Method to fabricate optimal HDD with dual diffusion process to optimize transistor drive current junction capacitance, tunneling current and channel dopant loss

摘要

Methods are discussed for forming a transistor comprising a source/drain region having both a graded HDD portion and a sharp HDD portion in a semiconductor substrate. The method comprises a dual diffusion process, wherein a gate structure is provided over the semiconductor substrate having an offset spacer associated therewith. A first dopant material is implanted around the gate structure in the source/drain area to form a grade-HDD region in the substrate that is aligned to the offset spacer. A sidewall spacer is formed around the gate structure and covers the offset spacer. A second dopant material is then implanted in the source/drain area to form a source/drain region in the substrate aligned to the sidewall spacer, and the device is thermally processed in a first anneal. The sidewall spacer and the offset spacer are removed from the gate structure. A third dopant material is implanted in the source/drain area to form a sharp HDD region aligned to the gate structure, and the device is flash annealed in a second anneal.