Factors influencing the purity of electronic grade phosphine delivered to MOCVD tools

Increasing mobility of InP films with usage time of one PH3 cylinder prompted an investigation into factors influencing the purity of delivered PH3. The presence of hygroscopic HxPOy residues in a delivery system greatly increases the dry-down time compared to that of a clean system. Static delivery system tests show increasing H2O concentration with time and twice the increase in PH3 versus N2 over 48 h indicating reaction of metal oxides in components with PH3 to generate H2O. Gas purity may also vary during cylinder usage. Depletion of a high-purity PH3 cylinder shows consistently low gas phase H2O levels before phase-break but increasing levels after phase-break, as the cylinder depressurizes. The results highlight the importance of using pure PH3, employing rigorous cycle-purging procedures to prevent HxPOy contamination, switching out cylinders in good time and using purification technology to control H2O.