Basic Principle
The basic principle is the same as in interferometry or holography. An interference pattern between two or more coherent light waves is set up and recorded in a recording layer (photoresist). This interference pattern consists of a periodic series of fringes representing intensity minima and maxima. Upon post-exposure photolithographic processing, a photoresist pattern corresponding to the periodic intensity pattern emerges.
For 2-beam interference, the fringe-to-fringe spacing or period is given by (λ/2)/sin(θ/2), where λ is the wavelength and θ is the angle between the two interfering waves. The minimum period achievable is then half the wavelength.
By using 3-beam interference, arrays with hexagonal symmetry can be generated, while with 4 beams, arrays with rectangular symmetry are generated. Hence, by superimposing different beam combinations, different patterns are made possible.
Read more about this topic: Interference Lithography
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