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Explain the Etching
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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.

Drychemical Etching

• 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