Investigation of the BN films prepared by low pressure chemical vapor deposition

A thermodynamic analysis of boron nitride (BN) films grown by the low press ure chemical vapor deposition (CVD) process using a boron trichloride (BCl3 )-ammonia (NH,) reaction system with or without a carrier gas (H-2 or N-2) has been undertaken. The dependence of the products and their thermodynamic yields on the reaction parameters were also predicted. The results indicat ed that the major species of the products at equilibrium included solid pha se EN and gaseous phase HCl in the BCl3-NH3 system with or without N-2. The processing parameters for depositing BN on a graphite substrate using l ow pressure BCl3NH3-N-2 CVD, an optimized system, were investigated. Amorph ous BN films, with some microcrystallinity, were successfully deposited ont o graphite plates by low pressure CVD at 1100 K. As the input gas ratio of NH3/BCl3 increased,the mole fractions of boron and nitrogen increased and t ended to approach stoichiometric composition;whereas that of chlorine decre ased. After heat treatment at 2023 to 2123 K for 1.5 h, amorphous BN transf ormed into, hexagonal BN. The extent of the phase transformation of BN film s depends on the temperature and duration of heat treatment. (C) 1999 Elsev ier Science S.A. All rights reserved.