Top Down Nano Fabrication

Top down fabrication methods Top down fabrication methods z z z z z z

Optical X‐Ray EUV EBeam SPM Imprinting

Optical Lithography Optical Lithography 1. Preparation p z Chemically Cleaning to remove contamination

2. Coat Resist z The wafer is covered with photo resist by spin i coating ti

3. Expose z typically uses ultraviolet light

4 Develop  4. D l z Positive photoresist – becomes soluble in basic devolper z negative photoresist -becomes insoluble in (organic) developer

5. Etching z liquid ("wet") or plasma ("dry") chemical agent removes the uppermost layer of the substrate

Optical Lithography  (Shadow and Projection)

Lithography Advantages Di d Disadvantages

Shadow

Projection

z Higher Resolution

z Defect due to direct contact

z Low defect o de ec z Reduction ratio

z Expensive system pe s e sys e z Lower resolution

• s = the gap between the 

• k1 = constant related to the resist

mask and photo resist • d = photo resist thickness

• NA = numerical aperture  • NA = nSina • n= refractive index • a = maximum cone angle

Optical Lithography  (Projection)

Extreme Ultraviolet Lithography (EUV) Extreme Ultraviolet Lithography (EUV) z z z z

Using the 13.5 nm EUV wavelength  EUV lithography needs to take place in a vacuum EUV lithography needs to take place in a vacuum  As refractive lenses absorbing UVR, reflecting mirrors are  used The precision machining of the mirror is required.

X‐Ray Lithography Ray Lithography z z z z z

X‐ray with wavelengths in the range of 0.04 to 0.5 nm X‐ray mask made with an x‐ray absorbing materials on a thin x‐ray  transparent membrane An x‐ray source with sufficient brightness to exposure the resist through  the shadow mask (there is no x‐ray lens) Advantages: high resolution, low defect Disadvantages: Expensive, 1:1 mass:pattern ratio

Nanosphere Lithography Nanosphere Lithography z z z z z

Cleaning the substrate Drop Coat Drying  Laying gold particles (Ag)  Lift off

E‐Beam Lithography Beam Lithography z z z z z z

Using scanning a beam of electrons E beam in a patterned fashion on a resist E‐beam in a patterned fashion on a resist Then removing the unnecessary  Etching Advantages: overcomes the diffraction limits of light and make features in nm Advantages: overcomes the diffraction limits of light and make features in nm region Disadvantages: beam drift or instability which may occur during the exposure