The PMOS Silicon Recess Process Control With Evolution of Trench Morphology

With the miniaturization of device structures, the implementation of source/drain germanium-silicon embedding technology in the PMOS region is commonly employed to enhance MOSFET performance by improving carrier mobility. The PMOS silicon recess process is used for dry etching to form silicon trenches. The initial morphology of the silicon trench is a trench with a sidewall angle (SWA) of approximately 80° along the Gate spacer. To reduce the etching time required for subsequent wet etching to form a sigma shaped recess, the dry etching trench morphology is modified to a bowl shape. Subsequently, to increase channel stress, the bowl-shaped trench evolved into a U-shaped trench. Theses transformations present significant challenges for dry etching process control: as the trench becomes bowl-shaped, relying solely on Halogen gas etching fails to satisfy lateral etching requirements. This study introduces a pullback step utilizing Fluorinated gas as the primary etching gas to achieve isotropic trench etching. Additionally, when etching U-shaped trenches, the removal of sharp corners proves challenging. This study addresses this issue through a high-temperature process to effectively eliminate byproducts and form the U-shaped morphology.