Abstract: A method for in-line monitoring of via/contact etching process based on a test structure is described. The test structure is comprised of via/contact holes of different sizes and densities in a layout such that, for a certain process, the microloading or RIE lag induced non-uniform etch rate produce under-etch in some regions and over-etch in others. A scanning electron microscope is used to distinguish these etching differences in voltage contrast images. Image processing and simple calibration convert these voltage contrast images into a “fingerprint” image characterizing the etching process in terms of thickness over-etched or under-etched. Tolerance of shifting or deformation of this image can be set for validating the process uniformity. This image can also be used as a measure to monitor long-term process parameter shifting, as well as wafer-to-wafer or lot-to-lot variations.

Abstract: A method for in-line monitoring of via/contact etching process based on a test structure is described. The test structure is comprised of via/contact holes of different sizes and densities in a layout such that, for a certain process, the microloading or RIE lag induced non-uniform etch rate produce under-etch in some regions and over-etch in others. A scanning electron microscope is used to distinguish these etching differences in voltage contrast images. Image processing and simple calibration convert these voltage contrast images into a “fingerprint” image characterizing the etching process in terms of thickness over-etched or under-etched. Tolerance of shifting or deformation of this image can be set for validating the process uniformity. This image can also be used as a measure to monitor long-term process parameter shifting, as well as wafer-to-wafer or lot-to-lot variations.

Abstract: A method for inspecting a semiconductor wafer using an SEM having a nominal focal plane and operable for guiding a beam. The SEM having a stage movable in each of an X-, Y-, and Z-direction, including moving the SEM stage in the XY-direction to a first location for inspection, optically sensing the location of the top surface of an area in relation to the focal plane of the stage, adjusting the position of the stage in the Z-direction so that the top surface of the area is substantially at the focal plane, inspecting the areas, and moving the stage in the XY-direction to the next location such that the next area is under the SEM beam for inspection. The Z-stage using a non-contact optical sensor to provide feedback to drive a plurality of piezoelectric actuator to move the wafer to the focal plane.