Transistor, method for fabricating the transistor, and semiconductor device comprising the transistor

A method for fabricating a transistor, comprising:

• providing a substrate and forming a first insulating layer on the substrate;
• defining a first device area on the first insulating layer;
• forming a spacer surrounding the first device area on the first insulating layer;
• defining a second device area on the first insulating layer, wherein the second device area is isolated from the first device area by the spacer;
• and
• forming transistor structures in the first and second device area, respectively;
• wherein the step of defining a first device area on the first insulating layer comprises:
• sequentially depositing a first semiconductor layer and a first mask layer on the first insulating layer;
• patterning the first semiconductor layer and the first mask layer to define the first device area;
• wherein the step of defining a second device area on the first insulating layer comprises:
• depositing a second semiconductor layer to cover the exposed portion of the first insulating layer, the spacer, and the first mask layer;
• depositing a second mask layer to fill in a recess over the second semiconductor layer on the exposed portion of the first insulating layer;
• polishing the second mask layer and the second semiconductor layer to flush with the top of the spacer and the first mask layer;
• removing the second semiconductor layer on side surfaces of the spacer by using the first mask layer and the second mask layer as a mask;
• and
• removing the first mask layer and the second mask layer.