Bob H. Yun

Silicon nitride trap properties as revealed by charge−centroid measurements on MNOS devices

Previous charge−centroid studies of MNOS devices have shown that electrons injected into the insulator structure from the silicon are trapped not solely at the dielectric interface, but can be distributed over nearly the entire nitride thickness. In this paper, results of charge−centroid measurements on thin−oxide MNOS devices are interpreted with a charge trapping model, leading to values for the nitride trap density, capture cross section, and average trapping distance of 6×1018/cm3, 5×10−13 cm2, and 35 A, respectively.

Measurements of charge propagation in Si3N4 films

A new experimental technique is described, which measures the injection and propagation of charge in the Si3N4 film of an MNOS structure caused by a pulsed electric field. Contrary to the widely held contention that the electrons injected from the Si are trapped in and very near the SiO2–Si3N4 interface, a contention resulting from the assumption that the trap density near this interface usually far exceeds the number of injected electrons, this work finds that the spatial distribution of the trapped electrons extends deep into the Si3N4 film. In fact, the centroid of the spatial distribution of the trapped electrons in a Si3N4 film ≃500 A thick can be as much as 150 A or more from the SiO2–Si3N4 interface, indicating that the span of the distribution extends across almost the entire thickness of the film with an average density of trapped electrons in the order of 3 × 1018/cm3. It is shown that, in general, the centroid of the trapped charge distribution in the Si3N4 film of a given device structure is a...

Electron and hole transport in CVD Si3N4 films

This letter reports on the finding that holes are more mobile than electrons in chemically vapor deposited (CVD) Si3N4. MIS structures with Si3N4 films as the insulating layers are used in the experiments. Holes are shown to be electrically injected from the silicon into the insulator when the aluminum‐gate electrode is pulsed negative, and electrons when pulsed positive, with subsequent trapping in the nitride. The centroid of the trapped‐hole distribution, Xh, and that of the trapped‐electron distribution, Xe, as functions of the voltage pulse amplitude and duration are measured. The ratio of Xh/Xe increases with the amplitude of the pulse and its duration, where the centroids are referenced from the injection source, and exceeds 3 when the hole distribution spans the entire nitride thickness. Data suggest that hole traps are perhaps shallower than electron traps, hence the enhanced hole conduction in the silicon nitride.

Direct display of electron back tunneling in MNOS memory capacitors

Direct observation of back tunneling in MNOS requires the direct and continuous display of the charge previously injected into the insulator. A new experimental technique having such a feature is presented. It is characterized by its simultaneous and direct measurements of both the change in charge in the insulator and the corresponding change in the devices flat‐band voltage. Charge loss via back tunneling in devices of different tunnel‐oxide thicknesses is presented.

Direct measurement of flat‐band voltage in MOS by infrared excitation

A photoexcitation technique for the direct measurement of metal‐oxide‐semiconductor (MOS) flat‐band voltage is described. The principle consists of generating excess carriers in the semiconductor space‐charge region by infrared pulses as a function of potential applied across the MOS capacitor and utilizing the fact that the current pulses induced in the external circuit become identically zero when the applied voltage is equal to the flat‐band voltage. Experimental results are presented for MOS on silicon substrates.

Effects of electron‐beam irradiation on the properties of CVD Si3N4 films in MNOS structures

The influence of energetic electron‐beam irradiation on the trap properties of CVD Si3N4 films in MNOS structures has been investigated by means of charge‐centroid and conduction measurements. Within the limit of our measurements, the results indicate that electron‐beam radiation up to 6.6×10−5 C/cm2 does not affect the trap properties of the nitride, such as the density, capture cross section, and average capture distance, although the charging of these traps may be altered. Furthermore, the effects of radiation in the Si‐SiO2 interface properties of MNOS structures have been examined by the C‐V method. For an MNOS capacitor with relatively thick oxide, radiation was found to cause a significant increase in the density of surface states, the effective insulator charge, and the slow states. For an MNOS capacitor with very thin oxide, by contrast, the radiation causes a significant change only in the insulator charge—none in the surface states. Since the properties of the nitride have not been affected by ...

Improved oxide of metal‐oxide‐silicon capacitors resulting from backsurface argon implantation

Argon ions were implanted at the backsurface of silicon wafers prior to the formation of the oxide of the metal‐oxide‐silicon capacitors. The implantation resulted in improved oxide. The improvement is speculated to be a consequence of the gettering of the metallic impurities by the dislocations caused by the ion implantation gettering which occurs during oxidation and prevents the impurities from being absorbed into the oxide of the subsequent capacitors.

Charge injection from polycrystalline silicon into SiO2 at low fields

Electron injection from polycrystalline silicon into thermal SiO2 at low fields is observed in polycrystalline‐silicon–SiO2–Si capacitors. C‐V, pulsed‐charge injection, and charge‐relaxation measurements show that the injected electrons are captured by centers in the SiO2. These trapping centers appear to be located at about 30 A from the polycrystalline‐silicon–SiO2 interface and are characterized by an energy level approximately 0.3 eV above the Fermi level of the degenerate n‐type polycrystalline silicon. Annealing of the samples in nitrogen or forming gas strongly affects the charge injection.

Opposite-polarity voltage generator by hole impact ionization in a silicon bipolar transistor

A single n-p-n transistor was used to generate a negative voltage at the collector terminal when a positive voltage was applied to the emitter relative to its grounded base. It is believed that this effect was a result of hole impact ionization at field E approximately=0 at the band-edge energy maximum in the base-collector junction, and some of the electrons so created diffused and drifted to the collector, thus accounting for the otherwise unexpected negative collector potential. Possible applications of this effect are given.<<ETX>>

Microstructural effects of emitter size on polysilicon‐emitter bipolar transistors

As the dimensions of semiconductor devices are reduced, changes in the structure of the devices can have a pronounced effect on their electrical parameters. In some cases it may no longer be correct to assume that the electrical parameters can simply be scaled with device area. In the present study it will be shown that when polysilicon‐emitter bipolar transistors are reduced to submicron dimensions, shadowing of the ion implant into the emitter sidewalls can alter the dopant concentration in the polysilicon diffusion source, thereby changing the dopant profiles in the single‐crystal silicon, and hence the junction depths. This shadowing effect, although present in all devices, is only found to affect the electrical parameters of transistors when the emitter size approaches submicron dimensions.