Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-08-23
2004-08-17
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S618000, C438S643000, C438S648000, C438S653000, C438S658000, C438S687000, C438S680000, C438S681000, C438S654000
Reexamination Certificate
active
06777331
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 copper to 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 dimensions of the interconnection between components and dielectric layers be as small as possible. Therefore, recent research continues into reducing 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 are popular because there are much knowledge, experience and expertise due to the long term usage in production environment.
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 more resistance to electromigration than aluminum. 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, 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 becomes small. Therefore new deposition processes have been used to deposit diffusion barrier and copper lines and interconnects in an integrated circuit. It is impractical to sputter metal, either aluminum or copper, to fill small diameter vias, since the gap filling capability is poor. One of the techniques to deposit copper that provide excellent gap fill capability is the chemical vapor deposition (CVD) technique.
In a typical copper CVD process, copper is combined with a ligand, or a 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 precursor in an elevated temperature environment. When the copper precursor decomposes, copper is left behind on the selected surfaces and the remaining gases (by-products) are exhausted away. 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 deposit on the selected surfaces) are often volatile and being exhausted away.
Another deposition technology similar to the CVD technique is atomic layer deposition (ALD). In ALD various gases are injected into the chamber for as short as 100-500 milliseconds in alternating sequences. For example, a first gas is delivered into the chamber for about 500 milliseconds and the substrate is heated, then the first gas (heat optional) is turned off. The residue from the first gas is then evacuated. Another gas is delivered into the chamber for another 500 milliseconds (heat optional). The residue from this gas is also evacuated before the next gas is delivered for about 500 milliseconds (and optionally heated). This sequence is done until all gases have been cycled through the chamber, each gas sequence typically forms a monolayer which is highly conformal. ALD technology thus pulses gas injection and heating sequences that are between 100 and 500 milliseconds. This approach has a high dissociation energy requirement to break the bonds in the various precursor gases such as silane and oxygen and thus requires the substrate to be heated to a high temperature, for example in the order of 600-800 degree Celsius for silane and oxygen processes.
ALD also uses radical generators, such as plasma generators, to increase the reactivity of the second gas and effectively the reaction between the first and the second gases at the substrate. U.S. Pat. No. 5,916,365 to Sherman entitled “Sequential chemical vapor deposition” provides for sequential chemical vapor deposition by employing a reactor operated at low pressure, a pump to remove excess reactants, and a line to introduce gas into the reactor through a valve. Sherman exposes the part to a gaseous first reactant, including a non-semiconductor element of the thin film to be formed, wherein the first reactant adsorbs on the part. The Sherman process produces sub-monolayer per gas injection due to adsorption. The first reactant forms a monolayer on the part to be coated (after multiple cycles), while the second reactant passes through a radical generator which partially decomposes or activates the second reactant into a gaseous radical before it impinges on the monolayer. This second reactant does not necessarily form a monolayer but is available to react with the deposited monolayer. A pump removes the excess second reactant and reaction products completing the process cycle. The process cycle can be repeated to grow the desired thickness of film.
Ther
Everhart Caridad
Keshhavan Belur V
Nguyen Tue
Simplus Systems Corporation
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