Question

From the following techniques:

Thermal CVD (Chemical Vapor Deposition),

Metalorganic CVD,

Plasma-enhanced CVD,

Atomic Layer Deposition (ALD),

Plating,

Sol-gel,

Sputtering,

Thermal evaporation,

Electron beam evaporation,

Molecular Beam Epitaxy (MBE),

Laser ablation,

Ion plating,

choose one that is best suited for depositing

a) 100 nm Al coating on a rolled polymer foil having width of 1 m and length of hundreds of meters,

b) High purity 10 nm Au coating on a Si₃N₄ on Si substrate to be used as a contact,

c) Insulating 50 nm thick layer of oxide on a highly porous piece of material, which needs to be coated throughout,

d) 20 µm of zinc on a frame of a car.

Motivate your selections and discuss qualitatively the resulting film quality, productivity, cost, possible hazards and environmental issues.

Answer 1

a) It can be done using PVD techniques and since its hundreds of meters long, sputtering is not favourable and also e-beam evaporation. The flim quality won't be that good if Thermal Evaporation is used, but since its polymer and in Thermal evaporation the polymer won't be heated to high temperature and so the danger of damage of polymer is not there. Since big chambers will be required the cost may go high, productivity is reliable, there is no hazards as such in theremal evaporation technique and no environmental issues.

b)Plating can be used for coating Silver but the thickness of layer by plating is not of the required range, thus Sputtering can be used. The film quality is very good in sputtering. The productivity is high and cost is very high as purity required is high, and the chamber used for coating is costly. No harmful hazards or enironmental issues.

c)ALD can be used foe this as it gives pin hole free deposition and film quality is very good, high aspect ratio and uniform film. Productivity is less, as it takes time for depostion. Insulating oxides are usually deposited by ALD only and the chamber used is very small, so productivity is less.Cost is very high since ALD Machine is costly but the amount of chemical used is very less so cost is moderate. The Hazadous is through the byproduct that is formed and the chamber is degassed by pump and the pump throws out the chemical byproduct in air which may cause environmental issues.

d)Zn is coated by Plating and the cost is less and is thus used by automobile manufacturers. Plating is ised for coating on large and complex parts. There is no hazads or environmental issues.