Thermal reaction of polycrystalline AlN with XeF2

Abstract

Detailed studies on the thermal reaction behavior of polycrystalline aluminum nitride (AlN) with effusive xenon difluoride (XeF2) have been carried out over the sample temperature (Ts) range from 300to920K using molecular beam mass spectrometry combined with a time-of-flight technique and ex situ surface analyses, i.e., X-ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning electron microscopy (SEM). The species desorbed from the AlN∕XeF2 system were monitored using molecular beam mass spectrometry, as a function of sample temperature. Above Ts=800K, the desorbed reaction products were identified as N2 and AlF3, and their flux intensities increase monotonically as the sample temperature is increased. The flux intensity of XeF2 desorbed after physisorption to the AlN surface is found to decrease as Ts is raised above Ts=800K, and approximately one half of the incoming XeF2 is consumed by the thermal reaction at 920K. The results of surface analyses show that the thermal reaction of AlN with XeF2 starts at approximately Ts=700K, forming a reaction layer composed of AlF3. The AlF3 layer becomes thick as Ts is increased from Ts=700–800K. Above Ts=800K, however, as a result of fast desorption of AlF3 and F atoms from the AlF3 layer, only partially fluorinated AlFx (x=1 and/or 2) layers are formed and the bulk AlN is revealed again. The SEM photographs indicate that the surfaces exposed above Ts=850K are strongly etched but a slight change is observed at Ts⩽800K. On the basis of these results, three reaction stages are proposed for the AlN∕XeF2 reaction depending on the sample temperature range: Stage 1 (300⩽Ts<700K); no reaction, stage 2 (700⩽Ts<800K); surface fluorination, and stage 3 (800⩽Ts); etching. At stage 3, AlF3 formed on the surface starts to evaporate and fast etching proceeds, since the vapor pressure of AlF3 is high enough in this temperature range.