An embodiment method includes bonding a first die to a first side of an interposer, the interposer comprising a substrate; after bonding the first die to the first side of the interposer, depositing a first insulating layer on a second side of the interposer opposite the first side; patterning an opening through the substrate and the first insulating layer; and depositing a second insulating layer over the first insulating layer and along sidewalls and a lateral surface of the opening. The second insulating layer comprises silicon. The method further includes removing lateral portions of the second insulating layer to define a sidewall spacer on sidewalls of the opening and forming a through via in the opening, wherein the through via is electrically connected to the first die.