Method for planarizing multilayer semiconductor devices

In accordance with the present invention a method for forming an insulating layer over a substrate surface comprises providing first and second raised portions extending from the substrate surface, the first and second portions extending distances X1 and X2 respectively, and X2 being greater than X1. An insulating layer of thickness T3 is deposited over the surface so as to conform to the topography of the substrate surface and raised portions and a flowable layer is then deposited over the insulating layer. The flowable layer is next flowed so as to yield a substantially planar surface and then thinned until that portion of the insulating layer that overlies the second portion is exposed. The flowable layer and the exposed surface of the insulating layer are then simultaneously thinned so as to remove a greater thickness of flowable layer than insulating layer. The thinning is stopped when that portion of the insulating layer that overlies the first portion is exposed. At this point the exposed insulating layer is thinned until a thickness D1 overlies the first portion and a thickness D2 overlies the second portion. Thickness T3 over the substrate surface is not reduced. This thinning is performed such that ¦D1-D2¦, ¦(D1+X1)-T3¦ and ¦(D2+X2)-T3¦ are within predetermined ranges.