it is the phase in physical design flow where we check for possible manufacturing defects coresponding to the technology node ....it must be done before mask information is generated ! Else you may forget about IC !! (and ofcourse....some crores of money !!!!)
Close, beta0... it's Design for Manufacturing. DFM is a set of technologies and methodologies that is still being defined in the industry, but is targeted toward counteracting adverse effects of the manufacturing process (as it becomes less robust at smaller geometries) during the design process. There are many techniques involved in DFM, and most are pertain to adjusting the drawn geometry and/or running additional DRC checks. It's a fascinating subject, and one that will be important in times to come...