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

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. NS-29, 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.

Mechanical stress control in a vlsi-fabrication process: a method for obtaining the relation between stress levels and stress-induced failures

“…The authors have reported that the reduction of mechanical stress in gate polysilicon film is an essential aspect of suppressing Manuscript dislocations at the gate edge [1], [2]. Worsened reliability because of the increase in mechanical stress in the oxide has been reported [3], [4]. Such problems have conventionally been solved by trial and error.…”

Enhanced thermally induced stress effect on an ultrathin gate oxide

“…Furthermore, the oxidation process accounts for the magnitude of such a gradient, which is related to the observed dependencies of the radiation sensitivity. 10 Thus, radiation seems to be an effective way to determine the extent of stress within the MOS structure. The stressed samples in this work were also subjected to receive Co-60 irradiation, and an interesting observation of the radiation hardness behavior for an exteriorly compressed sample is shown.…”

Thickness-dependent stress effect in p-type metal–oxide–semiconductor structure investigated by substrate injection current

“…For example, mechanical stress which is induced by the gate dielectrics 6 influences the interface trap density, causing a threshold voltage shift, 7 increasing the cumulative failure rate of time-dependent dielectric breakdown. 8 Ma and co-workers studied the dependencies of radiation-induced 9 and hot carrier-induced effects 10 on the thickness of gate Al in MOS capacitors. However, the relationship between the substrate injection current (J sub ) and the thickness of gate Al of MOS capacitors is still unknown.…”

“…For a certain oxide thickness, the Si wafer is generally under tensile stress. After the gate Al deposition, if the Al film is sufficiently thick, the chip curvature changes from convex to concave, 9 as shown by the schematic diagram in Fig. 5, such that the silicon wafer is now under compressive stress.…”