Passivated copper surfaces

Details Passivated copper surfaces Passivated copper surfaces

1998-06-13

2001-11-27

Chaudhuri, Olik (Department: 2814)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C428S418000, C428S425800

Reexamination Certificate

active

06323131

ABSTRACT:

FIELD OF THE INVENTION
This invention is directed to a method for passivating copper surfaces to prevent air corrosion of the surface and the passivated article produced thereby. More particularly, it is primarily directed to the passivation of the surfaces of copper interconnects and electrodes in ultra high scale integration integrated circuits (ULSI).
BACKGROUND OF THE INVENTION
A major limiting factor in ULSI interconnect technology is RC time delay introduced by the coupling of metal-insulator characteristics. An efficient interconnection scheme for advanced ULSI circuits requires materials with low effective time constants. In this regard, metals with low resistivity such as copper and the noble metals are emerging as materials of choice.
Some of the issues to be addressed in order for Cu-based interconnects to be a viable choice, especially as integration density continues to rise, involves the processes for patterning the copper lines, the prevention of diffusion of the copper into the underlying active substrate, and the prevention of air corrosion on the surface of the copper. The latter mentioned issues being the most important at this time.
Currently, new barrier materials deposited between the copper and the substrate or dielectric layer and processes related to their application to reliably prevent or substantially reduce copper contamination of the underlying material are under investigation. One reported barrier layer is a plasma assisted silicon nitride deposited film.
In order to passivate the copper surface subsequent to formation of the patterned copper interconnect lines, to both avoid interaction with adjacent dielectrics, e.g. SiO
2
, and to avoid air oxidation, the current state of the art employs various techniques including the formation of a silicide coating over the exposed copper; encapsulation with thin deposited inorganic films such as a-Si or Si
3
N
4
; alloying of the copper surface to form Cu
3
Ti, Cu
3
Pd or CuAl
2
; and implantation of boron into the copper. These passivation steps usually involve harsh conditions such as elevated process temperatures (300° C.-400° C.), ion implantation and/or exposure to a plasma, which could adversely effect device fabrication. Also, these processes are relatively costly and time consuming. It would therefore be advantageous to find a less costly and/or less time consuming passivation process which preferably can be done in a single step without the need for specialized expensive capital equipment, and which does not employ harsh processing parameters. It is also desirable to find alternative barrier materials and processes to prevent migration of copper into the underlying substrate.
In the unrelated field of electrochemistry wherein gold electrodes are immersed in liquid electrochemical plating baths, spontaneously self-assembling mono-layer organic films have been employed to modify the surfaces of the gold electrodes. Such films have also been employed as biologically active membranes. These films have been described in various publications such as R. J. P. Williams, Self-Assembling Surfaces,
Nature
332, 393, Mar. 31, 1988; I. Rubenstein et al., Ionic Recognition and Selective Response in Self Assembling Monolayer Membranes on Electrodes,
Nature
332, 426-429, 1988; S. Steinberg et al., Ion-Selective Monolayer Based on Self Assembling Tetradentate Ligand Monolayers on Gold Electrodes. 2. Effect of Applied Potential on Ion Binding,
J. American Chemical Society
113, 5176-5182, 1991; S. Steinberg et al., Ion-Selective Monolayer Based on Self Assembling Tetradentate Ligand Monolayers on Gold Electrodes. 3.
Langmuir
8, 1183-1187, 1992; and M. M. Walczak et al., Modified Electrode Surfaces,
The Electrochemical Society
, 4th Edition, 39-40, 1997, all of which are incorporated herein by reference. We have now discovered that these same kinds of films can be employed to provide a passivation layer to prevent air corrosion of copper and more particularly to passivate copper interconnects in ULSI integrated circuits to substantially eliminate corrosion of the interconnects without any detrimental effects to the IC device. The same layers can also provide an effective barrier layer between the copper and its underlying substrate.
SUMMARY OF THE INVENTION
A process for passivating the surface of copper to prevent air corrosion thereof which process is particularly useful in the manufacture of high density integrated circuits utilizing copper interconnects comprises forming, preferably in a single step, a self-assembled mono- or multi-layer organic passivating film or membrane over an exposed copper surface by treating the copper surface with a dilute solution of the film forming molecules for a time sufficient for the spontaneous adsorption of these molecules in the form of a densely packed self-assembled layer on the copper surface. The same kind of self assembled layer may be formed on the material underlying the copper interconnects to provide a barrier layer which prevents migration of copper into the underlying substrate.
The invention further includes the article of manufacture having such a passivating, corrosion protection, or barrier layer film thereon.
It should be understood that while the invention is described in terms of the manufacture of ULSI circuits having copper interconnects, it is useful to protect any copper surface from air corrosion, e.g. copper roofing and copper pipes and the like.


REFERENCES:
patent: 5508141 (1996-04-01), Hart et al.
patent: 5677545 (1997-10-01), Shi et al.
patent: 5721056 (1998-02-01), Wessling
patent: 5779818 (1998-07-01), Wessling
patent: 2679240 (1993-01-01), None
M. M. Walczak et al., Modified Electrode Surfaces, The Electro-chemical Society, 4th Ed., 1997 39-40.
S.P. Murarka et al., Copper Metallization for ULSI and Beyond, Critical Reviews in Solid State & Materials Sciences, 20(2), 87-124 (1995).
J.M. Steigerwald, et al., Chemical Processes in the Chemical Mechanical Polishing of Copper, Materials Chemistry and Physics 41 (1995) 217-228.
S. Lakshminarayanan, et al., Contact and Via Structures with Copper Interconnects Fabricated Using Dual Damascene Technology, IEEE Electron Device Letters 15(8) 1994, 307-309.
S. Steinberg, et al., Ion Selective MOnolayer Membranes Based Upon Self-Assembling Tetradente Ligand Monolayers on Gold Electrodes. 3. Langmuir 8, 1992, 1183-1187.
S. Steinberg et al., Ion Selective Monolayer Membranes Based Upon Self-Assembling Tetradente Ligand Monolayers on Gold Electrodes. 2. J. Amer. Chem. Soc. 113, 1991, 5176-5182.
I. Rubenstein et al., Ionic Recognition and Selective Response in Self-Assembling Monolayer Membranes on Electrodes. Nature 332, 1988 426-429.
R.J.P. Williams, Self-Assembling Surfaces, Nature 332, 1988, 393.

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