Nobuyoshi Hattori

Local Bonding Structure of High-Stress Silicon Nitride Film Modified by UV Curing for Strained Silicon Technology beyond 45 nm Node SoC Devices

Silicon nitride films (p-SiN) with different high stresses were formed by changing the monosilane-to-ammonia source gas ratio, RF power, and deposition temperature in a conventional plasma-enhanced chemical vapor deposition (PECVD). PECVD was used to deposit p-SiN films with high-stresses because it can flexibly change the stress of the film to be formed from tensile to compressive direction. The formed films were analyzed by Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nanoindentation, and positron-beam annihilation to obtain data on local bonding structure, mechanical properties and the behavior of vacancies in the p-SiN films. In this study, to clarify the local bonding structure of high stress SiN films, we investigated p-SiN films with and without ultraviolet (UV) curing that is effective in tensile stress. It has been confirmed that total hydrogen (Si–H+N–H) concentration decreases with increasing film stress of p-SiN films. It has been found that UV curing promotes Si–N–Si crosslinking due to dehydrogenization, leading to the formation of a stoichiometric silicon nitride, Si3N4, network structure, and the vacancies in the p-SiN films shrink during UV curing. Finally, we proposed a structural model for the local bonding arrangement in p-SiN films with UV curing.

Impact of additional Pt and NiSi crystal orientation on channel stress induced by Ni silicide film in metal?oxide?semiconductor field-effect transistors

The impact of additional Pt and Ni monosilicide (NiSi) crystal orientation on channel stress from Ni silicide in metal–oxide–semiconductor field-effect transistors (MOSFETs) has been demonstrated. The channel stress generation mechanism can be explained by the NiSi crystal orientation. In pure Ni silicide films, the channel stress in the p-type substrate is much larger than that in the n-type one, since the NiSi a-axis parallel to the channel direction is strongly aligned on the p-type substrate compared with on the n-type one. On the other hand, in NiPt silicide films, the difference in the channel stress between the p- and n-type substrates is small, because the NiSi crystal orientation on the p-type substrate is similar to that on the n-type one. These results can be explained by the Pt segregation at the interface between the NiSi film and the Si surface. Segregated Pt atoms cause the NiSi b-axis to align normal to the Si(001) surface in the nucleation step owing to the expansion of the NiSi lattice spacing at the NiSi/Si interface. Furthermore, the Pt segregation mechanism is considered to be caused by the grain boundary diffusion in the Ni2Si film during NiSi formation. We confirmed that the grains of Ni2Si on the p-type substrate are smaller than those on the n-type one. The Ni2Si film on the p-type substrate has more grain boundary diffusion paths than that on the n-type one. Therefore, the amount of Pt segregation at the NiSi/Si interface on the p-type substrate is larger than that on the n-type one. Consequently, the number of NiSi grains with the b-axis aligned normal to the Si(001) in the p-type substrate is larger than that in the n-type one. As a result, the channel stress induced by NiPt silicide in PMOS is larger than that in NMOS. According to this mechanism, controlling the Pt concentration at the NiSi/Si interface is one of the key factors for channel stress engineering.

Evaluation of Strain in Si-on-Insulator Substrate Induced by Si3N4 Capping Film

Strain introduced to Si-on-insulator (SOI) substrates by Si3N4 capping film was evaluated by UV-Raman spectroscopy. The induced strain became larger with increasing Si3N4 film thickness. SOI substrates originally had tensile strain and the Si3N4 cap shifted the strain toward the compressive direction. The induced strain was larger in thinner SOI substrates with the same thickness of the Si3N4 capping film. In the SOI substrates with patterned Si3N4 film, the strain was in different directions between the regions with and without Si3N4 film; i.e., if the strain was compressive in the region beneath the Si3N4 film, it was tensile beneath the space between the Si3N4 lines. We also evaluated substrates after Si3N4 patterning with a high spatial resolution of 200 nm, and observed strain enhancement near the pattern edge on both sides.

Characterizing Metal-Oxide Semiconductor Structures Consisting of HfSiOx as Gate Dielectrics using Monoenergetic Positron Beams

Metal–oxide–semiconductor structures consisting of HfSiOx as the gate dielectric were characterized by using monoenergetic positron beams. 200-nm-thick polycrystalline-Si (poly-Si) and 5-nm HfSiOx films were grown on Si substrates by chemical vapor deposition. Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons were measured as a function of incident positron energy for ion-implanted and unimplanted samples. For the unimplanted sample after rapid thermal annealing (RTA: 1030°C, 10 s), the lifetime of positrons in the HfSiOx film was 448±2 ps. Since the obtained lifetime was longer than the lifetime of positrons trapped by point defects in metal oxides, the positrons in HfSiOx films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. After P+, As+ and BF2+-implantation into the poly-Si film and RTA, the lifetime of positrons was 420–430 ps. This decrease in the lifetime was attributed to the shrinkage of the open spaces in the HfSiOx film due to the accumulation of implanted impurities in the film during RTA. The diffusion length of positrons in Si substrates was found to depend on the implanted species of ions. This fact was attributed to the electric field introduced by charged defects in the HfSiOx films.

NiPt silicide agglomeration accompanied by stress relaxation in NiSi(010) ∥ Si(001) grains

Pt-doped Ni (NiPt) silicide agglomeration in terms of NiSi crystal orientation, Pt segregation at the NiSi/Si interface, and residual stress is studied for the first time. In the annealing of Ni monosilicide (NiSi), the growth of NiSi grains whose NiSi b-axes are aligned normal to Si(001) [NiSi(010) ∥ Si(001)] with increasing Pt segregation at the NiSi/Si interface owing to a high annealing temperature was observed. The residual stress in NiSi(010) ∥ Si(001) grains also increases with increasing annealing temperature. Furthermore, the recrystallization of NiSi(010) ∥ Si(001) grains with increasing residual stress continues through additional annealing after NiSi formation. After the annealing of NiSi(010) ∥ Si(001) grains with their strain at approximately 2%, the start of NiPt silicide agglomerates accompanied by stress relaxation was observed. This preferential recrystallization of NiSi(010) ∥ Si(001) grains with increasing residual stress is considered to enhance the NiPt silicide agglomeration.

Analysis of Channel Stress Induced by NiPt-Silicide in Metal–Oxide–Semiconductor Field-Effect Transistor and Its Generation Mechanism

Channel stress induced by NiPt-silicide films in metal–oxide–semiconductor field-effect transistors (MOSFETs) was demonstrated using UV-Raman spectroscopy, and its generation mechanism was revealed. It was possible to accurately measure the channel stress with the Raman test structure. The channel stress depends on the source/drain doping type and the second silicide annealing method. In order to discuss the channel stress generation mechanism, NiPt-silicide microstructure analyses were performed using X-ray diffraction analysis and scanning transmission electron microscopy. The channel stress generation mechanism can be elucidated by the following two factors: the change in the NiSi lattice spacing, which depends on the annealing temperature, and the NiSi crystal orientation. The analyses of these factors are important for controlling channel stress in stress engineering for high-performance transistors.

Analysis of Junction Leakage Current Failure of Nickel Silicide Abnormal Growth Using Advanced Transmission Electron Microscopy

This is the first paper to reveal the formation mechanism of the abnormal growth of nickel silicide that causes leakage-current failure in complementary metal-oxide- semiconductor (CMOS) devices by using advanced transmission electron microscope (TEM) techniques: electron tomography and spatially-resolved electron energy-loss spectroscopy (EELS). We reveal that the abnormal growth of Ni silicide results in a single crystal of NiSi2 and that it grows toward Si <;110> directions along (111) planes with the Ni diffusion through the silicon interstitial sites. In addition, we confirm that the abnormal growth is related to crystal microstructure and crystal defects. These detailed analyses are essential to understand the formation mechanism of abnormal growths of Ni silicide.

Annealing properties of open volumes in strained SiN films studied by monoenergetic positron beams

The effect of annealing on open volumes in strained SiN films deposited on Si by plasma enhanced chemical vapor deposition was studied using monoenergetic positron beams. For compressive SiN, the stress was reduced by postdeposition annealing; this effect was attributed to the relaxation of matrix structures accompanied by an expansion of small open spaces intrinsically existing in the matrix and the introduction of large open volumes. For tensile SiN, although annealing tends to decrease the concentration of large open volumes, the size of the small open spaces and the film stress were almost constant up to 1000°C annealing. This was attributed to the network structure related to the open spaces remaining stable even at 1000°C annealing, and this mainly determines the stress in the tensile film.

Vacancy-type defects in strained-Si layers deposited on SiGe∕Si structures probed by using monoenergetic positron beams

Vacancy-type defects in strained-Si layers deposited on Si0.75Ge0.25∕graded-SiGe∕Si structures were probed by using monoenergetic positron beams. The Doppler broadening spectra of the annihilation radiation and the lifetime spectra of the positrons were measured for samples before and after annealing (800–1050 °C). For an as-received sample, the defects in the strained-Si layer were identified as vacancy-type defects coupled with Ge. The mean open size of these defects was estimated to be close to that of a divacancy. The line-shape parameter, S, corresponding to the positron annihilation in the strained-Si layers decreased with increasing annealing temperature, but no large change in the positron lifetime was observed. From a comparison between the Doppler broadening profiles for the strained-Si films and those calculated using the projector augmented-wave method, it was found that the number of Ge atoms forming a complex by coupling with a defect increased with increasing annealing temperature. The numb...

Study of formation mechanism of nickel silicide discontinuities in high-performance complementary metal–oxide–semiconductor devices

We performed detailed analysis of nickel silicide discontinuities induced by agglomeration, which causes the increased electric resistance in high-performance complementary metal–oxide–semiconductor devices, by using advanced physical analysis techniques: transmission electron microscopy (TEM), scanning electron microscopy (SEM) electron backscatter diffraction (EBSD) analysis, and three-dimensional atom-probe (AP) analysis. We confirmed that the agglomeration of the nickel silicide is related to elongated-triangular-shaped splits, which cause discontinuities that occur at low-angle grain boundaries pinned by boron clusters even with small stress. We successfully determined the formation mechanism of these nickel silicide discontinuities in detail.