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List types of lithography. Explain in detail X-ray lithography with its major features.
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Types of lithography :

  • Electron beam lithography

  • Ion beam lithography

  • Ion track lithography

  • x-ray lithography

  • Nanoimprint lithography

  • Extreme ultraviolet lithography

x-ray lithography :

  • x-ray lithography is a process used in electronic industry to selectively remove parts of a thin film.

  • It uses x-rays to transfer a geometric pattern from a mask to a light sensitive chemical photoresist or simply "resist" on the substrate.

  • A series of chemical treatments then engraves the produced pattern into the material underneath the photoresist.

  • The x-ray lithography is almost identical to photolithography and extreme ultraviolet lithography but uses a mask in made from an x-ray transparent material with a pattern of high z material either etched or deposited on it.

  • Exposure of the substrate resist is done using a parallel beam of x-rays.

  • The x-rays source begins with an electron beam than is converted to an x-ray beam in a synchrotron.

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Exposure source : x-ray (synchrotron)

  • resist :

  • PMMA

  • Mask : SIC

membrane covered by high 2 - metal [fabricated by e-beam writer]

Advantages :

  • Fast process

  • high resolution of $\backsim$ 5 $\mu$ m

  • not affected by organic defects in mask

  • reduction in diffraction, reflection and scattering effects

  • solves depth of focus problem

  • high aspect ratio.

Disadvantages :

  • shadow printing

  • lateral magnification error

  • brighter x-ray sources needed

  • more sensitive resists needed

  • difficult fabrication of x-ray mask

Applications :

  • Most commonly used in computer chips and other semiconductor related devices.
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