Gaseous phase chemical treatment reactor

Reactor for the gaseous phase chemical treatment of at least one wafer (1) having a face (3) to be treated and a face (7) to be protected, said reactor comprising a main chamber (9) maintained at a first pressure (P.sub.1) and within which are located the said wafer (1), a susceptor (13) for heating said wafer, means (15) for securing the wafer and means (17) for injecting the treatment gas onto the face (3) of the wafer to be treated, characterized in that it comprises at least one treatment chamber (19) defined by its side walls (21), said treatment chamber (19) being provided within the main chamber (9) and being connected by one of its ends to the means (17) for injecting the treatment gas and by its other end to the securing means (15), in that the wafer (1) is gripped between the heating susceptor (13) and the securing means (15) in such a way that the latter rests on the periphery of the face (3) to be treated, so that the wafer (1) closes said treatment chamber (19) and in that within the said treatment chamber there is a second pressure (P.sub.2 ) lower than the pressure (P.sub.1) of the main chamber (9).