in order to determine the dielectric constant of a layer deposited on a semiconducotr wafer , the density of the layer is obtained . to obtain that density , the wafer without the layer is weighed in a weighing chamber in which a weighing pan supports the wafer on a weighing balance . the weight of the wafer is determined taking into account the buoyancy exerted by the air on the wafer . then the layer is deposited on the wafer and the weighing operation repeated . alternatively a reference wafer may be used . if the material of the layer is known , the weight of the layer can be used to derive its density using a thickness measurement . alternatively , if the density is known , the thickness can be obtained .