Patent ID: 6917064

Claim:
A trench capacitor comprising: a semiconductor substrate; a trench formed in the semiconductor substrate; a first doped polysilicon layer filled in the trench through a first dielectric film and doped with a first impurity having a first conductivity type; a second doped polysilicon layer filled in the trench through a second dielectric film, formed on the first doped polysilicon layer and doped with the first impurity having the first conductivity type; a third doped polysilicon layer formed on the second doped polysilicon layer through the second dielectric film and doped with a second impurity having the first conductivity type, the second impurity being different from the first impurity and having a greater diffusion coefficient than that of the first impurity; and a fourth doped polysilicon layer provided in the trench, formed on the third doped polysilicon layer and doped with the first impurity having the first conductivity type.