Koji Watanabe

A highly manufacturable low power and high speed HfSiO CMOS FET with dual poly-Si gate electrodes

For 90 nm node poly-Si gated MISFETs with HfSiO (1.8 nm) insulator, a nearly symmetrical set of Vths for NFET and PFET: (0.38 V and -0.46 V, respectively) have been realized for low power device operation. The key technology is the suppression of Vth instability in PFETs arising from oxidation of the poly-Si/HfSiO interface, combined with channel engineering for the PFET. Our poly-Si/HfSiO gate-stacked CMOSFETs realize low I/sub off/ (N/PFET: 4.8/3.6 pA//spl mu/m) and high I/sub on/ (N/PFET: 469/140 /spl mu/A//spl mu/m) at V/sub DD/=1.2 V. Further, for SRAM cell using this CMOS, normal operation has been achieved.

The influence of incorporated nitrogen on the thermal stability of amorphous HfO2 and Hf silicate

We investigated the thermal stability of a N-incorporated amorphous Hf silicate film in terms of Hf diffusion in the film using high-angle annular-dark-field scanning transmission electron microscopy. We first examined HfxSi1−xO2 (x=0.5,1.0) films with and without N incorporation. Our analysis showed that N incorporation (15at.% of N) into the Hf0.5Si0.5O2 film significantly suppressed chemical component separation during annealing at 1000°C. In contrast, clear separation of Hf-rich and Hf-poor (SiO2-rich) regions occurred in the Hf0.5Si0.5O2 film without N incorporation. In addition, HfO2 crystalline particle formation was observed in the HfO2 films with and without N incorporation (25at.% of N). These results strongly suggest that Si–N bonding in the N-incorporated Hf0.5Si0.5O2 film, rather than Hf–N chemical bonding, is the main cause of the suppression of the chemical component separation and HfO2 crystallization. Second, we examined Hf diffusion in a SiO2 film with and without N incorporation and fou...

Controlling the concentration and position of nitrogen in ultrathin oxynitride films formed by using oxygen and nitrogen radicals

The formation of oxynitride films less than 2.0 nm by using oxygen and nitrogen radicals produced by an electron cyclotron resonance plasma in an ultrahigh-vacuum system has been studied. We found that the N concentration can be controlled at values up to 15% and that, although the interface roughness tends to increase with increasing N concentration, supplying oxygen and nitrogen radicals simultaneously decreases the roughness of the film and increases its nitrogen concentration (N: 12.1%, root mean square: 0.12 nm). We also could easily control the nitrogen profile in the oxynitride less than 2.0-nm-thick by using different processing sequences.

Effect of Nitrogen Profile and Fluorine Incorporation on Negative-Bias Temperature Instability of Ultrathin Plasma-Nitrided SiON MOSFETs

The effects of plasma nitridation and fluorine incorporation on the components of negative-bias temperature instability (NBTI) in p-type MOSFETs with plasma-nitrided SiON gates were investigated. To clarify these effects, NBTI-induced threshold-voltage shift was separated into two components: one for generation of traps at the SiON/Si-substrate interface and one for positive charges within the SiON bulk. It was found that the proportions of the interface and bulk components can be controlled with the plasma nitridation method: The bulk component was increased by radio-frequency plasma nitridation, while the interface component was dominant in the case of electron-cyclotron-resonance plasma nitridation. Lowering the nitrogen concentration near the SiON/Si-substrate interface decreased the interface component. Lowering the nitrogen concentration near the poly-Si/SiON interface did not decrease NBTI, while it decreased positive oxide charges in the as-fabricated MOSFETs. Furthermore, it was demonstrated that the fluorine incorporation decreases the interface component in plasma-nitrided SiON gates, while it does not decrease the bulk component.

Dependence of electrical properties on nitrogen profile in ultrathin oxynitride gate dielectrics formed by using oxygen and nitrogen radicals

We studied nitrogen incorporation in ultrathin oxynitride films by using oxygen and nitrogen radicals, and investigated the dependence of the electrical properties on the nitrogen profile. We found that the nitrogen position in the films could be controlled by using different processing sequences, and that the N concentration could be controlled at values up to 16%. In this process, the interface roughness depends on nitrogen position and nitrogen concentration: the interface roughness tends to increase as the N position close to the SiO2–Si interface and increase with N concentration. The results of an analysis of the electrical properties of these oxynitride films indicated that the best way to form the film was by radical nitridation after radical oxidation. These results show that the nitrogen position should be kept away from the SiO2–Si interface and nitrogen amount should be localized at the surface. Using this process, we have successfully achieved a low-leakage 1.5 nm oxynitride (equivalent oxide...

Thermal stability of a HfO2∕SiO2 interface

Using high-angle annular-dark-field scanning transmission electron microscopy, we showed how annealing at 1000°C changes the chemical composition distribution at a HfO2∕SiO2 interface. The observed change in the distribution was analyzed in terms of Hf diffusion in SiO2; the diffusion coefficient was estimated to be 2.5×10−18cm2∕s. This diffusion coefficient indicates that the high-temperature annealing, such as that in the conventional dopant activation process used to fabricate semiconductor devices, barely changes the chemical composition distribution at the HfO2∕SiO2 interface.

TiSi2/Si interface instability in plasma-assisted chemical vapor deposition of titanium

The heterointerface between a Si(1 0 0) substrate and a TiSi2 layer becomes rough when the substrate temperature during the formation of the TiSi2 layer by plasma-assisted chemical vapor deposition using the TiCl4/H2/Ar gas system is between 650 and 750°C. In this temperature range, the Si substrate is etched and pits that have (1 0 0) and (1 1 1) vicinal surfaces can be observed at the heterointerface. At higher or lower temperatures, however, a smooth interface is created. This morphological instability appears to be due to the processes of Cl desorption from the surface during the Ti deposition.

Atomic structures at a Si–nitride/Si(001) interface

We used high-resolution transmission electron microscopy to show that the atomic structures at a Si3N4/Si interface are clearly different from those at a SiO2/Si interface. Using first-principles calculations, we also found that, in one of the observed N-induced interfacial geometries, a dangling bond was produced on a Si atom adjacent to a N atom. We thus argue that such N-induced interfacial dangling bonds can cause degradation in the performance of metal–oxide–semiconductor transistors with Si–oxynitride (SiON) gate dielectrics when the N concentration is increased at the SiON/Si interfaces. We also argue that the difference in flatness between Si3N4 and SiON/Si interfaces and SiO2/Si interfaces is the result of the difference between their atomic structures.

Electrical properties of 1.5-nm SiON gate-dielectric using radical oxygen and radical nitrogen

We have developed a low-leakage and highly reliable 1.5-nm SiON gate-dielectric by using radical oxygen and nitrogen. In this development, we introduce a new method for determining an ultrathin SiON gate-dielectric thickness based on the threshold voltage dependence on the substrate bias in MOSFETs. It was found that oxidation using radical oxygen followed by nitridation using radical nitrogen provides the 1.5-nm (oxide equivalent thickness) SiON, in which leakage current is two orders of magnitude less than that of 1.5-nm SiO/sub 2/ without degrading device performance in NMOSFETs. The 1.5-nm (oxide equivalent thickness) SiON was also found to be ten times more reliable than 1.5-nm SiO/sub 2/.

Oxynitridation using radical-oxygen and -nitrogen for high-performance and highly reliable n/pFETs

We report the importance of oxynitridation using radical-oxygen and -nitrogen to form a low-leakage and highly reliable 1.6-nm SiON gate-dielectric without performance degradation in n/pFETs. It was found that oxidation using radical-oxygen forms high-density 1.6-nm SiO/sub 2/, which is ten times more reliable than low-density SiO/sub 2/ formed by oxygen-ions in n/pFETs and is suitable for the base layer of nitridation. Nitrifying SiO/sub 2/ using radical-nitrogen facilitates surface nitridation of SiO/sub 2/, maintains an ideal SiON-Si substrate interface, and reduces the gate leakage current. The 1.6-nm SiON formed by radical-oxygen and -nitrogen produces comparable drivability in n/pFETs, has one and half orders of magnitude less gate leakage in nFETs, one order of magnitude less gate leakage in pFETs, and is ten times more reliable in n/pFETs than 1.6-nm SiO/sub 2/ formed by radical-oxygen.