[en] Specimens of silicon and silicon with a thermally grown Si₃N₄ layer were implanted at room temperature with 40 keV He ions at a dose of 5x10¹⁶ions/cm². Transmission electron microscopy (TEM) and thermal desorption spectroscopy (THDS) have been used to investigate the effects of the Si₃N₄ layer on cavity growth and thermal release of He atoms. TEM results show that the presence of the top Si₃N₄ layer can suppress the growth of cavities after subsequent annealing at 800 deg. C for 1 h. The thermal desorption results reveal that the top Si₃N₄ layer can act as an effective barrier to the permeation of He from bubbles to the surface, which gives rise to disappearance of the weak release peak at the low temperature region and occurrence of a new release peak at the intermediate temperature region. The results are qualitatively discussed