Paper TF-WeM4
Field Emission Suppression from Stainless Steel Using Silicon Oxynitride Coatings

Wednesday, October 17, 2007, 9:00 am, Room 613/614

We have developed a new RF inductively-coupled, plasma-based, reactive sputtering procedure to deposit high-purity silicon oxynitride (SiO_XN_Y) films. Oxynitride formation was verified using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Using profilometry, we determined that increasing the nitrogen plasma pressure or the RF power raises the deposition rate. However, FTIR results show that adjusting the plasma pressure also altered the amount of bound nitrogen in the silicon oxynitride layer. The resulting silicon oxynitride coatings have also been characterized with Auger electron spectroscopy (AES), Rutherford backscattering spectrometry (RBS), and elastic recoil detection analysis (ERDA) to determine their elemental composition and density. This silicon oxynitride coating drastically reduced field emission from large area, stainless steel electrodes. High voltage tests showed that a polished, 180 cm², stainless steel electrode exhibited 27 μA of field-emitted current at 15 MV/m; however, by applying a silicon oxynitride coating to a similarly polished electrode, emission current was drastically reduced to less than 300 pA at 30 MV/m. The field emission from these silicon oxynitride coatings seems to follow the electron emission mechanisms proposed by Schottky and Poole-Frenkel. Both of their emission equations predict that increasing the band gap, dielectric constant, and electron affinity of the silicon oxynitride coatings could further reduce field emission. Our most recent high voltage tests of two polished electrodes coated with a 'graded' silicon oxynitride layer supports these predictions; at 30 MV/m, the field emitted current was below 4 pA, the detection limit of our high voltage test system.