Plasma Etch Chambers

Plasma etch system

• It is used to etch silicon and its compounds with fluorine-containing gas such as CF₄ as the etchants, with SiF₄ as the gaseous etch byproducts.

Fig.7 (a) Schematic of a barrel etch system [3]

Down-stream or Remote plasma system

• It generates plasma in a remote chamber.

• The etchant gases are allowed to flow through the plasma chamber and dissociate into the plasma, and the free radicals are allowed to flow to the process chamber to react with and etch the materials on the wafer. [3]

Fig.7 (b) Schematic of a down-stream plasma etch system [3]

Note: The barrel and downstream systems are designed as isotropic etch systems. Following systems were developed to get a directional/anisotropic etch.

Parallel Plate Plasma etch system

• It operates at about 0.1 to 10 Torr and the wafer sits on the grounded electrode.

• To increase etch rate and improve the directional etch, we need to increase ion bombardment by increasing RF power and by reducing pressure.

Fig. 7 (c) Schematic of the parallel plate plasma etch system.[3]

Batch Reactive Ion Etch System

• Here an RF-driven electrode instead of the grounded electrode holds the wafer. This allows the grounded electrode to have a significantly larger area because it is in fact the chamber itself.

• This larger grounded area combined with the lower operating pressures leads to significantly higher plasma-sheath potentials at the wafer surface, which results in higher energy ion bombardment.

Fig 7 (d) Schematic of a batch RIE system [3]

Single-wafer Magnetically enhanced (MERIE) system

• As device dimensions shrink; the requirements for etch uniformity become more stringent.

• Single wafer process tools, which have better wafer-to-wafer process control become important, for example, MERIE system.

Fig. 7(e) Schematic of single-wafer MERIE system [3]