Joonho You

GPU-accelerated white-light scanning interferometer for large-area, high-speed surface profile measurements

A special-purpose design of white-light scanning interferometer is described here for the high-speed 3-D profile measurement of micro- and nano-patterned surfaces. Parallel processing of fringe data is accomplished by adopting a graphics processing unit (GPU), which allows a great reduction in the computational time in implementing a recursive, weighted algorithm to detect the envelop peak of low-coherence interferograms without any post-processing. Experimental result shows that the processing time of the used GPU is at least 160 times faster than that of the conventional method relying on the central processing unit (CPU) in handling interferometric fringe data of four megabytes.

Dispersive white light interferometry for 3D inspection of thin film layers of flat panel displays

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.

Simultaneous measurements of thin-film thickness and refractive index .. by dispersive white-light interferometry

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.

Angle-resolved reflectometer for thickness measurement of multi-layered thin-film structures

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.