Lecture
This lecture covers etch stop techniques in micro and nanofabrication, including the use of B implantation to reduce etch rate in KOH-based solutions, electrochemical etch stops, and examples of bulk micromachining. The B implantation in Si leads to a drop in the Si Fermi level, causing the etching to stop. Different anisotropic etching baths exhibit similar effects upon B implantation. Electrochemical etch stops involve applying a bias voltage to selectively etch p-doped Si. Bulk micromachining techniques are demonstrated through KOH etching of silicon wafers with various mask configurations, resulting in the formation of inverted pyramids or 'roofs'.