Fast surface profiling by spectral analysis of white-light interferograms with Fourier transform spectroscopy

Abstract

We present a fast white-light interference method for measuring surface depth profiles at nanometer scales. Previously reported white-light profilers have relied either on path difference scanning or on spectral analysis of the reflection from a fixed interferometer. We show that by performing this spectral analysis with an imaging Fourier transform spectrometer, the high speed of spectral techniques may be combined with the simple data interpretation characteristic of the scanning method. Giving experimental results from a profiler based on this principle, we show that real-time visualization of surface profiles is possible and we report measurements with a repeatability of approximately 5 nm rms. We also demonstrate good agreement with stylus profiler measurements.

Fringe modulation skewing effect in white-light vertical scanning interferometry

“…One method of determining surface height involves the use of a broad-spectral-width light source in an interferometer and measurement of the degree of modulation contrast as a function of path difference. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Because of the large spectral bandwidth of the source, the coherence length of the source is short, so good contrast fringes will be obtained only when the two paths of the interferometer are closely matched in length. By looking at the sample position for which the fringe contrast is a maximum while the optical path difference is varied, one can determine the height variations across the sample.…”

“…Many excellent features of whitelight vertical scanning interferometry were published previously. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Although this is a good technique for measuring many surfaces, it does not work especially well with step heights 16 that are less than the coherence length of the light source in use. The problem has been known as batwings because of the shape of the false information.…”

On-line surface inspection using cylindrical lens–based spectral domain low-coherence interferometry

“…It has the disadvantage of utilizing mechanical scanning in the depth direction to localize the fringes in the vicinity of zero OPD, which is time consuming and permits measurement only for stationary objects [9]. As for WSI and SD-LCI, they belong to spectral interferometry, which takes advantage of spectral interference fringes for a wide range of wavelengths without any mechanical scanning [8,10,11].…”

Wide band interferometry for thickness measurement

“…As a consequence, scanning white-light interferometry (SWLI) has been extensively used for unambiguous distance measurement with nanometer resolution along the propagation direction of a light beam. The use of a low coherence light source combined with the scanning of one arm of the interferometer provided a very useful way of measuring surface profiles [3][4][5]. Different techniques were developed to increase the system resolution over the coherence length of the source [6] and continuously provide diverse solutions to a variety of configurations [7,8].…”