Minority Carrier Generation Lifetime Research Articles

Minority-carrier lifetime analysis of silicon epitaxy and bulk crystals with nonuniformly distributed defects

Existing analyses of the pulsed response of an MOS capacitor for minority-carrier lifetime determination result in a lifetime value averaged over most of the depletion region width. The authors present an analysis of MOS capacitance-versus-time data that enables minority-carrier generation lifetime to be plotted as function of depletion-region depth. The technique is shown to be useful for samples with bulk or buried interfacial layer defects that have defect-free surfaces. Data are presented for intrinsically gettered bulk crystals and extrinsically gettered Si (2%Ge) epitaxial layers with misfit dislocations. For samples that do have uniform lifetimes, the measurement time required for determining carrier lifetime is reduced by more than an order of magnitude. >

Application of deep level transient spectroscopy to metal-oxide-semiconductor relaxation transients

A method for determining minority carrier generation lifetimes and hold times in metal-oxide-semiconductor devices is presented. The technique overcomes some of the uncertainties inherent in the commonly used Zerbst lifetime measurement and can be used on very small devices. In the method a deep level transient spectroscopy system is used to separate generation currents of different activation energies, and to provide values for these energies, so indicating the source of the generation at a particular temperature. In the range where generation in the depletion region is dominant, the minority-carrier generation lifetime can be derived. In all cases the data can be directly related to the ‘‘hold’’ time of a metal-oxide-semiconductor capacitor.

Gated diode leakage and lifetime measurements of misfit dislocation gettered Si epitaxy

Gated diode leakage current and minority-carrier lifetime are compared between Si wafers extrinsically gettered with epitaxial misfit dislocations and reference homoepitaxial material. The stability and gettering efficiency of the interfacial misfit dislocations have been verified by measuring leakage currents of less than 1 nA/cm2 for both gate depletion and accumulation for a large number of diodes. In either mode, the gated diodes with misfit dislocation gettering exhibited more than an order of magnitude lower leakage current than that produced by standard epi without misfit dislocations. In addition, minority-carrier generation lifetimes greater than 2 ms were typical of material extrinsically gettered via misfit dislocations, while reference epi was two to three times lower. The lifetme was found to be uniform in the near-surface region, but was drastically reduced in the immediate vicinity of the misfit locations, indicating that the defects may provide useful options in high-speed devices, latch-up control, and radiation hard devices.

Properties of Atmospheric and High Pressure Oxide Capacitors with Laser‐Recrystallized Polysilicon Electrodes

A study concerning the effects of cw laser recrystallization of polysilicon electrodes on the integrity of the underlying oxide and the interface properties has been carried out. Thicknesses of the oxides used in this study ranged from 300 to 1100Å. There was no significant change in the breakdown field strength, in the I‐V characteristics, or in the minority carrier generation lifetime of the oxides due to laser annealing. A slight undesirable shift of the C‐V curves was observed as a result of laser processing, but was eliminated with a subsequent thermal anneal at 900°C or higher in ambient. SEM examination of the recrystallized polysilicon surface morphology revealed that large, smooth grains were formed, with no undesirable effects on the oxide integrity. However, for laser powers above the threshold for melting of the silicon substrate, degradation of the electrical and structural properties was observed. This result was difficult to avoid for the case of thin oxides (≤ 300Å), due to the narrow laser processing window. Therefore, it is concluded that cw laser recrystallization does not adversely affect the properties of the oxide layer, the starting substrate, or the interface, if it is carried out at a laser power within the useful laser processing window.

Determination of minority-carrier generation lifetime in beam-recrystallized silicon-on-insulator structure by using a depletion-mode transistor

We describe a technique for measuring minority-carrier lifetime on a very small area of material and apply this technique to recrystallized silicon layers on an insulating substrate where the localization of the crystalline defects gives rise to small defect-free regions actually used for devices. The method uses a depletion-mode transistor in which drain-source conductance yields a signal equivalent to capacitance signal, thus allowing measurements equivalent to conventional Zerbst transient capacitance to be made in the defect-free regions.

Determination of surface- and bulk-generation parameters from dark-current measurements in surface-channel CCD's

A technique for determining surface-generation velocity and bulk minority-carrier generation lifetime from measurements in surface-channel charge-coupled devices (SCCD) is described. Depleted surface-generation velocity of 1.1 cm/s and bulk minority-carrier generation lifetime of 130 µs have been determined in the channel region for the devices used, and are in good agreement with data obtained by other techniques.

A fast extrapolation technique for measuring minority-carrier generation lifetime

The transient response of a pulsed MOS capacitor is used to calculate the minority-carrier generation lifetime. For Si substrate with a long lifetime, traditional approaches suffer from the inefficiency of long measurement times. An extrapolation technique presented here significantly reduces the measurement time while still maintaining good accuracy. This method applies to capacitors with constant bulk-generation rates. The linear correlation coefficient of the 1n W- t plot is monitored to ensure accuracy of the measurement technique.

Oxygen Precipitation in N+ Silicon

The advantages of oxygen precipitation in terms of intrinsic gettering to reduce oxidation induced surface defect densities and improve minority carrier generation lifetimes (τ) are well documented in the literature (1–3). Various gettering cycles to establish oxygen precipitation in n type and p type nondegenerate substrates have been developed (4–6), based on homogeneous nucleation theory. For nondegenerate silicon no differences in oxygen precipitation kinetics related to the dopant type have been reported. However, with the increasing interest in both p/p+ and n/n+ epitaxial layers for CMOS devices (7), work on the precipitation of oxygen in both p+ and n+ degenerate silicon substrates has revealed a dependence of oxygen precipitation kinetics on dopant type (8–11). In the case of p+ silicon the differences in precipitation kinetics are small when compared to p- silicon (10,11). For n+ silicon it has been reported (8–11) that the dopant concentration plays a major role and that a significant retardation of oxygen precipitation is observed. There are currently two different explanations for the difficulty encountered in producing sufficient oxygen precipitation in n+ Si. These are the failure to incorporate sufficient oxygen into the crystal during crystal growth (12) and an interaction between intrinsic point defects and the n type dopant, which influences the oxygen precipitation kinetics (8,13).

The Effects of Substrate Oxygen Content and Preannealing on the Properties of Silicon Epitaxial Layers

A study was carried out to evaluate whether the quality of Si epitaxial layers could improve if they were deposited on substrates intrinsically gettered through thermal annealing. Three different two‐step procedures were used to preanneal the substrates prior to deposition. Optical microscopy revealed the presence of defect‐free (denuded) zones at the surfaces of preannealed substrates only when the initial concentrations of interstitial oxygen in the substrates were , and if the high temperature step of the preannealing was carried out in a nonoxygen ambient. While the density of oxidation‐induced stacking faults in the epitaxial layers showed no such dependence, the minority carrier generation lifetimes in the layers were strongly dependent on the oxygen content and thermal history of the substrates. Layers deposited on preannealed substrates of high initial oxygen content exhibited the greatest lifetimes. It is believed that oxygen precipitates and related defects, when present in a substrate, getter metallic impurities introduced during processing away from the epitaxial layer and thus improve lifetimes. Such gettering appeared to be most effective when the substrates had both surface denuded zones and high densities of bulk defects.

Oxygen Precipitation in Silicon - Its Effects on Minority Carrier Recombination and Generation Lifetime

ABSTRACTThe effects of oxygen precipitation on the minority carrier recombination lifetime (TR) and the carrier generation lifetime (TG) have been characterized for a ‘typical’ silicon crystal grown with the Czochralski method. Infrared (IR) absorption measurements were obtained on polished wafers, before and after 2 step thermal anneals at 800°C and 1050°C to characterize the axial distribution of interstitial and precipitated oxygen in the ingot. Computerized measurements on NMOS diode and capacitor arrays were used to characterize the axial and radial distributions of carrier lifetime. The results indicate that oxygen precipitation is the dominant mechanism contributing to the degradation of both minority carrier recombination andgeneration lifetime.

Field enhanced carrier generation in MOS-capacitors containing defects

Minority carrier generation lifetime was measured as a function of depletion width on wafers with different densities of defects. The results were compared with theoretical predictions for field enhanced carrier emission from coulomb centers. We found that capacitors with a very low lifetime due to stacking faults or metallic precipitations show a drastically enhanced field dependence of generation rate. Agreement with theory can be obtained if we assume a locally enhanced electric field at the defects which can be one order of magnitude higher than the average bulk field.

Lifetime in ion implant damage gettered silicon by MOS voltage ramping

The Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion implant damage gettering of silicon has been investigated using non-steady-state linear voltage ramp technique on MOS devices. Generation lifetimes were measured on devices that have been ion implant damaged and annealed in nitrogen at high temperature. The results were compared with control devices. It was found that a gettering treatment consisting of a high-temperature nitrogen anneal following "room temperature" implant increased the generation lifetime of minority carriers in the device by an order of magnitude.

Measurement of minority-carrier lifetime in GaAs using the transient response of MOS capacitors

The minority-carrier generation lifetime has been measured in GaAs by observing the transient capacitance that occurs when an MOS is switched from accumulation to deep depletion. Application of this technique requires the fabrication of an MOS that shows inversion; this has been done by growing a native GaAs oxide with plasma oxidation. Preliminary results are reported on both lifetime and surface recombination velocity in p-type GaAs.