An apparatus for use in manufacturing a semiconductor device allows one or more substrates treated substantially free of the metal particles released from the chamber wall and the high energy particles emitted from the plasma and also allows them to uniformly heated to a relatively high temperature. The apparatus comprises a reaction chamber wherein one or more substrates to be treated are disposed, a plasma source arranged outside of and in proximity to the reaction chamber, an active species supply port for providing active species generated by the plasma source to the reaction chamber and arranged at a side of the reaction chamber and an exhaust port provided at the opposite side to the active species supply port. The active species flows parallel to the surfaces of the substrates.