Three-step Etching to Form RDL

A method comprising:

• forming an adhesion layer;
• forming a plurality of copper-containing features over the adhesion layer;
• selectively etching the adhesion layer, thereby removing portions of the adhesion layer not underlying the plurality of copper-containing features and laterally undercutting portions of the adhesion layers under the plurality of copper-containing features to form undercuts;
• and
• selectively etching the plurality of copper-containing features to reduce the undercuts.

A structure comprising:

• a device die;
• an encapsulant encapsulating the device die therein;
• a first plurality of Redistribution Lines (RDLs) overlying and electrically coupling to the device die, wherein the first plurality of RDLs have a first pitch, and the first plurality of RDLs are substantially free from undercuts;
• and
• a second plurality of RDLs overlying and electrically coupling to the device die, wherein the second plurality of RDLs have a second pitch greater than the first pitch, and the second plurality of RDLs have undercuts.