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Equipment

Interference Lithography

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General Information:

FIC: Peter Bermel and Minghao Qi
Process/Equipment Owner: Bill Rowe
Location: Cleanroom N-Bay
Max Wafer Size: 8

System Information:

General Description:

Fabricating high-performance 2D and 3D nanophotonic structures requires advanced lithography tools. While steppers are an industry standard, they are generally high in cost, and suited primarily for large-scale manufacturing of 2D structures. Other lithography tools, such as laser writers and e-beam lithography, can be much lower in cost, but also are impeded by throughput that is many orders of magnitude lower as well. At Purdue we are building the high-accuracy and throughput laser interference lithography system. The principle behind this method is that two coherent laser beams of wavelength L, when intersecting at a particular angle Q, will form a standing wave with a periodicity L / 2 sin Q. This standing wave can be recorded in a layer of photoresist. Upon immersion in developer, the result will be in a grating pattern. If two consecutive exposures are conducted before the photoresist is developed, a grid pattern will appear. An exposure setup with an 248-nm wavelength KrF excimer laser inside the Birck Nanotechnology Center’s class-1 cleanroom, run jointly by Prof. Bermel and Prof. Qi, is already funded. We plan to modify our interference lithography setup to achieve overlay alignment. The standing wave pattern, when laid over the grid pattern that is already on the wafer, will form a diffraction pattern. Such a diffraction pattern can be captured with a digital camera; the phase and intensity of the interference pattern will reveal the alignment of the standing wave pattern with regard to the previous grid pattern that is already on the wafer. With piezo-electrically controlled stages that hold the wafer, the position of the wafer could be adjusted to achieve alignment. This is the same method that has been applied in wafer fusion bonding. Compared to other high-throughput lithography tools in semiconductor manufacturing, the set-up is relatively low in cost and high in throughput.

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