SiO2 Side Research Articles

An electrically detected magnetic resonance study of performance limiting defects in SiC metal oxide semiconductor field effect transistors

In this study, we utilize electrically detected magnetic resonance (EDMR) techniques and electrical measurements to study defects in SiC based metal oxide semiconductor field effect transistors (MOSFETs). We compare results on a series of SiC MOSFETs prepared with significantly different processing parameters. The EDMR is detected through spin dependent recombination (SDR) in most cases. However, in some devices at a fairly high negative bias, the EDMR likely also involves spin dependent trap-assisted tunneling (SDT) between defects on both sides of the SiC/SiO2 interface. At least three different defects have been detected in the magnetic resonance measurements. The defects observed include two at the SiC/SiO2 interface or on the SiC side of the SiC/SiO2 interface: one is very likely a vacancy center with a distribution which extends into the bulk of the SiC and the other is likely a “dangling bond” defect. A third defect, located on the SiO2 side of the SiC/SiO2 interface, has a spectrum very similar to that previously reported for an oxygen deficient silicon coupled to a hydrogen atom. In nearly all cases, we observe a strong dominating single line EDMR spectrum with an isotropic g≈2.0027. In some samples, this strong central line is accompanied by two pairs of considerably weaker side peaks which we link to hyperfine interactions with nearby Si and C atoms. The pattern is physically reasonable for a silicon vacancy in SiC. We therefore tentatively assign it to a silicon vacancy or silicon vacancy associated defect in the SiC. In one set of devices with very high interface trap density we observe another dominating spectrum with g∥=2.0026 and g⊥=2.0010 with the symmetry axis coincident with the [0001] and nearly the SiC/SiO2 interface normal. We ascribe this EDMR spectrum to a “dangling bond” defect. A third EDMR spectrum shows up in some devices at a fairly large negative gate bias. The phase of this spectrum is quite consistently opposite to that of the SDR detected EDMR at other biases. Part of this inverted phase spectrum involves two narrow lines which are separated by ≈10.5 G. Since the center responsible for this spectrum is almost certainly in the SiO2, it is likely due to the so called 10.4 G doublet center, an unpaired electron residing on an oxygen deficient silicon atom coupled to a hydrogen in SiO2. The likely presence of one oxygen deficient silicon defect suggests that other oxygen deficient silicon atom defect sites in the oxide may also be important in SiC/SiO2 devices. Oxygen deficient silicon defects in SiO2 are typically called E′ centers. Our results collectively demonstrate considerable complexity in both the chemical composition and physical distribution of performance limiting defects in SiC transistors, with defects observed on both sides of the SiC/SiO2 interface. Our results most strongly indicate that fairly high densities of intrinsic deep-level defects, likely due to a Si vacancy or a closely related defect, extend into the bulk of the SiC in all but one of the devices prepared utilizing a fairly wide range of processing parameters.

Interfacial reaction of Si islands on SiO2 during high-temperature annealing

We examine the interfacial reaction between submicron Si islands and SiO2 during high-temperature annealing under ultrahigh vacuum, using atomic force microscopy and transmission electron microscopy. We show that Si island/SiO2 interfaces are much more reactive than interfaces of wetting thin Si films on SiO2. This indicates that important processes responsible for the reaction occur at the Si island edges. During the reaction removal of O atoms from the SiO2 side of the interface occurs, resulting in depression of the Si island/SiO2 interface. Our observations indicate that the interfacial reaction advances via O out-diffusion from SiO2 into the Si island, O lateral diffusion along the interface, SiO formation at the edge of the Si island, and SiO desorption from the surface.

X-ray Microdiffraction Study on Crystallinity of Micron-Sized Ge Films Selectively Grown on Si(001) Substrates

Using X-ray microdiffraction with a focused beam size of about 0.4 × 1.0 μm2, we investigated the strain relaxation and crystallinity of Ge thin films with areas of 2 × 2 μm2 and 250 × 250 μm2 grown on Si (001) substrates with SiO2 standard shallow-trench-isolation patterning. Results showed slower progression of strain relaxation in the 2 × 2 μm2 Ge films compared to the 250 × 250 μm2 films, which can be attributed to the effects of the SiO2 side walls during annealing.

Physical origin of dipole formation at high-k/SiO2 interface in metal-oxide-semiconductor device with high-k/metal gate structure

A physical model on dipole formation at high-k/SiO2 interface is proposed to study possible mechanism of flatband voltage (VFB) shift in metal-oxide-semiconductor device with high-k/metal gate structure. Dielectric contact induced gap states (DCIGS) on high-k or SiO2 side induced by high-k and SiO2 contact are assigned to dominant origin of dipole formation. DCIGS induced interface dipole is considered to cause VFB shift through charge transfer effect. Based on the proposed model, directions of dipoles at several high-k/SiO2 interfaces are predicted, and magnitudes of dipoles are approximately calculated. Both directions and magnitudes are in agreement with the reported results.

Analysis of dielectric constant of a self-forming barrier layer with Cu–Mn alloy on TEOS-SiO2

A Cu–Mn alloy film was deposited on SiO2 to self-form a diffusion barrier layer of MnOx at their interface. Transmission electron microscopy revealed that the barrier layer was formed not on the Cu alloy side but on the SiO2 side. Capacitance-voltage measurement revealed the decrease in the dielectric constant of the barrier layer from 11.4 to 5.1 with increasing annealing temperature. The obtained results indicated that the self-forming barrier layer with Cu–Mn is an excellent barrier layer without posing any negative influences on the interconnect line resistance and on the insulator capacitance.

Light scattering and plasmon resonances in a metal film with sub-wavelength nano-holes

We report on a theoretical study of optical extinction in a metal film of 15–230 nm in thickness patterned periodically with sub-wavelength nano-holes of 140 nm in diameter. The gold plate was on a thick SiO2 wafer and the nano-holes as well as the top side of the metal plate were filled with water or solvent. Light was sent in toward the plate from the SiO2 side. The simulations were performed by solving the Maxwell equations using the scattering matrix method. It was seen that the extinction can, depending on the periodicity of the hole array, show one or several peaks in the visible wavelength range. The positions of the peaks were redshifted when the thickness of the gold plate was decreased. It was found that the peak positions for a thick plate can be identified from a simple surface plasmon dispersion relation.

Physical mechanism of effective work function modulation caused by impurity segregation at Ni silicide/SiO2 interfaces

An effective work function (Φeff) modulation caused by impurity doping in Ni-FUSI/SiO2 systems has been systematically investigated. To clarify the physical origin, we reveal the relationship between changes of Φeff modulation factors at gate electrode interfaces and Φeff modulation ranges (ΔΦeff) in two different doping processes (predoping and post-doping). In the predoping process, in which impurities (As or B) are implanted into polycrystalline Si gate before Ni fully silicided gate formation, both the crystal structure of the Ni silicide layer and the impurity concentration at the Ni silicide/SiO2 interface change depending on the impurity species. On the other hand, the impurity post-doping process, in which impurities are implanted and introduced to the Ni silicide/SiO2 interface after Ni silicide formation, makes it possible to introduce the desired amount of impurities into the interface without any structural change of the Ni silicide. In both cases, dependence of ΔΦeff on interface impurity concentration is almost the same, indicating that impurity segregation is the main cause of Φeff modulation. From the results of hard x-ray photoelectron spectroscopy and back-side x-ray photoelectron spectroscopy, the segregated As atoms, which change Φeff to lower values, are mainly located at the Ni silicide side of the Ni silicide/SiO2 interface. On the contrary, B atoms, which change Φeff to higher values, diffuse into SiO2 and are located at the SiO2 side of the interface. Based on these experimental results, we propose a physical model for Φeff modulation with impurity doping such that the position and concentration of impurity at the interface determine the direction and the extent of Φeff modulation with impurity segregation.

Nano-Scale Profile of the Dielectric Constant Near the Si/oxide Interface: A First-Principles Approach

Spatial variation in dielectric constants near the Si/SiO2 interfaces has been revealed using the first-principles ground-states calculations in external electrostatic fields. It has been shown that both the optical and the static dielectric constants change abruptly in the vicinity of the SiO2/Si interfaces, while the energy gap changes gradually on SiO2 side. These results indicate that the profile of dielectric constant is determined by the local polarization which directly reflects the local atomic arrangement. Dielectric properties of isolated ultra-thin Si(111), SiO2, and La2O3(0001) films have also been investigated. Both the optical and the static dielectric constants of oxide films hardly depend on the film thickness and the spatial variation of the local dielectric constant is also very small as contrasted to the semiconducting Si film.

Dielectric Properties of the Interface between Si and SiO2

We studied the electronic structure and dielectric properties of a SiO2(quartz)–(1100)/Si(001) interface, using first-principles ground-state calculations in a finite electric field. We evaluated the optical and the static dielectric constants for the stable SiO2/Si(001) interface model. Both the optical and the static dielectric constants change abruptly in the vicinity of the SiO2/Si interface, while the energy gap changes gradually on the SiO2 side. These results indicate that the profile of the dielectric constant is determined by the local polarization which directly reflects the local atomic arrangement.

Behavior of Si Interstitials and Boron-Interstitial Pairs at the Si/SiO2 Interface

ABSTRACTUsing density functional theory calculations within the generalized gradient approximation, we have investigated the structure, energetics, bonding, and diffusion behavior of Si interstitials and boron-interstitial pairs at the Si/SiO2 interface. We find that interstitials are significantly stabilized at the Si/SiO2 interface and prefer to reside on the SiO2 side rather than the Si side. Due to the interstitial stabilization, boron-interstitial pairs are likely to be easily dissociated in the vicinity of the Si/SiO2 interface. This study provides valuable insight into interstitial annihilation and boron precipitation at the interface.

Tight-binding model and electronic structure of tetrahedral zirconium silicate

We present a tight-binding model of Zr silicate in the limit that every Zr and Si atom is bonded to four O atoms. We view the material as being composed of small, relatively uncoupled collections of atoms, called bonding units, with stoichiometries SiSiO4 and ZrSiO4. The SiSiO4 bonding unit constitutes a model for pure SiO2, and the ZrSiO4 bonding unit represents the fundamental element distinguishing tetrahedral Zr silicate from pure SiO2. In the first part of this article we look at the electronic structure of “ideal” bonding units in which the O atoms are arranged in a perfect tetrahedron and the M–O–Si angle is 180° (M=Si or Zr). We find the valence levels of both bonding units to be dominated by O p states, and the lowest conduction levels of the ZrSiO4 bonding unit to derive primarily from Zr d states, whose energy depends sensitively upon the charge transfer to the O atoms. The energy gap of the ideal ZrSiO4 bonding unit is found to be 5.9 eV, compared to 8.0 eV for the SiSiO4 bonding unit. Finally, for the ZrSiO4 bonding unit, we present a simplification which allows the energy levels of the ZrSiO4 bonding unit to be obtained approximately in terms of decoupled Zr–O and Si–O interactions. In the next part of the article we investigate how bond angle and bond length distortions affect the electronic structure of the ZrSiO4 bonding unit. In particular, we note that significant distortions of the Zr–O–Si angle could produce Zr-based localized states that could act as traps for electrons tunneling through the material. In the last part of the article we discuss the basic principles governing band lineups for Si/silicate interfaces constructed by substituting Zr atoms for Si atoms on the SiO2 side of crystalline Si/SiO2 interfaces. We calculate the band lineups as a function of Zr concentration for one particular interface.

Direct observation of Si lattice strain and its distribution in the Si(001)–SiO2 interface transition layer

In the transition layer of the Si(001)–SiO2 interface, Si lattice strain and its distribution were directly observed by medium energy ion scattering spectroscopy for thermal and ion beam oxides. The strain was in the vertical direction, and the maximum values at the SiO2 side of the transition layer were 0.96% and 2.8% for the thermal and ion beam oxides, respectively.

Diffusion and Segregation of Carbon in SiO2 Films

Diffusion of carbon in SiO2 films and its segregation at the Si/SiO2 interface were investigated using carbon-incorporated borophosphosilicateglass (BPSG) films and carbon-implanted SiO2 films. It was found that carbon atoms diffuse in SiO2 film at a temperature as low as 500° C. Carbon atoms segregated at the Si/SiO2 interface and induced positive charge. The positive charge density was proportional to the segregated carbon concentration. Field emission transmission electron microscopy (FE-TEM) and electron energy loss spectra (EELS) observations revealed that carbon atoms exist on the SiO2 side of the interface, and another carbon-rich phase is formed in SiO2.

ＳｎＯ‐ＳｉＯ２系状態図に関する基礎的研究

In the pyrometallurgical treatment of tin, it is necessary to identify the proper chemical composition of slag based on the thermodynamic behavior and phase diagram for decreasing of tin losses with effective recovery of tin from slag. Although some studies were reported about the phase diagram of SnO-SiO2 binary system, which is basic system of slag in the tin smelting, those results show always disagreement. W hereas it is necessary to consider closely the stability of solid SnO with increasing in temperature when the specimen contains SnO component, because solid SnO decomposes easily by a disproportionation with increasing in temperature.In the present study, firstly, the disproportionation of solid SnO with increasing in temperature was examined, and then the liquidus of SnO-SiO2 binary system was also investigated by SnO or SiO2 saturation method.Furthermore the influence of CaO and FeO addition on the liquidus in SnO-SiO2 system was investigated. The results obtained were summarized as follows:Solid SnO decomposed with increasing in temperature in the following manner: SnO→Sn, SnO, Sn3O4→Sn, Sn3O4→Sn, Sn3O4, SnO2→Sn, SnO2.It was confirmed that the phase diagram of SnO-SiO2 system is an eutectic type and the rising of liquidus at SiO2 side is very sharp. And it was thought to be appropriate that a metasilicate phase, such as SnO·SiO2is existed in this system, and it seemed metastably intermediate product.The melting point of SnO-SiO2 system raised by CaO addition, while it lowered by FeO addition.

The correlation between selective oxide etching and thermodynamic prediction

This article will report the qualitative connection between chemical predictions based on thermodynamics and the selective oxide etching in a hot wall commercial high-density plasma system. The relationship between the experimentally observed protective carbon-based deposit on nonoxide surfaces such as Si and the theoretically predicted selective deposition of carbon will be explored. While carbon is deposited on both Si and SiO2, the oxygen in the SiO2 leads to the ion-enhanced removal of this deposited carbon so that plasma etching of the oxide can continue. It will be shown that CO gas and the chamber/wafer temperature play a major role in this carbon deposition. The chemical role of H in increasing this deposit will also be examined. The model predicts that the carbon deposition increases exponentially with chamber temperature, and that this deposition occurs only on the nonoxide underlying layer at the bottom of the contact. This is consistent with the experimental observation that increasing chamber temperature increases the protective deposition on the underlying Si, but does not deposit on the SiO2 side walls and change their angle. This is not to suggest that such a simple thermodynamic model can quantitatively explain all of the observed effects, but it clearly is very effective in understanding the qualitative dependence on such ‘‘chemistry’’ process parameters as temperature, gas flow, and chemical composition.

Determination of phosphorus distribution in the region of a SiO2−Si interface by substoichiometric analysis

A simplified method for the substoichiometric analysis of phosphorus has been developed and applied to determine the concentration distribution of phosphorus in the region of a SiO2−Si interface in order to explain why phosphorus is lost from the ion-implanted silicon surface throughout the oxidation and oxide removal processes. It is revealed that phosphorus piles up on the SiO2 side at the interface by the thermal oxidation of silicon surface and is removed with the oxide by wet etching and with the resulting silicon by RCA cleaning. This results in a total loss of ion-implanted phosphorus of 3.5%.

A novel x-ray photoelectron spectroscopy study of the Al/SiO2 interface

We report on the first nondestructive measurement of the chemical and physical characteristics of the interface between bulk SiO2 and thick aluminum films. Both x-ray photoelectron spectroscopy (XPS) and electrical measurements of unannealed, resistively evaporated Al films on thermal SiO2 indicate an atomically abrupt interface. Post metallization annealing (PMA) at 450 °C induces reduction of the SiO2 by the aluminum, at a rate consistent with the bulk reaction rate. The XPS measurement is performed from the SiO2 side after the removal of the Si substrate with XeF2 gas and thinning of the SiO2 layer with HF:ETOH. This represents a powerful new approach to the study of metal-insulator and related interfaces.

XPS Study of the Al/SiO2 Interface Viewed From the SiO2 Side

ABSTRACTWe report on the first non-destructive measurement of the chemical and physical characteristics of the interface between bulk SiO2 and thick aluminum films. Both X-Ray Photoelectron Spictroscopy (XPS) and electrical measurements of unannealed, resistively evaporated Al films on thermal SiO2 indicate an atomically abrupt interface. Post metallization annealing (PMA) at 450°C induces reduction of the SiO2 by the aluminum, resulting in the layer ordering SiO2/Al2O3/Si/Al. The XPS measurement is performed from the SiO2 side after the removal of the Si substrate after etching with XeF2 gas and thinning of the SiO2 layer with HF:ETOH. This represents a powerful new approach to the study of metal-insulator and other interfaces.

Vapor Transport Reaction of MgO and SiO<sub>2</sub>

Vapor transport reaction of sintered polycrystalline MgO and quartz glass was examined using vapor transport couple. MgO and SiO2 were separated by 0.1mm platinum wire and firing was carried out at 1400°C for 24hrs.X-ray examination of the surface of MgO and SiO2 did not establish the development of reaction product. However, electron microprobe X-ray analysis proved the vapor transport of Si (or Si oxide) to the surface of MgO as well as that of Mg (or MgO) to the surface of SiO2. In addition, it was found that the amount of Si on the MgO surface was considerably larger than that of Mg on the SiO2 surface.Previous study using MgO-SiO2 contact diffusion couple indicated that the reaction product mainly developed on the SiO2 side. Therefore, it will be concluded that vapor transport did not play an important part on the development of the reaction product in the solid state reaction.Platinum wire had an shielding effect on the vapor transport of Mg, but, on the other hand, there was evidence of the rapid movement of MgO toward SiO2 along the surface of platinum wire.

Kinetics and Mechanisms of Formation of Enstatite by Solid State Reaction of Forsterite and SiO<sub>2</sub>

The development of enstatite by solid state reaction in mixed powders of forsterite and SiO2 in various mole ratios at the temperature range 1150°-1350°C and for times up to 580 hrs is followed by quantitative X-ray measurements. Powders are used consisting of coarse (mostly 10μ) particles of one component in a fine-grained (mostly 1μ) matrix of the other component. Although the results are not precisely consistent with a diffusion-controlled mechanism, the rate of reaction is estimated to be about one-third (or even smaller) of that of MgO-SiO2 reaction.Studies, using mixed powder, indicate the development of enstatite on the forsterite side as well as on the SiO2 side, suggesting that one MgO of 2MgO⋅SiO2 reacts with SiO2. Mg is believed to be the main diffusing species.The results of firing in vacuum suggest that the reaction is possibly controlled by the diffusion of Mg ion through the enstatite.Putting all results obtained by our previous and present works together, the rate of reactions of the systems containing MgO and SiO2, i.e. MgO-SiO2, MgO-MgO⋅SiO2 and 2MgO⋅SiO2-SiO2, is conceivable to be controlled by the diffusion of Mg through the reaction product layer (s).