In-depth oxygen contamination produced in silicon by pulsed laser irradiation

Abstract

Ion-implanted Si wafers were irradiated in air with a Q-switched ruby laser and then isochronally annealed between 450 and 850 degrees C. Within the depth corresponding to the melted thickness, a considerable amount of alpha-quartz was detected in the 700-800 degrees C range. Copper precipitation was observed associated with alpha-quartz formation. The role of a dissolved oxygen supersaturation, which seems to be generated by laser irradiation of air-exposed samples, is discussed briefly in the light of the use of laser annealing techniques for electronic device fabrication.

An Ion-Scattering Study of Oxygen Indiffusion During Pulsed Laser Annealing/Cleaning of Silicon

“…As "a matter of fact, Hoh et al [18] have found already that the introduction of 180 in Si which was laser irradiated in 1802 atmosphere, giving rise to concentrations well above the solid solubility of oxygen in Si, was blocked when the Si surface is covered with Si0 2 . On the other hand, our results are in strong contradiction with those of Garulli et al [19], who state that a 1.5 J/cm 2 , 20 ns pulse air anneal of Si causes an oxygen super saturation in the molten region, which oxygen concentration is distributed such that a peak is present in the middle region of this area. We cannot account for this difference; our way of determining oxygen atoms, however, seems to be more straightforward.…”

Residual lattice disorder in self-implanted silicon after pulsed laser irradiation

“…For pulse widths and energy densities used for our laser irradiations, the melting front in a silicon single crystal covered with a 200 nm thick amorphous layer reaches a depth of about 0.5 pm [28], so that the presence of C in a 0.12 p, thick surface layer and 0 in a deeper region up to 0.6 pm is reasonable. This result is in agreement with that reported in [19]. During that investigation, a large amount of oxygen was found to be localized a t depths between 0.12 and 0.5 pm, whereas carbon was not detected by TEM a t the surface.…”

“…The discrepancy with the value of 2.0 x 1020 ~m -~ obtained from DCD does not result from the uncertainties in the mean diameter of the precipitates (10%) and their surface density measured on TEM micrographs (10%) ; the possible reasons for this will be discussed later. As to the 0.2 pm stripped specimens (B-type), TEM observations confirmed the results obtained in a preceding work [19]. The formation of a surface film of u-quartz was in fact detected after annealing at 1000 "C for 30 min.…”

Caractéristiques électriques de diodes Au-Si(N) réalisées après irradiation par laser

“…Il est ainsi apparu que pour une irradiation effectuée sous ultravide, la concentration d'impuretés à la surface, en particulier de carbonè et d'oxygène, diminuait fortement, conduisant à des surfaces atomiquement propres et que la structure de la surface n'était en outre pas reconstruite, contrairement à ce qui résulte d'un recuit thermique conventionnel; elle serait même assez désordonnée [10]. Le mécanisme qui permet le nettoyage du silicium demeure cependant mal compris : si l'évaporation sous irradiation paraît très probable, la diffusion des impuretés, en particulier de l'oxygène, durant la période où le matériau passe par une phase liquide, est controversée [9,11,12,13]. Ce problème est particulièrement important lorsque les irradiations sont effectuées à l'air ou lorsqu'une couche d'oxyde est présente sur les échantillons [14], ce qui est généralement le cas dans les applications pratiques.…”