Aluminum plasma etching process using vacuum systems without cold traps

A suitable vacuum pump system used in plasma or RIE‐mode dry etching of Al and Al alloys with CCl₄/Cl₂ enables to operate without LN₂ cold traps. A Roots pump plus rotary vane pump combination, both using inert fluid lubricant, pumps and exhausts all occurring volatile products. Condensing solid AlCl₃ is quantitatively removed from the backing pump sealing fluid by means of a high speed, main stream oil purification system via an Al₂O₃ deep bed filter. Maintenance of the pump system is limited to just changing the Al₂O₃ filter elements, each time after etching of 4000 4 in. wafers. No decomposition of the sealing fluid could be observed. Any fluid remaining when exchanging the filter elements can practically be recovered by centrifuging.