ClF3 is sp3d hybridised. In this molecule we consider Cl as the central atom. Chlorine needs 3 unpaired electrons to bond with fluorine. During this hybridisation one 3s, three 3p and one 3d orbitals are involved which leads to 5 sp3d orbitals. Out of these 5 orbitals three are used to overlap with 1s orbitals of fluorine and other two orbitals contain the lone pair of electrons. The structure of the molecule is T shaped because of the presence of lone pair of electrons on the equatorial positions.