The use of concentrated hydrogen peroxide for the removal of a TiW ARC from aluminum bond pads

The use of concentrated hydrogen peroxide as an agent which etches TiW is well known in the metals industry. Although hydrogen peroxide is used in most semiconductor manufacturing processes, its' application as an etchant for TiW has been limited. Since some Micro-Rel product uses a composite metallization scheme containing a TiW/AlSiCu/TiW sandwich, the bonding pad etch process must include a TiW removal step. Without this step, a residual TiW layer is left on the metal pads causing wire adhesion problems (non-sticks) during the wire bonding processes. Current plasma etch techniques still leave a TiW residue on the aluminum surface. The hydrogen peroxide clean was instituted to minimize the presence of the TiW residue. By inserting this clean as the last step of the pad masking module, a cleaner metal surface was developed. To test the new process, wire pulls were done on product by two separate business units within Medtronic. Results from both areas showed no lifts. Surface analyses of metal bond pads treated with hydrogen peroxide shows a significant decrease in the concentrations of metallic oxides and tungsten. The SEM images of bonding pads show no loss in metal thickness and the metal surface is relative smooth with no trace of TiW visually evident.