SURFACE EVOLUTION DURING SEMICONDUCTOR PROCESSING

We discuss our approach to using the Riemann problem to compute surfac e profile evolution during the simulation of deposition, etch and refl ow processes. Each pair of segments which represents the surface is pr ocessed sequentially, For cases in which both segments are the same ma terial, the Riemann problem is solved. For cases in which the two segm ents are different materials, two Riemann problems are solved. The mat erial boundary is treated as the right segment for the left material a nd as the left segment for the right material. The critical equations for the analyses are the characteristics of the Riemann problem and th e 'jump conditions' which represent continuity of the surface. Example s are presented to demonstrate selected situations. One limitation of the approach is that the velocity of the surface is not known as a fun ction 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 assum ed for the explicit integration procedure used. Numerical implementati on is briefly discussed.