Atomic Layer Deposition
ALD processes are being increasingly introduced into the fabrication sequence, as the technology of choice for highly conformal, ultra-thin films. Specific ALD application examples already exist in production, including the deposition of High-k capacitor dielectric, High-k gate stack layers, and thin barrier metals such as W or Ta. ALD, which offers a direct control of composition and thickness, creates metrology challenges in characterising the actual process result. The ultra-thin nature of the films challenges film thickness measurement techniques, while the conformal growth over high-aspect ratio features may otherwise require destructive methods. Mass metrology measures the whole-wafer deposition, encompassing the 3D step-coverage; with the associated amplified response to film composition or thickness variation. Mass metrology is an ideal R&D tool for defining and measuring film properties and an ideal production monitoring solution for ALD, capable of measuring film deposition on product wafers, affirming film parameters, layer-stack and step coverage consistency.
Mass metrology effectively supports ALD development activities, with feedback on early stage film growth, which may be non-linear. In addition, understanding the self limiting growth mechanism provides an opportunity for maximising the efficient use of deposition precursors. Mass change is valuable additional information in revealing growth cycle saturation or in addressing density/composition control during process, and device development.
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