Evaluation of device damage from e-beam curing of ultra low-k BEOL dielectrics

Abstract

The next generation of BEOL dielectrics (k<2.5) requires UV irradiation or e-beam assisted curing for improvement of mechanical properties and often, for the removal of porogen. The present study critically evaluates e-beam curing induced damage to pFETs and nFETs with different gate oxide thicknesses on bulk Si device structures. The results show that pFETs are more sensitive to damage than nFETs. The degree of damage increases with the size of the antenna connected to the gate (antenna-ratio) and with the thickness of the gate oxide; the thickest (5.2 nm) oxide showing the greatest sensitivity to damage. The damage depends on both electron dose and energy; damage increases with dose and is more likely at higher energy for a given dose. Device damage is relatively insensitive to the beam current. Charge damage is observed for thick gate oxide pFETs under conditions only slightly greater than those required to cure an M2/V1 PECVD porous ILD layer, even at a very low antenna ratio. Diode tie-downs to substrate were shown to protect bulk devices. © 2006 Materials Research Society.