This article describes fundamental studies on oxide thin film growth at low substrate temperatures (T_s) by ion beam sputtering (IBS) technique, and roles of excited oxygen. It consists of four parts; (1) growth of Bi₂(Sr,Ca)₂CuO_x (Ca-doped Bi2201) and effects of oxygen molecular and plasma supplies, (2) effects of plasma cleaning of substrate surface, (3) growth of Bi₂Sr₂CuO_x (nondoped Bi2201) and the effects of molecular and plasma supplies, and (4) effects of oxygen-ion assist on the growth of Ca-doped Bi2201.

The excellent crystalline Ca-doped Bi2201 can be grown at T_s>550°C both for the molecular and plasma supplies, then the growth is dominated by thermal energy in this higher temperature region. The plasma has prominent effects of enhancement and improvement on the crystal growth in the low temperature region of T_s<550°C. The considerably fine Ca-doped Bi2201 can be grown at ultralow T_s as 450°C by the plasma. The growth of Ca-doped Bi2201 is remarkably enhanced and improved by the plasma cleaning in the higher T_s region. On the other hand, the growth of nondoped Bi2201 is enhanced by the molecules instead of the plasma in the low T_s region unexpectedly. It can be grown at 400°C by the molecules. The oxygen-ion assist has great effects such as compositional transfer adjustment and surface smoothening.  From these results, origins for the low temperature growth and plasma effects are discussed.

Five factors are proposed for the successful low temperature growth; (1) moderate thermal energy, (2) ultralow growth rate, (3) collision-induced moderate kinetic energy of sputtered particles, (4) collision-induced excited energy of the oxygen molecules, and (5) the plasma energy or assist ion energy. It is strongly proposed that total energy and energy balance are critically important for the low temperature growth.  Unique mechanisms for the plasma effects are suggested.  The Sr and Ca atom arrangement can be ordered by the plasma energy, leading to reduction of surface energy. This results in the enhancement and improvement of the crystal growth.