Semiconductor device having insulated gate field effect transistors and method of fabricating the same

A semiconductor device, comprising:

• a first insulated gate field effect transistor formed on a semiconductor substrate of a first conductive type;
• a second insulated gate field effect transistor formed on the semiconductor substrate and having a gate being adjacent to a gate of the first insulated gate field effect transistor;
• a semiconductor layer of a second conductive type formed in a surface region of the semiconductor substrate between the gates of the first and the second insulated gate field effect transistors as a source or a drain of the first and the second insulated gate field effect transistors;
• and
• a contact plug composed of a silicon plug, a barrier metal film and a metal plug in a contact hole, a side portion of the contact plug being separated from the gates of the first and the second insulated gate field effect transistors by a dielectric film,
• wherein the silicon plug has a pyramid-shaped section structure and is formed in a bottom portion of the contact hole, and wherein the barrier metal film is formed on the silicon plug, and wherein the metal plug is formed on the barrier metal film.

A method of fabricating a semiconductor device, comprising:

• forming a side wall dielectric film on a side of gates of a first and a second insulated gate field effect transistors;
• forming a dielectric film on gates of the first and the second insulated gate field effect transistors, a side of the side wall dielectric film and a source or a drain of the first and the second insulated gate field effect transistors;
• forming a interlayer dielectric film on the dielectric film;
• forming a contact hole between a gate of the first insulated gate field effect transistor and a gate of the second insulated gate field effect transistor being adjacent to the first insulated gate field effect transistor;
• forming a polycrystalline silicon film in a bottom portion of the contact hole and a side of the contact hole and on the interlayer dielectric film;
• forming a polycrystalline silicon film having a U-shaped section structure in a bottom portion of the contact hole as a polycrystalline silicon plug, by removing a portion of the polycrystalline silicon film formed on the interlayer dielectric film and another portion of the polycrystalline silicon film formed in a upper portion of the contact hole using a etch back process;
• forming a barrier metal film on the polycrystalline silicon plug;
• and
• burying a metal plug on the barrier metal film so that covering on the contact hole.