wafers 12 such that the reaction product is formed on the shielding plate 50 b rather than directly on the top surface of the base 40 b consequently it is not necessary for the operators to replace the base 40 b before performing the next deposition process to bake the processing chamber 20 at high temperature to remove the reaction products on the top surface or to perform an etching process to remove the reaction products on the top surface furthermore since the shielding plate 50 b is positioned on the top surface of the base 40 b in a disassembled manner the operators need only to replace the used shielding plate 50 b with a new one before performing the next deposition process instead of replacing the base 40 b after each deposition process consequently the thermal conductivity of the base 40 b can be kept consistent and the temperature of the wafer 12 on the base 40 b can be easily controlled to increase the yield fig7 to fig9 illustrate an epitaxy machine 10 c according to a third embodiment of the present invention fig7 is a cross sectional view of the epitaxy machine 10 c according to the third embodiment of the present invention the epitaxy machine 10 c comprises a.