Plasma etching safety

Plasma etching, of silicon, 22 492 Plasma FPDs, 22 259 Plasma fractionation, 12 128-159 economic aspects of, 12 147-150 health, safety, and environmental factors related to, 12 153... 

As in any process that uses cheniicals and electronic and mechanical equipment, a concerted safety effort is required in plasma etching. Proper shielding of reactors and power supplies to minimize operator exposure to rf radiation is imperative. An exposure level below 1 mW/cm has been suggested as a safe operating point (150). 

As with many new processes, the goal of plasma etching was to find a more cost effective, environmentally sound, safer alternative to a chemically intensive procedure, in this case wet resist stripping. However, as with many new processes, new or subtle hazards may be introduced. Plasma-assisted etching was welcomed by the safety community since early plasma systems used nonhazardous gases such as oxygen and freons to perform operations that were traditionally performed in open tanks of corrosives and solvents. 

The immediate concern about the presence of phosphine in doped oxide films was safety in handling these materials. The permissible exposure limit (PEL) set by OSHA is 0.3 ppm, and the concentration immediately dangerous to life and health (IDLH) is 200 ppm. All precautions must be taken when etching plasma PSG of BPSG wafers. A basket of twenty 3 inch wafers, 5000 angstroms thick, containing 5 wt. % phosphorus could release as much as 2500 ppm of phosphine or 12.5 times the IDLH. 

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