A high level of immunity to vibration required for on-machine measurements is demonstrated by the continuous phaseshifting
interferometer described in this work. Phase measurement errors caused by environmental disturbance and
mechanical instability are eliminated by Fourier analysis on a few hundreds of fringes captured by a high-speed CMOS
camera. For the purpose, phase shifting is applied in a continuous mode. The proposed continuous phase-scanning
method is proposed to apply the phase-extraction principle on a specific heterodyne frequency generated from multiple
cycles of 2π-scanning by the uniform translation of PZT-driven stage. As a result, inherent drawbacks of conventional
PSI algorithms, such as nonlinearity errors of PZT, measurement speed, complexity of phase analysis algorithm, can be
overcome effectively. The experimental results about surface measurement of 1" spherical concave mirror show that
superior phase reconstruction performance with good quality can be achieved even under severe vibration circumstances
simulated by target excitation along a lateral direction.
The principle of angle-resolved reflectometry is exploited for thin-film thickness measurements. Within an optical
microscope equipped with a high NA objective, a sequence of quasi-monochromatic light of different wavelengths is
generated from a white-light source through spectral filters. Then for each wavelength, the reflectance intensity from the
thin-film sample is monitored on the back focal plane of the objective. This enables collection of reflectance with
varying incident angles. The film thickness is then uniquely determined by fitting the measured data to an ideal multi-reflection
model of thin films. This method can be readily extended to multi-layered film structures, finding applications
for industrial inspection of semiconductor devices and flat panel display products.
A dispersive method of white-light interferometry for measuring the tomographical thickness profile of a thin-film layer
through a Fourier-transform analysis of a spectrally-resolved interference signal is proposed. The refractive index is also
determined without prior knowledge of the geometrical thickness of the film layer. In contrast with standard white-light
scanning interferometry, dispersive white-light interferometry generates the spectral distribution of interferograms
directly by means of dispersive optics without mechanical depth scanning. Therefore, the proposed method in this paper
is well suited for in-line 3-D inspection of dielectric thin-film layers, particularly for the semiconductor and flat-panel
display industry, with high immunity to external vibration and high measurement speed.
Emerging possibility of applying white-light interferometry to the area of thin-film metrology is addressed. Emphasis is
given to explaining underlying spectrally-resolved interferometric principles of white-light interferometry for measuring
the top surface profile as well as the thickness of thin-film layers, which enables one to reconstruct the complete 3-D
tomographical view of the target surface coated with thin-film layers. Actual measurement results demonstrate that
white-light interferometry in either scanning or dispersive scheme is found well suited for high speed 3-D inspection of
dielectric thin-film layers deposited on semiconductor or glass substrates.