[en] Chemical and radiation-enhanced gas-solid etching of materials that are important in microelectronics, fusion and space technologies, are compared and reviewed. The basic processes that drive spontaneous etching of several etchant-material combinations are similar: F/Si, H/Si and H/C can be cited as examples. On the other hand, many etchant-material systems appear to involve system-specific processes that should not be generalized: examples are the XeF₂/Si and Cl/Si systems. Experiments show that chemical etching is generally enhanced when the flux of thermalized active species to surfaces is accompanied by energetic particle or photon bombardment. In microelectronic materials etching, investigators have systematically studied etching product yield and product kinetic energy as a function of ion mass, ion energy and angle of incidence; data on temperature dependence of etching are more limited. By contrast, the temperature dependence of etching C and C-composites in fusion technology has been studied extensively, but there is a lack of data on ion mass and angle dependence, and on the kinetic energy of products. There appears to be no comparable data on ion-assisted etching of materials in typical space environments. These fundamental parameters are essential for formulating and testing models of ion-enhanced etching chemistry. The available data are discussed in terms of phenomenological models and calculations that have been developed. It is clear that further work will be required to provide a solid understanding of the phenomena discussed in this review. 86 refs., 16 figs

[en] Experimental results are presented on the trapping of sub-eV hydrogen and deuterium atoms in pyrolytic graphite (irradiated in the c direction) and papyex. Measurements were made by thermal desorption spectrometry, with the D(³He,p)⁴He nuclear reaction analysis being used in some cases to check the validity of the thermal desorption results. Although some variation exists in the magnitude of trapped fluences for the different cases studied, the shapes of the trapped fluence vs. incident fluence curves are similar. The trapped fluences of sub eV D⁰ are about an order of magnitude lower than those obtained for 50 eV D⁺ ions, with a trend to saturation for fluences > 2 x 10¹⁹/cm²

[en] Retention levels for sub-eV D⁰ atoms in single crystal and pyrolytic graphite were measured using a newly-developed Laser Thermal Desorption (LTD) technique. Retention levels for single crystals were approx. 3 x 10¹³ D⁰/cm² for incident fluences of approx. 10¹⁹D⁰/cm². This is about two orders of magnitude lower than D⁰ retention in pyrolytic graphite, and correlates very well with the differences in effective surface areas. The D(³He,p)⁴H/sub e/ Nuclear Reaction Analysis (NRA) was used to confirm retention levels as measured by the LTD technique. A further finding was the influence of a small layer of evaporated tungsten on the sample surface. Such W impurity resulted in an increase of D⁰ retention of up to a factor of ten

[en] In an attempt to lower radiation losses due to metal plasma impurities in the JET fusion device, the use of low-Z wall coatings has been proposed (Si, TiC, SiC, TiO₂, Al₂O₃ and MgAl₂O₄ on Inconel 600). This report presents experimental results obtained by exposing these samples to electron, laser radiation and atomic hydrogen impact. The studies performed include measurements of (i) gases evolved due to low energy (300 eV) electron bombardment, (ii) inherent gas content in the near-surface region, and (iii) retained deuterium subsequent to exposure sub-eV D⁰. Also described is the Laser Release Analysis technique which has been developed to enable us to perform the last two sets of measurements. Electron impact desorption rates for hydrogen and methane due to electron bombardment span the range 10^-1 to 10^-3 H₂/e^- and 10^-2 to <10^-4 CH₄/e^-. Following normal system bakeout at 500 K for 24h, the major species released by laser heating were found to be H₂ and CO, with levels up to ∼7x10¹⁶ H/cm² and ∼4x10¹⁶ CO/cm². A similar concentration of argon was found for the TiC coating produced by sputter ion plating. Further heating of the samples to 800-900K for 1h resulted in a reduction of hydrogen and CO release levels by about an order of magnitude. Subsequent to the 800-900 K heating procedure, the samples were exposed to sub-eV D⁰ atoms to fluences of ∼2x10¹⁹ D⁰/cm², and deuterium retention levels were measured to be of the order of 10¹⁴ - 10¹⁶ D/cm² for the various coatings. Implications of these results for JET's first-wall tritium inventory are discussed. 23 refs

[en] Conducting diffusion barrier layers play a critical role in high-density memory integration. We recently demonstrated that Ti--Al can be used as a diffusion barrier layer for the integration of ferroelectric capacitors with complementary metal--oxide semiconductor devices for the fabrication of nonvolatile ferroelectric random access memories (NVFRAMs). Here, we discuss results from systematic studies designed to understand Ti--Al film growth and oxidation processes using in situ ion beam sputter deposition in conjunction with complementary in situ atomic layer-resolution mass spectroscopy of recoil ion (MSRI) and surface sensitive x-ray photoelectron spectroscopy (XPS). The concurrent MSRI/XPS analysis revealed that amorphous Ti--Al layers produced by tailored sputter-deposition methods are resistant to oxidation to at least 600^oC, and that oxidation occurs only when the a-Ti--Al layers are exposed to oxygen at >600^oC, via the segregation of Ti species to the surface and TiO₂ formation. The a-Ti--Al layers discussed in this letter could be used in the double functionality of a bottom electrode/diffusion barrier for the integration of ferroelectric capacitors with Si substrates for the fabrication of NVFRAMs and other devices. Copyright 2001 American Institute of Physics

[en] Electron emission from bulk Pt/PZT/Pt and RuO₂/PZT/RuO₂ ferroelectric cathodes is reported. The total emission current (0.8 A) and polarization fatigue are high for ferroelectric cathodes with Pt electrodes, while emission current (0.18 A) and polarization fatigue are significantly lower for cathodes with RuO₂ electrodes. The data correlate with earlier results from research on ferroelectric memories, which suggest that oxygen vacancies near the electrode/ferroelectric interface and through the bulk of the ferroelectric layer play a major role in controlling the polarization switching of PZT-based capacitors and consequently in controlling the electron emission process in PZT cathodes. The strong correlation between polarization fatigue and emission observed in the present investigation provides evidence for the role of polarization inversion on the electron emission phenomenon. In addition, the data provide evidence for the role that oxygen vacancies play in controlling electron emission from PZT cathodes

[en] The two most important phenomena relating to ion bombardment modification of surfaces are sputtering and ion implantation. In spite of their similar degree of relevance, the evolution in the understanding of the underlying mechanisms has been quite different. A historical overview of the main advances in the understanding of ion bombardment modification of surfaces, due to erosional and depositional phenomena is presented. (Auth.)

[en] An historical overview of the main advances in the understanding of ion bombardment modification of surfaces, due to erosional and depositional phenomena is presented. 176 refs.; 13 figs.; 1 table

[en] A critical analysis on the origin, stability, relative sputtering yield and related phenomena of surface texturing under ion bombardment, is presented in an attempt to clarify some 'apparent' discrepancies in the experimental results reported by different groups. It is shown that clean surfaces under ion bombardment develop cones and/or pyramids mainly from surface discontinuities reshaped by the irradiation. The discontinuities result from either sub-surface defects which are preferentially eroded with respect to neighbour areas or by pre-existing and/or bombardment-induced asperities with convex-up curvature. It is shown additionally, that the impurity-induced mechanism for pyramid development, on surfaces seeded with atoms other than those of the substrate, may involve the formation of asperities as a necessary first step. Therefore, the impurity-induced mechanism may not be a different alternative. On the other hand, it is shown that seed materials need not possess lower sputtering yield than the substrate in order to generate pyramids. It is shown that the reduced or enhanced sputtering yield of textured surfaces with respect to smooth surfaces of the same material, as observed by different groups, might reflect the behaviour of the textured surfaces under different irradiation conditions. (author)

[en] The texturing of surfaces by ion bombardment of chemical vapor deposition (CVD), particularly the formation of conical and/or faceted structures, has been extensively studied both from the theoretical and experimental points of view during recent years. A relatively high feed-back between basic and applied research has been the main driving force behind the rapid growth in the understanding of the underlying mechanisms of surface texturing, and in the number of technologies and experimental techniques in which these surfaces have been shown to be important and/or useful. It has been shown (O. Auciello, J. Vac. Sci. Technol., 19 (1981) 841) that textured surfaces are already used in some technologies, have the potential to be useful in others, and are relevant either on a detrimental or beneficial basis in different experimental techniques. (Auth.)