Anodic aluminum isolation

In anodic aluminum isolation the selective N+ sub collector is replaced by a blanket N+ epi layer. The P+ isolation is replaced by a silicon-etch, aluminum-evap-oration and partial-anodization. The aluminum down in the etched moats is electrically continuous and is partially anodized swelling to fill the moats, but still retaining a core of aluminum which can be used for a ground buss. The aluminum up on the active areas is electrically isolated, not anodized and stripped in a selective-etch leaving a reasonably planar structure. A²I gives higher yields and better performance in less space at lower costs.