Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-11-13
2003-12-30
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S644000, C438S654000, C438S769000
Reexamination Certificate
active
06670266
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to integrated circuit processes and fabrication, and more particularly, to a method of improving the adhesion property of a diffusion barrier structure.
BACKGROUND OF THE INVENTION
The demand for progressively smaller, less expensive, and more powerful electronic products creates 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 dimension of interconnections between the components and the dielectric layers be as small as possible. Therefore, recent research continues to focus on reduction of the cross section area 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 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 have been used for a long time in the production environment because the processing technologies for these metals were available. Experience and expertise on these metals have also been acquired in the process due to the long-term usage.
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 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.
However, there have been problems associated with the use of copper in IC processing. Copper poisons the active area of silicon devices, creating unpredictable responses. Copper also diffuses easily through many materials used in IC processes and, therefore, care must be taken to keep copper from migrating.
Various means have been suggested to deal with the problem of copper diffusion into integrated circuit materials. Several materials, including metals and metal alloys, have been suggested for use as barriers to prevent the copper diffusion process. The typical conductive diffusion barrier materials are TiN, TaN and WN. Addition of silicon into these materials, TiSiN, TaSiN, WSiN, could offer improvement in the diffusion barrier property. For non-conductive diffusion barrier, silicon nitride has been the best material so far. However, the adhesion of copper to these diffusion barrier materials has been, and continues to be, an IC process problem.
The conventional process of sputtering, used in the deposition of aluminum, will not work well when the geometry of the selected IC features are small. It is impractical to sputter metals, either aluminum or copper, to fill small diameter vias, since the gap filling capability is poor. Therefore new deposition processes have been used with diffusion barrier and copper in the lines and interconnects of an integrated circuit. To improve the gap fill capability, one of the techniques to deposit copper is the chemical vapor deposition (CVD) technique.
In a typical copper 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, called precursor that is vaporized into a gas. Selected surfaces of an integrated circuit, such as that of diffusion barrier materials, are exposed to the copper gas in an elevated temperature environment. When the copper gas compound decomposes, copper is left behind on the selected surfaces. Several copper precursors are available for use with the CVD process. It is generally accepted that the configuration of the copper precursors, at least partially, affects the ability of the copper residue to adhere itself to the selected surfaces. 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 unsatisfactory adhesion of copper to a selected surface.
Similarly, diffusion barrier materials could be deposited by the chemical vapor deposition technique. For example, in the case of TiN CVD deposition, a precursor that contains Ti and optionally nitrogen, is used. The precursor decomposes at the selected surfaces, and the decomposed elements react together to form a TiN layer on these selected surfaces. Precursor by-products (products formed as the precursor decomposes that do not participate in the reactions) and reaction by-products (products formed from the reaction that do not deposited on the selected surfaces) are often volatile and being exhausted away.
It has become a standard practice in the semiconductor industry to apply CVD copper immediately after the deposition of the diffusion barrier material to the integrated circuit to improve the adhesion and to reduce the contact resistance. 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 and free of contaminants. Hence, the diffusion barrier surface is often kept under vacuum, or in a 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.
Charneski et al., U.S. Pat. No. 5,909,637, entitled “Copper adhesion to a diffusion barrier surface and method for same”, proposed a method to use reactive gas species to clean the surface of the diffusion barrier to improve the adhesion to the subsequently deposited copper layer. This method has very limited success and often does not provide enough adhesion to be practical. Nguyen et al., U.S. Pat. No. 5,913,144, entitled “Oxidized diffusion barrier surface for the adherence of copper and method for same”, further proposed a method to use reactive oxygen species to oxidize the diffusion barrier surface to improve the adhesion to the subsequently deposited copper layer. This method works well to improve the adhesion property, but by oxidizing the barrier material, it produces a non-conductive layer that significantly increases the contact resistance of the integrated circuit even at a very small thickness.
It would be advantageous to understand the mechanism of the adhesion of CVD copper to a diffusion barrier material surface.
It would be advantageous to employ a method of improving the adhesion of CVD copper to a diffusion barrier material surface without increasing the contact resistance.
It would be advantageous to employ a method of improving the adhesion of CVD copper to a diffusion barrier material surface that can be optimized with respect to the contact resistance.
Accordingly, a method of improving the adhesion to the diffusion barrier surface is provided based on the analysis and understanding of the properties of th
Nguyen Tai Dung
Nguyen Tue
Nguyen Tue
Picardat Kevin M.
Simplus Systems Corporation
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