The invention relates to a positioning device for positioning a substrate, in particular a wafer, comprising: a process chamber; a base body; a carrier element which comprises a support for supporting the substrate, the carrier element being arranged above the base body and formed movable in terms of distance from the base body; and a holder for an additional substrate, in particular an additional wafer or a mask, the holder being arranged opposite the carrier element; wherein there is, between the base body and the carrier element, a sealed-off cavity to which a pressure, in particular a negative pressure, can be applied so as to prevent undesired movement of the carrier element as a result of the action of an external force.