Sub-2nm On Product Overlay (OPO), scribe line width reduction, and high-order scanner correctibles are driving innovative overlay (OVL) targets. One promising new imaging-based overlay (IBO) OVL target to address such challenging trends in multiple semiconductor segments is a small pitch AIM (sAIM). sAIM is in essence an IBO target with grating (previous layer) beside grating (current layer) which could be placed in a few layouts: square, rectangular, and Mosaic. In this work, we will present the sAIM operational concept and performance including Total Measurement Uncertainty (TMU), residuals, and accuracy (ADI on-target offset vs. ACI on-device or target), which is often referred to as Non-Zero Offset (NZO).
The current state of the art ADI overlay metrology relies on multi-wavelength uDBO techniques. Combining the wavelengths results in better robustness against process effects like process induced grating asymmetries. Overlay information is extracted in the image plane by determining the intensity asymmetry in the 1st order diffraction signals of two grating pairs with an intentional shift (bias). In this paper we discuss a next evolution in DBO targets where a target is created with multiple biases. These so called cDBO (continuous bias DBO) targets have a slightly different pitch between top and bottom grating, which has the effect of having a different bias values along the grating length and are complimentary to the uDBO technology. Where for the uDBO target, the diffraction results in a uniform Intensity pattern that carries the Overlay signal, for cDBO, an oscillating intensity pattern occurs, and the Overlay information is now captured in the phase of that pattern. Phase-based Overlay has an improved, intrinsic robustness over intensity-based overlay and can reduce the need for multi-wavelength techniques in several cases. Results on memory technology wafers confirm that the swing-curve (through-wavelength) behavior is indeed more stable for phase-based DBO target and that for accurate Overlay, this target can be qualified with a single wavelength recipe (compared to the uDBO dual wavelength recipe). In this paper, both initial results on a Micron feasibility wafer will be shown as well as demonstrated capability in a production environment.
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