On product overlay (OPO) is one of the most critical parameters for the continued scaling according to Moore’s law. Without good overlay between the mask and the silicon wafer inside the lithography tool, yield will suffer1. As the OPO budget shrinks, non-lithography process induced stress causing in-plane distortions (IPD) becomes a more dominant contributor to the shrinking overlay budget2. To estimate the process induced in-plane wafer distortion after cucking the wafer onto the scanner board, a high-resolution measurement of the freeform wafer shape of the unclamped wafer with the gravity effect removed is needed. Measuring both intra and inter die wafer distortions, a feed-forward prediction algorithm, as has been published by ASML, minimizes the need for alignment marks on the die and wafer and can be performed at any lithography layer3. Up until now, the semiconductor industry has been using Coherent Gradient Sensing (CGS) interferometry or Fizeau interferometry to generate the wave front phase from the reflecting wafer surface to measure the free form wafer shape3,4,5. In this paper, we present a new method, Wave Front Phase Imaging (WFPI) for generating a very high-resolution wave front phase map of the light reflected off of the patterned silicon wafer surface. The wafer is held vertically to allow for the free wafer shape to be measured without having the wafer shape be impacted by gravity. We show data using a WFPI patterned wafer geometry tool that acquires 16.3 million data points on a 300mm patterned silicon wafer with 65μm spatial resolution using a total data acquisition time of 14 seconds.
Wave Front Phase Imaging (WFPI) is a new wafer shape measurement technique that acquires millions of data points in just seconds or less, on a full 300mm silicon wafer. This provides lateral resolution well below 100μm with the possibility of reaching the lens’ optical resolution limitation between 3-4μm. The system has high repeatability with root-mean-square (RMS) standard deviation (σRMS) in the single digit nm for the global wafer shape geometry and for nanotopography it reaches in the sub ångström (Å = 10-10 m) range. WFPI can collect data on the entire wafer to within a single pixel away from the wafer edge roll off1. The flatness of the silicon wafers used to manufacture integrated circuits (IC) is controlled to tight tolerances to help ensure that the full wafer is sufficiently flat for lithographic processing. Advanced lithographic patterning processes require a detailed map of the wafer shape to avoid overlay errors caused by depth-of-focus issues2. In this paper we go deep into the theoretical explanation as to how the wave front phase sensor works.
Wave Front Phase Imaging (WFPI) is a new wafer shape measurement technique that acquires millions of data points in just seconds or less, on a full 300mm silicon wafer. This provides lateral resolution well below 100μm with the possibility of reaching the lens’ optical resolution limitation between 3-4μm. The system has high repeatability with root-mean-square (RMS) standard deviation (σRMS) in the single digit nm for the global wafer shape geometry and for nanotopography it reaches in the sub ångström (Å = 10-10 m) range. WFPI can collect data on the entire wafer to within a single pixel away from the wafer edge roll off1. The flatness of the silicon wafers used to manufacture integrated circuits (IC) is controlled to tight tolerances to help ensure that the full wafer is sufficiently flat for lithographic processing. Advanced lithographic patterning processes require a detailed map of the wafer shape to avoid overlay errors caused by depth-of-focus issues2. In this paper we go deep into the theoretical explanation as to how the wave front phase sensor works.
We present a new wave front sensing technique based on detecting the propagating light waves. This allows the user to acquire millions of data points within the pupil of the human eye; a resolution several orders of magnitude higher than current industry standard ophthalmic devices. The first instrument was built and tested using standard calibration surfaces in addition to using an artificial eye. The paper then presents the first characterization of the optics of a real human eye measured using the newly developed high-resolution wave front phase sensing technique showing the complexity of the human eye’s ocular optics.
We present our latest advances in the design and implementation of a tunable automultiscopic display based on the tensor display model. A design comprising a three-layer display was introduced. In such design, front and rear layers were enabled to be controlled in a six-degree of freedom manner related to the central layer of the system. A calibration method consisting on displaying a checkerboard pattern in each layer was proposed. By computing the homography of these patterns with respect to the reference plane, it was possible to estimate the needed adjustments. An implementation based on such design was carried over and calibrated following the aforementioned technique. The obtained results demonstrated the feasibility of such implementation.
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