E. A. Wolicki

Correlation of Particle-Induced Displacement Damage in Silicon

Correlation is made between the effects of displacement damage caused in several types of silicon bipolar transistors by protons, deuterons, helium ions, and by 1 MeV equivalent neutrons. These measurements are compared to calculations of the nonionizing energy deposition in silicon as a function of particle type and energy. Measurements were made of displacement damage factors for 2N2222A and 2N2907A switching transistors, and for 2N3055, 2N6678, and 2N6547 power transistors, as a function of collector current using 3.7 - 175 MeV protons, 4.3 - 37 MeV deuterons, and 16.8 - 65 MeV helium ions. Long term ionization effects on the value of the displacement damage factors were taken into account. In calculating the energy dependence of the nonionizing energy deposition, Rutherford, nuclear elastic, and nuclear inelastic interactions, and Lindhard energy partition were considered. The main conclusions of the work are as follows: 1) The ratio of the displacement damage factors for a given charged particle to the 1 MeV equivalent neutron damage factor, as a function of energy, falls on a common curve which is independent of collector current. 2) Deuterons of a given energy are about twice as damaging as protons and helium ions are about eighteen times as damaging as protons.

Single Event Upset of Dynamic Rams by Neutrons and Protons

Dynamic 16K random access memories (RAMs) have been irradiated with neutrons having mean energies of 6.5, 9 and 14 MeV and with 32 MeV protons and have been found to undergo single event upset. For both particles, one upset is expected for approximately 108 particles/cm2. The upsets are statistical and the affected cells can be reset and continue normal operation. Both HIGH and LOW storage elements are upset though at different rates. The cause of the upsets is most probably a multi-MeV alpha particle created by an (n, alpha) or (p, alpha) or similar nuclear reaction. The alpha particle discharges either the storage capacitor, the floating bit line, or the reference capacitor used by the sense amplifier.

High energy electron induced displacement damage in silicon

New measurements of displacement damage factors for electron-irradiated (4 to 53 MeV) bipolar silicon transistors have extended the correlation between nonionizing energy loss and damage factors reported previously another three orders of magnitude downward, to cover a total of six decades. To first order, the correlation remains linear for both n- and p-type silicon, but deviations are observed and explained in terms of differences in the fraction of initial vacancy interstitial pairs that recombines. These differences correlate linearly with the low-energy component of the PKA spectrum. Deep level transient spectroscopy measurements show oxygen- and dopant-related defect levels as well as divacancies. Defect concentrations scaled linearly with gain degradation, and no differences were seen between electron and proton plus neutron irradiated material. The results are consistent with a damage mechanism involving migration of vacancies to form well-separated stable defects. >

Charge Collection in Multilayer Structures

Charge collection measurements using energetic ions have been performed on layered structures in bulk and epitaxial silicon. Both fast transient digitizer and slower charge sensitive preamplifier measurements have been made as a function of bias, ion type, energy, and angle of incidence. The existence of pulses of both polarities on a node after passage of a charged particle has been seen in certain Cases.

Energy Dependence of Proton Displacement Damage Factors for Bipolar Transistors

Displacement damage factors, p, have been measured as a function of collector current for proton irradiations of 2N2222A (npn) and 2N2907A (pnp) switching transistors and 2N3055 (npn) power transistors over the energy range 5.0 to 60.3 MeV. The measurements of Kp were made on specially selected lots of devices and were compared to values of the neutron damage factors, Kn, for 1 MeV displacement damage equivalent neutrons made on the same devices. The results show that so far as device operation is concerned, the nature of the displacement damage produced by high energy protons and by fission neutrons is essentially the same. Over the energy range studied, protons were found to be more damaging than neutrons. For 5.0 MeV protons Kp/Kn was about 8.5 compared to about 1.8 for 60.3 MeV protons.

Displacement damage equivalent to dose in silicon devices

Particle‐induced displacement damage effects in silicon bipolar transistors, including those due to electrons and to fission neutrons, are correlated on the basis of the nonionizing energy deposited in the lattice by the primary knock‐on atoms. Deviations from linearity between damage effects and energy deposition are in a direction opposite to those expected from defect cluster models but can be accounted for in terms of the fraction of vacancy‐interstitial pairs initially formed that survive recombination.

Single Event Upsets in RAMs Induced by Protons at 4.2 GeV and Protons and Neutrons below 100 MeV

Several different types of random-access-memories (RAMs) have been tested for soft upset susceptibility under a variety of different particle bombardments including thermal neutrons, GeV protons, and protons and neutrons below 100 MeV and with few exceptions found to suffer single event upsets. Devices tested included 4K, 16K and 64K dynamic RAMs and 4K NMOS and 256×4 CMOS static RAMs. Mean upset fluences varied from 106 particles/cm2-upset for 64K dynamic RAMs up to no upsets observed for the 256×4 CMOS RAM. No thermal neutron induced upsets are believed to have occurred. GeV protons, simulating primary cosmic rays, caused upsets at levels of 107 particles/cm2-upset.

Proton, neutron and electron-induced displacement damage in germanium

Displacement damage factors for several types of germanium bipolar transistors have been measured for 15- and 30-MeV electrons, 22-, 40-, and 63-MeV protons, and fission neutrons. Each device was irradiated with both neutrons and either electrons or protons so that damage factor ratios could be determined. In this way dependence on resistivity, injection level, and device variability could be removed. The damage factor ratios were found to be directly proportional to the calculated nonionizing energy loss for electrons and protons over approximately two orders of magnitude. This means that the damage factors are directly proportional to the number of defects initially formed, whether as point defects or in cascades, and that the stable defects act independently so far as transistor gain is concerned. No evidence of cluster-space-charge effects was found. The implication of the results for a determination of a 1-MeV (GE) neutron damage equivalent fluence is discussed. >

Average Silicon Neutron Displacement Kerma Factor at 1 MeV

The average neutron displacement kerma factor in the vicinity of 1 MeV is difficult to derive for silicon because of sharp neutron cross section resonances in that region. To avoid these difficulties, the function AE(1-e-B/E) was fitted to tabulations of D(E) vs. E, where E is energy and D(E) is the neutron displacement kerma factor for silicon at 1 MeV. The values of A and B obtained from a least squares fit yielded an average value at 1 MeV of D¿(1 MeV)=95±4 MeV-mb.

Soft Upsets in 16K Dynamic RAMs Induced by Single High Energy Photons

Soft upsets have been observed in dynamic random access memories (RAMs) that can be attributed to single high energy photon interactions. In the experiments, bremsstrahlung produced by the interaction of 40 MeV electrons with a thin tungsten converter has been found to produce soft upsets at flux levels well below those where photocurrent generation of upsets dominates. The number of upsets observed at low photon fluxes depends on the total number of photons which have been incident on the device but is independent of the dose rate. This behavior is consistent with preliminary calculations which assume that the upsets are caused by alpha particles Produced in the silicon chip by the nuclear reaction 28Si(¿,¿)24Mg. In these calculations the bremsstrahlung spectrum and the reaction cross section were integrated over the range from 15 to 22 MeV.