In general, other than named MBAs like MBA ( investment banking) or MBA ( Retail), one does not get to do super specialisation in MBA degree. So while you will do courses in equity research, investment banking, asset managment etc as a part of the finanace curriculum, you will not able to  further specialise at this level. And unless you are totally convinced,  and completely commited to say equity reserach, it may not even make sense to specialise in a narrow domain at the MBA stage itself.

You must look at opportunties available in the finanacial sector as a whole, work for a few years in your choosen domain, if you are convinced that is what you want to do for the rest fo your life, then go ahead and do a certification in that domain...