forming a first dielectric layer on a first substrate;

forming a second dielectric layer on a second substrate;

performing a first heat treatment on the first dielectric layer and the second dielectric layer, wherein a temperature of the first heat treatment is between 300° C. and 400° C.;

forming a first conductive via in the first dielectric layer;

forming a second conductive via in the second dielectric layer; and

bonding the first substrate and the second substrate in a manner that the first dielectric layer faces the second dielectric layer, so as to connect the first conductive via and the second conductive via,

wherein the first heat treatment is performed after forming the first dielectric layer and the second dielectric layer and before forming the first conductive via and the second conductive via.