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
1999-02-09
2001-04-17
Pham, Long (Department: 2823)
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
06218734
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates generally to integrated circuit processes and fabrication, and more particularly, to a system and method of adhering copper to a diffusion barrier surface.
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.
There is a need for interconnects and vias to have both low resistivity, and the ability to withstand volatile process environments. Aluminum and tungsten metals are often used in the production of integrated circuits for making interconnections or vias between electrically active areas. These metals are popular because they are easy to use in a production environment, unlike copper which requires special handling.
Copper is a natural choice to replace 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.
There have been problems associated with the use of copper, however, in IC processing. Copper pollutes many of the materials used in IC processes and, therefore, care must be taken to keep copper from migrating. The migration of copper into silicon semiconductor regions is especially harmful. The conduction characteristics of the semiconductor regions are a consideration in the design of a transistors. Typically, 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, have been suggested for use as barriers to prevent the copper diffusion process. For example, Cho et al., in the article entitled “Copper Interconnection with Tungsten Cladding for ULSI,” 1991 Symposium on VLSI Technology, pg. 39, suggests the use of tungsten as a diffusion barrier. Molybdenum and titanium nitride (TiN) have also been suggested for use as copper diffusion barriers. Gardner, et al., in an article entitled “Encapsulated Copper Interconnection Devices Using Sidewall Barriers,” in 1991 VMIC Conference, pg. 99, suggests the use of sidewall structures to completely encapsulate the copper. However, the adhesion of copper to these diffusion barrier materials has been, and continues to be, an IC process problem.
Copper cannot be deposited onto substrates using the conventional processes for the deposition of aluminum when the geometries of the selected IC features are small. That is, new deposition processes have been developed for use with copper in the lines and interconnects of an IC interlevel dielectric. 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, a chemical vapor deposition (CVD) technique has been developed in the industry.
In a typical CVD process, copper is combined with a ligand, or organic compound, to make the copper volatile. That is, copper becomes an element in a compound that is vaporized into a gas. Selected surfaces of an integrated circuit, such as difflusion 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. Several copper gas compounds are available for use with the CVD process. It is generally accepted that the configuration of the copper gas compound, at least partially, affects the ability the copper residue to adhere itself to the selected surface.
Wang, et al. in the article “Chemical Mechanical Polishing of Copper Metalized Multi-level Interconnection Devices,” 1995 VMIC Conference, pg. 505, suggests the use of one particular copper gas compound, or precursor, for improving the adhesion of copper to a TiN barrier surface. Although certain precursors may improve the copper adhesion process, variations in the diffusion barrier surfaces to which the copper is applied, and variations in the copper precursors themselves, often result in the unsatisfactory adhesion of copper to a selected surface.
It has become standard practice in the industry to apply CVD copper immediately after the deposition of the diffusion barrier material to the IC. Typically, the processes are performed in a single chamber or an interconnected cluster chamber. It has generally been thought that the copper layer has the best chance of adhering to the diffusion barrier material when the diffusion barrier material surface is clean. Hence, the diffusion barrier surface is often kept in a vacuum, or controlled environment, and the copper is deposited on the diffusion barrier as quickly as possible. However, even when copper is immediately applied to the diffusion barrier surface, problems remain in keeping the copper properly adhered. A complete understanding of why copper does not always adhere directly to a diffusion barrier surface is lacking.
It would be advantageous to employ a method of improving the adhesion of CVD copper to a diffusion barrier material surface.
It would also be advantageous if a method were employed for preparing a diffusion barrier surface, in advance of CVD copper deposition, to improve the adhesion of copper of the diffusion barrier surface.
Further, it would be advantageous if the adhesion improving process did not degrade the electrical conductivity between the deposited copper and a conductive diffusion barrier material. It would also be advantageous if the process did not disrupt the silicon bonds and structures in adjoining IC substrates.
Accordingly, a method of applying copper to selected integrated circuit surfaces is provided. The selected copper-receiving surfaces being predominantly on diffusion barrier material applied to selected regions of the IC. The method comprises the steps of: exposing each selected copper-receiving surface to a reactive gas species; permitting the reactive gas species to interact with molecules of the copper-receiving surface, whereby higher energy molecular bonds are replaced with lower energy bonds between the reactive gas species and the exposed copper receiving surface, changing the surface characteristics of the exposed copper-receiving surface to promote the formation of bonds between the copper-receiving surface and subsequently deposited copper; and depositing CVD copper on the copper-receiving surface, whereby copper adhesion to the diffusion barrier is improved.
In a
Charneski Lawrence J.
Nguyen Tue
Coleman William David
Krieger Scott C.
Pham Long
Rabdau Matthew D.
Ripma David C.
LandOfFree
Copper adhered to a diffusion barrier surface does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Copper adhered to a diffusion barrier surface, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Copper adhered to a diffusion barrier surface will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2527769