Scalable high-k metal-insulator-metal capacitors with low leakage, high breakdown fields and improved voltage linearity

Abstract

Initial electrical results of scalable high dielectric constant metal-insulator-metal capacitors with low leakage, high breakdown fields, and improved voltage linearity are reported. Excellent combined properties are achieved with an optimised atomic layer deposition process to obtain a dielectric with a reproducible atomic structure that gives the optimum electrical properties of high temperature stability; scalability of capacitance density; linearity of capacitance with voltage; a high capacitor quality factor; low leakage at estimated operating voltages; and high breakdown fields. Applications of this technology development are many and varied owing to the capacitor being a key component in analogue-based circuitry, including analogue mixed signals units; radio frequency devices; microelectromechanical systems; capacitive tuning; resistive and dynamic random access memory, automotive, space, and medical devices.Introduction: Capacitors are key components of all electronic circuitry, whether it is a metal-oxide-semiconductor capacitor to be integrated into new technology metal-gate/high-k/[Si or III-V] MOS field-effect transistors [1-3], or metal-insulator-metal capacitors (MIMCAPS) for applications such as analogue mixed signals (AMS) units; radio frequency (RF) devices; microelectromechanical systems (MEMS); capacitive tuning; resistive and dynamic random access memory (RRAM/DRAM), automotive, space, and medical devices [4,5]. Presently used MIMCAPS rely on SiO 2 , Si x O y N z , or Si 3 N 4 based dielectrics. Such capacitors can be optimised through processing to achieve the desired electrical properties, but the maximum capacitance density (C D ) of the MIMCAPS is limited owing to the upper limit of the dielectric constant value (k 4-7) that can be achieved [6]. High-k dielectrics (k . 8) have been under investigation for some time to replace the lower-k materials, but they typically exhibit high leakage current densities (J . 1 × 10 27 A/cm 2 ) at device operating voltages (V op ); low breakdown fields (E BD , 6 MV/cm), and significant nonlinearity of capacitance with voltage as measured by the quadratic voltage coefficient of capacitance (QCC, or a, with a . .|100|ppm/V 2 ), in which the bulk high-k oxide contributes substantially to the nonlinearity in addition to the oxide/metal interfaces. High-k MIMCAPS typically have significant variations in leakage mechanisms, and exhibit soft breakdown events prior to hard breakdown. Poor repeatability and reliability are commonplace, and there is generally significant change in the electrical properties with changing temperature and operating frequency. Among these non-ideal properties is an empirical inverse relation between k-value and E BD , as well as an empirical non-constant E BD with changing high-k thickness [7].Background methods: We use atomic layer deposition (ALD) techniques to deposit a particular metal-in-silicon-oxide material system (known for the purpose of this Letter as 'MISO' [8]) based on an M x Si 12x O 2 (M ¼ Hf and/or Zr) composition with...

Influence of Substrate on Hafnium Silicate Metal-Insulator-Metal Capacitors Grown by Atomic Layer Deposition

“…Although both materials exhibit little or no hysteresis in the capacitance-voltage response, the extracted k values are very different; platinum bottom electrode ~18.8 and aluminium bottom electrode ~14.3 (extracted from the capacitance at zero volts and 1 kHz). The clear electrical differences between the two dielectric materials grown under identical processing conditions is surprising, particularly as little difference in properties was reported for differing electrode materials in the previous study (6). To elucidate possible reasons for the observed electrical differences electron microscopy was performed on both the 130 nm aluminium bottom electrode and 50 nm platinum bottom electrode devices.…”

“…For the 130 nm hafnium silicate film previously reported with aluminium electrodes the response is symmetrical with a 7.5 MVcm -1 electrical field breakdown (1). The clear electrical differences between the two dielectric materials grown under identical processing conditions is surprising, particularly as little difference in properties was reported for differing electrode materials in the previous study (6). To elucidate possible reasons for the observed electrical differences electron microscopy was performed on both the 130 nm aluminium bottom electrode and 50 nm platinum bottom electrode devices.…”

“…The top aluminium electrode was deposited by an evaporation process. The previously reported sample is described fully elsewhere, briefly the only discernible difference is that the bottom electrode is sputtered aluminium and the top aluminium electrode is sputtered not evaporated (6). For both the current and previous samples discussed, devices, defined by lift-off, were 1×10 -8 m 2 .…”

“…Many high k materials are under investigation to replace these lower k dielectrics to substantially increase the maximum capacitance density and reduce the area associated with the integration of MIM structures. In our previously published work hafnium silicate MIM capacitors with excellent electrical properties were obtained, including an electric breakdown field of ~ 7.5 MVcm -1 , a k value of ~ 14 and no hysteresis or dispersion at frequencies of 1 kHz -100 kHz (6). These MIM capacitors were produced on a range of electrode materials with no apparent variation in the electrical properties.…”