Process for CMP with large feature size variation
Embodiments of the present invention relate to reducing the size variation on a wafer fabrication. In some embodiments, at least a portion the backfill material over features larger than a threshold size is etched or milled to provide backfill protrusions over those features. The backfill protrusions are configured to reduce the size variation across the fabrication. Embodiments of the invention may be used in fabrication of many types of devices, such as tapered wave guides (TWG), near-field transducers (NFT), MEMS devices, EAMR optical devices, optical structures, bio-optical devices, micro-fluidic devices, and magnetic writers.
1. A method, comprising:
obtaining a substrate patterned with a plurality of features and having a backfill material deposited over the plurality of features,
the backfill material deposited over the plurality of features forming a corresponding plurality of backfill feature projections,
a first group of the plurality of backfill feature projections having sizes greater than or equal to a threshold size and a second group of the backfill feature projections have sizes less than the threshold size; and
removing a portion of the backfill material of a first backfill feature projection of the first group of backfill feature projections without removing the backfill material from a second backfill feature projection of the second group of backfill feature projections.
2. The method of claim 1 , wherein, after the step of removing the portion of the backfill material from the first backfill feature projection, the first backfill feature projection comprises an inner sidewall, an outer sidewall, and a region of backfill material between the inner and outer sidewalls, deposited along at least a portion of a periphery of the first backfill feature projection.
3. The method of claim 2 , wherein, after the step of removing the portion of the backfill material from the first backfill feature projection, the first backfill feature projection further comprises a layer of backfill material deposited over the feature corresponding to the first backfill feature projection.
4. The method of claim 2 , wherein the inner sidewall of backfill material is not disposed over the feature corresponding to the first backfill feature projection.
5. The method of claim 2 , wherein the width of the region of backfill material varies along the height of the region of backfill material.
6. The method of claim 1 , further comprising applying a photoresist material over the substrate using a mask configured to prevent application of the photoresist material to the portion of the backfill material that is removed from the first backfill feature projection.
7. The method of claim 6 , wherein the step of removing the portion of the backfill material of the first backfill feature projection comprises reactive ion etching, wet etching, or ion milling after application of the photoresist material.
8. The method of claim 6 , wherein the step of removing comprises:
isotropic etching; and
anisotropic etching; and
wherein after the step of removing, the first backfill feature projection comprises an inner sidewall, an outer sidewall, and a region of backfill material between the inner and outer sidewalls, deposited along at least a portion of a periphery of the first backfill feature projection, the width of the region of backfill material varying along the height of the region of backfill material.
9. The method of claim 1 , further comprising, after the step of removing the portion of the backfill material from the first backfill feature projection, chemical-mechanical polishing to remove the plurality of backfill feature projections.
10. The method of claim 1 , wherein the size threshold is between 1.25 and 3 times the size of the smallest feature patterned on the substrate.