A. A. Stolyarov

Plasma and injection modification of the gate dielectric in MOS structures

Abstract It has been shown that both RF plasma and plasma-jet treatments led to the creation of electron traps in the bulk of SiO2 film. As a result, it is possible to increase the breakdown voltage of a metal–oxide–semiconductor (MOS) structure when the breakdown probability is significantly decreased. It has been found that injection treatment of MOS structures with thermal SiO2 film allows control of the statistical distribution of charge defects, and thus the mean charge injected into the dielectric to breakdown is increased. The modification of MOS devices having a gate dielectric of SiO2/phosphosilicate glass by Fowler–Nordheim (FN) electron injection taking place in high-fields was also studied. Constant-current FN electron injection from the silicon substrate and the metal electrode was used to modify the charge state of the MOS structure.

Multilevel current stress technique for investigation thin oxide layers of MOS structures

In this study, a new technique of multilevel current stress for investigation thin oxide layers of MOS structures is proposed. This technique allows to investigate the generation and relaxation of positive and negative charges, accumulating in, nano-thickness gate dielectric of MOS structures under many stressing situations. The parameters characterizing the change of charge state in the thin oxide layers of MOS structures during the stress have been monitored by means of time dependence of voltage shift applied to a sample during the injection. The method takes into account the process of the MOS capacitance charging by the constant current pulse. In comparison with the conventional techniques our method is nondestructive and enables to reduce the high-field stress time while measuring the injection current-voltage characteristics of the MOS-structure. We consider this method to provide higher accuracy and to decrease the probability of dielectric breakdown. The application of present technique was carr mied out during the investigation of charge generation and relaxation, during and after high-field tunnel injection of electrons in thin thermal film of SiO2. The thin oxide layers of MOS structures after plasma and irradiation treatments also are investigated.

Method of metal-insulator-semiconductor structure interface analysis

The method of metal-insulator-semiconductor (MIS) structure interface analysis, based on applying a direct current pulse of preset amplitude to a MIS structure, is proposed. The variation of the voltage across the MIS structure is recorded while the current flows. The method allows measurement of interface characteristics such as the interface states density, the flat band voltage, the surface potential value for a given bias and the potential barrier height on the injection interface. In addition, the method enables us to determine the charge degradation parameters of the MIS structure under and after high-field stressing.

Modification of MIS structures by electron irradiation and high-field electron injection

The change in the charge state of metal–insulator–semiconductor (MIS) structures with a two-layer silicon-dioxide–phosphosilicate-glass gate insulator upon their modification under electron irradiation and high-field electron injection is studied. A thin glass film is formed by doping a thermal SiO2 film formed on the surface of a silicon wafer with phosphorus. It is found that the negative charge accumulated in a thin film of phosphosilicate glass during high-field tunneling electron injection or electron irradiation can be used to adjust the threshold voltage and to increase the charge stability and the breakdown voltage of MIS devices. It is shown that MIS structures need to be annealed at a temperature of approximately 200°C to obtain high thermal-field stability after modification of their charge state by the electron injection or electron irradiation. It is found that the use of a two-layer silicon-dioxide–phosphosilicate-glass gate dielectric increases the average value of the charge injected into the insulator to breakdown and decreases the amount of defect structures.

Modification of thin oxide films of MOS structure by high-field injection and irradiation

We have investigated processes of modification and changing of the charge state of MOS structures having a multilayer gate dielectric based on a thermal SiO2 film doped with phosphorus under conditions of different modes of high-field electron injection and an electron irradiation. We have determined that negative charge, accumulating in the phosphosilicate glass (PSG) ultra thin film of the MOS structures having the two-layer gate dielectric SiO2-PSG under conditions of both high-field tunneling injection of electrons and electron beam, could be used for a modification of devices having the same structure (e.g. correction of threshold voltage, increase of charge stability and breakdown voltage of MOS structure). We have shown that when thickness of PSG film increased, a raising of the electron traps density occurred, but the value of the cross-section of electron traps was the same. It was established that in order to obtain MOS structures with high thermal stability, one has to anneal them at 200° C after performing irradiation treatment.

Modification of dielectric films in MIS structures using the injection-thermal treatment

Dielectric films and silicon-insulator interfaces in metal-insulator-semiconductor (MIS) structures are modified using injection-thermal treatment, which involves high-field injection of a specified charge into the gate dielectric and subsequent annealing of the structure. The effect of the injection-thermal treatment modes on the MIS structure modification is investigated. The injection-thermal treatment is shown to reduce imperfection of the dielectric films and, thus, enhance reliability of the MIS devices. It is established that the MIS structure modification processes occurring at the injection-thermal treatment are largely identical to those occurring at the radiation-thermal treatment; therefore, for certain MIS devices, the radiation-thermal treatment can be replaced by the injection-thermal one.

Investigation of Injection- and Radiation-Thermal Processes in Thin Gate Dielectric Films of MIS Structures

In order to modify the gate dielectric of MIS structures we suggest to implement the injection-thermal treatment which consists in the high-field injection of electrons of set density into the thin dielectric film and the subsequent annealing of the structure. We investigate an influence of modes of the injection-thermal treatment onto the modification of MIS structures. We demonstrate that the processes of MIS structure modification taking place at the injection-thermal treatment in many respects are identical to the processes taking place at the radiation-thermal treatment. We study an influence of modes of the high-field electron injection into the gate dielectric of MIS structure onto densities of charge defects and the injection hardness of samples. Besides, we research an influence of doping of the silicone dioxide film by phosphorus onto the same characteristics.

Method of stress and measurement modes for research of thin dielectric films of MIS structures

The paper proposes a new method of stress and measurement modes for research of thin dielectric films of MIS structures. The method realizes injection of the most part of charge into gate dielectric in one of stress modes: either current owing through dielectric is constant or voltage applied to gate is constant. In order to acquire an additional information about changing of charge state of MIS structure, the stress condition is interrupted in certain time ranges and during these time ranges the mode, in which structure is, is the mode of measurement. In measurement mode, changing of electric fields at interfaces between dielectric and semiconductor is monitored. By using these data, density of charge, which is accumulated in gate dielectric, and its centroid are calculated. Besides, by using these data, one studies processes of generation and relaxation of charge in dielectric. In order to raise precision of the method and reduce an influence of switching effects in measurement mode, density of measurement current should be much lower than density of stress current.

Charge characteristics of MOS structure with thermal SiO2 films doped with phosphorus under high-field electron injection

The processes of changing the charge state of metal–oxide–semiconductor (MOS) structures that contain a multilayer gate dielectric on the basis of a thermal SiO2 film doped with phosphorus under the influence of high-field electron injection are investigated. It is determined that a negative charge accumulating in a thin phosphosilicate glass (PSG) film of MOS structures containing a SiO2–PSG two-layer gate dielectric under high-field tunneling injection of electrons can be used for the correction of the threshold voltage, for the enhancement of the charge stability, and for an increase in the breakdown voltage of devices with MOS structure. It is shown that the density of electron traps increases with an increase in the thickness of the PSG film containing them, while their capture cross section remains unchanged. The method for the modification of the electrophysical characteristics of MOS structures by the high-field tunneling injection of electrons into a dielectric under a controlled current load is proposed. The method allows one to control changes in the parameters of MOS structures directly in the process of their modification. It is established that a MOS structure with a high thermal field stability can be obtained by its annealing at 200°C after the modification of its charge state by the electron injection.

Injection modification of multilayer dielectric layers of metal-oxide-semiconductor structures at different temperatures

The charge state change of MOS structures with multilayer dielectric films SiO2-PSG under high-field injection modification at different temperatures is studied in this article. The effect of temperature on the thermal stability of the negative charge component used to adjust the threshold voltage of MOS transistors is investigated. It is found that the performance of the high-field injection modification of MOS structures in the mode of constant current at elevated temperatures increases not only the density of the trapped negative charge but also its thermally stable component.