Phase intergrowth among some kinds of the Bi2Sr2Can-1CunOy phases is observed in the thin film fabrication at ultralow co-deposition with multitargets by means of ion beam sputtering. The molar fraction of the Bi2212 phase in the mixed crystal of the grown films is investigated as a function of the applied ozone pressure and the substrate temperature. The activation energy for the phase transformation from the Bi2201 to the Bi2212 is estimated in terms of the Avrami equation. This study reveals that the formation of a liquid phase contributes significantly to the construction of the Bi2212 phase in the thin films, differing from the bulk synthesis. © 1997 American Institute of Physics.