Active solid-state devices (e.g. – transistors – solid-state diode – With means to control surface effects – Insulating coating
Reexamination Certificate
2001-04-25
2002-04-02
Smith, Matthew (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
With means to control surface effects
Insulating coating
C257S758000, C438S624000, C438S788000
Reexamination Certificate
active
06365959
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a semiconductor device, and more particularly relates to a semiconductor device including a fluorine-containing insulating film, made of an insulator doped with fluorine, between metal interconnects and a method for fabricating such a device.
Hereinafter, a semiconductor device including a fluorine-containing insulating film, made of an insulator doped with fluorine, between metal interconnects will be described with reference to FIG.
9
.
As shown in
FIG. 9
, an insulating film
2
, made of silicon dioxide, is formed on a semiconductor substrate
1
. on the insulating film
2
, a plurality of lower-level metal interconnects
3
are formed. Each of these metal interconnects
3
has a multilayer structure formed by stacking a first titanium film
3
a
, a first aluminum alloy film
3
b
and a first titanium nitride film
3
c
in this order. A fluorine-containing silicon dioxide film
4
is formed by doping a silicon dioxide film with fluorine to fill in the gaps between adjacent ones of the lower-level metal interconnects
3
and to cover all of these metal interconnects
3
.
An ordinary silicon dioxide film
5
is formed on the fluorine-containing silicon dioxide film
4
. And on the silicon dioxide film
5
, a plurality of upper-level metal interconnects
6
are formed. Each of these metal interconnects
6
also has a multilayer structure formed by stacking a second titanium film
6
a
, a second aluminum alloy film
6
b
and a second titanium nitride film
6
c
in this order.
The relative dielectric constant of the fluorine-containing silicon dioxide film
4
, formed by doping a silicon dioxide film with fluorine, is lower than that of the ordinary silicon dioxide film
5
, which is not doped with fluorine. Thus, by providing an interlevel insulating film including the fluorine-containing silicon dioxide film
4
to fill in the gaps between the lower-level metal interconnects
3
and cover all of these interconnects
3
, parasitic capacitances between the interconnects
3
themselves and between the lower- and upper-level metal interconnects
3
,
6
can be reduced. As a result, signals can be transmitted with a reduced delay, thus enabling the use of signals with a higher frequency.
However, if the fluorine-containing silicon dioxide film
4
is interposed between the lower- and upper-level metal interconnects
3
,
6
, then fluorine, contained in the fluorine-containing silicon dioxide film
4
, is likely to diffuse into the silicon dioxide film
5
during a subsequent heat treatment process. Such a phenomenon is called “auto-doping” in the pertinent art. Once fluorine has diffused into the silicon dioxide film
5
, a degraded layer is formed in the interface between the second titanium film
6
a
, which is the lowermost layer of the upper-level metal interconnects
6
, and the silicon dioxide film
5
. Accordingly, the upper-level metal interconnects
6
come to make poorer contact with the silicon dioxide film
5
, resulting in deterioration in reliability of the semiconductor device.
SUMMARY OF THE INVENTION
An object of this invention is improving the contact between upper-level metal interconnects and an interlevel insulating film by preventing fluorine, contained in a fluorine-containing silicon dioxide film filling in the gaps between lower-level metal interconnects and between the lower- and upper-level metal interconnects, from degrading the upper-level metal interconnects.
To achieve this object, the semiconductor device of the present invention includes: a plurality of lower-level metal interconnects formed over a semiconductor substrate; a first fluorine-containing insulating film made of a fluorine-doped insulator and formed to fill in gaps between adjacent ones of the lower-level metal interconnects over the semiconductor substrate; an interlevel insulating film formed over the lower-level metal interconnects and the first fluorine-containing insulating film; and a plurality of upper-level metal interconnects formed on the interlevel insulating film. The interlevel insulating film includes: a second fluorine-containing insulating film made of a fluorine-doped insulator; and a silicon-rich insulating film containing a larger quantity of silicon than a quantity defined by stoichiometry.
In the semiconductor device of the present invention, the first fluorine-containing insulating film is formed between adjacent ones of the lower-level metal interconnects land the second fluorine-containing insulating film is interposed between the lower- and upper-level metal interconnects. Accordingly, parasitic capacitances between the lower-level metal interconnects themselves and between the lower- and upper-level metal interconnects can be reduced, thus reducing the propagation delay of a signal transmitted through the device.
In addition, the interlevel insulating film includes a silicon-rich insulating film containing a larger quantity of silicon than a quantity defined by stoichiometry. Thus, during a subsequent heat treatment process, even if fluorine atoms, contained in the first or second fluorine-containing insulating film, are going to diffuse, these fluorine atoms are trapped by the dangling bonds of silicon atoms contained in the silicon-rich insulating film. As a result, the fluorine atoms are less likely to pass through the silicon-rich insulating film to reach the upper-level metal interconnects. Accordingly, no degraded layers are formed in the interface between the lower- or upper-level metal interconnects and the interlevel insulating film, thus improving the contact between the lower- or upper-level metal interconnects and the interlevel insulating film.
If a silicon-rich insulating film is formed over the second fluorine-containing insulating film, then the silicon-rich insulating film prevents the fluorine atoms, contained in the first and second fluorine-containing insulating films, from reaching the upper-level metal interconnects. And, if an additional silicon-rich insulating film is formed under the second fluorine-containing insulating film, then the silicon-rich insulating films prevent the fluorine atoms, contained in the first and second fluorine-containing insulating films, from reaching the upper- and lower-level metal interconnects, respectively.
Therefore, in the semiconductor device of the present invention, not only reduction in parasitic capacitances between the lower-level metal interconnects themselves and between the lower- and upper-level metal interconnects, but also improvement of contact between the lower- or upper-level metal interconnects and the interlevel insulating film are realized. As a result, a highly reliable semiconductor device can be provided.
In one embodiment of the present invention, the silicon-rich insulating film preferably includes: a first silicon-rich insulating film formed under the second fluorine-containing insulating film; and a second silicon-rich insulating film formed over the second fluorine-containing insulating film.
In such an embodiment, the fluorine atoms, contained in the first fluorine-containing insulating film, cannot reach the upper-level metal interconnects, while the fluorine atoms, contained in the second fluorine-containing insulating film, cannot reach the upper- or lower-level metal interconnects.
In another embodiment of the present invention, the silicon-rich insulating film is preferably a silicon-rich oxide film containing a larger quantity of silicon than a quantity defined by stoichiometry.
In this embodiment, the refractive index of the silicon-rich oxide film is preferably 1.48 or more. Then, the passage of fluorine atoms through the silicon-rich oxide film can be prevented with much more certainty.
In an alternate embodiment of the present invention, the silicon-rich insulating film is preferably a silicon-rich nitride film containing a larger quantity of silicon than a quantity defined by stoichiometry.
In this embodiment, the refractive index of the silicon-rich nitride film is preferably 2.05 or more. Then
Ueda Satoshi
Yuasa Hiroshi
Lee Calvin
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Robinson Eric J.
Smith Matthew
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