Effect of the dielectric–substrate interface on charge accumulation from vacuum ultraviolet irradiation of low-k porous organosilicate dielectrics

a r t i c l e i n f o Keywords: Vacuum ultraviolet irradiation Low-k dielectrics Charge accumulation Dielectric–substrate interface We compare the effect of various dielectric–substrate interfaces on charge accumulation during vacuum ultraviolet irradiation of capped low-k porous organosilicates to find that more charges are trapped in a dielectric stack deposited on silicon compared with the same stack deposited on copper. Insertion of a 5-nm interfacial thermal oxide layer further increases the amount of trapped charges in the dielectric. The difference between the photoemission and injection currents determines the number of charges trapped in the dielectric as a result of irradiation. Fewer charges are trapped when the injection current increases. Low-k porous organosilicate glass (SiCOH) is being used to replace silicon dioxide as an interconnect dielectric [1]. SiCOH is often exposed to plasma processing during fabrication, which results in exposure to both to charged-particle bombardment and vacuum ultraviolet (VUV) irradiation [2,3]. It is known that VUV irradiation can generate trapped positive charges in the dielectric [4–7]. The trapped charges can also be generated in pattern dielectrics depending on the energy of the VUV photons [8]. In this letter, we find that the number of trapped positive charges generated in the dielectric under VUV irradiation is related to the properties of the dielectric– substrate interface. In back of the line processing, SiCOH/SiCN stacks are now deposited on Cu, whereas much previous work on characterizing this effect has been on Si [9,10]. Here we irradiate films deposited on Cu and, for comparison, model Si/SiO 2 films with VUV of energies and fluxes typically generated during plasma processing. We find that the nature of the dielectric–substrate interface changes the number of trapped charges in the dielectric. The trapped charge generated in a dielectric under VUV irradiation appears because of the processes of photoemission and injection [4–6]. Trapped positive charges are generated when electrons are photo-emitted from defect states in the bandgap of the dielectric. Conversely, photoinjection of electrons from the substrate into the dielectric repopulates the defect states, hence reducing the amount of trapped positive charges. A self-consistent electric field is induced by the trapped charges in the dielectric [6,11]. The self-consistent electric field increases with increasing VUV photon dose because the number of trapped charges increases. As the self-consistent electric field increases, photoemission is reduced [6]. On the other hand, photoinjection of electrons from the substrate into the dielectric can …