A. C. Campbell

Effects of anneal ambients and Pt thickness on Pt/Ti and Pt/Ti/TiN interfacial reactions

Using x‐ray diffraction, Rutherford backscattering spectrometry, Auger electron spectroscopy, and scanning electron microscopy, effects of ambient anneal and Pt thickness on the interdiffusion of Pt/Ti bilayers deposited on SiO2/Si and on reactively sputtered TiN/Ti/Si substrates have been investigated. The Pt layer was 2000 or 930 A thick while the Ti thickness was fixed at 1000 A. The wafers were annealed in either O2 or N2 ambients or in N2 followed by O2, with temperatures ranging from 600 to 800 °C for 30 min. The anneal ambients and the thickness of Pt relative to the Ti layer had tremendous effects on the interdiffusion processes, the reaction products, and the surface morphology of the multilayer structures. Samples annealed in O2 were generally rough, with bumps of the order of 1000 A, while those annealed in N2 were relatively smooth. With lead zirconium titanate on top, the surface of Pt/Ti electrode annealed in O2 at 650 °C was relatively smooth.

A model for electrical conduction in metal‐ferroelectric‐metal thin‐film capacitors

Time‐zero current‐voltage characteristics and time‐dependent current behavior of metal‐ferroelectric‐metal (Pt‐PZT‐Pt) capacitor structures have been studied. Under constant‐voltage stressing, the current density through the 1500‐A‐thick lead‐zirconate‐titanate (PZT) film exhibits a power‐law dependence on time, with the exponent (∼0.33) independent of temperature and voltage. Electrode material dependence of current density indicates that the conventional model of trap‐limited single‐carrier injection over nonblocking contacts is inadequate to explain the time‐zero current. A change in top electrode material from Pt to In leads to the observation of work‐function‐driven Schottky contacts between the metal and ferroelectric. The current‐voltage characteristics fit a two‐carrier injection metal‐semiconductor‐metal model incorporating blocking contacts, with distinct low‐ and high‐current regimes (PZT is assumed to be p‐type and trap‐free in this model). Temperature‐dependent I‐V measurements indicate a Pt‐...

Electrical characteristics of paraelectric lead lanthanum zirconium titanate thin films for dynamic random access memory applications

Paraelectric lead lanthanum zirconium titanate (PLZT) films, 150 nm thick, were deposited using a spin‐coat, sol‐gel process followed by a 650 °C oxygen anneal. X‐ray diffraction indicated complete conversion to the perovskite phase. Sputter‐deposited platinum electrodes were employed with the PLZT films to form thin‐film capacitors with the best combination of high charge storage density (26.1 μC/cm2 at 3 V and 36.4 μC/cm2 at 5 V) and leakage current density (0.2 μA/cm2 at 3 V and 0.5 μA/cm2 at 5 V ) reported to date. The electrical characteristics of these thin‐film capacitors meet the requirements for a planar bit cell capacitor for 64‐Mbit dynamic random access memories.

Materials interactions in the integration of PZT ferroelectric capacitors

Abstract Investigations of materials interactions that complicate the integration of PZT ferroelectric capacitors into CMOS technologies are discussed. These include interactions within the Pt/Ti electrodes structure, the reactions of sol-gel deposited PZT during crystallization with various underlying dielectrics (SiO2, Si3N4, Al2O3, and TiO2), and the impact of other integrated circuit processes on fabricated capacitors.

Impact of Backend Processing on Integrated Ferroelectric Capacitor Characteristics

Integration of a ferroelectric capacitor module in a standard CMOS process subjects the ferroelectric to various ambients during backend processing, some of which can render the ferroelectric essentially non-operational for NVRAM applications. Post-crystallization processing of sol-gel deposited integrated ferroelectric PZT capacitors in the presence of hydrogen-containing, reducing ambients is observed to degrade the nonvolatile polarization. Low-pressure hydrogen anneals at temperatures as low as 200°C substantially degrade the nonvolatile polarization while the DRAM polarization remains roughly constant. Leakage current drops by one order of magnitude and fatigue is accelerated. A ferroelectric capacitor module can be integrated with minimal degradation with careful modifications in the backend processing.

High-permittivity lead-based perovskite dielectrics for DRAM applications

Abstract Suppression of the nonvolatile polarization in lead zirconate titanate films by La doping or by use of films 100 nm or less in thickness provides the highest charge storage densities yet observed. These films also satisfy leakage current density and TDDB requirements for very high density DRAMs, and show good resistance to fatigue.

Analyses of Pt/Ti Electrodes for Plzt Capacitors

A suitable choice of an electrode material is important for an acceptable electrical contact to a high-permittivity dielectric, such as PLZT. A material which does not form a low-permittivity oxide is necessary, since these dielectrics generally require high temperature deposition or annealing in an oxidizing environment. Platinum, which is one of the few metals that satisfy this requirement, has been widely employed for contacting PLZT. However, for integrated circuit applications, an adhesion layer must be superposed between Pt and the substrate, and Ti is used frequently. Therefore, we have investigated the Pt/Ti combination to determine its suitability as an electrode for contacting PLZT. Using x-ray diffraction, Rutherford backscattering spectrometry, Auger electron microscopy, and scanning electron microscope techniques, interdiffusion of Pt/Ti bilayers has been investigated. Pt/Ti films with or without PLZT overlay were annealed in either O 2 or N 2 ambients or in N 2 followed by O 2 . Annealing temperatures varied from 500 to 800 °C. It was observed that the anneal ambient has a marked effect on the interdiffusion processes, the reaction products, the morphology of the structures, and the crystallization of PLZT.