Techniques For Forming 3D Structures

A technique for forming 3D semiconductor structure is disclosed. In one embodiment, a substrate having at least two vertically extending fins is provided. An insulating material is deposited in the trench between the fins. After planarization, an ion implant process is performed to change the properties of the insulating material, specifically, the implanted region has a higher etch rate than the remainder of the insulating material. This higher etch rate region is then removed. This process of implanting and removing can be repeated until the insulating material reaches the desired height. In some embodiments, the substrate may be subjected to an anneal process prior to the removal of the higher etch rate region. The Gaussian implant depth profile may change into a box-like implant depth profile during the anneal process via thermal diffusion.