화학공학소재연구정보센터
Journal of Vacuum Science & Technology B, Vol.15, No.4, 1080-1088, 1997
Investigation of Existing Defects and Defect Generation in Device-Grade SiO2 by Ballistic-Electron-Emission Spectroscopy
Degradation processes initiated by defect generation in device-grade SiO2 were studied by locally injecting hot electrons from a scanning tunneling microscope tip into Pd/SiO2/p-Si(100) metaloxide semiconductor (MOS) structures. An analysis of the emerging collector current in the Si substrate, a technique known as ballistic electron emission microscopy, provides electron transport information, from which the oxide defect generation process was studied. The charging of the defects resulted in shifts of threshold energies for electron transport across the oxide. A novel sheet charge model was developed to assess the in-depth distribution and charge densities in the oxide from field-induced threshold shifts obtained from experiment. An as-fabricated MOS system with an oxide thickness of 71 Angstrom was investigated and found to contain existing electron traps of charge densities in the range (0.7-2.8) X 10(13) e/cm(2) that are distributed within a 30 Angstrom region adjacent to the metal/oxide interface. Further stressing was performed at zero oxide bias with increasing tip voltages of up to -10 V. New electron traps characterized by charge densities of (1.9-3.6) x 10(13) e/cm2 and located within 40 Angstrom of the SiO2/Si interface were generated when the kinetic energy of the electrons injected into the SiO2 conduction band exceeded 1.9 eV. This energy threshold is in very good agreement with the hydrogen-release energy that is frequently invoked to explain oxide degradation.