The Effects of Lead-Compensation and Thermal Processing on the Characteristics of DC-Magnetron Sputtered Lead Zirconate
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THE EFFECTS OF LEAD-COMPENSATION AND THERMAL PROCESSING ON THE CHARACTERISTICS OF DC-MAGNETRON SPUTTERED LEAD ZIRCONATE TITANATE THIN FILMS Vinay Chikarmane, Chandra Sudhama, Jiyoung Kim, Jack Lee and Al Tasch Microelectronics Research Center, Electrical & Computer Engineering Department, The University of Texas at Austin, Austin, TX 78712 ABSTRACT The feasibility of the fabrication of thin film capacitors of Lead Zirconate Titanate (PZT) by reactive DC-Magnetron sputtering, with large switched charge and low leakage current densities for ultra-large scale integration Dynamic Random Access Memory (ULSI DRAM) applications has been demonstrated. As-deposited films were found to be predominantly pyrochlore; therefore, a subsequent phase transformation-inducing thermal processing step was key to obtaining device quality films. The importance of the thermal budget in optimizing the device characteristics of PZT films is discussed. The importance of the role of Pb compensation in lowering the required thermal budget and significantly enhancing device characteristics is shown. INTRODUCTION Limitations on dielectric thickness reduction due to tunneling, pinholes and reliability, and on cell structure complexity posed by processing technology, have recently led to considerable research activity in very high dielectric constant materials such as ferroelectrics for ULSI DRAM applications [1]. DRAM operation involves unipolar switching of the dielectric. Thus, it is necessary to maximize the switched charge density Qc' (defined as the difference between the maximum and the remnant polarization) for this application. The large switched charge density in capacitors fabricated from ferroelectrics such as PZT permits a reduction in device area, and is an important measure of film quality. These dielectrics must also have low leakage current in order to be candidates for use in semiconductor memories. EXPERIMENTAL PZT thin films of thickness 400nm were deposited at temperatures ranging from 32500 0 C on Pt/TiO2/SiO2/Si multi-layered substrates by reactive DC-Magnetron sputtering from a multi-component Pb/Zr/Ti metal target in a pure oxygen ambient. The design of the target was similar to the one previously used by Croteau and Sayer [2]. The Pb content in the film was adjusted (compensated) by co-sputtering from a separate pure Pb metal target (r-f magnetron sputtering). Variations in the r-f power input to the pure Pb target were applied. The asdeposited films were annealed at different temperatures (300-9000 C) in a tube furnace in a 100% nitrogen ambient. The top electrodes (also of Pt) were fabricated by a lift-off process and were 87ptnx87j.tm square. Compositional analysis was performed using a Physical Electronics Scanning Auger Microscope with a single pass cylindrical mirror analyzer. X-Ray Diffraction (XRD) was performed on a Philips Diffractometer and Nomarski Microscopy on an Olympus BH-2 microscope. The Quasi-static capacitance-voltage (QSCV, sweep range +/-3V, ramp rate 0.3V/s), and leakage current density measurements
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