Lifetime In Silicon Research Articles

Rapid thermal oxidation of porous silicon for surface passivation

Rapid thermal oxidation with dry oxygen has been carried out on porous silicon (PS) films formed by electrochemical etching. The purpose of the paper was to investigate the surface passivation capability of the oxidized PS layers and to understand the oxidation mechanism. Rutherford back scattering (RBS) and X-ray photoemission spectroscopy (XPS) analyses confirmed the formation of a stoichiometric quasi-silicon dioxide. Besides, elastic recoil diffusion analysis (ERDA) demonstrated that a high concentration of hydrogen is still present in the PS film even after oxidation. RTO resulted in a good surface passivation effect at high temperature (>1000°C) as seen by internal quantum efficiency analysis. However, lifetime in bulk silicon is affected by the RTO process.

Dopant diffusion studies and free carrier lifetimes during rapid thermal processing of semiconductors

Rapid thermal processing of semiconductors involves significant photonic and subsequent thermal excitation. In the past, photonic excitation during rapid thermal annealing had been speculated to lead to significant enhancement of dopant diffusion or activation. In this work we present some experimental results indicating the absence of any such enhancement at high temperatures (∼1000–1050°C) which most often are employed during the metal-oxide–semiconductor device processing. The implanted dopant (boron, arsenic or phosphorus) movement in silicon during different rapid thermal annealing conditions was studied using secondary ion mass spectroscopy (SIMS) technique. To understand the effect of point defects in controlling the diffusion process, the concentrations of charged and neutral point defects were calculated as a function of carrier concentration using previously published defect-carrier relations. The dependence of free carrier concentration on lattice perturbation parameters such as impurities and temperature was formulated and used in calculating carrier lifetimes ( τ) in silicon. We qualitatively analyze two competing reactions, (i) the phonon release at the defect sites and (ii) the Auger electron process due to many electron interactions, to explain the apparent absence of any enhanced dopant diffusion. In our analyses, we obtain a highest free carrier lifetime of about 442 ns in the case of low dose (1e13/cm 2) implanted sample during the transient stage (700°C) of the dopant activation cycle. The corresponding smallest (∼17 fs) free carrier lifetime was obtained for the high dose implanted sample (dopants already activated) at 1000°C, the steady state part of an extended anneal cycle. Based on the detailed free carrier lifetime analyses, we suggest that any enhanced dopant activation or diffusion, at the best, may occur only at very low temperatures in the samples implanted with low doses of dopant atoms.

An optical technique to measure the bulk lifetime and the surface recombination velocity in silicon samples based on a laser diode probe system

A high sensitivity, pump–probe optical method to measure the bulk minority-carrier lifetime and surface recombination velocity in silicon is proposed. A pig-tailed 1.55 μm CW laser diode is used to detect the transient of the excess carriers generated by a short Nd:YAG laser pulse. The probe beam is launched parallel to the sample surface while the pump beam uniformly illuminates the sample perpendicular to its surface. Separation between bulk lifetime and surface recombination velocity is achieved by performing the measurement on samples of different thickness. Experimental results indicate that separation of bulk and surface contribution is feasible in a wide range of surface recombination velocities thus making this method suitable to investigate the effects of surface passivation techniques.

Calculation of vibrational lifetimes in amorphous silicon using molecular dynamics simulations

The decay of normal-mode excitations is calculated for amorphous silicon through molecular-dynamics simulations within periodic supercells consisting of 216 and 4096 atoms. Phenomenological structural and interatomic potential models are employed. At moderate temperatures, lifetimes are found to be on the order of 10 ps and lifetimes of localized and extended nonpropagating modes are comparable. These features are in agreement with related perturbation theory calculations, and in strong disagreement with the frustrated anharmonic decay predicted by the fracton model and apparently with the results of anti-Stokes Raman experiments performed at $T=10$ K.

Contactless measurements of the photocarrier lifetime in amorphous silicon by a heterodyne experiment

We describe a heterodyne detection scheme for an optical measurement of the photocarrier lifetime in semiconductors. The setup utilizes the Doppler shift of a laser beam that is diffracted from a periodic modulation of the optical constants of a sample, when it is illuminated with a moving interference grating. The advantage of heterodyne detection is its high sensitivity and the extraction of phase information of the diffracted beam. We present measurements on amorphous hydrogenated silicon.

Temperature and injection dependence of the Shockley–Read–Hall lifetime in electron-irradiated p-type silicon

The Shockley–Read–Hall (SRH) carrier lifetime in electron-irradiated low-doped p-type silicon was measured at different injection levels and various temperatures. The lifetime under high-level injection was determined using the open-circuit carrier decay technique. The reverse recovery technique was used to determine the lifetime under low-level injection. The defect composition was studied using deep-level transient spectroscopy, and according to that the SRH lifetime is calculated. The good agreement between the calculated and the measured lifetimes strongly indicates that the lifetime is controlled by two different deep levels. At low injection levels, the lifetime is mainly controlled by the singly negative charge state of the divacancy center, HC−HT=0.421 eV, and at high injection levels by the vacancy–oxygen complex, HC−HT=0.164 eV. These are the same levels controlling the lifetime in electron-irradiated n-type silicon.

Molecular dynamics simulations of vibrational lifetimes in amorphous silicon

Molecular dynamics simulations of vibrational lifetimes in amorphous silicon

Molecular dynamics simulations of vibrational lifetimes in amorphous silicon

Abstract Recent theoretical and time resolved Raman studies disagree on the lifetime of high energy vibrational modes in amorphous silicon. The latter suggests that the lifetime increases with increasing frequency and is of the order of 10 ns for the highest frequency modes, while the former predicts a picosecond timescale that follows the two-phonon density of states. Here we present the results of molecular dynamics simulations which are complementary to the perturbative calculations. At different temperatures, kinetic energy is put into selected modes of vibration in 216 and 4096 atom systems with periodic boundary conditions and the Stillinger—Weber potential. The lifetime of medium and high frequency modes is found to be of the order of 1 ops at 5, 10 and 30 K, in qualitative agreement with the perturbative calculations.

RF technique for determining ambipolar carrier lifetime in pin RF switching diodes

A new method is presented for determining the carrier lifetime in silicon or gallium arsenide pin RF switching diodes using microwave and RF measurements. Swept frequency measurements are used to determine the reactance minimum of the pin diode. This frequency of the pin diode reactance minimum is shown to be inversely proportional to the I-region carrier lifetime. The procedure can be performed at high or low bias levels on any pin diode technology.

Electrical properties of platinum-hydrogen complexes in silicon

The interaction between hydrogen and platinum is studied in n- and p-type silicon using deep-level transient spectroscopy. Hydrogen is introduced by wet-chemical etching or during crystal growth. In both cases we find that hydrogen forms only electrically active complexes with platinum. Four platinum-hydrogen related deep levels are identified: E(90) at ${\mathrm{E}}_{\mathrm{C}}$-0.18 eV, E(250) at ${\mathrm{E}}_{\mathrm{C}}$-0.50 eV, H(150) at ${\mathrm{E}}_{\mathrm{V}}$+0.30 eV, and H(210) at ${\mathrm{E}}_{\mathrm{V}}$+0.40 eV. These levels belong to at least three different platinum-hydrogen complexes. Level E(250) is identical to the so-called midgap level in Pt-doped Si, which is believed to control the minority-carrier lifetime in Pt-doped silicon. Level H(150) is an acceptor and is present both in n- and p-type samples after hydrogenation. It belongs to a platinum-hydrogen complex which contains more hydrogen atoms than the complexes responsible for the other hydrogen-related levels. Annealing at temperatures above 600 K results in a complete dissociation of all the platinum-hydrogen related defects and the substitutional platinum concentration is fully restored.

Carrier lifetimes in silicon

Carrier lifetimes in semiconductors are being rediscovered by the Si IC community, because the lifetime is a very effective parameter to characterize the purity of a material or device. It has become a process and equipment characterization parameter. The various recombination mechanisms are discussed and the concept of recombination and generation lifetime is presented. We show that surface recombination/generation plays an important role in today's high purity Si and will become yet more important as bulk impurity densities in Si are reduced further. Furthermore, the dependence of lifetime on impurity energy level and minority carrier injection level is discussed. Concepts are stressed in the paper, with the necessary equations to clarify these concepts. Wherever possible, the concepts are augmented with experimental data, with particular emphasis on the case of iron in silicon, because Fe is one of the most important impurities in Si today. We have used Si in the examples because lifetime measurements are most commonly made in Si.

Lifetime control in silicon devices by voids induced by He ion implantation

A method to control carrier lifetime in silicon locally and efficiently is presented. Voids, formed by high dose He implants, have been characterized by transmission electron microscopy demonstrating they are well localized in depth within layers thinner than 100 nm while their lateral extent is limited only by the masking capability during He implantation. Deep level transient spectroscopy measurements, performed on diodes containing different void densities, revealed the presence of two well defined trap levels, independent of void characteristics, at Ev+0.53 for holes and Ec−0.55 for electrons. These characteristics make them ideal for lifetime control in reducing parasitic transistor gain. Gummel plots on transistors have shown that when voids are formed the gain decreases from 1 to 10−3. The other transistor characteristics are only slightly influenced by the presence of voids.

Identification of Cr in p-type silicon using the minority carrier lifetime measurement by the surface photovoltage method

The effect of CrB pair dissociation on the minority carrier lifetime in p-type silicon is studied using the surface photovoltage (SPV) and deep level transient spectroscopy (DLTS) methods. Experiments were conducted using Cr doped samples (0.5×1012–5×1012 cm−3) with resistivity ranging from 1 to 50 Ω cm. The minority carrier lifetime, increased after the dissociation of CrB by a factor ranging, depending upon resistivity, approximately from 2.0 to 10. This is in contrast to a tenfold reduction observed in the minority carrier lifetime following the dissociation of FeB pairs. The resistivity dependence of the minority carrier lifetime in Cr doped sample can be successfully predicted according to the Shockley–Reed–Hall (SRH) model. It is demonstrated that the defects with energy levels of Ev+0.27 eV and Ec −0.22 eV are the main recombination centers for CrB and Cri, respectively.

Effect of nitrogen doping on microdefects and minority charge carrier lifetime of high-purity, dislocation-free and multicrystalline silicon

We studied the effects of Si growth in atmospheres containing N 2 on minority charge carrier lifetime τ using a high-purity, induction-heated, float-zone (FZ) crystal growth method. Ingots were grown with purge gases that ranged from pure argon (99.9995%) to pure N 2 (99.999%). τ was measured as a function of position along the ingots using the ASTM F28–75 photoconductive decay (PCD) method. We found that Ga-doped, multi-crystalline silicon ingot growth in a partial or total nitrogen ambient has a negligible effect on minority charge carrier lifetime and no significant grain boundary passivation effect. Values of 40 μms < τ < 100 μs were typical regardless of ambient. For dislocation-free (DF) growth, the degradation of τ is minimal and τ values above 1000 μs are obtained if the amount of N 2 in the purge gas is below the level at which nitride compounds form in the melt and disrupt DF growth.

Effects of carbon implantation on generation lifetime in silicon

In this study, we present characterization of metal–oxide–silicon (MOS) capacitors fabricated on carbon (C12) implanted Si substrates. Carbon was implanted at an energy of 50 keV with doses ranging from 1×1012 cm−2 to 4.1×1015 cm−2. Metal–oxide silicon capacitors were fabricated and used to determine the MOS capacitance–voltage (C–V) and capacitance–time (C–t) behavior. These measurements revealed a strong correlation between carrier lifetime and the C dose. Degradation in lifetime was observed for C dose levels as low as 4×1012 cm−2. At C doses equal to and above 6.4×1013 cm−2, extremely low generation lifetimes were obtained (∼10−7 s). On the other hand, for C dose levels higher than 2.7×1014 cm−2, a low accumulation capacitance was observed at high frequencies and attributed to hole traps. Below this dose, both flatband voltage and interface trap density of the C implanted samples were comparable to those of the monitors.

Exploratory Observations of Effect of Rapid Thermal Processing on Silicon Minority Carrier Lifetime Using Laser Microwave Photoconductance Method

The effect on the minority carrier lifetime of Czochralski wafers undergoing rapid thermal processing is being examined. It was found that the minority carrier lifetime of silicon increased significantly after the rapid thermal process was completed. It was also discovered that the lifetime took more than 200 h to reach a steady‐state value after the rapid thermal process. Once this value had been reached, it remained fairly stable even at elevated (150°C) temperature. Oxygen annihilation of Czochralski wafer and modification of the interface by RTP are suggested as possible explanations for the observation.

SPICE analysis of the SEU sensitivity of a fully depleted SOI CMOS SRAM cell

SPICE analysis of SEU sensitivity of a 6-T SRAM cell using commercially-representative fully depleted SOI CMOS technology parameters indicates that reduction of the minority carrier lifetime (parasitic bipolar gain) and use of thinner silicon can significantly reduce SEU sensitivity. >

Intrinsic upper limits of the carrier lifetime in silicon

We have measured the carrier lifetime in ultrapure n- and p-type silicon with carrier densities between 1015 cm−3 and 1019 cm−3. At high carrier densities the dominant recombination mechanism is known to be band-to-band Auger recombination. At carrier densities below some 5×1018 cm−3 experimentally determined carrier lifetimes in n- and p-type silicon were always found to be smaller than expected for band-to-band Auger recombination. Our results are explained by taking into account electron–hole correlations in the Auger process. Since Auger recombination is an unavoidable material property this represents a new intrinsic upper limit of the carrier lifetime in silicon.

Relaxation processes induced in Si-SiO 2 systems by ionizing radiation and pulsed magnetic field treating

Comparison of prolonged relaxation processes induced by ionizing radiation (IR) and pulsed magnetic field treating (PMFT) in p-channel MOSFET elements of integral circuits as well as in the concomitant test MOS-capacitors has been carried out for the first time. Time dependent changes of oxide charge density and interface states energy distribution after the end of X-ray (20 keV, 5 × 10 4 rad (Si)) were investigated. The unusual result is the appearance of considerable changes of MOS system's characteristics only several days after PMFT with the amplitude 0.3 MA m −1. It was discovered that PMFT caused the considerable unmonotonous changes of shallow donor concentration and generation lifetime in silicon. The PMFT induced the impurity and intrinsic defect reaction in silicon contrary to the defect generation in the oxide and SiSiO 2 interface by the IR.

Increase in effective carrier lifetime of silicon at low carrier injection levels

The increase in the effective carrier lifetime of oxidized p-type silicon at low carrier injection levels is studied from the viewpoint of silicon surface effects. The effective carrier lifetime is measured by a microwave photoconductive decay method. A gold/oxide/silicon structure is used to examine the dependence of effective carrier lifetime on injected carrier concentration. The effective carrier lifetime is measured at various voltages applied between the gold electrode and the silicon substrate in order to change the silicon surface conditions, i.e. accumulation, depletion or inversion. Increase in the effective carrier lifetime at low carrier injection levels is observed only when the inversion layer is induced at the silicon surface. The increase in effective carrier lifetime may be due to slow recombination of excess minority carriers stored in the inversion layer at the SiO2/Si interface with a low interface trap density and/or slow diffusion of the excess minority carriers into the bulk of the silicon.