Jiro Ushio

Interface structures generated by negative-bias temperature instability in Si/SiO2 and Si/SiOxNy interfaces

We used a density functional method to investigate the mechanism of negative-bias temperature instability (NBTI) and resultant structural changes of Si/SiO2 and Si/SiOxNy interfaces. The reaction energies for the water- and hydrogen-originated instabilities of several interface defects show that water-originated reactions of oxygen and nitrogen vacancies occur most easily. The larger instability of the Si/SiOxNy interface, compared with the Si/SiO2 interface, can be understood in terms of the difference in reaction energies. According to the calculated nitrogen 1s core-level shifts of the nitrogen atoms at the Si/SiOxNy interface, it is possible to identify a NBTI-generated structure at the Si/SiOxNy interface by x-ray photoelectron spectroscopy.We used a density functional method to investigate the mechanism of negative-bias temperature instability (NBTI) and resultant structural changes of Si/SiO2 and Si/SiOxNy interfaces. The reaction energies for the water- and hydrogen-originated instabilities of several interface defects show that water-originated reactions of oxygen and nitrogen vacancies occur most easily. The larger instability of the Si/SiOxNy interface, compared with the Si/SiO2 interface, can be understood in terms of the difference in reaction energies. According to the calculated nitrogen 1s core-level shifts of the nitrogen atoms at the Si/SiOxNy interface, it is possible to identify a NBTI-generated structure at the Si/SiOxNy interface by x-ray photoelectron spectroscopy.

Effect of nitrogen at SiO2/Si interface on reliability issues—negative-bias-temperature instability and Fowler–Nordheim-stress degradation

Degradation process of a metal–oxide–semiconductor (MOS) structure with NO-nitrided SiO2 under negative-bias-temperature (NBT) and Fowler–Nordheim (FN) stresses has been investigated. The FN stress immunity improves with increasing nitrogen concentration at the SiO2/Si interface, while the incorporation of excess nitrogen (more than 3 at. %) at the SiO2/Si interface accelerates NBT instability (NBTI). This stronger immunity of NO-nitrided SiO2 under FN stress is due to the stronger Si–N bonds formed by NO nitridation at the interface. Without hydrogen annealing to form Si–H bonds, the MOS capacitors do not show NBTI. This indicates that the Si–N bonds are not broken under NBT stress and the main cause of the NBTI is the breaking of the Si–H bonds. The NO nitridation decreases the number of Si–H bonds and thus suppresses NBTI. However, nitrogen provides hole-trap centers. Hydrogen at the interface is dissociated and bonds to the hole-trapping nitrogen, so interface traps are left behind. An excess amount o...

A model for the segregation and pileup of boron at the SiO2/Si interface during the formation of ultrashallow p+ junctions

We have quantitatively investigated how boron segregates to regions close to the surface, and what controls this phenomenon, using x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and backside secondary ion mass spectrometry measurement techniques. We found that, contrary to the equilibrium segregation, the pileup of boron is mainly on and within 0.6 nm of the Si side of the interface, and that there is no difference between the kind of encapsulation. This also suggests that the pileup of boron is mainly on the Si side, and implies that the main factor in this segregation is the existence of the Si surface. From the viewpoint of device fabrication, this result seems to be useful in terms of the fabrication of sidewalls. The possibility of boron pileup to occurring in the interstitial state was also shown. Our results suggested a way of looking at dopant profiles by predictive computer modeling.

An atomic model of the nitrous-oxide-nitrided SiO2/Si interface

The interfacial structure of nitrous-oxide- (NO-)nitrided SiO2/Si is determined on the basis of the configuration of the Pb centers and the results of physical analysis. We used electron spin-resonance analysis to observe a decrease in the number of Pb centers after NO annealing, which corresponds to the decrease in the density of interface traps. The nitrogen bonds at the interface were analyzed by x-ray photoelectron spectroscopy. An asymmetric N 1s peak at around 398 eV was detected; the peak may be decomposed into two peaks with a binding-energy difference of 0.6 eV. This core-level shift originates in the difference between the numbers of oxygen atoms that are second-nearest neighbors of the nitrogen which terminates the Pb0 and Pb1 centers.

Ultraviolet-Curing Mechanism of Porous-SiOC

Utilizing the structure of porous SiOC determined in our previous study, we investigated a mechanism for improving the properties of porous SiOC film by ultraviolet irradiation (UV curing). The generation of a Si–O–Si cross link from an OH group and its adjacent CH3 group is the primary process in UV curing. This cross-link generation enhances mechanical strength of the material and lowers the dielectric constant. Decrease in the number of CH3 groups and increase in the number of Si–H bonds, both due to UV curing, cause slight increases in mass density and dielectric constant of the film.

INCORPORATION OF N INTO SI/SIO2 INTERFACES : MOLECULAR ORBITAL CALCULATIONS TO EVALUATE INTERFACE STRAIN AND HEAT OF REACTION

The determining factor for the accumulation of N at a Si/SiO2 interface during oxynitridation of the interface was investigated using a quantum-chemical method. Both mechanical and chemical factors (the interface strains and the heats of reaction of the oxynitridation) were considered. Though a slight relaxation of interface strain occurs when the interface has a certain type of oxygen-vacancy defect, we found the N incorporation does not relax the interface strain in most cases. The exothermicity and endothermicity of the oxynitridation reaction in the Si and SiO2 films, respectively, are the primary cause of the accumulation of N at the interface.

Subnitride and valence band offset at Si3N4∕Si interface formed using nitrogen-hydrogen radicals

The authors measured soft x-ray-excited angle-resolved photoemission from Si 2p, N 1s, and O 1s core levels, and valence band for nitride films formed on Si(100), Si(111), and Si(110) using nitrogen-hydrogen radicals with the same probing depth. The Si3N4∕Si interfaces formed exhibited an almost abrupt compositional transition. Furthermore, the crystal orientation of Si substrate affects the total areal density of subnitrides but not the valence band offset at the Si3N4∕Si interface.

Interface structures generated by negative-bias temperature instability in Si/SiO/sub 2/ and Si/SiO/sub x/N/sub y/ interfaces

Accordingly, we investigated possible NBTI mechanisms and resultant structural changes at Si/SiO/sub 2/ and Si/SiO/sub x/N/sub y/ interfaces. To determine if it is possible to identify a NBTI-generated structure through XPS of the interface, the N 1s core-level shifts of various structures at the Si/SiO/sub x/N/sub y/ interface were also evaluated. We further considered the important role of hydrogen to localize the hole trapped in the interface.

UV/EB Cure Mechanism for Porous PECVD/SOD Low-k SiCOH Materials

The mechanism of UV and EB cure processes for porous low-k SiCOH materials was investigated by using experimental results obtained using PECVD and SOD films as well as simulated results. Both UV and EB cures induced dielectric constant change and Youngs modulus improvement because Si-OH elimination (moisture removal) and cross-link formation occurred during film shrinkage. Excess UV curing, however, caused defects in the porous SiCOH film, as indicated by ESR analysis. The mechanism discussed in this work is applicable to most UV/EB cure systems and PECVD/SOD SiCOH materials for 45-nm-node Cu interconnects

Angle-resolved photoelectron study on the structures of silicon nitride films and Si3N4/Si interfaces formed using nitrogen-hydrogen radicals

Soft x-ray-excited angle-resolved photoemission results for nitride films formed using nitrogen–hydrogen radicals on Si(100), Si(111), and Si(110) are reported. The data were obtained using synchrotron radiation, which allowed the Si 2p, N 1s, and O 1s levels to be investigated with the same probing depth. The following main results were obtained: (1) the Si3N4 film is covered with one monolayer of Si–(OH)3N. Its areal density is 15% smaller on Si(111) than on Si(100) and Si (110), (2) the Si3N4/Si interfaces on all three surfaces are compositionally abrupt. This conclusion is based on the observation that no Si atoms bonded with three N atoms and one Si atom were detected, and (3) the observation that the number of Si–H bonds at the Si3N4/Si(110) interface is 38%–53% larger than those at the Si3N4/Si(100) and Si3N4/Si(111) interfaces indicates a dependence of the interface structure on the orientation of the substrate.Soft x-ray-excited angle-resolved photoemission results for nitride films formed using nitrogen–hydrogen radicals on Si(100), Si(111), and Si(110) are reported. The data were obtained using synchrotron radiation, which allowed the Si 2p, N 1s, and O 1s levels to be investigated with the same probing depth. The following main results were obtained: (1) the Si3N4 film is covered with one monolayer of Si–(OH)3N. Its areal density is 15% smaller on Si(111) than on Si(100) and Si (110), (2) the Si3N4/Si interfaces on all three surfaces are compositionally abrupt. This conclusion is based on the observation that no Si atoms bonded with three N atoms and one Si atom were detected, and (3) the observation that the number of Si–H bonds at the Si3N4/Si(110) interface is 38%–53% larger than those at the Si3N4/Si(100) and Si3N4/Si(111) interfaces indicates a dependence of the interface structure on the orientation of the substrate.