A backside alignment apparatus for aligning a substrate having at least one backside alignment mark thereon, the backside alignment apparatus comprising: a workpiece stage assembly for supporting the substrate, the workpiece stage assembly including a workpiece stage and a base under the workpiece stage, the workpiece stage being enabled to move in at least three degrees of freedom with respect to the base; a reference plate assembly supported by the workpiece stage and including a reference plate alignment mark; only one illumination apparatus for emanating an infrared light, the illumination apparatus being disposed on one side of the workpiece stage; and only one imaging apparatus disposed on the other side of the workpiece stage and positioned in correspondence with a location of the illumination apparatus, characterized in that: the base comprises a base aperture for the infrared light emanated from the illumination apparatus to pass through; the workpiece stage comprises at least two workpiece stage apertures positioned in correspondence with locations of the reference plate alignment mark and the at least one backside alignment mark; wherein the workpiece stage moves the reference plate alignment mark or any one of the at least one backside alignment mark to a position between the illumination apparatus and the imaging apparatus such that the infrared light emanated from the illumination apparatus illuminates the reference plate alignment mark or said one of the at least one backside alignment mark and the imaging apparatus detects an image of the illuminated reference plate alignment mark or said one of the at least one illuminated backside alignment mark. a workpiece stage assembly for supporting the substrate, the workpiece stage assembly including a workpiece stage and a base under the workpiece stage, the workpiece stage being enabled to move in at least three degrees of freedom with respect to the base; a reference plate assembly supported by the workpiece stage and including a reference plate alignment mark; only one illumination apparatus for emanating an infrared light, the illumination apparatus being disposed on one side of the workpiece stage; and only one imaging apparatus disposed on the other side of the workpiece stage and positioned in correspondence with a location of the illumination apparatus, characterized in that: the base comprises a base aperture for the infrared light emanated from the illumination apparatus to pass through; the workpiece stage comprises at least two workpiece stage apertures positioned in correspondence with locations of the reference plate alignment mark and the at least one backside alignment mark; wherein the workpiece stage moves the reference plate alignment mark or any one of the at least one backside alignment mark to a position between the illumination apparatus and the imaging apparatus such that the infrared light emanated from the illumination apparatus illuminates the reference plate alignment mark or said one of the at least one backside alignment mark and the imaging apparatus detects an image of the illuminated reference plate alignment mark or said one of the at least one illuminated backside alignment mark. the base comprises a base aperture for the infrared light emanated from the illumination apparatus to pass through; the workpiece stage comprises at least two workpiece stage apertures positioned in correspondence with locations of the reference plate alignment mark and the at least one backside alignment mark; wherein the workpiece stage moves the reference plate alignment mark or any one of the at least one backside alignment mark to a position between the illumination apparatus and the imaging apparatus such that the infrared light emanated from the illumination apparatus illuminates the reference plate alignment mark or said one of the at least one backside alignment mark and the imaging apparatus detects an image of the illuminated reference plate alignment mark or said one of the at least one illuminated backside alignment mark.