Environmental, Safety and Health Benefits of Using Sub-Atmospheric Hydride Sources for MOCVD
Raynor *’, Mark; Hess ‘, Don; Olander ², Karl
(‘Matheson Tri-Gas, Inc. 1861 Lefthand Circle, Longmont, CO ; ²ATMI, Inc., MLS Division, 7 Commerce Drive, Danbury, CT)
There are a number of concerns in using high-pressure (HP) sources of arsine and phosphine for MOCVD processes. Because HP hydride sources are both highly toxic and flammable, and are supplied as compressed liquids in cylinders at 205 psig for arsine and 607 psig for phosphine (at 20°C), they pose significant safety hazards, especially during cylinder transportation, storage and change-out. Sub-atmospheric delivery systems developed for use in MOCVD overcome many of these problems. Sub-atmospheric pressure gas (SAGE) sources consist of DOT approved cylinder packages that contain a high purity adsorbent medium that has been activated under special conditions. Hydride gases are adsorbed onto the medium to a pressure of 650 torr at room temperature. The high surface area of the adsorbent allows the storage of large amounts of highly toxic arsine or phosphine at sub-atmospheric pressure. In use, the adsorbed hydride gas is pulled from the SAGE source using a specially designed bellows-based pumping system that maintains a set outlet pressure to the tool (~600 torr) at volumetric flows up to 10 slpm. If a vacuum is not applied, gas release from the cylinder will only be diffusion-limited and amount to <100 sccm. Due to the inherent safety of the technology, sub-atmospheric pressure gas sources have been adopted as the first bulk sources of arsine and phosphine for MOCVD processes. For example, 78 lb of arsine can be delivered from a 200 L sub-atmospheric pressure cylinder, based on a final cylinder pressure of 50 torr. This paper will discuss sub-atmospheric pressure gas sources and focus on the important environmental, health and safety aspects of the technology.