Reduction of Polysilicon Gate Depletion Effect in NMOS Devices Using Laser Thermal Processing

One critical issue in advanced semiconductor processing is to have adequate dopant activation in the polycrystalline silicon (poly-Si) gate to minimize carrier depletion at the gate/gate oxide interface (poly-depletion). We demonstrate a novel technique, using laser thermal processing, to form super-doped n⁺-poly-Si gates on ultrathin gate oxides. The results indicate that the poly-depletion effect in n-channel metal-oxide-semiconductor (NMOS) devices can be significantly reduced if the entire as-deposited amorphous silicon gate melts upon laser irradiation. Time-dependent dielectric breakdown studies show that the gate oxide reliability is not degraded even after laser processing at a high fluence.