An apparatus for bonding substrates includes a base member having a top surface and a recessed region which is configured for receiving at least a first substrate. The apparatus also has a plurality of support members disposed over the top surface for supporting a second substrate peripherally over the first substrate. Each support member is configured to vary a separation between the first substrate and the second substrate. Moreover, a pressure bar is configured to cause a center portion of the second substrate to contact the first substrate while the support members maintain peripheral separation between the first substrate and the second substrate. In operation, a bonded region between the first and the second substrates is expanded radially from the center portion when the support members are positioned to reduce the separation between the first and the second substrates.