Siva Prasad Devireddy

Low-frequency noise characteristics of HfSiON gate-dielectric metal-oxide-semiconductor-field-effect transistors

High dielectric constant materials are being developed as possible replacements for SiO2 as the gate dielectric. Although these materials do overcome the issue of gate leakage current because of increased thickness for a given equivalent capacitance, several other problems arise, such as degraded carrier mobility and higher low-frequency noise due to increased fixed charges and traps in the high-k film. HfSiON gate-dielectric metal-oxide-semiconductor field-effect transistors (MOSFETs), presented here, offer lower 1∕f noise compared to other high-k materials, but the noise levels are relatively higher than in SiO2 devices. Oxide-trap-induced correlated carrier number-mobility fluctuations dominate in all of these devices. Measured noise characteristics as well as extracted oxide trap density values are discussed for various geometries and sizes. The latter, measured to be 1.5×1019–1.6×1020cm−3eV−1, is higher than that for SiO2 MOSFETs with similar dimensions (4.1×1016–7.8×1016cm−3eV−1). This work represen...

Impact of interfacial layer on low-frequency noise of HfSiON dielectric MOSFETs

Low-frequency noise measurements and analysis were performed on n-channel MOSFETs with HfSiON as the gate-dielectric material. The role of SiON interfacial-layer thickness was investigated. It was observed that these fluctuations can be described by the unified flicker-noise model that attributes noise to correlated carrier-number/mobility fluctuations due to trapping states in the gate dielectric. The model was modified to include the effect of different gate stack layers on the observed noise. The carrier-number fluctuations were found to dominate over the correlated mobility fluctuations in the measured bias range and more so at the lower gate overdrives. The noise magnitude showed a decrease with increasing SiON interfacial-layer thickness. Furthermore, an inverse-proportionality relationship was revealed between the effective oxide trap density and SiON thickness.

Low-frequency noise in TaSiN/HfO/sub 2/ nMOSFETs and the effect of stress-relieved preoxide interfacial layer

Low-frequency noise characteristics are reported for TaSiN-gated n-channel MOSFETs with atomic-layer deposited HfO/sub 2/ on thermal SiO/sub 2/ with stress-relieved preoxide (SRPO) pretreatment. For comparison, control devices were also included with chemical SiO/sub 2/ resulting from standard Radio Corporation of America clean process. The normalized noise spectral density values for these devices are found to be lower when compared to reference poly Si gate stack with similar HfO/sub 2/ dielectric. Consequently, a lower oxide trap density of /spl sim/4/spl times/10/sup 17/ cm/sup -3/eV/sup -1/ is extracted compared to over 3/spl times/10/sup 18/ cm/sup -3/eV/sup -1/ values reported for poly Si devices indicating an improvement in the high-/spl kappa/ and interfacial layer quality. In fact, this represents the lowest trap density values reported to date on HfO/sub 2/ MOSFETs. The peak electron mobility measured on the SRPO devices is over 330 cm/sup 2//V/spl middot/s, much higher than those for equivalent poly Si or metal gate stacks. In addition, the devices with SRPO SiO/sub 2/ are found to exhibit at least /spl sim/10% higher effective mobility than RCA devices, notwithstanding the differences in the high-/spl kappa/ and interfacial layer thicknesses. The lower Coulomb scattering coefficient obtained from the noise data for the SRPO devices imply that channel carriers are better screened due to the presence of SRPO SiO/sub 2/, which, in part, contributes to the mobility improvement.

Effect of nitrogen incorporation on 1/f noise performance of metal-oxide-semiconductor field effect transistors with HfSiON dielectric

Nitrided hafnium silicate is the leading candidate for possible replacement of SiON as a gate dielectric. 1/f noise characteristics of plasma and thermally nitrided Hf-based high-dielectric constant (high-k) gate dielectrics were investigated. Plasma nitrided samples showed less noise than thermally nitrided samples. The mobility fluctuation component of 1/f noise was found to show a strong process dependence, specifically on the nitridation technique. Increase in the number of Coulomb scattering sites due to the additional Si–N bonds near the high-k/Si interface is suggested as the reason for this dependence. This work represents the first investigation on the effect of different nitridation methodologies on low-frequency noise mechanisms in ultrathin (∼2 nm) Hf-based high-k nMOSFET (metal-oxide-semiconductor field effect transistor).

Improved low frequency noise characteristics of sub-micron MOSFETs with TaSiN/TiN gate on ALD HfO2 dielectric

Low frequency noise measurements were performed on n- and p-channel MOSFETs with TaSiN and TiN metal gates, respectively, deposited on ALD HfO2 gate dielectric. Lower normalized current noise power spectral density is reported for these devices in comparison to poly-Si/HfO2 devices and that yielded one order lower magnitude for extracted average effective dielectric trap density. In addition, the noise levels in PMOS devices were found to be higher than NMOSFETs and the dielectric trap distribution less dense in the upper mid-gap than the lower mid-gap region. The screened carrier scattering coefficient extracted from the noise measurements was approximately the same for metal and poly-Si high-k stacks but higher than that for the poly-Si SiO2 system, implying higher Coulomb scattering effects. It is believed that the elimination of dopant penetration seen in poly-Si system and low thermal budgets for metal gate deposition helped lower the noise magnitude and yielded better mobility and effective trap density values.

A new model for 1/f noise in high-κ MOSFETs

A new 1/f noise model based on correlated number-mobility fluctuations theory is proposed to account for the low frequency noise in MOSFETs with multi-layered gate dielectrics. In this new model, the trap density profile takes into account the effects of energy and spatial distribution as well as the multilayer structure of the gate-stack. Correlated number and mobility fluctuation was experimentally verified as the dominant mechanism for 1/f noise, with no contribution from remote phonon scattering to the observed fluctuations. The model was experimentally verified on devices having different interfacial layer (IL) thicknesses and various fabrication processes over a wide temperature and bias range.

Flicker noise in nitrided high-k dielectric NMOS transistors

In order to replace the conventional SiO2 in MOSFETs and minimize gate tunneling currents, high permittivity dielectric materials have been proposed as alternatives. These materials have successfully resolved the gate leakage problem with thicker oxide dielectric. However, other issues such as lower effective mobility and increased low frequency noise due to higher oxide trap density, limit its further development. Among these candidates, HfSiON offers many advantages compared to other high-k devices such as suppression of Boron penetration, remaining amorphous during high temperature annealing, and offering better thermal stability and interface quality. In addition, the extracted oxide trap density from measured 1/f noise shows lower values compared to other high-k MOSFETs. This paper presents low frequency noise characteristics of MOSFETs with HfSiON and SiON gate dielectrics of varying gate length dimensions and effective oxide thickness. The measured noise spectra as well as DC parameters will be compared between HfSiON and SiON MOSFETs. The noise parameters are extracted from the measured noise data using the interface-generated, correlated number and mobility fluctuation model.

Variable Temperature Characteristics of Devices With HfSiON as The High‐κ Dielectric on Nitrided Silicate (SiON) Interfacial Layer

Variable temperature device characteristics have been studied on polycrystalline silicon gate MOSFETs with HfSiON as the high‐κ dielectric on SiON interfacial layer (IL). The effects of phonon scattering were investigated. Variable temperature noise and electron transport measurements revealed that soft‐optical phonon scattering does not have any effect on the low frequency noise characteristics, even though it affects the electron mobility behavior. Correlated number and mobility fluctuations were identified as the dominant noise mechanism for 1/f noise. The previously reported discrepancies in the application of the Unified 1/f Noise Model to MOSFETs with high‐κ gate dielectrics were eliminated by generalizing the model to include energy and spatial distribution of the dielectric traps responsible for the fluctuations. Excellent fit was observed between the predictions of the Multi‐Stack Unified Noise (MSUN) Model and the data over the experimental temperature range for all IL thickness values. The extr...

Effect of Nitrogen Incorporation Methods on 1/f Noise and Mobility Characteristics in HfSiON NMOSFETs

Low frequency noise (LFN) characteristics of HfSiO and HfSiON nMOS with TiN metal gate were compared. Two different methods to introduce nitrogen in HfSiO, plasma and thermal nitridation, were discussed from LFN point of view. Using Multi‐stack Unified Noise (MSUN) model, number and mobility fluctuation components were separated to find out the effects of processing on LFN characteristics. Different processing techniques have negligible effects on number fluctuation components. However, mobility fluctuation components were significantly affected. The reason might be due to the presence and distribution of various Coulomb scattering sites at the silicon‐high‐k interface and in the bulk of high‐k oxide due to different nitridation processes.

Low Frequency Noise Characterization of TaSiN/HfO2 MOSFETs Below Room Temperature

Low frequency noise characteristics are presented for TaSiN/HfO2/SiO2 n‐MOSFETs in the 78–300K range. The general validity of the carrier number /correlated mobility fluctuations as the underlying noise mechanism at low temperatures was confirmed. The temperature independence of normalized noise implied that phonon scattering has no affect on high‐k device noise. The dielectric trap density extracted using Unified Flicker Noise Model varied by an order of magnitude in the considered temperature range that is self‐contradictory. Modifications are hereby proposed to the unified model that account for the non‐uniform trap profile among other physical properties of dielectric materials in the gate stack. The new multi‐stack unified noise (MSUN) model is shown to be in good agreement with the experimental data.