Effect of ion-beam milling on lips prior to lift-off process

One of the key-processing steps for fabrication of semiconductor devices is the formation of metal contacts to semiconductor surfaces by appropriate metal. In many cases, this metal is usually patterned by single-step lift-off process. However, in many situations, before making actual deposition of metal, a fresh native surface is desirable so that it does not contain any uncontrollable oxide, photo resists complexes or other un-desirable residues. One of the techniques, to achieve above requirement, is to use ion beam milling process. Additionally, this process is used for various other purposes in device fabrication. However, its effect on photolithography step for lift-off process may change the profile of developed photo resist and hence affect the lift-off process. Using scanning electron microscopy (SEM), here we show the results on the effect of milling current on lip formation (a pre-condition for proper lift-off) and identify the current levels at which the lip is significantly affected. The optimized milled conditions for proper lip formation have been applied on actual lift-off and on actual devices.