Tantalum oxide as an alternative dielectric material for polyimide integrated passive devices and dynamic random access memory applications

Currently, there is a need for the deposition of amorphous tantalum oxide (TaOx) films (100-300 nm) on polyimides for embedded capacitor applications such as microwave down-converter modules. The requirements of high capacitance density (100 nanofarad per square centimeter), high breakdown voltage (greater than 30 Volts), and low leakage current density (0.1 microampere per square centimeter at 10 Volts), coupled with the need for low-temperature deposition (ambient to 200 degrees Celsius) necessitated the use of plasma-enhanced chemical vapor deposition (CVD). Specifically, due to the high plasma density at low pressures and temperatures, Electron Cyclotron Resonance (ECR) CVD was used. Following statistical design of experiments, and due to the need to determine the interrelationships between processing, chemical (including phases), structural (i.e., roughness, thickness, morphology) and electrical properties, the characteristics of the TaOx films were determined by Rutherford Backscattering Spectroscopy (RBS), Spectroscopic Ellipsometry (SE), Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), Auger Electron Spectroscopy (AES), Secondary Ion Mass Spectrometry (SIMS), X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The TaOx capacitors on polyimide with various electrode areas exhibited breakdown fields of 1.7-2.8 MV/cm, and the highest breakdown voltage and lowest current density observed were 92 Volts and 4 nanoamperes per square centimeter at an operating voltage of 10 Volts, respectively. Finally, a working down-converter with embedded passives, including 140 nanometers thick amorphous TaO x capacitors deposited at Arizona State University by ECR-CVD, was demonstrated at General Electric Company, Corporate R&D Laboratories in Schenectady, New York.;A second but minor component of the research included the characterization of crystalline tantalum oxide (Ta2O5) film-capacitors for Dynamic Random Access Memory (DRAM) applications. These films were deposited by Applied Materials Incorporated (AMAT) in Santa Clara, California. The goal was to determine the chemical integrity at interfaces of Ta2O 5/Silicon Nitride/poly-Silicon stacks by Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS). The studies revealed that during the processing of Ta2O5, oxygen reacted with the silicon nitride layer, and unexpectedly created a thin amorphous region of non-stoichiometric silicon oxynitride (SiOxNy).