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Sub-wavelength holographic lithography (SWHL)

Since the 1970s, the cost of photolithography in IC manufacturing has reached nearly 70% of the total production cost. The cost of production lithography equipment has grown almost 160 times reaching ~$80M (193i scanner) and exceeding $200M (EUV scanner). Such high costs have caused a significant market concentration in equipment and chip manufacturing. Historically, the projection exposure technology was developed on the foundation of geometrical optics. A projection mask was a magnified stencil of the projected pattern. To achieve resolution, extensive development efforts have been made to increase the projection optics numerical aperture (NA), reduce exposure wavelength, minimize distortions of the projection lens and destructive diffraction effects. Complicated and highly costly RETs (OPC, PSM, SMO etc.) are used to suppress distortions in the pattern image induced by diffraction and aberrations of the projection optics. Sub-Wavelength Holographic Lithography (SWHL) is an unconventional imaging approach in photolithography that utilizes diffraction and interference effects to create high-quality images in photoresist, whilst decreasing exposure steps’ cost, including higher resolution nodes. The ability to construct arbitrary wavefronts opens multiple opportunities like printing on various 3-D surfaces. The SWHL is capable of dramatic reduction of the lithography cost and opens new opportunities in 3D imaging. Two proof-of-concept exposure systems were designed and built to verify the SWHL capabilities: the first for imaging patterns with sub-wavelength resolution, the second for printing on 3D surfaces. The fidelity and computation efficiency of mask synthesis and RET algorithms were verified.