Ferroelectric memory device and method of manufacturing the same

Abstract

A ferroelectric memory device includes: a substrate; a ferroelectric capacitor which is formed on the substrate and includes a lower electrode, a ferroelectric film, and an upper electrode; a hydrogen barrier film provided to cover the ferroelectric capacitor; and an interlayer dielectric provided on the hydrogen barrier film. A thickness of an area of the hydrogen barrier film provided on the upper electrode is greater than a thickness of an area of the hydrogen barrier film provided on a sidewall of the ferroelectric capacitor.

Description

[0001] Japanese Patent Application No. 2004-087622, filed on Mar. 24, 2004, and Japanese Patent Application No. 2005-005341, filed on Jan. 12, 2005 are hereby incorporated by reference in their entireties. BACKGROUND OF THE INVENTION [0002] The present invention relates to a ferroelectric memory device and a method of manufacturing the same. [0003] A nonvolatile memory device using spontaneous polarization specific to a ferroelectric (ferroelectric memory device) has attracted attention as an ultimate memory having the possibility of replacing not only a conventional nonvolatile memory but also most memories such as a static RAM (SRAM) and a DRAM due to its characteristics such as a high-speed write / read and low-voltage operation. As the ferroelectric material, a number of candidate materials have been proposed. In particular, a perovskite-type oxide such as lead zirconate titanate (Pb(Zr,Ti)O3 hereinafter abbreviated as “PZT”) and a bismuth-layered compound such as SrBi2Ta2O9 are c...

AI Technical Summary

Benefits of technology

[0004] In general, when using the above-mentioned oxide material as a capacitor insulating layer, an interlayer dielectric such as SiO2 is deposited after forming an upper electrode in order to provide electrical insulation between each memory element as the major objective. As the deposition method, a chemical vapor deposition (CVD) method excelling in step coverage is generally used. However, use of such a deposition method causes hydrogen to be generated as a reaction by-product. In particular, if activated hydrogen passes through SiO2 and the upper electrode and reaches the ferroelectric thin film, the crystallinity of the ferroelectric is impaired due to the reducing effect of hydrogen, whereby the electrical characteristics deteriorate to a considerable extent. The characteristics of a MOS transistor as a switching element deteriorate due to lattice defects occurring in the silicon single crystal during the device manufacturing step. Therefore, it is necessary to subject the MOS transistor to a heat treatment in a hydrogen-containing nitrogen gas in the final stage. However, since the hydrogen concentration in this step is higher than that during formation of the interlayer dielectric, damage occurring to the ferroelectric thin film is more acute.

Problems solved by technology

However, use of such a deposition method causes hydrogen to be generated as a reaction by-product.

In particular, if activated hydrogen passes through SiO2 and the upper electrode and reaches the ferroelectric thin film, the crystallinity of the ferroelectric is impaired due to the reducing effect of hydrogen, whereby the electrical characteristics deteriorate to a considerable extent.

The characteristics of a MOS transistor as a switching element deteriorate due to lattice defects occurring in the silicon single crystal during the device manufacturing step.

However, since the hydrogen concentration in this step is higher than that during formation of the interlayer dielectric, damage occurring to the ferroelectric thin film is more acute.

Specifically, once the ferroelectric capacitor is covered with the hydrogen barrier film, it is extremely difficult to recover the crystallinity of the ferroelectric to secure the electrical characteristics of the capacitor.

However, damage to the ferroelectric often occurs during formation of the ferroelectric capacitor.

However, if hydrogen generated during the resist combustion process, a water molecule, or a reducing etching gas passes through the upper electrode and reaches the interface between the upper electrode and the ferroelectric, the ferroelectric is reduced in this region, whereby the crystallinity is impaired to a considerable extent.

Since such damage cannot be sufficiently corrected by subsequent heating and is more sensitive to the reducing atmosphere in the subsequent step, the crystallinity is easily disordered.

Therefore, a damaged region which cannot contribute to polarization switching occurs.

In particular, a minute capacitor cannot exhibit sufficient characteristics.

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