  We study the origin of broadening of superconducting transition in sputtered
Nb films. From simultaneous tunneling and transport measurements we conclude
that the upper critical field Hc2 always corresponds to the bottom of
transition R~0, while the top R~Rn occurs close to the critical field for
destruction of surface superconductivity Hc3 ~ 1.7 Hc2. The two-dimensional
nature of superconductivity at H>Hc2 is confirmed by cusp-like angular
dependence of magnetoresistance. Our data indicates that surface
superconductivity is remarkably robust even in disordered polycrystalline films
and, surprisingly, even in perpendicular magnetic fields.
