F. Olivie

Electrically active defects in BF2+ implanted and germanium preamorphized silicon

Abstract Ultra-shallow p+-n junctions have been formed using 15 keV/1015 cm−2 BF2+ implantation into both Ge+-preamorphized and crystalline 〈1 0 0〉 silicon substrates. Rapid thermal annealing (RTA) for 15 s at 950°C was used for dopant electrical activation and implantation damage gettering. The electrically active defects present in these samples were characterized using Deep Level Transient Spectroscopy (DLTS) and isothermal transient capacitance (ΔC(t, T)). Two electron traps were detected in the upper half of the band gap at, respectively, Ec - 0.20 eV and Ec - 0.45 eV. They are shown to be related to Ge+ implantation-induced damage. On the other hand, BF2+ implantation along with RTA give rise to a depth distributed energy continuum which lies within the forbidden gap between Ec - 0.13 eV and Ec - 0.36 eV. From isothermal transient capacitance (ΔC(t, T)), reliable damage concentration profiles were derived. They revealed that preamorphization induces not only defects in the regrown silicon layer but also a relatively high concentration of electrically active defects as deep as 3.5 μm into the bulk.

Deep levels induced by low energy B+ implantation into Ge-preamorphised silicon in correlation with end of range formation

Abstract It is well established that low energy B+ ion implantation into Ge- (or Si) implantation pre-amorphised silicon allows ultra-shallow p+n junctions formation. However, this process is known to generate defects such as dislocation loops, vacancies and interstitials which can act as vehicles to different mechanisms inducing electrically active levels into the silicon bulk. The junctions studied have been obtained using 3 keV/ 10 15 cm −2 B + implantation into Ge-implantation pre-amorphised substrates and into a reference crystalline substrate. Accurate measurements using deep level transient spectroscopy (DLTS) and isothermal transient capacitance ΔC(t,T) were performed to characterise these levels. Such knowledge is crucial to improve the device characteristics. In order to sweep the silicon band gap, various experimental conditions were considered. The analysis of DLTS spectra have first showed three deep levels associated to secondary induced defects. Their concentration profiles were derived from isothermal transient capacitance at depths up to 3.5 μm into the silicon bulk and allowed us to detect a new deep level. The evolution of such defect distribution in correlation with the technological steps is discussed. The end of range (EOR) defect influence on electrical activity of secondary induced defects in ultra-shallow p+n diodes is clearly demonstrated.

On the use of the matrix pencil method for deep level transient spectroscopy: MP-DLTS

A new approach to capacitance transient analysis, based on the matrix pencil (MP) method, is proposed for deep level transient spectroscopy (DLTS) (MP-DLTS). The MP method offers the least statistical variance of the estimates in the presence of noise. Simulation tests have shown this method to lead to a significant improvement in DLTS resolution even for low trap concentrations. Its noise sensitivity and resolution are quantified and compared with five different DLTS analysis techniques. The MP-DLTS method is found to outperform both DLTS spectrum and direct transient analysis techniques. An experimental investigation of the electrically active defects induced by a germanium preamorphization step prior to dopant implantation was undertaken using the MP-DLTS method. Two electron traps were detected in all samples and characterized.

Electronic Defect Levels in Ultra-Shallow p+n-Junctions Formed by Low-Energy B Ion Implantation into Ge-Preamorphized Silicon

Ultra-shallow p+n-junctions were formed by low-energy boron implantation into n-type monocrystalline silicon preamorphized with germanium. The boron implantation was performed at 3 keV and 1015 cm-2. The crystallization and the electrical activity were obtained by rapid thermal annealing (RTA) at a control thermocouple setting of 950° C for 15 s. In this work, the electrical defects induced by this process were characterized by isothermal transient capacitance (ΔC(t, T)) measurements and deep level transient spectroscopy (DLTS). The electron emission spectrum is dominated by two kinds of defects. The first is classical and is represented by two discrete levels related to germanium implantation. The second, observed for the first time in such structures, seems to be an energy distributed continuum located between 0.18 eV and 0.33 eV below the conduction band edge. It is most probably related to both boron implantation and RTA. Its concentration profile depth of 4 mm within the silicon substrate may be associated with defect complexes originating either from interstitials or vacancies. The profiles were used to distinguish between the two types of defect and to evaluate accurately their signature.

Magnetic susceptibility of P+N junctions in correlation with the nature of silicon substrate: crystalline or pre-amorphised

Abstract Ge pre-amorphisation step is used to reduce the high diffusivity and the transient-enhanced diffusion of boron implanted in silicon. The aim of the process is to obtain shallow P + N junctions. The pre-amorphisation step was performed under different conditions (in ambient temperature and in nitrogen). Following the rapid thermal annealing step, end of range (EOR) defects appear at the amorphous–crystalline interface. These defects could influence the electrical characteristics of the P + N junctions. An experimental study concerning three samples has been performed without and under a magnetic field of 800 G. The magnetic susceptibility was essentially observed in the case of the reverse current. The impact of the magnetic field, studied by varying the sample temperature, permits us to show an increase of the magnetic susceptibility when the defects present in such structures are electrically active. These results are discussed in comparison with their deep-level transient spectroscopy (DLTS) spectra.

Design and modelling of a photovoltaic system optimized by an analog control provided with a detection circuit of dysfunction and restarting of the system

In this article we analyze the design and the simulation of photovoltaic system (PV) optimized by an analog control (MPPT) provided with a detection dysfunction circuit and restarting of system. The unit guaranteed the tracking of the maximum power provided by generator statement and transfers it to the load. The results obtained show that the PV system thus conceived converges even in a random environment in a time lower than 100 ms towards the optimal conditions independently of the weather conditions and the load variation. The generator PV used in such system is module SP75 producing a power peak of 75 W.

Electrical characterizations of preamorphized junctions under LF magnetic field

Abstract The increased requirements for reduction of electronic system dimensions, essentially in embedded equipment such as automotive and avionics, lead to juxtapose high power modules and low level modules on the same printed circuit. This juxtaposition induces electromagnetic perturbations that can disturb or damage the operation of the system. In order to study thoroughly these phenomena, a low frequency (LF) magnetic field was applied to shallow P+N junctions obtained by the preamorphization technique, at two temperatures: ambient and nitrogen temperature. Electrical characterizations were performed on the different samples. The results show that the impact of the LF magnetic field is essentially observed in the generation-recombination region of the junction. Moreover, it appears that crystalline sample presents a good immunity to the LF magnetic field perturbation at high temperature. On the other hand, the preamorphization temperature influences the response of the sample. So, a good control of the technological parameters will permit to reduce or cancel the effect of the magnetic perturbations on the electronic components since conception.

Effect of the Ge preamorphization dose on boron diffusion and defect evolution in silicon

Abstract In this paper, we study the effect of the Ge+ preamorphization dose on boron diffusion and on the thermal evolution of end of range (EOR) defects during annealing. Amorphizations were carried out by implanting Ge+ at 150 keV to doses ranging from 1×1015 to 8×10 15 ions/cm 2 . Boron was subsequently implanted at 3 keV with a dose of 1×10 14 ions/cm 2 . Rapid thermal annealing (RTA) was performed for various time/temperature combinations in nitrogen ambient. Secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) were used to study boron diffusion and defect evolution, respectively. We have found that after a given annealing, both the defect size and boron diffusivity are independent on the Ge ion dose. Increasing this dose only results in an increase of the defect density. These results are discussed and definitely show that EOR defects are involved in a quasi-conservative Ostwald ripening process during annealing. The diffusive behavior of boron suggests that the coupling of boron atoms with the “mean field” of Si interstitial atoms in dynamical equilibrium with the defects is responsible for transient enhanced diffusion (TED).