Semiconductor device manufacturing: process – Chemical etching
Reexamination Certificate
2000-06-12
2002-10-15
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
C438S700000, C438S706000, C438S709000, C438S710000, C438S712000, C438S745000
Reexamination Certificate
active
06465352
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device fabricating process, and more specifically to a method for removing a resist film and a deposition after a dry-etching is carried out using the resist film as a mask in a semiconductor device fabricating process.
In a semiconductor device fabricating process, a through-hole or others is formed by utilizing a lithography process. Ordinarily, after a patterned resist film is formed, a dry-etching is carried out using the resist film as a mask, and thereafter, the resist film is removed. Here, when the dry-etching is carried out, an etching residue and a resist surface hardened layer occur. It is an important technical problem to remove these deposits without damaging metal layers and semiconductor layers which constitute a semiconductor device. In the following, a prior art example for removing the etching residue and the resist surface hardened layer will be described on an example of a process for forming a through-hole on a copper interconnection.
As shown in
FIG. 1A
, a buried copper interconnection is formed. After an HSQ (hydrogen silsesquoxane file
1
is formed on a semiconductor substrate (not shown) on which circuit-components such as transistors are formed, a copper interconnection composed of a TaN film
2
(barrier metal film) and a copper film
3
is formed in the HSQ film
1
by using a Cu damascene process. Then, a silicon nitride film
4
and another HSQ film
5
are formed on the HSQ film
1
in the named order. Furthermore, a resist film
6
patterned to have a predetermined shape is formed on the HSQ film
5
. Here, the silicon nitride film
4
has a film thickness on the order of 20 nm. The resist film
6
is constituted of for example a chemical amplification resist.
Next, the HSQ film
5
and the silicon nitride film
4
are dry-etched using the resist as a mask until the copper film
3
is exposed, so that a through-hole
7
is formed as shown in FIG.
1
B. An opening diameter of the through-hole is on the order of 0.2 &mgr;m. An etching gas being used is a fluorocarbon based gas. In this dry-etching, an etching residue
8
, which is a reaction product of the etching gas and the copper film
3
, is deposited on an inner wall surface of the through-hole. In addition, a resist surface hardened layer
9
is formed on the resist film
6
. The resist surface hardened layer
9
is composed of a reaction product of the etching gas and a resist material, copper, etc., and is generally difficult to remove.
Thereafter, as shown in
FIG. 1C
, the resist film
6
is ordinarily removed by an oxygen plasma ashing while maintaining the substrate temperature at 150° C. to 250° C., and then, deposits such as the etching residue
8
and a resist residue
11
are removed by a wet treatment using a liquid remover.
The oxygen plasma ashing causes an active species such as oxygen radicals generated by a plasma discharging, to react with the resist resin activated by the heating. Thus, an organic resin, which is the base of the resist, reacts with the oxygen active species generated by the plasma discharging, to be broken down into a gas such as CO
2
and H
2
O, with the result that the resist is removed from the surface of the substrate. When the active oxygen species and the oxygen ion species in the oxygen plasma chemically react with the organic resin in the resist, since a threshold temperature exists, it is necessary to maintain the resist at a temperature not less than a predetermined constant temperature, in order to perform the oxygen plasma ashing. For this purpose, it is an ordinary practice to maintain the substrate at a temperature in the range of 150° C. to 250° C. However, if the ashing is carried out at this temperature, oxidation proceeds from a surface of the copper film into the inside of the copper film, so that an oxidized region
12
is formed as shown in FIG.
1
C. If the oxidized region
12
is formed, an interconnection resistance increases, and in addition, a contact resistance between the copper film
3
and a through-hole filling metal is also increased.
In order to avoid this problem, it may be considered to remove the resist film and the deposits by only a wet treatment using a resist remover liquid, without using the oxygen plasma ashing.
FIG. 2
schematically illustrate a condition after the wet treatment is carried out. With this wet treatment, the resist film
6
and the etching residue
8
are removed, but the resist surface hardened layer
9
is not removed and still remains on the HSQ film
5
. As mentioned above, since the resist surface hardened layer
9
is composed of the reaction product of the etching gas and the resist material, the copper, etc., it is difficult to remove the resist surface hardened layer
9
by the wet treatment using the resist remover liquid. If the resist surface hardened layer
9
remains, when an upper level interconnection is formed later, a defective deposition of a barrier metal film occurs, with the result that the yield of production is lowered.
As a method for avoiding the remains of the resist surface hardened layer
9
and also for preventing oxidation of the copper film
3
, it is carried out to thicken the silicon nitride film
4
to form an etching stopper film and to form a through-hole by a two-step dry etching. This process will be described with reference with
FIGS. 3A
to
3
F,
4
,
5
A and
5
B.
Similarly to
FIG. 1A
, a buried copper interconnection as shown
FIG. 3A
is formed. However, the silicon nitride film
4
is formed to have a film thickness of about
50
nm, which is larger than that in the example shown in FIG.
1
A. This silicon nitride film
4
will be used as an etching stopper in a later step.
The HSQ film
5
is dry-etched using the resist
6
as a mask until the silicon nitride film
4
is exposed, so that a through-hole is formed as shown in FIG.
3
B. An opening diameter of the through-hole is on the order of 0.2 &mgr;m. As an etching gas, a gas is used which can etch the silicon oxide film at an etching rate higher than that for a silicon nitride film. After the etching, an etching residue
10
is deposited on an inner wall surface of the through-hole, and a resist surface hardened layer
9
is formed on the resist film
6
.
Thereafter, the resist
6
is removed by an oxygen plasma ashing. At this time, a resist residue
11
remains on the HSQ film
5
as shown in FIG.
3
C. After the ashing, a wet treatment using a resist remover liquid is carried out to remove the resist residue
11
and the etching residue
10
, as shown in FIG.
3
D. Then, the silicon nitride film
4
is dry-etched to expose a surface of the lower level interconnection
3
, as shown in FIG.
3
E. As an etching gas, a fluorocarbon based gas is used. At this time, an etching residue
8
is deposited on the inner wall surface of the through-hole. Succeedingly, the wet treatment using the resist remover liquid is carried out again to remove the etching residue, as shown in FIG.
3
F. Thereafter, a barrier metal is deposited on an inner surface of the through-hole, and-a buried conducting film is deposited, and then, a surface is planarized. Thus, a multi-level interconnection is completed.
As mentioned above, if the method of thickening the silicon nitride film to use the thickened silicon nitride film as the etching stopper is utilized, it is possible to prevent the oxidation of the copper film
3
-to some degree. However, this method needs an increased number of steps, and in some cases, it is not possible to stop the dry etching at the silicon nitride film with good controllability, so that deterioration of the copper film
3
caused by the oxidation cannot be satisfactorily prevented. The reason for this will be described in the following.
When the lower level interconnection is formed of copper which is difficult to etch, a buried structure is ordinarily adopted, and an interconnection is completed by means of a Cu damascene process utilizing a CMP (chemical mechanical polishing) process. However, in the CMP process
Hayes & Soloway P.C.
NEC Corporation
Perez-Ramos Vanessa
Utech Benjamin L.
LandOfFree
Method for removing dry-etching residue in a semiconductor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for removing dry-etching residue in a semiconductor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for removing dry-etching residue in a semiconductor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2966734