Residual stress in thin silicon dioxide films has been studied as a function of storage time. Films of varying microstructure and impurity content were deposited by plasma-enhanced chemical vapor deposition. Initially, all the films exhibited compressive stress, the magnitude of which was found to increase rapidly with time for the first few hours after deposition. For all the deposited thin films, this increasing compressive stress eventually saturates and then begins to decrease with time. The time at which the transition occurs depends on film thickness and quality, whereas, for relatively thicker films deposited under identical conditions, a saturation in compressive stress after long aging time was observed. No existing model of thin oxide films successfully explains the observed time variation of stress. In this paper, the variation of film stress as a function of storage time and film properties, such as porosity and impurity content, is discussed. Three driving forces, namely, surface reactivity, silanol buildup, and water dipole interaction, each of whose contribution varies depending on film thickness and quality, have been identified as potential mechanisms behind stress change in oxide films. A unified model consisting of these driving forces can explain the time variation of stress behavior in oxide films, irrespective of film quality and thickness.
Articles you may be interested inProperties of metalorganic chemicalvapordeposition mercury telluride contacts on ptype cadmium telluride The deposition ofCdTe films on foreign substrates by the direct combination of the elements in a gasflow system has the ft.exibility that the conductivity type and electrical resistivity of the film can be controlled by adjusting the composition of the reaction mixture. The deposition and properties of p-type CdTe films are emphasized in this paper because of its importance in thin-film solar cells. Graphite, W Igraphite, mullite, and Corning 7059 glass were used as substrates for the deposition process. While CdTe films deposited on W Igraphite and mullite substrates could be n or p type, depending on the composition of the reaction mixture, all films deposited on graphite substrates were p type, irrespective of the reactant composition, substrate temperature, or the purification of graphite, suggesting that carbon is electrically active in CdTe. The resistivity of ptype CdTe films on W Igraphite and mullite substrates has been controlled for the first time by (1) using a Cd-deficient reaction mixture, and (2) adding dopants (AsH3 or PH 3 ) to the reaction mixture. The resistivity versus composition relation was studied in detail. The optical properties ofneariy stoichiometric, Cd-deficient and Te-deficient CdTe films were also investigated.though the partial pressures of Cd and Te in the reaction 1349
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