Moreover, instead of using the plurality of protrusions (not shown), faces of the first and second support parts 410 a and 410 b that contact the surface portions of the first substrate 510 may be coated with materials such as polytetrafluoroethylene or polyetheretherketone, for example, to prevent damage caused by the contact between the first and second support parts 410 a and 410 b and the firs