The integration of high value capacitors in integrated circuits (ICs) is limited by the fact that conventional high value capacitors take up large areas of the IC chip, thus reducing device packing density and layout efficiency. Many applications require a large number of capacitors. Often the capacitors must be incorporated as discrete off-chip components, substantially increasing the bulk of the peripheral circuitry. In view of the increasing demand for compact lightweight electronic equipment, it is desirable that the number of discrete components be reduced.
The minimum dimensions of IC capacitors are determined primarily by the relatively low dielectric constant (.di-elect cons.&lt;10) of conventional capacitor dielectrics, e.g. SiO.sub.2 and Si.sub.3 N.sub.4. Thus, as device dimensions decrease, there is increasing interest in other dielectrics having higher dielectric constants than conventional dielectric materials.
Ferroelectric (FE) and high-epsilon (HE) dielectrics (.di-elect cons.=20 or greater) have found application in random access memory (RAM) cells since they provide for the formation of NVRAMs and DRAMs. Moreover, when used as NVRAM, ferroelectric dielectrics advantageously provide low voltage programmability, fast access times and low power consumption.
FE materials pose several integration problems. In particular, most ferroelectric materials require high temperature post-deposition oxygen anneals (600.degree. C. or above) to achieve properties desirable for storage media. However, such high anneal temperatures can be incompatible with the CMOS devices already fabricated on the wafer. Furthermore, any subsequent forming gas or hydrogen anneals (highly desirable for CMOS devices) degrade the ferroelectric material, thus requiring additional high temperature oxygen anneals late in the processing sequence which in turn are detrimental to the CMOS circuitry.
In view of the above drawbacks with prior art methods of integrating ferroelectric capacitors with CMOS structures, there is a continued need for developing a new and improved method which is capable of providing an integrated FE capacitor/CMOS structure without subjecting the CMOS structure to high temperature steps that are typically required in the prior art for ferroelectric processing.