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A structure and a method to determine annular TSV depth

IP.com Disclosure Number: IPCOM000240430D
Publication Date: 2015-Jan-29
Document File: 2 page(s) / 48K

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Disclosed is a system for measuring the dimensions of an annular shaped through silicon silicon via (TSV) by measuring the resonant frequency of the center post.

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A structure and a method to determine annular TSV depth

Small, recessed features with large depth/width aspect ratios (e.g., a through-silicon via (TSV)) are difficult to measure with high accuracy.

There are several current attempts to address this problem. Interferometry relies on collecting reflected light from bottom of feature, which becomes increasingly difficult as the feature width becomes smaller. Atomic force microscopy is limited by tip length and sharpness; it cannot measure high aspect, recessed features. Scanning Electron Microscopy (SEM) requires cross sectioning of sample (i.e., destructive technique) to achieve depth measurements.

A simple, non-destructive method to determine the depth of a TSV structure is needed.

The novel method measures the dimensions of an annular TSV via resonant frequency (RF). TSVs are annular in shape, with a copper (Cu)-filled cylinder with a Silicon (Si) center post. The Si center post remains intact during the Reactive Ion Etching (RIE) process that forms the void for Cu fill. The post length corresponds to the depth of the TSV. The Si center post vibrates at a resonant frequency according to the following formula:

… where E is the Young's modulus of the Si, I is the moment of inertia, L is the length of the center post, and is the length density of the Si post.

A light (e.g., laser) is reflected off the top of the Si post and directed toward a photodetector. The resonant vibration of the Si post causes the reflect...