The trapped charge interfacial modulation of the electron beam induced current in metal oxide semiconductor capacitors

Radiation-hardened (15) MOS capacitors were fabricated on 1-10 ohm-cm, p-type 100 silicon and were placed in the focal plane of a scanning electron microscope (SEM) to selectively populate and generate the oxide traps. As the electron beam scans from a region of the MOSC in the WRITE state to a region in the ERASE state, the electron beam induced current (EBIC) exhibits an abrupt reduction in the lateral current response--the trapped charge interfacial modulation (TCIM) of the EBIC. A new technique for extracting the Fu and Sah (23) device model parameters from a single spot-mode transient was developed. Using this technique, the excess-current component was separated from the lateral current component of the transient response. The lateral current was measured for both the WRITE and the ERASE states as a function of the applied gate bias to plot the characteristic curve which determines the magnitude of the TCIM turn-off transient and which accounts for the memory hysteresis of the device.;The spot-mode, turn-on transient of a MOSC was recorded after an annular ERASE to model the TCIM of the EBIC. The growth of the interfacial traps reduces the conductance of the inversion layer which limits the lateral spread of the electrons about the beam impact region. These electrons accumulate in the conduction band, fill the interfacial oxide traps, screen the oxide trapped charge, and abruptly reduce the depletion layer width and the effective source current. The excess-current component equals the source current reduction which must await the growth of the interfacial traps. The model combines the MOS junction capacitances, the Fu and Sah device model parameters, the beam current, the electron-beam scan speed and the surface diffusion length to determine the contrast and resolution limitations of the EBIC imaging (TCIM) of localized oxide trapped charge designed as a potential fast random-access, mass-memory storage device.