Sodium distribution in oxide by radiochemical analysis and its effect on silicon surface potential

Radioactive Na²⁴distribution has been measured and correlated with MOS electrical data in over 20 samples of 6000 Å of SiO2grown by conventional wet oxidation of 10 ohm-cm phosphorus doped silicon. Neutron activation by a high flux of thermal neutrons at 50°C maximum showed that total Na was less than 10¹⁷cm^-3in oxide grown in a conventional bubbled-oxygen all-quartz system. Edges were removed and sectioning done by etching. Planarity of sectioning was verified by uniformity of interference colors. Gamma-ray spectrometry and both radiotracer Na²⁴and neutron activation were used. Sections as thin as 250 Å could be counted.