Stepped Polysilicon Contact Structure to Reduce Voids

The fabrication process is divided into multiple stages: forming a first polysilicon layer with a first mask layer, performing a first etching process to create a stepped structure, then performing a second etching process to form a trench, and finally depositing a second polysilicon layer. This segmentation allows each stage to be optimized independently to prevent void and hole formation.

The first etching process is performed in advance to create a stepped structure before the second etching process. This preliminary action prepares the surface geometry that prevents void formation during subsequent polysilicon deposition, addressing the quality issue before the main polysilicon layer is formed.

The first mask layer is selectively removed in specific regions to create the stepped structure, where the width of the first mask layer is smaller than the width of the first polysilicon layer. This local modification creates geometric features that guide polysilicon deposition and prevent void formation in critical areas.

The fabrication process transitions from a planar structure to a three-dimensional stepped structure through the first etching process. This dimensional change creates depth variation that controls polysilicon layer formation and eliminates voids and holes during subsequent deposition.

The etching process is segmented into two distinct stages: a first etching process that creates the stepped structure by selectively removing the first mask layer, and a second etching process that forms the trench. This segmentation enables precise geometric control while maintaining overall process efficiency.

The first etching process is performed as a preliminary step before the second etching process to establish the stepped structure. This preliminary action creates the necessary geometric foundation that prevents void formation, allowing the main trench formation to proceed efficiently.