Semiconductor device having semiconductor pillar

1. A semiconductor device comprising:

a semiconductor substrate including an active region having a semiconductor pillar, the semiconductor pillar having first and second side surfaces substantially perpendicular to a main surface of the semiconductor substrate;

an element isolation region surrounding the active region, the element isolation region including a first insulating pillar that is in contact with the first side surface of the semiconductor pillar;

a gate electrode that covers the second side surface of the semiconductor pillar with an intervention of a gate insulating film;

a first impurity diffusion layer formed on an upper surface of the semiconductor pillar;

a second impurity diffusion layer formed in the active region located below the semiconductor pillar; and

an etching protection wall that is arranged to surround the semiconductor pillar.

2. The semiconductor device as claimed in claim 1 , wherein

the etching protection wall includes an interlayer insulating film that is embedded in a groove of closed loop shape surrounding the semiconductor pillar and the first insulating pillar, and

the upper surface of the semiconductor pillar and an upper surface of the first insulating pillar are substantially coplanar.

3. The semiconductor device as claimed in claim 2 , wherein

the element isolation region further includes a second insulating pillar,

the semiconductor pillar, the first insulating pillar and the second insulating pillar constitute a cylindrical structure having an inner wall and an outer wall; and

the gate electrode is formed on the inner wall of the cylindrical structure.

4. The semiconductor device as claimed in claim 3 , wherein the interlayer insulating film covers the outer wall of the cylindrical structure.

5. The semiconductor device as claimed in claim 4 , wherein the element isolation region further includes a third insulating pillar that surrounds the interlayer insulating film.

6. The semiconductor device as claimed in claim 3 , further comprising:

a signal wiring; and

a contact plug connected between the gate electrode and the signal wiring, the contact plug being arranged on the element isolation region.