Influence of substrate freeze-out on the characteristics of MOS transistors at very low temperatures

The low temperatures current-voltage characteristics of N-channel MOS transistors have been analysed. An excess drain current is observed for intermediate values of drain voltage. This anomalous drain current is explained in terms of substrate freeze-out, since at very low temperatures the MOS structure has a type of floating substrate potential within the depletion region. Due to the increase of the majority carrier current, flowing through the substrate to the source at increasing drain voltage, this substrate potential increases and causes a change of threshold voltage. This change is observed in the current-drain voltage characteristics of the MOSFET. Various experiments, such as measurements of substrate current, effects of temperature, gate and substrate voltages, support this interpretation. MOS transistors with various geometries and various dopings are analysed.     

Hot-electron trapping in thin LPCVD SiO2dielectrics

The electron-trapping and surface-state generation characteristics of thin LPCVD SiO2dielectrics have been studied using avalanche hot-electron injection. Layered structures of thermal and LPCVD oxide have been examined as a function of anneal time and temperature. After a 1000°C anneal, bulk trapping in the LPCVD oxide was reduced to levels comparable to those in a high-quality dry thermal oxide. Sensitivity to remaining traps was reduced by the presence of a thermal oxide layer on the semiconductor surface. After a post-deposition anneal (PDA), these layered surfaces demonstrated hot-electron performance equal to that of thermal oxide within measurable limits. Also, layered structures generally demonstrated better resistance to surface-state generation than thermal oxides alone. Since less chlorine is incorporated into the layered structures during fabrication, this result is consistent with a recent model identifying broken chlorine bonds as the origin of surface states.     

Hole trapping and breakdown in thin SiO2

The field dependence of the hole generation rate, also known as the impact ionization coefficient α, in thin SiO2(< 20 nm) was characterized by measuring the negative flat-band shift due to hole trapping. In thicker oxides,alpha = alpha_{0}e^{-H/E}where H = 78 MV/cm for electric fields ranging from 7 to 14 MV/cm, which covers the field range from the onset of significant Fowler-Nordheim current to instant breakdown. The similar field dependences of α and charge-to-breakdown supports the model that hole generation and trapping leads to oxide wearout. Because of the fact that positive charge generation is observed for oxide voltage well below the SiO2bandgap, we propose that the generated holes arise from transition between band tails in the amorphous SiO2. It is also observed that α decreases rapidly when the applied oxide voltage is very low; thus α is a function of both oxide field and voltage in general. This suggests that ultra-thin oxide with low operating voltages might be a good candidate for high endurance E²PROM devices at very low oxide field.     

Characteristics of CO2deposited SIPOS films

The current-voltage characteristics of CO2CVD SIPOS films were studied. Structures have been used in which the low-field and high-field conduction regimes were covered. The conduction mechanism corresponds to the general symmetrical Schottky-barrier model with a modified number of grains parameter. It has been shown that the high-field regime (2 × 10⁵V/cm) is characterized by nonohmic behavior, which is an important design factor in the design of high-voltage SIPOS passivated devices.     

Effect of thermally nitrided SiO2thickness on MIS characteristics

The flatband voltage of metal-insulator-semiconductor (MIS) structures with thermally nitrided SiO2(nitroxide) insulators has been studied as a function of the nitroxide thickness in the range of 10-60 nm, for different nitridation conditions. The most striking result is that 10-nm nitroxide films are far less susceptible than thicker ones to the degradation of the electrical properties of the starting SiO2films induced by nitridation, as revealed by a negative shift of the flatband voltage. For nitridation cycles at relatively low temperatures (900° 120 min or 1000°C 60 min) the shift in the 10-nm films is practically negligible.     

High-performance detector read-out at very low temperatures

An infra-red detection system must be physically colder than the objects it needs to observe. As some of the objects to be observed by the European Space Agency's Infra-red Space Observatory (ISO) might be as cold as a few tens of degrees Kelvin, it is essential that the ISO's detectors should themselves operate at temperatures close to absolute zero. To avoid problems with electromagnetic interference, it is also necessary that detector read-out (i.e. first-stage signal amplification) be located as close as possible to the detectors. As conventional amplifiers cannot work at temperatures close to absolute zero, special techniques had to be used for the ISO's detectors     

Silicon-rich SiO2and thermal SiO2dual dielectric for yield improvement and high capacitance

The use of silicon-rich SiO2and thermal SiO2dual dielectric in memory capacitors and FET's is investigated. It is shown that the silicon-rich layer was conductive and introduced only a small decrease in the series capacitance of the dual dielectric. Consequently, the capacitance of the dual dielectric is close to that of the thermal oxide only. The response time of the silicon-rich layer is measured by using FET response time and is shown to be in the nanosecond range. With this fast response time, it is possible to use the dual dielectric in memory and logic circuits. Another advantage of the dual dielectric is the very high yield due to the field screening of the silicon-rich layer to any nonuniformities in the thermal oxide or at the SiO2-contact interface. This dual dielectric has the promise of high yield and high capacitance for future VLSI circuits.     

Buckling of thermally-grown SiO2thin films

The difference in thermal expansion causes compression in SiO2thermally grown on Si wafers. Unsupported windows of SiO2buckle if the oxide thickness/window width ratio (t/w) is too small. This correspondence presents the experimentally determined t/w ratio for stable films.     

High-voltage planar structure using SiO2-SIPOS-SiO2film

The BVCB0leakage current hFEwere studied for high-voltage planar transistors which had three kinds of passivation films; SiO2-semi-insulating polycrystalline silicon (SIPOS)-SiO2; SIPOS-SiO2; and SiO2-phosphosilicate glass (PSG)-SiO2. The SiO2-SIPOS-SiO2type had a lower leakage current (surface generation current) and higher hFEthan the conventional SIPOS-SiO2type. The SiO2-SIPOS-SiO2type also had the highest BVCB0due to the field-plate effect.     

低温下H_2中的反斯托克斯受激喇曼散射

本文描述了低温下H_2中266nm和283nm激光的受激喇曼散射过程(ASSRS).在液氮温度下,2～6级反斯托克斯(AS)散射均比常温时的结果高.这一低温效应对高级AS散射尤其有效..     

Operation of bulk CMOS devices at very low temperatures

Low-temperature (77K, 4.2K) operation is proposed for bulk CMOS devices to be used in superfast VLSI applications. Symmetrical variation of the parameters of both n-channel and p-channel MOSFETs with respect to the temperature and latch-up immunity makes CMOS a very promising device technology at low temperatures. To demonstrate the performance advantage of circuit operation at low temperatures, inverter chains and 16-kb static random-access memories (RAMs) with 2-/spl mu/m gate length were measured. Average propagation delay for an inverter chain has been reduced to 175 ps (77K) and 104 ps (4.2K) from 296 ps at 300K without sacrificing power dissipation. The power-delay product is less 1 fJ, which is the smallest for silicon devices reported to date. The chip select-access time of the RAM has been reduced to 14.3 ns (77K) from 24 ns (300K).     

Observations on phosphorus stabilized SiO2films

Two experiments were performed with phosphorus stabilized and untreated silicon dioxide films on silicon substrates. In the first, the interaction of phosphorus and boron was studied; it was found that diffusion of boron over a phosphorus stabilized film destroyed its stabilization against ion drift effects at 400°C, but that diffusion of phosphorus over a boron diffused film resulted in a stabilized oxide. In the second experiment, a slowly varying voltage was applied at 600°C to a silicon-silicon dioxide-gold structure and the current through the oxide film was recorded. Both phosphorus stabilized and untreated silicon dioxide films show rectifying characteristics, the more highly conducting direction being that with the silicon negative. In the case of the untreated film, a large peak of current is superimposed on this characteristic at -2.5 volts. This peak is absent in phosphorus stabilized films. Discharge currents equivalent to the charging currents are not observed on removing voltage from the specimen, as they are at 400°C. Five distinguishable types of charge transfer in silicon dioxide films are tabulated, and compared with those described in the literature as occurring in crystal quartz.     

A planarized SiO2interlayer dielectric with bias-CVD

A Bias-CVD^TMprocess has been developed for depositing planarized silicon dioxide films. The process uses, in addition to PECVD deposition, an argon ion etch for planarization. A distinguishing feature of this process is the use of a unique sequence of depositions and etching to control contour and topography, eliminate keyholing, and reduce pinhole density. By varying this Sequence, the film topography can range from conformal to fully planarized. A cold-wall low-pressure CVD system with an eight-wafer batch and 13.56-MHz RF capability was used in this study. Because of the chamber geometry, a dc bias is induced in the wafer support during the RF plasma processing. This bias, typically a few hundred volts, provides the accelerating field for the ion etching of the film. It is the anisotropy of this etch that makes planarization possible. The film has the density and index of refraction of thermally grown oxide. The Si to O ratio is 1 to 1.9 with 8-percent nitrogen and 0.1-percent argon, by RBS. SIMS analysis shows no trace of heavy metals. The effect of process parameters has been characterized. Dynamic RAM's deposited with the sloped film show normal yield and electrical properties; there is no evidence of radiation damage.     

Energy relaxation of photoexcited hot electrons at very low temperatures

The scattering of electrons with energy $\text{?<}\text{1}\text{2}\text{ms}{}^2$ by acoustical phonons at very low temperatures T?ms² is investigated.     

低温下激光辐照BCl_3的研究

用TEA CO_2激光辐照低温下的BCl_3时,从红外吸收光谱观察到硼同位素~(10)BCl_3、~(11)BCl_3有明显的选择性离解,并获得低温下硼同位素浓缩系数较室温下有显著的提高。     

Dielectric relaxation in thermally grown SiO2films

An extensive investigation of the dielectric properties of thermally grown silicon dioxide films was performed in the temperature range from 400°C to 525°C. Principally, the variation of dissipation factor with frequency was observed at various applied peak fields and oxide thicknesses. In the temperature and frequency domain investigated, a large peak in the dissipation factor occurred. This peak corresponded to a massive capacitance dispersion with accompanying peaking of the loss factor at low frequencies. The phenomenon was apparently an ionic space-charge polarization. Theoretical developments based on this model were verified by experiment. The activation energy for the relaxation time was 10.1 ± 0.4 kcal/mole. Examination of the oxide thickness dependence indicated that the carriers were not uniformly distributed initially, but a fixed number was present at a particular temperature and this number was independent of thickness. Further investigation led to the conclusion that a reaction between the metal electrode and the SiO2produced positively charged oxygen vacancies which migrated through the oxide under the influence of an electric field. A mechanism for the production and migration of these vacancies is proposed which complies with the low activation energy as well as the observed temperature and electrode dependence.     

Proton and sodium transport in SiO2films

The results of an investigation into the relative roles of sodium and proton transport in silicon-dioxide films are presented. Tritium oxide (³H2O), tritiated ethanol, neutron activation, and sodium 22 tracer analyses are used to identify the mobile ions directly, and the results of these analyses are then directly correlated with the observed electrical behavior.