Researchers from the National Institute of Standards and Technology (NIST) and KLA Corporation, a provider of inspection and measurement systems for the semiconductor and related industries, have improved the accuracy of scanning electron microscope (SEM) measurements. Used for process control applications in semiconductor manufacturing, SEMs help ensure high-yield production of functional, high-performance chips.
A SEM uses a focused electron beam to image features as small as one nanometer, making it an important instrument for characterizing semiconductor device structures. During chip manufacturing, high-resolution SEMs are used for many inspection and metrology applications, including detection of very small defects, identification and classification of defects found by optical inspectors, critical dimension measurements of pattern features, overlay measurements, and more. This information helps chip engineers characterize and fine tune their manufacturing processes.
As the electron beam travels through a SEM, it is carefully controlled. A slight deviation of the electron beam from the ideal path or a tiny misalignment of the angle at which the beam strikes the surface of the chip can distort the resulting SEM image and misrepresent the structure of the device. NIST and KLA improved the accuracy of SEMs by accounting for these angular misalignments of the electron beam. The joint research project measures beam tilt with an accuracy of less than one milliradian, or five hundredths of a degree, which required advances in angular resolution and measurement validation.
To measure the beam tilt, NIST and KLA created a prototype standard for electron microscopy and analyzed the resulting electron micrographs in a new way. The prototype standard consists of an array of tapering pillars of silicon, known as conical frusta, which form images that are highly sensitive to beam tilt. The tilt shows up as a shift between the centers of images of ..
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