Semiconductor device and manufacturing method thereof

1. A semiconductor device comprising:

an insulating layer;

a semiconductor layer formed on the insulating layer;

a first partially depleted transistor formed in the semiconductor layer; and

a first diode formed in the semiconductor layer, wherein

the first transistor has

a first gate electrode formed above the semiconductor layer via an insulating film and

a first source or a first drain of a first conductivity type formed in the semiconductor layer below both sides of the gate electrode,

the first diode has

a first impurity layer of a second conductivity type formed in a shallow portion of the semiconductor layer and

a second impurity layer of the first conductivity type formed in a deep portion of the semiconductor layer,

the first impurity layer and the second impurity layer are stacked in a depth direction of the semiconductor layer, and

a side surface of the first impurity layer and a side surface of the second impurity layer are in contact with the semiconductor layer in a region just below the first gate electrode.

2. The semiconductor device according to claim 1 , wherein the boundary between the first impurity layer and the second impurity layer is located at a depth from the surface of the semiconductor layer shallower than the boundary between a neutral region and a depletion layer generated in the semiconductor layer in the region just below the first gate electrode when at least a threshold voltage is applied to the first gate electrode.

3. The semiconductor device according to claim 1 , further comprising a sidewall formed on a side surface of the first gate electrode.

4. The semiconductor device according to claim 1 , further comprising a third impurity layer of the second conductivity type formed at an end portion of the semiconductor layer in the region just below the first gate electrode on the side of the diode, wherein

a concentration of impurity of the second conductivity type in the third impurity layer is lower than that in a portion other than the end portion of the semiconductor layer in the region just below the first gate electrode.

5. The semiconductor device according to claim 1 , further comprising:

a second partially depleted transistor formed in the semiconductor layer; and

a second diode formed in the semiconductor layer, wherein

the second transistor has

a second gate electrode formed above the semiconductor layer via an insulating film and

a second source or a second drain of the second conductivity type formed in the semiconductor layer below both sides of the second gate electrode,

the second diode has

a fourth impurity layer of the first conductivity type formed in a shallow portion of the semiconductor layer and

a fifth impurity layer of the second conductivity type formed in a deep portion of the semiconductor layer,

the fourth impurity layer and the fifth impurity layer are stacked in the depth direction of the semiconductor layer,

a side surface of the fourth impurity layer and a side surface of the fifth impurity layer are in contact with the semiconductor layer in a region just below the second gate electrode, and

the first transistor and the second transistor constitute an inverter circuit.

6. A method of manufacturing a semiconductor device, comprising:

forming a first partially depleted transistor in a semiconductor layer on an insulating layer; and

forming a first diode in which a first impurity layer and a second impurity layer are stacked in a depth direction of the semiconductor layer, wherein

forming the first transistor includes

forming a first gate electrode above the semiconductor layer via an insulating film and

forming a first source or a first drain of a first conductivity type in the semiconductor layer below both sides of the gate electrode, and

forming the first diode includes

introducing an impurity of a second conductivity type to a shallow portion of the semiconductor layer to form the first impurity layer of the second conductivity type such that a side surface of the first impurity layer is in contact with the semiconductor layer in a region just below the first gate electrode and

introducing an impurity of the first conductivity type to a deep portion of the semiconductor layer to form the second impurity layer of the first conductivity type such that a side surface of the second impurity layer is in contact with the semiconductor layer in the region just below the first gate electrode.

7. The method of manufacturing the semiconductor device according to claim 6 , further comprising forming a sidewall on a side surface of the first gate electrode, wherein

in forming the first impurity layer, the impurity of the second conductivity type is introduced to the shallow portion of the semiconductor layer by using the gate electrode and the sidewall as masks.

8. The method of manufacturing the semiconductor device according to claim 6 , further comprising forming a third impurity layer of the second conductivity type at an end portion of the semiconductor layer in the region just below the first gate electrode on the side of the diode, wherein

a concentration of impurity of the second conductivity type in the third impurity layer is lower than that in a portion other than the end portion of the semiconductor layer in the region just below the first gate electrode.