Characteristics of photosensitive low-k methylsilsesquioxane (MSQ) were investigated by the use of electron-beam lithography. Photosensitive low-k MSQ makes it possible to realize via and trench structures for Cu damascene technology without dry etching processes in the multilevel interconnect integration of ultralarge scale-integrated circuits. In this paper the dependences of critical dimensions of developed patterns on exposure dose and hold time after exposure were investigated. Consequently the aspect ratio of the developed trench structure of 3.9 and the minimal feature size of 90 nm were achieved. (c) 2005 The Electrochemical Society. All rights reserved.