Silane remains unpredictable suppliers adapt

11/01/1997

Silane remains unpredictable; suppliers adapt

The Silane Conference, held in conjunction with ASMC in Cambridge, MA, and cosponsored by the Semiconductor Safety Association (SSA), SEMATECH, SEMI, and the SIA, included discussions about the reactivity of silane, from both a historical and recent perspective, as well as discussions about wet bench fire safety. Approximately 50 attendees participated. An often-discussed topic at SSA meetings - the sometimes unpredictable tendency of silane to burn or explode - occupied the majority of the talks. While the data to date do not give a clear picture of why silane ignites in some cases and not others, some controversy centered on whether or not air turbulence causes silane to auto-ignite.

The Compressed Gas Association (CGA) has been experimenting with bulk silane containers to understand the possible results of a catastrophic failure. Their preliminary report includes video footage of releases from a 200-kg cylinder. The 70-ft-long plume from some of these releases has caused at least one bulk supplier, Praxair, to recommend bulk storage tanks be located at least 45 ft from site roads, instead of the 20 ft required by the Uniform Fire Code.

Factory Mutual`s Roger Benson offered details on the cost of a wet bench fire, and suggested concrete ways to reduce the potential for fires in the future. Factory Mutual researchers developed three indices to determine the acceptability of wet bench plastics in terms of the tendency to propagate fire, potential for smoke damage, and release of corrosive byproducts.

In terms of fire propagation, a plastic is termed "acceptable" if it does not propagate the fire beyond the ignition area. Early experimentation showed unacceptable indices for all common wet bench plastics. The plastics manufacturers, however, took this information back to their laboratories and have developed new formulations of plastics. Very recent results from these new plastics show huge promise for the future, offering a range of properties, such as machinability, transparency, etc., and more acceptable fire characteristics. Because many of these plastics are variations on the older types, it is expected that the cost, while initially high, will come down over time, offering users a cost-effective way to improve the fire prevention characteristics of their fab.

- Lise Laurin, Clear Tech