Semiconductor die stack structure

A semiconductor die stack structure comprising:

• a base die;
• a plurality of semiconductor die stack units stacked over the base die;
• and
• bumps between the base die and the plurality of semiconductor die stack units and between the plurality of semiconductor dies stack units,
• wherein each of the plurality of semiconductor die stack units includes a lower semiconductor die and an upper semiconductor die stacked over the lower semiconductor die,
• wherein each of the lower semiconductor die and the upper semiconductor die includes:
• a body having a front-side and a back-side;
• and
• a front-side pad structure disposed over the front-side of the body,
• wherein the front-side pad structure includes:
• a front-side pad seed layer;
• and
• a front-side pad pattern over the front-side pad seed layer,
• wherein the front-side pad pattern includes:
• a first front-side pad portion having a plate shape;
• a second front-side pad portion over the first front-side pad portion, wherein the first front-side pad portion and the second front-side pad portion forms a staircase;
• and
• a third front-side pad portion under the first front-side pad portion, wherein the first front-side pad portion and the third front-side pad form a reverse staircase,
• wherein the first front-side pad portion, the second front-side pad portion, and the third front-side pad include a same metal.