Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2000-06-19
2003-03-25
Thomas, Tom (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S762000
Reexamination Certificate
active
06538324
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a semiconductor integrated circuit including a copper wiring layer, and more particularly to a barrier film which prevents copper diffusion from such a copper wiring layer.
2. Description of the Related Art
As a semiconductor device has been designed to be smaller and smaller in size, wiring delay exerts greater influence on a silicon ULSI device. As a result, though a wiring layer has been composed of aluminum, it is necessary to compose a wiring layer of copper in place of aluminum.
Resistivity of copper is equal to about 70% of resistivity of aluminum. However, since copper does not form passive state composed of an oxide film, at a surface thereof, unlike aluminum, copper is more corrosive than aluminum.
In addition, since copper has a high diffusion rate in both silicon (Si) and silicon dioxide (SiO
2
), if copper enters MOSFET formed on a silicon substrate, copper would induce reduction in carrier lifetime.
Hence, it is absolutely necessary for a semiconductor device having a copper wiring layer to have a diffusion-barrier film for preventing diffusion of copper into an interlayer insulating film formed between copper wiring layers. In addition, since such a diffusion-barrier film has to have high adhesion characteristic to both an interlayer insulating film and a copper wiring layer in order to keep reliability in wiring.
Thus, there have been made many suggestions about a structure of a barrier metal layer and a method of fabricating the same, in order to prevent copper diffusion form a copper wiring layer.
For instance, a structure of a barrier metal layer is suggested in the following articles:
(a) Semiconductor World, Nobuyoshi Awaya, February 1998, pp. 91-96 (hereinafter, referred to as Prior Art 1);
(b) Advanced Metallization and Interconnect Systems for ULSI Applications in 1997, Kee-Won Kwon et al., 1998, pp. 711-716 (hereinafter, referred to Prior Art 2);
(c) Journal Electrochemical Society, M. T. Wang et al., July 1998, pp. 2538-2545 (hereinafter, referred to as Prior Art 3); and
(d) 1998 Symposium on VLSI Technology Digest of Technical Papers, D. Denning et al., 1998, pp. 22-23.
In addition, a structure of a barrier metal layer and a method of fabricating the same both for preventing copper diffusion is suggested also in Japanese Unexamined Patent Publications 8-139092, 8-274098, 9-64044 and 10-256256, and Japanese Patent Application No. 10-330938. Herein, Japanese Patent Application No. 10-330938 is not published yet, and hence does not constitute prior art to the present invention. However, it is explained in the specification only for better understanding of the present invention. The applicant does not admit that Japanese Patent Application No. 10-330938 constitutes prior art to the present invention.
It is quite difficult to dry-etch copper, and hence, a copper wiring layer is formed generally by chemical mechanical polishing (CMP).
Specifically, a copper wiring layer is formed as follows.
An insulating film is formed on an underlying copper wiring layer. Then, the insulating film is formed with a recess and a through-hole reaching the underlying copper wiring layer. Then, a thin diffusion-barrier film is formed on surfaces of the recess and the through-hole therewith such that the recess and the through-hole is completely covered at surfaces thereof with the diffusion-barrier film in order to prevent copper diffusion from uncovered region.
Thereafter, a copper film is deposited filling the recess and the through-hole therewith by CVD or sputtering. Then, the copper film and the diffusion-barrier film are removed in selected regions by CMP. Thus, a copper wiring layer is completed.
As will be obvious to those skilled in the art, the diffusion-barrier film is required to have high coverage as well as capability of preventing copper diffusion and adhesion to copper.
The diffusion-barrier film is composed, for instance, of refractive metal such as tungsten (W), tantalum (Ta) or titanium (Ti), or nitride of such refractive metal such as tungsten nitride (WN), titanium nitride (TiN) or tantalum nitride (TaN).
As explained in Prior Art 2, for instance, a tantalum (Ta) barrier film has high adhesion with a copper film formed on the tantalum barrier film by sputtering, ensuring improvement in crystallinity of the copper film. However, since copper is diffused into the tantalum film, it would be necessary for the tantalum barrier film formed below the copper film, to have a thickness of 50 nm or greater.
Prior Art 4 reports that if a copper film is formed on a tantalum film by CVD, fluorine (F) segregates at an interface between the copper film and TaN, resulting in degradation in adhesion therebetween.
Prior Art 3 reports that a crystalline TaN barrier film oriented in directions of (200) and (111) can prevent copper diffusion more highly than a crystalline Ta barrier film.
As an solution to enhance a characteristic of preventing copper diffusion and adhesion to copper, a multi-layered structure of a metal film and a metal nitride film has been suggested.
For instance, the above-mentioned Japanese Patent Application No. 10-330938 has suggested a method of fabricating a multi-layered barrier film including a titanium film and formed by sputtering.
As illustrated in
FIG. 1
, in accordance with the suggested method, only an argon gas is introduced into a sputter chamber to thereby form a titanium film
1
. Then, a nitrogen gas is introduced into the sputter chamber, and a thin titanium nitride film
2
is formed on the titanium film
1
auxiliarily making use of reaction between titanium and nitrogen. Thus, there is formed a multi-layered barrier structure
3
comprised of the titanium film
1
and the thin titanium nitride film
2
.
In the method, a metal oxide film formed on an underlying wiring film is removed by argon plasma prior to carrying out sputtering.
However, the conventional barrier film for preventing copper diffusion is accompanied with the following problems.
The first problem is that it is quite difficult to make a diffusion-barrier film have both a characteristic of preventing copper diffusion and a sufficient adhesive force with copper.
As illustrated in
FIG. 2
, it is now assumed to form a metal film
5
having a crystallized pillar structure, on a semiconductor substrate
4
. In the metal film
5
, a lot of grains each comprised of individual crystals, and grain boundaries
7
each defining an interface between the grains
6
exist throughout the metal film
5
, that is, from an upper surface to a bottom of the metal film
5
. The grain boundaries
7
define paths
8
through which copper is diffused. As a result, the metal film
5
has low barrier characteristic of preventing copper diffusion.
As illustrated in
FIG. 3
, it is now assumed to form a metal film
5
a
on a semiconductor substrate
4
. If the metal film
5
a
is composed of metals having small resistivity, such as tungsten (W), titanium (Ti) or tantalum (Ta), the metal film
5
would have a polycrystal structure. As a result, the metal film
5
a
would have a pillar-like structure similarly to the metal film
5
illustrated in
FIG. 2
, and accordingly, the metal film
5
a
would have small barrier characteristic of preventing copper diffusion.
However, it should be noted that if a copper film is formed on a crystalline metal film, such as a &bgr;-Ta (002) film as obtained in sputtering of a tantalum film, by sputtering, the copper film would have high adhesion and rich crystal orientation, though a barrier characteristic of preventing copper diffusion would be deteriorated. As a result, the copper film would enhance reliability in copper wiring.
In contrast, the metal film
5
a
illustrated in
FIG. 3
, which is composed of particles
9
such as amorphous TaN and formed on the semiconductor substrate
4
, has small resistivity, specifically in the range of about 200 to 250 &mgr;&OHgr;cm, and does not have the paths through which copper is diffused unlike the crystalline metal film
5
illustrated in
Hayashi Yoshihiro
Tagami Masayoshi
NEC Corporation
Scully Scott Murphy & Presser
Thomas Tom
Vu Hung Kim
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