J. A. Felix

Radiation Effects in MOS Oxides

Electronic devices in space environments can contain numerous types of oxides and insulators. Ionizing radiation can induce significant charge buildup in these oxides and insulators leading to device degradation and failure. Electrons and protons in space can lead to radiation-induced total-dose effects. The two primary types of radiation-induced charge are oxide-trapped charge and interface-trap charge. These charges can cause large radiation-induced threshold voltage shifts and increases in leakage currents. Two alternate dielectrics that have been investigated for replacing silicon dioxide are hafnium oxides and reoxidized nitrided oxides (RNO). For advanced technologies, which may employ alternate dielectrics, radiation-induced voltage shifts in these insulators may be negligible. Radiation-induced charge buildup in parasitic field oxides and in SOI buried oxides can also lead to device degradation and failure. Indeed, for advanced commercial technologies, the total-dose hardness of ICs is normally dominated by radiation-induced charge buildup in either parasitic field oxides and/or SOI buried oxides. Heavy ions in space can also degrade the oxides in electronic devices through several different mechanisms including single-event gate rupture, reduction in device lifetime, and large voltage shifts in power MOSFETs.

Production and propagation of single-event transients in high-speed digital logic ICs

The production and propagation of single-event transients in scaled metal oxide semiconductor (CMOS) digital logic circuits are examined. Scaling trends to the 100-nm technology node are explored using three-dimensional mixed-level simulations, including both bulk CMOS and silicon-on-insulator (SOI) technologies. Significant transients in deep submicron circuits are predicted for particle strikes with linear energy transfer as low as 2 MeV-cm/sup 2//mg, and unattenuated propagation of such transients can occur in bulk CMOS circuits at the 100-nm technology node. Transients approaching 1 ns in duration are predicted in bulk CMOS circuits. Body-tied SOI circuits produce much shorter transients than their bulk counterparts, making them more amenable to transient filtering schemes based on temporal redundancy. Body-tied SOI circuits also maintain a significant advantage in single-event transient immunity with scaling.

Current and Future Challenges in Radiation Effects on CMOS Electronics

Advances in microelectronics performance and density continue to be fueled by the engine of Moores law. Although lately this engine appears to be running out of steam, recent developments in advanced technologies have brought about a number of challenges and opportunities for their use in radiation environments. For example, while many advanced CMOS technologies have generally shown improving total dose tolerance, single-event effects continue to be a serious concern for highly scaled technologies. In this paper, we examine the impact of recent developments and the challenges they present to the radiation effects community. Topics covered include the impact of technology scaling on radiation response and technology challenges for both total dose and single-event effects. We include challenges for hardening and mitigation techniques at the nanometer scale. Recent developments leading to hardness assurance challenges are covered. Finally, we discuss future radiation effects challenges as the electronics industry looks beyond Moores law to alternatives to traditional CMOS technologies.

Impact of Ion Energy and Species on Single Event Effects Analysis

Experimental evidence and Monte-Carlo simulations for several technologies show that accurate SEE response predictions depend on a detailed description of the variability of radiation events (e.g., nuclear reactions), as opposed to the classical single-valued LET parameter. Rate predictions conducted with this simulation framework exhibit excellent agreement with the average observed SEU rate on NASAs MESSENGER mission to Mercury, while a prediction from the traditional IRPP method, which does not include the contribution from ion-ion reactions, falls well below the observed rate. While rate predictions depend on availability of technology information, the approach described here is sufficiently flexible that reasonably accurate results describing the response to irradiation can be obtained even in the absence of detailed information about the device geometry and fabrication process.

Effects of radiation and charge trapping on the reliability of high-κ gate dielectrics

Abstract The radiation response and long term reliability of alternative gate dielectrics will play a critical role in determining the viability of these materials for use in future space applications. The total dose radiation responses of several near and long term alternative gate dielectrics to SiO 2 are discussed. Radiation results are presented for nitrided oxides, which show no change in interface trap density with dose and oxide trapped charge densities comparable to ultra thin thermal oxides. For aluminum oxide and hafnium oxide gate dielectric stacks, the density of oxide trapped charge is shown to depend strongly on the film thickness and processing conditions. The alternative gate dielectrics discussed here are shown to have effective trapping efficiencies that are up to ∼15 to 20 times larger than thermal SiO 2 of equivalent electrical thickness. A discussion of single event effects in devices and ICs is also provided. It is shown that some alternative gate dielectrics exhibit excellent tolerance to heavy ion induced gate dielectric breakdown. However, it is not yet known how irradiation with energetic particles will affect the long term reliability of MOS devices with high- κ gate dielectrics in a space environment.

Effects of particle energy on proton-induced single-event latchup

The effect of proton energy on single-event latchup (SEL) in present-day SRAMs is investigated over a wide range of proton energies and temperature. SRAMs from five different vendors were irradiated at proton energies from 20 to 500 MeV and at temperatures of 25/spl deg/ and 85/spl deg/C. For the SRAMs and radiation conditions examined in this work, proton energy SEL thresholds varied from as low as 20 MeV to as high as 490MeV. To gain insight into the observed effects, the heavy-ion SEL linear energy transfer (LET) thresholds of the SRAMs were measured and compared to high-energy transport calculations of proton interactions with different materials. For some SRAMs that showed proton-induced SEL, the heavy-ion SEL threshold LET was as high as 25MeV-cm/sup 2//mg. Proton interactions with Si cannot generate nuclear recoils with LETs this large. Our nuclear scattering calculations suggest that the nuclear recoils are generated by proton interactions with tungsten. Tungsten plugs are commonly used in most high-density ICs fabricated today, including SRAMs. These results demonstrate that for system applications where latchups cannot be tolerated, SEL hardness assurance testing should be performed at a proton energy at least as high as the highest proton energy present in the system environment. Moreover, the best procedure to ensure that ICs will be latchup free in proton environments may be to use a heavy-ion source with LETs /spl ges/40 MeV-cm/sup 2//mg.

Impact of Heavy Ion Energy and Nuclear Interactions on Single-Event Upset and Latchup in Integrated Circuits

The effects of heavy ion energy and nuclear interactions on the single-event upset (SEU) and single-event latchup (SEL) response of commercial and radiation-hardened CMOS ICs are explored. Above the threshold LET for direct ionization-induced upsets, little difference is observed in single-event upset and latchup cross sections measured using low versus high energy heavy ions. However, significant differences between low- and high-energy heavy ion test results are observed below the threshold LET for single-node direct ionization-induced upsets. The data suggest that secondary particles produced by nuclear interactions play a role in determining the SEU and SEL hardness of integrated circuits, especially at low LET. The role of nuclear interactions and implications for radiation hardness assurance and rate prediction are discussed.

Enhanced Degradation in Power MOSFET Devices Due to Heavy Ion Irradiation

Large, unexpected shifts in the current-voltage (IV) characteristics of commercial power MOSFETs irradiated with heavy ions have been observed. The shifts can be more than sixty-five times larger than the shifts resulting from total dose irradiation with gamma rays or electrons, and are shown to strongly depend on both the irradiation bias and the ion linear energy transfer (LET). These large shifts are a significant concern for devices intended to operate in low power space applications because it is shown that they can lead to off-state leakage currents greater than 1 A. The data are consistent with the formation of parasitic transistors resulting from the microdose deposited in the gate oxides of these devices by the heavy ions. These results have significant implications for hardness assurance testing of MOS devices for use in space.

Radiation-induced charge trapping in thin Al/sub 2/O/sub 3//SiO/sub x/N/sub y//Si(100) gate dielectric stacks

We examine the total-dose radiation response of capacitors and transistors with stacked Al/sub 2/O/sub 3/ on oxynitride gate dielectrics with Al and poly-Si gates after irradiation with 10 keV X-rays. The midgap voltage shift increases monotonically with dose and depends strongly on both Al/sub 2/O/sub 3/ and SiO/sub x/N/sub y/ thickness. The thinnest dielectrics, of most interest to industry, are extremely hard to ionizing irradiation, exhibiting only /spl sim/50 mV of shift at a total dose of 10 Mrad(SiO/sub 2/) for the worst case bias condition. Oxygen anneals are found to improve the total dose radiation response by /spl sim/50% and induce a small amount of capacitance-voltage hysteresis. Al/sub 2/O/sub 3//SiO/sub x/N/sub y/ dielectrics which receive a /spl sim/1000/spl deg/C dopant activation anneal trap /spl sim/12% more of the initial charge than films annealed at 550/spl deg/C. Charge pumping measurements show that the interface trap density decreases with dose up to 500 krad(SiO/sub 2/). This surprising result is discussed with respect to hydrogen effects in alternative dielectric materials, and may be the result of radiation-induced hydrogen passivation of some of the near-interfacial defects in these gate dielectrics.

Negative bias-temperature instabilities in metal–oxide–silicon devices with SiO2 and SiOxNy/HfO2 gate dielectrics

Negative bias-temperature instability (NBTI) in metal–oxide–semiconductor capacitors with SiOxNy/HfO2 gate dielectrics is compared to those with thermal SiO2 oxides. Activation energies for interface and oxide-trap charge densities for each device type, estimated from capacitance–voltage measurements versus temperature and electric field, lie in the range 0.2–0.4 eV. This suggests that the release of hydrogen from, e.g., oxide protrusions in Si, followed by the lateral motion of protons along the interface (activation energy ∼0.3 eV), may play a key role in NBTI. Passivation reactions between protons and Si–H can create interface traps, and proton capture by sub-oxide bonds (O vacancies) can lead to positive trapped-oxide charge.