1. Technical Field
The present invention relates to semiconductor memory devices, and is particularly suitable when applied in controlling the crystal orientation in ferroelectric capacitors.
2. Related Art
In order to improve characteristics of ferroelectric capacitors in ferroelectric memories, a reset film may be provided to control the crystal orientation of a lower electrode. Also, in order to planarize a surface of a contact plug on which the lower electrode is formed, the surface of the contact plug is polished by a CMP method. Furthermore, for example, Japanese laid-open patent application JP-A-2001-345432 describes a method for improving oxidation resistance of capacitor electrodes without inhibiting an improvement in the degree of integration, in which a metal nitride layer is provided on a surface of an embedded conductive body embedded in an insulation layer, and a ferroelectric capacitor is provided on the metal nitride layer through an intermediate layer composed of a conductive oxide and having an oxygen barrier property.
However, in the ferroelectric memories described above, erosion, dishing and recess may be generated, when the surface of the contact plug is planarized by CMP, due to the difference in polishing rate between the contact plug and the insulation film in which the contact plug is embedded. For this reason, it is difficult to finish smoothly the surface of the contact plug on which the lower electrode is formed, and it is difficult to maintain well the surface condition and crystal structure of the base layer where the lower electrode is formed, such that ferroelectric capacitors with good characteristics cannot be formed. Furthermore, even when a reset film is provided according to the aforementioned reset film forming method, is it difficult to control accurately the crystal orientation of the lower electrode due to the difference in material (orientation property) between the plug and the insulation film in which the plug is embedded, such that ferroelectric capacitors with good characteristics cannot be stably formed.