Electron spin and cyclotron resonance of laser annealed silicon

EPR and cyclotron resonance investigations have been performed on laser annealed Si wafers, leading to the identification of the [V + Oi]complex in virgin Si and to a donor signal quenching in P-implanted Si. Revue Phys. Appl. 15 (1980) 21-23 JANVIER 1980, PAGE 1 Classification Physics Abstracts 73.20Hb 76.30 79.20Ds Introduction. Laser annealing techniques have been investigated recently for improving various semiconducting devices such as integrated circuits and solar cells. Initial studies have shown that the restoring mechanism of the damaged surface layers or of amorphous deposits on top of the single crystalline silicon substrate will depend on the lasing mode. CW illumination is believed to initiate a solid phase epitaxial process, whereas the pulsed mode induces a liquid epitaxial regrowth as soon as the power density exceeds some threshold, lying close to 1 J/cm2 [1]. To our knowledge, no direct determination of the residual defects which remain in these restored layers have been tempted, although some deep levels have already been identified by sensitive electrical transport measurement such as DLTS [2] or TSC [3]. Therefore the aim of this work was to investigate these defects by electron paramagnetic resonance (EPR), which is a very specific technique. In some instances, it will also allow to record cyclotron resonance (CR) data simultaneously. Expérimental. EPR and CR have been performed on high purity and on phosphorus implanted silicon. The high purity silicon was float zone material of n-type, with a high resistivity of 104 Q cm. The concentrations of the residual impurities were as fo llows : 0 1’-1 1016 cm 3, B and P N 1012 cm 3 ; wafer orientation was [110]. (*) Conférence présentée au Congrès de la Société Française de Physique (Toulouse, 25-30 juin 1979). The implanted material was of low resistivity (160 S2 cm) and of initial p-type (B doped). Doses of 5 x 1016 to 10" cm 2 p31 ions were implanted at 10-15 keV on each side of [111] ] oriented wafers. The expected penetration depth at these energies is about 50 nm. The anneals were performed in air with a Q-switched ruby laser (03BB = 694.3 nm) with a pulse duration of 25 ns at half power. The power density was 2.7 J cm-2 for the virgin silicon to be well above the melting temperature and up to 10 successive shots have been employed. For the implanted silicon, the laser energy was set just up to the threshold energy (~ 1.1 J cm2). After this operation, samples of 3 x 4 x 1 mm3 were cut out from the 6 mm diameter spots in order to insure a good homogeneity. EPR and CR measurements were done at 4.2 K and 9.3 GHz on stacks made of 2 or 3 samples to enhance the lowest signals. Results. The virgin silicon samples are EPR signal free. After the laser anneal, an isotropic line appears with a Landé factor 91 = 2.005 5 ± 0.000 5. After etching off the surface layer, or after a thermal anneal at 500°C for 30 min, this signal disappears again. Maximum signal intensity corresponds to some 1013 spins. A light irradiation is needed to observe a CR signal (Fig. 2). It is performed using an unfiltered 55 W quartz iodine lamp, illuminating the sample within the cavity through an optical port. After the laser anneal only slight variations are observed : the hole CR linewidth decreases, whereas the electron Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:0198000150102100