Ion beam deposition and surface characterization of thin multi-component oxide films during growth1

Ion beam deposition of either elemental targets in a chemically active gas such as oxygen or nitrogen, or of the appropriate oxide or nitride target, usually with an additional amount of ambient oxygen or nitrogen present, is an effective means of depositing high quality oxide and nitride films. However, there are a number of phenomena that can occur, especially during the production of multicomponent films such as the ferroelectric perovskites or high temperature superconducting oxides, which make it desirable to monitor the composition and structure of the growing film in situ. These phenomena include thermodynamic (Gibbsian), and oxidation or nitridation-driven segregation, enhanced oxidation or nitridation through production of a highly reactive gas phase species such as atomic oxygen or ozone via interaction of the ion beam with the target, and changes in the film composition due to preferential sputtering of the substrate via primary ion backscattering and secondary sputtering of the film. Ion beam deposition provides a relatively low background pressure of the sputtering gas, but the ambient oxygen or nitrogen required to produce the desired phase, along with the gas burden produced by the ion source, result in a background pressure which is too high by several orders of magnitude to perform in situ surface analysis by conventional means. Similarly, diamond is normally grown in the presence of a hydrogen atmosphere to inhibit the formation of the graphitic phase. A surface analysis system incorporating pulsed beam ion scattering spectroscopy, direct recoil spectroscopy, and mass spectroscopy of recoiled ions (MSRI) with differentially pumped ion beam and detector lines has been integrated with a multi-target ion beam deposition system, permitting the characterization of the surface composition and structure of a thin film surface during growth at ambient pressures in the range of 10−8 bar . A number of phenomena are observed which are not amenable to study in systems which require cessation of film deposition in order to study surface properties. In addition, it has been found that the positive-to-negative ion ratio of the MSRI signal provides a unique ‘phase fingerprint’ which in a number of cases permits ready identification of the chemical phase of the growing film. Data will be presented showing representative applications in the area or multicomponent oxide film growth for which the in situ ion beam characterization methods described here provide a unique means for understanding thin film growth phenomena.