DIELECTRIC BREAKDOWN IN HIGH-E FILMS FOR ULSI DRAMS

Dielectric breakdown has been studied in several materials intended for high-dielectric DRAMs (dynamic random access memories), emphasizing lead zirconate-titanate (PZT) and barium strontium titanate (BST) ceramics. In this paper recent results from PZT are presented. In order to distinguish among impulse thermal breakdown, dc thermal breakdown. and avalanche breakdown mechanisms, studies have been carried out as functions of temperature, electrode material and shape, frequency and duration of applied fields, and specimen size and shape. Notable in the results is the fact that maximum breakdown field varies directly with electrode work function but is uncorrelated with electrode thermal conductivity; this militates against a purely thermal breakdown interpretation and instead favors an avalanche mechanism in which the initial step is electronic followed by thermal run-away. Thickness dependence also favors avalanche mechanisms, but dependence upon applied field ramp rate favors an impulse thermal mechanism.