Summer04 inline nondestructive

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Inline and Non-destructive Analysis of Epitaxial Si1-x -yGexCy R. Loo, R. Delhougne, L. Geenen, B. Brijs and W. Vandervorst, IMEC P. Meunier-Beillard, Philips Research T. Koumoto, Sony Corporation Semiconductor Network Company

The implementation of silicon germanium (SiGe) and silicon germanium with substitutional carbon incorporation (SiGe:C) in BiCMOS and CMOS technologies requires very good control of epitaxial layer thickness and layer composition. In contrast with most of the characterization methods, spectroscopic ellipsometry (SE) allows a fast, inline and non-destructive analysis, including fast wafer mapping facilities. In this paper, the existing SE measurement routine for SiGe is extended to SiGe:C with substitutional carbon (C) incorporation. The optical dispersion is described by means of the harmonic oscillator model. The extraction of the C content is based on a well-defined shift of the resonant energy of the first oscillator. The SE system is a small spot (28x14 Âľm2) spectroscopic ellipsometer, which allows the characterization of epitaxial SiGe and SiGe:C layers grown on patterned wafers, while this small window size prevents measurements by RBS. The SE technique is therefore a very powerful tool for optimization of the layer uniformities in both thickness and composition.

Introduction

The implementation of SiGe layers in active device structures is nowadays recognized as an efficient way to improve device characteristics by band offsets and/or increased carrier mobility. Currently, chip manufacturers focus mainly on the integration of SiGe in hetero bipolar transistors (HBT) in BiCMOS technology1-3 and on the fabrication of Si/SiGe hetero CMOS devices to improve performance of n- and p-type MOS devices4-9. In a next phase, attention will go to elevated SiGe source/drain contacts to reduce short channel effects in CMOS technology10, 11. Recently, a strong interest in SiGe alloys containing carbon arises. The strong suppression of boron (B) diffusion by substitutional carbon (C), leads to an important improvement in HBT device performance12. Other publications predict 40

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greater flexibility to control strain and band-offsets, which might be beneficial for MOS applications13, 14. All these applications contain a SiGe/Si or SiGe:C/Si heterostructure in the active device. Industrial applications require very good control of the heterostructure in terms of epitaxial thickness and composition (Ge and C content) with layer uniformities in the range of 1-2 percent. The reproducibility from one epi layer to the other has to be in the same order of magnitude. In general, Rutherford backscattering spectroscopy (RBS), secondary ion mass spectroscopy (SIMS) or photoluminescence measurements (PL) are used to measure the layer thickness and composition. These techniques are very well developed but are unsuitable as production measurement tools. RBS and SIMS are destructive, while PL requires cryogenic conditions, which makes the technique quite time-consuming. On the other hand, SE allows a fast, inline and non-destructive analysis, including fast wafer mapping facilities. Indeed, SiGe has become a routine technique to study strained epitaxial


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