AN XPS AND THERMOGRAVIMETRIC STUDY OF OXIDIZED ALN AND ALN-SI3N2 LAYERS DEPOSITED BY LIQUID-PHASE CHEMICAL-VAPOR-DEPOSITION

The results of a comparative study of the resistance to oxidation of A IN and a codeposit of AlN-Si3N4 a re presented. The oxidation of both types of layer was performed at 1200 degrees C in an oxygen gas flow ( p(O2) similar to 1 atm). A thermogravimetric analysis was made, record ing the weight gain throughout the oxidation process, and revealed a d ramatic improvement in the resistance to oxidation of the codeposit la yer when com pared with the aluminium nitride layer. An X-ray photoele ctron spectroscopy depth-profile analysis was made by performing a ser ies of successive abrasive polishes on the oxidized layers. After each abrasive polish the sample surface was cleaned by ionic bombardment u nder ultrahigh vacuum and the photoemission spectra recorded. This pro cess of polishing, etching and analysis was continued until the oxygen content decreased to a level comparable with that observed in the lay ers before oxidation. The changes in chemical bonding throughout the v arious depth profiles were examined by deconvolution of the Al 2p and Si 2p photoelectron peaks and by analysis of the Auger KLL lines. It w as concluded that the slower rate of oxidation of the codeposit could be attributed to either the formation of silica or a mixed oxide phase of the mullite type (3 Al2O3-2 SiO2).