E-Beam System Provides Volume Production Capability

Alexander E. Braun, Associate Editor -- Semiconductor International, 8/1/1999

The coming of copper and increasingly challenging high-aspect ratio structures is making defect detection extremely difficult. While E-beam technology would appear to be the best way to detect problems in this type of structure, typically it has been too slow for use in a production environment.

KLA-Tencor (San Jose, Calif.) has introduced what it describes as the first in-line scanning E-beam inspection system for l 0.18 µm aluminum device shrinks and copper devices, and it expects it to meet this need. The eS20 is designed for use in volume production and is touted to be -- depending on the application -- up to 75 times faster than any other tool currently available. Although suitable for other applications, the system achieves its greatest speed in voltage contrast applications, where a very high signal-to-noise ratio exists. Its high spatial resolution also has proven effective in detecting physical defects such as copper flakes at high speeds.

Copper is of special interest in this case because it poses defect detection challenges that are difficult or impossible to address any other way. With the coming of copper, defect mechanisms are migrating from surface -related defects, as is the case with aluminum technology, to subsurface defects affecting the seed and barrier layers, such as delamination and voids. Other concerns lie with the types of particles or defects that reside in trenches or via holes after etch, such as residues or particles.

The system's voltage contrast capability enables it to detect electrical failures like voids, and its high DOF locates defects and residues within the trenches before further processing. When viewed under a SEM, copper flakes show high contrast, and the system's capabilities enable it to detect extremely small copper flakes (l 0.10 µm) -- a matter of concern to manufacturers, since residual copper can damage devices.

The system's primary application is expected to be post-CMP and post-etch monitoring, as the system is not limited by resolution, color, grain or pattern noise. A 200/300 mm bridge tool, the eS20 is singular in its capability to perform die-to-die comparison needed for logic device inspection. It should be of considerable utility to manufacturers developing, ramping and maintaining yields for sub-0.18 µm design-rule copper processes.   

	The eS20 will detect electrical failures, such as voids. Figures 1 and 2 show hidden voids in the tungsten plug fill. Figures 3 and 4 show hidden copper voids in the damascene process. (Source: KLA-Tencor)