Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Removal of imaged layers
Reexamination Certificate
2002-03-07
2004-06-22
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Removal of imaged layers
C430S313000, C216S041000, C134S001100
Reexamination Certificate
active
06753133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device and more particularly to a method for fabricating a semiconductor device, wherein an ashing of a resist film formed over a ruthenium film or a ruthenium oxide film can be performed at a high selectivity.
2. Description of the Prior Art
In recent years, semiconductor devices including ruthenium or ruthenium oxide have been actively studied and developed in the art. Among them, a capacitor having electrodes made of ruthenium or ruthenium oxide and a dielectric material such as Pb(Zr
x
Ti
1−x
)O
3
, (Ba
x
Sr
1−x
)TiO
3
, or Ta
2
O
5
has been employed in some Ferroelectric Random Access Memory (FeRAM) or Dynamic Random Access Memory (DRAM).
Ruthenium and ruthenium oxide are capable of being processed into a high-anisotropic form by reactive ion etching using oxygen gas (e.g., U.S. Pat. No. 5,254,217 Maniar et al.) and a gas mixture of oxygen gas and halogen gas (e.g., U.S. Pat. No. 5,624,583 Tokashiki et al.). While it become possible to make the size of a capacitor electrode minimized with above etching method, there is a necessity to conduct an ashing of a photo-sensitive material (i.e., photoresist) formed over the electrode made of ruthenium or ruthenium oxide using oxygen plasma.
FIGS. 1
a
to
1
e
are cross sectional views for illustrating substantial steps in an exemplified conventional method for fabricating a semiconductor device having a ruthenium (Ru) film, wherein the step of ashing is performed after the step of contact hole etching.
First, as shown in
FIG. 1
a
, a Ru film
12
and a silicon dioxide (SiO
2
) layer
14
are formed over a silicon (Si) substrate
11
. As shown in
FIG. 1
b
, a photoresist is then applied on the SiO
2
layer
14
followed by a patterning step using photolithography process to form a resist pattern
13
. As shown in
FIG. 1
c
, subsequently, a contact hole
16
for connecting a wiring to the Ru film
12
is formed through the SiO
2
layer
14
by a dry etching process using CF
4
or the like. After that, as shown in
FIG. 1
d
, the resist pattern
13
is subjected to a plasma ashing process using O
2
gas. During the ashing, the Ru film
12
is also gradually eroded because of the formation of volatile RuO
3
or RuO
4
as a result of reacting Ru with oxygen plasma
22
. Consequently, the complete removal of the resist pattern
13
involves a substantial erosion of the Ru film
12
. In some cases, the Ru film
12
under the contact hole
16
may be vanished as shown in
FIG. 1
e.
In the described conventional example, the ashing is performed after the contact hole etching. In the actual fabrication of the semiconductor device, there may be cases where such an ashing step in which the Ru film
12
may be exposed to oxygen plasma is performed more than one time. Thus, there is a possibility of vanish away the Ru film
12
from the structure after repeating the ashing step several times even though the entire Ru film
12
cannot be removed by the one ashing step.
For solving such a problem, Yunogami et al. (U.S. Pat. No. 6,326,218) disclose a method for preventing the Ru film
12
from erosion at the time of ashing the resist pattern
13
by forming a platinum (Pt) film
15
on a Ru film
12
.
FIGS. 2
a
to
2
e
are cross sectional views for illustrating the steps in such a method disclosed in the above document. In this method, as shown in
FIG. 2
a
, at first, the Ru film
12
is deposited over a Si substrate
11
. Then, the platinum (Pt) film
15
is deposited on the Ru film
12
. After patterning of the Pt film
15
and Ru film
12
, a SiO
2
layer
14
is deposited on the Pt film
15
. Then, as shown in
FIG. 2
b
resist pattern
13
is formed on the SiO
2
layer
14
. Furthermore, as shown in
FIG. 2
c
, a contact hole
16
is formed through the SiO
2
layer
14
by a dry etching process using CF
4
or the like. After that, as shown in
FIG. 2
d
, the resist pattern
13
is subjected to a plasma ashing process using oxygen plasma
22
. In this case, as the Ru film
12
is covered with the Pt film
15
, the Ru film
12
is not eroded at all, while the resist pattern
13
is completely incinerated by the ashing process as shown in
FIG. 2
e.
As described above, in the method for fabricating the conventional semiconductor device, the Ru film
12
may be eroded at the time of ashing. For preventing the Ru film
12
from the erosion, there is a necessity to deposit the Pt film
15
on the Ru film
12
to prevent it from erosion or disappearance. In this case, however, the fabrication becomes more complicated because of the additional steps of forming and patterning the Pt film
15
on the Ru film
12
. In addition, the cost of fabricating the semiconductor device becomes increased because of costly Pt. Consequently, a sufficient productivity cannot be attained in the conventional method for fabricating a semiconductor device including Ru or Ru oxide. Furthermore, in some case, the formation of Pt film
15
on the Ru film
12
cannot be done as the need for directly forming a dielectric layer on the Ru film
12
comes out.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for fabricating a semiconductor device with a high productivity, wherein an ashing of a photo-sensitive material formed over ruthenium or ruthenium oxide can be easily realized at a high selectivity.
In a first aspect of the present invention, a method for fabricating a semiconductor device including at least one of a ruthenium and a ruthenium oxide comprises the step of ashing a photo-sensitive material over the ruthenium or the ruthenium oxide using a gas mixture containing oxygen gas or ozone gas and nitrogen gas, wherein the percentage composition of nitrogen gas is 50% or more.
Here, the ashing step may be performed by heating a substrate over which the ruthenium or the ruthenium oxide is formed at a temperature of 200° C. or more.
The ashing step may be performed after etching an interlayer insulation film on the ruthenium or the ruthenium oxide using a photo-sensitive material as a mask. Alternatively, the ashing step may be performed after etching of the ruthenium or the ruthenium oxide using a photo-sensitive material as a mask.
In a second aspect of the present invention, a method for fabricating a semiconductor device including at least one of a ruthenium and a ruthenium oxide, comprising the steps of: forming a film made of the ruthenium or the ruthenium oxide over a substrate; forming an interlayer insulation film on the ruthenium or the ruthenium oxide film; applying a photo-sensitive material on the interlayer insulation film and patterning the applied photo-sensitive material; etching the interlayer insulation film using the patterned photo-sensitive material as a mask; and ashing the patterned photo-sensitive material using an ashing gas provided as a mixture of a gas that contains oxygen gas or ozone gas and a gas that contains nitrogen gas, wherein the percentage composition of nitrogen gas is 50% or more.
Here, a contact hole for exposing the ruthenium film or the ruthenium oxide film may be formed in the step of etching the interlayer insulation film.
According to the above first or second aspect of the invention, there is an advantage of effectively performing the ashing of the photo-sensitive material with a high selectivity and a high ashing rate while preventing a partial disappearance of the ruthenium film or the ruthenium oxide film.
The reason for such an advantage is as follows. In the prior art method, the ruthenium is etched by oxygen plasma because ruthenium is oxidized to form a volatile compound, i.e., RuO
3
or RuO
4
. In this case ruthenium may be eroded or disappeared at the time of performing ashing of the photoresist using oxygen plasma.
On the other hand, according to the present invention the gas for ashing is prepared by mixing O
2
gas with a large amount of N
2
gas, so that the probability of a collision of oxygen with ruthenium can be decreased
Ono Yasuhiro
Shinohara Sota
Duda Kathleen
Elpida Memory Inc.
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