FAILURE MECHANISMS OF ANODIZED ALUMINUM PARTS USED IN CHEMICAL-VAPOR-DEPOSITION CHAMBERS

Anodized aluminum parts used in chemical vapor deposition (CVD) reacto r chambers for TEOS (tetra ethyl ortho silicate), passivation, and tun gsten process clean chemistries were analyzed using scanning electron microscopy and energy-dispersive spectroscopy x-ray maps. Examination reveals that the primary cause of failure for all anodized Al parts is the same while individual mechanisms vary depending on the process ch emistry used. The fundamental reason for failure of anodized aluminum part in CVD reactors is the formation and growth of aluminum fluoride below the anodized film at point defect sites. These point defect site s are imperfections in the anodized layer caused by precipitate partic les such as Fe and Si, voids, sharp comers, and cracks due to differen tial expansion. In the 6061 alloy, the point defect sites act as high energy sites for the plasma fluorine attack. However, such defect site s can be capped off by the formation of a layer of MgF2 below the anod ized film. The formation of MgF2 is dependent upon the availability of elemental Mg to diffuse to these point defect sites and also the numb er of defect sites. Some of the Mg is typically tied up with precipita tes like Fe and Si. When free Mg is unavailable to form a barrier laye r, subsequent fluorination of the substrate causes formation of AlF3. This results in stresses in the anodized layer that can ultimately lea d to delamination of the anodized layer and failure of the part. The 1 100 alloy does not contain Mg and thus fluorination results in the dir ect formation of AlF3 at point defect sites with no protective MgF2 la yer present. An enhanced performance of anodized Al parts can be achie ved by using pure aluminum alloys with controlled quantities of Mg to form the MgF2 barrier layer. (C) 1996 American Vacuum Society.