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The Role of E-Beam Inspection in a Production Environment by Jeff Hamilton, Senior Product Marketing Manager
The process and yield challenges that face today’s device manufacturers are increasing dramatically. The combination of new materials such as copper, low-k and DUV resists, new processes such as dual damascene, and rapidly shrinking design rules necessitate solutions that detect and identify all defect mechanisms. With manufacturers moving from traditional alu minum processing to dual damascene, defect mechanisms will switch from surface-related defects to defects within metal fills and high aspect ratio structures. In addition, design rule shrinks below 0.18 µm will require the detection of defects down to below 50 percent of the minimum design rule. Further, the accelerated development cycles of today plus the requirements for high yields at process transfer and higher yield ramps significantly compound the challenge. The nature of defects is changing as customers develop processes with design rules less than 0.18 µm. As a result, new materials and fabrication techniques are being introduced at an unprecedented rate. Defects associated with high aspect ratio lithography and etch, as well as high aspect ratio fills will predominate in these new processing schemes (such as copper dual damascene). With each progression in device generation, the increased aspect ratios of damascene structures and the variety of new materials place a larger burden on etch and fill processes. Specific detection needs include:
conventional optical inspections. Defects such as voids within metals (copper, tungsten, aluminum), residues at the bottom of contact/via holes and poor silicide formation cause electrical signatures that can be easily detected with this method. 3. High depth of focus imaging: A high depth of focus is needed that allows for the detection of physical defects (residues, particles, etc) within vias and trenches that cause failures and/or reliability issues. Electron-beam inspection effectively addresses these needs. In order to reliably detect all yield limiting defects, customers must now develop strategies that utilize both optical and e-beam inspection solutions.
1. High resolution imaging: Sensitivities below 100 nm are needed that can detect very small residues and stringers at the bottom of high aspect ratio structures (vias and trenches), as well as very small surface defects. 2. Voltage contrast imaging: Due to the nature of “hidden” defects, voltage contrast imaging offers a quick method to identify these defect types. The interaction between electrons and specific defect mechanisms enable this imaging capability to detect the “hidden” defects that cause electrical yield failures and/or reliability issues. Detection of these defects within the process is critical since these defects are undetectable through 6
Autumn 1999
Yield Management Solutions
F i g u re 1. “Hig h aspect ratio” a nd “hig h resol ution, hig h depth of f ield ” via/trench i nspecti on technolo gy is re q u i r ed (i.e., e-beam) to identify defects in the ppb level in today ’s new fabr ication pro c e s s e s .