Etch microloading creates damaging
07/01/1997
Etch microloading creates damaging "latent antenna effect"
The "latent antenna" effect, a very interesting cause of plasma-charging gate-oxide damage, was presented by Kobe Steel, Texas Instruments, and Stanford University at the recent Plasma Process-Induced Damage Symposium in Monterey, CA. In a 0.8-?m/min metal etch process, microloading effects reduce the etch rate inside dense structures by 5%. Until the field metal clears, there is no charging (Fig. 1a). After all the metal, including in the bottom of dense structure, clears, there are slight (perhaps 10:1 antenna:gate ratios) antennas (Fig. 1c). However, for approximately 3 sec, a latent antenna exists connecting the bottoms of the dense areas (Fig. 1b). The vast majority of damage occurs during these few seconds, since this is when most of the injected charge develops.
Increased microloading increases the problem. A 10% etch rate reduction inside dense structures will leave the latent antenna in place long enough to nearly guarantee catastrophic breakdown by the end of the etch process. - E.K.
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The latent antenna charging effect. At the beginning of the etch a), the continuous metal field has no antenna effect. When the metal outside the dense structures clears b), metal still remains inside the structures, creating a "latent antenna." Once the field metal is completely cleared c), the antenna effect is negligible.