Dependence of radiation-induced interface traps on gate Al thickness in metal/SiO2/Si structures

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Abstract
Generation of interface traps by ionizing radiation at the Si interface of an Al/SiO2/Si structure has been studied for Al thicknesses in the 500–13000 Å range for devices both with and without post‐metal‐anneal (PMA) treatment. In parallel with that, the interfacial stresses have been determined for the same structures by means of a laser beam reflection technique. The generation of radiation‐induced interface traps, as well as the interfacial stresses, depend strongly on Al thickness and PMA treatment. Results suggest that radiation sensitivity and interfacial stresses are closely related. Two mechanisms, both of which depend on the interfacial strained bonds, can explain the results. According to the first one, reformation of bonds broken by radiation depends on the Si surface strain, which in turn is a function of Al thickness and PMA. The second one is based on the bond strain gradient model proposed by F. J. Grunthaner, P. J. Grunthaner, and J. Maserjian [IEEE Trans. Nuc1. Sci. N S ‐ 2 9, 1462 (1982)] in which interface trap generation is a consequence of the propagation of the radiation‐induced bonding defects under the bond strain gradient. This process depends on the magnitude of such a gradient, in consistency with the observed dependencies of the radiation sensitivity.