An interesting article on Habermas Heidegger relation is available online Heidegger's Challenge and the Future of Critical Theory
The article seems to be a previous version of what finally appeared in Habermas: A Critical Reader Edited By: PETER DEWS as "Heidegger's Challenge and the Future of Critical Theory / Nikolas Kompridis." I have not checked it though.
There is an interesting discussion of this paper here and here
Earlier I had come across another interesting article on Heidegger's conception of freedom called Primordial freedom: The Authentic Truth of Dasein in Heidegger's 'Being and Time' from here. I have not thoroughly studied it yet but it might be very relevant to Habermas Heidegger debate.
Also see this article which has been very fruitful for my pursuit of Habermas Heidegger connections
Christopher McNicholls (1991) “Ontological Freedom as the essence of Dasein: Heidegger’s overcoming of Objectivism and Subjectivism” Gnosis; 3(4): 1-33.