Chia Ching Yeo

Energy gap and band alignment for (HfO2)x(Al2O3)1−x on (100) Si

High-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials (HfO2)x(Al2O3)1−x grown on (100) Si substrate with different HfO2 mole fraction x. Al 2p, Hf 4f, O 1s core levels spectra, valence band spectra, and O 1s energy loss all show continuous changes with x in (HfO2)x(Al2O3)1−x. These data are used to estimate the energy gap (Eg) for (HfO2)x(Al2O3)1−x, the valence band offset (ΔEν) and the conduction band offset (ΔEc) between (HfO2)x(Al2O3)1−x and the (100) Si substrate. Our XPS results demonstrate that the values of Eg, ΔEν, and ΔEc for (HfO2)x(Al2O3)1−x change linearly with x.

Formation of hafnium-aluminum-oxide gate dielectric using single cocktail liquid source in MOCVD process

We demonstrate that a high quality metal organic chemical vapor deposition (MOCVD) HfAl/sub x/O/sub y/ (hereafter HfAlO) dielectric film can successfully be deposited with a wide range of composition controllability between HfO/sub 2/ and Al/sub 2/O/sub 3/ in HfAlO using a single cocktail liquid source HfAl(MMP)/sub 2/(OiPr)/sub 5/. A composition ratio between 45 to 90% of HfO/sub 2/ in HfAlO is achieved by controlling deposition process parameters. The effect of the composition ratio between HfO/sub 2/ and Al/sub 2/O/sub 3/ on the electrical properties of the film is also investigated. The HfAlO film with 90% HfO/sub 2/ (10% Al/sub 2/O/sub 3/), which has minimum sacrifice of K value (around 19), shows a great improvement in thermal stability and significant reduction of interfacial layer growth during subsequent thermal processes, leading to the reduction in leakage current by around 2 orders of magnitude compared to pure HfO/sub 2/ film. The HfAlO film also shows good compatibility with TaN metal gate electrode under high temperature annealing process.

Electron mobility enhancement using ultrathin pure Ge on Si substrate

We demonstrate enhancement of electron mobility in nMOSFET using an ultrathin pure Ge crystal channel layer directly grown on a bulk Si wafer. A thin Si crystal layer is also grown on top of a Ge crystal channel layer as a capping layer. Using the Si/Ge/Si structure, a maximum 2.2X enhancement in electron mobility is achieved while good gate dielectric properties and junction qualities of bulk Si devices are maintained.

Border-Trap Characterization in High-

In this letter, we focus on the border-trap characterization of TaN/HfO₂/Si and TaN/HfO₂/strained-Si/Si_0.8Ge_0.2 n-channel MOSFET devices. The equivalent oxide thickness for the gate dielectrics is 2 nm. Drain-current hysteresis method is used to characterize the border traps, and it is found that border traps are higher in the case of high-kappa films on strained- Si/Si_0.8Ge_0.2 .These results are also verified by the 1/f-noise measurements. Possible reasons for the degraded interface quality of high-kappa films on strained-Si are also proposed.

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The electrical properties of Hf–Al–O alloy films with various composition ratios prepared by atomic layer chemical vapor deposition (ALCVD) have been investigated to find the optimum composition ratio. The Hf–Al–O alloy with 67% composition of HfO2, (HfO2)0.67(Al2O3)0.33, shows a good thermal stability comparable to Al2O3 film and a lower amount of negative fixed charge similar to pure HfO2 film. A significant reduction in leakage current of 67%-HfO2 film compared to that of pure HfO2 film has been achieved, which is attributed to the improved thermal stability. From the results, it is found that the optimum composition ratio in Hf–Al–O alloy lies at around 60–70% of HfO2.

Strained-Si MOSFETs

Metal gate/High-K stack CMOSFETs on ultra thin Ge epi channel on relaxed Si, capped with ultra thin Si (Si/Ge/Si substrate) were evaluated. NMOSFET shows enhanced mobility at low field while pMOSFET shows degraded peak mobility, with enhancement observed only at high field.

Dependence of chemical composition ratio on electrical properties of HfO2-Al2O3 gate dielectric

Hafnium oxide thin films deposited by MOCVD were annealed in nitrogen at various temperatures. The as‐deposited films and annealed films were characterized using Auger electron spectroscopy (AES), atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The films were found to be slightly oxygen deficient. Angle‐resolved XPS revealed oxygen to be residing in two different chemical states, that of oxygen in hafnium oxide, and possibly, a hafnium silicate. Auger depth profiling revealed nitrogen enrichment in an interfacial layer at the film‐substrate interface, which could be the result of an ammonia pre‐treatment prior to deposition. The thickness of this interfacial layer was determined to be ∼ 15 A from TEM. Progressively larger grains were found from AFM measurements with increasing annealing temperature.

Metal Gate/High-K Dielectric Stack on Si Cap/Ultra-Thin Pure Ge epi/Si Substrate

The thermal stabilities of MOSFETs with high-K gate dielectric on both Si/ultrathin Ge/Si (SGS) and strained Si on relaxed Si1?xGex (SS) substrates are studied. Though an initial drivability enhancement of 29% is shown for the SGS nMOSFET, annealing at 750 ?C has resulted in drastic degradation in its drivability, lowering its Id beyond that of the Si nMOSFETs by 52%. Despite lowering in the junction leakage current, Ge diffusion to the near surface region, indicated by Vth and surface roughness change, degrades the SGS device performance significantly. For the SS nMOSFET, drivability varies with Ge content, whereby a maximum of 86% improvement over that of the Si nMOSFET is observed for 30% Ge. In contrast to the SGS nMOSFET, the SS nMOSFET is able to retain its Id improvement, even after annealing at 950 ?C, as the in-plane tensile strain is preserved. Ge diffusion to the surface does not affect the device significantly, as the strained Si thickness is about 10 nm compared to a Si cap thickness of only 1.5 nm for the SGS substrate.