An apparatus for attaching substrates includes a first chamber for supporting a first substrate and a second chamber for supporting a second substrate. A main seal member is placed between the first chamber and the second chamber so as to maintain a seal and a gap between the chambers. An alignment control part is placed between the first chamber and the second chamber so as to maintain the seal, and also to allow the second chamber to move with respect to the first chamber in order to align the substrates. The alignment control part may also control a gap between the chambers, to thereby maintain a uniform gap between the substrates.