Advanced, High-Sensitivity, Multi-Species, In-Situ Film Growth Monitor Utilizing Atomic Absorption Spectroscopy

Advanced thin-film multilayer x-ray optics such as multilayer Laue lenses (MLLs) are typically fabricated using physical vapor deposition (PVD) processes. Such optics play a critical role in the application of x-ray beams for research in many diverse scientific disciplines. Due to the large number of layers required, and thus the long fabrication time, the deposition rate must be precisely controlled over long time scales in order to produce high-quality films. A highly-sensitive instrument that is capable of in-situ measurements of the flux density of individual species such as silicon, aluminum, and metal-silicides is desired. All of the commercially available in-situ growth monitoring techniques has certain limitations for this application. Of these, the Atomic Absorption Spectroscopy (AAS) approach seems to offer the most advantages. In this technique, a UV light beam, matched to the absorption energy of the species of interest, passes through the flux coming from the source, and the attenuation resulting from resonant atomic absorption is measured. The attenuation is proportional to the atomic density within the illuminated volume, and therefore can be used to determine the deposition rate. By simultaneously monitoring multiple species, the film composition can be tightly controlled. However, in order to produce an instrument that meets the stringent requirements set forth for this particular application, significant development is required to overcome certain limitations of previous AAS instruments. k-Space therefore proposes to develop an advanced, multi-species, AAS-based film growth monitor that is robust and non-intrusive, with very low long-term drift, high material selectivity and sensitivity, fast response time, and wide operating pressure range capable of covering both ultra-high vacuum (UHV) and sputtering processes. k-Space will be drawing on its considerable experience in developing custom in-situ metrology solutions in order to deliver a cost-effective system that can be commercialized for other flux monitoring applications. The proposed instrument will be capable of providing highly accurate control of deposition rate during the fabrication of many thin film structures. With its high sensitivity and long-term accuracy under continuous operation, it should find immediate application in the fabrication of MLLs, as well as many other thin-film products including lasers, photovoltaics, and LEDs, to name a few. It is expected that the proposed instrument, when successfully developed, will become a standard tool for both the R&D and manufacturing of thin-film devices. Key Words: atomic absorption spectroscopy (AAS), film growth, flux monitoring, in-situ metrology, molecular beam epitaxy (MBE), multilayer Laue lens (MLL), physical vapor deposition (PVD), sputtering, thin-film, ultra-high vacuum (UHV), x-ray optics k-Space proposes to develop an advanced film growth monitor that will be capable of providing highly accurate control during the fabrication of thin-film devices for the laser, photovoltaic, and LED industries, to name a few.