We discuss our approach to using the Riemann problem to compute surface profile evolution
during the simulation of deposition, etch and reflow processes. Each pair of segments which
represents the surface is processed sequentially. For cases in which both segments are the
same material, the Riemann problem is solved. For cases in which the two segments are different
materials, two Riemann problems are solved. The material boundary is treated as the
right segment for the left material and as the left segment for the right material. The critical
equations for the analyses are the characteristics of the Riemann problem and the ‘jump conditions’
which represent continuity of the surface. Examples are presented to demonstrate
selected situations. One limitation of the approach is that the velocity of the surface is not
known as a function of the surface angle. Rather, it is known for the angles of the left and
right segments. The rate as a function of angle must be assumed for the explicit integration
procedure used. Numerical implementation is briefly discussed.