Metrological Step Height Verification for Cluster Processed Amorphous Substrates
Step height verification on cluster-processed amorphous substrates requires guardbanded metrology and tip-force or dispersion compensation to prevent yield loss.
Refractive Index Dispersion
Optical Property
Physical phenomena describing how the refractive index of a material changes as a function of the wavelength of light determine the performance of lenses and optical coatings. Understanding refractive index dispersion is necessary for designing waveguides and sensors where light of different colors must stay in phase or focus at the same point. This variation is a fundamental characteristic of all transparent media, including the polymers and glass used in circuit substrates.
It influences how signals propagate through high-speed optical backplanes, as different frequencies of light will travel at slightly different speeds, potentially causing timing jitter in data transmission.
Wavelength Dependence
Blue light typically bends more than red light when passing through a medium because the index is higher at shorter wavelengths. This separation of colors can cause chromatic aberration in imaging systems or signal spreading in fiber optics. Engineers use mathematical models like the Cauchy or Sellmeier equations to predict these changes across the visible and infrared spectrum.
Material Characterization
Thin film metrology uses this property to calculate the thickness of transparent layers on a wafer. By measuring the interference patterns of light across many wavelengths, an ellipsometer can solve for both the thickness and the dispersive nature of the coating simultaneously. This dual calculation prevents errors that would occur if the index were assumed to be a single constant value.