Wafer surface protection in a gas deposition process

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BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to semiconductor processing, and more particularly to the protection of backside and edge of wafers during semiconductor processing operations.

2. Description of Related Art

Chemical vapor deposition ("CVD") is a gas reaction process commonly used in the semiconductor industry to form thin layers of material known as films over an integrated circuit substrate. The CVD process is based on the thermal, plasma, or thermal and plasma decomposition and reaction of selected gases. The most widely used CVD films are silicon dioxide, silicon nitride, and polysilicon, although a wide variety of CVD films suitable for insulators and dielectrics, semiconductors, conductors, superconductors, and magnetics are well known.

Particulate contamination of CVD films must be avoided. A particularly troublesome source of particulates in the chemical vapor deposition of metals and other conductors such as tungsten, tungsten silicide, and titanium nitride, is the film that forms on the edge and backside of the wafer under certain conditions. For example, if the wafer edge and backside are unprotected or inadequately protected during deposition, a partial coating of the CVD material forms on the wafer edge and backside, respectively. This partial coating tends to peel and flake easily for some types of materials, introducing particulates into the chamber during deposition and subsequent handling steps.

Many approaches have been developed for addressing the problem of material deposition on the wafer backside. In one approach, the material is permitted to form on the backside, but then is removed immediately following the deposition step using an in-situ plasma etch. This approach entails additional process steps and requires additional equipment capabilities, and also affects the flatness of the wafer. In another approach, the wafer is clamped onto a substrate holder in an attempt to seal and isolate the backside region from the CVD gas. An adequate seal tends to be difficult to achieve in practice, and the mechanical motion between the clamp and the wafer itself causes particulates. Yet another approach is disclosed in U.S. Pat. No. 4,817,558, issued Apr. 4, 1989 to Itoh. A substrate support member having the form of a cylinder is provided with a flat bearing surface on which the substrate rests. Three pins protrude from the peripheral edge portion of the bearing surface. The sidewalls of the substrate are insulated from the reactive gases by a cover, which is further provided with a lifted and bent region that surrounds the substrate at the level of the substrate. The lifted and bent region is said to trap the reactive gas on the lateral face of the wafer, thereby preventing a film from being deposited on the wafer backside.

SUMMARY OF THE INVENTION

Undesirable deposition of materials on the wafer backside and edge, is diminished or eliminated in the present invention, while good temperature and material deposition uniformity is maintained across the frontside of the wafer. An apparatus for supporting a wafer during wafer processing in a process chamber and for preventing deposition on a frontside peripheral region and edge of the wafer, comprising a platen having a wafer contact to support the wafer, having a deposition control gas pathway, and having a periphery surface region surrounding the wafer contact, and an exclusion guard having a platform surface removably positioned on the periphery surface region, having an extension extending over a frontside peripheral region of the wafer, wherein the extension is separated from the wafer frontside peripheral region by a restrictive opening during wafer processing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, in which like reference numerals refer to like parts,

FIG. 1 is a cross-sectional view of a process chamber for a chemical vapor deposition system, as viewed from above;

FIG. 2 is a cross-sectional view of the process chamber of FIG. 1 illustrating exclusion guards and an exclusion guard lift assembly;

FIG. 3 is a cross-sectional view of the process chamber of FIG. 1, as viewed from a side;

FIG. 4 is a top plan view of a platen illustrative of one embodiment of the platens shown in FIG. 3;

FIG. 5 is a cross sectional view of the platen of FIG. 4;

FIG. 6 is a view through a cross-section of a portion of the platen of FIG. 4;

FIG. 7 is a cross-sectional view of a first exclusion guard embodiment in combination with a platen;

FIG. 8 is a partial cross-sectional view of the exclusion guard and platen shown in FIG. 7;

FIG. 9 is a cross-sectional view of the exclusion guard and platen of FIG. 7 modified to include holes for venting deposition control gas during wafer processing;

FIG. 10 is a bottom view of the exclusion guard of FIG. 9;

FIG. 11 is a partial cross-sectional view of the exclusion guard of FIG. 9 shown in isolation; and

FIG. 12 is a partial cross-sectional view of a another exclusion guard embodiment in combination with a platen.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An illustrative reaction chamber of a high pressure chemical vapor deposition ("CVD") apparatus is shown in FIG. 1 from a top cross sectional view, cross sectioned directly above wafer transport mechanism 10 in an "up" position. The process chamber 2 communicates with a load lock chamber 1, from which wafers to be proc