Charge Injection in MAOS Systems

Abstract

A study of charge injection in metal-A120~-SiO2-silicon (MAOS) structures has been made using the capacitance-voltage technique. Thin SiO2 films were grown thermally on the Si substrates, whereas A1203 layers were obtained by pyrolytic deposition from A1Br3 in a NO-forming gas mixture. Independent of the electrode material, negative charge is introduced into the oxide system when a positive voltage is applied to the metal. With A1 electrodes, the oxide also becomes negatively charged under negative bias. Only for large negative voltages will a gradual loss of negative charge occur, leading to a net positive oxide charge. Charge injection under negative bias is not observed on 02 annealed Al_oO3 layers, or on samples with Au electrodes. The results are discussed in terms of a qualitative model.Charge storage in metal-Si~N4-SiO2-silicon (MNOS) structures has attracted considerable interest since the late sixties because of its potential for memory device application. For stressing voltages exceeding a threshold value carriers will, depending on the direction of the electric field, enter or leave traps near the Si3N~-SiO2 interface, thus changing the state of charge of the system, and thereby the threshold voltages of IGFET devices incorporating such double layers as gate insulators (1-7). Particularly for very thin SiO2 layers (<30A), when the charging takes place by direct tunneling through this oxide film into the traps, these processes are quite fast. The field and time dependencies of the charging processes are determined by the trap energies and by the spatial distribution of the traps. These characteristics will depend, in turn, on the method by which the layers were prepared. The somewhat different results obtained in ReL (5) and (6) (logarithmic increase in induced charge with time under electric stress vs. relatively rapid saturation of the charging process) must be related to details of the sample preparation process.The discovery of such charge storage behavior in the MNOS system raises the question of similar effects occurring in sandwich structures with other insulators. Indeed, it has been reported recently that also in MAOS structures (A : A1203) with A1 electrodes the charge can be varied easily in an electric field. However, here both positive and negative voltage stress tends to induce negative oxide charge. The behavior appears to be independent of the method by which the A120~ film was obtained: reactive evaporation of A1 in O2 (8), pyrolysis of trimethyl-A1 in O2 at 450~ (4) or of Al-isopropoxide in O2 at 420~ (9), pyrolysis of A1CI~ in CO.~-H2 at 850~ (10), or of A1Br3 in NO-H2-N2 at 900~ (11). Only for rf sputtered A1203 films does the injection of negative charge under negative bias on the metal appear to be absent (12). Although some authors (8, 10) have not mentioned the occurrence of SiO2 in their insulator system, it appears likely that in all cases a layer of native oxide was present on the silicon wafers used as substrates for A1203 deposition.In the present study we have explored the ...

Creation of interface defects in thermal Si/ through annealing

“…The model, as atomically probed through 29 Si and 17 O hyperfine interactions, is firmly corroborated by theory [7]. From early in the Si era, interface defects were technologically put under control [8]-either intentionally or process driven-through inactivation by hydrogen, leading, with respect to P b , to the simple formation of HP b entities. It thus emerged that the thermo-chemical properties of interface states are dominated by interaction with hydrogen.…”

Charge in SiO[sub 2]-Al[sub 2]O[sub 3] Double Layers on Silicon

“…This would suggest that the traps in the A1203 are oxygen vacancies and that an excess oxygen during deposition will reduce them. Balk (16) in his studies of metal-Al~O3-SiO2-Si structures found that charge injection under negative bias is not observed in polycrystalline A1203, which was oxygen annealed at 900~ for 1 hr, and suggested that the trapping centers could be oxygen vacancies. From the electron microprobe analysis of N2-deposited and O2-deposited amorphous A1203 and polycrystalline A120~ (see Table II), it was not possible to differentiate the variation of the aluminum or oxygen content in the bulk of the film.…”

The influence of counter-ion adsorption on the ψ0/pH characteristics of insulator surfaces

“…The gate insulator was polycrystalline y-Al *03 deposited by a process described by Balk and Stephany [32]. The grain size of the 500 to 600 A thick Al,O, layer was verified by SEM observation to be about 400 A.…”