Optical Thickness and Flatness Measurement of Bonded Silicon Wafer Assemblies

Abstract—The silicon wafer manufacturing process relies heavily on precision polished wafers that have uniform thickness and, depending on the application, also control parallelism to a secondary wafer after bonding.
Lumetrics’ low coherence interferometer, commercially marketed as OptiGauge II, is a device capable of measuring the simultaneous wafer thickness, adhesive thickness, and parallelism between surfaces to sub-micron precision. Combined with custom software and a precision XY raster scanner, a wafer or wafer assembly can be fully characterized with respect to layer thicknesses and surface parallelism.
Index Terms—adhesive, flatness, interferometry, metrology, optical thickness measurement, parallelism, silicon, wafer

I. Introduction:

Lumetrics is the market leader in providing high-precision, non-contact optical thickness measurements to medical, scientific, and ophthalmic industries.

A unique capability of our flagship thickness measurement device, OptiGauge II, is its ability to measure the individual layer thickness of a multiple-layer sample.

The OptiGauge II measures using a 1310nm wavelength. This is an ideal wavelength for measuring through nearly all visually transparent and semi-transparent objects.

A visually opaque material that is highly transmissive at 1310nm is silicon. This makes silicon an ideal sample for optical thickness measurement.

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