Overhang test structure deposition profiles of pulsed plasma fluorocarbon films from hexafluoropropylene oxide, 1,1,2,2-tetrafluoroethane, and difluoromethane

Films from pulsed plasmas of hexafluoropropylene oxide (HFPO), 1,1,2,2-tetr afluoroethane (C2H2F4), and difluoromethane (CH2F2) were deposited onto ove rhang test structures to investigate the different film formation mechanism s. Four growth mechanisms were considered: direct or ion-induced deposition , low-pressure CVD (LPCVD) from neutral species. redeposition, and sputteri ng. All of the films investigated were: dominated by direct or ion-induced deposition but the role of the other mechanisms varied with both pulse cond itions and precursor choice. Growth from continuous plasma enhanced CVD (PE CVD) from HFPO showed significant sputtering but little LPCVD or redepositi on. The opposite behavior resulted from pulsed HFPO plasma films, which sho wed considerable contributions from LPCVD and redeposition growth, but no o bvious sputtering. As with the pulsed HFPO films, 10/100 pulsed plasma film s from C2H7F4 and CH2F2 also exhibit LPCVD and redeposition growth, but lit tle sputtering. However, redeposition was found to play a smaller role in t he HFPO system than that of the other two precursors. The similarity of the C2H2F4 and CH2F2 film profiles can be attributed to their similar pulsed p lasma chemistries, whereas the non-hydrofluorocarbon HFPO has a significant ly different pulsed plasma chemistry, and therefore a different profile. In all cases, systematic trends in the film growth profiles were observed wit h the dimension of the opening separating the two cantilevers of the test s tructure. Tensile stress on the order of 3.3 GPa was observed for the conti nuous HFPO film, whereas compressive stresses of -1.2 and -3.8 GPa were see n in the C2H2F4 and CH2F2 films, respectively.