Depth of focus•Latent image must remain in focus through the depth of the resist layer•Focus depth (or defocus tolerance)–equ. (1.29) •DOF = (+/-) k2λ/(NA2)•Using equ. (1.15) •equ. (1.15): R = k1λ/ (NA)•-> •DOF = (+/-) k2R2/(k12 λ)–K2•A process-dependent constant •~ 0.5
Depth of focus•In microscopy, small DOF is highly demanded•However, in MEMS, larger DOF is disirable•High R could cause penaltyof DOF reduction: a focused image through a typical 1-1.5 μm thick resist cannot be achieved•Variable NA is available•This is a challenge for miniaturization
has intentionally blurred sections.
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