Copper film including laminated impurities

Details Copper film including laminated impurities Copper film including laminated impurities

2000-07-13

2001-05-22

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

C428S675000, C428S628000, C428S629000, C205S157000, C205S228000

Reexamination Certificate

active

06235406

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process and structure for producing electromigration-resistant interconnect films used in semiconductor chips and packages. More particularly, the present invention is related to processes and structures used to enhance the electromigration resistance of plated metal interconnect films, such as electroplated copper, by enhancing the microstructure of metal films formed for use in chip wiring and packaging applications. Indium, tin, titanium, their compounds with oxygen, and their complexes with oxygen, carbon, and sulfur are incorporated into the films to suppress metal grain boundary growth and metal surface mobility.
BACKGROUND OF THE INVENTION
Aggressive device scaling and interconnection ground rules are challenging the physical limits of materials, processes, and structures in the semiconductor industry. For wiring patterns formed on semiconductor chips and packages, copper has emerged as the metallurgy of choice because of various beneficial properties. Despite the various advantages of copper, the electromigration lifetime of a copper film depends strongly on the processes used to form the copper film. For example, the activation energy required to create failures, due to electromigration of a copper film, typically ranges from 0.7 to 1.0 eV. It is desirable to produce a copper-containing film in which the activation energy required to cause failure is increased beyond 1.3 ev. It is further desirable to produce such a film without major processing modifications and without the addition of multiple processing steps. It is also desirable to produce such a film without bringing about any performance degradation.
The thermo-mechanical, electrical, and metallurgical properties, microstructure, and etching characteristics of a film depend on the process used to produce the film. More specifically, these qualities depend upon the microstructure of the metal film so produced. The microstructure of the metal film is enhanced when dopant impurity materials are disposed along the grain boundaries of the film. These impurities help to suppress grain growth and grain recovery within the film. Uncontrolled grain recovery and grain growth may cause defects during subsequent processes, in addition to compromising the qualities noted above.
The presence of partially soluble and insoluble intermetallic materials within a heat-treated metal film produce a microstructure which includes a high twinning density (multiple twins per grain). These intermetallic materials will be preferentially segregated along grain boundary regions and near the surface of the copper-containing film. The presence of these partially soluble and insoluble intermetallic materials, along copper grain boundaries and near the copper surface, reduces copper grain boundary mobility and the mobility of copper atoms along the surface. The interaction of the impurities and the high twinning density formed within the copper microstructure enhances the electromigration lifetime of the entire film structure being used as an interconnect material. This enhancement occurs because such a structure requires more energy to cause atomic migration preferentially in any given direction. Electromigration failures happen when significant atomic migration occurs preferentially in one direction.
What is needed is an improved process and structure, for producing a copper film used as a wiring interconnection material, offering increased resistance to electromigration failures.
SUMMARY OF THE INVENTION
The present invention addresses the shortcomings of the conventional art by replacing the conventional seed layer used in electrodeposition processes with an alloy seed layer having a copper alloy which may include copper, indium, tin, titanium, and chromium. After the seed layer is formed on a substrate, a copper film is formed on the seed layer. Within or on top of the bulk copper film, an impurity film with comparatively large amounts of impurities such as oxygen, sulfur, nitrogen, and carbon is laminated. After the in-situ impurity electro-lamination is completed, additional films may be added to form a composite interconnect film which includes copper. After the composite film structure is completed, the substrate is annealed. During the annealing process, impurity compounds such as indium oxide, tin oxide, and their complexes are formed as the additives from the alloy seed layer combine with the oxygen, for example, included in the high impurity content laminated film.
The presence of high temperature intermetallic compounds such as indium oxide and other oxides, segregated to the grain boundaries of the copper film, dramatically reduces grain boundary and surface diffusion and mobility. This reduction in copper atom mobility increases the electromigration resistance and the electromigration lifetime of a newly formed copper-containing film. A further aspect of the present invention is the use of high temperature inter-diffusion of an additive, included in an alloy seed layer, to form a barrier layer by combining with materials otherwise unsuitable for barrier material functions. The addition and formation of such a barrier material improves various electromechanical aspects of the film formed.
The present invention provides various processes and structures which improve the electrical, metallurgical, thermo-mechanical, and other properties of copper-containing films. By its nature, copper has a short electromigration lifetime. A pure copper film is highly susceptible to rapid grain growth and particularly high surface mobility at comparatively moderate temperatures. One process of the present invention to enhance the electromigration of a copper thin film is to add impurities, which retard grain growth and surface mobility. A preferred process for accomplishing this result is to laminate impurities into the structure of a deposited metal film. The laminated impurities within the metal interact, in turn, with other species in the metal composite film to form high temperature compounds. The high temperature compounds are not readily soluble in copper; rather, they segregate preferentially to copper grain boundaries where they retard grain boundary growth and copper surface mobility during the application of electromotive forces. This retardation increases the electromigration lifetime of the film.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.


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