The molecule (SiH3)3N is

Due to availability of empty d-orbitals in the valency shell of "Si" the lone [pair electron which are available on nitrogen involves in π bond (dative bond ) formation with the empty d-orbitals.In SiH33N the "N" undergoes sp2 hybridisation and attains trigonal planority.Due to the involvement of lone pair on nitrogen in the pi bond formation ,hence the availability of electron pair  for H+ ion ↓es & Hence basic nature ↓es