Method of forming a metal gate electrode

Details Method of forming a metal gate electrode Method of forming a metal gate electrode

2001-11-06

2004-07-20

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

By reaction with substrate

C438S785000, C257S412000

Reexamination Certificate

active

06764961

ABSTRACT:

This application relies for priority upon Korean Patent Application No. 2001-15150, filed on Mar. 23, 2001, the contents of which are herein incorporated by reference in their entirety.
FIELD OF THE INVENTION
The present invention generally relates to a method of making a semiconductor device and, more specifically, to a method of forming a metal gate electrode.
BACKGROUND OF THE INVENTION
A gate electrode is fabricated by forming a conductive film having a uniform thickness on a semiconductor substrate and subsequently etching the conductive film to be a predetermined shape. Generally, polysilicon has been used to make a typical gate electrode due to its excellent interface characteristics with a gate oxide at a high temperature. However, as the semiconductor devices are becoming highly integrated, the typical polysilicon gate electrode cannot satisfy manufacturers of the semiconductor devices with its operation speed and sheet resistance. Thus, a metal gate electrode comprised of a polysilicon and a refractory metal such as tungsten formed on the polysilicon has been used. However, the metal gate electrode has a problem due to an abnormal oxidation that is caused by excellent oxidation characteristics of tungsten used for metal gate electrodes.
FIGS. 1A
,
1
B,
2
A and
2
B are cross-sectional views showing a method of making a metal gate electrode in accordance with the conventional art.
First, as shown in
FIG. 1A
, a gate oxide layer
12
is formed on a semiconductor substrate
10
. Then, a polysilicon layer
14
, a tungsten layer
16
and a gate electrode capping layer
18
are sequentially formed on the gate oxide layer
12
. Further, a conductive barrier layer (not shown) is formed between the polysilicon layer
14
and the tungsten layer
16
to prevent a chemical reaction therebetween. Next, a gate electrode
20
is formed by sequentially etching the gate electrode capping layer
18
, the tungsten layer
16
, the polysilicon layer
14
and the gate oxide layer
12
. Subsequently, an oxidation process is performed to cure damage
22
on the semiconductor substrate
10
and ensure reliability of the gate oxide layer
12
. As a result, as shown in
FIG. 1B
, the damage
22
is cured and an oxide layer
12
a
is formed on the semiconductor substrate
10
and side walls of the polysilicon layer
14
and the gate oxide layer
12
. However, an abnormal oxidation
12
b
is caused on side walls of the tungsten layer
16
because an oxidation rate of the tungsten layer
16
is higher than that of the polysilicon layer
14
. Accordingly, to prevent the abnormal oxidation
12
b
during forming a metal gate electrode, a selective oxidation process has been developed. The selective oxidation process oxidizes only silicon layer but does not oxidize a metal layer after patterning a metal gate electrode. The selective oxidation process is performed by adjusting partial pressures of hydrogen gas and H
2
O to selectively oxidize the silicon layer. Further, partial pressures are adjusted by controlling oxygen gas and hydrogen gas of a source gas. For example, the selective oxidation process such as wet hydrogen oxidation selectively oxidizes silicon by controlling the following chemical reaction.
Si+2H
2
O⇄SiO
2
+2H
2
  (1)
W+3H
2
O⇄WO
3
+3H
2
  (2)
That is, by controlling the partial pressures of H
2
O and the hydrogen gas, reactions are favored toward the right side in equation 1 and in the direction of the left side in equation 2, respectively. Therefore, the oxidation of tungsten can be prevented.
However, the selective oxidation process described above has a narrow process margin, and it is difficult to adjust the partial pressures of the hydrogen gas and H
2
O to only oxidize the silicon. Accordingly, as shown in
FIG. 2A
, a small amount of the tungsten is oxidized, so that tungsten oxide
12
c
is formed on side walls of the tungsten layer
16
. As shown in
FIG. 2B
, the insulative tungsten oxides
12
c
causes whiskers
24
due to a thermal energy that is applied to the tungsten oxide
12
c
during a heating process of subsequent semiconductor device manufacturing processes. Thus, an electrical short between the gate electrodes adjacent each other can be caused by the whiskers. The whiskers
24
are formed due to an amorphous phase and nucleation cites on the surface of the tungsten oxide
12
c.
That is, surface mobility of the tungsten oxide
12
c
having amorphous phase is increased by the thermal energy during a beating process, then the amorphous tungsten oxide
12
c
is moved toward the nucleation cites and crystallized at the nucleation cites, so that the whiskers
24
are formed. Accordingly, it is required to completely suppress the oxidation reaction of the tungsten during the selective oxidation process.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a method of forming a metal gate electrode that is capable of preventing whiskers by ensuring reliability of a selective oxidation process.
In accordance with one aspect of the present invention, there is provided a method of making a metal gate electrode wherein a selective oxidation process to be performed after patterning the metal gate electrode is carried out under a nitrogen containing gas ambient to ensure a reliability of the selective oxidation process.
In the method of making the metal gate electrode according to the present invention, the nitrogen containing gas prevents a metal layer of the metal gate electrode from being oxidized. The reason is that nitrogen is unstably combined with the metal layer having high reactivity, so that it prevents the metal layer from reacting with oxygen. Further, the nitrogen containing gas suppresses formation of the nucleation cites on a metal oxide layer and decreases surface mobility of the metal oxide layer, so that the whiskers are not formed during a subsequent heating process.
In accordance with the method of the invention, a metal gate electrode having a silicon layer, a conductive barrier layer and a metal layer is formed. A metal gate electrode pattern including the silicon layer, the conductive barrier layer and the metal layer is formed. The selective oxidation process is performed on the metal gate electrode pattern in the nitrogen containing gas ambient.
In the method of making the metal gate electrode, one of nitrogen N
2
, nitrogen monoxide NO, nitrogen oxide N
2
O and ammonia NH
3
is used as the nitrogen containing gas. The gases are used by themselves, or one or more of the gases are mixed with each other.
In the method of making the metal gate electrode, the selective oxidation process can be performed at a temperature lower than that of a conventional thermal oxidation process, so that the process margin is increased.
The present invention will be better understood from the following detailed description of the exemplary embodiment thereof taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.


REFERENCES:
patent: 4505028 (1985-03-01), Kobayashi et al.
patent: 4505082 (1985-03-01), Kobayashi et al.
patent: 5633212 (1997-05-01), Yuuki
patent: 6197702 (2001-03-01), Tanabe et al.
patent: 6284634 (2001-09-01), Rha
patent: 6323115 (2001-11-01), Tanabe et al.
patent: 6348380 (2002-02-01), Weimer et al.

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