The metal thickness of surface finish is an important consideration when plating on microelectronics. Metal finish thickness should comply with specification requirements to prevent serious reliability concerns. The thickness of metallic coatings is routinely determined by X-ray fluorescence (XRF) spectrometry. For conventional XRF instrumentation, typical focal spot sizes at the sample surface range in diameter from several hundred micrometers up to several millimeters. Micro- XRF focuses or collimates the X-ray beam to significantly smaller spot sizes, ranging from ~30 µm to 2 mm, thus obtaining a representative average of layer properties both at the surface and in-depth layers. This is a critical property for application in semiconductor industry where feature size is becoming progressively smaller. This work describes how a mid-range cost conventional XRF tool can be utilized for small spot size thickness measurement with the addition of a 0.25 mm diameter collimator.

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