Hardmask to substrate pattern transfer method for Microfabrication of micro to mesoscale, high aspect ratio, multi-level, 3D Structures
We provide a novel cleanroom-based process flow that allows for easy creation of multi-level, hierarchical 3D structures in a substrate. This is achieved by introducing an ultra-thin sacrificial hardmask layer on the substrate which is first 3D patterned via multiple rounds of lithography. This 3D pattern is then scaled vertically by a factor of 200 - 300 and transferred to the substrate underneath via a single shot deep etching step. This method is also easily characterizable - using features of different topographies and dimensions, the etch rates and selectivities were quantified; this characterization information was later used while fabricating specific target structures.
1 . A method of deep-etching a substrate, the method comprising:
disposing a hard mask layer on the substrate;
etching a first multi-level pattern into the hard mask layer using two or more iterations of photoresist patterning followed by etching to provide etched features in the hard mask layer having two or more depths;
performing a deep etch of the structure using a single etch recipe that etches both the hard mask and the substrate, wherein the single etch recipe has an etch rate in the substrate at least 10× its etch rate in the hard mask layer;
wherein the deep etch is performed for a time sufficient to at least partially etch through the hard mask layer, thereby deep-etching a second multi-level pattern into the substrate that corresponds to the first multi-level pattern, but has magnified vertical feature dimensions.
2 . The method of claim 1 , wherein the hard mask layer comprises silicon dioxide, and wherein the substrate comprises silicon.
3 . The method of claim 1 , wherein a thickness of the hard mask layer is 3 microns or less.
4 . The method of claim 1 , wherein the single etch recipe has an etch rate in the substrate at least 100× its etch rate in the hard mask layer.
5 . The method of claim 1 , wherein the second multi-level pattern includes features having a height/width aspect ratio of 10 or more.