A method includes: forming a gate over a semiconductor substrate; forming doped regions in the semiconductor substrate; depositing a dielectric layer on sidewalls of the gate, the dielectric layer including vertical portions laterally surrounding a sidewall of the gate; depositing a spacer laterally surrounding the dielectric layer, the spacer including a carbon-free portion laterally surrounding the vertical portions of the dielectric layer and a carbon-containing portion laterally surrounding the carbon-free portion; forming source/drain regions in the semiconductor substrate; performing an etching operation to remove the gate and vertical portions of the dielectric layer using the carbon-free portion as an etching stop layer to thereby expose the carbon-free portion and form a recess; and forming a gate dielectric layer and a conductive layer in the recess, wherein the gate dielectric layer extends in at least a portion of an area where the vertical portions of the dielectric layer are etched.