Suppression of Threshold Voltage Variation by H₂ Plasma Improved KrF Photoresist Profile

The effect of H2 plasma improved KrF photoresist (PR) profile after exposure without bottom anti-reflection coating (BARC) on planar PMOSFET performance in static random access memory (SRAM) is investigated. The proposed H2 plasma treatment is revealed to be able to obtain a well-controlled KrF PR profile with a more PR-safer process. It is demonstrated that such a KrF PR profile can effectively prevent the ions of NMOSFET pocket ion implantation from entering the substrate of PMOSFET. Hence, ~17% reduction of threshold voltage local variation for PMOSFETs in SRAM and ~8 mV improvement of static noise margin (SNM) for SRAM cell can be obtained without performance degradation for both NMOSFETs and PMOSFETs.