Modulation of Electrical Properties of RF Sputtered Tantalum Oxide Based Thin Films for High-k dielectric Applications

Abstract

In the past decade, significant research efforts have focused on integrating high-k dielectric materials to replace traditional low-k dielectrics like SiO2. Among these materials, tantalum oxide (Ta2O5) has garnered substantial attention and appears particularly promising due to its high dielectric constant (≈25-30), relatively large energy bandgap (~4.5 eV), better amorphous to crystallization temperatures, and good thermal stability in contact with both silicon and metal gates. These exceptional material properties have made Ta2O5 highly attractive for use as a gate dielectric in Metal-Oxide-Semiconductor Field- Effect Transistors (MOSFETs). Furthermore, resistive switching in metal-oxide-metal structures fabricated using Ta2O5 thin films have demonstrated excellent memory effects, making it a suitable candidate for advanced memristor device applications. Integrating these devices into a monolithic structure, such as a one transistor one resistor (1T-1R) configuration, could potentially achieve high-speed operation, high storage density, and low power consumption. This advancement is facilitated by the use of multifunctional high-k dielectric materials like Ta2O5. Thin films of Ta2O5 have been produced using the radio frequency (RF) magnetron sputtering method. The study investigates the influence of sputtering parameters such as RF power, sputtering pressure, Ar/O2 gas flow ratio, and substrate temperature on the structural, morphological, and electrical properties of the films. The optimizing conditions are found to be RF power of 150 W, sputtering pressure of 1.0 × 10-2 mbar, Ar/O2 gas flow ratio of 3:2 and substrate temperature of 300 °C. Additionally, the impact of conventional annealing and rapid thermal annealing (RTA) at different process conditions, (temperature and duration) on the properties of Ta2O5 films is examined. 800 °C for conventional annealing and 750 °C for 10 min duration for RTA Process were found to be the optimal post-deposition treatment. At these optimal conditions, high dielectric constant, low leakage current, low oxide charge density, and low interface state density are observed. Doped versions of Ta2O5 films, incorporating Zr, and Hf, are synthesized on silicon substrates using RF co-sputtering. The dopant concentration is adjusted by varying the RF power applied to the dopant target while maintaining the RF power of the Ta target at an optimized level. To further modulate the electrical properties of the Ta2O5 thin film, a ZrO2 and HfO2 stacking layer was incorporated with different thickness configurations. An initial investigation was conducted to examine the resistive switching (RS) behavior of Ta2O5 films using a metal/insulating/metal (MIM) structure for memory device applications. This research work aims to investigate the enhanced RS characteristics of Ta2O5 films with varying different process parameter. Specifically, the study explores the effects of dopants and stack layer on the switching behavior of the as-deposited and modified Ta2O5 films. To investigate the structural, morphological, elemental and electrical properties of RF sputtered Ta2O5 thin film with various growth process parameters different characterization techniques were used. A Rigaku Ultima IV multipurpose X-ray diffractometer was used to study the structural properties of all the Ta2O5 based thin film. Nova Nano SEM/EFI field emission scanning electron microscope (EFSEM) was used to performed the morphological study on all sputtered Ta2O5 based samples, while X-ray photoelectron spectroscopy (XPS) from Omicron technology was used to study the compositional analyses of the sputtered films. Park XE7 atomic force microscope (AFM) was used to determine the roughness of the films. Al/Ta2O5/Si MOS capacitors were fabricated to study the electrical properties of the RF sputtered Ta2O5 films. Capacitance- voltage (C-V) and current-voltage (I-V) measurements were performed on the MOS structures using an Agilent E4980A precision LCR meter and a Keithley 6487 Picoammeter, respectively. Further, current-voltage measurements were performed on the metal-insulator-metal (MIM) structures using a Keithley 2410 sourcemeter to study the resistive switching behavior of the sputtered films.