Overhang Test Structure Deposition Profiles of Pulsed Plasma Fluorocarbon Films from Hexafluoropropylene Oxide, 1,1,2,2-Tetrafluorethane, and Difluoromethane

Abstract

Films from pulsed plasmas of hexafluoropropylene oxide (HFPO), 1,1,2,2-tetrafluoroethane (C2H2F4), and difluoromethane (CH2F2) were deposited onto overhang test structures to investigate the different film formation mechanisms. Four growth mechanisms were considered: direct or ion-induced deposition, low-pressure CVD (LPCVD) from neutral species, redeposition, and sputtering. All of the films investigated were dominated by direct or ion-induced deposition, but the role of the other mechanisms varied with both pulse conditions and precursor choice. Growth from continuous plasma enhanced CVD (PECVD) from HFPO showed significant sputtering but little LPCVD or redeposition. The opposite behavior resulted from pulsed HFPO plasma films, which showed considerable contributions from LPCVD and redeposition growth, but no obvious sputtering. As with the pulsed HFPO films, 10/100 pulsed plasma films from C2H2F4 and CH2F2 also exhibit LPCVD and redeposition growth, but little sputtering. However, redeposition was found to play a smaller role in the 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 plasma chemistries, whereas the non-hydrofluorocarbon HFPO has a significantly different pulsed plasma chemistry, and therefore a different profile. In all cases, systematic trends in the film growth profiles were observed with the dimension of the opening separating the two cantilevers of the test structure. Tensile stress on the order of 1.3 GPa was observed for the continuous HFPO film, whereas compressive stresses of –1.2 and –1.8 GPa were seen in the C2H2F4 and CH2F2 films, respectively.