Probing SRAM Signals for Yield Management

Abstract

Probing is increasingly utilized for characterization of local electrical properties of ICs, as well as for defect isolation. Test structures and/or SRAM arrays were examined with various probing modes, i.e. Electron Beam Induced Current (EBIC), both one and two probe Electron Beam Absorbed Current (EBAC), and EBIRCH (Electron Beam Induced Resistance CHange). The results demonstrate the value of using each for SRAM yield management. EBIC provides for imaging of depletion zones between p-wells and n-wells, even in a planar view. EBAC can provide information on basic connectivity as well as enabling isolation of resistive areas along a conductor. EBIRCH, being driven by two different mechanisms (thermal coefficient of resistivity and Seebeck effect) can provide two different analysis types, depending on conditions. EBIRCH not only precisely isolated the fin responsible for a short, but also highlighted the thermal relations between the elements of a pulldown device in an SRAM. These techniques together provide multiple forms of process feedback in an integrated yield management program involving analysis of via chains, SRAM parallel array test structures, and SRAMs.