Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-04-09
2001-01-09
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S629000, C438S630000, C438S658000
Reexamination Certificate
active
06171960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to ultra scale integrated circuits, and more particularly to a method of fabricating copper interconnects in ultra scale integrated circuits.
2. Description of the Related Art
The fabrication of deep submicron ultra large scale integrated (ULSI) circuits requires long interconnects having small contacts and small cross-sections. To achieve the above objectives, the preferred interconnect material is copper. Copper provides a number of advantages for wiring applications including low resistivity and a high melting point.
At present, aluminum is the material used in fabricating interconnects on most integrated circuits. This invention seeks to replace the aluminum with copper in the fabrication of advanced circuits and ultra-fast logic devices.
Many problems, however, are encountered in fabricating circuit interconnects with copper. Some of the major difficulties include: (a) copper oxidizes easily at low temperatures; (2) copper has poor adhesion to substrates; (3) copper diffuses into silicon dioxide and other dielectric material used in micro-circuitry; and (4) copper requires a high temperature for patterning by reactive ion etching.
In order to overcome these disadvantages when using copper as an interconnect material, it is necessary to passify the copper surfaces and provide diffusion barriers between the copper and the adjacent layers. A layer of titanium nitride (TiN) has been suggested as a possible diffusion barrier due to its inert and conductive nature.
FIGS.
1
A-
1
D are cross-sectional views showing a conventional method of fabricating copper interconnects. Referring to
FIG. 1A
, a semiconductor substrate
100
is provided. A dielectric layer
104
with a via
102
is formed on the semiconductor substrate
100
. A titanium layer
106
is formed, for example, by sputtering in the via
102
and on the dielectric layer
104
under argon gas. The titanium layer
106
has a thickness of about 200-500 Å.
Referring to
FIG. 1B
, a first titanium nitride layer
108
is formed, for example, by nitriding under N
2
gas or NH
3
gas at high temperature on the titanium layer
106
as a adhesion layer.
Referring to
FIG. 1C
, a copper layer
110
is formed on the first titanium nitride layer
108
. Excess copper material outside of the via
102
is removed by chemical mechanical polishing to expose the semiconductor substrate
100
.
Referring to
FIG. 1D
, a second titanium nitride layer
112
is formed on the copper layer
110
to avoid the oxidation and preserve the characters of the interconnections. The process of fabricating copper interconnects described above provides a copper layer in the via as an interconnect. A titanium layer and a titanium nitride layer are deposited between the copper layer and other dielectric layers as a barrier layer and an adhesion layer to protect the copper layer from oxidation and prevent it form diffusing.
A number of limitation to the above method have been discovered, however, particularly when forming fully-planar copper lines by filling grooves in a dielectric and removing the excess. In this case, the copper must be deposited into a feature without leaving a void, so electroplating or chemical vapor deposition is required. It is difficult to deposit refractory copper or metal-copper alloys, such as copper-titanium, with electroplating or chemical vapor deposition techniques.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide an improved and simplified method of fabricating copper interconnects. The present invention skips the step of depositing a barrier layer. An impurity doped in the copper layer diffuses toward the surface of the copper layer and reacts with the titanium or a gas to form the barrier layer. The method reduces the cost and the steps to form the barrier layer.
The invention achieves the above-identified objects by providing one new method of fabricating copper interconnection. First, a semiconductor substrate with a trench or a via is provided. A titanium layer is form as a barrier layer on the semiconductor substrate. A copper layer doped with light silicon is formed in the trench or the via. The excess of the copper layer is removed by CMP to expose the surface of the semiconductor substrate. The copper layer is annealed under nitrogen gas to make silicon doped in the copper layer diffuse toward the surface of the copper layer. Silicon reacts with the titanium layer and nitrogen gas to form a silicon nitride layer and a titanium silicide layer to encapsulate the copper layer.
The invention achieves the above-identified objects by providing another new method of fabricating copper interconnection. First, a semiconductor substrate with a trench or a via is provided. A titanium layer is formed as a barrier layer on the semiconductor substrate. A copper layer doped with light silicon is formed in the trench or the via. The excess of the copper layer is removed by CMP to expose the surface of the semiconductor substrate. Then, a second titanium layer is formed on the copper layer. The copper layer is annealed under argon gas to make the silicon doped in the copper layer diffuse toward the surface of the copper layer. Silicon reacts with the titanium layer, the second titanium layer forms a titanium silicide layer to encapsulate the copper layer.
REFERENCES:
patent: 5447887 (1995-09-01), Filipiak
Everhart Caridad
Thomas Kayden Horstemeyer & Risley
United Microelectronics Corp.
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