  Ion bombardment has been shown to be capable of enhancing the interlayer
exchange coupling in a trilayer system that exhibits giant magnetoresistance.
We demonstrate that this phenomenon can be derived from the phase coherence
among scattered paths within the two rough interfaces when their topographies
are correlated. In the case of mild corrugations, our method reproduces the
predictions by the proximity force approximation which does not consider the
interference. When the characteristic Fourier conjugate of the tomography
becomes large and comparable to the Fermi momentum, interesting new features
arise and can only be captured by our more general approach. Among our
findings, the scenario of an enhanced interlayer exchange coupling due to the
interface roughness is explained, along with how it depends on the sample
parameters. An additional channel for the resonant transmission is identified
due to extra scattering paths from the roughness.
