Spectrally resolved white–light phase–shifting interference microscopy for thickness–profile measurements of transparent thin film layers on patterned substrates

Sanjit K Debnath,Parameswaran Hariharan,Joanna Schmit,Mahendra P Kothiyal

doi:10.1364/oe.14.004662

Abstract

We describe how spectrally-resolved white-light phase-shifting interference microscopy with a windowed 8-step algorithm can be used for rapid and accurate measurements of the thickness profile of transparent thin film layers with a wide range of thicknesses deposited upon patterned structures exhibiting steps and discontinuities. An advantage of this technique is that it can be implemented with readily available hardware.

Highlights

An area of increasing importance in the optoelectronics industry is the development of noncontact techniques for rapidly and accurately mapping micromachined surfaces
We describe how spectrally-resolved white-light phase-shifting interference microscopy with a windowed 8-step algorithm can be used for rapid and accurate measurements of the thickness profile of transparent thin film layers with a wide range of thicknesses deposited upon patterned structures exhibiting steps and discontinuities
This technique has the advantage that it can be implemented with readily available hardware

Summary

Introduction

An area of increasing importance in the optoelectronics industry is the development of noncontact techniques for rapidly and accurately mapping micromachined surfaces. The position along the depth axis corresponding to maximum fringe visibility (the coherence peak) for each pixel in the image can be located by using Fourier transforms [1, 2] or by other techniques such as achromatic phase-shifting. A problem is that, in many cases, transparent film layers are deposited on these patterned structures, making it difficult to obtain accurate 3-D surface profiles. [4] This problem can be solved and the 3-D volumetric thickness profiles of such structures obtained by measurements of the spectral phase function at an array of points using Fourier transforms. The major drawback of this technique is that it involves using a spectral scanning device, such as an acousto-optic tunable filter, to make a series of measurements of the phase difference between the beams, at an array of points, at a number of wavelengths. The major drawback of this technique is that it involves using a spectral scanning device, such as an acousto-optic tunable filter, to make a series of measurements of the phase difference between the beams, at an array of points, at a number of wavelengths. [7]

Spectrally–resolved phase–shifting interference microscopy

Experimental arrangement

Measurements and results

Conclusion