Uniform trench fill recess by means of isotropic etching

A procedure for forming uniformly recessed fills of trench structures which maintains a planar wafer surface without need of any intermediate or final planarization technique comprising the steps of:

• providing an initial structure comprising at least a sacrificial layer over a substrate wherein said sacrificial layer may be non-uniform, said structure further comprising a plurality of trenches formed in said sacrificial layer and extending into said substrate and a fill material deposited over said sacrificial layer and filling said trenches, said trenches having a smallest dimension smaller than or equal to twice a desired recess depth;
• isotropically etching said fill material to remove the fill material from said sacrificial layer but not below an interface of the sacrificial layer;
• removing said sacrificial layer by an isotropical etch selective to the fill material to leave projecting studs of fill material;
• and
• isotropically etching the projecting studs of fill material with an etch that is highly selective to said wafer to produce a uniform depth in each of said trenches.