D. J. DiMaria

MECHANISM FOR STRESS-INDUCED LEAKAGE CURRENTS IN THIN SILICON DIOXIDE FILMS

Leakage currents introduced in the low‐field, direct‐tunneling regime of thin oxides during high‐field stress are related to defects produced by hot‐electron transport in the oxide layer. From these studies, it is concluded that the ‘‘generation’’ of neutral electron traps in thin oxides is the dominant cause of this phenomenon. Other mechanisms due to anode hole injection or oxide nonuniformities are shown to be unrealistic for producing these currents. Exposure of thin oxides to atomic hydrogen from a remote plasma is shown to cause leakage currents similar to those observed after high‐field stress, supporting the conclusion that these currents are related to hydrogen‐induced defects.

Electroluminescence studies in silicon dioxide films containing tiny silicon islands

Electroluminescence from metal‐insulator‐semiconductor structures with silicon dioxide (SiO2) layers containing varying amounts of excess silicon (Si) in the form of tiny Si precipitates have been studied in detail. Bulk insulator emission from the Si islands is shown to dominate over emission from either the SiO2 matrix material or the metallic gate material by studies of oxide or metal gate material, voltage polarity, and insulator thickness dependencies. Several distinct spectral peaks are observed in the energy range from 1.5 to 5 eV which cannot be attributed to optical interference effects. The higher‐energy peaks show a strong dependence on electric field relative to that at the lowest energy (1.7–2 eV). The entire spectral amplitude shows a strong dependence on high‐temperature annealing and excess Si content, decreasing drastically with increasing Si or decreasing annealing temperature. These results are shown to be consistent with light emission during electronic transitions between discrete ene...

Electron trapping in SiO2 at 295 and 77 °K

The electron trapping behavior of SiO2 has been measured as a function of thickness at 295 and 77 °K. The devices used were metal‐oxide‐semiconductor devices with the SiO2 grown thermally. The results indicate bulk traps are dominant at 295 °K and traps associated with the Si‐SiO2 interface are dominant at 77 °K. The effect of processing conditions was also studied and the optimum conditions are different for the two temperatures used for the measurements. These observations have been verified using a photo I‐V technique. The generation of donor states in the SiO2 near the Si‐SiO2 interface was observed as a result of the electron current through the SiO2.

The effects of water on oxide and interface trapped charge generation in thermal SiO2 films

Water was diffused into very dry thermal SiO2 films under conditions such that the penetration of water related electron trapping centers was of the order of the oxide thickness. In both dry oxides and water diffused oxides, production of negative bulk oxide charge Qot and positive interface charge Qit by an avalanche‐injected electron flux was observed. The efficiencies of both processes were enhanced by water indiffusion. Analysis of the kinetics of charge generation indicated that production of trapped electron centers (Qot ) was required for subsequent production of interface states and charge (Qit ). Models for both processes are discussed. We suggest that inelastic collisions of conduction electrons with the trapped electron centers releases mobile hydrogen atoms or excitons. The mobile species migrate to the Si–SiO2 interface and form states and fixed charge.

Electron heating in silicon dioxide and off‐stoichiometric silicon dioxide films

Electron heating in silicon dioxide (SiO2) at electric fields ≲5 MV/cm is demonstrated using three different experimental techniques: carrier separation, electroluminescence, and vacuum emission. Gradual heating of the electronic carrier distribution is demonstrated for fields from 5 to 12 MV/cm with the average excess energy of the distribution reaching ≳4 eV with respect to the bottom of the SiO2 conduction band edge. Off‐stoichiometric SiO2 (OS‐SiO2) layers are shown to behave similarly to very thin SiO2(≲70 A in thickness) with a transition occurring from ‘‘cool’’ to ‘‘hot’’ electrons as the conduction mechanism changes from direct tunneling between silicon (Si) islands in the SiO2 matrix of the OS‐SiO2 material to Fowler‐Nordheim emission into the conduction band of the SiO2 regions. The relationship of electron heating to electron trapping, positive charge generation, interface state creation, and dielectric breakdown is treated. The importance of various scattering mechanisms for stabilizing the el...

Trapping and trap creation studies on nitrided and reoxidized‐nitrided silicon dioxide films on silicon

Alternative gate insulators for silicon‐based technologies involving nitridation or reoxidation‐nitridation of silicon dioxide layers are shown to be inferior to as‐grown oxide in terms of charge trapping over a wide range of fields under uniform electron‐injection conditions. Although nitrided layers seem to suppress trap generation more effectively than does silicon dioxide, background trapping in the as‐fabricated oxynitride layers formed near their interfaces is greatly increased. The apparent reduction in trapped charges universally reported in reoxidized‐nitrided oxides under high‐field injection conditions is shown to be due to a decrease in occupation of these sites at fields exceeding 8 MV/cm.

High current injection into SiO2 from Si rich SiO2 films and experimental applications

Chemically vapor deposited (CVD) Si rich SiO2 layers on thermal or CVD SiO2 layers incorporated into metal‐insulator‐semiconductor (MIS) capacitor structures are shown to give very large injected electron currents at low to moderate negative gate voltage biases. The dependence of this injection mechanism on the Si rich SiO2 composition and thickness, temperature, capacitor area, annealing conditions, gate metal (Al or Au), and underlying SiO2 thickness is described. Photocurrent measurements are discussed and are shown to give similar barrier energies as seen for ’’uniform’’ internal photoemission into SiO2. From the experimental electrical and photoelectrical measurements described here and transmission electron microscopy (TEM) and Auger studies of others, a possible model to explain this phenomenon based on electric field distortion caused by a two phase mixture of amorphous Si and SiO2 is presented. Two experimental applications of these structures are described. In one application, an electrically al...

Anode hole injection, defect generation, and breakdown in ultrathin silicon dioxide films

Using a variety of experimental techniques, hot holes are demonstrated to produce bulk and interfacial defect sites in silicon dioxide layers of metal–oxide–semiconductor structures. Similar to defect production by hot electrons, hot holes are shown to generate these sites by the energy they deposit in contacting silicon layers near the oxide interface. This deposited energy is believed to release hydrogenic species which can move into and through the oxide layer producing defects. The buildup of these defect sites is related to the destructive breakdown of ultrathin gate oxides in p-channel field-effect transistors under inversion conditions where direct tunneling of energetic holes to the gate electrode would occur and dominate the current in the external circuit at low gate voltages. However, the results presented here are inconsistent with current reliability models which use anode hole injection to explain destructive breakdown of the oxide layer in n-channel field-effect transistors where hole currents are small relative to electron currents.

Direct measurement of the energy distribution of hot electrons in silicon dioxide

The energy distribution of hot electrons in high‐field stressed amorphous silicon dioxide (SiO2) films have been measured using a vacuum emission technique. Electrons having average energies ≳2 eV and an energy relaxation length of λ≊32 A are observed at all fields studied (≳ 2 MV/cm). However, contrary to previous theoretical expectations, the majority of carriers in the distribution remains stable at all fields. The results are in agreement with other recent experiments (electroluminescence and carrier separation) which only measure the average energy of hot electrons in SiO2 and with recent Monte Carlo transport calculations which include scattering by both optical and acoustic phonon modes. Results for varying SiO2 thickness, metal gate thickness, oxide composition, and metal gate composition will be discussed.

Charge transport and trapping phenomena in off‐stoichiometric silicon dioxide films

The electrical characteristics of off‐stoichiometric silicon dioxide films have been investigated. The off‐stoichiometric oxide films studied had an excess atomic silicon (Si) content in the range of 1%–6%. Raman spectroscopy and photoconductivity measurements indicate that the excess Si is present as amorphous Si islands or small crystallites embedded in silicon dioxide (SiO2) forming a two‐phase material. These films differ in structure from previously reported films where dual dielectric layers of stoichiometric SiO2 and Si‐rich SiO2 with ≥13% excess atomic Si were used. These dual dielectric films were observed to produce electron injection from contacting electrodes via the Si‐rich SiO2 layer into the SiO2 at lower average electric fields. This injection mechanism was believed to be due to localized electric field enhancement near the SiO2–Si‐rich SiO2 interface caused by the curvature of the tiny Si islands in the SiO2 matrix. The current versus voltage characteristics of the off‐stoichiometric oxid...