Electrical Properties of Integrated Ta 2 O 5 Metal-Insulator-Metal Capacitors
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METAL CAPACITORS B. C. MARTIN*, C. BASCERIt, S. K. STREIFFER', and A. I. KINGONI Materials Research and Strategic Technologies, Semiconductor Products Sector, Motorola, Mesa, Arizona 85202. Science and Engineering, tDepartment of Materials North Carolina State University, Raleigh NC 27695-7907. *
ABSTRACT We demonstrate the feasibility of a Ta2O5-based metal-insulator-metal (MIM) capacitor module which is integrated into the backend-of-the-line of a 0.5 gim CMOS process flow. The demonstration utilizes 6-inch wafers, sputtered Ta20 5 films with TaN and TiN electrodes, reactive ion etch (RIE) processes for defining the capacitor stack, and a metallization scheme which uses hot A1(Cu) and W plugs and a standard forming gas anneal (N2-5% H2). Acceptable electrical properties have been achieved within these processing constraints for the integrated MINM capacitor module, including specific capacitance (C/A) and leakage current density (J) of> 5 fF/jim 2 and < 1 pA/pF-V, respectively. In addition, we compare the fundamental properties of the Ta20 5 dielectric with literature reports and point out that leakage mechanisms must be analyzed with care due to significant dielectric relaxation in the films under certain processing/measurement conditions. For the baseline integrated films, we confirm that leakage is most consistent with a Poole-Frenkel mechanism. INTRODUCTION Increasing semiconductor device performance requirements make it desirable to integrate capacitors, such as bypass capacitors, directly on-chip. The value of the on-chip silicon real estate makes it important to minimize the capacitor area. As the thickness of Si0 2 or oxide-nitride-oxide (ONO) reaches an effective minimum imposed by charge tunneling and reliability constraints, it becomes necessary to consider a dielectric with a larger permittivity. Ta20 5 is being considered for these on-chip applications, as well as for DRAMs. While Ta2O5 displays a lower permittivity than alternatives such as (Ba,Sr)TiO3 (BST), it has the advantage of having only two components, and therefore being significantly simpler to deposit. A development program was undertaken to demonstrate the feasibility of the integration of a Ta20 5 MIM capacitor module in the backend of an existing 0.5 jtm CMOS process flow. The final process is described below, and it is the first such description to our knowledge. We then compare the properties obtained from the capacitors to the literature. In doing so we have emphasized the issues of leakage currents and time dependent polarization. We have shown previously for the BST system that it is necessary to take into account the dielectric relaxation, which corresponds to a time dependent polarization over a large time domain, when one considers the capacitor performance. In particular, the time dependent polarization can result ina voltage drop under open circuit conditions after pulse charging [1,2]. Similarly, we have shown that these polarization currents can be mistaken for leakage currents when undertaking an analysis of leakage mecha
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