M. L. Polignano

Gettering mechanisms in silicon

Various procedures for heavy metal gettering in silicon p‐n junctions have been compared in order to test the effectiveness of dopants and extended defects as getter sites; the role of silicon interstitials in the gettering process has also been studied. It has been found that only phosphorus and boron atoms are effective getter sites, while arsenic and antimony are not; such gettering effectiveness is independent of the presence of extended defects in the heavily doped regions. During a moderate temperature annealing (segregation annealing) dissolved metal impurities diffuse from the space‐charge region of the devices and segregate at getter sites. Extended defects generated by oxygen precipitation and stacking fault backside damage have some ability to capture metal impurities, but electrical tests show that they do not provide a satisfactory gettering technique. The role of self‐interstitials consists of increasing the dissolution rate of metal precipitates with subcritical radii, so that the segregati...

Generation‐recombination phenomena in almost ideal silicon p‐n junctions

A systematic analysis of static current‐voltage characteristics at variable temperatures of almost ideal silicon p‐n junctions has been carried out. This analysis shows that while in neutral region the generation and recombination mechanisms are characterized by the same lifetime, in the space‐charge region the generation lifetime may be significantly lower than the recombination lifetime: hence we infer the existence of a field‐assistance pure generation phenomenon. Evidence supporting the hypothesis that a unique center is responsible for all of the recombination phenomena is presented. This center is not related to erratic contamination, but pertains to silicon. The Shockley–Read–Hall generation‐recombination mechanism (leading to the Sah–Noyce–Shockley theory of the p‐n junction) is proved to give an unsatisfactory description of the almost ideal diode.

The impact of the metallization technology on junction behavior

The influence of a titanium‐titanium nitride (Ti/TiN) barrier metallization on the behavior of junctions has been investigated. Different geometries have been used in order to separate the various contributions to the electrical behavior of junctions. An increase of the reverse current of junctions is observed in the presence of Ti/TiN/Al:Si contacts. This fact does not produce an increase of junction defect density, since the reverse current of junctions remains within an acceptable range. The contribution to junction reverse current induced by Ti/TiN/Al:Si contacts has been characterized; it has been shown that it is related to contact perimeter, it is independent of many relevant process steps, and it is reduced by thermal treatments after metal deposition. By assuming that this contribution is due to a generation‐recombination center induced by Ti/TiN contacts, the analysis of current‐voltage characteristics versus temperature gives an activation energy for this contribution. However, at present the a...

Spectrometry of very long‐current transients in almost ideal silicon p‐n junctions

Proper gettering and annealing processes allow construction of silicon p‐n junctions whose current‐voltage characteristic either completely obeys the Shockley equation (ideal junctions) or, for reverse bias, has three components (almost ideal junctions): a voltage‐independent term, which may be much smaller than the diffusion saturation current, a generation‐recombination contribution, and an ohmic component. The last two currents are due to defect centers that have the same activation energy and which are electrically neutral. In preceding works it has been shown that such an experimental finding may be ascribed to four‐state traps, i.e., to defect centers that may be empty of carriers, or filled by an electron or a hole, or both, and which are created by localized states, with different positions and energy levels, due to the oxygen. In the present work an experimental system for measuring, at 0±0.05 °C, the current transients produced in almost ideal junctions by changes of the reverse‐bias voltage, an...

Denuded zone and diffusion length investigation by electron beam induced current technique in intrinsically gettered Czochralski silicon

Electron beam induced current (EBIC) technique is successfully used to characterize intrinsically gettered Czochralski silicon. The impact of three different sequences of thermal treatments, typically used in ultralarge scale integration device manufacturing, on the denuded zone (DZ) formation and oxygen precipitation in the bulk is evaluated. EBIC technique is applied in a nonstandard configuration, where a Schottky diode is evaporated on the wafer cross section, for the direct observation of the DZ and oxygen related defects in the silicon bulk. The reduction of minority carrier diffusion length, due to the formation of recombination centers after oxygen precipitation, is also estimated by EBIC in planar collector geometry. The DZ determination by EBIC technique is in good agreement with surface photovoltage measurements and microscopical inspections after chemical etching.