Semiconductor Recess Etching with Spacer-Based Shape Correction

The etching process is divided into multiple sequential steps: first etching to form an initial recessed portion, then forming a spacer film, followed by isotropic etching, and finally anisotropic etching. This segmentation allows each step to address specific shape control requirements, enabling precise circular cross-section formation that cannot be achieved through a single etching step.

A spacer film is formed on the side surface of the recessed portion before the final etching step. This preliminary action creates a template that guides the subsequent isotropic and anisotropic etching processes, ensuring the recessed portion achieves the desired circular cross-section shape with high precision.

Different etching methods are applied at different stages: isotropic etching is used first to correct shape deviations and achieve circular cross-section, then anisotropic etching is applied to define the final vertical walls. This localized application of different etching qualities ensures both circular accuracy and vertical precision without requiring excessive process steps.

The patent changes etching parameters by switching between isotropic and anisotropic etching modes. Isotropic etching with appropriate selectivity corrects the shape to achieve circular cross-section, while subsequent anisotropic etching maintains productivity by efficiently defining the final structure with vertical walls.