A study of trenched capacitor structures

Abstract

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 N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> , 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 N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> and the oxide thickness on each wall determine the flat-band voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fb</inf> of 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 N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> than previously reported is found with the etching technique used. It is also shown that an improvement of N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> can be obtained by aligning the trench sidewall along 〈100〉 plane.