Strained transistor structure

1. A semiconductor device comprising:

a transistor structure including:

a channel region formed in a monocrystalline semiconductor substrate;

a source region formed at least partially in the monocrystalline semiconductor substrate adjacent the channel region;

a drain region formed at least partially in the monocrystalline semiconductor substrate adjacent the channel region;

a gate dielectric layer formed on the channel region; and

a gate electrode formed on the gate dielectric layer, the gate electrode having a conductive portion over the channel region having inwardly sloping sidewalls such that the conductive portion of the gate electrode has a bottom cross-section length that is greater than an upper portion cross-section length;

a contact plug contacting the gate electrode at a gate contact region of the gate electrode having inwardly sloping sidewalls, wherein at least part of the contact plug is on the inwardly sloping sidewalls at the gate contact region of the gate electrode; and

a strain inducing layer formed over the transistor structure.

2. The semiconductor device of claim 1 comprising a gate contact on the gate electrode at a gate contact region of the gate electrode having vertical sidewalls, the gate contact region of the gate electrode being adjacent to the conductive portion having inwardly sloping sidewalls.

3. The semiconductor device of claim 1 , wherein a dopant concentration of the channel region has a gradient inversely proportional to the slope of the inwardly sloping sidewalls of the gate electrode portion over the channel region.

4. The semiconductor device of claim 1 , wherein the inwardly sloping sidewalls of the gate electrode make an angle Ø in a range between 20° and 45° with respect to a vertical direction.

5. The semiconductor device of claim 1 comprising sidewall spacers including dielectric material formed on at least part of the inwardly sloping sidewalls of the gate electrode portion over the channel region.

6. The semiconductor device of claim 1 ,

wherein at least a base portion of the conductive portion of the gate electrode includes polysilicon;

wherein the monocrystalline semiconductor substrate includes silicon; and

wherein the strain inducing layer includes silicon nitride.

7. The semiconductor device of claim 1 wherein the transistor structure is part of an N-type transistor, and the strain inducing layer is inducing compressive strain on the transistor structure.

8. The semiconductor device of claim 1 wherein the transistor structure is part of a P-type transistor, and the strain inducing layer is inducing tensile strain on the transistor structure.

9. A semiconductor device comprising:

a transistor structure including:

a channel region formed in a monocrystalline semiconductor substrate;

a gate dielectric overlying the channel region;

a gate electrode overlying the gate dielectric, the gate electrode having a conductive portion overlying the channel region, the conductive portion of the gate electrode having a cross-section shape with a bottom side, a top side, and two sidewalls, the two sidewalls being opposite each other and extending from the bottom side to the top side, wherein each of the sidewalls is sloped inward from the bottom side to the top side at an angle of at least 20 degrees relative to a vertical direction;

a contact plug contacting the gate electrode at a gate contact region of the gate electrode having inwardly sloping sidewalls, wherein at least part of the contact plug is on the inwardly sloping sidewalls at the gate contact region of the gate electrode; and

a strain inducing layer formed over the transistor structure.

10. The semiconductor device of claim 9 ,

wherein the gate dielectric includes one or more layers of dielectric material formed directly on the channel region; and

wherein the gate electrode includes doped polysilicon formed directly on the gate dielectric.