G. Benassayag

Basic mechanisms involved in the Smart-Cut® process

Abstract The Smart-Cut process used to produce SOI wafers is based on proton implantation and wafer bonding. In this paper, the behavior of the cavities induced by hydrogen implantation in silicon is studied. The effect of a bonded stiffener on the splitting mechanism is shown. The quality of bonding depends greatly on the cleaning process which enables a high bonding energy and a high quality material to be achieved.

Effect of annealing environment on the memory properties of thin oxides with embedded Si nanocrystals obtained by low-energy ion-beam synthesis

The effect of annealing in diluted oxygen versus inert environment on the structural and electrical characteristics of thin silicon dioxide layers with embedded Si nanocrystals fabricated by very low-energy silicon implantation (1 keV) is reported. Annealing in diluted oxygen increases the thickness of the control oxide, improves the integrity of the oxide and narrows the size distribution of the nanocrystals without affecting significantly their mean size (∼2 nm). Strong charge storage effects at low gate voltages and enhanced charge retention times are observed through electrical measurements of metal-oxide-semiconductor capacitors. These results indicate that a combination of low-energy silicon implants and annealing in diluted oxygen allows for the fabrication of improved low-voltage nonvolatile memory devices.

Amorphization kinetics of germanium during ion implantation

We have experimentally studied by using transmission electron microscopy the kinetics of Ge amorphization during ion implantation at room temperature. We show that the critical damage energy density model, widely used in silicon under this or different names, can also be used in germanium to predict the existence, position, and extension of amorphous layers resulting from the implantation of ions for almost all mass/energy/dose combinations reported here and in literature. In germanium, the crystalline to amorphous phase transition occurs through the accumulation of damage (point defects and/or clusters), and this damage linearly increases with the dose (the damage is additive) until a certain threshold is reached above which the material turns amorphous. However, for light ions such as boron amorphization occurs, at room temperature, closer to the surface than expected. This demonstrates that the interstitials and vacancies generated by such implants are not stable at room temperature and that defect ann...

TRANSIENT ENHANCED DIFFUSION OF BORON IN PRESENCE OF END-OF-RANGE DEFECTS

The presence of a supersaturation of Si self-interstitials in ion implanted silicon has been shown to be the origin of several physical phenomena such as transient enhanced diffusion (TED) of boron, the formation of extended defects at the projected range of implanted atoms at doses below the amorphization threshold, and the formation of end-of-range (EOR) defects in the case of a preamorphization stage. In this article, we discuss the relation between boron anomalous diffusion and end-of-range defects. Modeling of the behavior of these defects upon annealing allows one to understand why and how they affect dopant diffusion. This is possible through the development of the Ostwald ripening theory applied to extrinsic dislocation loops. This theory is shown to give access to the variations of the mean supersaturation of Si self-interstitial atoms between the loops and also to be responsible for anomalous diffusion. This initial supersaturation is, before annealing, at least five decades larger than the equi...

Effect of ion energy and dose on the positioning of 2D-arrays of Si nanocrystals ion beam synthesised in thin SiO2 layers

Silicon nanocrystals (ncs) buried in a thin oxide can be used as charge storage elements and be integrated in standard CMOS technology to fabricate new non-volatile memory devices. In this work, we report on a systematic study of the effect of varying the beam energy (0.65–2 keV) and the dose (1015–1016 cm−2) on the positioning of 2D-arrays of ncs within 10 nm thick oxide after annealing at 950 and 1050 °C. For this, different Transmission Electron Microscopy (TEM) methods have been used including High Resolution Electron Microscopy (HREM) for imaging isolated ncs and Fresnel contrast imaging of populations of ncs. Our results show that the ‘injection distance’ can be precisely tuned in the 5–8 nm range by varying the beam energy. Moreover, very large swelling of the SiO2 layer has been observed when increasing the implanted dose which could be the result of a partial oxidation of the Si ncs layer and/or of the SiO2/Si interface.

White electroluminescence from C- and Si-rich thin silicon oxides

White electroluminescence from carbon- and silicon-rich silicon oxide layers is reported. The films were fabricated by Si and C ion implantation at low energy in 40nm thick SiO2, followed by annealing at 1100°C. Structural and optical studies allow assigning the electroluminescence to Si nanocrystals for the red part of the spectrum, and to C-related centers for the blue and green components. The external efficiency has been estimated to 10−4%. Electrical characteristics show a Fowler-Nordheim behavior for voltages above 25V, corresponding to the onset of electroluminescence. This suggests that light emission is related to the impact ionization of radiative centers.

Diameter of As clusters in LT-GaAs by Raman spectroscopy

Raman scattering measurements on low temperature GaAs layers are presented. Phonons in both GaAs and As are studied. The transition from diluted As in the GaAs matrix to the small As clusters formed after annealing is analyzed. This is performed by observing the reduction of the GaAs bound charge, i.e., the longitudinal optical GaAs frequency downshift, to the appearance of the crystalline As vibrational mode. From the phonon shifts of crystalline As, the diameter and the strain are derived, accordingly to transmission electron microscopy measurements.

Synthesis of MnAs ferromagnets by Mn+ ion implantation

Abstract Ferromagnetic (FM) nanostructures embedded in semiconductors are attracting interest because their physical properties could be used in new devices such as memories, sensors or more generally involving “spintronics”. In this work, we will present experimental results on the influence of the thermal annealing on the structural and magnetic properties of nanosized MnAs ferromagnets buried in GaAs. These nanocrystals have been obtained by Mn+As co-implantation at a dose of 2×10 16 ions cm −2 for each species, performed at room temperature into GaAs wafers followed by thermal annealing at 750°C. Increasing the duration of the annealing process (tanneal=15,60, and 120 s ) leads to a reduction of the Mn atomic densities. High-resolution transmission electron microscopy and diffraction analysis exhibit unambiguously a population of MnAs precipitates located at the projected range. Their mean diameters are ranged from 8 to 10 nm as tanneal is longer. The nanocrystals display the expected ferromagnetic behavior with Curie temperatures in the range of 360 K . The extracted spontaneous magnetizations from the FM response are found slightly smaller than expected for the bulk phase, probably due to a small fraction of diluted Mn. The influence of the nanoparticle size histogram and concentration on the superparamagnetic behavior is briefly discussed.

Electrical transport characterization of nano CMOS devices with ultra-thin silicon film

Regarding short channel GAA, FD-SOI and FinFET MOS devices, we have clearly shown that the mobility is degraded at small gate length, whatever the architecture, the gate stack and the measurement method used. In particular, it has been found that, for FD-SOI, the mobility is more degraded at the top interface than at the bottom interface, indicating that defects are more numerous at the top channel region. The negative role of the nitrogen diffusion from TiN/TaN metal gates has been confirmed revealing a significant reduction of low field mobility with the TiN thickness increase. Low temperature measurements of the mobility have clearly indicated that the scattering processes are strongly modified for short channel devices, which demonstrates that there is an increasing role of channel diffusion scattering centres, most likely neutral point defects, for gate length below 100nm. These extra defects in the channel are likely suspected to be Silicon interstitials injected from the source and drain junction during the S/D implantation process as confirmed by 2D Monte Carlo collision simulations. The concentration and the lateral spatial profile of the generated defects have been implemented into a mobility model that explains reasonably well both the gate length dependence and the temperature variation of the mobility, reinforcing the physical merits of the proposed interpretation for the mobility collapse observed at small channel lengths.

Effects of annealing conditions on charge storage of Si nanocrystal memory devices obtained by low-energy ion beam synthesis

The structural and electrical characteristics of thin silicon dioxide layers with embedded Si nanocrystals are reported fabricated by low-energy silicon implantation and with subsequent annealing in inert and diluted oxygen. Thermal treatment in diluted oxygen increases the thickness of the control oxide, does not affect significantly the size of the nanocrystals, and improves the integrity of the oxide. As a result, strong charge storage effects at low gate voltages and enhanced charge retention times are observed through electrical measurements of MOS capacitors. These results indicate that a combination of low-energy silicon implants and annealing in diluted oxygen permits the fabrication of low-voltage nonvolatile memory devices.