Etching

An important step in IC Fabrication

1. Etching By Deepak Rawat GBPEC Pauri Uttarakhand India(246001) ( An important step in IC fabrication )

2. Outline What is Etching Steps preceding Etching in IC Fabrication Types of Etching Simple Idea of Wet Etching Plasma Etching What is Plasma Anisotropy and Selectivity Advantage of Plasma Etching over Wet Etching

3. What is Etching Simply removing unwanted materials from the surface to form a required pattern

4. Steps Preceding Etching in IC Fabrication 1. 2. 3 . 4.

5. Types of Etching Two types of Etching Wet Etching: Etching is done by liquid chemicals Unmasked areas are etched away by the chemical reactions (Oxidation and Reduction ) Plasma Etching (Dry Etching): Etching is done exposing the material into bombardment of ions in Plasma

6. Simple idea of Wet Etching Etchants: KOH, HF, BF 6 , BCl 3

7. Plasma Etching (Dry Etching) Faster and Easier way Both chemical and ionic species play the roll

8. What is Plasma State of mater which consist free electrons and cations Plasma looks similar to the gases Plasma is also called as ionised gases

9. In Plasma high number of electrons does not move around in orbits Plasma is created when gas is either exposed to high temp. Or high voltage

10. Due to these free electrons and cations Plasma easily conducts electricity and also produce magnetic field. Nature also produces plasma by means of fire and lightning.

11. What happens inside plasma

12. Physical Etching inside the Plasma Etching species are ions like CF 3 + or Ar + which remove material by ion-bombardment. Ion etching is much more directional (anisotropic) due to directional acceleration of ions by high E field

13. Anisotropy Etchant can not distinguishes b/w vertical or horizontal dimensions (isotropic). Anisotropy = 1 – dH/ dV Wet etching is isotropic and dry etching is anisotropic.

14. Selectivity Etchant should distinguish b/w SiO 2 and Si wafer. Wet Etching is Selective than Dry Etching.

15. Advantages of Plasma Etching over Wet Etching Eliminates handling of dangerous acids and solvents. Uses small amounts of chemicals. Anisotropic etch profiles. High resolution and cleanliness. Less undercutting. Better process control.