Ryangsu Kim

Boron segregation to extended defects induced by self-ion implantation into silicon

The evolution of boron segregation to extended defects during thermal annealing was studied with secondary ion mass spectrometry and cross-sectional transmission electron microscopy. Czochralski Si wafers with a boron concentration of 3×1017 cm−3 were implanted with 50 keV Si ion for doses from 5×1013 to 2×1015 cm−2 and then annealed at 720, 820, or 870 °C in nitrogen ambient for various annealing times. The evolution of boron segregation peaks to three types of dislocation loops, end-of-range (EOR) dislocation loops, clamshell defects, and Rp (the projected range) defects, is closely related to the evolution of dislocation loops. As annealing temperature and time increase, the boron segregation peaks grow, remain stable, and then disappear together with the dislocation loops. For lower temperature annealing, the boron segregation peaks grow more slowly and reach higher peak concentrations. In addition to the boron segregation to dislocation loops, boron segregation to {311} defects was also found. The bo...

Influences of Point and Extended Defects on As Diffusion in Si

The influences of point and extended defects introduced by ion implantation on the transient enhanced diffusion (TED) of As have been examined. The implantation of a subamorphizing dose of Si into Si wafers with nearly uniform As background doping results in the slight segregation of As into {311} defects after annealing at 670°C, whereas an amorphizing dose of Si is found to induce significant segregation of As into end-of-range (EOR) dislocation loops after annealing at 820°C, regardless of the background As concentration. In the second experiment, As ions were implanted into Si wafers at 30 keV to low and medium doses. Some of the wafers were preannealed in order to recrystallize the amorphous layer and subsequently implanted with subamorphizing doses of Si at 50 keV. The resulting profiles reveal that the TED of As increases with Si implantation dose, indicating that transient As diffusion occurs via Si self-interstitials in the same way as for B and P. A suppression of the TED of As in the early stages of annealing at higher As and Si implantation doses is also observed. This is considered to originate from the formation of immobile arsenic-vacancy clusters.

Anomalous phosphorus diffusion in Si during post-implantation annealing

The transient behavior of P diffusion in Si implanted with As or Ge above the amorphizing threshold has been investigated. Annealing at 720 °C after Ge implantation induces extensive P segregation into the extended defect layer formed by implantation damage. This segregation is attributed to P trapping to end-of-range {311} defects and dislocation loops. For As implantation, P segregation was also observed only after 1 min annealing. However, in contrast to the Ge implantation, in the As-implanted samples, significant P depletion occurs in the As-tail region after further annealing. Nonequilibrium simulation that takes into account both Fermi-level and electric field effects shows the P depletion during transient enhanced diffusion. Furthermore, simulation results based on the coexistence of neutral and positively charged phosphorus-interstitial pairs agree well with the obtained experimental results.

Single electron transistors fabricated with AFM ultrafine nanooxidation process

Detailed conditions of the fabrication of devices by SPM ultrafine oxidation are discussed and a new process is conceived for reducing the surface roughness compared with the conventional process. A single electron transistor (SET) with a side gate electrode is fabricated on an ultrathin Ti film deposited on an SiO2/Si substrate. Current oscillation with gate voltage is clearly observed for the first time in a Ti-based SET.

Studies of Boron Segregation to {311} Defects in Silicon-Implanted Silicon

Czochralski Si wafers with a boron concentration of 2.7×1017 cm-3 were implanted with 50 keV or 150 keV Si+ with doses from 5×1012 cm-2 to 5×1015 cm-2, followed by annealing at 670°C, 720°C or 820°C in nitrogen ambient. During thermal annealing, boron pile-up in the {311} defect region was observed for the first time. In higher temperature annealing, the boron pile-up forms and dissolves more quickly, but has a lower peak value. The boron pile-up forms in the region where the self-interstitial concentration exceeds 3×1017 cm-3 regardless of implant energy and dose. The boron pile-up originates from the boron segregation to {311} defects. The process of boron segregation is limited by boron diffusion. The number of boron atoms segregated to {311} defects increases with annealing time, as t1/2. After reaching its maximum, the number of segregated boron atoms falls exponentially with a characteristic decay time of 14 h at 670°C or 3 h at 720°C. Spreading resistance profiling reveals that boron atoms segregated to {311} defects are electrically inactive.

Atomic configuration study of implanted F in Si based on experimental evidences and ab initio calculations

Abstract The effects of F on B diffusion and activation in Si were investigated through experiments and ab initio calculations. It was found that F atoms captured by vacancy type defects originating from ion implantation form two stable F–V configurations, while the F atoms remaining in Si affect B activation by forming stable F–B complex. During the initial stage of annealing, B diffusion in highly F-doped regions is suppressed significantly due to the recombination of generated self-interstitials with F atoms, resulting in a decrease in self-interstitial concentration.

Photoluminescence and ab initio study of {311} defect nucleation in Si

Photoluminescence (PL) study using Ar laser revealed that {311} defect-precursors exist in the samples annealed at either 620 or 670/spl deg/C after silicon implantation. The peak energy shift from 0.94 to 0.90 eV is a direct evidence of atomic structural transformation from the smaller precursor interstitial clusters to {311} defects. The atomic structure of the precursor was investigated by using the ab initio calculation program. The numerical calculation demonstrated that one of the most plausible structures for the precursors is the di-interstitial.

Dopant segregation to {311} defects during low temperature annealing

Boron segregation to {311} defects and transient enhanced diffusion (TED) of boron atoms during thermal annealing were investigated in detail using implanted superlattice and Si bulk wafers. We observed that (1)boron atoms segregate to {311} defects during low temperature annealing, (2){311} defects were formed in the area where the self-interstitial concentration exceeds 3×10 17 cm 3 , (3)free self-interstitials in the region beyond the implanted range causes initial rapid enhanced diffusion prior to the onset of normal TED.

Boron Segregation to {311} Defects Induced by Self-Implantation Damage in Si

1. Inhoduction For implant damage below the amorphization threshold, the pair difrrsion model predicts a boron pile-up ar the surface during thennal annealing due to the existence of a large gradient of interstitial concenffation. This has been used to explain the reverse short channel effect t11. However, the boron pile-up at the surface has not yet been observed directly. We present the experimental observation of boron redistribution near the surface induced by silicon self-implantation damage. It was observed for the first time that boron atoms pile-up drning annealing in the {311} defect region rather than at the surface. A new diffrrsion model is required to predict the boron profile near the surface, which has a great influence on the threshold voltage of MOSFETs.