1. Field of the Invention
The present invention relates to a method for forming a capacitor of a nonvolatile semiconductor memory device that includes a ferroelectric film and the capacitor.
2. Description of the Background Art
A ferroelectric memory device is generally nonvolatile. Accordingly, even when no power is supplied, previously stored data is maintained. In the case that the ferroelectric memory device is sufficiently thin, spontaneous polarization is rapidly inverted, and thus read and write operations can be performed at a high speed such as in a DRAM.
In addition, one transistor and one ferroelectric capacitor can form a one-bit memory cell, thereby obtaining large capacity. SrxBi2+yTa2O9 (SBT) film and SrxBi2+y(TaiNb1xe2x88x92i)2O9 (SBTN) film are examples of ferroelectric films used to form the ferroelectric capacitor.
FIG. 1 illustrates a conventional method for forming a capacitor using the SBT or SBTN film as a dielectric film. As shown in FIG. 1, a first interlayer insulation film 12 is deposited on a semiconductor substrate 11 where a node (not shown) has been formed. Thereafter, a glue layer 13 and a conductive layer 14, or a storage electrode, are sequentially formed on the interlayer insulation film 12. Preferably, the glue layer 13 consists of a Ti, TiN or TiOx layer, and the conductive layer 14 for the storage electrode consists of a Pt layer.
An SBT film 15 is deposited on the conductive layer 14. A conductive layer 16 for a plate electrode is deposited on the SBT film 15. Although not illustrated, additional processes are consecutively performed, thereby finishing formation of the capacitor.
This conventional method suffers from several drawbacks. For instance, the Ti of the glue layer 13 is rapidly diffused into the SBT or SBTN film 15 on the lower electrode 14 during a crystallization annealing process carried out in forming the capacitor, thereby deteriorating an electrical property of the capacitor.
In addition, the glue layer 13 is oxidized by oxygen flowing through the lower electrode 14 during the crystallization annealing process, and thus gaps are generated due to an increased volume. Moreover, voids and interface lifting are generated at the lower electrode 14 interface due to the re-crystallization of the lower electrode 14 and the fluidity caused during annealing. As a result, it is more difficult to form the capacitor.
Accordingly, at least two objects of the present invention are to provide a method for forming a capacitor of a nonvolatile semiconductor memory device which can prevent deterioration of the capacitor and to provide the capacitor.
In order to achieve the above-described object of the present invention, there is provided a method for forming a capacitor of a nonvolatile semiconductor memory device including the steps of: forming a first interlayer insulation film on a semiconductor substrate; forming a TaON film for a glue layer on the first interlayer insulation film; forming a lower electrode on the TaON film; forming an SBT or SBTN film for a ferroelectric film on the lower electrode; and forming an upper electrode on the ferroelectric film. In subsequent processing a second interlayer insulation film having a contact hole for contacting the upper electrode is formed and a metal film to fill up the contact hole is formed.
These and other objects are also achieved by providing a semiconductor device, comprising: a semiconductor substrate; a TaON glue layer formed over the semiconductor substrate; a lower electrode formed on the TaON glue layer; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film.