Charging response of back-end-of-the-line barrier dielectrics to VUV radiation

a r t i c l e i n f o Keywords: Barrier dielectric Vacuum ultraviolet radiation Low-k dielectrics Back end of the line The response of SiN, N-SiC, O-SiC, and SiC dielectrics of varying thickness deposited on Si substrates to irradiation with vacuum ultraviolet (VUV) was compared. The resulting charge was evaluated by measuring the surface potential on the dielectrics after irradiation with 9.5 eV photons. The surface potential on all of the dielectrics was positive due to charge accumulation in traps located within the dielectrics. By comparing the surface potential on several thicknesses of dielectrics after VUV irradiation we can determine whether the trapped charges are in the bulk of the dielectric or at the dielectric–substrate interface. The minimum spacing between conductive lines in advanced integrated circuits (ICs) continues to decrease with each generation of technology [1]. As a result, the long-term reliability of ICs is becoming increasingly dependent on the reliability of the intermetal dielectrics [2] that often become damaged during back-end-of-the-line (BEOL) processing [3]. The local electric field, valence-band structure [4] and traps/defects within the intermetal dielectrics are very important parameters [5] that control the magnitude and path of the line-to-line leakage currents. In particular, traps located at or near the interface [6] between the low-k dielectric material and the dielectric diffusion-barrier/etch-stop layers act as a source of leakage current in Cu/low-k damascene structures [7]. Traps provide both a path for conduction [6] and enhancement of the local electric field [8] due to space-charge accumulation. Dielectrics used in BEOL structures are often irradiated with pho-tons of various energies during plasma processing [3,9], annealing [10], and curing [11,12] of porous materials. In particular, processing plasmas produce significant amounts of vacuum ultraviolet (VUV) radiation [13–15] which are capable of creating electron–hole pairs within dielectrics. As a result, VUV radiation has an impact on the electrical conductivity of dielectrics during plasma processing which can either contribute to [16–19] or mitigate [20–23] the trapped charge within dielectrics. It is very important to determine the trapping properties of BEOL-barrier dielectrics especially under irradiation with VUV photons because knowledge of the location and densities of the traps can be used to improve the fabrication process. For example, dielectrics are often directly exposed to the plasma-processing environment, and there is evidence that defects/traps generated during plasma processing [3,24] contribute to leakage currents [25]. The leakage current degrades both the performance and reliability of …