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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.

Exposure source : x-ray (synchrotron)

• resist :

• PMMA

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

• 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.

• 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.