Transistor and fabriation method

A method for forming a complementary junctionless transistor device comprising:

• providing a semiconductor substrate, wherein the semiconductor substrate includes an NFET (N-field-effect transistor) portion and a PFET portion neighboring with each other;
• forming an isolation layer on the semiconductor substrate and an active layer on the isolation layer;
• forming a P-well in the NFET portion of the semiconductor substrate, and forming an N-well in the PFET portion of the semiconductor substrate;
• forming a P-doped isolation layer by doping a portion of the isolation layer on the NFET portion, and forming an N-doped isolation layer by doping a portion of the isolation layer on the NFET portion;
• forming an N-doped active layer by doping a portion of the active layer on the P-doped isolation layer, and forming a P-doped active layer by doping a portion of the active layer on the N-doped isolation layer;
• etching the active layer and the isolation layer to form an opening to expose a surface of the semiconductor substrate covering an interface portion between the NFET portion and PFET portion;
• removing a portion of the P-doped isolation layer to suspend the N-doped active layer from opposing ends of the N-doped active layer, and removing a portion of the N-doped isolation layer to suspend the P-doped active layer from opposing ends of the P-doped active layer;
• forming a dielectric layer between the N-doped active layer and the semiconductor substrate, between the P-doped active layer and the semiconductor substrate, and in the opening;
• forming a first gate structure on the N-doped active layer disposed on a remaining P-doped isolation layer, forming a second gate structure on the P-doped active layer disposed on a remaining N-doped isolation layer;
• and
• forming an N-doped source and an N-doped drain in the N-doped active layer on both sides of the first gate structure, and forming a P-doped source and a P-doped drain in the P-doped active layer on both sides of the second gate structure.