Pillar-type field effect transistor having low leakage current
A pillar-type field effect transistor having low leakage current is provided. The pillar-type field effect transistor includes: a semiconductor body, source and drain formed in a semiconductor pillar; a gate insulating layer formed on a surface of the semiconductor body; a gate electrode formed on a surface of the gate insulating layer. The gate electrode includes a first gate electrode and a second gate electrode being electrically connected with the first gate electrode. The first gate electrode has a work function higher than that of the second gate electrode. Accordingly, the gate induced drain leakage (GIDL) can be reduced, so that an off-state leakage current can be greatly reduced.
1. A pillar-type field effect transistor having low leakage current, comprising:
a substrate;
a semiconductor pillar formed substantially perpendicular to the substrate, the semiconductor pillar being elongated in a direction substantially perpendicular to the substrate and having a length substantially perpendicular to the substrate, the semiconductor pillar forming along the length of the semiconductor pillar a source region at one end thereof, a drain region at the other end thereof, and a semiconductor body between the source region and the drain region;
a gate insulating layer formed around the semiconductor pillar along the length thereof;
a gate electrode formed around the gate insulating layer, the gate electrode being divided into a first gate electrode and a second gate electrode along the length of the semiconductor pillar,
wherein one of the first gate electrode and the second gate electrode is a source-side gate electrode, the other one thereof is a drain-side gate electrode electrically connected to the source-side gate electrode, and the drain-side gate electrode has a work function smaller than that of the source-side gate electrode to thereby reduce a gate-induced-drain leakage.
2. The pillar-type field effect transistor of claim 1 , further comprising a third gate electrode between the first gate electrode and the second gate electrode.
3. The pillar-type field effect transistor of claim 2 , further comprising inter-gate insulating layers formed between the first gate electrode and the third gate electrode, and between the third gate electrode and the second gate electrode.
4. The pillar-type field effect transistor of claim 1 , wherein a cross-sectional area of the semiconductor body surrounded by the second gate electrode is smaller than that of the semiconductor body surrounded by the first gate electrode.
5. The pillar-type field effect transistor of claim 1 , wherein a cross-sectional area of the semiconductor pillar is varied with the length of the semiconductor pillar.
6. The pillar-type field effect transistor of claim 1 , wherein the first gate electrode and the second gate electrode are formed of a same material with different impurity doping types, different materials, or different materials with different impurity doping types.
7. The pillar-type field effect transistor of claim 1 , wherein a thickness of the gate insulating layer formed under the second gate electrode is larger than that under the first gate electrode.
8. The pillar-type field effect transistor of claim 1 , wherein each of the source region and the drain region is partially overlapped with the gate electrode.
9. The pillar-type field effect transistor of claim 1 , further comprising a contact window for reducing contact resistance between the drain region and a drain electrode, wherein the contact window has an area wider than a cross-sectional area of the semiconductor pillar.
10. The pillar-type field effect transistor of claim 1 , further comprising a selective epitaxial layer formed on a surface of the semiconductor pillar where the drain region is formed, wherein a total cross-sectional area of the semiconductor pillar where the drain region and the selective epitaxial layer are formed is wider than a cross-sectional area of the semiconductor body where the gate electrode is formed.
11. The pillar-type field effect transistor of claim 1 , wherein the semiconductor pillar is formed by patterning a bulk semiconductor substrate or an SOI (Silicon on Insulator) substrate.
12. The pillar-type field effect transistor of claim 1 , further comprising an inter-gate insulating layer is formed between the first gate electrode and the second gate electrode.
13. The pillar-type field effect transistor of claim 12 , wherein the first gate electrode and the second gate electrode are electrically connected to each other by a contact or metal interconnection line.
14. The pillar-type field effect transistor of claim 12 , wherein a cross-sectional area of the semiconductor body surrounded by the second gate electrode is smaller than that of the semiconductor body surrounded by the first gate electrode.
15. The pillar-type field effect transistor of claim 12 , wherein a cross-sectional area of the semiconductor pillar is varied with the length of the semiconductor pillar.
16. The pillar-type field effect transistor of claim 12 , wherein a thickness of the gate insulating layer formed under the second gate electrode is larger than that of the gate insulating layer formed under the first gate electrode.
17. The pillar-type field effect transistor of claim 12 , wherein the first gate electrode and the second gate electrode are formed of a same material with different impurity doping types, different materials, or different materials with different impurity doping types.