MEMS_05 guiren photolithography_resolution_01

MEMS_05 guiren photolithography_resolution_01 - Chapter 1...

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Unformatted text preview: Chapter 1 Resolution in photolithography 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 = (+/-) k 2 /(NA 2 ) Using equ. (1.15) equ. (1.15): R = k 1 / (NA) -> DOF = (+/-) k 2 R 2 /(k 1 2 ) K 2 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 penalty of DOF reduction: a focused image through a typical 1-1.5 m thick resist cannot be achieved Variable NA is available This is a challenge for miniaturization Mask alignment in projection printing: fiducial marks Alignment importance: High resolution, repeatability for product Misalignment can cause catastrophic effect on performance of IC and MEMS devices e.g. line width of 1-1.5 m can only tolerate +/-0.25 m variation Main cause of product failure: poor alignment between the image being projected and the preexisting patterned on the wafer Mask alignment in projection printing: fiducial marks Source of errors Misalignment to mask Optical distortion Wafer or mask expansion Magnification change To improve alignment Appropriate fiducial marks are created on the wafer A scribe lane around each chip is required for cutting when it is diced Mask alignment in projection printing: fiducial marks To improve alignment A unique mask number and indication of layer names on the mask make it possible to visually determine the progress of the wafer Optical vernier patterns on different layers: Mask alignment in projection printing: fiducial marks To improve alignment Mask alignment in projection printing: fiducial marks...
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This note was uploaded on 10/03/2011 for the course BMEN 589 taught by Professor Wang during the Spring '11 term at South Carolina.

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MEMS_05 guiren photolithography_resolution_01 - Chapter 1...

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