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Nearly every semiconductor fab has now, or has had in the recent past, production tools which exhibit process interruptions due to unknown causes. Often, the search for the causes of these problems is a time-consuming process of investigation by fab engineers and technicians in conjunction with the tool providers own technical staff. Depending upon the severity of the problem, the final cost of meetings, software and hardware revisions, and the loss of product or yield reduction, this can be very expensive – and still not solve the problem.
Modern semiconductor production equipment manufacturers have made great strides in hardening tools against electromagnetic interference (EMI) at the same time as they have met compliance standards for emissions. After all, the production environment is a crowded environment with many different processes and tools in close proximity. With processors reaching everhigher clock speeds and the number of secondary processors in tools climbing as machine intelligence is distributed throughout the tools, the opportunity for interruptions due to interference has also become greater.
Broadband Interference Issues
The most common radiated interference, both pulse-field and continuous wave (CW), usually falls within the low kilohertz (kHz) to 3 Gigahertz (GHz) range. This encompasses an enormous region of communication, processor and general equipment operating frequencies.
In addition, ESD (electrostatic discharge) events put out multi-frequency broadband energy across this region in the form of fast rise-time pulse fields, often of surprising amplitudes (e.g., 50 V/m = 6.6 W/m2). This type of event, caused by an electrostatic discharge (ESD) in close proximity to production tools, can cause energy coupling to improperly grounded tool surfaces or can enter interior tool spaces through vents, ports or other unprotected openings. When it does so, it can interrupt tool operation through direct coupling to unshielded data or analog signal lines, or interrupt processors based upon the wide-band frequency component present in many ESD events. This type of scenario can be caused by nothing more complicated than an operator bumping an ungrounded cart into a tool or other nearby object. Even doors into critical areas have been known to create large ESD/EMI events.
Tools that are not designed to safely conduct this radiated interference to ground risk lockup, data corruption or mysterious soft errors which so annoy operators. Identifying what is actually causing the interference can be difficult or impossible, depending upon the method employed.
Equipment and Technique
The good news is that this interference region can be readily diagnosed using specialized antennas, probes, scopes (oscilloscopes and spectrum analyzers) and techniques. The equipment needs to be very mobile, of small footprint, and capable of performing broadband sweeps both inside and outside of confined tool spaces without disrupting the surrounding production process. Often a combination of radiated antenna and probe can be used in tandem to capture both the radiated source and the conductive path that noise takes through...
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