Method of epitaxially forming contact structures for semiconductor transistors

1. A method comprising:

providing a semiconductor substrate having a first and a second gate structure of a first and a second transistor formed on top thereof, said first and second gate structures being embedded in a first inter-layer-dielectric (ILD) layer;

epitaxially forming a first semiconductor region between said first and second gate structures inside said first ILD layer;

epitaxially forming a second semiconductor region directly on top of said first semiconductor region, said second semiconductor region being inside a second ILD layer that is on top of said first ILD layer and having a width wider than a width of said first semiconductor region; and

forming a silicide in a top portion of said second semiconductor region,

wherein epitaxially forming said first and second semiconductor regions comprises:

etching a first via hole inside said first ILD layer between said first and second gate structures;

epitaxially growing said first semiconductor region inside said first via hole;

depositing said second ILD layer on top of said first ILD layer as well as on top of said first semiconductor region;

etching a second via hole inside said second ILD layer in an etching process selective to said first ILD layer, said second via hole, at a bottom thereof, being equal to or bigger than a cross-sectional area of said first semiconductor region; and

epitaxially growing said second semiconductor region inside said second via hole.

2. The method of claim 1 , wherein etching said second via hole comprises forming said second via hole to have a funnel shape with tapered sidewalls.

3. The method of claim 2 , wherein a bottom cross-section of said funnel shape is at least as big as a cross-section of said first semiconductor region, said first semiconductor region being isolated from said first and second gate structures by said first ILD layer and said cross-section thereof being uniform from a top surface to a bottom surface of said first semiconductor region.

4. The method of claim 1 , wherein forming said silicide further comprises forming said silicide to have an interface with rest of said second semiconductor region, said interface having multiple facets and a total combined width of said multiple facets being wider than a width of said second semiconductor region.

5. A method comprising:

providing a semiconductor substrate;

forming a first and a second field-effect-transistors to have a first and a second gate structure located on top of said semiconductor substrate;

covering said first and second gate structures with a first inter-layer-dielectric (ILD) layer;

forming a first silicon region between said first and second gate structures inside said first ILD layer;

forming a second silicon region directly on top of said first silicon region, said second silicon region being inside a second ILD layer on top of said first ILD layer and having a width wider than a width of said first silicon region; and

forming a silicide in a top portion of said second silicon region,

wherein forming said first and second silicon regions comprises:

etching a first opening inside said first ILD layer;

epitaxially growing said first silicon region inside said first opening;

depositing said second ILD layer on top of said first ILD layer as well as on top of said first silicon region;

etching a second opening inside said second ILD layer in an etching process selective to said first ILD layer, said second opening being equal to or bigger than a cross-section area of said first silicon region; and

epitaxially growing said second silicon region inside said second opening.

6. The method of claim 5 , wherein etching said second opening comprises forming said second opening to have a funnel shape with tapered sidewalls, said funnel shape being formed directly on top of said first silicon region.

7. The method of claim 6 , wherein a bottom cross-section area of said funnel shape is at least as big as said cross-section area of said first silicon region, said first silicon region being isolated from said first and second gate structures by said first ILD layer, said cross-section area of said first silicon region being uniform from a top to a bottom surface thereof.

8. The method of claim 5 , wherein forming said silicide further comprises forming said silicide to have an interface with rest of said second silicon region, said interface having at least two facets and a total combined width of said two facets being wider than a width of said second silicon region.