Method of manufacturing a semiconductor device having transistors and semiconductor device having transistors

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

forming over a semiconductor substrate a first mask pattern in which a first region for forming a first transistor as well as a second region for forming a second transistor having the same channel type as that of the first transistor are opened;

performing a first ion implantation to implant, using the first mask pattern, a first dopant into the first region and the second region to form well regions;

performing a second ion implantation to implant, using the first mask pattern, a second dopant into the first region and the second region to adjust a threshold voltage (Vth) of the first transistor;

removing the first mask pattern and forming a second mask pattern in which the first region is covered and the second region is opened;

performing a third ion implantation to implant, using the second mask pattern, a third dopant into the second region to adjust a Vth of the second transistor;

forming a first gate insulating film in the first region and forming a second gate insulating film in the second region, the second gate insulating film being thinner than the first gate insulating film; and

forming a first gate electrode over the first gate insulating film of the first region and forming a second gate electrode over the second gate insulating film of the second region, the second gate electrode having a gate length shorter than that of the first gate electrode; wherein

in the second and third ion implantation, the second dopant and the third dopant are dopants comprising the same constituent element and are implanted at the same energy.

2. The method according to claim 1 , wherein:

in the first ion implantation, conditions are set such that a concentration peak position in a depth direction of the first dopant in the well region is deeper than those of the second dopant and the third dopant.

3. The method according to claim 1 , further comprising, after forming the first and second gate electrodes:

forming LDD regions in the first and second regions;

forming sidewall spacers on the sidewalls of first and second gate electrodes; and

forming source/drain regions in the first and second regions.

4. The method according to claim 1 , further comprising, after forming the first and second gate electrodes:

forming a pocket region in the first region of the semiconductor substrate.

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

forming over a semiconductor substrate a first mask pattern in which a first region for forming a first transistor as well as a second region for forming a second transistor having the same channel type as that of the first transistor are opened;

performing a first ion implantation to implant, using the first mask pattern, a first dopant into the first region and the second region to form well regions;

performing a second ion implantation to implant, using the first mask pattern, a second dopant into the first region and the second region to adjust a threshold voltage (Vth) of the first transistor;

removing the first mask pattern and forming a second mask pattern in which the first region is covered and the second region is opened;

performing a third ion implantation to implant, using the second mask pattern, a third dopant into the second region to adjust a Vth of the second transistor;

forming a first gate insulating film in the first region and forming a second gate insulating film in the second region, the second gate insulating film being thinner than the first gate insulating film; and

forming a first gate electrode over the first gate insulating film of the first region and forming a second gate electrode over the second gate insulating film of the second region, the second gate electrode having a gate length shorter than that of the first gate electrode; wherein

in the third ion implantation, the third dopant has a mass number larger than that of the second dopant and is implanted such that a depth of a concentration peak position of the third dopant is equal to that of the second dopant.

6. The method according to claim 5 , wherein:

in the first ion implantation, conditions are set such that a concentration peak position in a depth direction of the first dopant in the well region is deeper than those of the second dopant and the third dopant.

7. The method according to claim 5 , further comprising, after forming the first and second gate electrodes:

forming LDD regions in the first and second regions;

forming sidewall spacers on sidewalls of the first and second gate electrodes; and

forming source/drain regions in the first and second regions.

8. The method according to claim 5 , further comprising, after forming the first and second gate electrodes:

forming a pocket region in the first region of the semiconductor substrate.