Nanosheet Gate Structure With Disposable Oxide for Germanium Removal

The patent applies preliminary action by performing source/drain formation and germanium removal before gate patterning. This sequence allows germanium to be removed from the channel region before subsequent processing steps, preventing germanium residue from degrading device performance at scaled dimensions. The early removal of sacrificial oxide layers and germanium-containing materials eliminates impurities that would otherwise contaminate the channel in advanced node devices.

The patent extracts germanium from the channel region by removing sacrificial oxide layers that contain germanium. The process involves etching away oxide layers formed during source/drain recess formation, which traps germanium. By removing these oxide layers before gate formation, germanium is extracted from the channel region, preventing it from degrading carrier mobility and device performance in scaled transistors.

The patent uses an intermediary approach by introducing disposable oxide layers as sacrificial materials that can be selectively removed. These oxide layers are formed in source/drain recesses and serve as intermediaries to hold and subsequently release germanium. The oxide layers can be cleanly removed via wet etching or vapor HF processes, acting as a mediator that enables germanium extraction without requiring complex additional processing steps.

The patent changes the material parameter from conventional sacrificial layers to oxide-based sacrificial layers. This parameter change enables selective removal through wet chemical etching or vapor HF processes, which can cleanly extract germanium from the channel region. The oxide material provides different etch selectivity and removal characteristics compared to traditional sacrificial layers, allowing for more effective germanium elimination while maintaining process integration.

The patent merges multiple functions into the oxide layer formation and removal steps. The same oxide layers that define source/drain recess boundaries also serve as sacrificial materials for germanium extraction. By combining the recess definition and germanium trapping functions into a single oxide layer structure, the process achieves germanium removal without requiring separate dedicated steps, thereby limiting the increase in process complexity.

The oxide layers perform self-service by simultaneously serving as recess boundaries, germanium traps, and sacrificial materials for extraction. The oxide formation process automatically creates structures that will later release germanium when removed, eliminating the need for separate germanium management steps. This self-service approach allows early germanium removal while minimizing additional process complexity.