Method for fabricating metal interconnect in a...

Details Method for fabricating metal interconnect in a... Method for fabricating metal interconnect in a...

2003-10-30

2004-11-09

Mai, Anh Duy (Department: 2814)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S675000, C430S313000

Reexamination Certificate

active

06815341

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device, including metal interconnects laid in an insulating film with a low dielectric constant (which will be herein called a low-dielectric-constant film), and also relates to a method for fabricating the same.
Hereinafter, the structure of a semiconductor device, including inlaid metal interconnects in a low-dielectric-constant film, will be described with reference to FIG.
6
.
As shown in
FIG. 6
, a second insulating film
102
is formed of a silicon dioxide film, for example, on a first insulating film
101
deposited on a semiconductor substrate
100
. In the second insulating film
102
, metal interconnects
105
have been formed. Specifically, each of the metal interconnects
105
consists of a barrier metal layer
105
a
of tantalum nitride, for example, and a main interconnect layer
105
b
of copper, for instance.
In this semiconductor device, the second insulting film
102
, which exists between the metal interconnects
105
, is made of silicon dioxide with a dielectric constant between about 3.9 and about 4.2. Therefore, a parasitic capacitance, generated between the metal interconnects
105
, increases, thereby interfering with high-speed operation of the semiconductor device.
To solve this problem, a carbon-containing silicon dioxide film with a low dielectric constant of about 2.5 may be used as the second insulating film
102
.
Hereinafter, a method for fabricating a semiconductor device, including inlaid metal interconnects formed in an insulating film of carbon-containing silicon dioxide, will be described with reference to FIG.
7
A through FIG.
7
E.
First, as shown in
FIG. 7A
, a second insulating film
110
of carbon-containing silicon dioxide, is deposited on a first insulating film
101
formed on a semiconductor substrate
100
. Then, a resist pattern
111
with openings for forming interconnect grooves is defined on the second insulating film
110
as shown in FIG.
7
B.
Next, as shown in
FIG. 7C
, the second insulating film
110
is plasma-etched using an etching gas, consisting essentially of fluorine and carbon, and being masked with the resist pattern
111
. In this manner, interconnect grooves
112
are formed in the second insulating film
110
. As a result, the upper part of the resist pattern
111
changes into a cured layer
111
a
. Specifically, the bonding states of atoms in the cured layer
111
a
are different from those of atoms in the original material of the resist pattern
111
that has not yet been plasma-etched. And the cured layer
111
a
is made of a polymer consisting essentially of fluorine and carbon and has a thickness of about 50 nm. The cured layer
111
a
cannot be removed by a wet etching process but can be removed by a plasma etching process using oxygen gas.
Accordingly, the resist pattern
111
is ashed away with oxygen plasma as shown in FIG.
7
D. In this case, the ashing process is performed by a down flow technique (in which no bias voltage is applied to the substrate) in a vacuum between about 267 Pa and about 400 Pa, for example, and with the substrate heated to a relatively high temperature between about 150° C. and about 250° C., for instance. In this manner, the resist pattern
111
with the cured layer
111
a
in its upper part can be stripped just as intended. Also, a silicon dioxide film
113
with a thickness of 200 nm, for example, is formed in the upper part of the second insulating film
110
of carbon-containing silicon dioxide.
In the ashing process using oxygen plasma, carbon is removed from the carbon-containing silicon dioxide for the second insulating film
110
, thereby producing silicon dioxide. Hereinafter, this mechanism will be described with reference to
FIGS. 8 and 9
.
FIG. 8
illustrates an example of a chemical formula representing a carbon-containing silicon dioxide. If the carbon-containing silicon dioxide represented by this chemical formula and oxygen are bonded together, the following chemical reaction
2CH
3
+7O→2CO
2
↑+3H
2
O↑
occurs. Then, CH
3
, which has been bonded to Si, disappears. That CH
3
disappeared is replaced with O to form SiO
2
bonds. Therefore, a silicon dioxide as represented by the chemical formula shown in
FIG. 9
is produced.
Next, a tantalum nitride film is deposited over the second insulating film
110
, or on the silicon dioxide film
113
more exactly, by a sputtering process. And then, a copper film is deposited on the tantalum nitride film by an electro-plating process. Thereafter, excessive parts of the copper and tantalum nitride films, existing over the second insulating film
110
, are removed by a CMP process, thereby defining metal interconnects
114
as shown in FIG.
7
E. The metal interconnects
114
are made up of a barrier metal layer
114
a
of tantalum nitride and a main interconnect layer
114
b
of copper.
However, the semiconductor device formed in this manner has the following problems.
First of all, in the step of ashing away the resist pattern
111
using oxygen plasma, the silicon dioxide film
113
is adversely formed in the upper part of the second insulating film
110
of carbon-containing silicon dioxide. Specifically, the silicon dioxide film
113
exhibits a high dielectric constant and has a thickness of 200 nm, for example. Therefore, although the carbon-containing silicon dioxide film is used as the second insulating film
110
, a parasitic capacitance generated between the metal interconnects
114
cannot be reduced sufficiently.
Also, the silicon dioxide film
113
has a density between 1.7 g/cm
3
and 1.8 g/cm
3
, which is lower than that of a silicon dioxide film formed by a plasma CVD process, for instance. Therefore, when oxygen plasma is supplied in a subsequent process step, oxygen ions go through the silicon dioxide film
113
to reach and oxidize the carbon-containing silicon dioxide film under the film
113
. As a result, the silicon dioxide film
113
has its film thickness increased undesirably. This phenomenon is observed, for example, in the subsequent process step of ashing away a resist pattern for forming via holes over the metal interconnects
114
. The phenomenon is also observed, for instance, in the subsequent process step of ashing away a resist pattern for forming interconnect grooves for upper-level metal interconnects to be formed over the via holes.
As described above, in the known semiconductor device including inlaid metal interconnects in an insulating film of carbon-containing silicon dioxide, a thick silicon dioxide film is unintentionally formed in upper parts of the insulting film that surround the metal interconnects. As a result, a parasitic capacitance generated between the metal interconnects increases disadvantageously.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to enhance the performance of a semiconductor device, including inlaid metal interconnects in an insulating film of carbon-containing silicon dioxide, by reducing a parasitic capacitance produced between the metal interconnects.
To achieve this object, a first inventive semiconductor device includes: an insulating film formed of a carbon-containing silicon dioxide film on a substrate; an interconnect groove formed in the insulating film; a silicon dioxide layer, which is formed on the bottom and side faces of the interconnect groove and has a density high enough to allow almost no oxygen to pass therethrough; and a metal interconnect formed on the silicon dioxide layer inside the interconnect groove.
In the first inventive device, the silicon dioxide layer with a density high enough to allow almost no oxygen to pass therethrough is formed on the bottom and side faces of the interconnect groove. Therefore, even if oxygen plasma is supplied in a subsequent process step, oxygen ions cannot pass through the silicon dioxide layer, and the carbon-containing silicon dioxide film surrounding the silicon dioxide layer is not oxidized. Accordingly, the thickness of the silicon dioxide layer, existing on

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