Topography transfer method with aspect ratio scaling
The present invention is a method of applying a topographical surface to a part such as a substrate without the need for low temperature softening of that part while retaining high aspect ratios and densely packed features in that topography. A substrate, selected for its ability to be processed at a given desired temperature, has a layer of material applied to its surface. This layer is selected, among other reasons, for its ability to be molded. Typically, it is expected that the substrate will be able to withstand the higher temperatures of semiconductor post-processing whereas the applied layer will be moldable at low temperatures. This combination enables low cost embossing of a topography into this surface layer. The present invention comprises means to transfer this topography from the low temperature material into the higher temperature substrate. In addition, the present invention comprises a means to scale the aspect ratio of the features of that topography when it is transferred into the substrate material. Since the sidewall angle must be opened enough to permit demolding of the master form from the substrate after molding, some very vertical sidewall angles may not be possible during a molding-demolding operation. The present invention is a means to achieve steeper sidewall angles on features in a substrate where those features are applied by way of a molding process.
1. A method for transferring a topography into a substrate from a layer of material on a surface of the substrate comprising the steps of:
a. applying said layer of material to the surface of said substrate,
b. pressing a mold featuring a topography into the layer of material, and
c. etching to transfer the topography into the substrate,
wherein etch rates of said layer of material and said substrate are different and a ratio of the difference in etch rates controls aspect-ratio scaling of the topography etched into said substrate.
2. The method of claim 1 wherein the layer of material has a slower rate of etching than the substrate.
3. A method for transferring a topography from a layer of material into a substrate comprising the steps of:
a. applying the layer of material to a surface of the substrate,
b. patterning a topography into the layer of material,
c. defining a scaling ratio of a depth of the topography of the layer of material versus a desired depth of corresponding features in the substrate,
d. selecting an etch chemistry, based on a selectivity of the substrate with respect to the etch chemistry and a selectivity of the layer of material with respect to the etch chemistry, consistent with the scaling ratio, and
e. using the etch chemistry to transfer the topography into the substrate.
4. The method of claim 3 wherein the topography is patterned using gray-scale lithography.
5. The method of claim 3 wherein the topography is applied using molding.
6. The method of claim 3 wherein the topography is applied by imprinting.
7. The method of claim 3 wherein the depth of a feature of the topography patterned into the layer of material is less than a thickness of the layer of material.