High Depth of Field MEMS Inspection

"A primary limitation in the implementation of new MEMs devices is the inability to inspect the 3-dimensional structures. Unlike semiconductor circuits, MEMS may contain structures with features extending tens of microns above the wafer's surface.Moreover, these features move, tilt, vibrate or rotate. Because the features in MEMS devices extend significantly along the z-axis, optical microscopes used in conventional semiconductor inspection are of limited use. The narrow field depth of an opticalmicroscope makes it impossible to have the entire MEMS design in focus all at one time. Historically, designers have addressed this issue by using scanning electron microscopes (SEMS). While the SEM is capable of providing a very large depth of field,they are expensive, stimulus must be brought in via cumbersome, hermetically sealed electrical headers and the electron beam used in SEM perturbs conductive elements in MEMS designs.Summit proposes a solution which allows the use of conventional microscopy to examine MEMS structures. Unlike conventional microscopes where the depth of field may be 1 micron or less, the technique proposed offers focal depths as high as hundreds ofmicrons. Moreover, since no vacuum chamber is involved, sophisticated electrical stimulus may be provided with relative ease. The ability to provide high depth of field microscopic analysis has direct application in MEMs manufacturing/inspection, medicalmicroscopy a