Reliability　of　through　silicon　via　(TSV)　structures　is　a　critical　issue　in　the　industrialization　of　TSV　technology.　One　of　the　most　important　problems　for　TSV　reliability　is　the　thermal　stress　induced　by　a　large　coefficient　of　thermal　expansion　mismatch　between　different　materials　in　the　TSV　structure.　This　mismatch　could　seriously　deteriorate　the　performance　of　the　TSVs,　and　even　lead　to　failure.　Here,　the　influence　of　heating　temperature　on　the　microstructure　evolution　in　the　TSV　structure　was　investigated.　The　microstructures　of　Cu-filled　TSV　samples　under　different　annealing　conditions　were　characterized,　and　the　phenomenon　of　global　Cu　protrusion　and　local　grain-like　Cu　protrusion　were　observed　in　Cu-filled　TSVs.　Mechanisms　of　Cu　protrusion　in　TSVs　during　heat　treatment　were　analyzed,　and　possible　factors　involving　thermal　stress,　grain　growth,　and　void　formation　are　discussed.　The　results　showed　that　the　origin　of　local　grain-like　TSV-Cu　protrusion　might　be　related　to　grain　growth　of　Cu　and　the　elastic　modulus　mismatch　between　coarse　Cu　grains.