Patent ID: 8420540

Claim:
A method for forming a trench structure disposed over a substrate, the method comprising: depositing a sacrificial layer of a sacrificial material over the substrate; forming a first set of trenches in the sacrificial layer with a lithographic mask; filling the first set of trenches completely with a first set of step spacer blocks using two alternating spacer materials, the two alternating spacer materials being separately removable; forming a second set of trenches by selectively removing the remaining sacrificial material after filling the first set of trenches; filling the second set of trenches completely with a second set of step spacer blocks using the two alternating spacer materials in continuing sequence with the first set of step spacer blocks in the first set of trenches; forming a hard mask by selectively removing one of the two alternating spacer materials; using the hard mask to etch the trench structure in the substrate; and polishing the first set of step spacer blocks and the sacrificial material such that the top surfaces of the first set of step spacer blocks and the sacrificial material are substantially parallel to the top surface of the substrate; and wherein forming the first set of step spacer blocks and the second set of step spacer blocks includes: forming a first pair of step spacers along the inside walls of the first set of trenches and the inside walls of the second set of trenches using a first spacer material; forming a second pair of step spacers along the inside walls of the first pair of step spacers using a second spacer material; and forming a spacer plug along the inside walls of the second pair of step spacers using the first spacer material such that the spacer plug completely fills the first set of trenches and the second set of trenches.