In this paper, we examine the sensitivity of scatterometry for the 2D and 3D isolation mounts on the substrate by applying the PML in the RCWA method. We analyze the reflectance from the silicon and resist single mount on the silicon substrates by changing the incident beam angles. First, we show the propagation properties of the electromagnetic fields propagating for the isolation mounts on the silicon substrates. Second, we examine the oblique incident reflectances for the TE and TM waves by changing the beam sizes and wavelengths. We show the reflectance properties by changing the mount length, width and height on the Si substrates. Finally, we examine the reflectances calculated by changing the wavelength for the oblique incident beams. Then, we understand that the scatterometry observation is possible for isolation mounts.