Martin F. Fay

Measuring High-Slope and Super-Smooth Optics with High-Dynamic-Range Coherence Scanning Interferometry

Advances in the implementation of coherence scanning interferometry have dramatically extended the range of application for this well-known technique. New data acquisition and data processing methods significantly improve dynamic range, enabling measurements of steeply-sloped surfaces usually considered beyond the reach of high-NA objectives. Hybrid data acquisition incorporating sinusoidally-modulated phase shifting reduces signal-to-noise to the 0.1 nm/√Hz level, extending the technique to super-polished surfaces. OCIS codes: 120.3180 Interferometry; 120.3940 Metrology; 120.6660; Surface measurements, roughness

Multi-purpose optical profiler for characterization of materials, film stacks and for absolute topography measurement

We have developed a scanning white-light interference microscope that offers two complementary modes of operation on a common metrology platform. The first mode measures the topography and the second mode measures the complex reflectivity of an object surface over a range of wavelengths, angles of incidence and polarization states. This second mode characterizes material optical properties and determines film thickness in multi-layer film stacks with an effective measurement spot size typically smaller than 10 μm. These data compensate for material and film effects in the surface topography data collected in the first mode. We illustrate the application of this dual-mode technology for post-CMP production-line metrology for the data storage industry. Our tool concurrently measures critical layer thickness and step height for this application. The accuracy of the latter measurement is confirmed by correlation to AFM measurements.

Interferometric microscope with true color imaging

Optical 3D profilers based on Coherence Scanning Interferometry (CSI) provide high-resolution non-contact metrology for a broad range of applications. Capture of true color information together with 3D topography enables the detection of defects, blemishes or discolorations that are not as easily identified in topography data alone. Uses for true color 3D imaging include image segmentation, detection of dissimilar materials and edge enhancement. This paper discusses the pros and cons of color capture using standard color detectors and presents an alternative solution that does not rely on color filters at the camera, thus preserving the high lateral and vertical resolution of CSI instruments.

Interference Microscopy For Semiconductor Back End Patterning Metrology

Interference microscopy satisfies many of the dimensional metrology requirements for semiconductor device interconnects manufacturing by providing 3D topography maps of patterned structures with sub‐nm vertical reproducibility. Analysis of topography maps and intensity images with pattern recognition software extends the metrology capability for CD, overlay and registration. This functionality is used in a flexible, multi‐purpose, inline process control tool for pre‐ and post‐metallization metrology on BEOL via and bump layers. Through Silicon Vias is another promising field of application, as demonstrated by the strong correlation of optical profiler results to cross‐section SEM reference metrology.

Applications of model-based transparent surface films analysis using coherence scanning interferometry

Surface metrology must increasingly contend with sub-micron films, whose prevalence now extends to products well beyond semiconductor devices. For optical technologies such as coherence-scanning interferometry (CSI), transparent sub-micron films pose a dual challenge: film effects can distort the measured top surface topography map, and metrology requirements may now include 3D maps of film thickness. Yet CSI’s sensitivity also presents an opportunity: modeling film effects can decode surface and thickness from the distorted signal. Early model-based approaches entailed practical trade-offs between throughput and field of view, and restricted the choice of objective magnification. However, more recent advances allow full-field surface films analysis using any objective, with sample-agnostic calibration and throughput comparable to film-free measurements. Beyond transparent films, model-based CSI provides correct topography for any combination of dissimilar materials with known visible-spectrum refractive indices. Results demonstrate single-nm self-consistency between topography and thickness maps.

Applications of model-based transparent surface films analysis using coherence-scanning interferometry

Abstract. Surface metrology must increasingly contend with submicron films, whose prevalence now extends to products well beyond semiconductor devices. For optical technologies such as coherence-scanning interferometry (CSI), transparent submicron films pose a dual challenge: film effects can distort the measured top surface topography map and metrology requirements may now include three-dimensional maps of film thickness. Yet CSI’s sensitivity also presents an opportunity: modeling film effects can extract surface and thickness information encoded in the distorted signal. Early model-based approaches entailed practical trade-offs between throughput and field of view and restricted the choice of objective magnification. However, more recent advances allow full-field surface films analysis using any objective, with sample-agnostic calibration and throughput comparable to film-free measurements. Beyond transparent films, model-based CSI provides correct topography for any combination of dissimilar materials with known visible-spectrum refractive indices. Results demonstrate single-nm self-consistency between topography and thickness maps.