We show that a careful examination of previous microscopic structural data from the Si/SiO2 interface reveals that the presence of an epitaxial interfacial oxide cannot be ruled out, and describe the conditions necessary for a definitive search for an intervening layer between c-Si and a-SiO2 We present electron diffraction and lattice imaging data, which establish the c-Si→a-SiO2 transition to take place via a crystalline layer ˜7 A thick. Modelling of lattice images in two projections indicates the crystalline oxide to be tridymite, a stable, bulk phase of SiO2

A dominant, intrinsic chemical reaction path in SiO2/Si systems is the decomposition reaction Si +SiO2 → 2 SiO. Controlled analytical studies have elucidated the microchemical and microstructural aspects of this process and revealed that nucleation of the reaction occurs at existing defect sites. At an earlier stage of reaction, the same decomposition chemistry leads to electricl activation of the defects, as seen in breakdown and hole trapping phenomena. By careful and systematic control of ambient conditions during annealing, it is shown that the evolution of electrically active defects follows the same decomposition chemistry as does the physical deterioration of an entire oxide layer. These aspects of defect chemical behavior suggest implications for both defect identification and defect control in thin SiO2 layers on Si.

The use of intense photon beams to initiate silicon oxidation is reviewed. In particular, recent experiments involving visible photons are discussed, which confirm a thermal domination and a clear photon enhancement. With equal powers of 488 and 514 nm radiation, the latter initiates faster reaction rates. Structural studies of the films are also reported using IR spectrometry, where we find broad similarities and intriguing differences the between laser and furnace grown films.

We present STM and photoemission studies of the reactions of Si(100)-(2×1) and Si(111)–(7×7) with NH3. STM allows us to image the occupied and unoccupied states of the reacting systems and to obtain electronic spectra with atomic lateral resolution. Thus, for the first time, a surface chemical reaction can be probed at the atomic level. We find that both surfaces are reactive even at 100K. However, both the extent of the reaction and the reaction products at 300K are different on the two surfaces. STM also shows that while surface dangling bonds are essential for low-temperature reactivity, not all triplycoordinated Si sites are chemically equivalent. On the 7×7 surface the rest-atoms are more reactive than center-adatoms which, in turn, are more reactive than corner-adatoms.

We have recently determined that anomalously low diffusion of high dose As implants in SiO2 is caused by phase separation. In an inert ambient, As segregates into spherical As-rich droplets of 50 to 500Å in diameter, which are essentially immobile when heated isothermally, even at 1405 °C. In a temperature gradient the droplets move toward the heat source.

The dependence of the segregation rate, drift, and diffusion on-the ambient and arsenic concentration is discussed here, and a new interpretation of the published arsenic diffusion data is provided.

The photo-chemical vapor deposition (CVD) of SiO2 and SiN2 were investigated using 185 nm light of a low pressure mercury lamp. The film thickness deposited on the substrate was the function of the distance from the substrate to the light source and its relation was investigated by changing the reaction pressure. From these investigations, the space migration length of the active species was estimated, which was, at the processing pressure of 400 Pa, about 10–20 mm. This migration length was confirmed by a model calculation. The step coverage of the film was investigated by the use of a two-dimensional capillary cavity. It was shown that the thickness decayed exponentially with the depth in the cavity. The decay constant did not show temperature dependence. From this result, the surface migration of the active species produced by photo-CVD was reported. To confirm this migration we presented a substrate- size effect of photo-CVD, which became obvious when the substrate size became smaller than the space migration length of the active species. From these results, the film growth mechanism of photo-CVD was discussed.

As silicon-based technologies move towards submicron dimensions, vertical and three dimensional structures, the need for reduced thermal processing becomes more evident than ever. Currently, insulator (usually SiO2) growth and deposition contribute significantly to the total thermal budget, and it is clear that this will have to be reduced in future processes. In addition, many other applications require the deposition of high quality dielectrics at very low substrate temperatures, typically ≳ 350°C. Plasma-enhanced chemical vapor deposition (PECVD) is a technique which can be used to deposit insulators at suitably low temperatures, although it tends to produce SiO2 which exhibits poor electrical and physical properties and which forms poor interfaces with semiconductor substrates. Direct exposure to the high energy environment of the plasma is generally thought to be the main reason for this.

This paper describes Optical Emission Spectrocopy (OES) and Mass Spectrometry (MS) studies of the plasma region in the Remote Plasma Enhanced Chemical Vapor Deposition (PECVD) of amorphous hydrogenated silicon (a-Si:H) and silicon oxide thin films. In Remote PECVD, only the O2/He mixture is plasma excited, silane is introduced into the deposition chamber well below the plasma region. Deposition of films has been studied over a wide range of relative He and O2flows, between 100% He and 100% O2. The incorporation of SiH in the oxides derives from the same mechanism as the deposition of a-Si:H, i.e., a metastable He induced fragmentation of silane.

Our Present Understanding of the Mechanisms of the transformation of SiO films under treatments in O2 or Ar plasma at room T, is presented. RBS, IR absorption, XPS, RHEED and TEM techniques have been used to investigate the composition, the chemical and structural nature of the films after oxidizing or non oxidizing treatments. In O2 plasma, SiO is converted into Si02 by room T plasma anodization. The initial step of SiO oxidation, which is believed to be the transformation 2SiO→Si+SiO2, was studied in Ar plasma. We show that the as deposited SiO (not a mixture of Si and SiO2) is subject to disproportionate into the later compounds and that the effects of irradiation by low energy electrons at room T (plasma treatment) are similar to those observed for high T treatments (rapid thermal annealing).

The effects of Si implantation (2×1015 · cm-2) on the diffusion of Sb in Sb doped silica (SiO2) spin-on layers and on their hardness were studied. RBS analysis and AES depth profiling showed that the implantation greatly retarded the Sb diffusion (1000–1200°C, 10 sec) in the oxide layer. Hence the high level of Sb near the SiO2/Si interface, which is clearly seen for the unimplanted part of the sample was not noticible in the non implanted part. AES depth profile measurements also showed that the deposited oxide layers were more sputter resistant as a result of the implantation. The above observations are related to the ion induced radiation damage.

Effects of post-well drive intrinsic gettering (PWIG) upon the integrity of thin gate oxide in Cz Si wafers with carbon levels, Cs, ranged from 0.2 - ∼ 4 ppma were investigated. A 10 nm thick gate oxide capacitor was used to study its time-dependent breakdown characteristics and minority carrier lifetime. Our data have shown that PWIG cycles and/or carbon impurity affect both bulk oxygen precipitation and minority carrier lifetime, but not the oxide integrity.

In this paper we present a comparison of the physical and electrical properties of high quality insulating thin films of silicon dioxide produced at low temperatures by three methods; standard plasma enhanced CVD of silane/nitrous oxide, photo enhanced CVD of silane/nitrous oxide using a novel internal nitrogen discharge lamp, and oxygen plasma anodisation.

The electrical and interface properties of the films, obtained from current-voltage and capacitance-voltage measurements are compared. The physical properties and composition of the films have been investigated by standard methods such as ellipsometry and p-etch rate, and spectroscopic techniques such as Auger, XPS, LIMA and Infrared absorption. The results of these investigations are reported.

The effects of low temperature annealing on the film properties have been examined and the suitability of each of the fabrication techniques to a variety of applications is discussed.

Three new reactions for depositing silicon dioxide at low temperatures using vacuum ultraviolet and ultraviolet radiation to initiate a reaction between silane and nitrogen dioxide have been developed. The optical and electrical properties of these films are reported. The effect of ion implantation on the infrared spectra of oxides grown by vacuum ultraviolet irradiation is also presented.

We have constructed an Ultra High Vacuum (UHV) multichamber system and have deposited ‘gate quality’ silicon dioxide by the remote plasma enhanced chemical vapor deposition (Remote PECVD) process at low substrate temperatures (Ts ≤400 °C). Native oxides and other surface contaminants are removed under ultra high vacuum (UHV) conditions and the character of the semiconductor surface is determined prior to film deposition using in-situ Reflection High Energy Electron Defraction (RHEED). Measurents made on MOS structures of capacitance-voltage, current-voltage, field break-down, hysteresis, and mobile ion drift indicate that these films are ‘comparable’ to thermally (Ts >1100 °C) grown oxides. The structural properties of the films arg studied by ir spectroscopy and ellipsometry.

A mechanistic study of the deposition of silicon oxide films (SiOx, 0 < x ≤2) from silanes with nitrous oxide was performed. The depositions of non-stoichiometric films from silane and stoichiometric silicon dioxide from disilane were dominated by SiH2 generation from the decomposition of the silicon-containing reactant. The depositions of stoichiometric films from silane were found to follow chain reaction kinetics initiated by the homogeneous decomposition of N2O.

The bulk and interfacial chemistry of a microwave plasma deposited SiO2 film has been studied. The SiO2 was deposited on single crystal Si<100> using a plasma enhanced chemical vapor deposition (PECVD) technique. The deposition was accomplished by injecting 2% SiH4 in helium downstream of a N20 microwave-generated discharge. Materials properties of these films were characterized using a combination of surface analytical techniques: Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS). The width of the interface was determined by AES-depth profiling to be less than 5.0 nm. Normal and grazing-angle XPS measurements indicated the presence of unique N and Si chemical species at the SiO2/Si interface. The SIMS data confirmed the presence of interfacial and bulk nitrogen, as well as detecting the presence of hydrogen and fluorine in the bulk oxide. The relationship between the analytical results and electrical data, obtained using MOS structures fabricated from the deposited oxide, will be discussed.

Based upon the linear-parabolic growth model of silicon oxidation, accurate kinetic rate constants are determined for various crystallographic orientation wafers in the 900 −1100°C range. The parabolic rate constant is independent of substrate orientation above 1000 °C, while, at 900°C, it depends on the orientation of the underlying substrate. The behavior of the parabolic rate constant at low temperature can be explained by accounting for Si-O bond-breaking due to stress during the oxide growth. The linear rate constant is observed to depend on the crystallographic orientation of the silicon surface in all temperature range. The orientation dependence of the linear rate constant is explained by both strain relaxation of the oxide film and areal atomic density of silicon at the silicon/oxide interface.

The interaction of O2(g) with clean Si(s) surfaces at high temperature and low pressure leads to an etching reaction, 1/2 O2(g) + Si(s) → SiO(g), which results in the evolution of SiO molecules from the surface. Above a critical O2 pressure, an oxide film SiO2(s) begins to grow. The evolution of diatomic SiO during the early stages of film growth may provide a mechanism to account for deviations from standard models of oxidation kinetics for thin oxides, and for the results of oxygen isotope tracer studies of oxide formation. In order to monitor the rate of SiO evolution, we have made in-situ measurements of the SiO concentration in the gas phase, using a laser-induced fluorescence technique. With this method, SiO(g) can be monitored in the furnace with good spatial resolution and a sensitivity limit of ˜ 106 molecules cm−3. Measurements of SiO evolution and the implications for oxide growth will be discussed.

This paper represents a study of the local atomic structure of SiO2 films formed by thermal oxidation in dry oxygen, pyrolytic steam, and a variety of different sequences of these ambients. All oxidations were carried out at 850 °C. Local atomic structure was studied via infrared spectroscopy (IR). The growth ambient dependence of the frequency v, and half-width Δv, of the bond stretching feature, and the refractive index, n, was investigated. Consistent with previous work [1,2] it was found that.when the majority of the sample thickness was grown in steam the oxides were generally less dense than dry oxides. Also, the last ambient in a sequential oxidation process was found to have the most influence on the oxide properties. The observed variations in v, Δv, and n could be readily explained in terms of systematic changes in the bond angle at the oxygen bonding site between corner connected tetrahedra.

The most intense feature in the infrared spectrum of SiO2 is the “νas band” near 1070 cm-1. Assigned to the asymmetric stretching mode, this peak exhibits a shoulder on the high frequency side of the band. In this study, Fourier transform infrared (FTIR) spectrophotometry is used to examine the effects of overlying, unpatterned layers of undoped polysilicon (poly) and of tungsten silicide (WSi) upon 0.08 μm of themal oxide grown on silicon. For the poly studies, the oxide is grown on both sides of double-side-polished wafers. 0.11 μm of poly is then deposited on each side of half of the set; 0.25 μm, on the remainder. For the WSi studies, 0.21 μm of undoped poly is deposited onto oxide grown on single-side-polished, low-oxygen wafers. WSi is then deposited on one side.

For the poly set, the peak position (PP) of the “νas band” shifts from 1074 to 1071 to 1066 cm-1 when comparing the uncoated oxide, 0.11 μm poly/oxide, and 0.21 μm poly/oxide samples, respectively. As a result of the observed shifts, the high frequency shoulder becomes resolved as a broad, weak band centered near 1168 cm-1. Thus, the “νas band” appears to be a doublet, consisting of a weak high-frequency component that is insensitive to, and an intense low-frequency component that is sensitive to. overlying films. For the WSi set, the PP of the “νas band” shifts from 1068 to 1076 to 1083 cm-1 for the poly/oxide, WSi/poly/oxide, and annealed-WSi/poly/oxide samples, respectively. Possible causes for the doublet character of the “νas band” and mechanisms for the film-film interactions, such as hydrostatic pressure, are discussed.