Search

Charge collection measurements on SOI diodes have been performed with heavy ion microbeam and pulsed focused laser. Both irradiation techniques show that no electrical coupling occurs. However, laser measurements show an optical coupling effect when irradiation occurs close to the isolation trench. Qualitative electromagnetic simulations have been performed to confirm and describe the optical coupling. Index Terms--Charge collection, heavy ion, pulsed laser, SOI.

Effects of the radial density distribution of carriers generated in a single ion track have been observed in thin silicon detectors. These devices have been irradiated with either an ion microbeam at low energy or a high-energy standard ion beam. We describe the mode of operation of the tested structure, and propose an interpretation of the experimental charge collection data to extract information on the ion track profile. Experimental results are compared to 3D simulations and simplified analytical profiles.

The first simultaneous microbeam mapping of single event upset (SEU) and latchup (SEL) in the CMOS RAM HM65162 is presented. We found that the shapes of the sensitive areas depend on [V.sub.DD], on the ions being used and on the site on the chip being hit by the ion. In particular, we found SEL sensitive sites close to the main power supply lines between the memory-bit-arrays by detecting the accompanying current surge. All these SELs were also accompanied by bit-flips elsewhere in the memory (which we call 'indirect' SEUs in contrast to the well known SEUs induced in the hit memory cell only). When identical SEL sensitive sites were hit farther away from the supply lines only indirect SEL sensitive sites could be detected. We interpret these events as 'latent' latchups in contrast to the 'classical' ones detected by their induced current surge. These latent SELs were probably decoupled from the main supply lines by the high resistivity of the local supply lines.

We present the first experimental determination of the SEB sensitive area in a power MOSFET irradiated with a high-LET heavy-ion microbeam. We used a spectroscopy technique to perform coincident measurements of the charge collected in both source and drain junctions together, with a non-destructive technique (current limitation). The resulting charge collection images are related to the physical structure of the individual cells. These experimental data reveal the complex 3-dimensional behavior of a real structure, which can not easily be simulated using available tools. As the drain voltage is increased, the onset of burnout is reached, characterized by a sudden change in the charge collection image. 'Hot Spots' are observed where the collected charge reaches its maximum value. Those spots, due to burnout triggering events, correspond to areas where the silicon is degraded through thermal effects along a single ion track. This direct observation of SEB sensitive areas as applications for, either device hardening, by modifying doping profiles or layout of the cells, or for code calibration and device simulation.

New experimental study of heavy ion and proton induced SEU at reduced voltage (i.e. reduced critical charge) reveals interesting results. It is shown that the heavy ion cross section and microprobe mapping scale like the threshold LET and the parameter, which is almost invariant under bias changes, is the effective charge collection depth. For studying proton induced SEU and surface-barrier-detector spectra we use protons with energies from 5.6 to 300MeV. The results are analyzed in view of the processes involved in low energy deposition by protons. Detailed calculations show the importance of straggling in proton direct ionization which might be the leading process in very sensitive devices like photodiodes.