the back pressure of 0 040 inch funnel design and yet the cleaning rate of the quad aperture design is higher than 0 040 inch funnel design this shows that recombination due to pressure difference alone does not explain the cleaning rate result the recombination in the diffuser also plays an important role table 4 compares the narrowest diameters lengths and volumes of the diffuser passages of quad aperture and 0 040 inch funnel designs the 0 040 inch funnel design has a larger passage volume compared to the quad aperture design the larger passage volume could allow additional fluorine radical recombination than in the narrow diffuser passage and affect the clean rate result quad aperture 0 040 in funnel narrowest diameter in 0 016 0 040 the diffuser passage in length of narrowest 0 046 0 565 diffuser passage in volume of narrowest 0 00001 0 00071 diffuser passage in 3 table 4 compares the diameter the length and the volume of the narrowest section in the diffuser for the quad aperture and 0 040 inch funnel designs clean rate is also dependent upon cleaning gas such as nf 3 dissociation efficiency table 5 shows the chamber pressure in the process volume 212 data of the three designs under rps cleaning process the chamber pressure for all three diffuser designs are all in a similar range flow pc mtorr pc mtorr pc mtorr slm quad aperture 0 055 inch funnel 0 040 inch funnel nf 3 pc plasma off pc plasma on pc plasma off pc plasma on pc plasma off pc plasma on 0 345 345 330 330 323 323 1 391 460 374 451 365 430 2 438 584 420 567 409 536 3 483 692 464 676 452 635 4 528.