Radiation Dose Due to Electron-Gun Metallization Systems

Electron beam evaporation is often selected as a method for depositing the gate metal for metal-oxidesemiconductor (MOS) devices. X-rays generated by electron impact on the metal to be evaporated may produce damage in the gate oxide. Several experimenters have reported that radiation-hardened MOS devices metallized in electron-gun systems appear to degrade at a faster rate than devices fabricated identically except for the metallization technique used. In order to examine ways of minimizing the damage introduced by electron beam systems and to develop a basis for understanding the physical phenomena observed, the physics of the x-ray energy deposition during the metallization process was explored. Details of the calculational procedure, the data necessary to calculate the x-ray absorbed dose in the oxide layer due to the electron-gun deposition of aluminum and chromium, and the calculations are presented. The results of experimental measurements of the x-ray dose are included for comparison. The implications of the results including the differences in the radiation susceptibility of MOS devices prepared with different gate metals are discussed.