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EETE NOV 2013

ANALOG design insertion is not feasible in regions with very high placement utilization. During the IC manufacturing process, the metal layer is exposed to conditions that lead to the build-up of an electrostatic charge. The amount of charge that builds up depends on a number of factors; the most important from an antenna standpoint is how much metal is exposed. As more metal is exposed, the maximum charge that accumulates on the net that the metal is part of also increases. The substrate remains at ground since it is connected to the fabrication device. As a result a voltage gradient develops across the gate oxide. When this gradient becomes large enough, it is relieved via an explosive discharge (i.e. “lightning”). The problem is more significant at smaller technologies because the damage resulting from the discharge is more likely to extend across the entire length of the gate. Antenna rule checking is different for every process technology Figure 5 because the method for expressing antenna ratio is not standardized. Antenna repair is accomplished by inserting a reverse-bias diode on the violating net as close to the gates being protected as practical. During normal chip operation, the reverse bias prevents electrons from flowing from the net through the diode and into the chip’s substrate. During fabrication, however, the charge on the net can build to the point where the voltage drop across the diode exceeds its break-down voltage. This voltage is greater than the normal operating voltage, but less than the voltage at which an electrostatic discharge at the gate can be expected. When this happens, the diode allows electrons to flow from the net to the substrate and thus limits how much charge can accumulate on the net. The process is non-destructive, and it’s possible that the net could discharge through the diode several times during the fabrication process. The other way to repair is to “break up” the antenna by shifting briefly to a different metal. When this metal layer is fabricated, the long piece on one side is no longer electrically connected to the gate and does not contribute to any antenna effects. When it is eventually connected through the higher-level metal “bridge,” it is no longer exposed to the charge accumulation and again does not contribute to an antenna violation – see Figure 4 figure 5. From entry level to high performance. Oscilloscopes from the T&M expert. Fast operation, easy to use, precise measurements – that’s Rohde & Schwarz oscilloscopes. R&S®RTO: high performance (Bandwidths: 600 MHz to 4 GHz) R&S®RTM: upper midrange (Bandwidths: 350 MHz and 500 MHz) HMO3000: midrange (Bandwidths: 300 MHz to 500 MHz) HMO: entry level (Bandwidths: 70 MHz to 200 MHz) All Rohde & Schwarz oscilloscopes incorporate time domain, logic, protocol and frequency analysis in a single device. Take the dive at www.scope-of-the-art.com/ad/all


EETE NOV 2013
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