Deflectometry/curvature measurements
Deflectometry for wafer curvature measurements
The ongoing trend towards bigger wafers in LED, laser and power devices production has created new challenges. Wafer bowing, an annoyance with two inch wafers, becomes critical at four inches and above. The curvature creates a gradient from the edge and the center of the wafer in its distance to the susceptor. This in turn causes surface temperature deviations across the wafer. The larger the wafer, the greater these temperature deviations.
Features
Asphericity monitoring with advanced resolution
Accurate in-situ monitoring of the wafer curvature helps to minimize bowing-related wafer temperature inhomogeneities, to achieve better uniformity and, ultimately, higher yields. One of the challenges during buffer growth is the increasing asphericity of the wafer. For processes that potentially cause aspherical wafer curvature, we offer the EpiCurve® TT with the Advanced Resolution (AR) option:
AR provides information on wafer curvature along two perpendicular directions, radial asphericity and azimuthal asphericity
AR measures the quantity of aspheric component and gives access to information about the layer formation
AR detects relaxation at an early stage and reduces signal fluctuations in the main (spherical) bow measurement caused by aspherical effects
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