# Following are the incident radiation used for lithography while making integrated circuit (depending upon the feature size). (a) Visible light (b) Ele

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Following are the incident radiation used for lithography while making integrated circuit (depending upon the feature size).

(a) Visible light

(b) Electron beam

(c) Ion beam

(d) UV light

Sequence the radiation used for increasing order of the feature size:

1. (c), (b), (d), (a)
2. (b), (a), (d), (c)
3. (a), (b), (c), (d)
4. (a), (d), (b), (c)

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Correct Answer - Option 1 : (c), (b), (d), (a)

Lithography:

• It is a series of steps that establishes shapes, dimension, and placement of various components of the chips and creates a pattern with specified dimensions.
• The feature size of semiconductor technology is defined as the minimum length of the MOS transistor channel between the drain and the source.
• The smallest feature size that is possible depends upon the wavelength of the incident radiation and the numerical Aperture as:

Feature size $\left( \sigma \right) = \frac{{k.\lambda }}{{NA}}$

k = Rayleigh const 0.5

λ = wavelength

NA = Numerical Aperture

• The best way to reduce the feature size (σ), is to reduce the wavelength i.e. smaller the wavelength of the incident radiation, smaller will be the feature size (σ).
• Visible light has a higher wavelength as compared to UV light. So visible light radiation will have a higher feature size than the UV light.
• Electron Beam and Ion Beam is used for making IC’s with small feature size. Comparatively, the feature size used for an ion beam is less than that used for an electron beam.

So, the correct sequence of increasing order of feature size is (c), (b), (d), (a)

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