Search

Ferroelectric random access memory (FeRAM) is an attractive candidate technology for embedded nonvolatile memory, especially in applications where low power and high program speed are important. Market introduction of high-density FeRAM is, however, lagging behind standard complementary metal-oxide semiconductor (CMOS) because of the difficult integration technology. This paper discusses the major integration issues for high-density FeRAM, based on SrBi2Ta2O9 (strontium bismuth tantalate or SBT), in relation to the fabrication of our stacked cell structure. We have worked in the previous years on the development of SBT-FeRAM integration technology, based on a so-called pseudo-three-dimensional (3D) cell, with a capacitor that can be scaled from quasi two-dimensional towards a true three-dimensional capacitor where the sidewalls will importantly contribute to the signal. In the first phase of our integration development, we integrated our FeRAM cell in a 0.35 μm CMOS technology. In a second phase, then, possibility of scaling of our cell is demonstrated in 0.18 μm technology. The excellent electrical and reliability properties of the small integrated ferroelectric capacitors prove the feasibility of the technology, while the verification of the potential 3D effect confirms the basic scaling potential of our concept beyond that of the single-mask capacitor. The paper outlines the different material and technological challenges, and working solutions are demonstrated. While some issues are specific to our own cell, many are applicable to different stacked FeRAM cell concepts, or will become more general concerns when more developments are moving into 3D structures. [ABSTRACT FROM AUTHOR]

Different aspects of the integration of strontium bismuth tantalate (SBT)-based high-density ferroelectric random access memory (FeRAM) is discussed in relation to the fabrication of pseudo-three-dimensional (3D) cell structure. The excellent electrical and reliability properties of the small integrated FeCAP prove the feasibility of the technology, while the verification of the potential electrical 3D effect confirms the basic scaling potential of the concept beyond that of the single-mask capacitor.

This paper reports on the integration of MOCVD SBT based stacked ferroelectric capacitors in a 0.35 μm CMOS technology for embedded FeRAM, using a ferroelectric capacitor (FeCap) that is scalable to a 3D configuration. The electrical parameters of the CMOS devices with and without FeCap integration are presented. No significant shifts of the CMOS characteristics are noticed after FeCap integration. Also the effects of the CMOS processing on the FeCaps are discussed. There is no degradation of the hysteresis loops of the FeCaps throughout the CMOS back-end-of-line processing, which proves that the integrated encapsulation layer effectively prevents any hydrogen induced damage. Another key element in the successful integration of stacked ferroelectric devices is the conductive oxygen barrier, which protects the plugs from oxidation. A low contact resistance and a high yield are obtained on plug contacts covered by the oxygen barrier. Also damage free etching is a critical issue in FeRAM integration. Excellent results are presented for the etch process to form the contacts to the electrodes. [ABSTRACT FROM AUTHOR]

As the sharpness of the metal–oxide interface is of major importance to develop efficient structures, we have studied the thermal stability of interfaces in a series of thin film samples where the metallic component was either Pt, Al, Pd, Ni, Nb or Ti deposited on a thin HfO2 film. Thermodynamic considerations have been carried out to determine the possible products of metal–oxide reaction at a temperature of 500 °C. The evolution of the as-deposited thin film structures as a function of annealing temperature has been analysed by combining various techniques and specifically using X-ray reflectometry. This particular technique allows one to detect very thin embedded interfaces, distinguish small density variations and determine accurately the thickness, the normal roughness and the density of each layer. In addition, reflectometry results have been correlated with atomic force microscopy and transmission electron microscopy observations of selected samples. Our results indicate that platinum, palladium and nickel are stable up to 500 °C on hafnium oxide. Annealed aluminium, an interfacial layer forms, whereas niobium and titanium present a diffuse interface. [Copyright &y& Elsevier]