E. Ntsoenzok

Helium desorption from cavities induced by high energy 3He and 4He implantation in silicon

A detailed study has been made of helium release from silicon wafers implanted with MeV helium ions at fluences of 5 × 10 16 cm -2 and 10 17 cm -2 . Thermal desorption spectrometry (TDS), neutron depth profiling (NDP), non-Rutherford elastic backscattering (NREBS) and nuclear reaction analysis (NRA) have been employed to measure the helium content and release rate during isothermal annealing at annealing temperatures of 800 and 1000°C. TDS has also been used for isochronal annealing. Transmission electron microscopy (TEM) is used to monitor changes in morphology in the formed bubble layer. The helium release results can be modeled rather well when it is assumed that the helium initially is present in overpressurized bubbles. The present study reveals a single activation energy for helium release of 1.83 (0.05) eV.

Cavities and dislocations induced in silicon by MeV He implantation

We implanted n-type silicon with 1.6 MeV helium at fluences ranging from 1×1016 to 1×1017 He/cm2 while keeping a constant dose rate. These samples were then subjected to 800 °C annealing for 30 min. The results obtained by means of cross-sectional transmission electron microscopy indicate that the density of cavities is fluence dependent with homogeneous distribution of cavity sizes when fluences of 5×1016 and 1017 He/cm2 are used. The threshold fluence required to form cavities is found to be between 1 and 2×1016 He/cm2. For the 2×1016 He/cm2 dose, we observed loop punching induced by a concerted action of overpressurized bubbles, whereas He implants at doses of 5×1016 and 1×1017/cm2 lead to the formation of {311} defects. At the same time, non Rutherford elastic backscattering (NREBS) experiments using 2.5 MeV H+ provide the fraction of helium remaining in cavities after different annealing times at 800 °C. The NREBS data show a fast He release process for short annealing times (<2000 s). Then, the He a...

PROXIMITY GETTERING OF PLATINUM IN PROTON IRRADIATED SILICON

Epitaxial silicon samples of n type have been implanted with 850 keV protons at doses of 5.8×1011 to 5×1013 H+ cm−2. Subsequent indiffusion of platinum at 700 °C for 30 min resulted in the presence of a single deep level, which is attributed to the platinum acceptor level, at 0.23 eV below the conduction band edge. Depth profiling of this level shows that the substitutional platinum is following the vacancy profile in the peak region around the projected range for the protons. In addition, at more shallow depths, a strong increase of the platinum concentration is also observed. Without ion implantation, no deep levels are detected after in-diffusion at 700 °C, while at 800 °C, the Pt deep level concentration is inferior to the one reached after preimplantation of hydrogen with a dose of at least 5×1012 H+ cm−2. In-diffusion at 600 °C into 5×1013 H+ cm−2 implanted samples did not lead to an enhanced platinum accumulation. A tentative explanation of this proximity gettering of Pt is proposed, which is for t...

The influence of diffusion temperature and ion dose on proximity gettering of platinum in silicon implanted with alpha particles at low doses

Platinum has been diffused into epitaxial n-type silicon at 600, 650, and 700 °C for 30 min following implantation with 3.3 MeV alpha particles. The doses employed were between 1×1011 and 1×1014 He+ cm−2. Thereafter the samples were characterized using deep level transient spectroscopy (DLTS). The samples diffused at 700 °C show only the deep level at 0.23 eV below the conduction band that is attributed to substitutional platinum. DLTS profiling reveals a decoration of the region of maximal damage by the platinum for lower doses while for higher ones the platinum concentration is observed to decrease or vanish in this region. In addition, other deep levels may appear (so-called K lines). As the implantation dose increases, so does the platinum concentration following diffusion at 700 °C at the shallow end of the DLTS working region. It is shown that, by controlling the amount of implantation induced defects and the diffusion temperature, one can steer the amount of platinum that arrives in the region of m...

Evolution of shallow donors with proton fluence in n‐type silicon

Bipolar components that consist of p+n junctions have been irradiated by MeV protons at fluences ranging from 1011 to 1013 particles cm−2. Capacitance‐voltage measurements have been used to investigate changes in the carrier concentration profiles. Shallow donors that can induce harmful effects in electronic devices have been studied as a function of fluence, flux, and annealing parameters.

Growth mechanism of cavities in MeV helium implanted silicon

A study of silicon implanted with 1.55 MeV helium 3 and thermally annealed to generate a subsurface cavity region was performed using neutron depth profiling and transmission electron microscopy (TEM). Results show that about 30% of the initial implanted helium is still present in cavities even after a 900 °C-1 h anneal. In addition, TEM measurement of cavity size on anneal temperature yields an activation energy of 1.65 eV for the growth of cavities. This value is very close to the activation energy (1.7 eV) reported for helium diffusion in silicon. Cavity growth hence results essentially from exchange of helium atoms between cavities.

Gettering of Diffused Au and of Cu and Ni Contamination in Silicon by Cavities Induced by High Energy He Implantation

Silicon samples were gold-diffused at different temperatures (870-950°C) and implanted with He ions at 1.6 MeV and fluences ranging from 2 × 10 16 up to 10 17 cm -2 . The implantation induced defects observed by conventional and high resolution cross section electron microscopy were found to be essentially cavities 10 to 100 nm in size which are faceted mainly along {111}, but also along {110} and {100} planes. The cavities are located at the sample depth predicted by the transport range of ions in matter simulation. Secondary ion mass spectroscopy profiles exhibit a shouldered shape with a maximum at the projected range. They demonstrate that the cavities are very efficient sinks for Au atoms; the shoulder of the profile could be related to the presence of smaller cavities and dislocations in the vicinity of the projected range. Gold concentration in the cavity area was below the detection limit of the energy dispersive spectroscopy technique, but both Cu and Ni contamination gave rise to silicides and could be chemically analysed. Cu 3 Si precipitates have grown in cavities as already reported in the literature, while NiSi 2 precipitates were observed for the first time in cavities.

Defect levels of proton-irradiated silicon with doses ranging from 1 × 1012 cm−2 to 1 × 1013 cm−2

Abstract Schottky diodes of n-type silicon have been irradiated by 800 keV and 1 MeV protons at doses ranging from 1 × 10 12 cm −2 to 1 × 10 13 cm −2 . Thermally Stimulated Capacitance (TSCAP), capacitance-voltage (CV) and Deep Level Transient Spectroscopy (DLTS) have been applied for sample analysis. By TSCAP measurements a strong compensation effect has been observed for irradiation doses up to 5 × 10 12 cm −2 . At least five deep levels have been observed in the DLTS spectra, but the E(200) trap, located at E c − 0.36 eV, was only revealed by the fitting procedure. An additional new pure damage level, labelled E(110), with an energy of E c − 0.19 eV and a capture cross section of about 5 × 10 −16 cm 2 has been also observed in the highly damaged region. The variations of the DLTS signal with pulse amplitude of the E c − 0.3 eV level, called E(170), has been found to be different of what is obtained at low dose irradiations: a dip followed by a peak in concentration near the maximum of implanted ions is suggested. A possible explanation of such behavior is discussed. We also report the possibility of an overdoping effect near the proton distribution before thermal annealing.

Anormal growth of cavities in MeV He implanted Si covered with a thin Al foil

Abstract Cavities were created by MeV He implantation in silicon through a 1.5 μm Al foil. After a 800 °C-annealing, unexpected growth mechanism was found: a non-uniform layer of cavities with a distribution where bigger cavities are surrounded by smaller ones. Neither Oswald ripening nor migration-coalescence mechanisms can be applied to describe the growth of these cavities. The role of dislocations seem to be important in that distribution. Indeed some cavities seem to be trapped by dislocations. However the motion of the helium does not appear to be the origin of that anormal growth mechanism.

Defects in silicon induced by high energy helium implantation and their evolution during anneals

Abstract Transmission electron microscopy has been used to study the bubbles and the extended defect formation in crystalline Si implanted with helium at a dose of 1017cm−2 at 1.6 MeV and annealed at 800°C, as a function of the annealing time of 16.7–1020 min. Below the bubble layer located near the mean projected range, Frank dislocation loops are observed in addition to long rod-like {113} defects. During the initial annealing stage only Frank loops bound to bubbles are present. Whereas the bubble morphology does not change greatly during longer annealing times, we observe a strong evolution of extended defects located behind the band of bubbles. Indeed, after a 30min annealing, Frank loops and {113} defects resulting from the precipitation of Si interstitials are observed. Then the dissolution of {113} defects takes place and only Frank loops remain. The Frank loops are homogeneously distributed up to 500 nm below the bubble layer and are of equal size. After a 1020 min anneal, no more extended defects are observed behind the buried layer. These results are discussed and compared with those obtained after keV implantation.