An apparatus for performing a selenization and sulfurization process on a glass substrate is introduced. A low-cost, non-toxic selenization and sulfurization process is performed on a large-area glass substrate in a normal-pressure environment with the apparatus to turn element selenium or sulfur into small molecules of high activity at high temperature by pyrolysis or by plasma, especially linear atmospheric pressure plasma. The process is finalized by dispersing the selenium or sulfur molecules uniformly and allowing the glass substrate to undergo reciprocating motion precisely, thereby achieving large-area, uniform selenization and sulfurization of the one-piece glass substrate.