O. Kononchuk

Impurity gettering to secondary defects created by MeV ion implantation in silicon

Impurities in MeV-implanted and annealed silicon may be trapped at interstitial defects near the projected ion range, Rp, and also at vacancy-related defects at approximately Rp/2. We have investigated the temperature dependence of impurity trapping at these secondary defects, which were preformed by annealing at 900 °C. The binding energies of Fe, Ni, and Cu are greater at the vacancy-related defects than at extrinsic dislocation loops. During subsequent processing at temperatures up to 900 °C, the amount of these impurities trapped at Rp/2 increases with decreasing temperature while the amount trapped at Rp decreases, with most of the trapped metals located at Rp/2 in samples processed at temperatures ≲ 700 °C. However, intrinsic oxygen is trapped at both types of defects; this appears to have little effect on the trapping of metallic impurities at extrinsic dislocations, but may inhibit or completely suppress the trapping at vacancy-related defects.

DIFFUSION OF IRON IN THE SILICON DIOXIDE LAYER OF SILICON-ON-INSULATOR STRUCTURES

The redistribution of iron implanted into the oxide layer of silicon-on-insulator structures has been measured using the secondary ion mass spectroscopy technique after annealing at 900–1050 °C. Iron diffusion has been found to be much faster in the oxide prepared by the separation-byimplantation-of-oxygen (SIMOX) procedure compared to the thermally grown oxide in the bonded and etched-back structures. In the latter case, the Fe diffusivity exhibits a thermal activation with an energy of 2.8 eV, confirming the literature data on silica glass. In the SIMOX oxide, the diffusivity depends only weakly on temperature, indicative of an essentially activation-free diffusion mechanism. Gettering of Fe at below-the-buried-oxide defects in SIMOX wafers has been observed. No iron segregation has been detected at the SiO2–Si interfaces.

Gettering of Fe to below 1010 cm−3 in MeV self‐implanted Czochralski and float zone silicon

The effects of Si ion fluence and oxygen concentration on secondary defect formation and gettering of metallic impurities in MeV self‐implanted silicon have been studied for Czochralski (Cz) and float zone (FZ) silicon by means of deep level transient spectroscopy, secondary ion mass spectroscopy, transmission electron microscopy, and optical microscopy/chemical etching. We found that the density, depth distribution, and number of extended defects is strongly dependent upon both the Si ion fluence and the oxygen concentration. Effective gettering of iron to below 1010 cm−3 can be achieved in both FZ and Cz wafers at implantation doses of 1015 cm−2.

Gettering of Cu and Ni in mega-electron-volt ion-implanted epitaxial silicon

Gettering of Cu and Ni by 2.3 MeV Si ion-implantation-induced defects has been investigated in epitaxial silicon as a function of annealing temperature, time, and cooling rate. Secondary ion mass spectrometry revealed two distinct gettering regions, the position of which correlated with the ion projected range Rp and approximately half of Rp. Gettering experiments performed on samples with low metal impurity concentration have shown that capture of Cu and Ni in the two gettering regions occurred during high-temperature annealing, indicating a segregation-induced gettering mechanism. The binding energies of Cu and Ni are higher in the shallow Rp/2 region than in the Rp region.

Metallic Impurity Gettering and Secondary Defect Formation in Megaelectron Volt Self‐Implanted Czochralski and Float‐Zone Silicon

Megaelectron volt (MeV) self-implantation has been investigated as a means of producing buried defect layers for gettering metallic impurities in Czochralski (CZ) and float-zone (FZ) silicon. The properties of implanted and annealed wafers were studied by generation lifetime (Zerbst) analysis of transient capacitance data, capacitance-voltage measurements, deep-level transient spectroscopy, scanning electron-beam-induced current microscopy, transmission electron microscopy, optical microscopy with preferential chemical etching, and secondary ion mass spectroscopy. We found that metallic contaminants such as Fe and Cu were effectively gettered to buried extended defect layers formed by implantation of ion fluences ≤1 x 10 15 Si cm -2 . For example, the concentration of iron in regions near the buried defects can be reduced to below 10 10 cm -3 in samples annealed at 900°C. The region above the damage layer appears to be free of electrically active defects, having very high generation lifetime values, and is therefore suitable for device processing. However, the structure and width of the buried defect band is sensitive to the implanted ion fluence and the oxygen content of the wafers. For example, the defect layers formed by high ion fluences (∼10 15 cm -2 ) are wider in FZ wafers than in CZ wafers. For fluences 1 x 10 14 cm 2 , dislocations extend from the buried damage band in both directions during annealing and are observed at depths up to 10 μm. These dislocations intersect the wafer surface in both CZ and FZ wafers, making fluences lower than ≃ 5 x 10 14 cm -2 unsuitable for device fabrication.

Gettering of iron in silicon-on-insulator wafers

Gettering of Fe in silicon-on-insulator material has been investigated on both the bonded and separation by implantation of oxygen (SIMOX) platforms. Reduction of electrically active iron in intentionally contaminated and annealed wafers has been measured by deep level transient spectroscopy. These data, coupled with structural characterization techniques, such as transmission electron microscopy and preferential chemical etching, provide evidence that structural postimplantation damage below the buried oxide (BOX) in SIMOX wafers is an effective site for gettering of iron with the iron gettering efficiency varying with the SIMOX processing. Gettering was not observed in bonded wafers, and the lower BOX interface did not provide any iron gettering in either bonded or SIMOX wafers.

Simulation of metallic impurity gettering in silicon by MeV ion implantation

Abstract A simple model for metallic impurity gettering by buried layers created by MeV ion implantation in silicon is presented. For our experimental conditions, the precipitation of supersaturated Fe at dislocation loops in silicon is not diffusion limited. Furthermore, a non-zero silicide-matrix interfacial energy density was required to fit our experimental data. In samples containing dislocations and boron-implanted layers, the dislocations trap more Fe than the boron, but the latter is more effective at reducing the concentration of ungettered Fe. Although we were able to simulate impurity distributions fairly well in many cases, the model is not free from adjustable parameters due to a lack of knowledge of detailed impurity–defect interactions and the silicide-matrix interfacial energy density.

Lateral Gettering of Fe on Bulk and Silicon‐on‐Insulator Wafers

Laterally displaced gettering sites have been studied as an alternative to traditional internal gettering and back-side gettering sites. Fe was diffused laterally and captured, first by coulombic pairing with B in p-type Si, and then by strategically placed ion implantation induced dislocation loops. This localization of Fe was tracked by both deep level transient spectroscopy and capacitance-voltage measurements. As proof of the viability of the gettering technique, laterally displaced gettering sites were formed adjacent to capacitors on various silicon-on-insulator (SOI) substrate types. Both implantation induced dislocation loops and P diffusion were used for gettering. An improvement in gate oxide integrity was observed for capacitors with lateral gettering on all SOI types studied.

EVOLUTION OF DEEP-LEVEL CENTERS IN P-TYPE SILICON FOLLOWING ION IMPLANTATION AT 85 K

In situ deep-level transient spectroscopy measurements have been carried out on p-type silicon following MeV He, Si, and Ge ion implantation at 85 K. Deep levels corresponding to intrinsic and impurity-related point defects are only detected after annealing at temperatures above 200 K. In addition to divacancies, interstitial carbon, and a carbon–oxygen complex, the formation of another defect, denoted as K2, has been observed during annealing at 200–230 K in epitaxial wafers, and at 200–300 K in Czochralski grown material. The energy level of the K2 defect is located 0.36 eV above the valence band, which is very close to a previously observed level of the carbon–oxygen pair. The relative concentration of this defect is ∼10 times higher in samples implanted with Ge than in those implanted with He. Due to its formation temperature, equal concentration in epitaxial and Czochralski grown wafers, and absence in n-type samples, the K2 trap has been tentatively identified as a vacancy-related complex which prob...

The effect of oxygen on secondary defect formation in MeV self-implanted silicon

Abstract The effects of ion fluence and oxygen concentration on secondary defect formation in MeV self-implanted silicon has been studied for Czochralski (Cz) and float zone (FZ) wafers by means of transmission electron microscopy (TEM) and optical microscopy with bevel polishing/chemical etching. We found that the density, distribution and number of extended defects is strongly dependent upon the oxygen concentration. The dislocation density was found to be up to one order of magnitude lower in FZ wafers. At high ion fluences (∼ 10 15 cm −2 ), secondary defects form in a well-defined band near the ion projected range, R p . At lower ion fluences, dislocations extend from the defect band to increasingly large depths. For ion fluences approaching the threshold for secondary defect formation (∼ 10 14 cm −2 ), defects are observed from the surface to depths of ⋍ 10 μm, i.e., five times R p .