Method of improving the adhesion of copper

Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonelectrolytic coating before depositing...

Reexamination Certificate

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C205S291000, C427S250000, C427S252000, C427S255180, C427S255700, C427S578000, C427S255395

Reexamination Certificate

active

06423201

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the fabrication of integrated circuits, and more particularly, to a system and method of adhering copper to a diffusion barrier surface.
2. Background of the Related Art
The demand for progressively smaller, less expensive, and more powerful electronic products, in turn, fuels the need for smaller geometry integrated circuits (ICs), and large substrates. It also creates a demand for a denser packaging of circuits onto IC substrates. The desire for smaller geometry IC circuits requires that the interconnections between components and dielectric layers be as small as possible. Therefore, research continues into reducing the width of via interconnects and connecting lines. The conductivity of the interconnects is reduced as the surface area of the interconnect is reduced, and the resulting increase in interconnect resistivity has become an obstacle in IC design. Conductors having high resistivity create conduction paths with high impedance and large propagation delays. These problems result in unreliable signal timing, unreliable voltage levels, and lengthy signal delays between components in the IC. Propagation discontinuities also result from intersecting conduction surfaces that are poorly connected, or from the joining of conductors having highly different resistivity characteristics.
To meet the need for interconnects and vias having both low resistivity, and the ability to withstand volatile process environments, aluminum and tungsten have been used in the production of integrated circuits. These metals are popular because they are easy to use in a production environment. However, as geometries have become smaller, copper has replaced aluminum in the effort to reduce the size of lines and vias in an electrical circuit. The conductivity of copper is approximately twice that of aluminum and over three times that of tungsten. As a result, the same current can be carried through a copper line having half the width of an aluminum line. The electromigration characteristics of copper are also much superior to those of aluminum. Copper is approximately ten times better than aluminum with respect to electromigration. As a result, a copper line, even one having a much smaller cross-section than an aluminum line, is better able to maintain electrical integrity.
Copper cannot be deposited onto substrates using the conventional processes for the deposition of other metals like aluminum when the geometries of the selected IC features are small. It is impractical to sputter metal, either aluminum or copper, to fill small diameter vias, since the gap filling capability is poor. To deposit copper in the lines and interconnects of an IC interlevel dielectric, a chemical vapor deposition (CVD) technique has been developed. In the CVD process, copper is combined with a ligand, or organic compound, to make the copper volatile. Copper then becomes an element in a compound that is vaporized into a gas. Several copper gas compounds are available and one includes, for example the liquid complex copper
+1
hfac,TMVS (hfac being an abbreviation for the hexafluoro acetylacetonate anion and TMVS being an abbreviation for trimethylvinylsilane) with argon as the carrier gas. Selected surfaces of an integrated circuit, such as diffusion barrier material, are exposed to the copper gas in an elevated temperature environment. When the copper gas compound decomposes, copper is left behind on the selected surface.
FIG. 1
is a side cross-sectional view, of a typical CVD processing chamber
10
, such as the TxZ Chamber made by Applied Materials, Inc. of Santa Clara, Calif. Chamber
10
includes a chamber body
20
that defines a cavity. A pedestal
30
is disposed in the cavity of the chamber body
20
and supports a substrate
40
on its upper surface
45
for processing. A gas supply unit (not shown) provides precursor gases to the chamber
10
which react with the substrate
40
. A vacuum pump
50
communicates with a pumping channel
60
formed in the chamber
10
to evacuate the gases from the chamber
10
. The vacuum pump
50
and the pumping channel
60
are selectively isolated by a valve disposed between the pumping channel
60
and the vacuum pump
50
.
There are problems associated with the use of copper in IC processing. One problem with the use of copper is that copper diffuses into silicon dioxide, silicon and other dielectric materials. Therefore, barrier layers become increasingly important to prevent copper from diffusing into the dielectric and compromising the integrity of the device. Barrier layers for copper applications are available for inter-dielectric applications. The use of a thin silicon nitride (SiN) layer on the interlayer dielectric will effectively inhibit interlayer diffusion. Within the same dielectric layer it is difficult to provide an effective barrier to prevent leakage between lines. Several technologies are presently under investigation which add a barrier liner to the via sidewall separating the copper metal from the interlayer dielectric. Common physical vapor deposition (PVD) technologies are limited in high aspect and re-entrant structures due to the directional nature of their deposition. The barrier thickness will depend directly upon the structure architecture with the barrier becoming thinner on the sidewall near the structure bottom. Under overhangs on re-entrant structures the barrier thickness, and therefore the barrier integrity, will be compromised.
In contrast, CVD deposited films are by their nature conformal in re-entrant structures. Further, CVD deposited films maintain a high degree of conformity to the structure's lower interface. Silicon nitride (Si
x
N
y
) and titanium nitride (TiN) prepared by decomposition of an organic material are common semiconductor manufacturing materials which display the described conformal performance. Both materials are perceived as being good barriers to Cu interdiffusion, but are considered unattractive due to their high resistivity. The high resistive nature of the material would detrimentally effect the via resistance performance which must be maintained as low as possible. The conduction characteristics of the semiconductor regions are also important considerations in the design of a transistors and the fabrication process is carefully controlled to produce semiconductor regions in accordance with the design. Elements of copper migrating into these semiconductor regions can dramatically alter the conduction characteristics of associated transistors.
Various means have been suggested to deal with the problem of copper diffusion into integrated circuit material. Several materials, especially metallic ones like titanium nitride (TiN) have been used as barriers to prevent the copper diffusion process. A barrier layer of TiN can be deposited by either CVD or PVD, but CVD enjoys the advantage of more easily forming conformal layers in a hole that is relatively deep and narrow.
One CVD process for conformally coating TiN in a narrow hole is the TDMAT process. Referring again to
FIG. 1
, in the TDMAT process, a precursor gas of tetrakis-dimethylamido-titanium, Ti(N(CH
4
)
2
)
4
, is injected into the chamber
10
through the showerhead
150
at a pressure from about 1 to about 9 Torr while the pedestal
30
holds the substrate
40
at an elevated temperature in a range of about 360° C. to about 450° C. Thereby, a conductive and conformal TiN layer is deposited on the substrate
40
in a CVD process. Because a TiN layer initially formed by the TDMAT process includes an excessive amount of carbon in the form of included polymers which can degrade its conductivity, the TDMAT deposition is usually followed by a second step wherein the deposited TiN layer is treated with a plasma. In the plasma step, the TDMAT gas in the chamber is replaced by a gas mixture of H
2
and N
2
in about a 50:50 ratio at a pressure of 0.5 to 10 Torr, and the power supply
170
is switched on to create electric fields between the showerhead
150

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