Coating apparatus – Gas or vapor deposition
Reexamination Certificate
1998-05-18
2001-09-04
Ahmad, Nasser (Department: 1772)
Coating apparatus
Gas or vapor deposition
C118S720000, C427S509000, C427S520000, C427S521000, C427S522000, C427S558000, C427S585000, C438S758000, C438S761000
Reexamination Certificate
active
06284050
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to deposition of films on a substrate by chemical vapor deposition and more particularly to deposition of films with improved properties by including exposure to ultraviolet light in the deposition process.
2. Description of Related Art
Advanced semiconductor devices having higher performance and greater functionality than previous devices are often characterized by decreasing device feature geometries. As device geometries become smaller, the dielectric constant of an insulating material used between conducting paths becomes an increasingly important factor in device performance. Reducing this value advantageously lowers power consumption, reduces crosstalk, and shortens signal delay for closely spaced conductors.
Organic polymers are advantageously used to provide insulating films for low dielectric constant applications. Many of these films are typically applied by chemical vapor deposition, a process that is widely used in the semiconductor industry. The dielectric constants of organic polymer films are typically between 1.5 and 3, considerably lower than the dielectric constant of approximately 4 of a silicon oxide (SiO
2
) film, the material often employed as an insulating material in conventional devices. However, while SiO
2
adheres easily to the silicon, silicon-containing, or metal surfaces of typical semiconductor devices, organic polymer films do not generally adhere as well to these semiconductor substrates. In addition, organic polymer films often do not exhibit the hardness and thermal stability desired of films used as insulating layers in semiconductor devices.
It is known that exposing organic polymer films to ultraviolet (UV) radiation promotes cross-linking of polymers in the films, a process which is associated with increased hardness, improved thermal stability, improved film cohesion, and reduced subsequent outgassing of the films. For example, the improved thermal and mechanical stability obtained by cross-linking fluorocarbon polymer chains is described in R. A. Flinn et al. in “Engineering Materials and Their Applications,” pp 370, 409 (2
nd
Ed., 1981). It is also known that simultaneous irradiation of organic materials during polymerization is often advantageous for promoting the completion of polymerization.
However, as stated previously, many low dielectric constant films are typically applied to semiconductor wafers in chemical vapor deposition (CVD) processes and conventional CVD systems are not designed to accommodate a light source directed at the wafer surface.
Thus, it would be desirable to provide a process to improve the hardness, thermal stability, and adhesion properties of low dielectric constant organic films. It would be desirable to improve these properties by cross-linking the polymer films by exposure to UV radiation. It would also be desirable to promote completion of polymerization during deposition by exposure to UV radiation. It would further be desirable to provide a CVD apparatus for the deposition of such films that includes a means to expose wafer surfaces to UV radiation.
SUMMARY OF THE INVENTION
The present invention is directed to a chemical vapor deposition (CVD) system for the deposition of polymer films on a semiconductor wafer which provides for exposure of the wafer surface to ultraviolet (UV) radiation before, during, and/or after the deposition process.
In one embodiment, the present invention is an ultraviolet-assisted chemical vapor deposition system, a CVD system that incorporates a UV light source. The CVD system includes a deposition chamber, a chuck disposed on a pedestal for supporting a semiconductor wafer, and a UV lamp positioned above the chamber, and directed toward the semiconductor wafer, so as to uniformly illuminate the wafer surface.
In one embodiment, the invention includes a tube-shaped monomer manifold for supplying the film precursor, disposed within the deposition chamber, above the semiconductor wafer. The central opening of the tube-shaped distribution system is aligned to allow light from the UV lamp to uniformly cover the wafer surface. In another embodiment, the CVD system of the present invention includes an optical window made of a suitable material that transmits ultraviolet light, such as quartz or sapphire, installed at the top of the deposition chamber, above the monomer distribution system, allowing light from the UV lamp to enter the chamber.
In further embodiments, the present invention includes processes for improving the properties of polymer films applied to semiconductor wafers in CVD processes by exposing them to UV radiation. The processes include one or more depositions, one or more UV exposures, and one or more anneals. In one embodiment, the process is a post-deposition process in which a polymer film on a wafer is irradiated after deposition is completed. In this case, the order of the process is: deposition, UV treatment, anneal. Alternatively, the UV exposure and anneal can be reversed so that the order of the process is: deposition, anneal, UV treatment, followed by an optional second anneal.
In another embodiment, the process has two depositions. According to one version of the multi-deposition process, first, a thin layer of film is deposited on a wafer surface. Second, the thin layer is exposed to UV radiation. Third, additional polymer is deposited on the UV-treated film until a desired thickness is achieved. According to a second version, the second deposition is followed by a second UV treatment. In both versions, the process also includes a final anneal.
The invention also includes an in situ UV-assisted deposition process in which the wafer surface is exposed during deposition. The deposition followed by UV treatment, at the start of the multi-deposition processes, could alternatively be replaced by an in situ UV-assisted deposition. In another embodiment, a UV-pre-cleaning process is provided in which a wafer surface is exposed to UV irradiation before deposition begins. Any of the post-deposition or multi-deposition processes presented above can be preceded by UV-pre-cleaning. Finally, a UV-assisted annealing procedure is provided in which the wafer is exposed to UV radiation during annealing. In either the post-deposition or multi-deposition processes, in versions when the UV exposure is followed by the final anneal, this part of the process can be replaced by a single UV-assisted anneal.
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patent: 4880493 (1989-11-01), Ashby
patent: 5122440 (1992-06-01), Chien
patent: 5538758 (1996-07-01), Beach
patent: 5711987 (1998-01-01), Bearinger
patent: 5846375 (1998-12-01), Gilchrist
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Mitchener James C.
Shi Jianou
Ahmad Nasser
Novellus Systems Inc.
Saxon Roberta P.
Skjerven Morrill & MacPherson LLP
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