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RESIDUAL DEFECTS AFTER PULSED LASER ANNEALING IMPLANTED SILICON

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OF ION

A. MESLI, J.C. MULLER, D. SALLES, P. SIFFERT Centre de Recherches Nucl6aires Groupe de Physique et Applications des Semiconducteurs (PHASE) 67037 STRASBOURG-Cedex ,FRANCE ABSTRACT Capacitance transient spectroscopy has been used to investigate the electrically active defects subsisting, after a ruby laser pulse annealing, in ion implanted silicon. In contrast to the common view, it is shown that the identified point defects are related to residual implantation related defects buried beyond the dopant distribution and not to the laser effect. INTRODUCTION The incorporation of dopant elements into the silicon lattice by a pulsed annealing induced either by lasers or electrons, has been intensively investigated during the last couple of years, with the hope that new device processing techniques can be developed. In principle, these methods offer several advantages related to the local heating and the high thermal gradients. In particular, it has been demonstrated that ion implanted silicon can be pulse annealed to a state of very high electrical activity of the dopants, without any visible crystallographic defects such as dislocations, stacking faults, precipitates, at least within the sensibility of the common techniques like Rutherford backscattering (RBS) or transmission electron microscopy (TEM). In view of all these advantages, one would expect large application in the device manufacturing technology. However, in practice, no structure has really been prepared having performance well in excess of the conventional structures. This is mainly due to different effects which can degrade the devices characteristics. Essentially, two categories can be considered : - defects due to the interaction of the laser's energy with the semiconductor : stresses, or quenching [1-3] which limit the carrier lifetime in the regrown layer, or which degrade the Schottky barrier performance when the starting material has been laser illuminated over a certain threshold [4] ; - defects resulting from the implantation and which subsist after laser treatment, due for example of an epitaxial regrowth on a damaged zone, extending deeper towards the bulk than the dopant distribution. We have investigated the residual damage subsisting after ion implantation and laser annealing by using the Capacitance Transient Spectroscopy. Strong arguments suggest that the observed damage does

not result from the laser bombardment.

452

w(t) = weighting Fig.

1.

function

Schematic of the DLTS experimental set-up.

250

u`4

T (OK) Fig. 2. DLTS signal for a P+ implanted junction (15 keV, 1016 cmand annealed with various ruby laser pulse energies.

2

)

--

50

-6 T000

Fig. 3. Thermal emission rates VS 1000 for the three electron traps. The capture cross section are also reported.

453 EXPERIMENTAL CONDITIONS Samples preparation P-type silicon samples, grown by floating zone (FZ) along an axis, having a resistivity in the range 1-5 Q2.cm have been implanted off-axis wit