Semiconductor device with protection layers and method for fabricating the same

A semiconductor device, comprising:

• a first die;
• a first conductive feature positioned in the first die;
• a first mask layer positioned on the first die;
• a conductive filler layer positioned along the first mask layer, extending to the first die, and contacting the first conductive feature;
• isolation layers positioned between the conductive filler layer and the first die and between the conductive filler layer and the first mask layer;
• and
• protection layers positioned between the conductive filler layer and the isolation layers;
• wherein bottommost points of the protection layers are at a vertical level lower than a vertical level of a bottom surface of the first mask layer.

A method for fabricating a semiconductor device, comprising:

• performing a bonding process to bond a second die onto a first die;
• forming a first mask layer on the second die;
• forming a first opening along the first mask layer and the second die, and extending to the first die;
• forming isolation layers on sidewalls of the first opening;
• forming protection layers covering upper portions of the isolation layers;
• and
• forming a conductive filler layer in the first opening.