Characterization of SiGe layers grown by Trisilane and Germane at low temperatures for BiCMOS application
Abstract: Low temperature epitaxy (LTE) of SiGe by chemical vapor deposition (CVD) has attracted dramatic attention during the last decade for CMOS and BiCMOS application. LTE relates to a temperature range of 350÷650 °C. The low temperature budget provides the possibility of integrating epitaxy in the process line when the sensitive active parts are already present on the chips. In this case, the benefits of LTE are to avoid the thermal mismatch between different layers in the transistors, preventing damages to the poly gate and to ensure the integrity of thin gate oxide. The challenge to deal with the lowering temperature process is the quality of epitaxial layer. In particular, the low temperature processing results in low growth rates and more oxygen (or water moisture) contamination in the layer growth. For these reasons, particular attention has been paid to islands formation at the interface and within the layer. Choosing appropriate Si precursor, optimizing the growth parameters and reducing oxygen (or moisture) contamination are critical issues for growing high quality epitaxial layers at low temperatures. This thesis work presents the characterization of layers grown using Trisilane (Si3H8), Germane (GeH4) and Hydrochloric acid (HCl) as precursor gases at LTE. Characterization tools were high-resolution scanning electron microscope (HRSEM), Secondary ion mass spectroscopy (SIMS), high-resolution x-ray diffraction (HRXRD) and noise measurements. The results of this work suggest that only electrical measurements are most sensitive way to study the effects of low amounts of contamination on crystal quality of LTE grown structures. It also shows that the presence of HCl in the chamber increases the noise level in these types of structures. This higher level of noise is believed to be a result of higher defect density due to the etching caused by HCl and metal contamination that could arise from the aging and the corrosion of the pipelines.
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