| CPC H01L 23/49827 (2013.01) [H01L 21/76837 (2013.01); H01L 21/76843 (2013.01); H01L 23/5384 (2013.01); H01L 27/0688 (2013.01)] | 20 Claims |

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1. A method comprising:
bonding a top die to a bottom die;
depositing a first dielectric liner on the top die;
depositing a gap-fill layer on the first dielectric liner, wherein the gap-fill layer has a first thermal conductivity value higher than a second thermal conductivity value of silicon oxide, wherein the depositing the gap-fill layer comprises:
depositing a first sub layer comprising a first material; and
depositing a second sub layer over the first sub layer, wherein the second sub layer comprises a second material different from the first material;
etching the gap-fill layer and the first dielectric liner to form a through-opening, wherein a metal pad in the bottom die is exposed to the through-opening, wherein the etching the gap-fill layer comprises etching the second sub layer, with the first sub layer being used as an etch stop layer;
depositing a second dielectric liner lining the through-opening;
filling the through-opening with a conductive material to form a through-via connecting to the metal pad; and
forming a redistribution structure over and electrically connecting to the top die and the through-via.
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