This paper reviews the basic physical mechanisms of the interactions of ionizing radiation with MOS oxides, including charge generation, transport, trapping and detrapping, and interface trap formation. Device and circuit effects are also discussed briefly.

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Total ionizing dose effects in MOS oxides and devices

Degradation of silicon dioxide films is shown to occur primarily near interfaces with contacting metals or semiconductors. This deterioration is shown to be accountable through two mechanisms triggered by electron heating in the oxide conduction band. These mechanisms are trap creation and band‐gap ionization by carriers with energies exceeding 2 and 9 eV with respect to the bottom of the oxide conduction band, respectively. The relationship of band‐gap ionization to defect production and subsequent degradation is emphasized. The dependence of the generated sites on electric field, oxide thickness, temperature, voltage polarity, and processing for each mechanism is discussed. A procedure for separating and studying these two generation modes is also discussed. A unified model from simple kinetic relationships is developed and compared to the experimental results. Destructive breakdown of the oxide is shown to be correlated with ‘‘effective’’ interface softening due to the total defect generation caused by both mechanisms.

Impact ionization, trap creation, degradation, and breakdown in silicon dioxide films on silicon

A new technique is presented for separating the threshold‐voltage shift of a metal‐oxide‐semiconductor transistor into shifts due to interface traps and trapped‐oxide charge. This technique is applied to threshold‐voltage shifts on an n‐channel transistor that result from ionizing radiation.

Simple technique for separating the effects of interface traps and trapped‐oxide charge in metal‐oxide‐semiconductor transistors

Trap creation in both the bulk of silicon dioxide films and at its interfaces with silicon and metallic contacting electrodes is shown to depend on the presence of hot electrons in the oxide. For thick oxides (≥100 A), little trap creation is observed in the near‐thermal transport regime at electric field magnitudes less than 1.5 MV/cm. At these low fields, electrons travel in a streaming fashion close to the bottom of the oxide conduction band at energies less than that of the dominant optical phonon mode at 0.153 eV. At higher electric fields, the rate of bulk trap creation is proportional to the average energy of the hot electrons, which move in a dispersive manner and can reach energies as large as 4 eV. For thin oxides (<100 A) where electrons can travel ballistically (i.e., without scattering), traps are not produced unless injected electrons acquire more than 2 eV of kinetic energy from the applied electric field, regardless of the magnitude of this field. All data on both thin and thick oxides are shown to give a threshold for trap creation of about 2.3 eV by the hot electrons in the oxide conduction band. Also, trap creation is shown to be suppressed by lowering the lattice temperature below ≊150 K. Our results are discussed in terms of a model involving hydrogen‐related‐species release from defect sites near the anode by the hot electrons and the subsequent motion of these molecules to regions near the cathode where they can interact with the lattice and form the trapping sites which are measured.

Trap creation in silicon dioxide produced by hot electrons

In this paper, we present a model for silicon dioxide breakdown characterization, valid for a thickness range between 25 /spl Aring/ and 130 /spl Aring/, which provides a method for predicting dielectric lifetime for reduced power supply voltages and aggressively scaled oxide thicknesses. This model, based on hole injection from the anode, accurately predicts Q/sub BD/ and t/sub BD/ behavior including a fluence in excess of 10/sup 7/ C/cm/sup 2/ at an oxide voltage of 2.4 V for a 25 /spl Aring/ oxide. Moreover, this model is a refinement of and fully complementary with the well known 1/E model, while offering the ability to predict oxide reliability for low voltages. >

Hole injection SiO/sub 2/ breakdown model for very low voltage lifetime extrapolation

A characteristic interface trap was observed in a hole trapping experiment when electrons were captured by trapped holes injected by an avalanche in the silicon. The observations could be explained by the generation of new electronic states through relaxation of strained bonds which were proposed to be the origin of hole traps. The result is either a weak bond in the network or two dangling bonds with no net charge. The weak bond or dangling bonds give rise to neutral traps in the bulk and interface traps at the interface of the oxide. The presence of interface traps for such defects at the interface is predicted by theoretical calculations.

S. K. Lai

Papers

Interface trap generation in silicon dioxide when electrons are captured by trapped holes