Gray scale x-ray mask
The present invention describes a method for fabricating an embossing tool or an x-ray mask tool, providing microstructures that smoothly vary in height from point-to-point in etched substrates, i.e., structure which can vary in all three dimensions. The process uses a lithographic technique to transfer an image pattern in the surface of a silicon wafer by exposing and developing the resist and then etching the silicon substrate. Importantly, the photoresist is variably exposed so that when developed some of the resist layer remains. The remaining undeveloped resist acts as an etchant barrier to the reactive plasma used to etch the silicon substrate and therefore provides the ability etch structures of variable depths.
1. An x-ray mask tool, comprising:
a silicon substrate having a first thickness, a top surface, and a bottom surface substantially parallel to said top surface; and
a three-dimensional metal structure embedded into said silicon substrate and about flush with said top surface, said three-dimensional metal structure comprising a second thickness less than said first thickness, and one or more regions, wherein said second thickness varies continuously across a length and width of said three-dimensional metal structure thereby providing a floor surface in each of said one or more regions which varies in a curvilinear manner.
2. The x-ray mask tool of claim 1 , wherein said metal structure is a metal selected from the group consisting of the Transition series of metals listed in New IUPAC Group Numbers 4–12 of the Period Table of elements, aluminum, tin, and alloys thereof.
3. The x-ray mask tool of claim 2 , wherein said metal structure comprises a thin vapor deposited metal layer.
4. The x-ray mask tool of claim 3 , wherein said thin vapor deposited metal layer comprises chromium.
5. The x-ray mask tool of claim 3 , wherein said metal deposit is deposited by electroplating.
6. The x-ray mask tool of claim 3 , wherein said metal deposit is deposited by electroless deposition.
7. The x-ray mask tool of claim 3 , wherein said metal deposit is deposited by thermal or particle vapor deposition, or by sputter deposition.
8. The x-ray mask tool of claim 1 , wherein said metal structure consists essentially of gold.