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Measurement of the internal geometry of MEMS structures.

Sun, W; Leach, R K (2010) Measurement of the internal geometry of MEMS structures. NPL Report. ENG 24

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Abstract

Increasingly, many modern MEMS devices incorporate multi-layered structures. However, the metrology of such structures is struggling to keep pace with their manufacture. In this project, the internal geometry of MEMS devices has been measured using optical coherence tomography and infra-red confocal microscopy, where both instruments provide non-contact, non-invasive measurements of internal geometry. However, both measurement techniques are relatively new technologies for measuring internal geometry and the understanding of their capabilities is limited. This study has mainly focused on the thickness measurement of layers. The axial resolution of the two instruments has been investigated, as is a vital parameter when measuring thickness. The performance of the axial axis of both instruments has been calibrated by measuring a 50 mm thickness artefact that has been calibrated using a traceable stylus instrument. The uncertainties associated with the measurements of the thickness artefact are 0.391 mm for optical coherence tomography and 1.085 mm for infra-red confocal microscopy. The capabilities of the two instruments have been extensively studied by measuring a pressure sensor with multi-layered structures. The thicknesses of the layers range from 20 mm to 300 mm with a total thickness of around 800 mm. These measurements demonstrated that both instruments have the ability to measure the thickness of layers and to image internal geometrical structures. This study has revealed that infra-red confocal microscopy has a larger range of depth scan and optical coherence tomography has better axial resolution. The characteristics of these two instruments are summarised and the potential to improve the performance of the instruments is discussed.

Item Type: Report/Guide (NPL Report)
NPL Report No.: ENG 24
Subjects: Engineering Measurements
Engineering Measurements > Dimensional
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/4598

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