Question

1. In the history of dry Etch, THE SELECTIVITY IS LOW AND THEIR IS NO DIFFERENTIATION OF INDIVIDUAL LAYERS. Please what does this actually mean?

Please Summarize it in one paragraph.

2. In etching, the pattern of the photo resist is been transferred to the water by means of etching agent. Please give me some examples of those etching agents

Answer 1

(1) Dry etching is a kind of plasma phase etching means we remove material by forming a plasma.Pulsed laser deposition is a kind of dry etching.Ion beam / laser is incident to ablate target material.Thats why it is very expensive.It makes use of gasous phase chemicals.

Selectivity issue- As incident beam is not preferential to particular type of atoms .It will ablate all types of atoms equally.so selectivity is very poor in dry etching.In lithography also if a light beam is incident upon photoresist covered by mask, pattern is being transferred to sample without differentiating between various layers(same for all).

(2) wet etching is very easy and highly selective as different chemicals react with materials differently.They can thus differentiate.

In it,pattern is being transferred to wafer.Different etchants are being used for different types of wafer materials.

For example HF and HNO ₃ is used for etching Silicon.

HF,HNO ₃ ,glycerol in proper proportion is used for etching Ti.