-type SOI·MOSFET is used the above SOI·MOSFET, the potential of the first electrode serving as a drain is boosted, the capacity coupling between the drain and the substrate portion of the SOI·MOSFET boosts the potential of this substrate portion, and the cut-off characteristics of the SOI·MOSFET are degraded. In the worst case, drain breakdown is caused. In addition, holes generated by slight drain breakdown are stored for a reason except for the above capacity coupling, and drain breakdown is caused by the substrate floating effect.
Furthermore, although an accurate reference voltage generation circuit is required to use the reference voltage as a reference for checking whether an input signal is set to be “H” or “L” in a DRAM or the like, a bulk type pn diode used in a conventional DRAM or the like cannot be used in the SOI·MOSFET without increasing the number of steps (costs). Therefore, means for generating a stable reference potential without largely increasing the number of steps is desired.
As described above, since no contact with the substrate can be obtained in the semiconductor device using the conventional SOI·MOSFET, a substrate floating effect is disadvantageously caused. In particular, in sense amplifiers for amplifying a fine potential read out on a bit line pair, since the substrate potentials of two transistors constituting a pair of sense amplifiers are set in a floating state, the threshold values of the transistors are difference from each other, and an accurate sensing operation cannot be performed (subject matter
1
). In addition to realization of the accurate sensing operation, high-density integration (subject matter
2
), moderation of design rules (subject matter
3
), and a countermeasure against noise (subject matter
4
) must be realized.
Furthermore, in a pump circuit constituting a boosting circuit or a lowering circuit, the cut-off characteristics of an SOI·MOSFET are degraded, and drain breakdown is caused in the worst case (subject matter
5
). In the SOI·MOSFET, a stable reference potential cannot be generated without largely increasing the number of steps (subject matter
6
).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device which can prevent a substrate floating effect of an SOI·MOSFET to realize a highly reliable sense amplifier or the like and realizes high-density integration, moderation of design rules, and a reduction in noise.
Means for solving subject matter
1
is as follows. That is, a diffusion layer region of the same conductivity type as that of a substrate is formed in a common source region, or a portion of each drain region in a sense amplifier formed by an SOI·MOSFET to connect the substrates of a pair of transistors to each other, thereby making the potentials of the substrates equal to each other (arrangement
1
-
1
). In order to make the above means further effective, a contact is formed in the common diffusion layer region to connect the common diffusion layer region to a power supply line or a signal line (arrangement
1
-
2
).
According to arrangement
1
of the present invention, in a sense amplifier constituted by an SOI·MOSFET which detects and amplifies a micro-potential difference, the substrate potentials of a pair of transistors are equal to each other. For this reason, the threshold values of the transistors change in the same manner, and a potential difference can be accurately detected. For this reason, an erroneous sensing operation can be prevented.
In addition, since the contact with a substrate is formed, the substrate potentials are not set in a floating state, and problems such as storage of holes in a channel portion and a decrease in drain breakdown voltage are solved. Therefore, a highly reliable DRAM can be realized.
Means for solving subject matter
2
is that the substrate contact and a source contact are used common (arrangement
2
-
1
), or that a p-type region is common to upper and lower (in a word line direction) sense amplifiers (arrangement
2
-
2
).
According to arrangement
2
, the substrate contact and the source contact are used common, a contact-contact interval is not required, and high-density integration can be obtained. When p-type regions are connected to each other in a word line direction, an implant-implant interval is not required, and high-density integration can be obtained. In addition, when p-type regions are connected to each other in a word line direction, the substrate potentials and threshold values of the sense amplifiers on pair of adjacent bits can be made equal to each other, and sensing operations can be started at the same timing. For this reason, a sense amplifier is not erroneously operated in reception of noise fr

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