Reactive Ion Etching (RIE):-
- RIE is performed by replacing a neutral gas in rf sputtering system by one or more chemical specier.
- Plasma interaction with these chemical results in production of both neutral and ionized energetic specier which an etch the substrate.
- A common RIE sys is shown in fig above.
- The substrate is normal to gas flow and are immersed in plasma allowing the use specier that are energetic with that life.
- The normal RF field that allows the movement ionized specier in both directions and rapidly.
- Due to these a high degree of an isotropic etching can occur which can be enforced by using chemical whose reaction products have large ionized components.
- Additionally the reactors can be separated with a large voltage drop across control to increase the velocity and aid in this process.
- Finally operation at reduced pressure minimizes collisions in sheets preventing the directionality of ionized specier by enhancing further anisotropic nature of etch process.
- Therefore RIE is combination of both physical and chemical dry etching process.
- This is basically widely used process in andustrier.
- This process is is highly anisotropic and has high etch rate.
- Etching occurs through both ionic bombardment and chemical reaction.
- Ion bombardment opens the area for reaction hence helps in making etching process faster.
- Dry chemical etching is extremely authorative for no. of reasons.
- Firstly a dry process avoids problems of undercutting of a patterning flim by capitalry action of liquid echanty
- Finally dry etching systems are automated rapidly with cassetle loading, automatic pumpdown and load lock and featurer.
Goreous chemical is used for there purpose
Ex. Anhydrous HCl and SF6 is been used to in etching of silicon prion to epitary.
- HCL and ASCl3vapours is used for Ga AS
- In both etching is varied out at high temperature comparable to those of epitorial growth.
- Gaseous etching can also be accomplished at room temperature by use of an interhalesonic compounds such as CIF3 BrF3, BrF5 and IFs.
- The essential process of active specier, their transport to substrate where etching reaction occurs and removal of reaction products from surface.
- The by products of etch process has to be volatile. For ex. Nitrogen floride (NF3), sulphurhexafloride (SF6) etc. are same ions used in chemical dry etching.
A typical reaction showing substrate etching as follows
$CF_4 ---\gt F, CF, CF, ------------ etc$
$Si (s) + 4F \rightarrow Si F4 (gas)$
Dry physical Etching:-
- It is based on ion bombardment for the use of chemical reactive gases.
- In this method, the removal of material is performed by using etchant gases or plasma.
- It does not involve any liquid chemical for etching.
- It can transfer patterns defined by mask with high resolution.
- It is controllable and capable of defining small features sizes.
- The dry etching methods are of two types:-
- Plasma etching
- Non-plasma etching