SSRM and SCM observation of modified lateral diffusion of As, BF2 and Sb induced by nitride spacers.
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SSRM and SCM observation of modified lateral diffusion of As, BF2 and Sb induced by nitride spacers. P. Eyben 1, N. Duhayon, C. Stuer, I. De Wolf, R. Rooyackers, T. Clarysse, W. Vandervorst and G. Badenes IMEC vzw, Kapeldreef 75, 3001 Leuven, Belgium ABSTRACT Initial studies (using Scanning Spreading Resistance Microscopy) on the lateral diffusion of B and As have shown an important influence of the thickness of oxy/nitride spacers. The latter phenomenon was tentatively ascribed to stress enhanced diffusion under the spacer region [1]. These studies have been complemented with Scanning Capacitance Microscopy (SCM) measurements, which confirm the SSRM-data. In fact both techniques shows a similar increase in lateral diffusion with increasing spacer thickness (~ 0.2 nm/nm spacer thickness), whereby no effect is observed on the vertical diffusion. When using spacers with or without TEOS-liner, fairly similar enhancements could be seen. Micro-Raman and CBED stress measurements for these cases do however show a large reduction in stress when a TEOS-liner is used, suggesting that the correlation (at least to the final) stress is not really justified. A possible explanation could however be that the lateral diffusion occurs before the stress relaxation within the thermal treatment. In order to elucidate the diffusion mechanism (initial stress, interstitials, hydrogen incorporation, TED,..) we have expanded the experimental matrix with a vacancy diffuser such as Sb and simulated the potential H-incorporation during the nitride deposition by a hydrogen anneal. Moreover we also have studied the impact of TED by splits with RTPanneals before the nitride deposition.
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Introduction
The control of the effective channel length is a major issue in the processing of modern CMOS devices. The electrical characteristics of the transistors are drastically affected by minor changes of this length. The study of the effects that may affect this value is thus crucial. Unfortunately, classical 1D dopant profiling techniques may not be used for that issue and the introduction of new characterization techniques that enables dopant profiling in the lateral direction as the AFM-based techniques (SCM, SSRM) has become a necessity. The lateral diffusion study presented in this paper originates from observations realized during two-dimensional dopant profiling of LDD/HDD structures in NMOS transistors with the SSRM (Scanning Spreading Resistance Microscopy) technique [2]. We have noticed that the effective channel length of the transistors was systematically affected by a change in the oxy/nitride spacer size (Fig. 1). An increase in the spacer size has shown to be responsible for an enhancement of the lateral diffusion of the source and drain n1
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doped (As) implants and thus for a decrease of the device’s effective channel length. In the meantime, no systematic increase of the implants’ depths (
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