Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
1998-06-26
2001-05-15
Booth, Richard (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C257S320000
Reexamination Certificate
active
06232179
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device including a capacitance portion composed of two conductive layers and a capacitance insulating film interposed therebetween, and also relates to a manufacturing method thereof.
Examples of conventionally known semiconductor devices including a capacitance portion, composed of two conductive layers and a capacitance insulating film interposed therebetween, in the semiconductor element thereof, include: a MOS transistor including a capacitance portion composed of a semiconductor substrate, a gate electrode and a gate insulating film; a dynamic RAM (Random Access Memory) including a memory capacitance portion composed of a storage node, a cell plate, and a capacitance insulating film; a floating-gate EEPROM (Electrically Erasable and Programmable Read Only Memory) including a memory capacitance portion composed of a floating gate, a control gate, and a capacitance insulating film; and a capacitance element provided in an analog circuit.
FIG. 11
is a cross-sectional view of a conventional floating-gate EEPROM. As shown in the drawing, a tunnel insulating film
110
, a floating gate electrode
111
, a capacitance insulating film
112
, and a control gate electrode
113
are provided on a semiconductor substrate
101
. In the semiconductor substrate
101
, a source region
108
and a drain region
109
are formed to be self-aligned with the floating gate electrode
111
and the overlying components identified above. The floating gate electrode
111
, the capacitance insulating film
112
, and the control gate electrode
113
constitute a capacitive coupling portion. The capacitive coupling portion has the function of causing the injection of electrons into the floating gate electrode
111
having its capacitance coupled with the capacitance of the control gate electrode
113
or the withdrawal of electrons therefrom by the application of a control voltage to the control electrode
113
.
In a semiconductor device including such a capacitance portion having a capacitance insulating film, a single-layer silicon oxide film, a silicon nitride film with a high dielectric constant, or the like is used as the capacitance insulating film. The capacitance insulating film
112
shown in
FIG. 11
is typically an insulating film containing silicon nitride such as a silicon-nitride/silicon-oxide two-layer film (ON film) and a silicon-oxide/silicon-nitride/silicon-oxide three-layer film (ONO film). An oxynitride film has also been employed in a MOS transistor in particular.
On the other hand, the two conductive layers are normally two high-melting-point polysilicon films. For example, the floating gate electrode
111
and the control electrode
113
of the EEPROM shown in
FIG. 11
are typically composed of polysilicon.
In recent years, as higher integration has been achieved in a semiconductor integrated circuit, further miniaturization and reduction of an operating voltage have been required for semiconductor devices including the above-mentioned capacitance portion. Lately, there has been an increasing demand for a semiconductor device with a capacitance portion having a typical size of 0.5 &mgr;m (half-micron) or less. Consequently, each of the gate electrodes
111
and
112
shown in
FIG. 11
tends to have a further reduced gate length.
However, if the lateral sizes of conductive layers overlying and underlying an electrostatic capacitance portion in a semiconductor device with a half-micron or smaller capacitance portion or the lateral sizes of the floating gate electrode and the control gate electrode in a floating-gate semiconductor memory device are adjusted at 0.5 &mgr;m or less, then the thickness of the capacitance insulating film
112
shown in
FIG. 11
is likely to be nonuniform and have a larger thickness at both end portions thereof. The electrostatic capacitance between the floating gate electrode
111
and the control gate electrode
113
is reduced accordingly, which makes it difficult to provide a specified value of capacitance necessary to secure inherent properties. Such a nonuniform film thickness may be caused as follows.
Normally, the floating gate electrode
111
, the capacitance insulating film
112
and the control gate electrode
113
, which have been formed by patterning, are used as a mask, thereby implanting impurity ions into the semiconductor substrate
101
to form the source and drain regions
108
and
109
. After the ion implantation, a heat treatment is performed in an oxidizing atmosphere at a high temperature of 800° C. to 1000° C. to activate the implanted impurity and thereby generate carriers. However, the heat treatment causes the phenomenon of the increased thickness at both ends of the capacitance insulating film
112
. Specifically, when the capacitance insulating film
112
interposed between the control gate electrode
113
as the upper conductive layer and the floating gate electrode
111
as the lower conductive layer is oxidized rapidly from both side faces thereof in a half-micron or smaller capacitance portion, the capacitance insulating film
112
has remarkably different thicknesses at the central and peripheral portions thereof.
As a result of experiments, the present inventors found that oxidization is accelerated rapidly when each of the electrodes
111
and
113
is composed of polysilicon having a size of 0.4 &mgr;m or less in the lateral or channel longitudinal direction. This may be attributed to the phenomenon of accelerated oxidization of the polysilicon films interposing the capacitance insulating film.
Thus, as a voltage applied to the control gate electrode
113
has been further reduced, it has become more and more difficult to secure a required capacitive coupling ratio for conventional floating-gate semiconductor memory devices. As a result, numerous problems, like deterioration of device characteristics, have been caused. For example, write/erase speed and the amount of read current are adversely decreased. Moreover, other types of semiconductor devices are also highly likely to cause various deficiencies in the characteristics thereof because of the deterioration in capacitance value of the capacitance portion thereof.
SUMMARY OF THE INVENTION
The present invention was made in view of the above-described conventional problems. An object of the present invention is to provide a semiconductor device including a capacitance portion having a capacitance insulating film with a more uniform thickness by adopting measures to suppress an increase in thickness of the capacitance insulating film at both end portions thereof even when the capacitance portion has a half-micron or smaller lateral dimension.
A first semiconductor device according to the present invention includes: a semiconductor substrate; a first conductive film provided over the semiconductor substrate; a dielectric film, which is provided on the first conductive film and contains an oxidizing material; a second conductive film provided on the dielectric film; a first spacer film composed of an oxide film covering respective side faces of the first conductive film, the dielectric film, and the second conductive film; and a second spacer film covering the first spacer film and having a function of preventing oxygen from passing therethrough.
In such a structure, the second spacer film having a function of preventing oxygen from passing therethrough suppresses the supply of oxygen to both end portions of the dielectric film and to the first and second conductive films adjacent thereto, even when the semiconductor device is subjected to a heat treatment in an oxygen atmosphere. Consequently, an increase in thickness of the dielectric film at both ends thereof is prevented and a decrease in capacitance between the first and second conductive films is suppressed. Even when the second spacer film has a relatively insufficient insulating function, since the first spacer film composed of the oxide film having a sufficient insulating function is provided, it is possible to prevent leakage c
Booth Richard
Matsushita Electronics Corporation
McDermott & Will & Emery
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