Erwan Oliviero

Helium implantation defects in SiC: A thermal helium desorption spectrometry investigation

Thermal helium desorption spectrometry was used to characterized helium implantation-induced defects in SiC. 6H–SiC, 4H–SiC, and β–SiC samples were implanted with helium at energies ranging from 100 to 3 keV and doses ranging from 1×1013 to 1×1015 cm−2. They were then subjected to ramp annealing up to 1800 K, with a constant heating rate of 10 K/s. Two groups of peaks contribute to the desorption spectrum: A low-temperature group centered at 600 K and a high-temperature group centered at 1200 K. The evolution of these desorption peaks with implantation dose and energy was studied. The first group (at 600 K) might be attributed to interstitial He and clusters of interstitial He. The second group (at 1200 K) could be related to He release from He-vacancy clusters. A shift of the latter group toward higher temperatures with increasing dose is ascribed to He-vacancy clustering in an Ostwald ripening process. However, the intrinsic properties of the materials used in the study seem to play an important role si...

Formation of bubbles by high dose He implantation in 4H–SiC

1.6 MeV He+ ions were implanted at room temperature into (0001)Si n-type 4H–SiC at a dose of 1×1017 cm−2. Cross-section transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to characterize the induced defects and the strain-induced effects before and after annealing. Infrared reflectivity was also used to localize changes in the microstructure. In the as-implanted samples, the TEM observations show a three layer damaged region consisting of a continuous amorphous layer surrounded with two buried crystalline zones. Bubbles of small diameter are readily formed in the as-implanted state. Only a few changes are observed after a 800 °C-30 min annealing. Voids formation and recrystallization of the amorphous state in different polytypes are observed for a 1500 °C-30 min annealing. Moreover, XRD shows that the dilatation of the c axis of the lattice observed after implantation completely disappears after the high temperature annealing implying the structural recovery of all the crystallin...

Helium implantation defects in SiC studied by thermal helium desorption spectrometry

Abstract Thermal helium desorption spectrometry (THDS) was used to characterize helium implantation induced defects in SiC. 6H–SiC and 4H–SiC single crystals were implanted with helium at energies ranging from 100 eV to 3 keV and doses ranging from 1013 to 10 15 cm −2 . They were then subjected to ramp annealing up to 1800 K, with a constant heating rate of 10 K s−1. To the desorption spectrum contribute two groups of peaks: one group at low temperature centered at 600 K and another group at high temperature centered at 1200 K. The evolution of these desorption peaks with implantation dose and energy has been studied. The first group (at 600 K) might be attributed to interstitial He and clusters of interstitial He. The second group (at 1200 K) could be related to the de-trapping of He from He–vacancies clusters. A shift of the latter group towards higher temperatures observed for increasing dose is ascribed to He–vacancy clustering in an Ostwald ripening process.

Dislocations induced by bubble formation in high energy He implantation in silicon

He+ ions were implanted into a (111) epitaxial n-type silicon wafer at 1.6 MeV and at a dose of 2×1016 cm−2. After implantation the samples were subjected to thermal annealing at 800 °C for 30 min. Cross section transmission electron microscopy (TEM) was used to characterize microstructural features of the induced defects. Even in the as-implanted samples the TEM observations revealed the formation of a buried layer containing a dense array of bubbles. After annealing, a large band of defects (bubbles, Frank dislocation loops) was observed as well as rows of prismatic punching related dislocations which can extend over several micrometers away from the buried layer. Planar clusters of helium bubbles, lying on the {001} planes, were also observed and were supposed to be involved in the generation of dislocation loops in the matrix. Their nucleation is discussed in terms of the trap-mutation process.

On the effects of implantation temperature in helium implanted silicon

He+ ions were implanted into silicon with a fluence of 5×10 16?cm?2 at different temperatures ranging from 473 to 1073 K. Samples were analyzed by thermal helium desorption spectroscopy and by transmission electron microscopy. As far as cavity formation is concerned, the behavior can be divided into three stages depending on the implantation temperature. However, it is found that helium release from cavities is governed by a single mechanism regardless of the implantation temperature.

Influence of dose rate on bubble formation by high energy He implantation in silicon

He+ ions were implanted into a (111) epitaxial n-type silicon wafer at different dose rates (fluxes) ranging from 2.5×1012 to 1.3×1013 cm−2 s−1 while keeping the incident energy and dose constant (1.6 MeV, 2×1016 cm−2). After implantation the samples were subjected to thermal annealing at 800 °C for 30 min. Cross section transmission electron microscopy (XTEM) was used to characterize the damage layer. Even in the as-implanted samples the TEM observations revealed the formation of a buried layer containing a dense array of small bubbles. After annealing, a large band of defects made up of bubbles and dislocations was observed in all samples. However, the characteristics of the damage layer found depended on the flux. For the lowest flux, only platelets and planar clusters of helium bubbles lying in the {001} planes were observed. Their nucleation is discussed in terms of the trap-mutation process. For higher fluxes a continuous band of bubbles with rows of prismatic punching related dislocation loops was ...

Helium implanted gallium nitride evidence of gas-filled rod-shaped cavity formation along the c-axis

The structural defects induced by He implantation in GaN epilayer at high fluence (1×1017He/cm2) and elevated temperature (750 °C) have been studied by conventional and high resolution transmission electron microscopy. In addition to the planar interstitial-type defects lying in the basal plane usually observed after high fluence implantation into GaN, a continuous layer of bubbles arranged in rows parallel to the implanted surface is observed in the region of maximum He concentration. This arrangement of bubbles is ascribed to interactions with dislocations. Beyond, one dimensional rod-shaped defects appear perpendicular to the implanted surface. Contrast analysis of high resolution images and atomistic simulations gives converging results in the determination of the nature and structure of these defects, i.e., gas-filled rod-shaped cavities in an overpressurized state.

Use of graphite cap to reduce unwanted post-implantation annealing effects in SiC

6H and 4H–SiC epilayers were Al-implanted at room temperature with multiple energies (ranging from 25 to 300 keV) in order to form p-type layers with an Al plateau concentration of 4.5×1019 cm-3 and 9×1019 cm-3. Post-implantation annealing were performed at 1700 or 1800 °C up to 30 min in Ar ambient. During this process, some samples were encapsulated with a graphite (C) cap obtained by thermal conversion of a spin-coated AZ5214E photoresist. From Atomic Force Microscope measurements, the roughness is found to increase drastically with annealing temperature for unprotected samples while the C capped samples show a preservation of their surface states even for the highest annealing temperature. After 1800°C/30 min annealing, the RMS roughness is 0.46 nm for the lower fluence implanted samples, slightly higher than for unimplanted samples (0.31 nm). Secondary Ion Mass Spectroscopy measurements confirm that the C cap was totally removed from the SiC surface. The total Al-implanted fluence is preserved during postimplantation annealing. A redistribution of the Al dopants is observed at the surface which might be attributed to Si vacancy-enhanced diffusion. An accumulation peak is also observed after annealing at 0.29 9m, depth corresponding to the amorphous/crystalline interface that was determined on the as-implanted samples by Rutherford Backscattering Spectroscopy in channeling mode. The redistribution of the dopants has an impact on their electrical activation. A lower sheet resistance (Rsh= 8 k) is obtained for samples annealed without capping than for samples annealed with C capping (Rsh= 15 k ).

Generation of defects induced by MeV proton implantation in silicon: Influence of nuclear losses

Abstract Deep level transient spectroscopy (DLTS) has been performed on p+–n–n+ silicon diodes subjected to medium-dose hydrogen implantation (10 13 cm −2 ) and then annealed (400 °C). Three different energies have been chosen to explore different parts of the damage profile. At least 10 DLTS lines have been resolved and in particular we confirm the presence of two levels located at 0.29 and 0.32 eV from the conduction band (Ec). Two electron traps located near the mid-gap and not observed for low-doses irradiation, are reported and found to be associated with complex defects including vacancies. Two other levels are also reported. The level at E c −0.20 eV is also observed in case of medium doses whereas the level at E c −0.36 eV is originating from an impurity-related complex involving carbon.

A New Approach to Study the Damage Induced by Inert Gases Implantation in Silicon

In the present work, we report on the effects of the implantation temperature on the formation of bubbles and extended defects in Ne+-implanted Si(001) substrates. The implantations were performed at 50 keV to a fluence of 5x1016 cm-2, for distinct implantation temperatures within the 250°C≤Ti≤800°C interval. The samples are investigated using a combination of cross-sectional and plan-view Transmission Electron Microscopy (TEM) observations and Grazing Incidence Small-Angle X-ray Scattering (GISAXS)measurements. In comparison with similar He implants, we demonstrate that the Ne implants can lead to the formation of a much denser bubble system.