One explanation is that Atika Kadisha is the inner Light of Atik Yomin and the three heads of Keter. Another view is that Atika Kadish and Atik Yomin are general names for the Sefirah of Keter of Atzilut that includes the three heads. The Ari explains that Atika Kadisha is the aspect of the Light of Keter of the world of ‘Nekudim’. Nekhdim (dots) is the world with the highest light that exist before the breaking of the vessels (Edomite kings) and the forming of the world of Atzilut.The breaking of the vessel established (Tikun/corrected) the Keter of Atzilut that includes Atik Yomin, Keter, and Chokmah.Atik is a ‘copy’ of a release of Light from Machut of Adam Kadmon. This Light created the world of Atzilut and its light spreads and nourishes all lower worlds. Meaning to Arich, Aba, Ima, etc.