Siddarth Krishnan

Electrical characterization and material evaluation of zirconium oxynitride gate dielectric in TaN-gated NMOSFETs with high-temperature forming gas annealing

The electrical, material, and reliability characteristics of zirconium oxynitride (Zr-oxynitride) gate dielectrics were evaluated. The nitrogen (/spl sim/1.7%) in Zr-oxynitride was primarily located at the Zr-oxynitride/Si interface and helped to preserve the composition of the nitrogen-doped Zr-silicate interfacial layer (IL) during annealing as compared to the ZrO/sub 2/ IL - resulting in improved thermal stability of the Zr-oxynitride. In addition, the Zr-oxynitride demonstrated a higher crystallization temperature (/spl sim/600/spl deg/C) as compared to ZrO/sub 2/ (/spl sim/400/spl deg/C). Reliability characterization was performed after TaN-gated nMOSFET fabrication of Zr-oxynitride and ZrO/sub 2/ devices with equivalent oxide thickness (EOTs) of 10.3 /spl Aring/ and 13.8 /spl Aring/, respectively. Time-zero dielectric breakdown and time-dependent dielectric breakdown (TDDB) characteristics revealed higher dielectric strength and effective breakdown field for the Zr-oxynitride. High-temperature forming gas (HTFG) annealing on TaN/Zr-oxynitride nMOSFETs with an EOT of 11.6 /spl Aring/ demonstrated reduced D/sub it/, which resulted in reduced swing (69 mV/decade), reduced off-state leakage current, higher transconductance, and higher mobility. The peak mobility was increased by almost fourfold from 97 cm/sup 2//V/spl middot/s to 383 cm/sup 2//V/spl middot/s after 600/spl deg/C HTFG annealing.

Structural and electrical properties of HfO 2 with top nitrogen incorporated layer

A novel technique to control the nitrogen profile in HfO/sub 2/ gate dielectric was developed using a reactive sputtering method. The incorporation of nitrogen in the upper layer of HfO/sub 2/ was achieved by sputter depositing a thin Hf/sub x/N/sub y/ layer on HfO/sub 2/, followed by reoxidation. This technique resulted in an improved output characteristics compared to the control sample. Leakage current density was significantly reduced by two orders of magnitude. The thermal stability in terms of structural and electrical properties was also enhanced, indicating that the nitrogen-doped process is effective in preventing oxygen diffusion through HfO/sub 2/. Boron penetration immunity was also improved by nitrogen-incorporation. It is concluded that the nitrogen-incorporation process is a promising technique to obtain high-k dielectric with thin equivalent oxide thickness and good interfacial quality.

Evaluation of silicon surface nitridation effects on ultra-thin ZrO2 gate dielectrics

The effects of silicon surface nitridation on metal–oxide–semiconductor capacitors with zirconium oxide (ZrO2) gate dielectrics were investigated. Surface nitridation was introduced via ammonia (NH3) annealing prior to ZrO2 sputter-deposition, and tantalum nitride (TaN) was used for the gate electrode. It was found that capacitors with the nitridation had thinner equivalent oxide thickness (∼8.7 A), comparable leakage current, and slightly increased capacitance–voltage hysteresis as compared to samples without nitridation. Additionally, transmission electron microscopy pictures revealed that nitrided samples had a thicker interfacial layer (IL), which had a higher dielectric constant than that of the non-nitrided IL.

Area dependence of TDDB characteristics for HfO 2 gate dielectrics

Weibull slopes, area scaling factors, and lifetime projection have been investigated for both soft breakdown and hard breakdown for the first time, in order to gain a better understanding of, the breakdown mechanism of HfO/sub 2/ gate dielectrics. The Weibull slope /spl beta/ of the hard breakdown for both the area dependence and the time-to-dielectric-breakdown distribution was found to be /spl beta/ = 2, whereas that of the soft breakdown was about 1.4. Estimated ten-year lifetime has been projected to be -2 V.

Fabrication of high quality ultra-thin HfO/sub 2/ gate dielectric MOSFETs using deuterium anneal

The effects of high-temperature deuterium annealing on MOSFETs with HfO/sub 2/ gate dielectric and TaN gate electrode has been studied and compared to the control and forming gas (FG) annealed samples. Both FG and D/sub 2/ anneal improved interface qualities and resulted in better MOSFET characteristics in comparison to control samples. These improvements resulted from both the additional thermal budget of high temperature anneal and the improvement of interface quality caused by the hydrogen and deuterium atoms. But unlike FG D/sub 2/ anneal showed negligible degradation of reliability.

Thickness dependence of Weibull slopes of HfO 2 gate dielectrics

Breakdown voltage distribution, Weibull slopes, and area scaling factors have been investigated for HfO/sub 2/ gate dielectrics in order to gain a better understanding of the breakdown mechanism. Weibull slope of thick HfO/sub 2/ (e.g., /spl beta//spl ap/4 for EOT=2.5 nm) is smaller than that of SiO/sub 2/ with similar physical thickness, whereas /spl beta/ of the thinner HfO/sub 2/ (e.g., /spl beta//spl ap/2 for EOT=1.4 nm) is similar to that of SiO/sub 2/. The implication of the thickness dependence of /spl beta/ is discussed.

Improved electrical and material characteristics of hafnium titanate multi-metal oxide n-MOSFETs with ultra-thin EOT (/spl sim/8 /spl Aring/) gate dielectric application

A novel approach of fabricating laminated TiO/sub 2//HfO/sub 2/ bi-layer multi-metal oxide dielectric was developed for high performance CMOS applications. Both layers showed negligible intermixing and no silicide formation. For the first time, ultra-thin EOT (/spl sim/8 /spl Aring/) was achieved with increased effective permittivity (k /spl sim/ 36) using the bi-layer dielectric. Leakage current characteristic was slightly higher than HfO/sub 2/ due to lower band offset of TiO/sub 2/. However, superior thermal stability (>950/spl deg/C), significantly reduced hysteresis characteristic, and comparable interface state density represent the high quality of TiO/sub 2//HfO/sub 2/ multi-metal oxide. Also, excellent subthreshold swing, increased transconductance, higher current drive, and -33% improved channel electron mobility compared to the control HfO/sub 2/ samples demonstrate the feasibility of new multi-metal oxide application for future CMOS technology.

The effect of interface thickness of high-k/metal gate stacks on NFET dielectric reliability

This paper explores the trade-offs of interface layer (IL) thickness, interface growth process, and interface nitrogen content on NFET dielectric reliability using ramp breakdown tests. The median breakdown voltage and the Weibull slope correlate strongly with the gate leakage irrespective of the IL process. Both reliability parameters are predominately modulated by the IL thickness.

Positive bias temperature instability effects of Hf-based nMOSFETs with various nitrogen and silicon profiles

Positive bias temperature instability (PBTI) effects of HfO/sub 2/-based nMOSFETs with various nitrogen profiles in HfO/sub 2/ were investigated. The nitrogen profile was modulated by an inserting Si layer (/spl sim/6/spl Aring/) into hafnium oxynitride gate dielectrics. The Si layer is used to trap nitrogen and to suppress nitrogen out-diffusion during subsequent anneals. Compared to control HfO/sub x/N/sub y/ without Si insertion, the Si-inserted HfO/sub x/N/sub y/ samples exhibited reduced PBTI degradation, especially if the Si layer was placed further from the Si interface. The improvement can be attributed to the reduction of oxide bulk trapped as well as reduced interface trapped charge generation resulting from compensation effect of inserted Si layer.

Impact of Nitrogen on PBTI Characteristics of HfSiON/TiN Gate Stacks

The impact of nitrogen on charge trapping induced positive bias temperature instability (PBTI) characteristics in HfSiON/TiN gate stacks is investigated. While thickness is found to be the primary parameter to reduce charge trapping, plasma nitrogen reduces PBTI effects in thick (2.7 nm) HfSiON films. Thin films (1.8 nm) show significantly lower threshold voltage (VTH) shift than thick films and seem to be insensitive to N content. Thermal nitridation exacerbates the PBTI effects more than plasma nitridation