Design and performance of a new type of Knudsen cell for chemical beam epitaxy using metal-organic precursors

A chemical beam epitaxy system (CBE) with a new type of Knudsen cell was constructed to deposit LiTaO3 films by the thermal decomposition of a double metal alkoxide precursor. The Knudsen cell facilitates molecular flow of the precursor to the substrate surface. It permits the use of metal-organic precursors of low volatility, and isolates the precursor from atmospheric moisture. The Knudsen cell is demonstrated to serve as a molecular flux source at controllable rates. The spatial distribution of the flux was measured and compared with Clausing's far field model and Monte Carlo simulations. Good agreement is seen between the measured intensity of the spatial flux distribution and the Monte Carlo simulation; however, the FWHM of the spatial distribution is much greater than that predicted by the far field model. The wider distribution and its Gaussian, rather than Cauchy, shape indicate that the Knudsen cell acts as an extended rather than a point source. This new Knudsen cell should be useful in the CVD growth of ferroelectric and superconductor thin films from low volatility, moisture sensitive precursors. (C) 1997 Elsevier Science Ltd.