Materials Science and Engineering B73 (2000) 1 – 6 Perpendicular excitation-probe microwave absorption technique for carrier lifetime analysis in layered Si structures E. Gaubas a, *, E. Simoen b , C. Claeys b,c , J. Vanhellemont d a Institute of Material Research and Applied Sciences, Vilnius Uniersity, Sauletekio a. 10, 2040 Vilnius, Lithuania b IMEC, Kapeldreef 75, B-3001 Leuen, Belgium c KU Leuen, ESAT-INSYS, Leuen, Belgium d Wacker Siltronic AG, PO Box 1140, D-84479 Burghausen, Germany Abstract The aim of this paper is to present a modified microwave absorption (MWA) technique using the partial filling mode, applicable when lifetime measurements are performed in the perpendicular excitation-probe regime. In this case, the carrier excitation is done by illuminating a cross-section of the layered structure through fiber optics. The excited area is then perpendicularly probed by microwave (MW) radiation when the MW antenna is partially filled with a sample. The potential of this technique is demonstrated on a set of Co-silicided n + -p junction diodes and on epitaxial-Si structures. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Carrier lifetime; Microwave absorption; Co-silicided n + -p junction diodes; Epitaxial silicon structures www.elsevier.com/locate/mseb 1. Introduction Interest in improved carrier lifetime measurements as a materials’ and processing evaluation tool has been largely driven by the introduction of new sensitive tools like the microwave (MWA) absorption technique. Due to the conductivity of the highly doped substrates of device wafers with different layers and metallic struc- tures on top, the conventional MWA technique [1,2] cannot be directly applied for carrier lifetime measure- ments. Therefore, new modes of the MWA method are desirable. Furthermore, for processed wafers and in order to study the impact of certain fabrication steps or modules, like for example silicidation, one should be able to assess the carrier lifetime close to the top surface where the active devices (p-n junctions) reside. It is therefore the aim of this paper to present a modified MWA technique, using the MW antenna partial filling regime and perpendicular small area excitation realized by single mode fiber. Here, it is applied to a set of Co-silicided n + -p junction diodes in order to investigate the impact of the silicidation conditions on both bulk and surface lifetime. In addition, the recombination properties of silicon epitaxial layers, deposited on a highly doped p + substrate, are investigated with the modified technique. It is shown that the analysis of the excess carrier decay measured by the perpendicular excitation-probe geometry allows the determination of the recombination properties for each individual layer in the structure. This measurement regime is compared with the oblique excitation-probe experimental mode. 2. Theoretical background It is accepted that the transient MW response is determined by the excess carrier concentration within an optically excited area of dimension  in the cross- section of the sample under investigation. As radial dimensions usually prevail under the sample thickness d, i.e. x, z d, the excess carrier variations within the x, z plane can be approximated by the semi-infinite problem, and the main consideration is addressed to describe the local time-space changes of the excess carrier concentration with the coordinate y on the sample cross-section (0 y d ). Excitation is approxi- mated by a square-wave space domain of width  and a -pulse of generated concentration n 0 at the initial * Corresponding author. Tel.: +370-2-769503; fax: +370-2- 769313/764455. E-mail address: eugenijus.gaubas@ff.vu.lt (E. Gaubas) 0921-5107/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0921-5107(99)00426-2