A process for reducing dishing in damascene structures formed in low k organic dielectrics is described. A key feature is the insertion of a liner layer between the low k dielectric layer and the etch stop layer. The only requirement for the liner material is that it should have different etching characteristics from the etch stop material so that when trenches are etched in the dielectric they extend as far as the etch stop layer, in the normal way. When this is done it is found that dishing, after CMP, is significantly reduced, particularly for trench structures made up of multiple narrow trenches spaced close together.