Mitchell C. Taylor

Mapping two-dimensional arsenic distributions in silicon using dopant-selective chemical etching technique

Transmission electron microscopy (TEM) image contrast was used to characterize doping-dependent etching of n+/p junctions in silicon. The local variations in crystal thickness give rise to the appearance of thickness fringes which may be interpreted as two-dimensional iso-concentration contours that map the dopant distribution. The etchant solution used for selective chemical etching of TEM samples prepared using wedge technique was modified to reduce the etch rate and maintain high selectivity to the n+ doped region. The two-dimensional dopant profiles were quantified by calibrating against one-dimensional secondary ion mass spectroscopy data and also compared with one-dimensional spreading resistance analysis data.

A detailed study of elemental contamination in a Varian 180XP high-current implanter

Abstract Contamination is a major focus for device manufacturers, especially as the industry moves towards 16–64 Mbit memory level integration. This places considerable constraints on the existing ion implantation technology and the choice of materials used in the manufacture and maintenance of ion implanters. Contamination in the ion implantation process can come from a variety of mechanisms: ion-beam sputtering of hardware, cross-contamination from previous implants, in cases of nondedicated systems, end stations (discs, platens etc.), and mass interference effects during species analysis. In this paper, results of contamination analysis of wafers implanted at a customer site on a 180XP Varian implanter will be represented. A wide range of elements, including Al, Fe, Ni, alkali and alkahne earth metals, and previously implanted species were studied. Characterization was done by several techniques including secondary-ion mass spectrometry (SIMS), inductively coupled plasma mass spectroscopy (ICPMS), total-reflection X-ray fluorescence (TXRF) and neutron-activation analysis (NAA). In addition, the effects of beam current on the amounts of sputtered contaminants will be discussed. Preventative measures and maintenance procedures, which can also be potential sources of contamination, will be highlighted.