Semiconductor manufacturing requires that wafers be exposed to a plasma for more than 1/3 of the manufacturing steps—including etching, deposition, ashing, etc. In many cases, plasma processing is the only way in which these manufacturing steps can be done. However, when dielectric surfaces which are present in various locations on the wafer are exposed to a plasma, both charged particles and radiation strike the dielectric. This often results in electric charge building up on the surface of the dielectric which can result in destruction of the dielectric by electric currents tunneling through or arcing across the dielectric. The figure below shows the absolute VUV spectrum from an oxygen plasma. Significant VUV radiation appears above the bandgap of SiO 2 where it can produce electron-hole pairs and photoemission. This can result in additional charge accumulating or depletion of existing charge, depending on the photon energy, the properties of the dielectric and its thickness. To mitigate the damage caused during plasma exposure by depleting excess charge. The effects of vacuum ultraviolet radiation on the processing of electronic materials J. Leon Shohet, Univ. of Wisconsin-Madison, DMR THE ISSUE OBJECTIVE When radiation in the ultraviolet to extreme ultraviolet portion of the spectrum strikes the dielectric layers, experimental evidence shows that excess charge can be drained off by photoconductive/photoinjection effects. However, this radiation can also cause photoemission of electrons that can work against the photoconductive effects especially for positively charged layers. We have shown that a positively charged dielectric can be depleted/neutralized of its charge by both photoinjective and/or photoconductive effects, while a negatively charged surface can be depleted/neutralized of its charge by photoemissive and/or photoconductive/photo- injective effects provided that the photon energy is adjusted for the dielectric properties and layer thickness. Thus, by carefully tailoring the wavelength of supplemental radiation to a particular dielectric, it is possible to deplete the charge THE PROPOSED SOLUTION

EXPERIMENTS SiO 2 layer Our measurements of the charging/discharging current during VUV exposure show that (1) dielectric space charge develops in the thick oxides, thus decreasing the substrate current. (2) As thickness decreases, this amount of charge produces tunneling currents which cause the current to increase, while (3) for the thinnest oxides, the current is nearly constant due to photoinjection from the substrate, because the VUV photons pass completely through the oxide. From these effects, we can determine the photon energies needed for charge depletion as a function of the dielectric and its thickness. Dielectric – Extreme UV interaction Many processing plasmas produce measurable amounts of Extreme Ultraviolet (EUV) radiation. The figure below shows the surface potential map measured using a Kelvin Probe on a 3000 Å SiO 2 layer after synchrotron EUV exposure. Peak potentials of the order of 28V are clearly seen in the surface-potential map (shown at the right) which is much higher than that formed by photoemission during VUV exposure. It is important to note that these high surface potentials are formed outside of the EUV exposure region, in contrast to VUV exposure where the highest potentials occur at the VUV beam location. The effects of vacuum ultraviolet radiation on the processing of electronic materials J. Leon Shohet, Univ. of Wisconsin-Madison, DMR In our laboratory, we simulate plasma processing exposure by placing silicon oxide dielectric layers of thickness between Ångstroms to plasmas generated by electron-cyclotron resonance. Depending on the operating parameters, the dielectric layer will be charged positively or negatively. After plasma exposure the charged dielectric layers are exposed to synchrotron radiation at wavelengths between 100 and 2000 Ångstroms and both photoemission and photoinjection/photocon-duction currents are measured during synchrotron exposure as shown below. These currents may charge or discharge the dielectric. The amount and distribution of charge before and after synchrotron exposure is measured with a Kelvin probe.

The effects of vacuum ultraviolet radiation on the processing of electronic materials J. Leon Shohet, Univ. of Wisconsin-Madison, DMR Jean Calderon from the University of Puerto Rico and Damien Kenney from Georgia Perimeter College spent eight weeks during the summer of 2005 working in our laboratory and at the UW Synchrotron (DMR ) learning how to perform plasma processing, expose test structures to synchrotron radiation and to measure the charge distribution. Jean Calderon using a Kelvin Probe to measure surface Potential Jean Calderon and Erik Hanley setting up VUV exposures at the Synchrotron Education and outreach to underrepresented minorities Erik Hanley and Damien Kenney exposing wafers to plasma before VUV exposure