A study of trenched capacitor structures

Trenched structures have been fabricated using a highly anisotropic low ion energy bombardment etching technique and evaluated using their CV characteristics. It is shown that the structure can be modeled by two capacitors in parallel, one for the bottom and the other for the sidewall. Obtained results indicate that the crystal orientation of the side and bottom surfaces of the trench determine the value of Nf, fixed charge, and oxide thickness, especially in the thin range. Orientation-dependent oxidation rates account for the different oxide thicknesses on the sides and bottoms of the trenches. Both the value of Nfand the oxide thickness on each wall determine the flat-band voltage Vfbof the corresponding capacitors so that the overall capacitance behavior is given by the relative importance of the side and bottom components. A lower value of Nfthan previously reported is found with the etching technique used. It is also shown that an improvement of Nfcan be obtained by aligning the trench sidewall along 〈100〉 plane.