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 technique for measuring the free shape of a silicon wafer. To avoid the effects of gravity affecting the wafer shape, the silicon wafer is held vertically while measured using a custom made three-point wafer holder. The wave front phase is measuring using a non-coherent light source that is collimated and then reflected off the silicon wafer surface. The wave front phase is measured using a unique new method that only needs to record the intensity of the reflected light at two or more distances along the optical path. Since only intensity images are used to generate the phase, commercially available CMOS sensors with very high pixel count are used, which enables very high number of data points to be collected at the time required by the cameras shutter speed when using a dual camera setup with simultaneous image acquisition. In the current lab system, a single camera on a linear translation stage is used that acquires 16.3 million data points in 12 seconds, including the stage motion, on a full 300mm wafer providing lateral pixel resolution of 65μm. 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 free, non-gravitational wafer shape, to avoid overlay errors caused by depth-of-focus issues. We present WFPI as a new technique for measuring the free shape of a silicon wafer with high resolution and high data count acquired at very high-speed using a system where the wafer is held vertically without the effects of gravity.
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.
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 suffer. As the OPO budget shrinks, non-lithography process induced stress causing in plane distortions (IPD) becomes a more dominant contributor to the shrinking overlay budget. 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 layer. 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 shape. In this paper, we present a new method to generate a very high-resolution wave front phase map of the reflected light from a patterned silicon wafer surface that can be used to generate the free form wafer shape. We show data using a WFPI patterned wafer geometry tool to acquire 3.4 million data points on a 200mm patterned silicon wafer with 96µm spatial resolution with a data acquisition time of 5 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), a new wafer geometry technique, is presented, that acquires 7.65 million data points in 5 seconds on a full 300mm wafer providing lateral resolution of 96µm. The system has high repeatability with root-mean-square (RMS) standard deviation (σRMS) in the single digit nm for the global wafer geometry and in the sub ångström (Å = 10-10 m) range for the full-wafer nanotopography for both 200mm and 300mm blank silicon wafer. WFPI can collect data on the entire wafer to within a single pixel, in our case 96µm, away from the wafer edge roll off. 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 issues. We present WFPI as a new technique with high resolution and high data count acquired at very high speed.
Wave Front Phase Imaging (WFPI) is used to measure the stria on an artificial, transparent plate made of Schott N-BK7® glass material by accurately measuring the Optical Path Difference (OPD) map. WFPI is a new technique capable of reconstructing an accurate high resolution wave front phase map by capturing two intensity images at different propagation distances. An incoherent light source generated by a light emitting diode (LED) is collimated and transmitted through the sample. The resultant light beam carries the wave front information regarding the refraction index changes inside the sample1. Using this information, WFPI solves the Transport Intensity Equation (TIE) to obtain the wave front phase map. Topography of reflective surfaces can also be studied with a different arrangement where the collimated light beam is reflected and carrying the wave front phase, which again is proportional to the surface topography. Three Schott N-BK7® glass block samples were measured, each marked in which location the wave front phase measurement will be performed2. Although WFPI output is an OPD map, knowing the value of refractive index of the material at the wavelength used in the measurements will lead to also knowing the thickness variations of the plate.
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 issues. A large variety of new materials are being introduced in Back-End of Lines (BEOL) to ensure innovative architecture for new applications. The standard in-line control plan for the BEOL layer deposition steps is based on film thickness and global stress measurements which can be performed on blanket wafers to check the process equipment performance. However, the challenge remains to ensure high performance metrology control for process equipment during high volume manufacturing. With the product tolerance getting tighter and tighter and architecture more and more complex, there is an increasing demand for knowledge of the wafer shape. In this paper we present Wave Front Phase Imaging (WFPI), a new wafer geometry technique, where 7.65 million data points were acquired in 5 seconds on a full 300mm wafer enabling a lateral resolution of 96μm.
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