M. N. Levin

Activation of a semiconductor surface by a pulsed magnetic field

The possibility of semiconductor surface activation, which shows up as a long-term increase in the adsorption capacity in response to a short exposure to a pulsed magnetic field, is demonstrated for the first time. Magnetic-field-induced surface activation is studied on silicon, germanium, and gallium arsenide crystals. The effect revealed extends the capabilities of thin-film growth on the semiconductor surface.

X-ray or UV adjustment of MOS threshold voltage: Analytical and numerical modeling

A model is formulated that describes how radiation-induced charge accumulates in the gate oxide of a MOS structure and how it decays through tunneling and thermal emission. The model is used in a numerical analysis of the x-ray or UV adjustment of threshold voltage in MOS-circuit manufacture. The limits of this process technique are evaluated.

X-ray and UV Adjustment of Threshold Voltage in MOS-Circuit Manufacture

Techniques are presented for the radiation fine adjustment of threshold voltage in MOS circuits, employing x-rays (photon energies 10–20 keV) and near-UV radiation. The adjustment consists in the controlled generation of heat-resistant charge in gate oxide under irradiation, due to the presence of phosphorus in the oxide. The experience gained by using the techniques in the mass production of a wide variety of MOS circuits is briefly reviewed.

Charge distribution in a MIS insulator from spectral characteristics of photoemission current

The field dependence of photoemission currents in a MIS structure was derived for the case when the space charge is randomly distributed over the insulating layer. It was found analytically that the position of the top of the potential barrier for electrons photoinjected from the gate into the insulator is defined by the derivative of this barrier with respect to the external field strength. A method for correctly determining the space charge profile in a MIS insulator is suggested. The profile is derived from a family of spectral characteristics taken at different gate voltages. The method is especially suitable for profiling the negative charge in MIS insulators.

Transient spectroscopy of surface states in a constant subthreshold current mode for MIS transistors

The spectrum of surface states at a semiconductor-insulator interface is studied through the relaxation of the gate voltage of an MIS transistor measured with a constant subthreshold current. The proposed method makes permits study of these states in both halves of the semiconductor gap and is convenient for testing integrated circuits. The possibilities of this method are illustrated using the example of radiation induced changes in the distribution of surface states.

Effect of periodically time-dependent magnetic fields on a population of spin states of radical pairs

The time dependences for a population of radical pair spin states and the amplitudes of the transitions between them are calculated for magnetic fields of complex configuration. The abovementioned values are derived directly from the solution to the Liouville equation for the components of a spin density matrix for a radical pair. The oscillating mechanism of the relaxation of partial populations of spin levels upon the monotonous reduction of the full population was established in the course of our calculations.

Method for evaluating the parameters of radiation defects and predicting the radiation resistance of MOS transistors

A new approach to analysis of the radiation resistance of MOS transistors is proposed, which takes into account both the accumulation of a radiation-induced charge on the surface states and in the volume of oxide and the relaxation processes involving thermal and tunneling leakage of the accumulated charge. The prediction of radiation stability is based upon the knowledge of parameters of the radiation-induced defects, which are determined from the experimental dose dependences established at high dose rates and from the temperature dependences and kinetics of relaxation of the threshold voltage. Once these parameters are determined, the behavior of a MOS transistor under the action of radiation of an arbitrary (including low) intensity can be predicted.

Influence of weak magnetic fields on radical-pair reactions

The time dependences of the populations of radical-pair spin states and transition amplitudes between them have been calculated for constant and pulsed magnetic fields, with allowance for hyperfine interaction. The above-mentioned characteristics have been found directly by solving the Liouville equation for the radical-pair spin density matrix. It is established that the relaxation of spin-level partial populations oscillates with a monotonic decrease in the total population.

Modeling of the effect of low intensity ionizing radiation on MOS elements of VLSI circuits

A method for predicting the tolerance of MOS VLSI circuits to low intensity cosmic rays is reported. The method is based on the analysis of the test MOS structure response to high-dose-rate radiation and on the solution of the system of equations describing the radiation-charge accumulation in the gate oxide of the poly-Si-SiO2(P)-Si structure and its relaxation by tunneling and thermal emission.

A noncontact method to study the charge state of the semiconductor-insulator interface

We present a method for investigating the charge state of the semiconductor-insulator interface using the measurements of the contact potential difference between the surface of the insulator film and a vibrating probe. In this method, the surface electrostatic potential is changed through charge variation at the outer surface of the insulator. The charge value is determined by the time of the structure exposure to a corona discharge. The method is applied for investigating the effect of exposure of a silicon-silicon dioxide system to radiation and pulse magnetic fields.