Capacitors include an integrated circuit (semiconductor) substrate and an interlayer dielectric disposed on the integrated circuit substrate and including a metal plug therein. A lower electrode is disposed on the interlayer dielectric and contacting the metal plug. The lower electrode includes a cavity therein and a buried layer in the cavity. The buried layer is an oxygen absorbing material. A dielectric layer disposed on the lower electrode and an upper electrode is disposed on the dielectric layer. The lower electrode may be a noble metal layer. The buried layer may fill in the cavity and may not contain oxygen (O₂) when initially formed.