Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1993-07-14
2002-03-12
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S680000, C438S685000, C438S694000, C438S720000
Reexamination Certificate
active
06355553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a metal plug in the manufacture of a semiconductor device and to a wafer processing apparatus used for forming the metal plug.
2. Description of the Prior Art
As a semiconductor device is micropatterned, the area of a contact hole is decreased, but the thickness of an interlayer insulator cannot be decreased because a high breakdown voltage must be assured. For this reason, the aspect ratio of the contact hole tends to be increased. Therefore, when a wiring layer consists of only aluminum, a disconnection easily occurs at a contact step portion due to the poor step coverage of aluminum, and the reliability of the semiconductor device is degraded.
In contrast to this, a method in which, after a contact hole is formed, a polysilicon film is deposited on the entire surface of the resultant structure, and the polysilicon film is etched back to leave the polysilicon film in only the contact hole is proposed. A so-called selective W-CVD method in which a W film is selectively formed in only the contact hole by using the reduction reaction of WF
6
is proposed (for example, Japanese Patent Laid-Open No. 62-229959).
Although the method of burying the contact with the polysilicon film can be realized by a prior art extension, the resistance of polysilicon itself is higher than that of a metal. In the selective W-CVD method, it is difficult to always obtain complete selectivity, and the theoretical problem that contact holes having different depths cannot be simultaneously buried with the W film is left.
A so-called blanket W-CVD method is proposed (for example, Japanese Patent Laid-Open No. 62-229959). In this blanket W-CVD method, after a contact hole is formed, a W film is deposited on the entire surface of the resultant structure, and the W film is etched back to leave the W film in only the contact hole. For this reason, the W film can be formed easier than that in the selective W-CVD method, and contact holes having different depths can be simultaneously buried with the W film.
In this blanket W-CVD method, even when a TiON layer is formed to improve the adhesion properties with the SiO
2
film serving as an insulating film, the contact holes can be buried with the W film. This TiON layer also functions as a barrier layer, and the melting point of W itself is high, i.e., 3,380° C. For this reason, even when the W film is formed at a relative high temperature, permeation of W into the Si substrate can be suppressed, thereby obtaining preferable electrical characteristics.
FIGS. 1A
to
1
C show a conventional method of forming a W plug using the above blanket W-CVD method and an etch-back technique. As shown in
FIG. 1A
as a state before a W plug is formed, a diffused layer
12
is formed in an Si substrate
11
, and an SiO
2
film
13
serving as an interlayer insulator is formed on the Si substrate
11
.
In this prior art, a contact hole
14
is formed in the SiO
2
film
13
to electrically connect with the diffused layer
12
. For this purpose, a resist film (not shown) having an opening corresponding to the contact hole
14
is formed on the SiO
2
film
13
by photolithography, and etching is performed using the resist film as a mask by an RIE apparatus at a reaction gas flow rate of O
2
/CHF
3
=8/75 SCCM, a reaction pressure of 50 mTorr and an RF power of 1 kW.
As shown in
FIG. 1B
, a TiON layer
15
serving as a titanium-based material layer for improving the adhesion properties between the SiO
2
film
13
and a W film (to be formed later) is formed on the entire surface of the resultant structure by reactive sputtering. As the titanium-based material layer, although a TiN layer or the like may be used, a TiON layer is preferably used. Thereafter, a W film
16
is deposited on the entire surface of the resultant structure by using, e.g., a cold-wall type CVD apparatus, at a reaction temperature of 400° C., a reaction pressure of 6.5 Torr and a reaction gas flow rate ratio of H
2
/WF
6
=1/19.
The entire surface of the W film
16
is etched back with a gas such as SF
6
containing fluorine, as shown in
FIG. 1C
, the W film
16
is left in only the contact hole
14
, and the W film
16
is used as a plug. At this time, when the TiON layer
15
is etched simultaneously with the W film
16
, etching back is preferably performed with a gas obtained by adding a gas such as Cl
2
containing chlorine to the gas containing fluorine.
As shown in
FIG. 1B
, however, the surface of the W film
16
has an uneven shape at the time the W film
16
is deposited. For this reason, as shown in
FIG. 1C
, the uneven shape is transferred to the SiO
2
film
13
. This transfer makes it impossible to form a high-quality wiring layer on the SiO
2
film
13
. In addition, since the surface of the W film
16
left in the contact hole
14
is kept uneven, a wiring layer formed on the SiO
2
film
13
cannot preferably be in electrical contact with the W film
16
.
When a gas such as SF
6
containing fluorine is used such that ion species are not mainly used in etching but a radical reaction is mainly used in the etching, the uneven shape is prevented from being transferred to the SiO
2
film
13
, and an etching rate is increased. However, a loading effect during etching is increased.
In over-etching after just-etching is performed to expose part of the SiO
2
film
13
, since the etching area of the W film
16
is abruptly decreased, an etching rate of the W film
16
in the contact hole
14
is abruptly increased. For this reason, the over-etching of the W film
16
cannot be easily controlled, and as shown in
FIG. 1C
, the contact hole
14
is buried or filled in a recessed form.
In addition, as shown in
FIG. 1C
, a recessed portion
17
may be formed at the central portion of the W film
16
in the contact hole
14
because of the following reason. That is, the W film
16
is formed from the bottom surface and side surface of the contact hole
14
during the CVD, a seam
18
is formed at the central portion as shown in
FIG. 1B
, and the W film
16
at the seam
18
is not rigid and is brittle, thereby increasing the etching rate of the W film
16
.
When the recessed portion
17
is present, the wiring layer formed on the SiO
2
film
13
cannot be in proper electrical contact with the W film
16
. For this reason, in the prior art shown in
FIGS. 1A
to
1
C, the reliability of a semiconductor device cannot be improved.
SUMMARY OF THE INVENTION
According to the present invention, a method of forming a metal plug, having the steps of forming a contact hole in an insulating film, depositing a metal film on the insulating film, and etching the metal film to bury the contact hole with the metal film, comprises the steps of forming a smoothing layer on the metal layer and the step of etching the smoothing layer and the metal layer as the step of etching the metal film.
As the smoothing layer, a W film formed by bias-sputtering, an SiN
x
(x=1 to 2) formed by competitive reactions as etching and deposition reactions, a resist film, an SOG film, an organic polymer layer or the like may be used.
In the method of forming a metal plug according to the present invention, the contact hole may be formed in a tapered shape.
A wafer processing apparatus according to the present invention comprises an organic polymer layer forming unit for forming an organic polymer layer and a heating unit for heating to fluidize the organic polymer layer to obtain a smooth organic polymer layer.
According to the present invention, a method of forming a metal plug, having the steps of forming a contact hole in an insulating film, depositing a metal film on the insulating film, and etching the metal film to bury the contact hole with the metal film, comprises the steps of performing first etching by a radical reaction as the step of etching the metal film and then performing second etching in which deposition and etching reactions of the metal layer are competitive reactions.
In the method of for
Everhart Caridad
Sonnenschein Nath & Rosenthal
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