1. Technical Field
The present invention relates generally to semiconductor processing, and more particularly, to methods and structure for preventing cavitation in high aspect ratio regions of a semiconductor device.
2. Related Art
In semiconductor processing, contact shorts have a tendency of occurring where the dielectric films for these levels have to fill high aspect ratio regions or reentrant profile regions. For example, FIG. 1 illustrates a high aspect ratio region 10 formed next to a silicon nitride barrier layer 12 covering two adjacent gates 14 in a semiconductor device. As illustrated, an interlayer dielectric (ILD) layer film 16 placed in high aspect ratio region 10 tends to cause cavitation, i.e., form a keyhole-shaped void or weak spot 20 (hereinafter “void) in the region. Void 20 extends into and out of the page. In particular, during prior processing, oxide under each spacer 22 formed on adjacent gates 14, are undercut 24 during formation of a silicide portion 26 such that deposition of silicon nitride barrier layer 12, especially at lower temperatures, forms a lower portion 30 above undercut 24. As a result of this situation, high aspect ratio region 10 formed between portions of silicon nitride layer 12 has a constrictive region 28 that is smaller than lower portion 30 of high aspect ratio region 10. Constrictive region 28 may also exist even where undercuts 24 are not present. When ILD layer 16 is deposited, it is incapable of completely filling the area in the constrictive region 28 and/or the area just below constrictive region 28, i.e., lower portion 30, resulting in void 20. During subsequent processing, such as clean processing of silicide portion 26, void 20 can be opened or enlarged. When the subsequent metal layers (not shown) are formed, the opened void is filled with metal, leading to a short. Currently, there is no adequate method of addressing these high aspect ratio region voids.
In view of the foregoing, there is a need in the art for prevention of cavitation in high aspect ratio dielectric regions that lead to contact shorts.