  Starting from a continuum description, we study the non-equilibrium
roughening of a thermal re-emission model for etching in one and two spatial
dimensions. Using standard analytical techniques, we map our problem to a
generalized version of an earlier non-local KPZ (Kardar-Parisi-Zhang) model. In
2+1 dimensions, the values of the roughness and the dynamic exponents
calculated from our theory go like $ \alpha \approx z \approx 1 $ and in 1+1
dimensions, the exponents resemble the KPZ values for low vapor pressure,
supporting experimental results. Interestingly, Galilean invariance is
maintained althrough.
