Atomic Layer Deposition of Sidewall Spacers: Process, Equipment and Integration Challenges in State-of-the-Art Logic Technologies
This paper discusses the properties of ALD silicon nitride and silicon oxide spacer films from the perspectives of ALD and MLD (Molecular Layer Deposition) techniques, precursor chemistries and compositional stability after subsequent integration steps like implant anneals and spacer sculpting reactive ion etching processes. Advanced imaging techniques like EELS (Electron Energy Loss Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) techniques have been used to analyze sidewall spacer transformation. Special attention has been paid to the microloading effect - the dependence of thin film deposition rate on pattern density . Microloading data for CVD, MLD and ALD techniques are compared based on a specially designed microloading measurement vehicle. This is especially useful with geometries needing a sub nm tolerance and when patterning endpoint detection schemes are highly dependent on film properties.
The effect of ALD deposition parameters on film electrical characteristics like dielectric breakdown and leakage are also delineated. Silicon strain engineering issues related to the implementation of ALD spacers and techniques aimed at varying and controlling an intrinsic stress level in ALD films are also discussed. The findings helped to optimize the existing ALD/MLD processes for conventional epi and source/drain spacers as well for oxide sidewall ALD spacers for SIT fins patterning and CD shrink on 14nm FinFET technology.
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