A well-established solution for measurement of aspheric surfaces relies on translating the test part along the optical axis of a precision laser Fizeau interferometer while collecting interference fringes from areas of low slope relative to a spherical reference surface. The data are assembled into a final surface profile using the instrument geometry and scan history. This principle has been the foundation of a commercial instrument for nearly two decades. Here we report on several key advances for this instrument: 1. Optical configuration management for improved automated alignment for flats, spheres, aspheres, and torics. 2. Upfront and re-callable distortion and magnification calibrations for each transmission sphere/zoom combination. 3. Job-centric user interface with improved ease-of-use, including importing of asphere definitions directly from standard lens design software files. We give an overview of the new system, show measurement examples, and discuss how the improvements mentioned above affect the metrology and the user experience.
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.
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.
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.
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.
A white-light interferometer with new signal analysis techniques provides 3D top surface and thickness profiles of
transparent films. With an additional change from conventional object imaging to pupil-plane imaging, the same
instrument platform provides detailed properties of multilayer film stacks, including material optical properties. These
capabilities complement conventional surface-topography measurements on the same platform, resulting in a highly
flexible tool.
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