A capacitor having high capacitance using a silicon-containing conductive layer as a storage node, and a method for forming the same, are provided. The capacitor includes a storage node, an amorphous Al.sub.2 O.sub.3 dielectric layer, and a plate node. The amorphous Al.sub.2 O.sub.3 layer is formed by a method in which reactive vapor phase materials are supplied on the storage node, for example, an atomic layered deposition method. Also, the storage node is processed by rapid thermal nitridation before forming the amorphous Al.sub.2 O.sub.3 layer. The amorphous Al.sub.2 O.sub.3 layer is densified by annealing at approximately 850.degree. C. after forming a plate node, to thereby realize the equivalent thickness of an oxide layer which approximates a theoretical value of 30 .ANG..