We have studied experimentally the propagation of the surface phonon modes in CaF₂/Si(110) heterostructures with h=0, 10 and 200 nm thickness by Brillouin light scattering spectroscopy. The angular azimuthal behaviour or the Rayleigh mode was found to be close to that of the material of the substrate in the case with h=10 nm, and to that of the layer in the case with h=200 nm. In an h=200 nm heterostructure for the azimuthal directions close to (110) it was concluded that the behaviour of the first localized mode is described well by the proper pseudo-surface mode of CaF₂ of the (110) plane, whereas higher-mode (i.e. second, third) velocity values were found to be close to that of the material of the substrate. Experimental and calculated velocity values match each other rather well.