In this letter, the effect of surface NH 3 nitridation on the electrical properties and reliability characteristics of aluminum oxide (Al 2 O 3 ) interpoly capacitors is studied. With NH 3 surface nitridation, the formation of an additional layer with lower dielectric constant during post-annealing process can be significantly suppressed, compared to that without nitridation treatment. Furthermore, the presence of a thin Si-N layer can make postdeposition annealing more effective in eliminating traps existing in the as-deposited films. As a result, a smoother interface and smaller electron trapping rate can contribute to the drastically reduced leakage current, enhanced breakdown field and charge to breakdown (Q bd ) of Al 2 O 3 interpoly capacitors with surface NH 3 nitridation.Index Terms-Al 2 O 3 , aluminum oxide, interpoly dielectric, IPD, surface NH 3 nitridation.