Nitrogen-implanted silicon oxynitride: A coating for suppressing field emission from stainless steel used in high-voltage applications

In this paper, the authors examine the field emission performance of stainless steel polished to varying degrees, both before and after being coated with a nitrogen-implanted silicon oxynitride layer. The deposition procedure utilizes the simultaneous sputtering of silicon dioxide from a dielectric quartz window and ion implantation of nitrogen from an RF inductively coupled plasma. Here, the scanning field emission microscopy results indicate that prior to being coated, the number of emission sites increased drastically from 12 to more than 300 as the surface roughness increased from 4 to 64 nm, corresponding to polishing with 1-mu m diamond paste to 15-mu m (600 grit) silicon carbide paper. However, after being coated with nitrogen-implanted silicon oxynitride, all the samples displayed zero to five emission sites at electric field strengths at least three times higher than the uncoated stainless samples. Thus, neither the roughness of the underlying stainless steel nor that of the top surface of the coating had an effect on suppressing field emission. Depth profiling using Auger electron spectroscopy determined that the 0.24-mu m-thick silicon oxynitride coating contained approximately 15% nitrogen. Fourier transform infrared spectroscopy of a coated silicon wafer confirmed this stoichiometry and bonding. The technical impact of this work is that coating the large contoured stainless steel surfaces with a nitrogen-implanted silicon oxynitride layer may eliminate the need for expensive labor-intensive polishing procedures currently used in high-voltage electrode structures, such as those found in electron injectors.