David Grigg

Optical interferometry for measurement of the geometric dimensions of industrial parts

We describe an instrument for the measurement of surface flatness, parallelism, and size (thickness) of plane-parallel parts in a single measurement to 1sigma gauge capability of 0.02, 0.03, and 0.06 microm, respectively. A low-coherence IR profiler viewing both sides of the part simultaneously, believed to be novel, accommodates a wide variety of industrial surface finishes, including machined, ground, or lapped parts, with a 75-mm field of view and 15,000 pixels per side. A heterodyne laser displacement gauge together with an integrated zeroing system allows for a range of part sizes from 0 to 100 mm.

Static and dynamic characterization of MEMS and MOEMS devices using optical interference microscopy

We report on characterization techniques for microstructures using white-light interference microscopy. Capabilities include surface profilometry, integrated profilometry and lateral metrology for full 3D characterization, defect detection, profilometry of thin film structures, stroboscopic interferometry of vibrating samples, and real-time profile snapshots of moving MEMS devices.

Step height measurements using a combination of a laser displacement gage and a broadband interferometric surface profiler

We describe techniques for measuring step heights between separated, nominally plane-parallel surface regions of a precision-engineered part. Our technique combines a broadband, 10-micron wavelength scanning interferometric profiler with a HeNe laser displacement gage. The infrared wavelength accommodates machined metal parts having a surface roughness in excess of what would be possible with a visible-wavelength interferometer. The combination of broadband interferometry, which removes fringe order ambiguity, with a laser displacement gage makes it possible to determine the relative heights of surfaces separated by several mm with a 2-σ uncertainty of 0.3 micron. We present the instrument theory, experimental implementation and results of instrument testing.

Surface profiling using a reference-scanning Mirau interference microscope

We compare two modes of measurement of shallow objects using a scanning interference microscope. In one mode the object is moved with respect to the Mirau interference objective while a camera records the interference pattern. In another mode the beam splitter is moved during the scan while the object remains in focus. We use both narrowband and broadband extended LED sources for the experiments with a modified 0.8-NA Mirau objective. A detailed analysis of the low-coherence interference signals in the spatial and spectral domains reveals small differences between the two scan mode. However, the comparison of surface profiles of objects having surface departures smaller than the depth of focus shows no appreciable differences. We conclude that the small amount of defocus that affects interference signals recorded during an object scan does not influence the quality of the measurement when using typical broadband extended sources.

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.