A method for forming a capacitor comprises providing a substrate. A bottom
electrode material layer is formed on the substrate. A first mask layer
is formed on the bottom electrode material layer. A second mask layer is
formed on the first mask layer. The second mask layer is patterned to
form a patterned second mask layer in a predetermined region for
formation of a capacitor. A plurality of hemispherical grain structures
are formed on a sidewall of the patterned second mask layer. The first
mask layer is etched by using the hemispherical grain structures and the
patterned second mask layer as a mask, thereby forming a patterned first
mask layer having a pattern. The pattern of the first mask layer is
transferred to the bottom electrode material layer. And, a capacitor
dielectric layer and a top electrode layer are formed on the bottom
electrode material layer to form the capacitor.