Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2000-04-17
2001-09-11
Powell, William A. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C216S067000, C438S735000, C438S743000
Reexamination Certificate
active
06287979
ABSTRACT:
BACKGROUND OF INVENTION
1) Field of the Invention
This invention relates generally to fabrication of a semiconductor device and more particularly to a method for forming an air gap as a low dielectric constant material between conductive lines or interconnects using Buckminsterfullerene as a porogen in an air bridge or dielectric material.
2) Description of the Prior Art
In aluminum and copper damascene BEOL interconnects, the reduction of the RC delay is a key design driver. The introduction of low dielectric constant (low-K) materials is one way of reducing the capacitance of the delay, and thereby reducing the delay. The ideal low-K material for reducing RC delay is air. However, introducing air as the dielectric material between metal lines presents processing difficulties.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,744,399 (Rostoker et al.) teaches a process for lowering the dielectric constant of an insulating layer by incorporating a fullerene within an organic or an inorganic matrix (e.g. composite layer) This patent teaches that the fullerenes can be removed to form pores which reduce the dielectric constant of the remaining matrix. This patent teaches that the preferred method for removing fullerenes is by using a liquid solvent, although an oxygen plasma is suggested as a possible alternative. However this patent does not disclose or suggest the use of fullerenes in an organic spin-on layer as a sacrificial layer or as a sacrificial layer consisting solely of fullerenes. This patent teaches away from the present invention, teaching that fullerene should be used in a mixture with a matrix material. Nor does this patent disclose or suggest the use of an air bridge. U.S. Pat. No. 5,510,645 (Fitch et al.) teaches a method for forming an air gap using a selective etch process to remove a sacrificial spacer.
U.S. Pat. No. 5,461,003 (Havemann et al.) shows a method for forming an air gap by removing a disposable solid layer, preferably photoresist through a porous dielectric layer using an oxygen plasma.
U.S. Pat. No. 5,750,415 (Gnade et al.) shows a method for forming an air gap by removing a disposable liquid through a porous silica precursor film.
U.S. Pat. No. 5,597,444 (Gilton) shows an etching method using a plasma comprising a mixture of a carbon compound, including buckminsterfullerene, and a halogen.
Buckminsterfullerenes (e.g. fullerenes, bucky balls) are a naturally occurring form of carbon named for Buckminster Fuller, the architect of the geodesic dome. Fullerenes can contain from 32 to 960 carbon atoms, and are all believed to have the structure of a geodesic dome. Sixty-carbon fullerenes and seventy-carbon fullerenes are highly stable molecules.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for forming an air gap using a sacrificial spin-on layer comprising buckminsterfullerene as a porogen in an inorganic matrix which is removed through an air bridge using an oxygen plasma to form the air gap.
It is another object of the present invention to provide a method for forming an air gap using buckminsterfullerene as a porogen in an air bridge layer, and using an oxygen plasma to remove the buckminsterfullerene from the air bridge layer, creating a porous air bridge, and to remove a reactive organic layer through the air bridge to form an air gap.
It is another object of the present invention to reduce RC delay in a semiconductor device by forming an air gap or air tunnel between adjacent conductive lines, such as interconnects, using buckminsterfullerene as a porogen according to any of the preceding objects.
It is yet another object of the present invention to provide a method for forming an air gap using buckminsterfullerene as a porogen in a sacrificial spin-on layer and in an air bridge.
To accomplish the above objectives, the present invention provides a method for reducing RC delay by forming an air gap between conductive lines, using buckminsterfullerene as a porogen in a sacrificial layer and/or in a composite air bridge layer. A porogen is a material which can be removed to leave a pore or gap in the remaining structure. An air bridge is a porous layer, through which a gas or liquid (in this invention an oxygen plasma) can penetrate, reacting with an underlying layer.
The present invention begins by providing a semiconductor structure having conductive lines thereon, wherein the conductive lines have a gap there between. An optional oxide liner can be formed over the semiconductor structure and conductive lines. A sacrificial layer is formed over the semiconductor structure, filling the gaps. An air bridge layer is formed over the sacrificial layer. The semiconductor structure is exposed to an oxygen plasma, whereby the sacrificial layer is removed through the air bridge layer.
In a first embodiment of the present invention, the sacrificial layer comprises buckminsterfullerene incorporated in an inorganic spin-on material, resulting in a partial air gap, or the sacrificial layer consists of buckminsterfullerene alone, resulting in a total air gap. In the first embodiment, the air bridge layer can be a porous film as is known in the art.
In the second embodiment of the present invention, the air bridge layer comprises buckminsterfullerene incorporated in an inorganic spin-on layer, such as HSQ. When the semiconductor structure is exposed to an oxygen plasma, the buckminsterfullerene is removed from the air bridge layer, forming a porous air bridge layer. The oxygen species in the plasma (e.g. radicals, atoms, ions) penetrate the porous layer and reacts with an underlying sacrificial layer, preferably comprising a reactive organic material, and the sacrificial layer is removed through the porons air bridge layer.
The present invention provides considerable improvement over the prior art. An air gap can be formed using spin-on and oxygen plasma treatment processes which are well known, easily controlled, and readily available in semiconductor manufacturing. Also, the present invention does not present the difficulty of working with a sacrificial liquid or the problem of shrinkage associated with other air bridge processes.
The present invention achieves these benefits in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.
REFERENCES:
patent: 5461003 (1995-10-01), Havemann et al.
patent: 5510645 (1996-04-01), Fitch et al.
patent: 5597444 (1997-01-01), Gilton
patent: 5744399 (1998-04-01), Rostoker et al.
patent: 5750415 (1998-05-01), Gnade et al.
Chooi Simon
Zhou Mei-Sheng
Chartered Semiconductor Manufacturing Ltd.
Pike Rosemary L. S.
Powell William A.
Saile George O.
Stoffel William J.
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