(a) Except as provided in section 697 of this title, an affidavit may be used —
(1) to prove the service of a summons, notice, or other paper in an action;
(2) to obtain a provisional remedy;
(3) to obtain the examination of a witness;
(4) to obtain a stay of proceedings;
(5) upon a motion; or
(6) in any other case expressly provided for by law or rules of court.
(b) In all cases other than those mentioned in subsection (a) of this section, where a written declaration under oath is used, it must be a deposition.