Scanning White Light Interferometry Research Articles

Thickness-profile measurement of transparent thin-film layers by white-light scanning interferometry

White-light scanning interferometry is increasingly used for precision profile metrology of engineering surfaces, but its current applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. A new attempt is made to extend the interferometric method to the thickness-profile measurement of transparent thin-film layers. An extensive frequency-domain analysis of multiple reflection is performed to allow both the top and the bottom interfaces of a thin-film layer to be measured independently at the same time by the nonlinear least-squares technique. This rigorous approach provides not only point-by-point thickness probing but also complete volumetric film profiles digitized in three dimensions.

Self-Compensation of PZT Errors in White Light Scanning Interferometry

One of main error sources in white light scanning interferometry is the inaccuracy of scanning mechanisms in that PZT(piezoelectric transducer) micro-actuators are preferably used. We propose a new calibration method that is capable of identifying actual scanning errors directly by analyzing the spectral distribution of sampled interferograms. This calibration provides an effective means of self-compensation for the non-linearity errors caused by PZT hysteresis, enhancing the measurement uncertainty to a level of 5 nanometers over an entire measuring range of 100 <TEX>${\mu}{\textrm}{m}$</TEX>.

Analysis of the spatial distribution of the constituting elements in amorphous solids: Laser ablation with ICP spectrometry

Amorphous materials of the systems Si/B/N/C and Ba/Si/Al/O/C, which are highly resistant against thermal and chemical attack, were analyzed using laser ablation inductively coupled plasma atomic emission (LA-ICP-AES) and mass spectrometry (MS) in order to prove the applicability of these techniques to this special type of materials. Homogeneity was evaluated and the concentrations of the main components were determined with a resolution of 50 μm. A good reproducibility was obtained using one element for internal standardization (0.3–0.7% RSD for Si and Al with Ba as internal standard and about 1.5% for B with Si as internal standard). Scanning white light interferometry employed for the measuring of the crater volumes was tested to support the internal standardization method.

Surface roughness in PMMA is linearly related to the amount of excimer laser ablation.

To determine if surface roughness after excimer laser ablation is a function of the amount of ablation and to identify a standard unit for ablation roughness. We used a VISX 20/20 excimer laser to perform a series of single zone 6-mm diameter ablations (photorefractive keratectomy [PRK]) in polymethylmethacrylate (PMMA). Corrections ranged from -1.00 diopter (D) to -15.00 D. A scanning white light interferometry microscope (Zygo Corp, Middlefield, Conn) was used to quantify the surface roughness at the center of each ablation. We found a linear increase in surface roughness as the refractive correction increased. Each diopter increment resulted in an approximately 300 nm increased peak-to-valley measurement. This represented an increase of 25 nm roughness per micron of ablation in PMMA. Surface irregularities in PMMA increase with ablation depth. We propose a unit of measure of roughness, the "ablation," expressed as the peak-to-valley distance in nm/divided by m of ablation.

High-speed non-contact profiler based on scanning white light interferometry

We describe a new profiler for fast 3-dimensional measurements of both optically smooth and optically rough surfaces based on scanning white light techniques. The profiler utilizes an efficient algorithm to extract and save only the region of interference, substantially reducing both the acquisition and analysis time while measuring rougher surfaces and larger step heights than conventional phase shifting techniques. The instrument measures steps to 100 microns, scans a 10 micron range in 5 seconds and has a smooth surface repeatability of 0.5nm.

High-speed noncontact profiler based on scanning white-light interferometry

We describe a system for fast three-dimensional profilometry, of both optically smooth and optically rough surfaces, based on scanning white-light techniques. The system utilizes an efficient algorithm to extract and save only the region of interference, substantially reducing both the acquisition and the analysis times. Rough and discontinuous surfaces can be profiled without the phase-ambiguity problems associated with conventional phase-shifting techniques. The system measures steps to 100 µm, scans a 10µLm range in 5 s, and has a smooth surface repeatability of 0.5 nm.