A cooling apparatus having an auxiliary chiller is provided. The apparatus can include a wafer chuck on which a wafer is mounted and in which a cooling cavity is formed. A main chiller having a main coolant reservoir can be spaced apart from the wafer chuck. The cooling cavity and the main coolant reservoir can be arranged in communication with each other through coolant passages. The coolant passages can include an auxiliary chiller detachably installed thereon, respectively. A method of cooling a wafer chuck or process chamber during a semiconductor device fabrication process is also provided. Using the method and apparatuses of this invention, fine temperature adjustments of the wafer chuck are possible.