Mask pattern for semiconductor device fabrication, method of forming the same, and method of fabricating finely patterned semiconductor device

Provided are a mask pattern including a self-assembled molecular layer, a method of forming the same, and a method of fabricating a semiconductor device. The mask pattern includes a resist pattern formed on a semiconductor substrate and the self-assembled molecular layer formed on at least a sidewall of the resist pattern. To form the mask pattern, first, the resist pattern is formed with openings on an underlayer covering the substrate to expose the underlayer to a first width. Then, the self-assembled molecular layer is selectively formed on a surface of the resist pattern to expose the underlayer to a second width smaller than the first width. The underlayer is etched using the resist pattern and the self-assembled molecular layer as an etching mask to obtain a fine pattern.