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Compressive biaxial stress fields in thin film boron nitride are shown to provide a means of accessing the region of the phase diagram in which cubic BN (c-BN) is the stable phase. This process differs from high pressure, high temperature synthesis in that c-BN is synthesised from an incoming flux of ions or atoms rather than converted from the hexagonal phase. Experimental evidence is presented that the compressive stress mechanism for c-BN formation is operating during the reactive ion plating deposition process. A well defined threshold stress value is found for the production of c-BN under a wide range of preparation conditions. The microstructure of the films as studied by electron optical methods and the behaviour of the infrared absorption spectrum after stress relief provides further confirmation of the compressive stress mechanism.