Nitride disposable spacer to reduce mask count in cmos transistor formation

Abstract

Semiconductor devices of different conductivity types with optimized junction locations are formed on a semiconductor substrate using a minimal number of critical masks. Embodiments include forming conductive gates on the main surface of the semiconductor substrate, sidewall spacers on side surfaces of the gates, and nitride disposable spacers on the sidewall spacers. A photoresist mask is then formed on gates and portions of the main surface intended to be implanted with impurities of a first conductivity type. Moderate or heavy source/drain implants of a second impurity type are then formed in the substrate, the nitride disposable spacers on the sidewall spacers on the unmasked gates removed, and lightly or moderately doped source/drain extension implants of the second impurity type formed in the substrate. The first mask is then removed and a second photoresist mask is formed on the previously uncovered gates and implanted portions of the main surface. Moderate or heavy source/drain implants with impurities of the first conductivity type are then formed, the remaining nitride disposable spacers removed, and lightly or moderately doped source/drain extension implants of the first conductivity type formed. By using nitride disposable spacers, the critical masking steps for source/drain ion implantation are reduced to two, thereby reducing production costs and increasing manufacturing throughput. By employing sidewall spacers, impurities are prevented from being implanted at the edges of the gates. Thus, when source/drain junctions are formed, as by heating and diffusing the implanted impurities, they are advantageously located proximal to the gate edges, and not under the gates, thereby improving device performance.