| abstract |
A method for removing Ball Limiting Metallurgy (BLM) layers (14, 15) from the surface of a wafer (10) in the presence of Pb/Sn solder bumps (17). In one embodiment, the BLM comprises two layers: titanium (14) and copper (15). After Pb/Sn solder-bumps (17) have been formed over the electrical contact pads (12) of the wafer (10), the BLM copper layer (15) is etched with a H 2 SO 4 +H 2 O 2 +H 2 O solution. While removing the copper layer (15), the H 2 SO 4 +H 2 O 2 +H 2 O etchant also reacts with the Pb/Sn solder bumps (17) to form a thin PbO protective layer (18) over the surface of the bumps (17). When the copper layer (15) has been etched away, the titanium layer (14) is etched with a CH 3 COOH+NH 4 F+H 2 O solution. The PbO layer (18) formed over the surface of the Pb/Sn solder bumps (17) remains insoluble when exposed to the CH 3 COOH+NH 4 F+H 2 O etchant, thereby preventing the solder bumps (17) from being etched in the presence of the CH 3 COOH+NH 4 F+H 2 O etchant. When the titanium etch is complete, the PbO layer (18) is removed from the surface of the Pb/Sn solder bumps (17) by exposing the bumps (17) to an HCI+NH 2 CSNH 2 +NH 4 Cl+H 2 O solution. |