Electron trapping in electron-beam irradiated SiO2

Abstract

In addition to the well-known positive space charge, electron irradiation of MOS capacitors with 25-keV electrons is shown to introduce additional uncharged electron traps into the oxide layer. These traps persist after most of the positively charged defects have been removed by the usual low-temperature (~ 0c) anneals. Their presence after this anneal is determined by injecting hot electrons into the oxide where they are captured by existing defects. The effective trap densities increase with increasing electron fluence and are reduced by forming-gas anneals at temperatures in excess of 500°C. Observed electron-capture cross sections are between 10-15 and 10-18 cm 2 • The residual radiation damage in oxides exposed to 10-4 Ccm-2 of 25-keV electrons and subsequently annealed at 4OQ°C results in an additional neutral density of 5 X 1011 trapscm-2 with cross sections distributed over the above range. Electron-trapping cross sections and effective trap densities associated with this damage are found to be identical at 77 and 295 K. The traps are possibly associated with dipolar defects formed when valence electrons localize around an ion after the bonds are broken.

Charging in scanning electron microscopy “from inside and outside”

“…Even for the best-known material, silicon dioxide used for its wide applications in microelectronics (metal-oxidesemiconductor devices), the capture cross sections range from 10 −15 cm 2 down to 10 −18 cm 2 depending upon the nature of the trapping sites being concerned (Aitken et al 1978). Furthermore, the density of traps depends upon the crystalline state and the density of impurities of the investigated specimen: with respect to the mean value of the atomic density of solids, 5 10 22 cm −3 , the atomic concentration of traps may vary from 10 −6 (nearly perfect crystal) up to10 −2 (disordered material with many impurities).…”

Sputter-Metallization-Induced Electronic Defects in Thermal SiO2

“…It should be noted, however, that traps with a larger capture cross section of about 10 --15 cm --2 , usually found in X-ray [16] or e-beam [15] irradiated oxides, were not observed in our samples. This points out to that sputter deposition has also the advantage of being a not very harmful metallization technique.…”

“…Traps with a similar capture cross section (s = 2 Â 10 --16 cm 2 ) were also observed in electron beam irradiated samples [15], SiO 2 , in MOS capacitors exposed to X-rays [16] or subjected to Mo sputtering metallization [17]. These traps have never been detected in unirradiated thermal oxides.…”

“…These values will be used further to identify the traps. Values of the capture cross sections of these orders of magnitudes are characteristic of neutral centers [15]. Because the neutral traps are not charged, they show up only upon injection of electrons.…”

Semiconductor Dimensional Metrology Using the Scanning Electron Microscope

“…Critical electrical or radiation damage such as dielectric breakdown and threshold shifts may occur when inspecting devices at certain process levels [16,17]. These effects may be related to the deep layer residual charge left by the injection of high energy primary electrons or the shallow layer charge depletion caused by secondary electron emission [18,19] as well as the creation of electron traps and fast surface states [19,20,21]. Frequently, these types of damage can be annealed out during subsequent process steps [22,23,24].…”