surface 28 while in the present example the second layer 26 is about 200 nm thick its thickness is not critical to the operation of the invention the only requirement being that the resulting surface 28 completely or very nearly cover the first layer 20 and be substantially planar the device 10 is then subjected to any suitable planar etch that will etch both silicon nitride and the material of the second layer 26 at approximately the same rate the planar etch procedure is such that material is removed substantially evenly from the surface 28 of the layer 26 so that the surface 28 gradually receeds toward the surface 12 while remaining substantially parallel thereto as the surface 28 reaches the position indicated by the dashed line 30 in fig3 the top most portion 32 of the layer 20 of silicon nitride becomes exposed to the etch since the materials of the two layers 20 and 26 will etch at approximately the same rate the top most portion 32 will be completely etched away as the surface 28 reaches the position shown at 36 in fig4 this exposes the top surface 40 of the mesa 14 at this point the remaining portions of the planarizing.