Ion bombardment conditions

The properties of silicon dioxide films also depend upon all plasma deposition parameters. Temperature is the critical parameter (240), although the compressive stress level varies with rf frequency (237, 240). Film topography can be varied during deposition by altering ion bombardment conditions (242, 243). In particular, the incorporation of Ar in the deposition atmosphere enhances sputtering and thus promotes conformal step coverage during film formation (243). 

Ion Bombardment Conditions. A base pressure of 10 9 Torr is maintained in this chamber the noble gas pressure (He, Xe) rises to about 10"7 Torr during the ion bombardment. The ion beam is rastered on (1.5 x 1.5) mm2 areas at normal incidence 4He-2 keV ions are used for the ISS analysis when Xe-4 keV ions are used for SIMS. The incident ion current is measured with the aid of a moveable Faraday cup. Since the investigated samples are electrical insulators, charge neutralization is performed with low energy electrons ( 10 eV) emitted from a heated W filament. 

It is of Interest at this point to add as a footnote to this work that we have found that for films formed under enhanced ion bombardment conditions (l.e., substrate biased... 

The chemical and electronic properties of elements at the interfaces between very thin films and bulk substrates are important in several technological areas, particularly microelectronics, sensors, catalysis, metal protection, and solar cells. To study conditions at an interface, depth profiling by ion bombardment is inadvisable, because both composition and chemical state can be altered by interaction with energetic positive ions. The normal procedure is, therefore, to start with a clean or other well-characterized substrate and deposit the thin film on to it slowly at a chosen temperature while XPS is used to monitor the composition and chemical state by recording selected characteristic spectra. The procedure continues until no further spectral changes occur, as a function of film thickness, of time elapsed since deposition, or of changes in substrate temperature. 

Local Thermodynamic Equilibrium (LTE). This LTE model is of historical importance only. The idea was that under ion bombardment a near-surface plasma is generated, in which the sputtered atoms are ionized [3.48]. The plasma should be under local equilibrium, so that the Saha-Eggert equation for determination of the ionization probability can be used. The important condition was the plasma temperature, and this could be determined from a knowledge of the concentration of one of the elements present. The theoretical background of the model is not applicable. The reason why it gives semi-quantitative results is that the exponential term of the Saha-Eggert equation also fits quantum-mechanical expressions. 

Also a frequency dependence was observed, especially in Voc, which was not expected from the material study. As only the deposition conditions of the i-layers are varied, a change at the p-i interface must be responsible for the change in Voc- The lower value of Vqc at low frequency was attributed to the difference in ion bombardment at the p-i interface [493]. 

FIG. 70. Voltammograms on an argon ion-bombarded, annealed CdTe( 100) surface in 50 mM K2SO4 pH = 5.6 (A) reduction from the open circuit potential to —2.0 V (B) oxidation from the open circuit potential to -1-0.30 V and reversing to —0.55 V, under illuminated conditions (C) reduction following (B) from open circuit potential to —1.8 V and reversing to —0.50 V. 

The conditions required for the construction of these cells place considerable strain on the phosphors. This is because setting up the transparent electrodes requires annealing in the range 500-600 °C. Additionally the phosphors must be able to stand the constant ion bombardment from the plasma and VUV radiation. Most importantly, the phosphors must convert the VUV into visible light with maximum... 

It should be noted that dielectric and optical properties of the near-the-surface layer of a semiconductor, which vary in a certain manner under the action of electric field, depend also on the physicochemical conditions of the experiment and on the prehistory of the semiconductor sample. For example, Gavrilenko et al (1976) and Bondarenko et al. (1975) observed a strong effect of such surface treatment as ion bombardment and mechanical polishing on electroreflection spectra. The damaged layer, which arises in the electrode due to such treatments, has quite different electrooptic characteristics in comparison with the same semiconductor of a perfect crystalline structure (see also Tyagai and Snitko, 1980). 

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