| 摘要 |
A method is taught for forming shallow LDD diffusions using polysilicon sidewalls as a diffusion source. The polysilicon sidewalls are formed along side squared-off silicon nitride sidewall spacers which have an essentially rectangular cross section and are in direct contact with the subjacent silicon wherein the shallow LDD elements are formed. The method is applied to the formation of a p-channel MOSFET with salicide contacts wherein the polysilicon sidewalls can be made full size because the essentially flat tops of the nearly rectangular silicon nitride sidewalls provide ample gate-to-source drain spacing to prevent silicide bridging and thereby reduce gate-to-source/drain shorts. In addition, the squared-off silicon nitride sidewalls are formed with parallel vertical sides. This permits improved control of their width, reduced lateral encroachment of boron dopant under the gate, and reduced gate-to-source drain silicide bridging. The reduced boron encroachment results in reduced source/drain series resistance as well as inhibition of short channel effects in the p-channel MOSFET. The full sized polysilicon sidewall also permits greater silicide contact area which fosters results in better contact to the LDD elements and overall lower contact resistance. The source/drain contacts are made not only to the single crystalline silicon of the main source/drain regions, as in conventional contacts, but also directly to the LDD region through the large area silicide region over the polysilicon sidewall. The process is applied to the formation of a CMOS structure having shallow, high concentration, p-type LDD elements on the p-channel device.
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