Flash Memory Isolation Structure for Controlled Gate Recess

The patent divides the single etching process into multiple sequential etching steps with different depths. First, a shallow opening is etched to a first depth, then a second opening is etched to a greater second depth. This segmentation allows precise control over the depth of each opening independently, solving the problem of depth control in small-dimensional devices.

The patent performs preliminary actions by forming masks on sidewalls before etching, and by creating the first opening to a controlled depth before proceeding to the second opening. These preliminary steps establish precise depth references and protective structures that enable accurate subsequent etching operations.

The patent applies preliminary anti-action by forming protective masks on the sidewalls of the opening before performing the etching process. These masks prevent the etching chemistry from attacking and removing the floating gate material, thereby protecting the floating gate integrity while still allowing the opening to be formed.

The patent introduces masks as intermediary structures between the etching process and the floating gate. These masks serve as a mediator that allows the etching process to proceed while blocking the harmful effect on the floating gate, enabling opening formation without floating gate loss.

The patent segments the recess formation into multiple controlled steps with distinct depth targets. By creating openings at different depths sequentially rather than as a single deep etch, the process maintains precision control over the recess geometry even as overall device dimensions are scaled down.

The patent uses partial action by creating openings to specific depths that are shallower than a single continuous etch would produce. This partial etching approach, combined with mask protection, prevents over-etching and maintains precise recess control in scaled-down devices.