Thermally grown oxide on poly silicon has poorer insulator properties than an oxide grown on single crystal silicon. Due to surface roughness of the polysilicon surface the localized oxide electric field is enhanced at the surface bumps and asperities. In order to minimize surface roughness attention has to be given to the poly silicon surface for the steps following deposition. This includes doping and annealing the polysilicon in order to increase the grain size and using care in cleaning the poly and growing the oxide. By minimizing the surface roughness the poly oxide has better insulating properties due to a decrease in the localized electric field and this oxide demonstrates a higher barrier height (≠~) and breakdown voltages.
Evaluation of the oxides were done using ramped I-V measurements. The measurements were taken at an area where Fowler-Nordhein~ tunneling ‘was taking place. That region of the curve was analyzed to find the breakdown voltages and barrier height, ØB. Breakdown voltages were found to be from a low of 37.85v to a high of 43.5v. Barrier heights ranged from 2.1eV to 2.6eV compared to 3.2eV which is the ØB for oxide grown on single crystal silicon. Edge length of the test structures was also evaluated and it was found that the barrier height decreased with increasing edge length indicating an increase in the local electric field along the edge regions.
Krott, Loren C.
"Evaluation of Polyoxide Capacitor Edge Effects Using Ramped I-V Measurements,"
Journal of the Microelectronic Engineering Conference: Vol. 5
, Article 13.
Available at: http://scholarworks.rit.edu/ritamec/vol5/iss1/13