K. S. Jones

A systematic analysis of defects in ion-implanted silicon

A classification scheme for the different forms of implant-related damage which arise upon annealing consisting of five categories is presented. Category I damage is “subthreshold” damage or that which results prior to the formation of an amorphous layer. If the dose is increased sufficiently to result in the formation of an amorphous layer then the defects which form beyond the amorphous/crystalline (a/c) interface are classified as category II (“end of range”) damage. Category III defects are associated with the solid phase epitaxial growth of the amorphous layer. The most common forms of this damage are microtwins, hairpin dislocations and segregation related defects. It is possible to produce a buried amorphous layer upon implantation, If this occurs, then the defects which form when the two a/c interfaces meet are termed category IV (“clamshell”, “zipper”) defects. Finally, category V defects arise from exceeding the solid solubility of the implanted species in the substrate at the annealing temperature. These defects are most often precipitates or dislocation loops.In addition to presenting examples of this classification scheme, new results emphasizing category II, IV, and V defects will be presented. For category II defects, the source, dose and mass dependence as well as the influence of pre- and post-amorphization is discussed. The category IV defects which arise from buried amorphous layers in {100} oriented As implanted samples is presented. Half loop dislocations which arise during annealing of high dose As implants, are shown to originate in the category V defects and grow upon dissolution of As clusters and precipitates.

In0.6Ga0.4As/GaAs quantum-dot infrared photodetector with operating temperature up to 260 K

A high-sensitivity In0.6Ga0.4As/GaAs quantum-dot infrared photodetector (QDIP) with detection wave band in 6.7–11.5 μm and operating temperature up to 260 K under normal incident illumination has been demonstrated. The peak detection wavelength shifts from 7.6 to 8.4 μm when the temperature rises from 40 to 260 K. The background limited performance (BLIP) detectivity (DBLIP*) measured at Vb=−2.0 V, T=77 K, and λp=7.6 μm was found to be 1.1×1010 cm Hz1/2/W, with a corresponding responsivity of 0.22 A/W. The high operating temperature is attributed to the very low dark current and long carrier lifetime in the quantum dots of this device. The results show that this QDIP can operate at high temperature without using the large band gap material such as AlGaAs or InGaP as blocking barrier to reduce the device dark current.

Transient enhanced diffusion without {311} defects in low energy B+‐implanted silicon

Low energy and low dose B+‐implanted Si has been studied using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). Czochralski‐grown (100) Si wafers were implanted with 4 keV B+ to a dose of 1×1014/cm2. Subsequently, anneals were performed between 700 and 800 °C for times between 15 s and 8 h in an ambient atmosphere of N2. SIMS results show transient enhanced diffusion (TED) of the boron that saturates in less than 15 min for all annealing temperatures studied. TED results in an increase in the junction depth by at least 60 nm at a 1×1016/cm3 concentration. TEM studies show that, even for the shortest times before TED is observed, {311} defects are not detected. These results imply that there may be more than one source of interstitials for TED.

Effect of fluorine on the diffusion of boron in ion implanted Si

Ion implants of 1 keV 11B+ and 5 keV BF2+, to a dose of 1×1015/cm2 at a tilt angle of 0°, were implanted into preamorphized (Si+,70 keV, 1×1015/cm2) wafers. These samples were rapid thermal annealed in an ambient of 33 ppm of oxygen in N2 at very short times (<0.1 s spike anneals) at 1000 and 1050 °C to investigate the effects of the fluorine in BF2 implants on transient enhanced diffusion (TED). By using a relatively deep preamorphization of 1450 A, any difference in damage between the typically amorphizing BF2 implants and the nonamorphizing B implants is eliminated because the entire profile (<800 A after annealing) is well contained within the amorphous layer. Upon annealing, the backflow of interstitials from the end-of-range damage from the preamorphization implant produces TED of the B in the regrown layer. This allows the chemical effect of the fluorine on the TED of the B in the regrown Si to be studied independent of the damage. The secondary ion mass spectroscopy results show that upon annealin...

{311} defects in silicon: The source of the loops

The annealing kinetics of extended defects in Si+-implanted Si have been investigated by in situ annealing plan-view transmission electron microscopy (TEM) samples in a TEM. A 〈100〉 Czochralski-grown silicon wafer was implanted with 100 keV Si+ at the subamorphizing dose of 2×1014 cm−2. Following implantation, the effect of annealing of 800 °C was studied by in situ annealing. After 5 min of annealing at 800 °C, a dense collection of both {311} defects (3×1011/cm2) and small subthreshold dislocation loops (1×1011/cm2) were observed. Upon subsequent annealing, the {311} defect density decreased rapidly and the loop density increased. The evolution of approximately 500 {311} defects could be followed as a function of annealing time. The unfaulting of a {311} defect was observed to be the source of every subthreshold loop observed to from (about 150 loops in the monitored region). After the initial 5 min anneal at 800 °C, the probability of a {311} unfaulting into a loop was about 50%. Based on these observa...

SiO2 thickness determination by x-ray photoelectron spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, Rutherford backscattering, transmission electron microscopy, and ellipsometry

As the Rp of ion implants steadily decreases an ever-increasing percentage of the implant species lies in the oxide layer and is, therefore, not electrically active. For this reason, it is important to have analytical techniques capable of accurately measuring the thickness of ultrathin oxide layers. A round-robin study was performed on a series of SiO2 films ranging from 0.3 to 20 nm in order to evaluate the advantages and disadvantages of five commonly used analytical techniques. High-resolution cross-section transmission electron microscopy (TEM) offers the only true measurement of oxide thickness because no density assumptions are made. In this study, TEM is used as the standard for all the other techniques. X-ray photoelectron spectroscopy and Auger electron spectroscopy offer precise measurements for ultrathin ( 15 nm) due to the exponential decay functions that describe the sampling depth in both techniques. Secondary ion mass spectrometry (SIMS) has...

The effect of implant energy, dose, and dynamic annealing on end‐of‐range damage in Ge+‐implanted silicon

A study of the effect of Ge+ implantation energy, dose, and temperature on the concentration of atoms bound by the extrinsic end‐of‐range dislocation loops in Si 〈100〉 wafers is presented. Plan‐view and cross‐sectional transmission electron microscopy observations of both the as‐implanted and annealed (900 °C, 30 min) morphology were made. The implant energy was varied from 30 to 150 keV, the dose varied from 2×1014 to 1×1016/cm2, and the temperature was varied by using three different wafer‐cooling methods during the implantation. Increasing the implant energy, dose, or wafer temperature all resulted in significant increases (as much as two orders of magnitude) in the concentration of atoms bound by the end‐of‐range loops. Recent models have suggested that the concentration of end‐of‐range defects is related to the integrated recoil concentration beyond the amorphous/crystalline (a/c) interface. Correlation of trim‐88 calculations with measured a/c depths show that the integrated recoil concentration bey...

Nanostructured ion beam-modified Ge films for high capacity Li ion battery anodes

Nanostructured ion beam-modified Ge electrodes fabricated directly on Ni current collector substrates were found to exhibit excellent specific capacities during electrochemical cycling in half-cell configuration with Li metal for a wide range of cycling rates. Structural characterization revealed that the nanostructured electrodes lose porosity during cycling but maintain excellent electrical contact with the metallic current collector substrate. These results suggest that nanostructured Ge electrodes have great promise for use as high performance Li ion battery anodes.

The Effect of Impurities on Diffusion and Activation of ion Implanted Boron in Silicon

The interaction between boron and silicon interstitials caused by ion implant damage is a physical process which hinders the formation of ultra-shallow, low resistivity junctions. The possibility of mitigating the effective interstitial point defect population via introduction of nonmetallic impurities in ion implanted silicon has been investigated. Amorphization of a n-type Czochralski wafer was achieved using a series of Si+ implants of 40 keV and 150 keV, each at a dose of 1×10 15 /cm 2 . The Si + implants produced a 2800A deep amorphous layer, which was then implanted with 8 keV 1×10 14 /cm 2 B + . The samples were then implanted with high doses of either carbon, oxygen, sulfur, chlorine, selenium, or bromine. The implant energies of the impurities were chosen such that the damage and ion profiles of the impurity were contained within the amorphous layer. This allowed for the chemical species effect to be studied independent of the implant damage caused by the impurity implant. Post-implantation anneals were performed in a tube furnace at 750° C. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Hall effect measurements were used to study the dopant activation. Transmission electron microscopy (TEM) was used to study the end-of-range defect evolution. The addition of carbon and chlorine appear to reduce the boron diffusion enhancement compared to the boron control. Carbon and chlorine also appear to prevent boron out-diffusion during annealing compared to the control, which exhibited 20% dose loss following annealing.

Enhanced elimination of implantation damage upon exceeding the solid solubility

Implantation of silicon wafers with Ga and P, under specific conditions, results in enhanced category‐II (end of range) dislocation loop elimination after short thermal cycling. Comparison of these results with transmission electron microscopy studies of Si‐, Ge‐, As‐, Al‐, and Sb‐implanted samples indicate that the enhanced elimination process occurs only when the peak of the impurity concentration exceeds the solid solubility of the impurity in silicon at the annealing temperature and the resulting precipitates are dissolving. The activation energy for enhanced elimination of these extrinsic catetory‐II dislocation loops is shown to be 5±0.5 eV. It is proposed that vacancy emission by the dissolving precipitates is responsible for the enhanced elimination.