Semiconductor device and method of producing same

1. A semiconductor device comprising:

a gate electrode formed over a semiconductor substrate;

a first conductivity type region formed in the semiconductor substrate under a conductive portion of the gate electrode and containing a first conductivity type impurity;

first source/drain regions of the first conductivity type impurity formed in the semiconductor substrate, the first source/drain regions being formed from a first ion implantation having a first implantation energy and a first dosage amount; and

second source/drain regions having a first conductivity type impurity concentration lower than that in the first source/drain regions and formed extending from beneath the gate electrode in the semiconductor substrate, the second source/drain regions being formed from a second ion implantation having a second implantation energy substantially greater than the first implantation energy and a second dosage amount substantially less than the first dosage amount.

2. A semiconductor device as set forth in claim 1 , wherein the gate electrode includes a second conductivity type impurity.

3. A semiconductor device as set forth in claim 1 , further comprising:

side wall insulation films formed at side walls of the conductive portion the gate electrode, and

wherein the first source/drain regions are formed and extended from edge portions of the side wall insulation films.

4. A method of producing a semiconductor device comprising, the steps of:

introducing a first conductivity type impurity into a semiconductor substrate,

forming a conductive portion of a gate electrode,

forming side wall insulation films on sides of the conductive portion of the gate electrode,

performing a first ion implantation treatment of the first conductivity type impurity by using the gate electrode and the side wall insulation films as masks to form first source/drain regions from both end portions of the gate insulation film in surface regions of the semiconductor substrate, the first ion implantation having a first implantation energy and a first dosage amount, and

performing a second ion implantation treatment in which the resultant concentration of the first conductivity type impurity is lower and an implantation depth of the first conductivity type impurity is deeper than that in the first ion implantation treatment to form second source/drain regions extending from perpendicularly beneath a gate insulation film to a region beneath the first source/drain regions in the semiconductor substrate, and wherein the second ion implantation energy is substantially greater than the first implantation energy and a second dosage amount substantially less than the first dosage amount.

5. A method of producing a semiconductor device as set forth in claim 4 , wherein, in the step of forming the gate electrode, the conductive portion of the gate electrode including a second conductivity type impurity is formed.

6. A method of producing a semiconductor device as set forth in claim 4 , wherein the dosage of the first conductivity type impurity of the total of the first ion implantation treatment and the second ion implantation treatment is set lower than the amount of the second conductivity type impurity introduced into the gate electrode.

7. A method of producing a semiconductor device as set forth in claim 4 , wherein, in the second ion implantation treatment, ions are implanted from an inclined direction with respect to a main surface of the semiconductor substrate.

8. A semiconductor device comprising:

a semiconductor substrate;

a gate insulation film formed over a surface of the semiconductor substrate;

a gate electrode formed over a surface of the gate insulation film;

a first conductivity type region having the first conductivity type impurity;

first source/drain regions having the first conductivity type impurity, the first source/drain regions being formed from a first ion implantation having a first implantation energy and a first dosage amount; and

second source/drain regions having the first conductivity type impurity at a concentration lower than a concentration in the first source/drain regions,

the first conductivity type region being opposed to the gate electrode with the gate insulation film therebetween and formed narrower than a width of a conductive portion of the gate electrode in a surface region of the semiconductor substrate,

the second source/drain regions being formed adjoining the first conductivity type region, and extending from under the gate insulation film to under portions of the first source/drain regions in the semiconductor substrate at regions separated from the gate electrode, the second source/drain regions being formed from a second ion implantation having a second implantation energy substantially greater than the first implantation energy and a second dosage amount substantially less than the first dosage amount.