Method of producing semiconductor device

Details Method of producing semiconductor device Method of producing semiconductor device

2001-10-23

2003-11-04

Nhu, David (Department: 2818)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S680000

Reexamination Certificate

active

06642143

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a semiconductor device, more particularly relates to a method of producing a semiconductor device able to form a contact having a low resistivity and less variability in resistivity even if an aspect ratio is high.
2. Description of the Related Art
As a related art, a method of producing a contact hole will be explained with reference to
FIGS. 1A
to
1
I.
First, as shown in
FIG. 1A
, a silicon substrate
1
is formed with an interlayer insulating film
2
comprised of for example a silicon oxide film. Alternatively, an interconnection layer comprised of metal can be used in place of the silicon substrate
1
.
Next, as shown in
FIG. 1B
, a photolithography step is used to form a resist
3
. Using the resist
3
as a mask, the interlayer insulating film
2
is etched to form an opening
4
. After this, as shown in
FIG. 1C
, the resist
3
is removed. The silicon substrate
1
at the bottom of the opening
4
is therefore formed with a native oxide
5
.
Next, as shown in
FIG. 1D
, reaction products deposited at the hatching part due to the etching for forming the opening
4
and the native oxide
5
are removed. Next, as shown in
FIG. 1E
, the opening
4
and the interlayer insulating film
2
are formed with a barrier metal layer
6
by for example chemical vapor deposition (CVD). After this, as shown in
FIG. 1F
, the barrier metal layer
6
is formed with a plug metal layer
7
a
comprised of for example tungsten (W) or another refractory metal by sputtering.
Next, as shown in
FIG. 1G
, the plug metal layer
7
a
and barrier metal layer
6
are etched back. Due to this, the opening
4
is formed with a plug
7
via the barrier metal layer
6
. Next, as shown in
FIG. 1H
, the entire surface including the surface of the opening
4
is formed with an interconnection metal layer
8
a
comprised of for example aluminum (Al) or Al alloy. Here, a barrier metal layer comprised of Ti etc. can be formed on the interlayer insulating film
2
and plug
7
before the interconnection metal layer
8
a
is formed in the same way as the barrier metal
6
in the opening
4
.
After this, using a not shown resist as a mask, the interconnection metal layer
8
a
is etched for forming interconnections
8
as shown in FIG.
1
I. Due to the above process, a contact hole connecting the silicon substrate
1
or conductive layer and the upper interconnection layer
8
is formed.
In the above conventional method of forming a contact hole, while the native oxide
5
in the opening
4
is removed as a pre-treatment of forming the barrier metal layer
6
, this process is often performed by wet-etching or argon (Ar) sputtering. A solution containing hydrofluoric acid (HF) is used for the wet-etching. Wet-etching has an advantage of a low cost of process.
On the other hand, Ar sputtering has become popularly employed as the aspect ratios of contact holes have increased. Since Ar sputtering can be performed using a conventional sputtering system, it is possible to form in-situ an interconnection or barrier metal layer by sputtering after removing a native oxide.
In recent years, the miniaturization of semiconductor devices has been accompanied by a miniaturization of contact holes and increase of aspect ratios. In the step of forming the barrier metal layer
6
shown in
FIG. 1E
, the aspect ratio becomes for example
7
or more. Even if the aspect ratio is a high one where a top diameter of the opening
4
is 0.4 &mgr;m, a bottom diameter is 0.22 pm, and a height of the opening
4
is equal to a thickness of the interlayer insulating film
2
of 3 &mgr;m, it is necessary to remove thoroughly the native oxide at the bottom of the opening
4
and the deposit on the sidewall of the opening
4
.
However, according to the wet-etching or Ar sputtering described above, along with the increase of the aspect ratio, the following problems have becomes prominent. Due to this, the increase in resistivity in a contact hole having a high aspect ratio has becomes a serious problem.
When the wet-etching is performed in the step shown in
FIG. 1D
, as shown in
FIG. 2A
, a center part in a vertical direction is more easily etched in its sidewall (the interlayer insulating film
2
) compared to the top and bottom of the opening
4
. Along with the increase of the aspect ratio, the time required for wet-etching has become longer. Therefore, etching progresses particularly at the center part in the vertical direction of the opening
4
and therefore the opening
4
forms a barrel shape after the etching.
Due to this, it becomes impossible to fill the opening
4
with the plug metal layer
7
a
comprised of for example W with a good step coverage. Consequently, as shown in
FIG. 2B
, the plug
7
forming a part of the interconnections is formed with voids
9
.
Also, as shown in
FIG. 2A
, the top diameter of the opening
4
becomes larger due to wet-etching. The dotted lines in
FIG. 2A
show an opening width of the resist
3
(see. FIG.
1
B). When the top diameter of the opening
4
becomes larger, it becomes difficult to maintain a withstand voltage between contact holes next to each other. In the worst case, there is a short-circuit between the contact holes.
In the case of Ar sputtering, it suffers from the disadvantage that the resistivity rises due to damage on the contact part. In a contact hole of a high aspect ratio, when Ar sputtering is performed, as shown in
FIG. 3A
, the native oxide
5
is not removed uniformly at the bottom of the opening
4
and often remains near the sidewall of the opening
4
. If the barrier metal
6
and plug
7
etc. are formed from this state as shown in
FIG. 3B
, a contact resistivity rises.
For the purpose of removing the native oxide
5
thoroughly and obtaining a predetermined resistivity, sputtering is performed by a certain amount on not only the native oxide
5
but also the surface of the underlying silicon substrate
1
. If the sputtering is performed excessively, a contact
10
is damaged. For example, when the surface of the silicon substrate
1
is damaged and made amorphous, the reactivity of the barrier metal layer
6
formed above the silicon decreases and defects more easily appear at an interface.
Alternatively, when the sputtering is performed excessively, sputtered material may re-deposit at the contact part
10
and the resistivity may rise.
As described above, in the case of Ar sputtering, in both cases of inadequate sputtering and excessive sputtering, the resistivity of the contact part increases.
A pre-treatment method for forming interconnections able to overcome the above disadvantages without changing the shape of a contact hole and prevent an increase in resistivity at the contact part has been desired. As another pre-treatment method than wet-etching and Ar sputtering, plasma etching can be mentioned.
For example, Japanese Unexamined Patent Publication (Kokai) No. 4-186827 discloses a method of producing a semiconductor device characterized in that a gas containing fluorine is used as an etching gas and hydrogen gas is added for plasma etching before a contact hole is buried with metal. When reactive ion etching (RIE) is performed using a halide as an etching gas, the etching rate of silicon becomes higher than that of the silicon oxide film and a diffusion layer on the silicon substrate is etched largely.
Therefore, according to the method described in Japanese Unexamined Patent Publication (Kokai) No. 4-186827, hydrogen gas is added for lowering the etching rate of silicon. However, there is no description about the relationship between an inside pressure of a chamber and etching rate. An example shows etching is performed at 26 mTorr.
Also, Japanese Unexamined Patent Publication (Kokai) No. 8-45915 discloses a method of forming a contact hole reaching a surface of a metal layer by dry-etching an insulating layer on the metal layer. The method of forming a contact hole is characterized in that a gas containing a nitrogen atom is added to an

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