The effects of vacuum ultraviolet radiation on dielectric materials

During plasma processing of microelectronic devices, the devices can become damaged due to the bombardment of energetic electrons, ions, and photons. In particular, vacuum-ultraviolet (VUV) photons can have an impact on the electrical conductivity of dielectrics during plasma processing which can either contribute to or mitigate charging damage produced by charged-particle flux. This is of particular importance for new and emerging low-k and high-k dielectrics since they are more susceptible to damage.;To determine how VUV affects the electrical properties of dielectrics, we utilize synchrotron radiation incident on Si-wafers coated with dielectrics of varying composition and thickness. During VUV-irradiation, we measure both the substrate and photoemission currents as well as any induced charge on the dielectric that remains after irradiation with a Kelvin probe and a Mercury probe. We show that photoemission, photoconduction and photoinjection affect the currents drawn during VUV-irradiation and the accumulation of charge within the dielectric. To quantify this, we develop a model that predicts the surface potential across the dielectric layers from the photoemission and substrate currents. In addition, we use electron-spin resonance (ESR) and VUV-spectroscopy to identify defect states responsible for trapping charge within dielectrics. To demonstrate just how significant the effects of VUV can be on "real" devices, we expose electrically erasable read-only memory transistors (CHARM wafers) to VUV irradiation.;We examine the response of SiO2 dielectrics to VUV radiation in order to demonstrate the experimental techniques in this work with a dielectric which has well documented VUV-absorption and charge-trapping properties. We extend our analysis to HfO2 and SiCOH dielectrics which are more relevant for the semiconductor industry. We find that all of the dielectrics accumulate positive charge during VUV irradiation. We show that PhD centers at the HfO2/Si interface are responsible for trapped charge. For SiCOH, we show that positive charge becomes trapped by defect states located 0.5 eV above the valence-band edge and the trapped charge can be neutralized with UV photons. The results of this work provide a much-needed understanding of VUV-dielectric interactions and will aid in the development of models that predict when dielectric materials are most vulnerable to VUV.