In situ analysis of thin film deposition process using time of flight (TOF) ion beam analysis methods

Abstract

The use of non-destructive, in situ methods for the characterization of thin film growth phenomena is the key both to obtaining a better understanding of thin film growth processes and to the development of more reliable deposition procedures, especially for complex layered structures involving multi-phase materials. However, surface characterization methods that utilize either electrons (e.g. AES or XPS) or low energy ions (SIMS) for the signal require an ultra-high vacuum (UHV) environment and utilize instrumentation which obstructs line of sight access to the substrate. These methods are therefore incompatible with line of sight deposition methods and thin film deposition processes which introduce gas, either as an intrinsic part of the deposition procedure or in order to produce the desired composition. We have developed a means of differentially pumping both the ion beam source and detectors of a TOF ion beam surface analysis spectrometer that does not interfere with the deposition process and permits compositional and structural analysis of the growing film in the present system, at pressures up to several mTorr. Higher pressures are feasible with modified source-detector geometry. In order to quantify the sensitivity of Ion Scattering Spectroscopy (ISS) and Direct Recoil Spectroscopy (DRS), we have measured the signal intensity for stabilized clean metals in a variety of gas environments as a function of the ambient gas species and pressure, and ion beam species and kinetic energy. The results are interpreted in terms of collision cross sections which are compared with known gas phase scattering data and provide an apriori basis for the evaluation of time-of-flight ion scattering and recoil spectroscopies (ToF-ISARS) for various industrial processing environments which involve both inert and reactive gases. The cross section data for primary ion-gas molecule and recoiled atom-gas molecule interactions are also provided, from which the maximum operating pressure in any experimental configuration can be obtained.