1. Field of the Invention
The present invention relates to a contact hole structure, and more particularly to a contact hole in the shape of a pacifier nipple.
2. Description of the Prior Art
Integrated circuits (ICs) are fabricated on wafers. Commonly, these wafers are semiconductor materials; for example, silicon. Research and development has seen a decrease in the size of the transistors making up the integrated circuits.
As transistor sizes shrink, the contact area between the source and drain regions and a metal contact plug for communicating with the transistor decreases proportionally. Contact resistance of the source and drain regions increases proportionally with the decrease in the contact area. Thus, smaller contact areas lead to higher contact resistances. The contact resistance is parasitic and degrades performance of the MOSFET. A portion of the contact resistance results from a Schottky barrier between the metal contact plug and the source/drain regions.